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• The GABA shunt contributes to ROS homeostasis in guard cells of Arabidopsis. Xu, B.; Feng, X. Y.; Piechatzek, A.; Zhang, S. Q.; Konrad, K. R.; Kromdijk, J.; Hedrich, R.; Gilliham, M. In New Phytologist, 241(1), pp. 73–81. 2024.
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  center dot gamma-Aminobutyric acid (GABA) accumulates rapidly under stress via the GABA shunt pathway, which has been implicated in reducing the accumulation of stress-induced reactive oxygen species (ROS) in plants.center dot gamma-Aminobutyric acid has been demonstrated to act as a guard-cell signal in Arabidopsis thaliana, modulating stomatal opening. Knockout of the major GABA synthesis enzyme Glutamate Decarboxylase 2 (GAD2) increases the aperture of gad2 mutants, which results in greater stomatal conductance and reduces water-use efficiency compared with wild-type plants.center dot Here, we found that the additional loss of GAD1, GAD4, and GAD5 in gad2 leaves increased GABA deficiency but abolished the more open stomatal pore phenotype of gad2, which we link to increased cytosolic calcium (Ca2+) and ROS accumulation in gad1/2/4/5 guard cells. Compared with wild-type and gad2 plants, glutamate was ineffective in closing gad1/2/4/5 stomatal pores, whereas lowering apoplastic calcium, applying ROS inhibitors or complementation with GAD2 reduced gad1/2/4/5 guard-cell ROS, restored the gad2-like greater stomatal apertures of gad1/2/4/5 beyond that of wild-type.center dot We conclude that GADs are important contributors to ROS homeostasis in guard cells likely via a Ca2+-mediated pathway. As such, this study reveals greater complexity in GABA's role as a guard-cell signal and the interactions it has with other established signals.

  @article{RN945, abstract = {center dot gamma-Aminobutyric acid (GABA) accumulates rapidly under stress via the GABA shunt pathway, which has been implicated in reducing the accumulation of stress-induced reactive oxygen species (ROS) in plants.center dot gamma-Aminobutyric acid has been demonstrated to act as a guard-cell signal in Arabidopsis thaliana, modulating stomatal opening. Knockout of the major GABA synthesis enzyme Glutamate Decarboxylase 2 (GAD2) increases the aperture of gad2 mutants, which results in greater stomatal conductance and reduces water-use efficiency compared with wild-type plants.center dot Here, we found that the additional loss of GAD1, GAD4, and GAD5 in gad2 leaves increased GABA deficiency but abolished the more open stomatal pore phenotype of gad2, which we link to increased cytosolic calcium (Ca2+) and ROS accumulation in gad1/2/4/5 guard cells. Compared with wild-type and gad2 plants, glutamate was ineffective in closing gad1/2/4/5 stomatal pores, whereas lowering apoplastic calcium, applying ROS inhibitors or complementation with GAD2 reduced gad1/2/4/5 guard-cell ROS, restored the gad2-like greater stomatal apertures of gad1/2/4/5 beyond that of wild-type.center dot We conclude that GADs are important contributors to ROS homeostasis in guard cells likely via a Ca2+-mediated pathway. As such, this study reveals greater complexity in GABA's role as a guard-cell signal and the interactions it has with other established signals.}, author = {Xu, B. and Feng, X. Y. and Piechatzek, A. and Zhang, S. Q. and Konrad, K. R. and Kromdijk, J. and Hedrich, R. and Gilliham, M.}, journal = {New Phytologist}, keywords = {calcium}, note = {Ej3r3 Times Cited:0 Cited References Count:36}, number = 1, pages = {73-81}, title = {The GABA shunt contributes to ROS homeostasis in guard cells of Arabidopsis}, type = {Journal Article}, volume = 241, year = 2024 }

  %0 Journal Article %1 RN945 %A Xu, B. %A Feng, X. Y. %A Piechatzek, A. %A Zhang, S. Q. %A Konrad, K. R. %A Kromdijk, J. %A Hedrich, R. %A Gilliham, M. %D 2024 %J New Phytologist %N 1 %P 73-81 %R 10.1111/nph.19390 %T The GABA shunt contributes to ROS homeostasis in guard cells of Arabidopsis %U /brokenurl#<Go to ISI>://WOS:001100328500001 %V 241 %X center dot gamma-Aminobutyric acid (GABA) accumulates rapidly under stress via the GABA shunt pathway, which has been implicated in reducing the accumulation of stress-induced reactive oxygen species (ROS) in plants.center dot gamma-Aminobutyric acid has been demonstrated to act as a guard-cell signal in Arabidopsis thaliana, modulating stomatal opening. Knockout of the major GABA synthesis enzyme Glutamate Decarboxylase 2 (GAD2) increases the aperture of gad2 mutants, which results in greater stomatal conductance and reduces water-use efficiency compared with wild-type plants.center dot Here, we found that the additional loss of GAD1, GAD4, and GAD5 in gad2 leaves increased GABA deficiency but abolished the more open stomatal pore phenotype of gad2, which we link to increased cytosolic calcium (Ca2+) and ROS accumulation in gad1/2/4/5 guard cells. Compared with wild-type and gad2 plants, glutamate was ineffective in closing gad1/2/4/5 stomatal pores, whereas lowering apoplastic calcium, applying ROS inhibitors or complementation with GAD2 reduced gad1/2/4/5 guard-cell ROS, restored the gad2-like greater stomatal apertures of gad1/2/4/5 beyond that of wild-type.center dot We conclude that GADs are important contributors to ROS homeostasis in guard cells likely via a Ca2+-mediated pathway. As such, this study reveals greater complexity in GABA's role as a guard-cell signal and the interactions it has with other established signals.

• Trigger hair thermoreceptors provide for heat-induced calcium-electrical excitability in Venus flytrap. Huang, S. G.; Hedrich, R. In Current Biology, 33(18), p. 3962-+. 2023.
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  Most plants suffer greatly from heat in general and fire in particular, but some can profit from what is called fire ecology.1 Dionaea muscipula, the Venus flytrap, is one such plant. In its natural habitat in the Green Swamps, Dionaea often faces challenges from excessive growth of grass and evergreen shrubs that overshadow the plant.2 Without natural fire, the Dionaea populations would decline.3 How does Dionaea survive and even thrive after swamp fires? Here, we ask whether flytraps recognize heat waves at the forefront of swamp fires and demonstrate that a heat-sensor-based alarm may provide a fire survival strategy for them. In this study, we show that flytraps become electrically excited and close in response to a heat wave. Over a critical tem-perature of 38 degrees C, traps fire action potentials (APs), which are interconnected with cytosolic Ca2+ transients. The heat-induced Ca2+-AP has a 3-min refractory period, yet traps still respond to cold, voltage, and gluta-mate. The heat responses were trap specific, emerging only when the trap became excitable. Upon heat stim-ulation, the Ca2+ wave originates in the trigger hair podium, indicating that the mechanosensory zone serves as a heat receptor organ. In contrast to the human heat receptor, the flytrap sensor detects temperature change rather than the absolute body temperature. We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers.

  @article{RN952, abstract = {Most plants suffer greatly from heat in general and fire in particular, but some can profit from what is called fire ecology.1 Dionaea muscipula, the Venus flytrap, is one such plant. In its natural habitat in the Green Swamps, Dionaea often faces challenges from excessive growth of grass and evergreen shrubs that overshadow the plant.2 Without natural fire, the Dionaea populations would decline.3 How does Dionaea survive and even thrive after swamp fires? Here, we ask whether flytraps recognize heat waves at the forefront of swamp fires and demonstrate that a heat-sensor-based alarm may provide a fire survival strategy for them. In this study, we show that flytraps become electrically excited and close in response to a heat wave. Over a critical tem-perature of 38 degrees C, traps fire action potentials (APs), which are interconnected with cytosolic Ca2+ transients. The heat-induced Ca2+-AP has a 3-min refractory period, yet traps still respond to cold, voltage, and gluta-mate. The heat responses were trap specific, emerging only when the trap became excitable. Upon heat stim-ulation, the Ca2+ wave originates in the trigger hair podium, indicating that the mechanosensory zone serves as a heat receptor organ. In contrast to the human heat receptor, the flytrap sensor detects temperature change rather than the absolute body temperature. We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers.}, author = {Huang, S. G. and Hedrich, R.}, journal = {Current Biology}, keywords = {myOwn}, note = {U4fj2 Times Cited:0 Cited References Count:18}, number = 18, pages = {3962-+}, title = {Trigger hair thermoreceptors provide for heat-induced calcium-electrical excitability in Venus flytrap}, type = {Journal Article}, volume = 33, year = 2023 }

  %0 Journal Article %1 RN952 %A Huang, S. G. %A Hedrich, R. %D 2023 %J Current Biology %N 18 %P 3962-+ %R 10.1016/j.cub.2023.07.069 %T Trigger hair thermoreceptors provide for heat-induced calcium-electrical excitability in Venus flytrap %U /brokenurl#<Go to ISI>://WOS:001084368300001 %V 33 %X Most plants suffer greatly from heat in general and fire in particular, but some can profit from what is called fire ecology.1 Dionaea muscipula, the Venus flytrap, is one such plant. In its natural habitat in the Green Swamps, Dionaea often faces challenges from excessive growth of grass and evergreen shrubs that overshadow the plant.2 Without natural fire, the Dionaea populations would decline.3 How does Dionaea survive and even thrive after swamp fires? Here, we ask whether flytraps recognize heat waves at the forefront of swamp fires and demonstrate that a heat-sensor-based alarm may provide a fire survival strategy for them. In this study, we show that flytraps become electrically excited and close in response to a heat wave. Over a critical tem-perature of 38 degrees C, traps fire action potentials (APs), which are interconnected with cytosolic Ca2+ transients. The heat-induced Ca2+-AP has a 3-min refractory period, yet traps still respond to cold, voltage, and gluta-mate. The heat responses were trap specific, emerging only when the trap became excitable. Upon heat stim-ulation, the Ca2+ wave originates in the trigger hair podium, indicating that the mechanosensory zone serves as a heat receptor organ. In contrast to the human heat receptor, the flytrap sensor detects temperature change rather than the absolute body temperature. We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers.
• Cracking the code of plant herbivore defense. Hedrich, R.; Roelfsema, R. G. In Cell, 186(7), pp. 1300–1302. 2023.
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  In 1916, Ricca hypothesized that plant defense mediators are transported by xylem vessels. While it was discovered that electrical waves generated at plant wounds also transmit information over great distances, the molecular nature of the so-called Ricca factor remained unclear. In this issue of Cell, Gao et al. identify thioglucoside glucohydrolases as a Ricca factor in Arabidopsis.

  @article{RN953, abstract = {In 1916, Ricca hypothesized that plant defense mediators are transported by xylem vessels. While it was discovered that electrical waves generated at plant wounds also transmit information over great distances, the molecular nature of the so-called Ricca factor remained unclear. In this issue of Cell, Gao et al. identify thioglucoside glucohydrolases as a Ricca factor in Arabidopsis.}, author = {Hedrich, R. and Roelfsema, R. G.}, journal = {Cell}, keywords = {long-distance}, note = {M0md7 Times Cited:2 Cited References Count:11}, number = 7, pages = {1300-1302}, title = {Cracking the code of plant herbivore defense}, type = {Journal Article}, volume = 186, year = 2023 }

  %0 Journal Article %1 RN953 %A Hedrich, R. %A Roelfsema, R. G. %D 2023 %J Cell %N 7 %P 1300-1302 %R 10.1016/j.cell.2023.02.025 %T Cracking the code of plant herbivore defense %U /brokenurl#<Go to ISI>://WOS:001027133100001 %V 186 %X In 1916, Ricca hypothesized that plant defense mediators are transported by xylem vessels. While it was discovered that electrical waves generated at plant wounds also transmit information over great distances, the molecular nature of the so-called Ricca factor remained unclear. In this issue of Cell, Gao et al. identify thioglucoside glucohydrolases as a Ricca factor in Arabidopsis.
• The CIPK23 protein kinase represses SLAC1-type anion channels in guard cells and stimulates stomatal opening. Huang, S. G.; Maierhofer, T.; Hashimoto, K.; Xu, X. Y.; Karimi, S. M.; Müller, H.; Geringer, M. A.; Wang, Y.; Kudla, J.; De Smet, I.; Hedrich, R.; Geiger, D.; Roelfsema, M. R. G. In New Phytologist, 238(1), pp. 270–282. 2023.
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  Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss of function of the CBL-interacting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified. CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogen-inducible system. Stomatal movements were linked to changes in ion channel activity, determined with double-barreled intracellular electrodes in guard cells and with the two-electrode voltage clamp technique in Xenopus oocytes. Expression of the phosphomimetic variant CIPK23(T190D) enhanced stomatal opening, while the natural CIPK23 and a kinase-inactive CIPK23(K60N) variant did not affect stomatal movements. Overexpression of CIPK23(T190D) repressed the activity of S-type anion channels, while their steady-state activity was unchanged by CIPK23 and CIPK23(K60N). We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1-type anion channels is an important facet of this response.

  @article{RN951, abstract = {Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss of function of the CBL-interacting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified. CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogen-inducible system. Stomatal movements were linked to changes in ion channel activity, determined with double-barreled intracellular electrodes in guard cells and with the two-electrode voltage clamp technique in Xenopus oocytes. Expression of the phosphomimetic variant CIPK23(T190D) enhanced stomatal opening, while the natural CIPK23 and a kinase-inactive CIPK23(K60N) variant did not affect stomatal movements. Overexpression of CIPK23(T190D) repressed the activity of S-type anion channels, while their steady-state activity was unchanged by CIPK23 and CIPK23(K60N). We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1-type anion channels is an important facet of this response.}, author = {Huang, S. G. and Maierhofer, T. and Hashimoto, K. and Xu, X. Y. and Karimi, S. M. and Müller, H. and Geringer, M. A. and Wang, Y. and Kudla, J. and De Smet, I. and Hedrich, R. and Geiger, D. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {akt1}, note = {C0tp2 Times Cited:3 Cited References Count:60}, number = 1, pages = {270-282}, title = {The CIPK23 protein kinase represses SLAC1-type anion channels in guard cells and stimulates stomatal opening}, type = {Journal Article}, volume = 238, year = 2023 }

  %0 Journal Article %1 RN951 %A Huang, S. G. %A Maierhofer, T. %A Hashimoto, K. %A Xu, X. Y. %A Karimi, S. M. %A Müller, H. %A Geringer, M. A. %A Wang, Y. %A Kudla, J. %A De Smet, I. %A Hedrich, R. %A Geiger, D. %A Roelfsema, M. R. G. %D 2023 %J New Phytologist %N 1 %P 270-282 %R 10.1111/nph.18708 %T The CIPK23 protein kinase represses SLAC1-type anion channels in guard cells and stimulates stomatal opening %U /brokenurl#<Go to ISI>://WOS:000919550100001 %V 238 %X Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss of function of the CBL-interacting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified. CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogen-inducible system. Stomatal movements were linked to changes in ion channel activity, determined with double-barreled intracellular electrodes in guard cells and with the two-electrode voltage clamp technique in Xenopus oocytes. Expression of the phosphomimetic variant CIPK23(T190D) enhanced stomatal opening, while the natural CIPK23 and a kinase-inactive CIPK23(K60N) variant did not affect stomatal movements. Overexpression of CIPK23(T190D) repressed the activity of S-type anion channels, while their steady-state activity was unchanged by CIPK23 and CIPK23(K60N). We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1-type anion channels is an important facet of this response.
• Integrative multi-omics analyses of date palm ( ) roots and leaves reveal how the halophyte land plant copes with sea water. Mueller, H. M.; Franzisky, B. L.; Messerer, M.; Du, B. G.; Lux, T.; White, P. J.; Carpentier, S. C.; Winkler, J. B.; Schnitzler, J. P.; El-Serehy, H. A.; Al-Rasheid, K. A. S.; Al-Harbi, N.; Alfarraj, S.; Kudla, J.; Kangasjärvi, J.; Reichelt, M.; Mithöfer, A.; Mayer, K. F. X.; Rennenberg, H.; Ache, P.; Hedrich, R.; Geilfus, C. M. In Plant Genome. 2023.
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  Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.

  @article{RN948, abstract = {Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.}, author = {Mueller, H. M. and Franzisky, B. L. and Messerer, M. and Du, B. G. and Lux, T. and White, P. J. and Carpentier, S. C. and Winkler, J. B. and Schnitzler, J. P. and El-Serehy, H. A. and Al-Rasheid, K. A. S. and Al-Harbi, N. and Alfarraj, S. and Kudla, J. and Kangasjärvi, J. and Reichelt, M. and Mithöfer, A. and Mayer, K. F. X. and Rennenberg, H. and Ache, P. and Hedrich, R. and Geilfus, C. M.}, journal = {Plant Genome}, keywords = {tolerance}, note = {N8fx2 Times Cited:0 Cited References Count:98}, title = {Integrative multi-omics analyses of date palm ( ) roots and leaves reveal how the halophyte land plant copes with sea water}, type = {Journal Article}, year = 2023 }

  %0 Journal Article %1 RN948 %A Mueller, H. M. %A Franzisky, B. L. %A Messerer, M. %A Du, B. G. %A Lux, T. %A White, P. J. %A Carpentier, S. C. %A Winkler, J. B. %A Schnitzler, J. P. %A El-Serehy, H. A. %A Al-Rasheid, K. A. S. %A Al-Harbi, N. %A Alfarraj, S. %A Kudla, J. %A Kangasjärvi, J. %A Reichelt, M. %A Mithöfer, A. %A Mayer, K. F. X. %A Rennenberg, H. %A Ache, P. %A Hedrich, R. %A Geilfus, C. M. %D 2023 %J Plant Genome %R 10.1002/tpg2.20372 %T Integrative multi-omics analyses of date palm ( ) roots and leaves reveal how the halophyte land plant copes with sea water %U /brokenurl#<Go to ISI>://WOS:001039319100001 %X Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.
• DYSCALCULIA, a Venus flytrap mutant without the ability to count action potentials. Iosip, A. L.; Scherzer, S.; Bauer, S.; Becker, D.; Krischke, M.; Al-Rasheid, K. A. S.; Schultz, J.; Kreuzer, I.; Hedrich, R. In Current Biology, 33(3), p. 589-+. 2023.
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  The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1-3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision -mak-ing are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea's hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunt-ing cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing.

  @article{RN950, abstract = {The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1-3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision -mak-ing are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea's hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunt-ing cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing.}, author = {Iosip, A. L. and Scherzer, S. and Bauer, S. and Becker, D. and Krischke, M. and Al-Rasheid, K. A. S. and Schultz, J. and Kreuzer, I. and Hedrich, R.}, journal = {Current Biology}, keywords = {calmodulin}, note = {J9ll3 Times Cited:4 Cited References Count:47}, number = 3, pages = {589-+}, title = {DYSCALCULIA, a Venus flytrap mutant without the ability to count action potentials}, type = {Journal Article}, volume = 33, year = 2023 }

  %0 Journal Article %1 RN950 %A Iosip, A. L. %A Scherzer, S. %A Bauer, S. %A Becker, D. %A Krischke, M. %A Al-Rasheid, K. A. S. %A Schultz, J. %A Kreuzer, I. %A Hedrich, R. %D 2023 %J Current Biology %N 3 %P 589-+ %R 10.1016/j.cub.2022.12.058 %T DYSCALCULIA, a Venus flytrap mutant without the ability to count action potentials %U /brokenurl#<Go to ISI>://WOS:001012767300001 %V 33 %X The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1-3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision -mak-ing are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea's hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunt-ing cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing.
• Chronic ozone exposure impairs the mineral nutrition of date palm ( ) seedlings. Arab, L.; Hoshika, Y.; Paoletti, E.; White, P. J.; Dannenmann, M.; Mueller, H.; Ache, P.; Hedrich, R.; Alfarraj, S.; Albasher, G.; Rennenberg, H. In Science of the Total Environment, 862. 2023.
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  Chronic ozone (O-3) exposure in the atmosphere preferentially disturbs metabolic processes in the roots rather than the shoot as a consequence of reduced photosynthesis and carbohydrate allocation from the leaves to the roots. The aim of the present study was to elucidate if mineral nutrition is also impaired by chronic O3 exposure. For this purpose, date palm (Phoenix dactylifera) plants were fumigated with ambient, 1.5 x ambient and 2 x ambient O-3 in a free air con-trolled exposure (FACE) system for one growing season and concentrations of major nutrients were analyzed in leaves and roots. In addition, concentrations of C and N and their partitioning between different metabolic C and N pools were determined in both organs. The results showed that calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), sodium (Na) and potassium (K) acquisition by roots was diminished by O-3 exposure of the shoot. For Ca, Mg, Fe and Zn reduced uptake by the roots was combined with reduced allocation to the shoot, resulting in a decline of foliar concentrations; for Na and K, allocation to the shoot was maintained at the expense of the roots. Thus, elevated O3 impaired both mineral uptake by the roots and partitioning of minerals between roots and shoots, but in an element specific way. Thereby, elevated O-3 affected roots and shoots differently already after one growing season. However, considerable changes in total C and N concentrations and their partitioning between different metabolic pools upon chronic O-3 ex-posure were not observed in either leaves or roots, except for reduced foliar lignin concentrations at 2 x ambient O-3. Significant differences in these parameters were shown between leaves and roots independent of O(3 )application. The physiological consequences of the effects of chronic O-3 exposure on mineral acquisition and partitioning between leaves and roots are discussed.

  @article{RN957, abstract = {Chronic ozone (O-3) exposure in the atmosphere preferentially disturbs metabolic processes in the roots rather than the shoot as a consequence of reduced photosynthesis and carbohydrate allocation from the leaves to the roots. The aim of the present study was to elucidate if mineral nutrition is also impaired by chronic O3 exposure. For this purpose, date palm (Phoenix dactylifera) plants were fumigated with ambient, 1.5 x ambient and 2 x ambient O-3 in a free air con-trolled exposure (FACE) system for one growing season and concentrations of major nutrients were analyzed in leaves and roots. In addition, concentrations of C and N and their partitioning between different metabolic C and N pools were determined in both organs. The results showed that calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), sodium (Na) and potassium (K) acquisition by roots was diminished by O-3 exposure of the shoot. For Ca, Mg, Fe and Zn reduced uptake by the roots was combined with reduced allocation to the shoot, resulting in a decline of foliar concentrations; for Na and K, allocation to the shoot was maintained at the expense of the roots. Thus, elevated O3 impaired both mineral uptake by the roots and partitioning of minerals between roots and shoots, but in an element specific way. Thereby, elevated O-3 affected roots and shoots differently already after one growing season. However, considerable changes in total C and N concentrations and their partitioning between different metabolic pools upon chronic O-3 ex-posure were not observed in either leaves or roots, except for reduced foliar lignin concentrations at 2 x ambient O-3. Significant differences in these parameters were shown between leaves and roots independent of O(3 )application. The physiological consequences of the effects of chronic O-3 exposure on mineral acquisition and partitioning between leaves and roots are discussed.}, author = {Arab, L. and Hoshika, Y. and Paoletti, E. and White, P. J. and Dannenmann, M. and Mueller, H. and Ache, P. and Hedrich, R. and Alfarraj, S. and Albasher, G. and Rennenberg, H.}, journal = {Science of the Total Environment}, keywords = {carbon}, note = {G9lu3 Times Cited:1 Cited References Count:64}, title = {Chronic ozone exposure impairs the mineral nutrition of date palm ( ) seedlings}, type = {Journal Article}, volume = 862, year = 2023 }

  %0 Journal Article %1 RN957 %A Arab, L. %A Hoshika, Y. %A Paoletti, E. %A White, P. J. %A Dannenmann, M. %A Mueller, H. %A Ache, P. %A Hedrich, R. %A Alfarraj, S. %A Albasher, G. %A Rennenberg, H. %D 2023 %J Science of the Total Environment %R ARTN 160675 10.1016/j.scitotenv.2022.160675 %T Chronic ozone exposure impairs the mineral nutrition of date palm ( ) seedlings %U /brokenurl#<Go to ISI>://WOS:000992292900001 %V 862 %X Chronic ozone (O-3) exposure in the atmosphere preferentially disturbs metabolic processes in the roots rather than the shoot as a consequence of reduced photosynthesis and carbohydrate allocation from the leaves to the roots. The aim of the present study was to elucidate if mineral nutrition is also impaired by chronic O3 exposure. For this purpose, date palm (Phoenix dactylifera) plants were fumigated with ambient, 1.5 x ambient and 2 x ambient O-3 in a free air con-trolled exposure (FACE) system for one growing season and concentrations of major nutrients were analyzed in leaves and roots. In addition, concentrations of C and N and their partitioning between different metabolic C and N pools were determined in both organs. The results showed that calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), sodium (Na) and potassium (K) acquisition by roots was diminished by O-3 exposure of the shoot. For Ca, Mg, Fe and Zn reduced uptake by the roots was combined with reduced allocation to the shoot, resulting in a decline of foliar concentrations; for Na and K, allocation to the shoot was maintained at the expense of the roots. Thus, elevated O3 impaired both mineral uptake by the roots and partitioning of minerals between roots and shoots, but in an element specific way. Thereby, elevated O-3 affected roots and shoots differently already after one growing season. However, considerable changes in total C and N concentrations and their partitioning between different metabolic pools upon chronic O-3 ex-posure were not observed in either leaves or roots, except for reduced foliar lignin concentrations at 2 x ambient O-3. Significant differences in these parameters were shown between leaves and roots independent of O(3 )application. The physiological consequences of the effects of chronic O-3 exposure on mineral acquisition and partitioning between leaves and roots are discussed.
• Differences of nitrogen metabolism in date palm (Phoenix dactylifera) seedlings subjected to water deprivation and salt exposure. Du, B. G.; Winkler, J. B.; Ache, P.; White, P. J.; Dannenmann, M.; Alfarraj, S.; Albasher, G.; Schnitzler, J. P.; Hedrich, R.; Rennenberg, H. In Tree Physiology, 43(4), pp. 587–596. 2023.
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  Drought and salt exposure are among the most prevalent and severe abiotic stressors causing serious agricultural yield losses, alone and in combination. Little is known about differences and similarities in the effects of these two stress factors on plant metabolic regulation, particularly on nitrogen metabolism. Here, we studied the effects of water deprivation and salt exposure on water relations and nitrogen metabolites in leaves and roots of date palm seedlings. Both, water deprivation and salt exposure had no significant effects on plant water content or stable carbon (C) and nitrogen (N) isotope signatures. Significant effects of water deprivation on total C and N concentrations were only observed in roots, i.e., decreased total C and increased total N concentrations. Whereas salt exposure initially decreased total C and increased total N concentrations significantly in roots, foliar total C concentration was increased upon prolonged exposure. Initially C/N ratios declined in roots of plants from both treatments and upon prolonged salt exposure also in the leaves. Neither treatment affected soluble protein and structural N concentrations in leaves or roots, but resulted in the accumulation of most amino acids, except for glutamate and tryptophan, which remained stable, and serine, which decreased, in roots. Accumulation of the most abundant amino acids, lysine and proline, was observed in roots under both treatments, but in leaves only upon salt exposure. This finding indicates a similar role of these amino acids as compatible solutes in the roots in response to salt und drought, but not in the leaves. Upon prolonged treatment, amino acid concentrations returned to levels found in unstressed plants in leaves of water deprived, but not salt exposed, plants. The present results show both water deprivation and salt exposure strongly impact N metabolism of date palm seedlings, but in a different manner in leaves and roots.

  @article{RN956, abstract = {Drought and salt exposure are among the most prevalent and severe abiotic stressors causing serious agricultural yield losses, alone and in combination. Little is known about differences and similarities in the effects of these two stress factors on plant metabolic regulation, particularly on nitrogen metabolism. Here, we studied the effects of water deprivation and salt exposure on water relations and nitrogen metabolites in leaves and roots of date palm seedlings. Both, water deprivation and salt exposure had no significant effects on plant water content or stable carbon (C) and nitrogen (N) isotope signatures. Significant effects of water deprivation on total C and N concentrations were only observed in roots, i.e., decreased total C and increased total N concentrations. Whereas salt exposure initially decreased total C and increased total N concentrations significantly in roots, foliar total C concentration was increased upon prolonged exposure. Initially C/N ratios declined in roots of plants from both treatments and upon prolonged salt exposure also in the leaves. Neither treatment affected soluble protein and structural N concentrations in leaves or roots, but resulted in the accumulation of most amino acids, except for glutamate and tryptophan, which remained stable, and serine, which decreased, in roots. Accumulation of the most abundant amino acids, lysine and proline, was observed in roots under both treatments, but in leaves only upon salt exposure. This finding indicates a similar role of these amino acids as compatible solutes in the roots in response to salt und drought, but not in the leaves. Upon prolonged treatment, amino acid concentrations returned to levels found in unstressed plants in leaves of water deprived, but not salt exposed, plants. The present results show both water deprivation and salt exposure strongly impact N metabolism of date palm seedlings, but in a different manner in leaves and roots.}, author = {Du, B. G. and Winkler, J. B. and Ache, P. and White, P. J. and Dannenmann, M. and Alfarraj, S. and Albasher, G. and Schnitzler, J. P. and Hedrich, R. and Rennenberg, H.}, journal = {Tree Physiology}, keywords = {amino}, note = {D0nd6 Times Cited:2 Cited References Count:63}, number = 4, pages = {587-596}, title = {Differences of nitrogen metabolism in date palm (Phoenix dactylifera) seedlings subjected to water deprivation and salt exposure}, type = {Journal Article}, volume = 43, year = 2023 }

  %0 Journal Article %1 RN956 %A Du, B. G. %A Winkler, J. B. %A Ache, P. %A White, P. J. %A Dannenmann, M. %A Alfarraj, S. %A Albasher, G. %A Schnitzler, J. P. %A Hedrich, R. %A Rennenberg, H. %D 2023 %J Tree Physiology %N 4 %P 587-596 %R 10.1093/treephys/tpac145 %T Differences of nitrogen metabolism in date palm (Phoenix dactylifera) seedlings subjected to water deprivation and salt exposure %U /brokenurl#<Go to ISI>://WOS:000944996600001 %V 43 %X Drought and salt exposure are among the most prevalent and severe abiotic stressors causing serious agricultural yield losses, alone and in combination. Little is known about differences and similarities in the effects of these two stress factors on plant metabolic regulation, particularly on nitrogen metabolism. Here, we studied the effects of water deprivation and salt exposure on water relations and nitrogen metabolites in leaves and roots of date palm seedlings. Both, water deprivation and salt exposure had no significant effects on plant water content or stable carbon (C) and nitrogen (N) isotope signatures. Significant effects of water deprivation on total C and N concentrations were only observed in roots, i.e., decreased total C and increased total N concentrations. Whereas salt exposure initially decreased total C and increased total N concentrations significantly in roots, foliar total C concentration was increased upon prolonged exposure. Initially C/N ratios declined in roots of plants from both treatments and upon prolonged salt exposure also in the leaves. Neither treatment affected soluble protein and structural N concentrations in leaves or roots, but resulted in the accumulation of most amino acids, except for glutamate and tryptophan, which remained stable, and serine, which decreased, in roots. Accumulation of the most abundant amino acids, lysine and proline, was observed in roots under both treatments, but in leaves only upon salt exposure. This finding indicates a similar role of these amino acids as compatible solutes in the roots in response to salt und drought, but not in the leaves. Upon prolonged treatment, amino acid concentrations returned to levels found in unstressed plants in leaves of water deprived, but not salt exposed, plants. The present results show both water deprivation and salt exposure strongly impact N metabolism of date palm seedlings, but in a different manner in leaves and roots.
• Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling. Graus, D.; Li, K. K.; Rathje, J. M.; Ding, M. Q.; Krischke, M.; Müller, M. J.; Cuin, T. A.; Al-Rasheid, K. A. S.; Scherzer, S.; Marten, I.; Konrad, K. R.; Hedrich, R. In New Phytologist, 237(1), pp. 217–231. 2023.
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  Salt stress is a major abiotic stress, responsible for declining agricultural productivity. Roots are regarded as hubs for salt detoxification, however, leaf salt concentrations may exceed those of roots. How mature leaves manage acute sodium chloride (NaCl) stress is mostly unknown. To analyze the mechanisms for NaCl redistribution in leaves, salt was infiltrated into intact tobacco leaves. It initiated pronounced osmotically-driven leaf movements. Leaf downward movement caused by hydro-passive turgor loss reached a maximum within 2 h. Salt-driven cellular water release was accompanied by a transient change in membrane depolarization but not an increase in cytosolic calcium ion (Ca2+) level. Nonetheless, only half an hour later, the leaves had completely regained turgor. This recovery phase was characterized by an increase in mesophyll cell plasma membrane hydrogen ion (H+) pumping, a salt uptake-dependent cytosolic alkalization, and a return of the apoplast osmolality to pre-stress levels. Although, transcript numbers of abscisic acid- and Salt Overly Sensitive pathway elements remained unchanged, salt adaptation depended on the vacuolar H+/Na+-exchanger NHX1. Altogether, tobacco leaves can detoxify sodium ions (Na+) rapidly even under massive salt loads, based on pre-established posttranslational settings and NHX1 cation/H+ antiport activity. Unlike roots, signaling and processing of salt stress in tobacco leaves does not depend on Ca2+ signaling.

  @article{RN955, abstract = {Salt stress is a major abiotic stress, responsible for declining agricultural productivity. Roots are regarded as hubs for salt detoxification, however, leaf salt concentrations may exceed those of roots. How mature leaves manage acute sodium chloride (NaCl) stress is mostly unknown. To analyze the mechanisms for NaCl redistribution in leaves, salt was infiltrated into intact tobacco leaves. It initiated pronounced osmotically-driven leaf movements. Leaf downward movement caused by hydro-passive turgor loss reached a maximum within 2 h. Salt-driven cellular water release was accompanied by a transient change in membrane depolarization but not an increase in cytosolic calcium ion (Ca2+) level. Nonetheless, only half an hour later, the leaves had completely regained turgor. This recovery phase was characterized by an increase in mesophyll cell plasma membrane hydrogen ion (H+) pumping, a salt uptake-dependent cytosolic alkalization, and a return of the apoplast osmolality to pre-stress levels. Although, transcript numbers of abscisic acid- and Salt Overly Sensitive pathway elements remained unchanged, salt adaptation depended on the vacuolar H+/Na+-exchanger NHX1. Altogether, tobacco leaves can detoxify sodium ions (Na+) rapidly even under massive salt loads, based on pre-established posttranslational settings and NHX1 cation/H+ antiport activity. Unlike roots, signaling and processing of salt stress in tobacco leaves does not depend on Ca2+ signaling.}, author = {Graus, D. and Li, K. K. and Rathje, J. M. and Ding, M. Q. and Krischke, M. and Müller, M. J. and Cuin, T. A. and Al-Rasheid, K. A. S. and Scherzer, S. and Marten, I. and Konrad, K. R. and Hedrich, R.}, journal = {New Phytologist}, keywords = {calcium}, note = {7d8wy Times Cited:2 Cited References Count:94}, number = 1, pages = {217-231}, title = {Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling}, type = {Journal Article}, volume = 237, year = 2023 }

  %0 Journal Article %1 RN955 %A Graus, D. %A Li, K. K. %A Rathje, J. M. %A Ding, M. Q. %A Krischke, M. %A Müller, M. J. %A Cuin, T. A. %A Al-Rasheid, K. A. S. %A Scherzer, S. %A Marten, I. %A Konrad, K. R. %A Hedrich, R. %D 2023 %J New Phytologist %N 1 %P 217-231 %R 10.1111/nph.18501 %T Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling %U /brokenurl#<Go to ISI>://WOS:000867857600001 %V 237 %X Salt stress is a major abiotic stress, responsible for declining agricultural productivity. Roots are regarded as hubs for salt detoxification, however, leaf salt concentrations may exceed those of roots. How mature leaves manage acute sodium chloride (NaCl) stress is mostly unknown. To analyze the mechanisms for NaCl redistribution in leaves, salt was infiltrated into intact tobacco leaves. It initiated pronounced osmotically-driven leaf movements. Leaf downward movement caused by hydro-passive turgor loss reached a maximum within 2 h. Salt-driven cellular water release was accompanied by a transient change in membrane depolarization but not an increase in cytosolic calcium ion (Ca2+) level. Nonetheless, only half an hour later, the leaves had completely regained turgor. This recovery phase was characterized by an increase in mesophyll cell plasma membrane hydrogen ion (H+) pumping, a salt uptake-dependent cytosolic alkalization, and a return of the apoplast osmolality to pre-stress levels. Although, transcript numbers of abscisic acid- and Salt Overly Sensitive pathway elements remained unchanged, salt adaptation depended on the vacuolar H+/Na+-exchanger NHX1. Altogether, tobacco leaves can detoxify sodium ions (Na+) rapidly even under massive salt loads, based on pre-established posttranslational settings and NHX1 cation/H+ antiport activity. Unlike roots, signaling and processing of salt stress in tobacco leaves does not depend on Ca2+ signaling.
• Demystifying the Venus flytrap action potential. Hedrich, R.; Kreuzer, I. In New Phytologist, 239(6), pp. 2108–2112. 2023.
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  All plants are electrically excitable, but only few are known to fire a well-defined, all-or-nothing action potential (AP). The Venus flytrap Dionaea muscipula displays APs with an extraordinarily high firing frequency and speed, enabling the capture organ of this carnivorous plant to catch small animals as fast as flies. The number of APs triggered by the prey is counted and serves as the basis for decisions within the flytrap's hunting cycle. The archetypical Dionaea AP lasts 1 s and consists of five phases: Starting from the resting state, an initial cytosolic Ca2+ transient is followed by depolarization, repolarization and a transient hyperpolarization (overshoot) before the original membrane potential is finally recovered. When the flytrap matures and becomes excitable, a distinct set of ion channels, pumps and carriers is expressed, each mastering a distinct AP phase.

  @article{RN954, abstract = {All plants are electrically excitable, but only few are known to fire a well-defined, all-or-nothing action potential (AP). The Venus flytrap Dionaea muscipula displays APs with an extraordinarily high firing frequency and speed, enabling the capture organ of this carnivorous plant to catch small animals as fast as flies. The number of APs triggered by the prey is counted and serves as the basis for decisions within the flytrap's hunting cycle. The archetypical Dionaea AP lasts 1 s and consists of five phases: Starting from the resting state, an initial cytosolic Ca2+ transient is followed by depolarization, repolarization and a transient hyperpolarization (overshoot) before the original membrane potential is finally recovered. When the flytrap matures and becomes excitable, a distinct set of ion channels, pumps and carriers is expressed, each mastering a distinct AP phase.}, author = {Hedrich, R. and Kreuzer, I.}, journal = {New Phytologist}, keywords = {potential}, note = {W7mi6 Times Cited:1 Cited References Count:41}, number = 6, pages = {2108-2112}, title = {Demystifying the Venus flytrap action potential}, type = {Journal Article}, volume = 239, year = 2023 }

  %0 Journal Article %1 RN954 %A Hedrich, R. %A Kreuzer, I. %D 2023 %J New Phytologist %N 6 %P 2108-2112 %R 10.1111/nph.19113 %T Demystifying the Venus flytrap action potential %U /brokenurl#<Go to ISI>://WOS:001024630100001 %V 239 %X All plants are electrically excitable, but only few are known to fire a well-defined, all-or-nothing action potential (AP). The Venus flytrap Dionaea muscipula displays APs with an extraordinarily high firing frequency and speed, enabling the capture organ of this carnivorous plant to catch small animals as fast as flies. The number of APs triggered by the prey is counted and serves as the basis for decisions within the flytrap's hunting cycle. The archetypical Dionaea AP lasts 1 s and consists of five phases: Starting from the resting state, an initial cytosolic Ca2+ transient is followed by depolarization, repolarization and a transient hyperpolarization (overshoot) before the original membrane potential is finally recovered. When the flytrap matures and becomes excitable, a distinct set of ion channels, pumps and carriers is expressed, each mastering a distinct AP phase.
• ALMT-independent guard cell R-type anion currents. Jaslan, J.; Marten, I.; Jakobson, L.; Arjus, T.; Deeken, R.; Sarmiento, C.; De Angeli, A.; Brosché, M.; Kollist, H.; Hedrich, R. In New Phytologist, 239(6), pp. 2225–2234. 2023.
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  Plant transpiration is controlled by stomata, with S- and R-type anion channels playing key roles in guard cell action. Arabidopsis mutants lacking the ALMT12/QUAC1 R-type anion channel function in guard cells show only a partial reduction in R-type channel currents. The molecular nature of these remaining R-type anion currents is still unclear. To further elucidate this, patch clamp, transcript and gas-exchange measurements were performed with wild-type (WT) and different almt mutant plants. The R-type current fraction in the almt12 mutant exhibited the same voltage dependence, susceptibility to ATP block and lacked a chloride permeability as the WT. Therefore, we asked whether the R-type anion currents in the ALMT12/QUAC1-free mutant are caused by additional ALMT isoforms. In WT guard cells, ALMT12, ALMT13 and ALMT14 transcripts were detected, whereas only ALMT13 was found expressed in the almt12 mutant. Substantial R-type anion currents still remained active in the almt12/13 and almt12/14 double mutants as well as the almt12/13/14 triple mutant. In good agreement, CO2-triggered stomatal closure required the activity of ALMT12 but not ALMT13 or ALMT14. The results suggest that, with the exception of ALMT12, channel species other than ALMTs carry the guard cell R-type anion currents.

  @article{RN949, abstract = {Plant transpiration is controlled by stomata, with S- and R-type anion channels playing key roles in guard cell action. Arabidopsis mutants lacking the ALMT12/QUAC1 R-type anion channel function in guard cells show only a partial reduction in R-type channel currents. The molecular nature of these remaining R-type anion currents is still unclear. To further elucidate this, patch clamp, transcript and gas-exchange measurements were performed with wild-type (WT) and different almt mutant plants. The R-type current fraction in the almt12 mutant exhibited the same voltage dependence, susceptibility to ATP block and lacked a chloride permeability as the WT. Therefore, we asked whether the R-type anion currents in the ALMT12/QUAC1-free mutant are caused by additional ALMT isoforms. In WT guard cells, ALMT12, ALMT13 and ALMT14 transcripts were detected, whereas only ALMT13 was found expressed in the almt12 mutant. Substantial R-type anion currents still remained active in the almt12/13 and almt12/14 double mutants as well as the almt12/13/14 triple mutant. In good agreement, CO2-triggered stomatal closure required the activity of ALMT12 but not ALMT13 or ALMT14. The results suggest that, with the exception of ALMT12, channel species other than ALMTs carry the guard cell R-type anion currents.}, author = {Jaslan, J. and Marten, I. and Jakobson, L. and Arjus, T. and Deeken, R. and Sarmiento, C. and De Angeli, A. and Brosché, M. and Kollist, H. and Hedrich, R.}, journal = {New Phytologist}, keywords = {almt}, note = {W7mi6 Times Cited:2 Cited References Count:44}, number = 6, pages = {2225-2234}, title = {ALMT-independent guard cell R-type anion currents}, type = {Journal Article}, volume = 239, year = 2023 }

  %0 Journal Article %1 RN949 %A Jaslan, J. %A Marten, I. %A Jakobson, L. %A Arjus, T. %A Deeken, R. %A Sarmiento, C. %A De Angeli, A. %A Brosché, M. %A Kollist, H. %A Hedrich, R. %D 2023 %J New Phytologist %N 6 %P 2225-2234 %R 10.1111/nph.19124 %T ALMT-independent guard cell R-type anion currents %U /brokenurl#<Go to ISI>://WOS:001027639800001 %V 239 %X Plant transpiration is controlled by stomata, with S- and R-type anion channels playing key roles in guard cell action. Arabidopsis mutants lacking the ALMT12/QUAC1 R-type anion channel function in guard cells show only a partial reduction in R-type channel currents. The molecular nature of these remaining R-type anion currents is still unclear. To further elucidate this, patch clamp, transcript and gas-exchange measurements were performed with wild-type (WT) and different almt mutant plants. The R-type current fraction in the almt12 mutant exhibited the same voltage dependence, susceptibility to ATP block and lacked a chloride permeability as the WT. Therefore, we asked whether the R-type anion currents in the ALMT12/QUAC1-free mutant are caused by additional ALMT isoforms. In WT guard cells, ALMT12, ALMT13 and ALMT14 transcripts were detected, whereas only ALMT13 was found expressed in the almt12 mutant. Substantial R-type anion currents still remained active in the almt12/13 and almt12/14 double mutants as well as the almt12/13/14 triple mutant. In good agreement, CO2-triggered stomatal closure required the activity of ALMT12 but not ALMT13 or ALMT14. The results suggest that, with the exception of ALMT12, channel species other than ALMTs carry the guard cell R-type anion currents.
• Carnivory on demand: phosphorus deficiency induces glandular leaves in the African liana. Winkelmann, T.; Bringmann, G.; Herwig, A.; Hedrich, R. In New Phytologist, 239(3), pp. 1140–1152. 2023.
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  center dot Triphyophyllum peltatum, a rare tropical African liana, is unique in its facultative carnivory. The trigger for carnivory is yet unknown, mainly because the plant is difficult to propagate and cultivate. This study aimed at identifying the conditions that result in the formation of carnivorous leaves. center dot In vitro shoots were subjected to abiotic stressors in general and deficiencies of the major nutrients nitrogen, potassium and phosphorus in particular, to trigger carnivorous leaves' development. Adventitious root formation was improved to allow verification of the trigger in glasshouse-grown plants. center dot Among all the stressors tested, only under phosphorus deficiency, the formation of carnivorous leaves was observed. These glandular leaves fully resembled those found under natural growing conditions including the secretion of sticky liquid by mature capture organs. To generate plants for glasshouse experiments, a pulse of 55.4 lM alpha-naphthaleneacetic acid was essential to achieve 90% in vitro rooting. This plant material facilitated the confirmation of phosphorus starvation to be essential and sufficient for carnivory induction, also under ex vitro conditions. center dot Having established the cultivation of T. peltatum and the induction of carnivory, future gene expression profiles from phosphorus starvation-induced leaves will provide important insight to the molecular mechanism of carnivory on demand.molecular mechanism of carnivory on demand.

  @article{RN946, abstract = {center dot Triphyophyllum peltatum, a rare tropical African liana, is unique in its facultative carnivory. The trigger for carnivory is yet unknown, mainly because the plant is difficult to propagate and cultivate. This study aimed at identifying the conditions that result in the formation of carnivorous leaves. center dot In vitro shoots were subjected to abiotic stressors in general and deficiencies of the major nutrients nitrogen, potassium and phosphorus in particular, to trigger carnivorous leaves' development. Adventitious root formation was improved to allow verification of the trigger in glasshouse-grown plants. center dot Among all the stressors tested, only under phosphorus deficiency, the formation of carnivorous leaves was observed. These glandular leaves fully resembled those found under natural growing conditions including the secretion of sticky liquid by mature capture organs. To generate plants for glasshouse experiments, a pulse of 55.4 lM alpha-naphthaleneacetic acid was essential to achieve 90% in vitro rooting. This plant material facilitated the confirmation of phosphorus starvation to be essential and sufficient for carnivory induction, also under ex vitro conditions. center dot Having established the cultivation of T. peltatum and the induction of carnivory, future gene expression profiles from phosphorus starvation-induced leaves will provide important insight to the molecular mechanism of carnivory on demand.molecular mechanism of carnivory on demand.}, author = {Winkelmann, T. and Bringmann, G. and Herwig, A. and Hedrich, R.}, journal = {New Phytologist}, keywords = {carnivory}, note = {L1vj3 Times Cited:1 Cited References Count:54}, number = 3, pages = {1140-1152}, title = {Carnivory on demand: phosphorus deficiency induces glandular leaves in the African liana}, type = {Journal Article}, volume = 239, year = 2023 }

  %0 Journal Article %1 RN946 %A Winkelmann, T. %A Bringmann, G. %A Herwig, A. %A Hedrich, R. %D 2023 %J New Phytologist %N 3 %P 1140-1152 %R 10.1111/nph.18960 %T Carnivory on demand: phosphorus deficiency induces glandular leaves in the African liana %U /brokenurl#<Go to ISI>://WOS:000988939000001 %V 239 %X center dot Triphyophyllum peltatum, a rare tropical African liana, is unique in its facultative carnivory. The trigger for carnivory is yet unknown, mainly because the plant is difficult to propagate and cultivate. This study aimed at identifying the conditions that result in the formation of carnivorous leaves. center dot In vitro shoots were subjected to abiotic stressors in general and deficiencies of the major nutrients nitrogen, potassium and phosphorus in particular, to trigger carnivorous leaves' development. Adventitious root formation was improved to allow verification of the trigger in glasshouse-grown plants. center dot Among all the stressors tested, only under phosphorus deficiency, the formation of carnivorous leaves was observed. These glandular leaves fully resembled those found under natural growing conditions including the secretion of sticky liquid by mature capture organs. To generate plants for glasshouse experiments, a pulse of 55.4 lM alpha-naphthaleneacetic acid was essential to achieve 90% in vitro rooting. This plant material facilitated the confirmation of phosphorus starvation to be essential and sufficient for carnivory induction, also under ex vitro conditions. center dot Having established the cultivation of T. peltatum and the induction of carnivory, future gene expression profiles from phosphorus starvation-induced leaves will provide important insight to the molecular mechanism of carnivory on demand.molecular mechanism of carnivory on demand.
• Subgenome dominance shapes novel gene evolution in the decaploid pitcher plant. Saul, F.; Scharmann, M.; Wakatake, T.; Rajaraman, S.; Marques, A.; Freund, M.; Bringmann, G.; Channon, L.; Becker, D.; Carroll, E.; Low, Y. W.; Lindqvist, C.; Gilbert, K. J.; Renner, T.; Masuda, S.; Richter, M.; Vogg, G.; Shirasu, K.; Michael, T. P.; Hedrich, R.; Albert, V. A.; Fukushima, K. In Nature Plants. 2023.
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  Subgenome dominance after whole-genome duplication generates distinction in gene number and expression at the level of chromosome sets, but it remains unclear how this process may be involved in evolutionary novelty. Here we generated a chromosome-scale genome assembly of the Asian pitcher plant Nepenthes gracilis to analyse how its novel traits (dioecy and carnivorous pitcher leaves) are linked to genomic evolution. We found a decaploid karyotype and a clear indication of subgenome dominance. A male-linked and pericentromerically located region on the putative sex chromosome was identified in a recessive subgenome and was found to harbour three transcription factors involved in flower and pollen development, including a likely neofunctionalized LEAFY duplicate. Transcriptomic and syntenic analyses of carnivory-related genes suggested that the paleopolyploidization events seeded genes that subsequently formed tandem clusters in recessive subgenomes with specific expression in the digestive zone of the pitcher, where specialized cells digest prey and absorb derived nutrients. A genome-scale analysis suggested that subgenome dominance likely contributed to evolutionary innovation by permitting recessive subgenomes to diversify functions of novel tissue-specific duplicates. Our results provide insight into how polyploidy can give rise to novel traits in divergent and successful high-ploidy lineages.

  @article{RN947, abstract = {Subgenome dominance after whole-genome duplication generates distinction in gene number and expression at the level of chromosome sets, but it remains unclear how this process may be involved in evolutionary novelty. Here we generated a chromosome-scale genome assembly of the Asian pitcher plant Nepenthes gracilis to analyse how its novel traits (dioecy and carnivorous pitcher leaves) are linked to genomic evolution. We found a decaploid karyotype and a clear indication of subgenome dominance. A male-linked and pericentromerically located region on the putative sex chromosome was identified in a recessive subgenome and was found to harbour three transcription factors involved in flower and pollen development, including a likely neofunctionalized LEAFY duplicate. Transcriptomic and syntenic analyses of carnivory-related genes suggested that the paleopolyploidization events seeded genes that subsequently formed tandem clusters in recessive subgenomes with specific expression in the digestive zone of the pitcher, where specialized cells digest prey and absorb derived nutrients. A genome-scale analysis suggested that subgenome dominance likely contributed to evolutionary innovation by permitting recessive subgenomes to diversify functions of novel tissue-specific duplicates. Our results provide insight into how polyploidy can give rise to novel traits in divergent and successful high-ploidy lineages.}, author = {Saul, F. and Scharmann, M. and Wakatake, T. and Rajaraman, S. and Marques, A. and Freund, M. and Bringmann, G. and Channon, L. and Becker, D. and Carroll, E. and Low, Y. W. and Lindqvist, C. and Gilbert, K. J. and Renner, T. and Masuda, S. and Richter, M. and Vogg, G. and Shirasu, K. and Michael, T. P. and Hedrich, R. and Albert, V. A. and Fukushima, K.}, journal = {Nature Plants}, keywords = {isoquinoline}, note = {Z0jr2 Times Cited:1 Cited References Count:117}, title = {Subgenome dominance shapes novel gene evolution in the decaploid pitcher plant}, type = {Journal Article}, year = 2023 }

  %0 Journal Article %1 RN947 %A Saul, F. %A Scharmann, M. %A Wakatake, T. %A Rajaraman, S. %A Marques, A. %A Freund, M. %A Bringmann, G. %A Channon, L. %A Becker, D. %A Carroll, E. %A Low, Y. W. %A Lindqvist, C. %A Gilbert, K. J. %A Renner, T. %A Masuda, S. %A Richter, M. %A Vogg, G. %A Shirasu, K. %A Michael, T. P. %A Hedrich, R. %A Albert, V. A. %A Fukushima, K. %D 2023 %J Nature Plants %R 10.1038/s41477-023-01562-2 %T Subgenome dominance shapes novel gene evolution in the decaploid pitcher plant %U /brokenurl#<Go to ISI>://WOS:001109037700002 %X Subgenome dominance after whole-genome duplication generates distinction in gene number and expression at the level of chromosome sets, but it remains unclear how this process may be involved in evolutionary novelty. Here we generated a chromosome-scale genome assembly of the Asian pitcher plant Nepenthes gracilis to analyse how its novel traits (dioecy and carnivorous pitcher leaves) are linked to genomic evolution. We found a decaploid karyotype and a clear indication of subgenome dominance. A male-linked and pericentromerically located region on the putative sex chromosome was identified in a recessive subgenome and was found to harbour three transcription factors involved in flower and pollen development, including a likely neofunctionalized LEAFY duplicate. Transcriptomic and syntenic analyses of carnivory-related genes suggested that the paleopolyploidization events seeded genes that subsequently formed tandem clusters in recessive subgenomes with specific expression in the digestive zone of the pitcher, where specialized cells digest prey and absorb derived nutrients. A genome-scale analysis suggested that subgenome dominance likely contributed to evolutionary innovation by permitting recessive subgenomes to diversify functions of novel tissue-specific duplicates. Our results provide insight into how polyploidy can give rise to novel traits in divergent and successful high-ploidy lineages.

• Transporter networks can serve plant cells as nutrient sensors and mimic transceptor-like behavior. Dreyer, I.; Li, K. K.; Riedelsberger, J.; Hedrich, R.; Konrad, K. R.; Michard, E. In Iscience, 25(4). 2022.
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  Sensing of external mineral nutrient concentrations is essential for plants to colonize environments with a large spectrum of nutrient availability. Here, we analyzed transporter networks in computational cell biology simulations to understand better the initial steps of this sensing process. The networks analyzed were capable of translating the information of changing external nutrient concentrations into cytosolic H+ and Ca2+ signals, two of the most ubiquitous cellular second messengers. The concept emerging from the computational simulations was confirmed in wet-lab experiments. We document in guard cells that alterations in the external KCl concentration were translated into cytosolic H+ and Ca2+ transients as predicted. We show that transporter networks do not only serve their primary task of transport, but can also take on the role of a receptor without requiring conformational changes of a transporter protein. Such transceptor-like phenomena may be quite common in plants.

  @article{RN964, abstract = {Sensing of external mineral nutrient concentrations is essential for plants to colonize environments with a large spectrum of nutrient availability. Here, we analyzed transporter networks in computational cell biology simulations to understand better the initial steps of this sensing process. The networks analyzed were capable of translating the information of changing external nutrient concentrations into cytosolic H+ and Ca2+ signals, two of the most ubiquitous cellular second messengers. The concept emerging from the computational simulations was confirmed in wet-lab experiments. We document in guard cells that alterations in the external KCl concentration were translated into cytosolic H+ and Ca2+ transients as predicted. We show that transporter networks do not only serve their primary task of transport, but can also take on the role of a receptor without requiring conformational changes of a transporter protein. Such transceptor-like phenomena may be quite common in plants.}, author = {Dreyer, I. and Li, K. K. and Riedelsberger, J. and Hedrich, R. and Konrad, K. R. and Michard, E.}, journal = {Iscience}, keywords = {nitrate}, note = {2p6ts Times Cited:3 Cited References Count:55}, number = 4, title = {Transporter networks can serve plant cells as nutrient sensors and mimic transceptor-like behavior}, type = {Journal Article}, volume = 25, year = 2022 }

  %0 Journal Article %1 RN964 %A Dreyer, I. %A Li, K. K. %A Riedelsberger, J. %A Hedrich, R. %A Konrad, K. R. %A Michard, E. %D 2022 %J Iscience %N 4 %R ARTN 104078 10.1016/j.isci.2022.104078 %T Transporter networks can serve plant cells as nutrient sensors and mimic transceptor-like behavior %U /brokenurl#<Go to ISI>://WOS:000819871400001 %V 25 %X Sensing of external mineral nutrient concentrations is essential for plants to colonize environments with a large spectrum of nutrient availability. Here, we analyzed transporter networks in computational cell biology simulations to understand better the initial steps of this sensing process. The networks analyzed were capable of translating the information of changing external nutrient concentrations into cytosolic H+ and Ca2+ signals, two of the most ubiquitous cellular second messengers. The concept emerging from the computational simulations was confirmed in wet-lab experiments. We document in guard cells that alterations in the external KCl concentration were translated into cytosolic H+ and Ca2+ transients as predicted. We show that transporter networks do not only serve their primary task of transport, but can also take on the role of a receptor without requiring conformational changes of a transporter protein. Such transceptor-like phenomena may be quite common in plants.
• The green light gap: a window of opportunity for optogenetic control of stomatal movement. Jones, J. J.; Huang, S. G.; Hedrich, R.; Geilfus, C. M.; Roelfsema, M. R. G. In New Phytologist, 236(4), pp. 1237–1244. 2022.
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  Green plants are equipped with photoreceptors that are capable of sensing radiation in the ultraviolet to blue and the red to far-red parts of the light spectrum. However, plant cells are not particularly sensitive to green light (GL), and light which lies within this part of the spectrum does not efficiently trigger the opening of stomatal pores. Here, we discuss the current knowledge of stomatal responses to light, which are either provoked via photosynthetically active radiation or by specific blue light (BL) signaling pathways. The limited impact of GL on stomatal movements provides a unique option to use this light quality to control optogenetic tools. Recently, several of these tools have been optimized for use in plant biological research, either to control gene expression, or to provoke ion fluxes. Initial studies with the BL-activated potassium channel BLINK1 showed that this tool can speed up stomatal movements. Moreover, the GL-sensitive anion channel GtACR1 can induce stomatal closure, even at conditions that provoke stomatal opening in wild-type plants. Given that crop plants in controlled-environment agriculture and horticulture are often cultivated with artificial light sources (i.e. a combination of blue and red light from light-emitting diodes), GL signals can be used as a remote-control signal that controls stomatal transpiration and water consumption.

  @article{RN962, abstract = {Green plants are equipped with photoreceptors that are capable of sensing radiation in the ultraviolet to blue and the red to far-red parts of the light spectrum. However, plant cells are not particularly sensitive to green light (GL), and light which lies within this part of the spectrum does not efficiently trigger the opening of stomatal pores. Here, we discuss the current knowledge of stomatal responses to light, which are either provoked via photosynthetically active radiation or by specific blue light (BL) signaling pathways. The limited impact of GL on stomatal movements provides a unique option to use this light quality to control optogenetic tools. Recently, several of these tools have been optimized for use in plant biological research, either to control gene expression, or to provoke ion fluxes. Initial studies with the BL-activated potassium channel BLINK1 showed that this tool can speed up stomatal movements. Moreover, the GL-sensitive anion channel GtACR1 can induce stomatal closure, even at conditions that provoke stomatal opening in wild-type plants. Given that crop plants in controlled-environment agriculture and horticulture are often cultivated with artificial light sources (i.e. a combination of blue and red light from light-emitting diodes), GL signals can be used as a remote-control signal that controls stomatal transpiration and water consumption.}, author = {Jones, J. J. and Huang, S. G. and Hedrich, R. and Geilfus, C. M. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {channel}, note = {7t8fe Times Cited:1 Cited References Count:79}, number = 4, pages = {1237-1244}, title = {The green light gap: a window of opportunity for optogenetic control of stomatal movement}, type = {Journal Article}, volume = 236, year = 2022 }

  %0 Journal Article %1 RN962 %A Jones, J. J. %A Huang, S. G. %A Hedrich, R. %A Geilfus, C. M. %A Roelfsema, M. R. G. %D 2022 %J New Phytologist %N 4 %P 1237-1244 %R 10.1111/nph.18451 %T The green light gap: a window of opportunity for optogenetic control of stomatal movement %U /brokenurl#<Go to ISI>://WOS:000859940000001 %V 236 %X Green plants are equipped with photoreceptors that are capable of sensing radiation in the ultraviolet to blue and the red to far-red parts of the light spectrum. However, plant cells are not particularly sensitive to green light (GL), and light which lies within this part of the spectrum does not efficiently trigger the opening of stomatal pores. Here, we discuss the current knowledge of stomatal responses to light, which are either provoked via photosynthetically active radiation or by specific blue light (BL) signaling pathways. The limited impact of GL on stomatal movements provides a unique option to use this light quality to control optogenetic tools. Recently, several of these tools have been optimized for use in plant biological research, either to control gene expression, or to provoke ion fluxes. Initial studies with the BL-activated potassium channel BLINK1 showed that this tool can speed up stomatal movements. Moreover, the GL-sensitive anion channel GtACR1 can induce stomatal closure, even at conditions that provoke stomatal opening in wild-type plants. Given that crop plants in controlled-environment agriculture and horticulture are often cultivated with artificial light sources (i.e. a combination of blue and red light from light-emitting diodes), GL signals can be used as a remote-control signal that controls stomatal transpiration and water consumption.
• The sugar transporter ZmSUGCAR1 of the nitrate transporter 1/peptide transporter family is critical for maize grain filling. Yang, B.; Wang, J.; Yu, M.; Zhang, M. L.; Zhong, Y. T.; Wang, T. Y.; Liu, P.; Song, W. B.; Zhao, H. M.; Fastner, A.; Suter, M.; Rentsch, D.; Ludewig, U.; Jin, W. W.; Geiger, D.; Hedrich, R.; Braun, D. M.; Koch, K. E.; McCarty, D. R.; Wu, W. H.; Li, X. X.; Wang, Y.; Lai, J. S. In Plant Cell, 34(11), pp. 4232–4254. 2022.
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  Maternal-to-filial nutrition transfer is central to grain development and yield. nitrate transporter 1/peptide transporter (NRT1-PTR)-type transporters typically transport nitrate, peptides, and ions. Here, we report the identification of a maize (Zea mays) NRT1-PTR-type transporter that transports sucrose and glucose. The activity of this sugar transporter, named Sucrose and Glucose Carrier 1 (SUGCAR1), was systematically verified by tracer-labeled sugar uptake and serial electrophysiological studies including two-electrode voltage-clamp, non-invasive microelectrode ion flux estimation assays in Xenopus laevis oocytes and patch clamping in HEK293T cells. ZmSUGCAR1 is specifically expressed in the basal endosperm transfer layer and loss-of-function mutation of ZmSUGCAR1 caused significantly decreased sucrose and glucose contents and subsequent shrinkage of maize kernels. Notably, the ZmSUGCAR1 orthologs SbSUGCAR1 (from Sorghum bicolor) and TaSUGCAR1 (from Triticum aestivum) displayed similar sugar transport activities in oocytes, supporting the functional conservation of SUGCAR1 in closely related cereal species. Thus, the discovery of ZmSUGCAR1 uncovers a type of sugar transporter essential for grain development and opens potential avenues for genetic improvement of seed-filling and yield in maize and other grain crops. Zea mays Sucrose and Glucose Carrier1 (ZmSUGCAR1) encodes a sugar transporter that functions in grain filling.

  @article{RN958, abstract = {Maternal-to-filial nutrition transfer is central to grain development and yield. nitrate transporter 1/peptide transporter (NRT1-PTR)-type transporters typically transport nitrate, peptides, and ions. Here, we report the identification of a maize (Zea mays) NRT1-PTR-type transporter that transports sucrose and glucose. The activity of this sugar transporter, named Sucrose and Glucose Carrier 1 (SUGCAR1), was systematically verified by tracer-labeled sugar uptake and serial electrophysiological studies including two-electrode voltage-clamp, non-invasive microelectrode ion flux estimation assays in Xenopus laevis oocytes and patch clamping in HEK293T cells. ZmSUGCAR1 is specifically expressed in the basal endosperm transfer layer and loss-of-function mutation of ZmSUGCAR1 caused significantly decreased sucrose and glucose contents and subsequent shrinkage of maize kernels. Notably, the ZmSUGCAR1 orthologs SbSUGCAR1 (from Sorghum bicolor) and TaSUGCAR1 (from Triticum aestivum) displayed similar sugar transport activities in oocytes, supporting the functional conservation of SUGCAR1 in closely related cereal species. Thus, the discovery of ZmSUGCAR1 uncovers a type of sugar transporter essential for grain development and opens potential avenues for genetic improvement of seed-filling and yield in maize and other grain crops. Zea mays Sucrose and Glucose Carrier1 (ZmSUGCAR1) encodes a sugar transporter that functions in grain filling.}, author = {Yang, B. and Wang, J. and Yu, M. and Zhang, M. L. and Zhong, Y. T. and Wang, T. Y. and Liu, P. and Song, W. B. and Zhao, H. M. and Fastner, A. and Suter, M. and Rentsch, D. and Ludewig, U. and Jin, W. W. and Geiger, D. and Hedrich, R. and Braun, D. M. and Koch, K. E. and McCarty, D. R. and Wu, W. H. and Li, X. X. and Wang, Y. and Lai, J. S.}, journal = {Plant Cell}, keywords = {zea-mays-l}, note = {5s1rc Times Cited:16 Cited References Count:82}, number = 11, pages = {4232-4254}, title = {The sugar transporter ZmSUGCAR1 of the nitrate transporter 1/peptide transporter family is critical for maize grain filling}, type = {Journal Article}, volume = 34, year = 2022 }

  %0 Journal Article %1 RN958 %A Yang, B. %A Wang, J. %A Yu, M. %A Zhang, M. L. %A Zhong, Y. T. %A Wang, T. Y. %A Liu, P. %A Song, W. B. %A Zhao, H. M. %A Fastner, A. %A Suter, M. %A Rentsch, D. %A Ludewig, U. %A Jin, W. W. %A Geiger, D. %A Hedrich, R. %A Braun, D. M. %A Koch, K. E. %A McCarty, D. R. %A Wu, W. H. %A Li, X. X. %A Wang, Y. %A Lai, J. S. %D 2022 %J Plant Cell %N 11 %P 4232-4254 %R 10.1093/plcell/koac256 %T The sugar transporter ZmSUGCAR1 of the nitrate transporter 1/peptide transporter family is critical for maize grain filling %U /brokenurl#<Go to ISI>://WOS:000849873100001 %V 34 %X Maternal-to-filial nutrition transfer is central to grain development and yield. nitrate transporter 1/peptide transporter (NRT1-PTR)-type transporters typically transport nitrate, peptides, and ions. Here, we report the identification of a maize (Zea mays) NRT1-PTR-type transporter that transports sucrose and glucose. The activity of this sugar transporter, named Sucrose and Glucose Carrier 1 (SUGCAR1), was systematically verified by tracer-labeled sugar uptake and serial electrophysiological studies including two-electrode voltage-clamp, non-invasive microelectrode ion flux estimation assays in Xenopus laevis oocytes and patch clamping in HEK293T cells. ZmSUGCAR1 is specifically expressed in the basal endosperm transfer layer and loss-of-function mutation of ZmSUGCAR1 caused significantly decreased sucrose and glucose contents and subsequent shrinkage of maize kernels. Notably, the ZmSUGCAR1 orthologs SbSUGCAR1 (from Sorghum bicolor) and TaSUGCAR1 (from Triticum aestivum) displayed similar sugar transport activities in oocytes, supporting the functional conservation of SUGCAR1 in closely related cereal species. Thus, the discovery of ZmSUGCAR1 uncovers a type of sugar transporter essential for grain development and opens potential avenues for genetic improvement of seed-filling and yield in maize and other grain crops. Zea mays Sucrose and Glucose Carrier1 (ZmSUGCAR1) encodes a sugar transporter that functions in grain filling.
• Sugar loading is not required for phloem sap flow in maize plants. Babst, B. A.; Braun, D. M.; Karve, A. A.; Baker, R. F.; Tran, T. M.; Kenny, D. J.; Rohlhill, J.; Knoblauch, J.; Knoblauch, M.; Lohaus, G.; Tappero, R.; Scherzer, S.; Hedrich, R.; Jensen, K. H. In Nature Plants, 8(2), p. 171-+. 2022.
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  Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.

  @article{RN967, abstract = {Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.}, author = {Babst, B. A. and Braun, D. M. and Karve, A. A. and Baker, R. F. and Tran, T. M. and Kenny, D. J. and Rohlhill, J. and Knoblauch, J. and Knoblauch, M. and Lohaus, G. and Tappero, R. and Scherzer, S. and Hedrich, R. and Jensen, K. H.}, journal = {Nature Plants}, keywords = {mobile}, note = {Zf6qr Times Cited:16 Cited References Count:85}, number = 2, pages = {171-+}, title = {Sugar loading is not required for phloem sap flow in maize plants}, type = {Journal Article}, volume = 8, year = 2022 }

  %0 Journal Article %1 RN967 %A Babst, B. A. %A Braun, D. M. %A Karve, A. A. %A Baker, R. F. %A Tran, T. M. %A Kenny, D. J. %A Rohlhill, J. %A Knoblauch, J. %A Knoblauch, M. %A Lohaus, G. %A Tappero, R. %A Scherzer, S. %A Hedrich, R. %A Jensen, K. H. %D 2022 %J Nature Plants %N 2 %P 171-+ %R 10.1038/s41477-022-01098-x %T Sugar loading is not required for phloem sap flow in maize plants %U /brokenurl#<Go to ISI>://WOS:000759690700015 %V 8 %X Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.
• The mutant of the salt-tolerant quinoa challenges our understanding of halophyte crop salinity tolerance. Moog, M. W.; Trinh, M. D. L.; Norrevang, A. F.; Bendtsen, A. K.; Wang, C. W.; Osterberg, J. T.; Shabala, S.; Hedrich, R.; Wendt, T.; Palmgren, M. In New Phytologist, 236(4), pp. 1409–1421. 2022.
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  Halophytes tolerate high salinity levels that would kill conventional crops. Understanding salt tolerance mechanisms will provide clues for breeding salt-tolerant plants. Many halophytes, such as quinoa (Chenopodium quinoa), are covered by a layer of epidermal bladder cells (EBCs) that are thought to mediate salt tolerance by serving as salt dumps. We isolated an epidermal bladder cell-free (ebcf) quinoa mutant that completely lacked EBCs and was mutated in REBC and REBC-like1. This mutant showed no loss of salt stress tolerance. When wild-type quinoa plants were exposed to saline soil, EBCs accumulated potassium (K+) as the major cation, in quantities far exceeding those of sodium (Na+). Emerging leaves densely packed with EBCs had the lowest Na+ content, whereas old leaves with deflated EBCs served as Na+ sinks. When the leaves expanded, K+ was recycled from EBCs, resulting in turgor loss that led to a progressive deflation of EBCs. Our findings suggest that EBCs in young leaves serve as a K+-powered hydrodynamic system that functions as a water sink for solute storage. Sodium ions accumulate within old leaves that subsequently wilt and are shed. This mechanism improves the survival of quinoa under high salinity conditions.

  @article{RN961, abstract = {Halophytes tolerate high salinity levels that would kill conventional crops. Understanding salt tolerance mechanisms will provide clues for breeding salt-tolerant plants. Many halophytes, such as quinoa (Chenopodium quinoa), are covered by a layer of epidermal bladder cells (EBCs) that are thought to mediate salt tolerance by serving as salt dumps. We isolated an epidermal bladder cell-free (ebcf) quinoa mutant that completely lacked EBCs and was mutated in REBC and REBC-like1. This mutant showed no loss of salt stress tolerance. When wild-type quinoa plants were exposed to saline soil, EBCs accumulated potassium (K+) as the major cation, in quantities far exceeding those of sodium (Na+). Emerging leaves densely packed with EBCs had the lowest Na+ content, whereas old leaves with deflated EBCs served as Na+ sinks. When the leaves expanded, K+ was recycled from EBCs, resulting in turgor loss that led to a progressive deflation of EBCs. Our findings suggest that EBCs in young leaves serve as a K+-powered hydrodynamic system that functions as a water sink for solute storage. Sodium ions accumulate within old leaves that subsequently wilt and are shed. This mechanism improves the survival of quinoa under high salinity conditions.}, author = {Moog, M. W. and Trinh, M. D. L. and Norrevang, A. F. and Bendtsen, A. K. and Wang, C. W. and Osterberg, J. T. and Shabala, S. and Hedrich, R. and Wendt, T. and Palmgren, M.}, journal = {New Phytologist}, keywords = {stress}, note = {7t8fi Times Cited:8 Cited References Count:29}, number = 4, pages = {1409-1421}, title = {The mutant of the salt-tolerant quinoa challenges our understanding of halophyte crop salinity tolerance}, type = {Journal Article}, volume = 236, year = 2022 }

  %0 Journal Article %1 RN961 %A Moog, M. W. %A Trinh, M. D. L. %A Norrevang, A. F. %A Bendtsen, A. K. %A Wang, C. W. %A Osterberg, J. T. %A Shabala, S. %A Hedrich, R. %A Wendt, T. %A Palmgren, M. %D 2022 %J New Phytologist %N 4 %P 1409-1421 %R 10.1111/nph.18420 %T The mutant of the salt-tolerant quinoa challenges our understanding of halophyte crop salinity tolerance %U /brokenurl#<Go to ISI>://WOS:000847312000001 %V 236 %X Halophytes tolerate high salinity levels that would kill conventional crops. Understanding salt tolerance mechanisms will provide clues for breeding salt-tolerant plants. Many halophytes, such as quinoa (Chenopodium quinoa), are covered by a layer of epidermal bladder cells (EBCs) that are thought to mediate salt tolerance by serving as salt dumps. We isolated an epidermal bladder cell-free (ebcf) quinoa mutant that completely lacked EBCs and was mutated in REBC and REBC-like1. This mutant showed no loss of salt stress tolerance. When wild-type quinoa plants were exposed to saline soil, EBCs accumulated potassium (K+) as the major cation, in quantities far exceeding those of sodium (Na+). Emerging leaves densely packed with EBCs had the lowest Na+ content, whereas old leaves with deflated EBCs served as Na+ sinks. When the leaves expanded, K+ was recycled from EBCs, resulting in turgor loss that led to a progressive deflation of EBCs. Our findings suggest that EBCs in young leaves serve as a K+-powered hydrodynamic system that functions as a water sink for solute storage. Sodium ions accumulate within old leaves that subsequently wilt and are shed. This mechanism improves the survival of quinoa under high salinity conditions.
• Molecular basis of multistep voltage activation in plant two-pore channel 1. Dickinson, M. S.; Lu, J. P.; Gupta, M.; Marten, I.; Hedrich, R.; Stroud, R. M. In Proceedings of the National Academy of Sciences of the United States of America, 119(9). 2022.
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  Voltage-gated ion channels confer excitability to biological membranes, initiating and propagating electrical signals across large distances on short timescales. Membrane excitation requires channels that respond to changes in electric field and couple the transmembrane voltage to gating of a central pore. To address the mechanism of this process in a voltage-gated ion channel, we determined structures of the plant two-pore channel 1 at different stages along its activation coordinate. These high-resolution structures of activation intermediates, when compared with the resting-state structure, portray a mechanism in which the voltage-sensing domain undergoes dilation and in-membrane plane rotation about the gating charge-bearing helix, followed by charge translocation across the charge transfer seal. These structures, in concert with patch-clamp electrophysiology, show that residues in the pore mouth sense inhibitory Ca2+ and are allosterically coupled to the voltage sensor. These conformational changes provide insight into the mechanism of voltage-sensor domain activation in which activation occurs vectorially over a series of elementary steps.

  @article{RN965, abstract = {Voltage-gated ion channels confer excitability to biological membranes, initiating and propagating electrical signals across large distances on short timescales. Membrane excitation requires channels that respond to changes in electric field and couple the transmembrane voltage to gating of a central pore. To address the mechanism of this process in a voltage-gated ion channel, we determined structures of the plant two-pore channel 1 at different stages along its activation coordinate. These high-resolution structures of activation intermediates, when compared with the resting-state structure, portray a mechanism in which the voltage-sensing domain undergoes dilation and in-membrane plane rotation about the gating charge-bearing helix, followed by charge translocation across the charge transfer seal. These structures, in concert with patch-clamp electrophysiology, show that residues in the pore mouth sense inhibitory Ca2+ and are allosterically coupled to the voltage sensor. These conformational changes provide insight into the mechanism of voltage-sensor domain activation in which activation occurs vectorially over a series of elementary steps.}, author = {Dickinson, M. S. and Lu, J. P. and Gupta, M. and Marten, I. and Hedrich, R. and Stroud, R. M.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {microscopy}, note = {0d3aa Times Cited:4 Cited References Count:58}, number = 9, title = {Molecular basis of multistep voltage activation in plant two-pore channel 1}, type = {Journal Article}, volume = 119, year = 2022 }

  %0 Journal Article %1 RN965 %A Dickinson, M. S. %A Lu, J. P. %A Gupta, M. %A Marten, I. %A Hedrich, R. %A Stroud, R. M. %D 2022 %J Proceedings of the National Academy of Sciences of the United States of America %N 9 %R ARTN e2110936119 10.1073/pnas.2110936119 %T Molecular basis of multistep voltage activation in plant two-pore channel 1 %U /brokenurl#<Go to ISI>://WOS:000775870300001 %V 119 %X Voltage-gated ion channels confer excitability to biological membranes, initiating and propagating electrical signals across large distances on short timescales. Membrane excitation requires channels that respond to changes in electric field and couple the transmembrane voltage to gating of a central pore. To address the mechanism of this process in a voltage-gated ion channel, we determined structures of the plant two-pore channel 1 at different stages along its activation coordinate. These high-resolution structures of activation intermediates, when compared with the resting-state structure, portray a mechanism in which the voltage-sensing domain undergoes dilation and in-membrane plane rotation about the gating charge-bearing helix, followed by charge translocation across the charge transfer seal. These structures, in concert with patch-clamp electrophysiology, show that residues in the pore mouth sense inhibitory Ca2+ and are allosterically coupled to the voltage sensor. These conformational changes provide insight into the mechanism of voltage-sensor domain activation in which activation occurs vectorially over a series of elementary steps.
• Chronic ozone exposure preferentially modifies root rather than foliar metabolism of date palm ( ) saplings. Arab, L.; Hoshika, Y.; Müller, H.; Cotrozzi, L.; Nali, C.; Tonelli, M.; Ache, P.; Paoletti, E.; Alfarraj, S.; Albasher, G.; Hedrich, R.; Rennenberg, H. In Science of the Total Environment, 806. 2022.
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  In their natural environment, date palms are exposed to chronic atmospheric ozone (O3) concentrations from local and remote sources. In order to elucidate the consequences of this exposure, date palm saplings were treated with ambient, 1.5 and 2.0 times ambient O3 for three months in a free-air controlled exposure facility. Chronic O3 exposure reduced carbohydrate contents in leaves and roots, but this effect was much stronger in roots. Still, sucrose contents of both organs were maintained at elevated O3, though at different steady states. Reduced availability of carbohydrate for the Tricarboxylic acid cycle (TCA cycle) may be responsible for the observed reduced foliar contents of several amino acids, whereas malic acid accumulation in the roots indicates a reduced use of TCA cycle intermediates. Carbohydrate deficiency in roots, but not in leaves caused oxidative stress upon chronic O3 exposure, as indicated by enhanced malonedialdehyde, H2O2 and oxidized glutathione contents despite elevated glutathione reductase activity. Reduced levels of phenolics and flavonoids in the roots resulted from decreased production and, therefore, do not indicate oxidative stress compensation by secondary compounds. These results show that roots of date palms are highly susceptible to chronic O3 exposure as a consequence of carbohydrate deficiency. (c) 2021 Published by Elsevier B.V.

  @article{RN968, abstract = {In their natural environment, date palms are exposed to chronic atmospheric ozone (O3) concentrations from local and remote sources. In order to elucidate the consequences of this exposure, date palm saplings were treated with ambient, 1.5 and 2.0 times ambient O3 for three months in a free-air controlled exposure facility. Chronic O3 exposure reduced carbohydrate contents in leaves and roots, but this effect was much stronger in roots. Still, sucrose contents of both organs were maintained at elevated O3, though at different steady states. Reduced availability of carbohydrate for the Tricarboxylic acid cycle (TCA cycle) may be responsible for the observed reduced foliar contents of several amino acids, whereas malic acid accumulation in the roots indicates a reduced use of TCA cycle intermediates. Carbohydrate deficiency in roots, but not in leaves caused oxidative stress upon chronic O3 exposure, as indicated by enhanced malonedialdehyde, H2O2 and oxidized glutathione contents despite elevated glutathione reductase activity. Reduced levels of phenolics and flavonoids in the roots resulted from decreased production and, therefore, do not indicate oxidative stress compensation by secondary compounds. These results show that roots of date palms are highly susceptible to chronic O3 exposure as a consequence of carbohydrate deficiency. (c) 2021 Published by Elsevier B.V.}, author = {Arab, L. and Hoshika, Y. and Müller, H. and Cotrozzi, L. and Nali, C. and Tonelli, M. and Ache, P. and Paoletti, E. and Alfarraj, S. and Albasher, G. and Hedrich, R. and Rennenberg, H.}, journal = {Science of the Total Environment}, keywords = {amino}, note = {2 Wh4mw Times Cited:8 Cited References Count:103}, title = {Chronic ozone exposure preferentially modifies root rather than foliar metabolism of date palm ( ) saplings}, type = {Journal Article}, volume = 806, year = 2022 }

  %0 Journal Article %1 RN968 %A Arab, L. %A Hoshika, Y. %A Müller, H. %A Cotrozzi, L. %A Nali, C. %A Tonelli, M. %A Ache, P. %A Paoletti, E. %A Alfarraj, S. %A Albasher, G. %A Hedrich, R. %A Rennenberg, H. %D 2022 %J Science of the Total Environment %R ARTN 150563 10.1016/j.scitotenv.2021.150563 %T Chronic ozone exposure preferentially modifies root rather than foliar metabolism of date palm ( ) saplings %U /brokenurl#<Go to ISI>://WOS:000707655000012 %V 806 %X In their natural environment, date palms are exposed to chronic atmospheric ozone (O3) concentrations from local and remote sources. In order to elucidate the consequences of this exposure, date palm saplings were treated with ambient, 1.5 and 2.0 times ambient O3 for three months in a free-air controlled exposure facility. Chronic O3 exposure reduced carbohydrate contents in leaves and roots, but this effect was much stronger in roots. Still, sucrose contents of both organs were maintained at elevated O3, though at different steady states. Reduced availability of carbohydrate for the Tricarboxylic acid cycle (TCA cycle) may be responsible for the observed reduced foliar contents of several amino acids, whereas malic acid accumulation in the roots indicates a reduced use of TCA cycle intermediates. Carbohydrate deficiency in roots, but not in leaves caused oxidative stress upon chronic O3 exposure, as indicated by enhanced malonedialdehyde, H2O2 and oxidized glutathione contents despite elevated glutathione reductase activity. Reduced levels of phenolics and flavonoids in the roots resulted from decreased production and, therefore, do not indicate oxidative stress compensation by secondary compounds. These results show that roots of date palms are highly susceptible to chronic O3 exposure as a consequence of carbohydrate deficiency. (c) 2021 Published by Elsevier B.V.
• A unique inventory of ion transporters poises the Venus flytrap to fast-propagating action potentials and calcium waves. Scherzer, S.; Böhm, J.; Huang, S. G.; Iosip, A. L.; Kreuzer, I.; Becker, D.; Heckmann, M.; Al-Rasheid, K. A. S.; Dreyer, I.; Hedrich, R. In Current Biology, 32(19), p. 4255-+. 2022.
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  Since the 19th century, it has been known that the carnivorous Venus flytrap is electrically excitable. Never-theless, the mechanism and the molecular entities of the flytrap action potential (AP) remain unknown. When entering the electrically excitable stage, the trap expressed a characteristic inventory of ion transporters, among which the increase in glutamate receptor GLR3.6 RNA was most pronounced. Trigger hair stimulation or glutamate application evoked an AP and a cytoplasmic Ca2+ transient that both propagated at the same speed from the site of induction along the entire trap lobe surface. A priming Ca2+ moiety entering the cytoplasm in the context of the AP was further potentiated by an organelle-localized calcium-induced calcium release (CICR)-like system prolonging the Ca2+ signal. While the Ca2+ transient persisted, SKOR K+ channels and AHA H+-ATPases repolarized the AP already. By counting the number of APs and long-lasting Ca2+ transients, the trap directs the different steps in the carnivorous plant's hunting cycle.

  @article{RN960, abstract = {Since the 19th century, it has been known that the carnivorous Venus flytrap is electrically excitable. Never-theless, the mechanism and the molecular entities of the flytrap action potential (AP) remain unknown. When entering the electrically excitable stage, the trap expressed a characteristic inventory of ion transporters, among which the increase in glutamate receptor GLR3.6 RNA was most pronounced. Trigger hair stimulation or glutamate application evoked an AP and a cytoplasmic Ca2+ transient that both propagated at the same speed from the site of induction along the entire trap lobe surface. A priming Ca2+ moiety entering the cytoplasm in the context of the AP was further potentiated by an organelle-localized calcium-induced calcium release (CICR)-like system prolonging the Ca2+ signal. While the Ca2+ transient persisted, SKOR K+ channels and AHA H+-ATPases repolarized the AP already. By counting the number of APs and long-lasting Ca2+ transients, the trap directs the different steps in the carnivorous plant's hunting cycle.}, author = {Scherzer, S. and Böhm, J. and Huang, S. G. and Iosip, A. L. and Kreuzer, I. and Becker, D. and Heckmann, M. and Al-Rasheid, K. A. S. and Dreyer, I. and Hedrich, R.}, journal = {Current Biology}, keywords = {carnivorous}, note = {7a4iu Times Cited:14 Cited References Count:54}, number = 19, pages = {4255-+}, title = {A unique inventory of ion transporters poises the Venus flytrap to fast-propagating action potentials and calcium waves}, type = {Journal Article}, volume = 32, year = 2022 }

  %0 Journal Article %1 RN960 %A Scherzer, S. %A Böhm, J. %A Huang, S. G. %A Iosip, A. L. %A Kreuzer, I. %A Becker, D. %A Heckmann, M. %A Al-Rasheid, K. A. S. %A Dreyer, I. %A Hedrich, R. %D 2022 %J Current Biology %N 19 %P 4255-+ %R 10.1016/j.cub.2022.08.051 %T A unique inventory of ion transporters poises the Venus flytrap to fast-propagating action potentials and calcium waves %U /brokenurl#<Go to ISI>://WOS:000898422800005 %V 32 %X Since the 19th century, it has been known that the carnivorous Venus flytrap is electrically excitable. Never-theless, the mechanism and the molecular entities of the flytrap action potential (AP) remain unknown. When entering the electrically excitable stage, the trap expressed a characteristic inventory of ion transporters, among which the increase in glutamate receptor GLR3.6 RNA was most pronounced. Trigger hair stimulation or glutamate application evoked an AP and a cytoplasmic Ca2+ transient that both propagated at the same speed from the site of induction along the entire trap lobe surface. A priming Ca2+ moiety entering the cytoplasm in the context of the AP was further potentiated by an organelle-localized calcium-induced calcium release (CICR)-like system prolonging the Ca2+ signal. While the Ca2+ transient persisted, SKOR K+ channels and AHA H+-ATPases repolarized the AP already. By counting the number of APs and long-lasting Ca2+ transients, the trap directs the different steps in the carnivorous plant's hunting cycle.
• The digestive systems of carnivorous plants. Freund, M.; Graus, D.; Fleischmann, A.; Gilbert, K. J.; Lin, Q. S.; Renner, T.; Stigloher, C.; Albert, V.; Hedrich, R.; Fukushima, K. In Plant Physiology, 190(1), pp. 44–59. 2022.
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  To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands. A comparison of the forms and functions of digestive and absorptive glands in carnivorous plants sheds light on their convergent evolution.

  @article{RN963, abstract = {To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands. A comparison of the forms and functions of digestive and absorptive glands in carnivorous plants sheds light on their convergent evolution.}, author = {Freund, M. and Graus, D. and Fleischmann, A. and Gilbert, K. J. and Lin, Q. S. and Renner, T. and Stigloher, C. and Albert, V. and Hedrich, R. and Fukushima, K.}, journal = {Plant Physiology}, keywords = {flytrap}, note = {4f2ba Times Cited:18 Cited References Count:188}, number = 1, pages = {44-59}, title = {The digestive systems of carnivorous plants}, type = {Journal Article}, volume = 190, year = 2022 }

  %0 Journal Article %1 RN963 %A Freund, M. %A Graus, D. %A Fleischmann, A. %A Gilbert, K. J. %A Lin, Q. S. %A Renner, T. %A Stigloher, C. %A Albert, V. %A Hedrich, R. %A Fukushima, K. %D 2022 %J Plant Physiology %N 1 %P 44-59 %R 10.1093/plphys/kiac232 %T The digestive systems of carnivorous plants %U /brokenurl#<Go to ISI>://WOS:000805444000001 %V 190 %X To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands. A comparison of the forms and functions of digestive and absorptive glands in carnivorous plants sheds light on their convergent evolution.
• Stalk cell polar ion transport provide for bladder-based salinity tolerance in. Bazihizina, N.; Böhm, J.; Messerer, M.; Stigloher, C.; Müller, H. M.; Cuin, T. A.; Maierhofer, T.; Cabot, J.; Mayer, K. F. X.; Fella, C.; Huang, S. G.; Al-Rasheid, K. A. S.; Alquraishi, S.; Breadmore, M.; Mancuso, S.; Shabala, S.; Ache, P.; Zhang, H.; Zhu, J. K.; Hedrich, R.; Scherzer, S. In New Phytologist, 235(5), pp. 1822–1835. 2022.
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  Chenopodium quinoa uses epidermal bladder cells (EBCs) to sequester excess salt. Each EBC complex consists of a leaf epidermal cell, a stalk cell, and the bladder. Under salt stress, sodium (Na+), chloride (Cl-), potassium (K+) and various metabolites are shuttled from the leaf lamina to the bladders. Stalk cells operate as both a selectivity filter and a flux controller. In line with the nature of a transfer cell, advanced transmission electron tomography, electrophysiology, and fluorescent tracer flux studies revealed the stalk cell's polar organization and bladder-directed solute flow. RNA sequencing and cluster analysis revealed the gene expression profiles of the stalk cells. Among the stalk cell enriched genes, ion channels and carriers as well as sugar transporters were most pronounced. Based on their electrophysiological fingerprint and thermodynamic considerations, a model for stalk cell transcellular transport was derived.

  @article{RN966, abstract = {Chenopodium quinoa uses epidermal bladder cells (EBCs) to sequester excess salt. Each EBC complex consists of a leaf epidermal cell, a stalk cell, and the bladder. Under salt stress, sodium (Na+), chloride (Cl-), potassium (K+) and various metabolites are shuttled from the leaf lamina to the bladders. Stalk cells operate as both a selectivity filter and a flux controller. In line with the nature of a transfer cell, advanced transmission electron tomography, electrophysiology, and fluorescent tracer flux studies revealed the stalk cell's polar organization and bladder-directed solute flow. RNA sequencing and cluster analysis revealed the gene expression profiles of the stalk cells. Among the stalk cell enriched genes, ion channels and carriers as well as sugar transporters were most pronounced. Based on their electrophysiological fingerprint and thermodynamic considerations, a model for stalk cell transcellular transport was derived.}, author = {Bazihizina, N. and Böhm, J. and Messerer, M. and Stigloher, C. and Müller, H. M. and Cuin, T. A. and Maierhofer, T. and Cabot, J. and Mayer, K. F. X. and Fella, C. and Huang, S. G. and Al-Rasheid, K. A. S. and Alquraishi, S. and Breadmore, M. and Mancuso, S. and Shabala, S. and Ache, P. and Zhang, H. and Zhu, J. K. and Hedrich, R. and Scherzer, S.}, journal = {New Phytologist}, keywords = {myOwn}, note = {3l5dn Times Cited:6 Cited References Count:57}, number = 5, pages = {1822-1835}, title = {Stalk cell polar ion transport provide for bladder-based salinity tolerance in}, type = {Journal Article}, volume = 235, year = 2022 }

  %0 Journal Article %1 RN966 %A Bazihizina, N. %A Böhm, J. %A Messerer, M. %A Stigloher, C. %A Müller, H. M. %A Cuin, T. A. %A Maierhofer, T. %A Cabot, J. %A Mayer, K. F. X. %A Fella, C. %A Huang, S. G. %A Al-Rasheid, K. A. S. %A Alquraishi, S. %A Breadmore, M. %A Mancuso, S. %A Shabala, S. %A Ache, P. %A Zhang, H. %A Zhu, J. K. %A Hedrich, R. %A Scherzer, S. %D 2022 %J New Phytologist %N 5 %P 1822-1835 %R 10.1111/nph.18205 %T Stalk cell polar ion transport provide for bladder-based salinity tolerance in %U /brokenurl#<Go to ISI>://WOS:000804173000001 %V 235 %X Chenopodium quinoa uses epidermal bladder cells (EBCs) to sequester excess salt. Each EBC complex consists of a leaf epidermal cell, a stalk cell, and the bladder. Under salt stress, sodium (Na+), chloride (Cl-), potassium (K+) and various metabolites are shuttled from the leaf lamina to the bladders. Stalk cells operate as both a selectivity filter and a flux controller. In line with the nature of a transfer cell, advanced transmission electron tomography, electrophysiology, and fluorescent tracer flux studies revealed the stalk cell's polar organization and bladder-directed solute flow. RNA sequencing and cluster analysis revealed the gene expression profiles of the stalk cells. Among the stalk cell enriched genes, ion channels and carriers as well as sugar transporters were most pronounced. Based on their electrophysiological fingerprint and thermodynamic considerations, a model for stalk cell transcellular transport was derived.
• Ether anesthetics prevents touch-induced trigger hair calcium-electrical signals excite the Venus flytrap. Scherzer, S.; Huang, S. G.; Iosip, A.; Kreuzer, I.; Yokawa, K.; Al-Rasheid, K. A. S.; Heckmann, M.; Hedrich, R. In Scientific Reports, 12(1). 2022.
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  Plants do not have neurons but operate transmembrane ion channels and can get electrical excited by physical and chemical clues. Among them the Venus flytrap is characterized by its peculiar hapto-electric signaling. When insects collide with trigger hairs emerging the trap inner surface, the mechanical stimulus within the mechanosensory organ is translated into a calcium signal and an action potential (AP). Here we asked how the Ca2+ wave and AP is initiated in the trigger hair and how it is feed into systemic trap calcium-electrical networks. When Dionaea muscipula trigger hairs matures and develop hapto-electric excitability the mechanosensitive anion channel DmMSL10/FLYC1 and voltage dependent SKOR type Shaker K+ channel are expressed in the sheering stress sensitive podium. The podium of the trigger hair is interface to the flytrap's prey capture and processing networks. In the excitable state touch stimulation of the trigger hair evokes a rise in the podium Ca2+ first and before the calcium signal together with an action potential travel all over the trap surface. In search for podium ion channels and pumps mediating touch induced Ca2+ transients, we, in mature trigger hairs firing fast Ca2+ signals and APs, found OSCA1.7 and GLR3.6 type Ca2+ channels and ACA2/10 Ca2+ pumps specifically expressed in the podium. Like trigger hair stimulation, glutamate application to the trap directly evoked a propagating Ca2+ and electrical event. Given that anesthetics affect K+ channels and glutamate receptors in the animal system we exposed flytraps to an ether atmosphere. As result propagation of touch and glutamate induced Ca2+ and AP long-distance signaling got suppressed, while the trap completely recovered excitability when ether was replaced by fresh air. In line with ether targeting a calcium channel addressing a Ca2+ activated anion channel the AP amplitude declined before the electrical signal ceased completely. Ether in the mechanosensory organ did neither prevent the touch induction of a calcium signal nor this post stimulus decay. This finding indicates that ether prevents the touch activated, glr3.6 expressing base of the trigger hair to excite the capture organ.

  @article{RN959, abstract = {Plants do not have neurons but operate transmembrane ion channels and can get electrical excited by physical and chemical clues. Among them the Venus flytrap is characterized by its peculiar hapto-electric signaling. When insects collide with trigger hairs emerging the trap inner surface, the mechanical stimulus within the mechanosensory organ is translated into a calcium signal and an action potential (AP). Here we asked how the Ca2+ wave and AP is initiated in the trigger hair and how it is feed into systemic trap calcium-electrical networks. When Dionaea muscipula trigger hairs matures and develop hapto-electric excitability the mechanosensitive anion channel DmMSL10/FLYC1 and voltage dependent SKOR type Shaker K+ channel are expressed in the sheering stress sensitive podium. The podium of the trigger hair is interface to the flytrap's prey capture and processing networks. In the excitable state touch stimulation of the trigger hair evokes a rise in the podium Ca2+ first and before the calcium signal together with an action potential travel all over the trap surface. In search for podium ion channels and pumps mediating touch induced Ca2+ transients, we, in mature trigger hairs firing fast Ca2+ signals and APs, found OSCA1.7 and GLR3.6 type Ca2+ channels and ACA2/10 Ca2+ pumps specifically expressed in the podium. Like trigger hair stimulation, glutamate application to the trap directly evoked a propagating Ca2+ and electrical event. Given that anesthetics affect K+ channels and glutamate receptors in the animal system we exposed flytraps to an ether atmosphere. As result propagation of touch and glutamate induced Ca2+ and AP long-distance signaling got suppressed, while the trap completely recovered excitability when ether was replaced by fresh air. In line with ether targeting a calcium channel addressing a Ca2+ activated anion channel the AP amplitude declined before the electrical signal ceased completely. Ether in the mechanosensory organ did neither prevent the touch induction of a calcium signal nor this post stimulus decay. This finding indicates that ether prevents the touch activated, glr3.6 expressing base of the trigger hair to excite the capture organ.}, author = {Scherzer, S. and Huang, S. G. and Iosip, A. and Kreuzer, I. and Yokawa, K. and Al-Rasheid, K. A. S. and Heckmann, M. and Hedrich, R.}, journal = {Scientific Reports}, keywords = {dionaea-muscipula}, note = {Zd0mb Times Cited:19 Cited References Count:40}, number = 1, title = {Ether anesthetics prevents touch-induced trigger hair calcium-electrical signals excite the Venus flytrap}, type = {Journal Article}, volume = 12, year = 2022 }

  %0 Journal Article %1 RN959 %A Scherzer, S. %A Huang, S. G. %A Iosip, A. %A Kreuzer, I. %A Yokawa, K. %A Al-Rasheid, K. A. S. %A Heckmann, M. %A Hedrich, R. %D 2022 %J Scientific Reports %N 1 %R ARTN 2851 10.1038/s41598-022-06915-z %T Ether anesthetics prevents touch-induced trigger hair calcium-electrical signals excite the Venus flytrap %U /brokenurl#<Go to ISI>://WOS:000757901500023 %V 12 %X Plants do not have neurons but operate transmembrane ion channels and can get electrical excited by physical and chemical clues. Among them the Venus flytrap is characterized by its peculiar hapto-electric signaling. When insects collide with trigger hairs emerging the trap inner surface, the mechanical stimulus within the mechanosensory organ is translated into a calcium signal and an action potential (AP). Here we asked how the Ca2+ wave and AP is initiated in the trigger hair and how it is feed into systemic trap calcium-electrical networks. When Dionaea muscipula trigger hairs matures and develop hapto-electric excitability the mechanosensitive anion channel DmMSL10/FLYC1 and voltage dependent SKOR type Shaker K+ channel are expressed in the sheering stress sensitive podium. The podium of the trigger hair is interface to the flytrap's prey capture and processing networks. In the excitable state touch stimulation of the trigger hair evokes a rise in the podium Ca2+ first and before the calcium signal together with an action potential travel all over the trap surface. In search for podium ion channels and pumps mediating touch induced Ca2+ transients, we, in mature trigger hairs firing fast Ca2+ signals and APs, found OSCA1.7 and GLR3.6 type Ca2+ channels and ACA2/10 Ca2+ pumps specifically expressed in the podium. Like trigger hair stimulation, glutamate application to the trap directly evoked a propagating Ca2+ and electrical event. Given that anesthetics affect K+ channels and glutamate receptors in the animal system we exposed flytraps to an ether atmosphere. As result propagation of touch and glutamate induced Ca2+ and AP long-distance signaling got suppressed, while the trap completely recovered excitability when ether was replaced by fresh air. In line with ether targeting a calcium channel addressing a Ca2+ activated anion channel the AP amplitude declined before the electrical signal ceased completely. Ether in the mechanosensory organ did neither prevent the touch induction of a calcium signal nor this post stimulus decay. This finding indicates that ether prevents the touch activated, glr3.6 expressing base of the trigger hair to excite the capture organ.

• Protein expression plasticity contributes to heat and drought tolerance of date palm. Ghirardo, A.; Nosenko, T.; Kreuzwieser, J.; Winkler, J. B.; Kruse, J.; Albert, A.; Merl-Pham, J.; Lux, T.; Ache, P.; Zimmer, I.; Alfarraj, S.; Mayer, K. F. X.; Hedrich, R.; Rennenberg, H.; Schnitzler, J. P. In Oecologia, 197(4), pp. 903–919. 2021.
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  Climate change is increasing the frequency and intensity of warming and drought periods around the globe, currently representing a threat to many plant species. Understanding the resistance and resilience of plants to climate change is, therefore, urgently needed. As date palm (Phoenix dactylifera) evolved adaptation mechanisms to a xeric environment and can tolerate large diurnal and seasonal temperature fluctuations, we studied the protein expression changes in leaves, volatile organic compound emissions, and photosynthesis in response to variable growth temperatures and soil water deprivation. Plants were grown under controlled environmental conditions of simulated Saudi Arabian summer and winter climates challenged with drought stress. We show that date palm is able to counteract the harsh conditions of the Arabian Peninsula by adjusting the abundances of proteins related to the photosynthetic machinery, abiotic stress and secondary metabolism. Under summer climate and water deprivation, these adjustments included efficient protein expression response mediated by heat shock proteins and the antioxidant system to counteract reactive oxygen species formation. Proteins related to secondary metabolism were downregulated, except for the P. dactylifera isoprene synthase (PdIspS), which was strongly upregulated in response to summer climate and drought. This study reports, for the first time, the identification and functional characterization of the gene encoding for PdIspS, allowing future analysis of isoprene functions in date palm under extreme environments. Overall, the current study shows that reprogramming of the leaf protein profiles confers the date palm heat- and drought tolerance. We conclude that the protein plasticity of date palm is an important mechanism of molecular adaptation to environmental fluctuations.

  @article{RN982, abstract = {Climate change is increasing the frequency and intensity of warming and drought periods around the globe, currently representing a threat to many plant species. Understanding the resistance and resilience of plants to climate change is, therefore, urgently needed. As date palm (Phoenix dactylifera) evolved adaptation mechanisms to a xeric environment and can tolerate large diurnal and seasonal temperature fluctuations, we studied the protein expression changes in leaves, volatile organic compound emissions, and photosynthesis in response to variable growth temperatures and soil water deprivation. Plants were grown under controlled environmental conditions of simulated Saudi Arabian summer and winter climates challenged with drought stress. We show that date palm is able to counteract the harsh conditions of the Arabian Peninsula by adjusting the abundances of proteins related to the photosynthetic machinery, abiotic stress and secondary metabolism. Under summer climate and water deprivation, these adjustments included efficient protein expression response mediated by heat shock proteins and the antioxidant system to counteract reactive oxygen species formation. Proteins related to secondary metabolism were downregulated, except for the P. dactylifera isoprene synthase (PdIspS), which was strongly upregulated in response to summer climate and drought. This study reports, for the first time, the identification and functional characterization of the gene encoding for PdIspS, allowing future analysis of isoprene functions in date palm under extreme environments. Overall, the current study shows that reprogramming of the leaf protein profiles confers the date palm heat- and drought tolerance. We conclude that the protein plasticity of date palm is an important mechanism of molecular adaptation to environmental fluctuations.}, author = {Ghirardo, A. and Nosenko, T. and Kreuzwieser, J. and Winkler, J. B. and Kruse, J. and Albert, A. and Merl-Pham, J. and Lux, T. and Ache, P. and Zimmer, I. and Alfarraj, S. and Mayer, K. F. X. and Hedrich, R. and Rennenberg, H. and Schnitzler, J. P.}, journal = {Oecologia}, keywords = {stress}, note = {Sp. Iss. SI Wx0gd Times Cited:14 Cited References Count:109}, number = 4, pages = {903-919}, title = {Protein expression plasticity contributes to heat and drought tolerance of date palm}, type = {Journal Article}, volume = 197, year = 2021 }

  %0 Journal Article %1 RN982 %A Ghirardo, A. %A Nosenko, T. %A Kreuzwieser, J. %A Winkler, J. B. %A Kruse, J. %A Albert, A. %A Merl-Pham, J. %A Lux, T. %A Ache, P. %A Zimmer, I. %A Alfarraj, S. %A Mayer, K. F. X. %A Hedrich, R. %A Rennenberg, H. %A Schnitzler, J. P. %D 2021 %J Oecologia %N 4 %P 903-919 %R 10.1007/s00442-021-04907-w %T Protein expression plasticity contributes to heat and drought tolerance of date palm %U /brokenurl#<Go to ISI>://WOS:000641640000001 %V 197 %X Climate change is increasing the frequency and intensity of warming and drought periods around the globe, currently representing a threat to many plant species. Understanding the resistance and resilience of plants to climate change is, therefore, urgently needed. As date palm (Phoenix dactylifera) evolved adaptation mechanisms to a xeric environment and can tolerate large diurnal and seasonal temperature fluctuations, we studied the protein expression changes in leaves, volatile organic compound emissions, and photosynthesis in response to variable growth temperatures and soil water deprivation. Plants were grown under controlled environmental conditions of simulated Saudi Arabian summer and winter climates challenged with drought stress. We show that date palm is able to counteract the harsh conditions of the Arabian Peninsula by adjusting the abundances of proteins related to the photosynthetic machinery, abiotic stress and secondary metabolism. Under summer climate and water deprivation, these adjustments included efficient protein expression response mediated by heat shock proteins and the antioxidant system to counteract reactive oxygen species formation. Proteins related to secondary metabolism were downregulated, except for the P. dactylifera isoprene synthase (PdIspS), which was strongly upregulated in response to summer climate and drought. This study reports, for the first time, the identification and functional characterization of the gene encoding for PdIspS, allowing future analysis of isoprene functions in date palm under extreme environments. Overall, the current study shows that reprogramming of the leaf protein profiles confers the date palm heat- and drought tolerance. We conclude that the protein plasticity of date palm is an important mechanism of molecular adaptation to environmental fluctuations.
• GABA signalling modulates stomatal opening to enhance plant water use efficiency and drought resilience. Xu, B.; Long, Y.; Feng, X.; Zhu, X.; Sai, N.; Chirkova, L.; Betts, A.; Herrmann, J.; Edwards, E. J.; Okamoto, M.; Hedrich, R.; Gilliham, M. In Nature Communications, 12(1). 2021.
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  The non-protein amino acid gamma -aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish endogenous GABA as a bona fide plant signal, acting via a mechanism not found in animals. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to reduce stomatal opening and transpirational water loss, which improves water use efficiency and drought tolerance, via negative regulation of a stomatal guard cell tonoplast-localised anion transporter. We find GABA modulation of stomata occurs in multiple plants, including dicot and monocot crops. This study highlights a role for GABA metabolism in fine tuning physiology and opens alternative avenues for improving plant stress resilience. GABA accumulates during stress in plants but how, where and when GABA acts is not clear. Here the authors show that GABA production in Arabidopsis guard cells reduces stomatal opening and transpirational water loss, thereby improving water use efficiency.

  @article{RN970, abstract = {The non-protein amino acid gamma -aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish endogenous GABA as a bona fide plant signal, acting via a mechanism not found in animals. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to reduce stomatal opening and transpirational water loss, which improves water use efficiency and drought tolerance, via negative regulation of a stomatal guard cell tonoplast-localised anion transporter. We find GABA modulation of stomata occurs in multiple plants, including dicot and monocot crops. This study highlights a role for GABA metabolism in fine tuning physiology and opens alternative avenues for improving plant stress resilience. GABA accumulates during stress in plants but how, where and when GABA acts is not clear. Here the authors show that GABA production in Arabidopsis guard cells reduces stomatal opening and transpirational water loss, thereby improving water use efficiency.}, author = {Xu, B. and Long, Y. and Feng, X. and Zhu, X. and Sai, N. and Chirkova, L. and Betts, A. and Herrmann, J. and Edwards, E. J. and Okamoto, M. and Hedrich, R. and Gilliham, M.}, journal = {Nature Communications}, keywords = {gamma-aminobutyric-acid}, note = {Rh5yl Times Cited:87 Cited References Count:69}, number = 1, title = {GABA signalling modulates stomatal opening to enhance plant water use efficiency and drought resilience}, type = {Journal Article}, volume = 12, year = 2021 }

  %0 Journal Article %1 RN970 %A Xu, B. %A Long, Y. %A Feng, X. %A Zhu, X. %A Sai, N. %A Chirkova, L. %A Betts, A. %A Herrmann, J. %A Edwards, E. J. %A Okamoto, M. %A Hedrich, R. %A Gilliham, M. %D 2021 %J Nature Communications %N 1 %R ARTN 1952 10.1038/s41467-021-21694-3 %T GABA signalling modulates stomatal opening to enhance plant water use efficiency and drought resilience %U /brokenurl#<Go to ISI>://WOS:000636293700005 %V 12 %X The non-protein amino acid gamma -aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish endogenous GABA as a bona fide plant signal, acting via a mechanism not found in animals. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to reduce stomatal opening and transpirational water loss, which improves water use efficiency and drought tolerance, via negative regulation of a stomatal guard cell tonoplast-localised anion transporter. We find GABA modulation of stomata occurs in multiple plants, including dicot and monocot crops. This study highlights a role for GABA metabolism in fine tuning physiology and opens alternative avenues for improving plant stress resilience. GABA accumulates during stress in plants but how, where and when GABA acts is not clear. Here the authors show that GABA production in Arabidopsis guard cells reduces stomatal opening and transpirational water loss, thereby improving water use efficiency.
• How to Grow a Tree: Plant Voltage-Dependent Cation Channels in the Spotlight of Evolution. Dreyer, I.; Sussmilch, F. C.; Fukushima, K.; Riadi, G.; Becker, D.; Schultz, J.; Hedrich, R. In Trends in Plant Science, 26(1), pp. 41–52. 2021.
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  Phylogenetic analysis can be a powerful tool for generating hypotheses regarding the evolution of physiological processes. Here, we provide an updated view of the evolution of the main cation channels in plant electrical signalling: the Shaker family of voltage-gated potassium channels and the two-pore cation (K+) channel (TPC1) family. Strikingly, the TPC1 family followed the same conservative evolutionary path as one particular subfamily of Shaker channels (K-out) and remained highly invariant after terrestrialisation, suggesting that electrical signalling was, and remains, key to survival on land. We note that phylogenetic analyses can have pitfalls, which may lead to erroneous conclusions. To avoid these in the future, we suggest guidelines for analyses of ion channel evolution in plants.

  @article{RN988, abstract = {Phylogenetic analysis can be a powerful tool for generating hypotheses regarding the evolution of physiological processes. Here, we provide an updated view of the evolution of the main cation channels in plant electrical signalling: the Shaker family of voltage-gated potassium channels and the two-pore cation (K+) channel (TPC1) family. Strikingly, the TPC1 family followed the same conservative evolutionary path as one particular subfamily of Shaker channels (K-out) and remained highly invariant after terrestrialisation, suggesting that electrical signalling was, and remains, key to survival on land. We note that phylogenetic analyses can have pitfalls, which may lead to erroneous conclusions. To avoid these in the future, we suggest guidelines for analyses of ion channel evolution in plants.}, author = {Dreyer, I. and Sussmilch, F. C. and Fukushima, K. and Riadi, G. and Becker, D. and Schultz, J. and Hedrich, R.}, journal = {Trends in Plant Science}, keywords = {channels}, note = {Ph7pc Times Cited:19 Cited References Count:108}, number = 1, pages = {41-52}, title = {How to Grow a Tree: Plant Voltage-Dependent Cation Channels in the Spotlight of Evolution}, type = {Journal Article}, volume = 26, year = 2021 }

  %0 Journal Article %1 RN988 %A Dreyer, I. %A Sussmilch, F. C. %A Fukushima, K. %A Riadi, G. %A Becker, D. %A Schultz, J. %A Hedrich, R. %D 2021 %J Trends in Plant Science %N 1 %P 41-52 %R 10.1016/j.tplants.2020.07.011 %T How to Grow a Tree: Plant Voltage-Dependent Cation Channels in the Spotlight of Evolution %U /brokenurl#<Go to ISI>://WOS:000600598700009 %V 26 %X Phylogenetic analysis can be a powerful tool for generating hypotheses regarding the evolution of physiological processes. Here, we provide an updated view of the evolution of the main cation channels in plant electrical signalling: the Shaker family of voltage-gated potassium channels and the two-pore cation (K+) channel (TPC1) family. Strikingly, the TPC1 family followed the same conservative evolutionary path as one particular subfamily of Shaker channels (K-out) and remained highly invariant after terrestrialisation, suggesting that electrical signalling was, and remains, key to survival on land. We note that phylogenetic analyses can have pitfalls, which may lead to erroneous conclusions. To avoid these in the future, we suggest guidelines for analyses of ion channel evolution in plants.
• Optogenetic control of plant growth by a microbial rhodopsin. Zhou, Y.; Ding, M. Q.; Gao, S. Q.; Yu-Strzelczyk, J.; Krischke, M.; Duan, X. D.; Leide, J.; Riederer, M.; Mueller, M. J.; Hedrich, R.; Konrad, K. R.; Nagel, G. In Nature Plants, 7(2). 2021.
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  The expression of a light-gated anion channelrhodopsin from a unicellular algae and a retinal-producing enzyme from a marine bacterium enable green light optogenetic manipulation of plant cells, as demonstrated in pollen tubes. While rhodopsin-based optogenetics has revolutionized neuroscience(1,2), poor expression of opsins and the absence of the essential cofactor all-trans-retinal has complicated the application of rhodopsins in plants. Here, we demonstrate retinal production in plants and improved rhodopsin targeting for green light manipulation of plant cells using the Guillardia theta light-gated anion channelrhodopsin GtACR1(3). Green light induces a massive increase in anion permeability and pronounced membrane potential changes when GtACR1 is expressed, enabling non-invasive manipulation of plant growth and leaf development. Using light-driven anion loss, we could mimic drought conditions and bring about leaf wilting despite sufficient water supply. Expressed in pollen tubes, global GtACR1 activation triggers membrane potential depolarizations due to large anion currents. While global illumination was associated with a reversible growth arrest, local GtACR1 activation at the flanks of the apical dome steers growth direction away from the side with increased anion conductance. These results suggest a crucial role of anion permeability for the guidance of pollen tube tip growth. This plant optogenetic approach could be expanded to create an entire pallet of rhodopsin-based tools(4), greatly facilitating dissection of plant ion-signalling pathways.

  @article{RN969, abstract = {The expression of a light-gated anion channelrhodopsin from a unicellular algae and a retinal-producing enzyme from a marine bacterium enable green light optogenetic manipulation of plant cells, as demonstrated in pollen tubes. While rhodopsin-based optogenetics has revolutionized neuroscience(1,2), poor expression of opsins and the absence of the essential cofactor all-trans-retinal has complicated the application of rhodopsins in plants. Here, we demonstrate retinal production in plants and improved rhodopsin targeting for green light manipulation of plant cells using the Guillardia theta light-gated anion channelrhodopsin GtACR1(3). Green light induces a massive increase in anion permeability and pronounced membrane potential changes when GtACR1 is expressed, enabling non-invasive manipulation of plant growth and leaf development. Using light-driven anion loss, we could mimic drought conditions and bring about leaf wilting despite sufficient water supply. Expressed in pollen tubes, global GtACR1 activation triggers membrane potential depolarizations due to large anion currents. While global illumination was associated with a reversible growth arrest, local GtACR1 activation at the flanks of the apical dome steers growth direction away from the side with increased anion conductance. These results suggest a crucial role of anion permeability for the guidance of pollen tube tip growth. This plant optogenetic approach could be expanded to create an entire pallet of rhodopsin-based tools(4), greatly facilitating dissection of plant ion-signalling pathways.}, author = {Zhou, Y. and Ding, M. Q. and Gao, S. Q. and Yu-Strzelczyk, J. and Krischke, M. and Duan, X. D. and Leide, J. and Riederer, M. and Mueller, M. J. and Hedrich, R. and Konrad, K. R. and Nagel, G.}, journal = {Nature Plants}, keywords = {myOwn}, note = {Qi7mk Times Cited:28 Cited References Count:36}, number = 2, title = {Optogenetic control of plant growth by a microbial rhodopsin}, type = {Journal Article}, volume = 7, year = 2021 }

  %0 Journal Article %1 RN969 %A Zhou, Y. %A Ding, M. Q. %A Gao, S. Q. %A Yu-Strzelczyk, J. %A Krischke, M. %A Duan, X. D. %A Leide, J. %A Riederer, M. %A Mueller, M. J. %A Hedrich, R. %A Konrad, K. R. %A Nagel, G. %D 2021 %J Nature Plants %N 2 %R 10.1038/s41477-021-00853-w %T Optogenetic control of plant growth by a microbial rhodopsin %U /brokenurl#<Go to ISI>://WOS:000619167300009 %V 7 %X The expression of a light-gated anion channelrhodopsin from a unicellular algae and a retinal-producing enzyme from a marine bacterium enable green light optogenetic manipulation of plant cells, as demonstrated in pollen tubes. While rhodopsin-based optogenetics has revolutionized neuroscience(1,2), poor expression of opsins and the absence of the essential cofactor all-trans-retinal has complicated the application of rhodopsins in plants. Here, we demonstrate retinal production in plants and improved rhodopsin targeting for green light manipulation of plant cells using the Guillardia theta light-gated anion channelrhodopsin GtACR1(3). Green light induces a massive increase in anion permeability and pronounced membrane potential changes when GtACR1 is expressed, enabling non-invasive manipulation of plant growth and leaf development. Using light-driven anion loss, we could mimic drought conditions and bring about leaf wilting despite sufficient water supply. Expressed in pollen tubes, global GtACR1 activation triggers membrane potential depolarizations due to large anion currents. While global illumination was associated with a reversible growth arrest, local GtACR1 activation at the flanks of the apical dome steers growth direction away from the side with increased anion conductance. These results suggest a crucial role of anion permeability for the guidance of pollen tube tip growth. This plant optogenetic approach could be expanded to create an entire pallet of rhodopsin-based tools(4), greatly facilitating dissection of plant ion-signalling pathways.
• The Developmental and Genetic Architecture of the Sexually Selected Male Ornament of Swordtails. Schartl, M.; Kneitz, S.; Ormanns, J.; Schmidt, C.; Anderson, J. L.; Amores, A.; Catchen, J.; Wilson, C.; Geiger, D.; Du, K.; Garcia-Olazábal, M.; Sudaram, S.; Winkler, C.; Hedrich, R.; Warren, W. C.; Walter, R.; Meyer, A.; Postlethwait, J. H. In Current Biology, 31(5), p. 911-+. 2021.
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  Sexual selection results in sex-specific characters like the conspicuously pigmented extension of the ventral tip of the caudal fin-the ``sword''-in males of several species of Xiphophorus fishes. To uncover the genetic architecture underlying sword formation and to identify genes that are associated with its development, we characterized the sword transcriptional profile and combined it with genetic mapping approaches. Results showed that the male ornament of swordtails develops from a sexually non-dimorphic prepattern of transcription factors in the caudal fin. Among genes that constitute the exclusive sword transcriptome and are located in the genomic region associated with this trait we identify the potassium channel, Kcnh8, as a sword development gene. In addition to its neural function kcnh8 performs a known role in fin growth. These findings indicate that during evolution of swordtails a brain gene has been co-opted for an additional novel function in establishing a male ornament.

  @article{RN971, abstract = {Sexual selection results in sex-specific characters like the conspicuously pigmented extension of the ventral tip of the caudal fin-the ``sword''-in males of several species of Xiphophorus fishes. To uncover the genetic architecture underlying sword formation and to identify genes that are associated with its development, we characterized the sword transcriptional profile and combined it with genetic mapping approaches. Results showed that the male ornament of swordtails develops from a sexually non-dimorphic prepattern of transcription factors in the caudal fin. Among genes that constitute the exclusive sword transcriptome and are located in the genomic region associated with this trait we identify the potassium channel, Kcnh8, as a sword development gene. In addition to its neural function kcnh8 performs a known role in fin growth. These findings indicate that during evolution of swordtails a brain gene has been co-opted for an additional novel function in establishing a male ornament.}, author = {Schartl, M. and Kneitz, S. and Ormanns, J. and Schmidt, C. and Anderson, J. L. and Amores, A. and Catchen, J. and Wilson, C. and Geiger, D. and Du, K. and Garcia-Olazábal, M. and Sudaram, S. and Winkler, C. and Hedrich, R. and Warren, W. C. and Walter, R. and Meyer, A. and Postlethwait, J. H.}, journal = {Current Biology}, keywords = {sex-chromosome}, note = {Rj9xb Times Cited:15 Cited References Count:89}, number = 5, pages = {911-+}, title = {The Developmental and Genetic Architecture of the Sexually Selected Male Ornament of Swordtails}, type = {Journal Article}, volume = 31, year = 2021 }

  %0 Journal Article %1 RN971 %A Schartl, M. %A Kneitz, S. %A Ormanns, J. %A Schmidt, C. %A Anderson, J. L. %A Amores, A. %A Catchen, J. %A Wilson, C. %A Geiger, D. %A Du, K. %A Garcia-Olazábal, M. %A Sudaram, S. %A Winkler, C. %A Hedrich, R. %A Warren, W. C. %A Walter, R. %A Meyer, A. %A Postlethwait, J. H. %D 2021 %J Current Biology %N 5 %P 911-+ %R 10.1016/j.cub.2020.11.028 %T The Developmental and Genetic Architecture of the Sexually Selected Male Ornament of Swordtails %U /brokenurl#<Go to ISI>://WOS:000637959400001 %V 31 %X Sexual selection results in sex-specific characters like the conspicuously pigmented extension of the ventral tip of the caudal fin-the ``sword''-in males of several species of Xiphophorus fishes. To uncover the genetic architecture underlying sword formation and to identify genes that are associated with its development, we characterized the sword transcriptional profile and combined it with genetic mapping approaches. Results showed that the male ornament of swordtails develops from a sexually non-dimorphic prepattern of transcription factors in the caudal fin. Among genes that constitute the exclusive sword transcriptome and are located in the genomic region associated with this trait we identify the potassium channel, Kcnh8, as a sword development gene. In addition to its neural function kcnh8 performs a known role in fin growth. These findings indicate that during evolution of swordtails a brain gene has been co-opted for an additional novel function in establishing a male ornament.
• Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel ACR1. Huang, S. G.; Ding, M. Q.; Roelfsema, M. R. G.; Dreyer, I.; Scherzer, S.; Al-Rasheid, K. A. S.; Gao, S. Q.; Nagel, G.; Hedrich, R.; Konrad, K. R. In Science Advances, 7(28). 2021.
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  Guard cells control the aperture of plant stomata, which are crucial for global fluxes of CO2 and water. In turn, guard cell anion channels are seen as key players for stomatal closure, but is activation of these channels sufficient to limit plant water loss? To answer this open question, we used an optogenetic approach based on the light-gated anion channelrhodopsin 1 (GtACR1). In tobacco guard cells that express GtACR1, blue- and green-light pulses elicit Cl- and NO3- currents of -1 to -2 nA. The anion currents depolarize the plasma membrane by 60 to 80 mV, which causes opening of voltage-gated K+ channels and the extrusion of K+. As a result, continuous stimulation with green light leads to loss of guard cell turgor and closure of stomata at conditions that provoke stomatal opening in wild type. GtACR1 optogenetics thus provides unequivocal evidence that opening of anion channels is sufficient to close stomata.

  @article{RN980, abstract = {Guard cells control the aperture of plant stomata, which are crucial for global fluxes of CO2 and water. In turn, guard cell anion channels are seen as key players for stomatal closure, but is activation of these channels sufficient to limit plant water loss? To answer this open question, we used an optogenetic approach based on the light-gated anion channelrhodopsin 1 (GtACR1). In tobacco guard cells that express GtACR1, blue- and green-light pulses elicit Cl- and NO3- currents of -1 to -2 nA. The anion currents depolarize the plasma membrane by 60 to 80 mV, which causes opening of voltage-gated K+ channels and the extrusion of K+. As a result, continuous stimulation with green light leads to loss of guard cell turgor and closure of stomata at conditions that provoke stomatal opening in wild type. GtACR1 optogenetics thus provides unequivocal evidence that opening of anion channels is sufficient to close stomata.}, author = {Huang, S. G. and Ding, M. Q. and Roelfsema, M. R. G. and Dreyer, I. and Scherzer, S. and Al-Rasheid, K. A. S. and Gao, S. Q. and Nagel, G. and Hedrich, R. and Konrad, K. R.}, journal = {Science Advances}, keywords = {activation}, note = {Ti5bx Times Cited:21 Cited References Count:76}, number = 28, title = {Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel ACR1}, type = {Journal Article}, volume = 7, year = 2021 }

  %0 Journal Article %1 RN980 %A Huang, S. G. %A Ding, M. Q. %A Roelfsema, M. R. G. %A Dreyer, I. %A Scherzer, S. %A Al-Rasheid, K. A. S. %A Gao, S. Q. %A Nagel, G. %A Hedrich, R. %A Konrad, K. R. %D 2021 %J Science Advances %N 28 %R ARTN eabg4619 10.1126/sciadv.abg4619 %T Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel ACR1 %U /brokenurl#<Go to ISI>://WOS:000672817500009 %V 7 %X Guard cells control the aperture of plant stomata, which are crucial for global fluxes of CO2 and water. In turn, guard cell anion channels are seen as key players for stomatal closure, but is activation of these channels sufficient to limit plant water loss? To answer this open question, we used an optogenetic approach based on the light-gated anion channelrhodopsin 1 (GtACR1). In tobacco guard cells that express GtACR1, blue- and green-light pulses elicit Cl- and NO3- currents of -1 to -2 nA. The anion currents depolarize the plasma membrane by 60 to 80 mV, which causes opening of voltage-gated K+ channels and the extrusion of K+. As a result, continuous stimulation with green light leads to loss of guard cell turgor and closure of stomata at conditions that provoke stomatal opening in wild type. GtACR1 optogenetics thus provides unequivocal evidence that opening of anion channels is sufficient to close stomata.
• Date palm responses to a chronic, realistic ozone exposure in a FACE experiment. Paoletti, E.; Hoshika, Y.; Arab, L.; Martini, S.; Cotrozzi, L.; Weber, D.; Ache, P.; Neri, L.; Baraldi, R.; Pellegrini, E.; Müller, H. M.; Hedrich, R.; Alfarraj, S.; Rennenberg, H. In Environmental Research, 195. 2021.
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  Date palms are highly economically important species in hot arid regions, which may suffer ozone (O-3) pollution equivalently to heat and water stress. However, little is known about date palm sensitivity to O-3. Therefore, to identify their resistance mechanisms against elevated O-3, physiological parameters (leaf gas exchange, chlorophyll fluorescence and leaf pigments) and biomass growth responses to realistic O-3 exposure were tested in an isoprene-emitting date palm (Phoenix dactylifera L. cv. Nabut Saif) by a Free-Air Controlled Exposure (FACE) facility with three levels of O-3 (ambient [AA, 45 ppb as 24-h average], 1.5 x AA and 2 x AA). We found a reduction of photosynthesis only at 2 x AA although some foliar traits known as early indicators of O-3 stress responded already at 1.5 x AA, such as increased dark respiration, reduced leaf pigment content, reduced maximum quantum yield of PSII, inactivation of the oxygen evolving complex of PSII and reduced performance index PITOT. As a result, O-3 did not affect most of the growth parameters although significant declines of root biomass occurred only at 2 x AA. The major mechanism in date palm for reducing the severity of O-3 impacts was a restriction of stomatal O-3 uptake due to low stomatal conductance and O-3-induced stomatal closure. In addition, an increased respiration in elevated O-3 may indicate an enhanced capacity of catabolizing metabolites for detoxification and repair. Interestingly, date palm produced low amounts of monoterpenes, whose emission was stimulated in 2 x AA, although isoprene emission declined at both 1.5 and 2 x AA. Our results warrant more research on a biological significance of terpenoids in plant resistance against O-3 stress.

  @article{RN973, abstract = {Date palms are highly economically important species in hot arid regions, which may suffer ozone (O-3) pollution equivalently to heat and water stress. However, little is known about date palm sensitivity to O-3. Therefore, to identify their resistance mechanisms against elevated O-3, physiological parameters (leaf gas exchange, chlorophyll fluorescence and leaf pigments) and biomass growth responses to realistic O-3 exposure were tested in an isoprene-emitting date palm (Phoenix dactylifera L. cv. Nabut Saif) by a Free-Air Controlled Exposure (FACE) facility with three levels of O-3 (ambient [AA, 45 ppb as 24-h average], 1.5 x AA and 2 x AA). We found a reduction of photosynthesis only at 2 x AA although some foliar traits known as early indicators of O-3 stress responded already at 1.5 x AA, such as increased dark respiration, reduced leaf pigment content, reduced maximum quantum yield of PSII, inactivation of the oxygen evolving complex of PSII and reduced performance index PITOT. As a result, O-3 did not affect most of the growth parameters although significant declines of root biomass occurred only at 2 x AA. The major mechanism in date palm for reducing the severity of O-3 impacts was a restriction of stomatal O-3 uptake due to low stomatal conductance and O-3-induced stomatal closure. In addition, an increased respiration in elevated O-3 may indicate an enhanced capacity of catabolizing metabolites for detoxification and repair. Interestingly, date palm produced low amounts of monoterpenes, whose emission was stimulated in 2 x AA, although isoprene emission declined at both 1.5 and 2 x AA. Our results warrant more research on a biological significance of terpenoids in plant resistance against O-3 stress.}, author = {Paoletti, E. and Hoshika, Y. and Arab, L. and Martini, S. and Cotrozzi, L. and Weber, D. and Ache, P. and Neri, L. and Baraldi, R. and Pellegrini, E. and Müller, H. M. and Hedrich, R. and Alfarraj, S. and Rennenberg, H.}, journal = {Environmental Research}, keywords = {ozone}, note = {Rm0bz Times Cited:11 Cited References Count:89}, title = {Date palm responses to a chronic, realistic ozone exposure in a FACE experiment}, type = {Journal Article}, volume = 195, year = 2021 }

  %0 Journal Article %1 RN973 %A Paoletti, E. %A Hoshika, Y. %A Arab, L. %A Martini, S. %A Cotrozzi, L. %A Weber, D. %A Ache, P. %A Neri, L. %A Baraldi, R. %A Pellegrini, E. %A Müller, H. M. %A Hedrich, R. %A Alfarraj, S. %A Rennenberg, H. %D 2021 %J Environmental Research %R ARTN 110868 10.1016/j.envres.2021.110868 %T Date palm responses to a chronic, realistic ozone exposure in a FACE experiment %U /brokenurl#<Go to ISI>://WOS:000639328800147 %V 195 %X Date palms are highly economically important species in hot arid regions, which may suffer ozone (O-3) pollution equivalently to heat and water stress. However, little is known about date palm sensitivity to O-3. Therefore, to identify their resistance mechanisms against elevated O-3, physiological parameters (leaf gas exchange, chlorophyll fluorescence and leaf pigments) and biomass growth responses to realistic O-3 exposure were tested in an isoprene-emitting date palm (Phoenix dactylifera L. cv. Nabut Saif) by a Free-Air Controlled Exposure (FACE) facility with three levels of O-3 (ambient [AA, 45 ppb as 24-h average], 1.5 x AA and 2 x AA). We found a reduction of photosynthesis only at 2 x AA although some foliar traits known as early indicators of O-3 stress responded already at 1.5 x AA, such as increased dark respiration, reduced leaf pigment content, reduced maximum quantum yield of PSII, inactivation of the oxygen evolving complex of PSII and reduced performance index PITOT. As a result, O-3 did not affect most of the growth parameters although significant declines of root biomass occurred only at 2 x AA. The major mechanism in date palm for reducing the severity of O-3 impacts was a restriction of stomatal O-3 uptake due to low stomatal conductance and O-3-induced stomatal closure. In addition, an increased respiration in elevated O-3 may indicate an enhanced capacity of catabolizing metabolites for detoxification and repair. Interestingly, date palm produced low amounts of monoterpenes, whose emission was stimulated in 2 x AA, although isoprene emission declined at both 1.5 and 2 x AA. Our results warrant more research on a biological significance of terpenoids in plant resistance against O-3 stress.
• Salinity Effects on Guard Cell Proteome in. Rasouli, F.; Kiani-Pouya, A.; Shabala, L.; Li, L. T.; Tahir, A.; Yu, M.; Hedrich, R.; Chen, Z. H.; Wilson, R.; Zhang, H.; Shabala, S. In International Journal of Molecular Sciences, 22(1). 2021.
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  Epidermal fragments enriched in guard cells (GCs) were isolated from the halophyte quinoa (Chenopodium quinoa Wild.) species, and the response at the proteome level was studied after salinity treatment of 300 mM NaCl for 3 weeks. In total, 2147 proteins were identified, of which 36% were differentially expressed in response to salinity stress in GCs. Up and downregulated proteins included signaling molecules, enzyme modulators, transcription factors and oxidoreductases. The most abundant proteins induced by salt treatment were desiccation-responsive protein 29B (50-fold), osmotin-like protein OSML13 (13-fold), polycystin-1, lipoxygenase, alpha-toxin, and triacylglycerol lipase (PLAT) domain-containing protein 3-like (eight-fold), and dehydrin early responsive to dehydration (ERD14) (eight-fold). Ten proteins related to the gene ontology term "response to ABA" were upregulated in quinoa GC; this included aspartic protease, phospholipase D and plastid-lipid-associated protein. Additionally, seven proteins in the sucrose-starch pathway were upregulated in the GC in response to salinity stress, and accumulation of tryptophan synthase and L-methionine synthase (enzymes involved in the amino acid biosynthesis) was observed. Exogenous application of sucrose and tryptophan, L-methionine resulted in reduction in stomatal aperture and conductance, which could be advantageous for plants under salt stress. Eight aspartic proteinase proteins were highly upregulated in GCs of quinoa, and exogenous application of pepstatin A (an inhibitor of aspartic proteinase) was accompanied by higher oxidative stress and extremely low stomatal aperture and conductance, suggesting a possible role of aspartic proteinase in mitigating oxidative stress induced by saline conditions.

  @article{RN972, abstract = {Epidermal fragments enriched in guard cells (GCs) were isolated from the halophyte quinoa (Chenopodium quinoa Wild.) species, and the response at the proteome level was studied after salinity treatment of 300 mM NaCl for 3 weeks. In total, 2147 proteins were identified, of which 36% were differentially expressed in response to salinity stress in GCs. Up and downregulated proteins included signaling molecules, enzyme modulators, transcription factors and oxidoreductases. The most abundant proteins induced by salt treatment were desiccation-responsive protein 29B (50-fold), osmotin-like protein OSML13 (13-fold), polycystin-1, lipoxygenase, alpha-toxin, and triacylglycerol lipase (PLAT) domain-containing protein 3-like (eight-fold), and dehydrin early responsive to dehydration (ERD14) (eight-fold). Ten proteins related to the gene ontology term "response to ABA" were upregulated in quinoa GC; this included aspartic protease, phospholipase D and plastid-lipid-associated protein. Additionally, seven proteins in the sucrose-starch pathway were upregulated in the GC in response to salinity stress, and accumulation of tryptophan synthase and L-methionine synthase (enzymes involved in the amino acid biosynthesis) was observed. Exogenous application of sucrose and tryptophan, L-methionine resulted in reduction in stomatal aperture and conductance, which could be advantageous for plants under salt stress. Eight aspartic proteinase proteins were highly upregulated in GCs of quinoa, and exogenous application of pepstatin A (an inhibitor of aspartic proteinase) was accompanied by higher oxidative stress and extremely low stomatal aperture and conductance, suggesting a possible role of aspartic proteinase in mitigating oxidative stress induced by saline conditions.}, author = {Rasouli, F. and Kiani-Pouya, A. and Shabala, L. and Li, L. T. and Tahir, A. and Yu, M. and Hedrich, R. and Chen, Z. H. and Wilson, R. and Zhang, H. and Shabala, S.}, journal = {International Journal of Molecular Sciences}, keywords = {quinoa}, note = {Pq0mg Times Cited:18 Cited References Count:69}, number = 1, title = {Salinity Effects on Guard Cell Proteome in}, type = {Journal Article}, volume = 22, year = 2021 }

  %0 Journal Article %1 RN972 %A Rasouli, F. %A Kiani-Pouya, A. %A Shabala, L. %A Li, L. T. %A Tahir, A. %A Yu, M. %A Hedrich, R. %A Chen, Z. H. %A Wilson, R. %A Zhang, H. %A Shabala, S. %D 2021 %J International Journal of Molecular Sciences %N 1 %R ARTN 428 10.3390/ijms22010428 %T Salinity Effects on Guard Cell Proteome in %U /brokenurl#<Go to ISI>://WOS:000606244700001 %V 22 %X Epidermal fragments enriched in guard cells (GCs) were isolated from the halophyte quinoa (Chenopodium quinoa Wild.) species, and the response at the proteome level was studied after salinity treatment of 300 mM NaCl for 3 weeks. In total, 2147 proteins were identified, of which 36% were differentially expressed in response to salinity stress in GCs. Up and downregulated proteins included signaling molecules, enzyme modulators, transcription factors and oxidoreductases. The most abundant proteins induced by salt treatment were desiccation-responsive protein 29B (50-fold), osmotin-like protein OSML13 (13-fold), polycystin-1, lipoxygenase, alpha-toxin, and triacylglycerol lipase (PLAT) domain-containing protein 3-like (eight-fold), and dehydrin early responsive to dehydration (ERD14) (eight-fold). Ten proteins related to the gene ontology term "response to ABA" were upregulated in quinoa GC; this included aspartic protease, phospholipase D and plastid-lipid-associated protein. Additionally, seven proteins in the sucrose-starch pathway were upregulated in the GC in response to salinity stress, and accumulation of tryptophan synthase and L-methionine synthase (enzymes involved in the amino acid biosynthesis) was observed. Exogenous application of sucrose and tryptophan, L-methionine resulted in reduction in stomatal aperture and conductance, which could be advantageous for plants under salt stress. Eight aspartic proteinase proteins were highly upregulated in GCs of quinoa, and exogenous application of pepstatin A (an inhibitor of aspartic proteinase) was accompanied by higher oxidative stress and extremely low stomatal aperture and conductance, suggesting a possible role of aspartic proteinase in mitigating oxidative stress induced by saline conditions.
• Stomata: the holey grail of plant evolution. McAdam, S. A. M.; Duckett, J. G.; Sussmilch, F. C.; Pressel, S.; Renzaglia, K. S.; Hedrich, R.; Brodribb, T. J.; Merced, A. In American Journal of Botany, 108(3), pp. 366–371. 2021.
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  @article{RN975, author = {McAdam, S. A. M. and Duckett, J. G. and Sussmilch, F. C. and Pressel, S. and Renzaglia, K. S. and Hedrich, R. and Brodribb, T. J. and Merced, A.}, journal = {American Journal of Botany}, keywords = {bryophytes}, note = {Rg2ko Times Cited:15 Cited References Count:67}, number = 3, pages = {366-371}, title = {Stomata: the holey grail of plant evolution}, type = {Journal Article}, volume = 108, year = 2021 }

  %0 Journal Article %1 RN975 %A McAdam, S. A. M. %A Duckett, J. G. %A Sussmilch, F. C. %A Pressel, S. %A Renzaglia, K. S. %A Hedrich, R. %A Brodribb, T. J. %A Merced, A. %D 2021 %J American Journal of Botany %N 3 %P 366-371 %R 10.1002/ajb2.1619 %T Stomata: the holey grail of plant evolution %U /brokenurl#<Go to ISI>://WOS:000626635100001 %V 108
• An optimized genetically encoded dual reporter for simultaneous ratio imaging of Ca and H reveals new insights into ion signaling in plants. Li, K. K.; Prada, J.; Damineli, D. S. C.; Liese, A.; Romeis, T.; Dandekar, T.; Feijó, J. A.; Hedrich, R.; Konrad, K. R. In New Phytologist, 230(6), pp. 2292–2310. 2021.
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  Whereas the role of calcium ions (Ca2+) in plant signaling is well studied, the physiological significance of pH-changes remains largely undefined. Here we developed CapHensor, an optimized dual-reporter for simultaneous Ca2+ and pH ratio-imaging and studied signaling events in pollen tubes (PTs), guard cells (GCs), and mesophyll cells (MCs). Monitoring spatio-temporal relationships between membrane voltage, Ca2+- and pH-dynamics revealed interconnections previously not described. In tobacco PTs, we demonstrated Ca2+-dynamics lag behind pH-dynamics during oscillatory growth, and pH correlates more with growth than Ca2+. In GCs, we demonstrated abscisic acid (ABA) to initiate stomatal closure via rapid cytosolic alkalization followed by Ca2+ elevation. Preventing the alkalization blocked GC ABA-responses and even opened stomata in the presence of ABA, disclosing an important pH-dependent GC signaling node. In MCs, a flg22-induced membrane depolarization preceded Ca2+-increases and cytosolic acidification by c. 2 min, suggesting a Ca2+/pH-independent early pathogen signaling step. Imaging Ca2+ and pH resolved similar cytosol and nuclear signals and demonstrated flg22, but not ABA and hydrogen peroxide to initiate rapid membrane voltage-, Ca2+- and pH-responses. We propose close interrelation in Ca2+- and pH-signaling that is cell type- and stimulus-specific and the pH having crucial roles in regulating PT growth and stomata movement.

  @article{RN977, abstract = {Whereas the role of calcium ions (Ca2+) in plant signaling is well studied, the physiological significance of pH-changes remains largely undefined. Here we developed CapHensor, an optimized dual-reporter for simultaneous Ca2+ and pH ratio-imaging and studied signaling events in pollen tubes (PTs), guard cells (GCs), and mesophyll cells (MCs). Monitoring spatio-temporal relationships between membrane voltage, Ca2+- and pH-dynamics revealed interconnections previously not described. In tobacco PTs, we demonstrated Ca2+-dynamics lag behind pH-dynamics during oscillatory growth, and pH correlates more with growth than Ca2+. In GCs, we demonstrated abscisic acid (ABA) to initiate stomatal closure via rapid cytosolic alkalization followed by Ca2+ elevation. Preventing the alkalization blocked GC ABA-responses and even opened stomata in the presence of ABA, disclosing an important pH-dependent GC signaling node. In MCs, a flg22-induced membrane depolarization preceded Ca2+-increases and cytosolic acidification by c. 2 min, suggesting a Ca2+/pH-independent early pathogen signaling step. Imaging Ca2+ and pH resolved similar cytosol and nuclear signals and demonstrated flg22, but not ABA and hydrogen peroxide to initiate rapid membrane voltage-, Ca2+- and pH-responses. We propose close interrelation in Ca2+- and pH-signaling that is cell type- and stimulus-specific and the pH having crucial roles in regulating PT growth and stomata movement.}, author = {Li, K. K. and Prada, J. and Damineli, D. S. C. and Liese, A. and Romeis, T. and Dandekar, T. and Feijó, J. A. and Hedrich, R. and Konrad, K. R.}, journal = {New Phytologist}, keywords = {abscisic}, note = {Sd1fk Times Cited:34 Cited References Count:147}, number = 6, pages = {2292-2310}, title = {An optimized genetically encoded dual reporter for simultaneous ratio imaging of Ca and H reveals new insights into ion signaling in plants}, type = {Journal Article}, volume = 230, year = 2021 }

  %0 Journal Article %1 RN977 %A Li, K. K. %A Prada, J. %A Damineli, D. S. C. %A Liese, A. %A Romeis, T. %A Dandekar, T. %A Feijó, J. A. %A Hedrich, R. %A Konrad, K. R. %D 2021 %J New Phytologist %N 6 %P 2292-2310 %R 10.1111/nph.17202 %T An optimized genetically encoded dual reporter for simultaneous ratio imaging of Ca and H reveals new insights into ion signaling in plants %U /brokenurl#<Go to ISI>://WOS:000619171500001 %V 230 %X Whereas the role of calcium ions (Ca2+) in plant signaling is well studied, the physiological significance of pH-changes remains largely undefined. Here we developed CapHensor, an optimized dual-reporter for simultaneous Ca2+ and pH ratio-imaging and studied signaling events in pollen tubes (PTs), guard cells (GCs), and mesophyll cells (MCs). Monitoring spatio-temporal relationships between membrane voltage, Ca2+- and pH-dynamics revealed interconnections previously not described. In tobacco PTs, we demonstrated Ca2+-dynamics lag behind pH-dynamics during oscillatory growth, and pH correlates more with growth than Ca2+. In GCs, we demonstrated abscisic acid (ABA) to initiate stomatal closure via rapid cytosolic alkalization followed by Ca2+ elevation. Preventing the alkalization blocked GC ABA-responses and even opened stomata in the presence of ABA, disclosing an important pH-dependent GC signaling node. In MCs, a flg22-induced membrane depolarization preceded Ca2+-increases and cytosolic acidification by c. 2 min, suggesting a Ca2+/pH-independent early pathogen signaling step. Imaging Ca2+ and pH resolved similar cytosol and nuclear signals and demonstrated flg22, but not ABA and hydrogen peroxide to initiate rapid membrane voltage-, Ca2+- and pH-responses. We propose close interrelation in Ca2+- and pH-signaling that is cell type- and stimulus-specific and the pH having crucial roles in regulating PT growth and stomata movement.
• Prospects for the accelerated improvement of the resilient crop quinoa (vol 72, pg 5333, 2020). López-Marqués, R. L.; Norrevang, A. F.; Ache, P.; Moog, M.; Visintainer, D.; Wendt, T.; Osterberg, J. T.; Dockter, C.; Jorgensen, M. E.; Salvador, A. T.; Hedrich, R.; Gao, C.; Jacobsen, S. E.; Shabala, S.; Palmgren, M. In Journal of Experimental Botany, 72(10), pp. 3929–3929. 2021.
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  @article{RN976, author = {López-Marqués, R. L. and Norrevang, A. F. and Ache, P. and Moog, M. and Visintainer, D. and Wendt, T. and Osterberg, J. T. and Dockter, C. and Jorgensen, M. E. and Salvador, A. T. and Hedrich, R. and Gao, C. and Jacobsen, S. E. and Shabala, S. and Palmgren, M.}, journal = {Journal of Experimental Botany}, keywords = {myOwn}, note = {Ss1vp Times Cited:1 Cited References Count:1}, number = 10, pages = {3929-3929}, title = {Prospects for the accelerated improvement of the resilient crop quinoa (vol 72, pg 5333, 2020)}, type = {Journal Article}, volume = 72, year = 2021 }

  %0 Journal Article %1 RN976 %A López-Marqués, R. L. %A Norrevang, A. F. %A Ache, P. %A Moog, M. %A Visintainer, D. %A Wendt, T. %A Osterberg, J. T. %A Dockter, C. %A Jorgensen, M. E. %A Salvador, A. T. %A Hedrich, R. %A Gao, C. %A Jacobsen, S. E. %A Shabala, S. %A Palmgren, M. %D 2021 %J Journal of Experimental Botany %N 10 %P 3929-3929 %R 10.1093/jxb/erab010 %T Prospects for the accelerated improvement of the resilient crop quinoa (vol 72, pg 5333, 2020) %U /brokenurl#<Go to ISI>://WOS:000661530200034 %V 72
• Rapid depolarization and cytosolic calcium increase go hand-in-hand in mesophyll cells’ ozone response. Nuhkat, M.; Brosché, M.; Stoelzle-Feix, S.; Dietrich, P.; Hedrich, R.; Roelfsema, M. R. G.; Kollist, H. In New Phytologist, 232(4), pp. 1692–1702. 2021.
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  Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown. We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1. We show that within 1 min, prior to stomatal closure, O-3 triggered a drop in whole-plant CO2 uptake. Within this early phase, O-3 pulses (200-1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O-3 induced cell death, systemic Ca2+ signals and an irreversible drop in stomatal conductance and photosynthetic capacity. We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca2+) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.

  @article{RN974, abstract = {Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown. We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1. We show that within 1 min, prior to stomatal closure, O-3 triggered a drop in whole-plant CO2 uptake. Within this early phase, O-3 pulses (200-1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O-3 induced cell death, systemic Ca2+ signals and an irreversible drop in stomatal conductance and photosynthetic capacity. We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca2+) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.}, author = {Nuhkat, M. and Brosché, M. and Stoelzle-Feix, S. and Dietrich, P. and Hedrich, R. and Roelfsema, M. R. G. and Kollist, H.}, journal = {New Phytologist}, keywords = {arabidopsis}, note = {Wj1yr Times Cited:3 Cited References Count:62}, number = 4, pages = {1692-1702}, title = {Rapid depolarization and cytosolic calcium increase go hand-in-hand in mesophyll cells' ozone response}, type = {Journal Article}, volume = 232, year = 2021 }

  %0 Journal Article %1 RN974 %A Nuhkat, M. %A Brosché, M. %A Stoelzle-Feix, S. %A Dietrich, P. %A Hedrich, R. %A Roelfsema, M. R. G. %A Kollist, H. %D 2021 %J New Phytologist %N 4 %P 1692-1702 %R 10.1111/nph.17711 %T Rapid depolarization and cytosolic calcium increase go hand-in-hand in mesophyll cells' ozone response %U /brokenurl#<Go to ISI>://WOS:000698433600001 %V 232 %X Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown. We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1. We show that within 1 min, prior to stomatal closure, O-3 triggered a drop in whole-plant CO2 uptake. Within this early phase, O-3 pulses (200-1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O-3 induced cell death, systemic Ca2+ signals and an irreversible drop in stomatal conductance and photosynthetic capacity. We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca2+) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.
• Metabolic responses of date palm ( L.) leaves to drought differ in summer and winter climate. Du, B. G.; Kruse, J.; Winkler, J. B.; Alfarraj, S.; Albasher, G.; Schnitzler, J. P.; Ache, P.; Hedrich, R.; Rennenberg, H. In Tree Physiology, 41(9), pp. 1685–1700. 2021.
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  Drought negatively impacts growth and productivity of plants, particularly in arid and semi-arid regions. Although drought events can take place in summer and winter, differences in the impact of drought on physiological processes between seasons are largely unknown. The aim of this study was to elucidate metabolic strategies of date palms in response to drought in summer and winter season. To identify such differences, we exposed date palm seedlings to a drought-recovery regime, both in simulated summer and winter climate. Leaf hydration, carbon discrimination (Delta C-13), and primary and secondary metabolite composition and contents were analyzed. Depending on season, drought differently affected physiological and biochemical traits of the leaves. In summer, drought induced significantly decreased leaf hydration, concentrations of ascorbate, most sugars, primary and secondary organic acids, as well as phenolic compounds, while thiol, amino acid, raffinose and individual fatty acid contents were increased compared with well-watered plants. In winter, drought had no effect on leaf hydration, ascorbate and fatty acids contents, but resulted in increased foliar thiol and amino acid levels as observed in summer. Compared with winter, foliar traits of plants exposed to drought in summer only partly recovered after re-watering. Memory effects on water relations, and primary and secondary metabolites seem to prepare foliar traits of date palms for repeated drought events in summer. Apparently, a well-orchestrated metabolic network, including the anti-oxidative system, compatible solutes accumulation and osmotic adjustment, and maintenance of cell-membrane stability strongly reduces the susceptibility of date palms to drought. These mechanisms of drought compensation may be more frequently required in summer.

  @article{RN987, abstract = {Drought negatively impacts growth and productivity of plants, particularly in arid and semi-arid regions. Although drought events can take place in summer and winter, differences in the impact of drought on physiological processes between seasons are largely unknown. The aim of this study was to elucidate metabolic strategies of date palms in response to drought in summer and winter season. To identify such differences, we exposed date palm seedlings to a drought-recovery regime, both in simulated summer and winter climate. Leaf hydration, carbon discrimination (Delta C-13), and primary and secondary metabolite composition and contents were analyzed. Depending on season, drought differently affected physiological and biochemical traits of the leaves. In summer, drought induced significantly decreased leaf hydration, concentrations of ascorbate, most sugars, primary and secondary organic acids, as well as phenolic compounds, while thiol, amino acid, raffinose and individual fatty acid contents were increased compared with well-watered plants. In winter, drought had no effect on leaf hydration, ascorbate and fatty acids contents, but resulted in increased foliar thiol and amino acid levels as observed in summer. Compared with winter, foliar traits of plants exposed to drought in summer only partly recovered after re-watering. Memory effects on water relations, and primary and secondary metabolites seem to prepare foliar traits of date palms for repeated drought events in summer. Apparently, a well-orchestrated metabolic network, including the anti-oxidative system, compatible solutes accumulation and osmotic adjustment, and maintenance of cell-membrane stability strongly reduces the susceptibility of date palms to drought. These mechanisms of drought compensation may be more frequently required in summer.}, author = {Du, B. G. and Kruse, J. and Winkler, J. B. and Alfarraj, S. and Albasher, G. and Schnitzler, J. P. and Ache, P. and Hedrich, R. and Rennenberg, H.}, journal = {Tree Physiology}, keywords = {system}, note = {Wm3ln Times Cited:9 Cited References Count:102}, number = 9, pages = {1685-1700}, title = {Metabolic responses of date palm ( L.) leaves to drought differ in summer and winter climate}, type = {Journal Article}, volume = 41, year = 2021 }

  %0 Journal Article %1 RN987 %A Du, B. G. %A Kruse, J. %A Winkler, J. B. %A Alfarraj, S. %A Albasher, G. %A Schnitzler, J. P. %A Ache, P. %A Hedrich, R. %A Rennenberg, H. %D 2021 %J Tree Physiology %N 9 %P 1685-1700 %R 10.1093/treephys/tpab027 %T Metabolic responses of date palm ( L.) leaves to drought differ in summer and winter climate %U /brokenurl#<Go to ISI>://WOS:000710990200010 %V 41 %X Drought negatively impacts growth and productivity of plants, particularly in arid and semi-arid regions. Although drought events can take place in summer and winter, differences in the impact of drought on physiological processes between seasons are largely unknown. The aim of this study was to elucidate metabolic strategies of date palms in response to drought in summer and winter season. To identify such differences, we exposed date palm seedlings to a drought-recovery regime, both in simulated summer and winter climate. Leaf hydration, carbon discrimination (Delta C-13), and primary and secondary metabolite composition and contents were analyzed. Depending on season, drought differently affected physiological and biochemical traits of the leaves. In summer, drought induced significantly decreased leaf hydration, concentrations of ascorbate, most sugars, primary and secondary organic acids, as well as phenolic compounds, while thiol, amino acid, raffinose and individual fatty acid contents were increased compared with well-watered plants. In winter, drought had no effect on leaf hydration, ascorbate and fatty acids contents, but resulted in increased foliar thiol and amino acid levels as observed in summer. Compared with winter, foliar traits of plants exposed to drought in summer only partly recovered after re-watering. Memory effects on water relations, and primary and secondary metabolites seem to prepare foliar traits of date palms for repeated drought events in summer. Apparently, a well-orchestrated metabolic network, including the anti-oxidative system, compatible solutes accumulation and osmotic adjustment, and maintenance of cell-membrane stability strongly reduces the susceptibility of date palms to drought. These mechanisms of drought compensation may be more frequently required in summer.
• A voltage-dependent Ca homeostat operates in the plant vacuolar membrane. Dindas, J.; Dreyer, I.; Huang, S. G.; Hedrich, R.; Roelfsema, M. R. G. In New Phytologist, 230(4), pp. 1449–1460. 2021.
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  Cytosolic calcium signals are evoked by a large variety of biotic and abiotic stimuli and play an important role in cellular and long distance signalling in plants. While the function of the plasma membrane in cytosolic Ca2+ signalling has been intensively studied, the role of the vacuolar membrane remains elusive. A newly developed vacuolar voltage clamp technique was used in combination with live-cell imaging, to study the role of the vacuolar membrane in Ca2+ and pH homeostasis of bulging root hair cells of Arabidopsis. Depolarisation of the vacuolar membrane caused a rapid increase in the Ca2+ concentration and alkalised the cytosol, while hyperpolarisation led to the opposite responses. The relationship between the vacuolar membrane potential, the cytosolic pH and Ca2+ concentration suggests that a vacuolar H+/Ca2+ exchange mechanism plays a central role in cytosolic Ca2+ homeostasis. Mathematical modelling further suggests that the voltage-dependent vacuolar Ca2+ homeostat could contribute to calcium signalling when coupled to a recently discovered K+ channel-dependent module for electrical excitability of the vacuolar membrane.

  @article{RN989, abstract = {Cytosolic calcium signals are evoked by a large variety of biotic and abiotic stimuli and play an important role in cellular and long distance signalling in plants. While the function of the plasma membrane in cytosolic Ca2+ signalling has been intensively studied, the role of the vacuolar membrane remains elusive. A newly developed vacuolar voltage clamp technique was used in combination with live-cell imaging, to study the role of the vacuolar membrane in Ca2+ and pH homeostasis of bulging root hair cells of Arabidopsis. Depolarisation of the vacuolar membrane caused a rapid increase in the Ca2+ concentration and alkalised the cytosol, while hyperpolarisation led to the opposite responses. The relationship between the vacuolar membrane potential, the cytosolic pH and Ca2+ concentration suggests that a vacuolar H+/Ca2+ exchange mechanism plays a central role in cytosolic Ca2+ homeostasis. Mathematical modelling further suggests that the voltage-dependent vacuolar Ca2+ homeostat could contribute to calcium signalling when coupled to a recently discovered K+ channel-dependent module for electrical excitability of the vacuolar membrane.}, author = {Dindas, J. and Dreyer, I. and Huang, S. G. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {arabidopsis}, note = {Rn2nt Times Cited:11 Cited References Count:71}, number = 4, pages = {1449-1460}, title = {A voltage-dependent Ca homeostat operates in the plant vacuolar membrane}, type = {Journal Article}, volume = 230, year = 2021 }

  %0 Journal Article %1 RN989 %A Dindas, J. %A Dreyer, I. %A Huang, S. G. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2021 %J New Phytologist %N 4 %P 1449-1460 %R 10.1111/nph.17272 %T A voltage-dependent Ca homeostat operates in the plant vacuolar membrane %U /brokenurl#<Go to ISI>://WOS:000634727800001 %V 230 %X Cytosolic calcium signals are evoked by a large variety of biotic and abiotic stimuli and play an important role in cellular and long distance signalling in plants. While the function of the plasma membrane in cytosolic Ca2+ signalling has been intensively studied, the role of the vacuolar membrane remains elusive. A newly developed vacuolar voltage clamp technique was used in combination with live-cell imaging, to study the role of the vacuolar membrane in Ca2+ and pH homeostasis of bulging root hair cells of Arabidopsis. Depolarisation of the vacuolar membrane caused a rapid increase in the Ca2+ concentration and alkalised the cytosol, while hyperpolarisation led to the opposite responses. The relationship between the vacuolar membrane potential, the cytosolic pH and Ca2+ concentration suggests that a vacuolar H+/Ca2+ exchange mechanism plays a central role in cytosolic Ca2+ homeostasis. Mathematical modelling further suggests that the voltage-dependent vacuolar Ca2+ homeostat could contribute to calcium signalling when coupled to a recently discovered K+ channel-dependent module for electrical excitability of the vacuolar membrane.
• Under salt stress guard cells rewire ion transport and abscisic acid signaling. Karimi, S. M.; Freund, M.; Wager, B. M.; Knoblauch, M.; Fromm, J.; Mueller, H. M.; Ache, P.; Krischke, M.; Mueller, M. J.; Müller, T.; Dittrich, M.; Geilfus, C. M.; Alfarhan, A. H.; Hedrich, R.; Deeken, R. In New Phytologist, 231(3), pp. 1040–1055. 2021.
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  Soil salinity is an increasingly global problem which hampers plant growth and crop yield. Plant productivity depends on optimal water-use efficiency and photosynthetic capacity balanced by stomatal conductance. Whether and how stomatal behavior contributes to salt sensitivity or tolerance is currently unknown. This work identifies guard cell-specific signaling networks exerted by a salt-sensitive and salt-tolerant plant under ionic and osmotic stress conditions accompanied by increasing NaCl loads. We challenged soil-grown Arabidopsis thaliana and Thellungiella salsuginea plants with short- and long-term salinity stress and monitored genome-wide gene expression and signals of guard cells that determine their function. Arabidopsis plants suffered from both salt regimes and showed reduced stomatal conductance while Thellungiella displayed no obvious stress symptoms. The salt-dependent gene expression changes of guard cells supported the ability of the halophyte to maintain high potassium to sodium ratios and to attenuate the abscisic acid (ABA) signaling pathway which the glycophyte kept activated despite fading ABA concentrations. Our study shows that salinity stress and even the different tolerances are manifested on a single cell level. Halophytic guard cells are less sensitive than glycophytic guard cells, providing opportunities to manipulate stomatal behavior and improve plant productivity.

  @article{RN979, abstract = {Soil salinity is an increasingly global problem which hampers plant growth and crop yield. Plant productivity depends on optimal water-use efficiency and photosynthetic capacity balanced by stomatal conductance. Whether and how stomatal behavior contributes to salt sensitivity or tolerance is currently unknown. This work identifies guard cell-specific signaling networks exerted by a salt-sensitive and salt-tolerant plant under ionic and osmotic stress conditions accompanied by increasing NaCl loads. We challenged soil-grown Arabidopsis thaliana and Thellungiella salsuginea plants with short- and long-term salinity stress and monitored genome-wide gene expression and signals of guard cells that determine their function. Arabidopsis plants suffered from both salt regimes and showed reduced stomatal conductance while Thellungiella displayed no obvious stress symptoms. The salt-dependent gene expression changes of guard cells supported the ability of the halophyte to maintain high potassium to sodium ratios and to attenuate the abscisic acid (ABA) signaling pathway which the glycophyte kept activated despite fading ABA concentrations. Our study shows that salinity stress and even the different tolerances are manifested on a single cell level. Halophytic guard cells are less sensitive than glycophytic guard cells, providing opportunities to manipulate stomatal behavior and improve plant productivity.}, author = {Karimi, S. M. and Freund, M. and Wager, B. M. and Knoblauch, M. and Fromm, J. and Mueller, H. M. and Ache, P. and Krischke, M. and Mueller, M. J. and Müller, T. and Dittrich, M. and Geilfus, C. M. and Alfarhan, A. H. and Hedrich, R. and Deeken, R.}, journal = {New Phytologist}, keywords = {abscisic}, note = {Tb7cy Times Cited:17 Cited References Count:92}, number = 3, pages = {1040-1055}, title = {Under salt stress guard cells rewire ion transport and abscisic acid signaling}, type = {Journal Article}, volume = 231, year = 2021 }

  %0 Journal Article %1 RN979 %A Karimi, S. M. %A Freund, M. %A Wager, B. M. %A Knoblauch, M. %A Fromm, J. %A Mueller, H. M. %A Ache, P. %A Krischke, M. %A Mueller, M. J. %A Müller, T. %A Dittrich, M. %A Geilfus, C. M. %A Alfarhan, A. H. %A Hedrich, R. %A Deeken, R. %D 2021 %J New Phytologist %N 3 %P 1040-1055 %R 10.1111/nph.17376 %T Under salt stress guard cells rewire ion transport and abscisic acid signaling %U /brokenurl#<Go to ISI>://WOS:000661910000001 %V 231 %X Soil salinity is an increasingly global problem which hampers plant growth and crop yield. Plant productivity depends on optimal water-use efficiency and photosynthetic capacity balanced by stomatal conductance. Whether and how stomatal behavior contributes to salt sensitivity or tolerance is currently unknown. This work identifies guard cell-specific signaling networks exerted by a salt-sensitive and salt-tolerant plant under ionic and osmotic stress conditions accompanied by increasing NaCl loads. We challenged soil-grown Arabidopsis thaliana and Thellungiella salsuginea plants with short- and long-term salinity stress and monitored genome-wide gene expression and signals of guard cells that determine their function. Arabidopsis plants suffered from both salt regimes and showed reduced stomatal conductance while Thellungiella displayed no obvious stress symptoms. The salt-dependent gene expression changes of guard cells supported the ability of the halophyte to maintain high potassium to sodium ratios and to attenuate the abscisic acid (ABA) signaling pathway which the glycophyte kept activated despite fading ABA concentrations. Our study shows that salinity stress and even the different tolerances are manifested on a single cell level. Halophytic guard cells are less sensitive than glycophytic guard cells, providing opportunities to manipulate stomatal behavior and improve plant productivity.
• Physiological responses of date palm ( ) seedlings to seawater and flooding. Du, B. G.; Ma, Y. H.; Yáñez-Serrano, A. M.; Arab, L.; Fasbender, L.; Alfarraj, S.; Albasher, G.; Hedrich, R.; White, P. J.; Werner, C.; Rennenberg, H. In New Phytologist, 229(6), pp. 3318–3329. 2021.
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  In their natural environment along coast lines, date palms are exposed to seawater inundation and, hence, combined stress by salinity and flooding. To elucidate the consequences of this combined stress on foliar gas exchange and metabolite abundances in leaves and roots, date palm seedlings were exposed to flooding with seawater and its major constituents under controlled conditions. Seawater flooding significantly reduced CO2 assimilation, transpiration and stomatal conductance, but did not affect isoprene emission. A similar effect was observed upon NaCl exposure. By contrast, flooding with distilled water or MgSO4 did not affect CO2/H2O gas exchange or stomatal conductance significantly, indicating that neither flooding itself, nor seawater sulfate, contributed greatly to stomatal closure. Seawater exposure increased Na and Cl contents in leaves and roots, but did not affect sulfate contents significantly. Metabolite analyses revealed reduced abundances of foliar compatible solutes, such as sugars and sugar alcohols, whereas nitrogen compounds accumulated in roots. Reduced transpiration upon seawater exposure may contribute to controlling the movement of toxic ions to leaves and, therefore, can be seen as a mechanism to cope with salinity. The present results indicate that date palm seedlings are tolerant towards seawater exposure to some extent, and highly tolerant to flooding.

  @article{RN986, abstract = {In their natural environment along coast lines, date palms are exposed to seawater inundation and, hence, combined stress by salinity and flooding. To elucidate the consequences of this combined stress on foliar gas exchange and metabolite abundances in leaves and roots, date palm seedlings were exposed to flooding with seawater and its major constituents under controlled conditions. Seawater flooding significantly reduced CO2 assimilation, transpiration and stomatal conductance, but did not affect isoprene emission. A similar effect was observed upon NaCl exposure. By contrast, flooding with distilled water or MgSO4 did not affect CO2/H2O gas exchange or stomatal conductance significantly, indicating that neither flooding itself, nor seawater sulfate, contributed greatly to stomatal closure. Seawater exposure increased Na and Cl contents in leaves and roots, but did not affect sulfate contents significantly. Metabolite analyses revealed reduced abundances of foliar compatible solutes, such as sugars and sugar alcohols, whereas nitrogen compounds accumulated in roots. Reduced transpiration upon seawater exposure may contribute to controlling the movement of toxic ions to leaves and, therefore, can be seen as a mechanism to cope with salinity. The present results indicate that date palm seedlings are tolerant towards seawater exposure to some extent, and highly tolerant to flooding.}, author = {Du, B. G. and Ma, Y. H. and Yáñez-Serrano, A. M. and Arab, L. and Fasbender, L. and Alfarraj, S. and Albasher, G. and Hedrich, R. and White, P. J. and Werner, C. and Rennenberg, H.}, journal = {New Phytologist}, keywords = {other}, note = {Qi2he Times Cited:10 Cited References Count:83}, number = 6, pages = {3318-3329}, title = {Physiological responses of date palm ( ) seedlings to seawater and flooding}, type = {Journal Article}, volume = 229, year = 2021 }

  %0 Journal Article %1 RN986 %A Du, B. G. %A Ma, Y. H. %A Yáñez-Serrano, A. M. %A Arab, L. %A Fasbender, L. %A Alfarraj, S. %A Albasher, G. %A Hedrich, R. %A White, P. J. %A Werner, C. %A Rennenberg, H. %D 2021 %J New Phytologist %N 6 %P 3318-3329 %R 10.1111/nph.17123 %T Physiological responses of date palm ( ) seedlings to seawater and flooding %U /brokenurl#<Go to ISI>://WOS:000605346500001 %V 229 %X In their natural environment along coast lines, date palms are exposed to seawater inundation and, hence, combined stress by salinity and flooding. To elucidate the consequences of this combined stress on foliar gas exchange and metabolite abundances in leaves and roots, date palm seedlings were exposed to flooding with seawater and its major constituents under controlled conditions. Seawater flooding significantly reduced CO2 assimilation, transpiration and stomatal conductance, but did not affect isoprene emission. A similar effect was observed upon NaCl exposure. By contrast, flooding with distilled water or MgSO4 did not affect CO2/H2O gas exchange or stomatal conductance significantly, indicating that neither flooding itself, nor seawater sulfate, contributed greatly to stomatal closure. Seawater exposure increased Na and Cl contents in leaves and roots, but did not affect sulfate contents significantly. Metabolite analyses revealed reduced abundances of foliar compatible solutes, such as sugars and sugar alcohols, whereas nitrogen compounds accumulated in roots. Reduced transpiration upon seawater exposure may contribute to controlling the movement of toxic ions to leaves and, therefore, can be seen as a mechanism to cope with salinity. The present results indicate that date palm seedlings are tolerant towards seawater exposure to some extent, and highly tolerant to flooding.
• On the Origin of Carnivory: Molecular Physiology and Evolution of Plants on an Animal Diet. Hedrich, R.; Fukushima, K. In Annual Review of Plant Biology, Vol 72, 2021, 72, pp. 133–153. 2021.
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  Charles Darwin recognized that carnivorous plants thrive in nutrient-poor soil by capturing animals. Although the concept of botanical carnivory has been known for nearly 150 years, its molecular mechanisms and evolutionary origins have not been well understood until recently. In the last decade, technical advances have fueled the genome and transcriptome sequencings of active and passive hunters, leading to a better understanding of the traits associated with the carnivorous syndrome, from trap leaf development and prey digestion to nutrient absorption, exemplified, for example, by the Venus flytrap (Dionaea muscipula), pitcher plant (Cephalotus follicularis), and bladderwort (Utricularia gibba). The repurposing of defense-related genes is an important trend in the evolution of plant carnivory. In this review, using the Venus flytrap as a representative of the carnivorous plants, we summarize themolecular mechanisms underlying their ability to attract, trap, and digest prey and discuss the origins of plant carnivory in relation to their genomic evolution.

  @article{RN981, abstract = {Charles Darwin recognized that carnivorous plants thrive in nutrient-poor soil by capturing animals. Although the concept of botanical carnivory has been known for nearly 150 years, its molecular mechanisms and evolutionary origins have not been well understood until recently. In the last decade, technical advances have fueled the genome and transcriptome sequencings of active and passive hunters, leading to a better understanding of the traits associated with the carnivorous syndrome, from trap leaf development and prey digestion to nutrient absorption, exemplified, for example, by the Venus flytrap (Dionaea muscipula), pitcher plant (Cephalotus follicularis), and bladderwort (Utricularia gibba). The repurposing of defense-related genes is an important trend in the evolution of plant carnivory. In this review, using the Venus flytrap as a representative of the carnivorous plants, we summarize themolecular mechanisms underlying their ability to attract, trap, and digest prey and discuss the origins of plant carnivory in relation to their genomic evolution.}, author = {Hedrich, R. and Fukushima, K.}, journal = {Annual Review of Plant Biology, Vol 72, 2021}, keywords = {carnivorous}, note = {Br7rg Times Cited:25 Cited References Count:123 Annual Review of Plant Biology}, pages = {133-153}, title = {On the Origin of Carnivory: Molecular Physiology and Evolution of Plants on an Animal Diet}, type = {Journal Article}, volume = 72, year = 2021 }

  %0 Journal Article %1 RN981 %A Hedrich, R. %A Fukushima, K. %D 2021 %J Annual Review of Plant Biology, Vol 72, 2021 %P 133-153 %R 10.1146/annurev-arplant-080620-010429 %T On the Origin of Carnivory: Molecular Physiology and Evolution of Plants on an Animal Diet %U /brokenurl#<Go to ISI>://WOS:000669645400006 %V 72 %X Charles Darwin recognized that carnivorous plants thrive in nutrient-poor soil by capturing animals. Although the concept of botanical carnivory has been known for nearly 150 years, its molecular mechanisms and evolutionary origins have not been well understood until recently. In the last decade, technical advances have fueled the genome and transcriptome sequencings of active and passive hunters, leading to a better understanding of the traits associated with the carnivorous syndrome, from trap leaf development and prey digestion to nutrient absorption, exemplified, for example, by the Venus flytrap (Dionaea muscipula), pitcher plant (Cephalotus follicularis), and bladderwort (Utricularia gibba). The repurposing of defense-related genes is an important trend in the evolution of plant carnivory. In this review, using the Venus flytrap as a representative of the carnivorous plants, we summarize themolecular mechanisms underlying their ability to attract, trap, and digest prey and discuss the origins of plant carnivory in relation to their genomic evolution.
• PYL8 ABA receptors of play a crucial role in response to abiotic stress and are stabilized by ABA. Garcia-Maquilon, I.; Coego, A.; Lozano-Juste, J.; Messerer, M.; de Ollas, C.; Julian, J.; Ruiz-Partida, R.; Pizzio, G.; Belda-Palazón, B.; Gomez-Cadenas, A.; Mayer, K. F. X.; Geiger, D.; Alquraishi, S. A.; Alrefaei, A. F.; Ache, P.; Hedrich, R.; Rodriguez, P. L. In Journal of Experimental Botany, 72(2), pp. 757–774. 2021.
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  The identification of those prevalent abscisic acid (ABA) receptors and molecular mechanisms that trigger drought adaptation in crops well adapted to harsh conditions such as date palm (Phoenix dactylifera, Pd) sheds light on plant-environment interactions. We reveal that PdPYL8-like receptors are predominantly expressed under abiotic stress, with Pd27 being the most expressed receptor in date palm. Therefore, subfamily I PdPYL8-like receptors have been selected for ABA signaling during abiotic stress response in this crop. Biochemical characterization of PdPYL8-like and PdPYL1-like receptors revealed receptor- and ABA-dependent inhibition of PP2Cs, which triggers activation of the pRD29B-LUC reporter in response to ABA. PdPYLs efficiently abolish PP2C-mediated repression of ABA signaling, but loss of the Trp lock in the seed-specific AHG1-like phosphatase PdPP2C79 markedly impairs its inhibition by ABA receptors. Characterization of Arabidopsis transgenic plants that express PdPYLs shows enhanced ABA signaling in seed, root, and guard cells. Specifically, Pd27-overexpressing plants showed lower ABA content and were more efficient than the wild type in lowering transpiration at negative soil water potential, leading to enhanced drought tolerance. Finally, PdPYL8-like receptors accumulate after ABA treatment, which suggests that ABA-induced stabilization of these receptors operates in date palm for efficient boosting of ABA signaling in response to abiotic stress.

  @article{RN983, abstract = {The identification of those prevalent abscisic acid (ABA) receptors and molecular mechanisms that trigger drought adaptation in crops well adapted to harsh conditions such as date palm (Phoenix dactylifera, Pd) sheds light on plant-environment interactions. We reveal that PdPYL8-like receptors are predominantly expressed under abiotic stress, with Pd27 being the most expressed receptor in date palm. Therefore, subfamily I PdPYL8-like receptors have been selected for ABA signaling during abiotic stress response in this crop. Biochemical characterization of PdPYL8-like and PdPYL1-like receptors revealed receptor- and ABA-dependent inhibition of PP2Cs, which triggers activation of the pRD29B-LUC reporter in response to ABA. PdPYLs efficiently abolish PP2C-mediated repression of ABA signaling, but loss of the Trp lock in the seed-specific AHG1-like phosphatase PdPP2C79 markedly impairs its inhibition by ABA receptors. Characterization of Arabidopsis transgenic plants that express PdPYLs shows enhanced ABA signaling in seed, root, and guard cells. Specifically, Pd27-overexpressing plants showed lower ABA content and were more efficient than the wild type in lowering transpiration at negative soil water potential, leading to enhanced drought tolerance. Finally, PdPYL8-like receptors accumulate after ABA treatment, which suggests that ABA-induced stabilization of these receptors operates in date palm for efficient boosting of ABA signaling in response to abiotic stress.}, author = {Garcia-Maquilon, I. and Coego, A. and Lozano-Juste, J. and Messerer, M. and de Ollas, C. and Julian, J. and Ruiz-Partida, R. and Pizzio, G. and Belda-Palazón, B. and Gomez-Cadenas, A. and Mayer, K. F. X. and Geiger, D. and Alquraishi, S. A. and Alrefaei, A. F. and Ache, P. and Hedrich, R. and Rodriguez, P. L.}, journal = {Journal of Experimental Botany}, keywords = {aba}, note = {Rz8yu Times Cited:6 Cited References Count:68}, number = 2, pages = {757-774}, title = {PYL8 ABA receptors of play a crucial role in response to abiotic stress and are stabilized by ABA}, type = {Journal Article}, volume = 72, year = 2021 }

  %0 Journal Article %1 RN983 %A Garcia-Maquilon, I. %A Coego, A. %A Lozano-Juste, J. %A Messerer, M. %A de Ollas, C. %A Julian, J. %A Ruiz-Partida, R. %A Pizzio, G. %A Belda-Palazón, B. %A Gomez-Cadenas, A. %A Mayer, K. F. X. %A Geiger, D. %A Alquraishi, S. A. %A Alrefaei, A. F. %A Ache, P. %A Hedrich, R. %A Rodriguez, P. L. %D 2021 %J Journal of Experimental Botany %N 2 %P 757-774 %R 10.1093/jxb/eraa476 %T PYL8 ABA receptors of play a crucial role in response to abiotic stress and are stabilized by ABA %U /brokenurl#<Go to ISI>://WOS:000648886400041 %V 72 %X The identification of those prevalent abscisic acid (ABA) receptors and molecular mechanisms that trigger drought adaptation in crops well adapted to harsh conditions such as date palm (Phoenix dactylifera, Pd) sheds light on plant-environment interactions. We reveal that PdPYL8-like receptors are predominantly expressed under abiotic stress, with Pd27 being the most expressed receptor in date palm. Therefore, subfamily I PdPYL8-like receptors have been selected for ABA signaling during abiotic stress response in this crop. Biochemical characterization of PdPYL8-like and PdPYL1-like receptors revealed receptor- and ABA-dependent inhibition of PP2Cs, which triggers activation of the pRD29B-LUC reporter in response to ABA. PdPYLs efficiently abolish PP2C-mediated repression of ABA signaling, but loss of the Trp lock in the seed-specific AHG1-like phosphatase PdPP2C79 markedly impairs its inhibition by ABA receptors. Characterization of Arabidopsis transgenic plants that express PdPYLs shows enhanced ABA signaling in seed, root, and guard cells. Specifically, Pd27-overexpressing plants showed lower ABA content and were more efficient than the wild type in lowering transpiration at negative soil water potential, leading to enhanced drought tolerance. Finally, PdPYL8-like receptors accumulate after ABA treatment, which suggests that ABA-induced stabilization of these receptors operates in date palm for efficient boosting of ABA signaling in response to abiotic stress.
• Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants. Fabricant, A.; Iwata, G. Z.; Scherzer, S.; Bougas, L.; Rolfs, K.; Jodko-Wladzinska, A.; Voigt, J.; Hedrich, R.; Budker, D. In Scientific Reports, 11(1). 2021.
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  Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electro- and magnetophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. Here we demonstrate that APs in a multicellular plant system produce measurable magnetic fields. Using atomic optically pumped magnetometers, biomagnetism associated with electrical activity in the carnivorous Venus flytrap, Dionaea muscipula, was recorded. Action potentials were induced by heat stimulation and detected both electrically and magnetically. Furthermore, the thermal properties of ion channels underlying the AP were studied. Beyond proof of principle, our findings pave the way to understanding the molecular basis of biomagnetism in living plants. In the future, magnetometry may be used to study long-distance electrical signaling in a variety of plant species, and to develop noninvasive diagnostics of plant stress and disease.

  @article{RN985, abstract = {Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electro- and magnetophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. Here we demonstrate that APs in a multicellular plant system produce measurable magnetic fields. Using atomic optically pumped magnetometers, biomagnetism associated with electrical activity in the carnivorous Venus flytrap, Dionaea muscipula, was recorded. Action potentials were induced by heat stimulation and detected both electrically and magnetically. Furthermore, the thermal properties of ion channels underlying the AP were studied. Beyond proof of principle, our findings pave the way to understanding the molecular basis of biomagnetism in living plants. In the future, magnetometry may be used to study long-distance electrical signaling in a variety of plant species, and to develop noninvasive diagnostics of plant stress and disease.}, author = {Fabricant, A. and Iwata, G. Z. and Scherzer, S. and Bougas, L. and Rolfs, K. and Jodko-Wladzinska, A. and Voigt, J. and Hedrich, R. and Budker, D.}, journal = {Scientific Reports}, keywords = {magnetic}, note = {Qt7nf Times Cited:26 Cited References Count:36}, number = 1, title = {Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants}, type = {Journal Article}, volume = 11, year = 2021 }

  %0 Journal Article %1 RN985 %A Fabricant, A. %A Iwata, G. Z. %A Scherzer, S. %A Bougas, L. %A Rolfs, K. %A Jodko-Wladzinska, A. %A Voigt, J. %A Hedrich, R. %A Budker, D. %D 2021 %J Scientific Reports %N 1 %R ARTN 1438 10.1038/s41598-021-81114-w %T Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants %U /brokenurl#<Go to ISI>://WOS:000626775600038 %V 11 %X Upon stimulation, plants elicit electrical signals that can travel within a cellular network analogous to the animal nervous system. It is well-known that in the human brain, voltage changes in certain regions result from concerted electrical activity which, in the form of action potentials (APs), travels within nerve-cell arrays. Electro- and magnetophysiological techniques like electroencephalography, magnetoencephalography, and magnetic resonance imaging are used to record this activity and to diagnose disorders. Here we demonstrate that APs in a multicellular plant system produce measurable magnetic fields. Using atomic optically pumped magnetometers, biomagnetism associated with electrical activity in the carnivorous Venus flytrap, Dionaea muscipula, was recorded. Action potentials were induced by heat stimulation and detected both electrically and magnetically. Furthermore, the thermal properties of ion channels underlying the AP were studied. Beyond proof of principle, our findings pave the way to understanding the molecular basis of biomagnetism in living plants. In the future, magnetometry may be used to study long-distance electrical signaling in a variety of plant species, and to develop noninvasive diagnostics of plant stress and disease.
• Acidosis-induced activation of anion channel SLAH3 in the flooding-related stress response of. Lehmann, J.; Jorgensen, M. E.; Fratz, S.; Müller, H. M.; Kusch, J.; Scherzer, S.; Navarro-Retamal, C.; Mayer, D.; Böhm, J.; Konrad, K. R.; Terpitz, U.; Dreyer, I.; Mueller, T. D.; Sauer, M.; Hedrich, R.; Geiger, D.; Maierhofer, T. In Current Biology, 31(16), p. 3575-+. 2021.
  • [ Abstract ]
  • [ BibTeX ]
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  • [ DOI ]
  Plants, as sessile organisms, gained the ability to sense and respond to biotic and abiotic stressors to survive severe changes in their environments. The change in our climate comes with extreme dry periods but also episodes of flooding. The latter stress condition causes anaerobiosis-triggered cytosolic acidosis and impairs plant function. The molecular mechanism that enables plant cells to sense acidity and convey this signal via membrane depolarization was previously unknown. Here, we show that acidosis-induced anion efflux from Arabidopsis (Arabidopsis thaliana) roots is dependent on the S-type anion channel AtSLAH3. Heterologous expression of SLAH3 in Xenopus oocytes revealed that the anion channel is directly activated by a small, physiological drop in cytosolic pH. Acidosis-triggered activation of SLAH3 is mediated by protonation of histidine 330 and 454. Super-resolution microscopy analysis showed that the increase in cellular proton concentration switches SLAH3 from an electrically silent channel dimer into its active monomeric form. Our results show that, upon acidification, protons directly switch SLAH3 to its open configuration, bypassing kinase-dependent activation. Moreover, under flooding conditions, the stress response of Arabidopsis wild-type (WT) plants was significantly higher compared to SLAH3 loss-of-function mutants. Our genetic evidence of SLAH3 pH sensor function may guide the development of crop varieties with improved stress tolerance.

  @article{RN978, abstract = {Plants, as sessile organisms, gained the ability to sense and respond to biotic and abiotic stressors to survive severe changes in their environments. The change in our climate comes with extreme dry periods but also episodes of flooding. The latter stress condition causes anaerobiosis-triggered cytosolic acidosis and impairs plant function. The molecular mechanism that enables plant cells to sense acidity and convey this signal via membrane depolarization was previously unknown. Here, we show that acidosis-induced anion efflux from Arabidopsis (Arabidopsis thaliana) roots is dependent on the S-type anion channel AtSLAH3. Heterologous expression of SLAH3 in Xenopus oocytes revealed that the anion channel is directly activated by a small, physiological drop in cytosolic pH. Acidosis-triggered activation of SLAH3 is mediated by protonation of histidine 330 and 454. Super-resolution microscopy analysis showed that the increase in cellular proton concentration switches SLAH3 from an electrically silent channel dimer into its active monomeric form. Our results show that, upon acidification, protons directly switch SLAH3 to its open configuration, bypassing kinase-dependent activation. Moreover, under flooding conditions, the stress response of Arabidopsis wild-type (WT) plants was significantly higher compared to SLAH3 loss-of-function mutants. Our genetic evidence of SLAH3 pH sensor function may guide the development of crop varieties with improved stress tolerance.}, author = {Lehmann, J. and Jorgensen, M. E. and Fratz, S. and Müller, H. M. and Kusch, J. and Scherzer, S. and Navarro-Retamal, C. and Mayer, D. and Böhm, J. and Konrad, K. R. and Terpitz, U. and Dreyer, I. and Mueller, T. D. and Sauer, M. and Hedrich, R. and Geiger, D. and Maierhofer, T.}, journal = {Current Biology}, keywords = {h+-atpase}, note = {Ue5sv Times Cited:17 Cited References Count:85}, number = 16, pages = {3575-+}, title = {Acidosis-induced activation of anion channel SLAH3 in the flooding-related stress response of}, type = {Journal Article}, volume = 31, year = 2021 }

  %0 Journal Article %1 RN978 %A Lehmann, J. %A Jorgensen, M. E. %A Fratz, S. %A Müller, H. M. %A Kusch, J. %A Scherzer, S. %A Navarro-Retamal, C. %A Mayer, D. %A Böhm, J. %A Konrad, K. R. %A Terpitz, U. %A Dreyer, I. %A Mueller, T. D. %A Sauer, M. %A Hedrich, R. %A Geiger, D. %A Maierhofer, T. %D 2021 %J Current Biology %N 16 %P 3575-+ %R 10.1016/j.cub.2021.06.018 %T Acidosis-induced activation of anion channel SLAH3 in the flooding-related stress response of %U /brokenurl#<Go to ISI>://WOS:000687948600010 %V 31 %X Plants, as sessile organisms, gained the ability to sense and respond to biotic and abiotic stressors to survive severe changes in their environments. The change in our climate comes with extreme dry periods but also episodes of flooding. The latter stress condition causes anaerobiosis-triggered cytosolic acidosis and impairs plant function. The molecular mechanism that enables plant cells to sense acidity and convey this signal via membrane depolarization was previously unknown. Here, we show that acidosis-induced anion efflux from Arabidopsis (Arabidopsis thaliana) roots is dependent on the S-type anion channel AtSLAH3. Heterologous expression of SLAH3 in Xenopus oocytes revealed that the anion channel is directly activated by a small, physiological drop in cytosolic pH. Acidosis-triggered activation of SLAH3 is mediated by protonation of histidine 330 and 454. Super-resolution microscopy analysis showed that the increase in cellular proton concentration switches SLAH3 from an electrically silent channel dimer into its active monomeric form. Our results show that, upon acidification, protons directly switch SLAH3 to its open configuration, bypassing kinase-dependent activation. Moreover, under flooding conditions, the stress response of Arabidopsis wild-type (WT) plants was significantly higher compared to SLAH3 loss-of-function mutants. Our genetic evidence of SLAH3 pH sensor function may guide the development of crop varieties with improved stress tolerance.
• Mechanosensitive channel gating by delipidation. Flegler, V. J.; Rasmussen, A.; Borbil, K.; Boten, L.; Chen, H. A.; Deinlein, H.; Halang, J.; Hellmanzik, K.; Löffler, J.; Schmidt, V.; Makbul, C.; Kraft, C.; Hedrich, R.; Rasmussen, T.; Böttcher, B. In Proceedings of the National Academy of Sciences of the United States of America, 118(33). 2021.
  • [ Abstract ]
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  The mechanosensitive channel of small conductance (MscS) protects bacteria against hypoosmotic shock. It can sense the tension in the surrounding membrane and releases solutes if the pressure in the cell is getting too high. The membrane contacts MscS at sensor paddles, but lipids also leave the membrane and move along grooves between the paddles to reside as far as 15 angstrom away from the membrane in hydrophobic pockets. One sensing model suggests that a higher tension pulls lipids from the grooves back to the membrane, which triggers gating. However, it is still unclear to what degree this model accounts for sensing and what contribution the direct interaction of the membrane with the channel has. Here, we show that MscS opens when it is sufficiently delipidated by incubation with the detergent dodecyl-beta-maltoside or the branched detergent lauryl maltose neopentyl glycol. After addition of detergent-solubilized lipids, it closes again. These results support the model that lipid extrusion causes gating: Lipids are slowly removed from the grooves and pockets by the incubation with detergent, which triggers opening. Addition of lipids in micelles allows lipids to migrate back into the pockets, which closes the channel even in the absence of a membrane. Based on the distribution of the aliphatic chains in the open and closed conformation, we propose that during gating, lipids leave the complex on the cytosolic leaflet at the height of highest lateral tension, while on the periplasmic side, lipids flow into gaps, which open between transmembrane helices.

  @article{RN984, abstract = {The mechanosensitive channel of small conductance (MscS) protects bacteria against hypoosmotic shock. It can sense the tension in the surrounding membrane and releases solutes if the pressure in the cell is getting too high. The membrane contacts MscS at sensor paddles, but lipids also leave the membrane and move along grooves between the paddles to reside as far as 15 angstrom away from the membrane in hydrophobic pockets. One sensing model suggests that a higher tension pulls lipids from the grooves back to the membrane, which triggers gating. However, it is still unclear to what degree this model accounts for sensing and what contribution the direct interaction of the membrane with the channel has. Here, we show that MscS opens when it is sufficiently delipidated by incubation with the detergent dodecyl-beta-maltoside or the branched detergent lauryl maltose neopentyl glycol. After addition of detergent-solubilized lipids, it closes again. These results support the model that lipid extrusion causes gating: Lipids are slowly removed from the grooves and pockets by the incubation with detergent, which triggers opening. Addition of lipids in micelles allows lipids to migrate back into the pockets, which closes the channel even in the absence of a membrane. Based on the distribution of the aliphatic chains in the open and closed conformation, we propose that during gating, lipids leave the complex on the cytosolic leaflet at the height of highest lateral tension, while on the periplasmic side, lipids flow into gaps, which open between transmembrane helices.}, author = {Flegler, V. J. and Rasmussen, A. and Borbil, K. and Boten, L. and Chen, H. A. and Deinlein, H. and Halang, J. and Hellmanzik, K. and Löffler, J. and Schmidt, V. and Makbul, C. and Kraft, C. and Hedrich, R. and Rasmussen, T. and Böttcher, B.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {microscopy}, note = {Uh1vl Times Cited:20 Cited References Count:70}, number = 33, title = {Mechanosensitive channel gating by delipidation}, type = {Journal Article}, volume = 118, year = 2021 }

  %0 Journal Article %1 RN984 %A Flegler, V. J. %A Rasmussen, A. %A Borbil, K. %A Boten, L. %A Chen, H. A. %A Deinlein, H. %A Halang, J. %A Hellmanzik, K. %A Löffler, J. %A Schmidt, V. %A Makbul, C. %A Kraft, C. %A Hedrich, R. %A Rasmussen, T. %A Böttcher, B. %D 2021 %J Proceedings of the National Academy of Sciences of the United States of America %N 33 %R ARTN e2107095118 10.1073/pnas.2107095118 %T Mechanosensitive channel gating by delipidation %U /brokenurl#<Go to ISI>://WOS:000689727600019 %V 118 %X The mechanosensitive channel of small conductance (MscS) protects bacteria against hypoosmotic shock. It can sense the tension in the surrounding membrane and releases solutes if the pressure in the cell is getting too high. The membrane contacts MscS at sensor paddles, but lipids also leave the membrane and move along grooves between the paddles to reside as far as 15 angstrom away from the membrane in hydrophobic pockets. One sensing model suggests that a higher tension pulls lipids from the grooves back to the membrane, which triggers gating. However, it is still unclear to what degree this model accounts for sensing and what contribution the direct interaction of the membrane with the channel has. Here, we show that MscS opens when it is sufficiently delipidated by incubation with the detergent dodecyl-beta-maltoside or the branched detergent lauryl maltose neopentyl glycol. After addition of detergent-solubilized lipids, it closes again. These results support the model that lipid extrusion causes gating: Lipids are slowly removed from the grooves and pockets by the incubation with detergent, which triggers opening. Addition of lipids in micelles allows lipids to migrate back into the pockets, which closes the channel even in the absence of a membrane. Based on the distribution of the aliphatic chains in the open and closed conformation, we propose that during gating, lipids leave the complex on the cytosolic leaflet at the height of highest lateral tension, while on the periplasmic side, lipids flow into gaps, which open between transmembrane helices.

• Sugar Beet ( ) Guard Cells Responses to Salinity Stress: A Proteomic Analysis. Rasouli, F.; Kiani-Pouya, A.; Li, L. T.; Zhang, H.; Chen, Z. H.; Hedrich, R.; Wilson, R.; Shabala, S. In International Journal of Molecular Sciences, 21(7). 2020.
  • [ Abstract ]
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  Soil salinity is a major environmental constraint affecting crop growth and threatening global food security. Plants adapt to salinity by optimizing the performance of stomata. Stomata are formed by two guard cells (GCs) that are morphologically and functionally distinct from the other leaf cells. These microscopic sphincters inserted into the wax-covered epidermis of the shoot balance CO2 intake for photosynthetic carbon gain and concomitant water loss. In order to better understand the molecular mechanisms underlying stomatal function under saline conditions, we used proteomics approach to study isolated GCs from the salt-tolerant sugar beet species. Of the 2088 proteins identified in sugar beet GCs, 82 were differentially regulated by salt treatment. According to bioinformatics analysis (GO enrichment analysis and protein classification), these proteins were involved in lipid metabolism, cell wall modification, ATP biosynthesis, and signaling. Among the significant differentially abundant proteins, several proteins classified as "stress proteins" were upregulated, including non-specific lipid transfer protein, chaperone proteins, heat shock proteins, inorganic pyrophosphatase 2, responsible for energized vacuole membrane for ion transportation. Moreover, several antioxidant enzymes (peroxide, superoxidase dismutase) were highly upregulated. Furthermore, cell wall proteins detected in GCs provided some evidence that GC walls were more flexible in response to salt stress. Proteins such as L-ascorbate oxidase that were constitutively high under both control and high salinity conditions may contribute to the ability of sugar beet GCs to adapt to salinity by mitigating salinity-induced oxidative stress.

  @article{RN993, abstract = {Soil salinity is a major environmental constraint affecting crop growth and threatening global food security. Plants adapt to salinity by optimizing the performance of stomata. Stomata are formed by two guard cells (GCs) that are morphologically and functionally distinct from the other leaf cells. These microscopic sphincters inserted into the wax-covered epidermis of the shoot balance CO2 intake for photosynthetic carbon gain and concomitant water loss. In order to better understand the molecular mechanisms underlying stomatal function under saline conditions, we used proteomics approach to study isolated GCs from the salt-tolerant sugar beet species. Of the 2088 proteins identified in sugar beet GCs, 82 were differentially regulated by salt treatment. According to bioinformatics analysis (GO enrichment analysis and protein classification), these proteins were involved in lipid metabolism, cell wall modification, ATP biosynthesis, and signaling. Among the significant differentially abundant proteins, several proteins classified as "stress proteins" were upregulated, including non-specific lipid transfer protein, chaperone proteins, heat shock proteins, inorganic pyrophosphatase 2, responsible for energized vacuole membrane for ion transportation. Moreover, several antioxidant enzymes (peroxide, superoxidase dismutase) were highly upregulated. Furthermore, cell wall proteins detected in GCs provided some evidence that GC walls were more flexible in response to salt stress. Proteins such as L-ascorbate oxidase that were constitutively high under both control and high salinity conditions may contribute to the ability of sugar beet GCs to adapt to salinity by mitigating salinity-induced oxidative stress.}, author = {Rasouli, F. and Kiani-Pouya, A. and Li, L. T. and Zhang, H. and Chen, Z. H. and Hedrich, R. and Wilson, R. and Shabala, S.}, journal = {International Journal of Molecular Sciences}, keywords = {guard}, note = {Lr3dn Times Cited:13 Cited References Count:65}, number = 7, title = {Sugar Beet ( ) Guard Cells Responses to Salinity Stress: A Proteomic Analysis}, type = {Journal Article}, volume = 21, year = 2020 }

  %0 Journal Article %1 RN993 %A Rasouli, F. %A Kiani-Pouya, A. %A Li, L. T. %A Zhang, H. %A Chen, Z. H. %A Hedrich, R. %A Wilson, R. %A Shabala, S. %D 2020 %J International Journal of Molecular Sciences %N 7 %R ARTN 2331 10.3390/ijms21072331 %T Sugar Beet ( ) Guard Cells Responses to Salinity Stress: A Proteomic Analysis %U /brokenurl#<Go to ISI>://WOS:000535574200073 %V 21 %X Soil salinity is a major environmental constraint affecting crop growth and threatening global food security. Plants adapt to salinity by optimizing the performance of stomata. Stomata are formed by two guard cells (GCs) that are morphologically and functionally distinct from the other leaf cells. These microscopic sphincters inserted into the wax-covered epidermis of the shoot balance CO2 intake for photosynthetic carbon gain and concomitant water loss. In order to better understand the molecular mechanisms underlying stomatal function under saline conditions, we used proteomics approach to study isolated GCs from the salt-tolerant sugar beet species. Of the 2088 proteins identified in sugar beet GCs, 82 were differentially regulated by salt treatment. According to bioinformatics analysis (GO enrichment analysis and protein classification), these proteins were involved in lipid metabolism, cell wall modification, ATP biosynthesis, and signaling. Among the significant differentially abundant proteins, several proteins classified as "stress proteins" were upregulated, including non-specific lipid transfer protein, chaperone proteins, heat shock proteins, inorganic pyrophosphatase 2, responsible for energized vacuole membrane for ion transportation. Moreover, several antioxidant enzymes (peroxide, superoxidase dismutase) were highly upregulated. Furthermore, cell wall proteins detected in GCs provided some evidence that GC walls were more flexible in response to salt stress. Proteins such as L-ascorbate oxidase that were constitutively high under both control and high salinity conditions may contribute to the ability of sugar beet GCs to adapt to salinity by mitigating salinity-induced oxidative stress.
• The MscS-like channel YnaI has a gating mechanism based on flexible pore helices. Flegler, V. J.; Rasmussen, A.; Rao, S. L.; Wu, N.; Zenobi, R.; Sansom, M. S. P.; Hedrich, R.; Rasmussen, T.; Böttcher, B. In Proceedings of the National Academy of Sciences of the United States of America, 117(46), pp. 28754–28762. 2020.
  • [ Abstract ]
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  The mechanosensitive channel of small conductance (MscS) is the prototype of an evolutionarily diversified large family that fine tunes osmoregulation but is likely to fulfill additional functions. Escherichia coli has six osmoprotective paralogs with different numbers of transmembrane helices. These helices are important for gating and sensing in MscS but the role of the additional helices in the paralogs is not understood. The medium-sized channel YnaI was extracted and delivered in native nanodiscs in closed-like and open-like conformations using the copolymer diisobutylene/ maleic acid (DIBMA) for structural studies. Here we show by electron cryomicroscopy that YnaI has an extended sensor paddle that during gating relocates relative to the pore concomitant with bending of a GGxGG motif in the pore helices. YnaI is the only one of the six paralogs that has this GGxGG motif allowing the sensor paddle to move outward. Access to the pore is through a vestibule on the cytosolic side that is fenestrated by side portals. In YnaI, these portals are obstructed by aromatic side chains but are still fully hydrated and thus support conductance. For comparison with large-sized channels, we determined the structure of YbiO, which showed larger portals and a wider pore with no GGxGG motif. Further in silico comparison of MscS, YnaI, and YbiO highlighted differences in the hydrophobicity and wettability of their pores and vestibule interiors. Thus, MscS-like channels of different sizes have a common core architecture but show different gating mechanisms and fine-tuned conductive properties.

  @article{RN998, abstract = {The mechanosensitive channel of small conductance (MscS) is the prototype of an evolutionarily diversified large family that fine tunes osmoregulation but is likely to fulfill additional functions. Escherichia coli has six osmoprotective paralogs with different numbers of transmembrane helices. These helices are important for gating and sensing in MscS but the role of the additional helices in the paralogs is not understood. The medium-sized channel YnaI was extracted and delivered in native nanodiscs in closed-like and open-like conformations using the copolymer diisobutylene/ maleic acid (DIBMA) for structural studies. Here we show by electron cryomicroscopy that YnaI has an extended sensor paddle that during gating relocates relative to the pore concomitant with bending of a GGxGG motif in the pore helices. YnaI is the only one of the six paralogs that has this GGxGG motif allowing the sensor paddle to move outward. Access to the pore is through a vestibule on the cytosolic side that is fenestrated by side portals. In YnaI, these portals are obstructed by aromatic side chains but are still fully hydrated and thus support conductance. For comparison with large-sized channels, we determined the structure of YbiO, which showed larger portals and a wider pore with no GGxGG motif. Further in silico comparison of MscS, YnaI, and YbiO highlighted differences in the hydrophobicity and wettability of their pores and vestibule interiors. Thus, MscS-like channels of different sizes have a common core architecture but show different gating mechanisms and fine-tuned conductive properties.}, author = {Flegler, V. J. and Rasmussen, A. and Rao, S. L. and Wu, N. and Zenobi, R. and Sansom, M. S. P. and Hedrich, R. and Rasmussen, T. and Böttcher, B.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {electron}, note = {Ou2jv Times Cited:23 Cited References Count:64}, number = 46, pages = {28754-28762}, title = {The MscS-like channel YnaI has a gating mechanism based on flexible pore helices}, type = {Journal Article}, volume = 117, year = 2020 }

  %0 Journal Article %1 RN998 %A Flegler, V. J. %A Rasmussen, A. %A Rao, S. L. %A Wu, N. %A Zenobi, R. %A Sansom, M. S. P. %A Hedrich, R. %A Rasmussen, T. %A Böttcher, B. %D 2020 %J Proceedings of the National Academy of Sciences of the United States of America %N 46 %P 28754-28762 %R 10.1073/pnas.2005641117 %T The MscS-like channel YnaI has a gating mechanism based on flexible pore helices %U /brokenurl#<Go to ISI>://WOS:000591360600003 %V 117 %X The mechanosensitive channel of small conductance (MscS) is the prototype of an evolutionarily diversified large family that fine tunes osmoregulation but is likely to fulfill additional functions. Escherichia coli has six osmoprotective paralogs with different numbers of transmembrane helices. These helices are important for gating and sensing in MscS but the role of the additional helices in the paralogs is not understood. The medium-sized channel YnaI was extracted and delivered in native nanodiscs in closed-like and open-like conformations using the copolymer diisobutylene/ maleic acid (DIBMA) for structural studies. Here we show by electron cryomicroscopy that YnaI has an extended sensor paddle that during gating relocates relative to the pore concomitant with bending of a GGxGG motif in the pore helices. YnaI is the only one of the six paralogs that has this GGxGG motif allowing the sensor paddle to move outward. Access to the pore is through a vestibule on the cytosolic side that is fenestrated by side portals. In YnaI, these portals are obstructed by aromatic side chains but are still fully hydrated and thus support conductance. For comparison with large-sized channels, we determined the structure of YbiO, which showed larger portals and a wider pore with no GGxGG motif. Further in silico comparison of MscS, YnaI, and YbiO highlighted differences in the hydrophobicity and wettability of their pores and vestibule interiors. Thus, MscS-like channels of different sizes have a common core architecture but show different gating mechanisms and fine-tuned conductive properties.
• Genomes of the Venus Flytrap and Close Relatives Unveil the Roots of Plant Carnivory. Palfalvi, G.; Hackl, T.; Terhoeven, N.; Shibata, T. F.; Nishiyama, T.; Ankenbrand, M.; Becker, D.; Förster, F.; Freund, M.; Iosip, A.; Kreuzer, I.; Saul, F.; Kamida, C.; Fukushima, K.; Shigenobu, S.; Tamada, Y.; Adamec, L.; Hoshi, Y.; Ueda, K.; Winkelmann, T.; Fuchs, J.; Schubert, I.; Schwacke, R.; Al-Rasheid, K.; Schultz, J.; Hasebe, M.; Hedrich, R. In Current Biology, 30(12), p. 2312-+. 2020.
  • [ Abstract ]
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  Most plants grow and develop by taking up nutrients from the soil while continuously under threat from foraging animals. Carnivorous plants have turned the tables by capturing and consuming nutrient-rich animal prey, enabling them to thrive in nutrient-poor soil. To better understand the evolution of botanical carnivory, we compared the draft genome of the Venus flytrap (Dionaea muscipula) with that of its aquatic sister, the waterwheel plant Aldrovanda vesiculosa, and the sundew Drosera spatulata. We identified an early whole-genome duplication in the family as source for carnivory-associated genes. Recruitment of genes to the trap from the root especially was a major mechanism in the evolution of carnivory, supported by family-specific duplications. Still, these genomes belong to the gene poorest land plants sequenced thus far, suggesting reduction of selective pressure on different processes, including non-carnivorous nutrient acquisition. Our results show how non-carnivorous plants evolved into the most skillful green hunters on the planet.

  @article{RN994, abstract = {Most plants grow and develop by taking up nutrients from the soil while continuously under threat from foraging animals. Carnivorous plants have turned the tables by capturing and consuming nutrient-rich animal prey, enabling them to thrive in nutrient-poor soil. To better understand the evolution of botanical carnivory, we compared the draft genome of the Venus flytrap (Dionaea muscipula) with that of its aquatic sister, the waterwheel plant Aldrovanda vesiculosa, and the sundew Drosera spatulata. We identified an early whole-genome duplication in the family as source for carnivory-associated genes. Recruitment of genes to the trap from the root especially was a major mechanism in the evolution of carnivory, supported by family-specific duplications. Still, these genomes belong to the gene poorest land plants sequenced thus far, suggesting reduction of selective pressure on different processes, including non-carnivorous nutrient acquisition. Our results show how non-carnivorous plants evolved into the most skillful green hunters on the planet.}, author = {Palfalvi, G. and Hackl, T. and Terhoeven, N. and Shibata, T. F. and Nishiyama, T. and Ankenbrand, M. and Becker, D. and Förster, F. and Freund, M. and Iosip, A. and Kreuzer, I. and Saul, F. and Kamida, C. and Fukushima, K. and Shigenobu, S. and Tamada, Y. and Adamec, L. and Hoshi, Y. and Ueda, K. and Winkelmann, T. and Fuchs, J. and Schubert, I. and Schwacke, R. and Al-Rasheid, K. and Schultz, J. and Hasebe, M. and Hedrich, R.}, journal = {Current Biology}, keywords = {factor}, note = {Mk0zw Times Cited:46 Cited References Count:69}, number = 12, pages = {2312-+}, title = {Genomes of the Venus Flytrap and Close Relatives Unveil the Roots of Plant Carnivory}, type = {Journal Article}, volume = 30, year = 2020 }

  %0 Journal Article %1 RN994 %A Palfalvi, G. %A Hackl, T. %A Terhoeven, N. %A Shibata, T. F. %A Nishiyama, T. %A Ankenbrand, M. %A Becker, D. %A Förster, F. %A Freund, M. %A Iosip, A. %A Kreuzer, I. %A Saul, F. %A Kamida, C. %A Fukushima, K. %A Shigenobu, S. %A Tamada, Y. %A Adamec, L. %A Hoshi, Y. %A Ueda, K. %A Winkelmann, T. %A Fuchs, J. %A Schubert, I. %A Schwacke, R. %A Al-Rasheid, K. %A Schultz, J. %A Hasebe, M. %A Hedrich, R. %D 2020 %J Current Biology %N 12 %P 2312-+ %R 10.1016/j.cub.2020.04.051 %T Genomes of the Venus Flytrap and Close Relatives Unveil the Roots of Plant Carnivory %U /brokenurl#<Go to ISI>://WOS:000548517000009 %V 30 %X Most plants grow and develop by taking up nutrients from the soil while continuously under threat from foraging animals. Carnivorous plants have turned the tables by capturing and consuming nutrient-rich animal prey, enabling them to thrive in nutrient-poor soil. To better understand the evolution of botanical carnivory, we compared the draft genome of the Venus flytrap (Dionaea muscipula) with that of its aquatic sister, the waterwheel plant Aldrovanda vesiculosa, and the sundew Drosera spatulata. We identified an early whole-genome duplication in the family as source for carnivory-associated genes. Recruitment of genes to the trap from the root especially was a major mechanism in the evolution of carnivory, supported by family-specific duplications. Still, these genomes belong to the gene poorest land plants sequenced thus far, suggesting reduction of selective pressure on different processes, including non-carnivorous nutrient acquisition. Our results show how non-carnivorous plants evolved into the most skillful green hunters on the planet.
• Pitfalls in auxin pharmacology. Dindas, J.; Becker, D.; Roelfsema, M. R. G.; Scherzer, S.; Bennett, M.; Hedrich, R. In New Phytologist, 227(2), pp. 286–292. 2020.
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  @article{RN999, author = {Dindas, J. and Becker, D. and Roelfsema, M. R. G. and Scherzer, S. and Bennett, M. and Hedrich, R.}, journal = {New Phytologist}, keywords = {(1-naa)}, note = {Lx7qj Times Cited:6 Cited References Count:42}, number = 2, pages = {286-292}, title = {Pitfalls in auxin pharmacology}, type = {Journal Article}, volume = 227, year = 2020 }

  %0 Journal Article %1 RN999 %A Dindas, J. %A Becker, D. %A Roelfsema, M. R. G. %A Scherzer, S. %A Bennett, M. %A Hedrich, R. %D 2020 %J New Phytologist %N 2 %P 286-292 %R 10.1111/nph.16491 %T Pitfalls in auxin pharmacology %U /brokenurl#<Go to ISI>://WOS:000520852200001 %V 227
• Calcium dynamics during trap closure visualized in transgenic Venus flytrap. Suda, H.; Mano, H.; Toyota, M.; Fukushima, K.; Mimura, T.; Tsutsui, I.; Hedrich, R.; Tamada, Y.; Hasebe, M. In Nature Plants, 6(10), p. 1219-+. 2020.
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  A transgenic Venus flytrap expressing a fluorescent calcium sensor allows real-time live quantification of calcium waves triggered by sensory hair movement. The study suggests that calcium levels represent the molecular basis for the memory effect that requires two stimulations within 30 s. The leaves of the carnivorous plant Venus flytrap,Dionaea muscipula(Dionaea) close rapidly to capture insect prey. The closure response usually requires two successive mechanical stimuli to sensory hairs on the leaf blade within approximately 30 s (refs.(1-4)). An unknown biological system in Dionaea is thought to memorize the first stimulus and transduce the signal from the sensory hair to the leaf blade(2). Here, we link signal memory to calcium dynamics using transgenic Dionaea expressing a Ca(2+)sensor. Stimulation of a sensory hair caused an increase in cytosolic Ca(2+)concentration ([Ca2+](cyt)) starting in the sensory hair and spreading to the leaf blade. A second stimulus increased [Ca2+](cyt)to an even higher level, meeting a threshold that is correlated to the leaf blade closure. Because [Ca2+](cyt)gradually decreased after the first stimulus, the [Ca2+](cyt)increase induced by the second stimulus was insufficient to meet the putative threshold for movement after about 30 s. The Ca(2+)wave triggered by mechanical stimulation moved an order of magnitude faster than that induced by wounding in petioles ofArabidopsis thaliana(5)and Dionaea. The capacity for rapid movement has evolved repeatedly in flowering plants. This study opens a path to investigate the role of Ca(2+)in plant movement mechanisms and their evolution.

  @article{RN991, abstract = {A transgenic Venus flytrap expressing a fluorescent calcium sensor allows real-time live quantification of calcium waves triggered by sensory hair movement. The study suggests that calcium levels represent the molecular basis for the memory effect that requires two stimulations within 30 s. The leaves of the carnivorous plant Venus flytrap,Dionaea muscipula(Dionaea) close rapidly to capture insect prey. The closure response usually requires two successive mechanical stimuli to sensory hairs on the leaf blade within approximately 30 s (refs.(1-4)). An unknown biological system in Dionaea is thought to memorize the first stimulus and transduce the signal from the sensory hair to the leaf blade(2). Here, we link signal memory to calcium dynamics using transgenic Dionaea expressing a Ca(2+)sensor. Stimulation of a sensory hair caused an increase in cytosolic Ca(2+)concentration ([Ca2+](cyt)) starting in the sensory hair and spreading to the leaf blade. A second stimulus increased [Ca2+](cyt)to an even higher level, meeting a threshold that is correlated to the leaf blade closure. Because [Ca2+](cyt)gradually decreased after the first stimulus, the [Ca2+](cyt)increase induced by the second stimulus was insufficient to meet the putative threshold for movement after about 30 s. The Ca(2+)wave triggered by mechanical stimulation moved an order of magnitude faster than that induced by wounding in petioles ofArabidopsis thaliana(5)and Dionaea. The capacity for rapid movement has evolved repeatedly in flowering plants. This study opens a path to investigate the role of Ca(2+)in plant movement mechanisms and their evolution.}, author = {Suda, H. and Mano, H. and Toyota, M. and Fukushima, K. and Mimura, T. and Tsutsui, I. and Hedrich, R. and Tamada, Y. and Hasebe, M.}, journal = {Nature Plants}, keywords = {mechanism}, note = {Oa3pt Times Cited:59 Cited References Count:28}, number = 10, pages = {1219-+}, title = {Calcium dynamics during trap closure visualized in transgenic Venus flytrap}, type = {Journal Article}, volume = 6, year = 2020 }

  %0 Journal Article %1 RN991 %A Suda, H. %A Mano, H. %A Toyota, M. %A Fukushima, K. %A Mimura, T. %A Tsutsui, I. %A Hedrich, R. %A Tamada, Y. %A Hasebe, M. %D 2020 %J Nature Plants %N 10 %P 1219-+ %R 10.1038/s41477-020-00773-1 %T Calcium dynamics during trap closure visualized in transgenic Venus flytrap %U /brokenurl#<Go to ISI>://WOS:000575344300001 %V 6 %X A transgenic Venus flytrap expressing a fluorescent calcium sensor allows real-time live quantification of calcium waves triggered by sensory hair movement. The study suggests that calcium levels represent the molecular basis for the memory effect that requires two stimulations within 30 s. The leaves of the carnivorous plant Venus flytrap,Dionaea muscipula(Dionaea) close rapidly to capture insect prey. The closure response usually requires two successive mechanical stimuli to sensory hairs on the leaf blade within approximately 30 s (refs.(1-4)). An unknown biological system in Dionaea is thought to memorize the first stimulus and transduce the signal from the sensory hair to the leaf blade(2). Here, we link signal memory to calcium dynamics using transgenic Dionaea expressing a Ca(2+)sensor. Stimulation of a sensory hair caused an increase in cytosolic Ca(2+)concentration ([Ca2+](cyt)) starting in the sensory hair and spreading to the leaf blade. A second stimulus increased [Ca2+](cyt)to an even higher level, meeting a threshold that is correlated to the leaf blade closure. Because [Ca2+](cyt)gradually decreased after the first stimulus, the [Ca2+](cyt)increase induced by the second stimulus was insufficient to meet the putative threshold for movement after about 30 s. The Ca(2+)wave triggered by mechanical stimulation moved an order of magnitude faster than that induced by wounding in petioles ofArabidopsis thaliana(5)and Dionaea. The capacity for rapid movement has evolved repeatedly in flowering plants. This study opens a path to investigate the role of Ca(2+)in plant movement mechanisms and their evolution.
• Channelrhodopsin-mediated optogenetics highlights a central role of depolarization-dependent plant proton pumps. Reyer, A.; Hässler, M.; Scherzer, S.; Huang, S. G.; Pedersen, J. T.; Al-Rasheid, K. A. S.; Bamberg, E.; Palmgren, M.; Dreyer, I.; Nagel, G.; Hedrich, R.; Becker, D. In Proceedings of the National Academy of Sciences of the United States of America, 117(34), pp. 20920–20925. 2020.
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  In plants, environmental stressors trigger plasma membrane depolarizations. Being electrically interconnected via plasmodesmata, proper functional dissection of electrical signaling by electrophysiology is basically impossible. The green alga Chlamydomonas reinhardtii evolved blue light-excited channelrhodopsins (ChR1, 2) to navigate. When expressed in excitable nerve and muscle cells, ChRs can be used to control the membrane potential via illumination. In Arabidopsis plants, we used the algal ChR2-light switches as tools to stimulate plasmodesmata-interconnected photosynthetic cell networks by blue light and monitor the subsequent plasma membrane electrical responses. Blue-dependent stimulations of ChR2 expressing mesophyll cells, resting around -160 to -180 my, reproducibly depolarized the membrane potential by 95 mV on average. Following excitation, mesophyll cells recovered their prestimulus potential not without transiently passing a hyperpolarization state. By combining optogenetics with voltage-sensing microelectrodes, we demonstrate that plant plasma membrane AHA-type H+-ATPase governs the gross repolarization process. AHA2 protein biochemistry and functional expression analysis in Xenopus oocytes indicates that the capacity of this H+ pump to recharge the membrane potential is rooted in its voltage-and pH-dependent functional anatomy. Thus, ChR2 optogenetics appears well suited to noninvasively expose plant cells to signal specific depolarization signatures. From the responses we learn about the molecular processes, plants employ to channel stress-associated membrane excitations into physiological responses.

  @article{RN992, abstract = {In plants, environmental stressors trigger plasma membrane depolarizations. Being electrically interconnected via plasmodesmata, proper functional dissection of electrical signaling by electrophysiology is basically impossible. The green alga Chlamydomonas reinhardtii evolved blue light-excited channelrhodopsins (ChR1, 2) to navigate. When expressed in excitable nerve and muscle cells, ChRs can be used to control the membrane potential via illumination. In Arabidopsis plants, we used the algal ChR2-light switches as tools to stimulate plasmodesmata-interconnected photosynthetic cell networks by blue light and monitor the subsequent plasma membrane electrical responses. Blue-dependent stimulations of ChR2 expressing mesophyll cells, resting around -160 to -180 my, reproducibly depolarized the membrane potential by 95 mV on average. Following excitation, mesophyll cells recovered their prestimulus potential not without transiently passing a hyperpolarization state. By combining optogenetics with voltage-sensing microelectrodes, we demonstrate that plant plasma membrane AHA-type H+-ATPase governs the gross repolarization process. AHA2 protein biochemistry and functional expression analysis in Xenopus oocytes indicates that the capacity of this H+ pump to recharge the membrane potential is rooted in its voltage-and pH-dependent functional anatomy. Thus, ChR2 optogenetics appears well suited to noninvasively expose plant cells to signal specific depolarization signatures. From the responses we learn about the molecular processes, plants employ to channel stress-associated membrane excitations into physiological responses.}, author = {Reyer, A. and Hässler, M. and Scherzer, S. and Huang, S. G. and Pedersen, J. T. and Al-Rasheid, K. A. S. and Bamberg, E. and Palmgren, M. and Dreyer, I. and Nagel, G. and Hedrich, R. and Becker, D.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {arabidopsis}, note = {Ns6cm Times Cited:33 Cited References Count:51}, number = 34, pages = {20920-20925}, title = {Channelrhodopsin-mediated optogenetics highlights a central role of depolarization-dependent plant proton pumps}, type = {Journal Article}, volume = 117, year = 2020 }

  %0 Journal Article %1 RN992 %A Reyer, A. %A Hässler, M. %A Scherzer, S. %A Huang, S. G. %A Pedersen, J. T. %A Al-Rasheid, K. A. S. %A Bamberg, E. %A Palmgren, M. %A Dreyer, I. %A Nagel, G. %A Hedrich, R. %A Becker, D. %D 2020 %J Proceedings of the National Academy of Sciences of the United States of America %N 34 %P 20920-20925 %R 10.1073/pnas.2005626117 %T Channelrhodopsin-mediated optogenetics highlights a central role of depolarization-dependent plant proton pumps %U /brokenurl#<Go to ISI>://WOS:000572347100012 %V 117 %X In plants, environmental stressors trigger plasma membrane depolarizations. Being electrically interconnected via plasmodesmata, proper functional dissection of electrical signaling by electrophysiology is basically impossible. The green alga Chlamydomonas reinhardtii evolved blue light-excited channelrhodopsins (ChR1, 2) to navigate. When expressed in excitable nerve and muscle cells, ChRs can be used to control the membrane potential via illumination. In Arabidopsis plants, we used the algal ChR2-light switches as tools to stimulate plasmodesmata-interconnected photosynthetic cell networks by blue light and monitor the subsequent plasma membrane electrical responses. Blue-dependent stimulations of ChR2 expressing mesophyll cells, resting around -160 to -180 my, reproducibly depolarized the membrane potential by 95 mV on average. Following excitation, mesophyll cells recovered their prestimulus potential not without transiently passing a hyperpolarization state. By combining optogenetics with voltage-sensing microelectrodes, we demonstrate that plant plasma membrane AHA-type H+-ATPase governs the gross repolarization process. AHA2 protein biochemistry and functional expression analysis in Xenopus oocytes indicates that the capacity of this H+ pump to recharge the membrane potential is rooted in its voltage-and pH-dependent functional anatomy. Thus, ChR2 optogenetics appears well suited to noninvasively expose plant cells to signal specific depolarization signatures. From the responses we learn about the molecular processes, plants employ to channel stress-associated membrane excitations into physiological responses.
• Prospects for the accelerated improvement of the resilient crop quinoa. López-Marqués, R. L.; Noerrevang, A. F.; Ache, P.; Moog, M.; Visintainer, D.; Wendt, T.; Osterberg, J. T.; Dockter, C.; Jorgensen, M. E.; Salvador, A. T.; Hedrich, R.; Gao, C. X.; Jacobsen, S. E.; Shabala, S.; Palmgren, M. In Journal of Experimental Botany, 71(18), pp. 5333–5347. 2020.
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  Crops tolerant to drought and salt stress may be developed by two approaches. First, major crops may be improved by introducing genes from tolerant plants. For example, many major crops have wild relatives that are more tolerant to drought and high salinity than the cultivated crops, and, once deciphered, the underlying resilience mechanisms could be genetically manipulated to produce crops with improved tolerance. Secondly, some minor (orphan) crops cultivated in marginal areas are already drought and salt tolerant. Improving the agronomic performance of these crops may be an effective way to increase crop and food diversity, and an alternative to engineering tolerance in major crops. Quinoa (Chenopodium quinoa Willd.), a nutritious minor crop that tolerates drought and salinity better than most other crops, is an ideal candidate for both of these approaches. Although quinoa has yet to reach its potential as a fully domesticated crop, breeding efforts to improve the plant have been limited. Molecular and genetic techniques combined with traditional breeding are likely to change this picture. Here we analyse protein-coding sequences in the quinoa genome that are orthologous to domestication genes in established crops. Mutating only a limited number of such genes by targeted mutagenesis appears to be a promising route for accelerating the improvement of quinoa and generating a nutritious high-yielding crop that can meet the future demand for food production in a changing climate.

  @article{RN996, abstract = {Crops tolerant to drought and salt stress may be developed by two approaches. First, major crops may be improved by introducing genes from tolerant plants. For example, many major crops have wild relatives that are more tolerant to drought and high salinity than the cultivated crops, and, once deciphered, the underlying resilience mechanisms could be genetically manipulated to produce crops with improved tolerance. Secondly, some minor (orphan) crops cultivated in marginal areas are already drought and salt tolerant. Improving the agronomic performance of these crops may be an effective way to increase crop and food diversity, and an alternative to engineering tolerance in major crops. Quinoa (Chenopodium quinoa Willd.), a nutritious minor crop that tolerates drought and salinity better than most other crops, is an ideal candidate for both of these approaches. Although quinoa has yet to reach its potential as a fully domesticated crop, breeding efforts to improve the plant have been limited. Molecular and genetic techniques combined with traditional breeding are likely to change this picture. Here we analyse protein-coding sequences in the quinoa genome that are orthologous to domestication genes in established crops. Mutating only a limited number of such genes by targeted mutagenesis appears to be a promising route for accelerating the improvement of quinoa and generating a nutritious high-yielding crop that can meet the future demand for food production in a changing climate.}, author = {López-Marqués, R. L. and Noerrevang, A. F. and Ache, P. and Moog, M. and Visintainer, D. and Wendt, T. and Osterberg, J. T. and Dockter, C. and Jorgensen, M. E. and Salvador, A. T. and Hedrich, R. and Gao, C. X. and Jacobsen, S. E. and Shabala, S. and Palmgren, M.}, journal = {Journal of Experimental Botany}, keywords = {quinoa}, note = {Nz4oa Times Cited:41 Cited References Count:180}, number = 18, pages = {5333-5347}, title = {Prospects for the accelerated improvement of the resilient crop quinoa}, type = {Journal Article}, volume = 71, year = 2020 }

  %0 Journal Article %1 RN996 %A López-Marqués, R. L. %A Noerrevang, A. F. %A Ache, P. %A Moog, M. %A Visintainer, D. %A Wendt, T. %A Osterberg, J. T. %A Dockter, C. %A Jorgensen, M. E. %A Salvador, A. T. %A Hedrich, R. %A Gao, C. X. %A Jacobsen, S. E. %A Shabala, S. %A Palmgren, M. %D 2020 %J Journal of Experimental Botany %N 18 %P 5333-5347 %R 10.1093/jxb/eraa285 %T Prospects for the accelerated improvement of the resilient crop quinoa %U /brokenurl#<Go to ISI>://WOS:000577073500006 %V 71 %X Crops tolerant to drought and salt stress may be developed by two approaches. First, major crops may be improved by introducing genes from tolerant plants. For example, many major crops have wild relatives that are more tolerant to drought and high salinity than the cultivated crops, and, once deciphered, the underlying resilience mechanisms could be genetically manipulated to produce crops with improved tolerance. Secondly, some minor (orphan) crops cultivated in marginal areas are already drought and salt tolerant. Improving the agronomic performance of these crops may be an effective way to increase crop and food diversity, and an alternative to engineering tolerance in major crops. Quinoa (Chenopodium quinoa Willd.), a nutritious minor crop that tolerates drought and salinity better than most other crops, is an ideal candidate for both of these approaches. Although quinoa has yet to reach its potential as a fully domesticated crop, breeding efforts to improve the plant have been limited. Molecular and genetic techniques combined with traditional breeding are likely to change this picture. Here we analyse protein-coding sequences in the quinoa genome that are orthologous to domestication genes in established crops. Mutating only a limited number of such genes by targeted mutagenesis appears to be a promising route for accelerating the improvement of quinoa and generating a nutritious high-yielding crop that can meet the future demand for food production in a changing climate.
• The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity. Thor, K.; Jiang, S. S.; Michard, E.; George, J.; Scherzer, S.; Huang, S. G.; Dindas, J.; Derbyshire, P.; Leitao, N.; DeFalco, T. A.; Köster, P.; Hunter, K.; Kimura, S.; Gronnier, J.; Stransfeld, L.; Kadota, Y.; Bücherl, C. A.; Charpentier, M.; Wrzaczek, M.; MacLean, D.; Oldroyd, G. E. D.; Menke, F. L. H.; Roelfsema, M. R. G.; Hedrich, R.; Feijó, J.; Zipfel, C. In Nature, 585(7826), p. 569-+. 2020.
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  Perception of biotic and abiotic stresses often leads to stomatal closure in plants(1,2). Rapid influx of calcium ions (Ca2+) across the plasma membrane has an important role in this response, but the identity of the Ca(2+)channels involved has remained elusive(3,4). Here we report that theArabidopsis thalianaCa(2+)-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid-a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca(2+)channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca(2+)influx mechanisms in response to different stresses. A study inArabidopsis thalianashows that the immune receptor-associated cytosolic kinase BIK1 phosphorylates OSCA1.3 and identifies OSCA1.3 as the pathogen-responsive Ca2+-permeable channel that regulates stomatal closure.

  @article{RN990, abstract = {Perception of biotic and abiotic stresses often leads to stomatal closure in plants(1,2). Rapid influx of calcium ions (Ca2+) across the plasma membrane has an important role in this response, but the identity of the Ca(2+)channels involved has remained elusive(3,4). Here we report that theArabidopsis thalianaCa(2+)-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid-a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca(2+)channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca(2+)influx mechanisms in response to different stresses. A study inArabidopsis thalianashows that the immune receptor-associated cytosolic kinase BIK1 phosphorylates OSCA1.3 and identifies OSCA1.3 as the pathogen-responsive Ca2+-permeable channel that regulates stomatal closure.}, author = {Thor, K. and Jiang, S. S. and Michard, E. and George, J. and Scherzer, S. and Huang, S. G. and Dindas, J. and Derbyshire, P. and Leitao, N. and DeFalco, T. A. and Köster, P. and Hunter, K. and Kimura, S. and Gronnier, J. and Stransfeld, L. and Kadota, Y. and Bücherl, C. A. and Charpentier, M. and Wrzaczek, M. and MacLean, D. and Oldroyd, G. E. D. and Menke, F. L. H. and Roelfsema, M. R. G. and Hedrich, R. and Feijó, J. and Zipfel, C.}, journal = {Nature}, keywords = {rbohd}, note = {Ns9dw Times Cited:166 Cited References Count:61}, number = 7826, pages = {569-+}, title = {The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity}, type = {Journal Article}, volume = 585, year = 2020 }

  %0 Journal Article %1 RN990 %A Thor, K. %A Jiang, S. S. %A Michard, E. %A George, J. %A Scherzer, S. %A Huang, S. G. %A Dindas, J. %A Derbyshire, P. %A Leitao, N. %A DeFalco, T. A. %A Köster, P. %A Hunter, K. %A Kimura, S. %A Gronnier, J. %A Stransfeld, L. %A Kadota, Y. %A Bücherl, C. A. %A Charpentier, M. %A Wrzaczek, M. %A MacLean, D. %A Oldroyd, G. E. D. %A Menke, F. L. H. %A Roelfsema, M. R. G. %A Hedrich, R. %A Feijó, J. %A Zipfel, C. %D 2020 %J Nature %N 7826 %P 569-+ %R 10.1038/s41586-020-2702-1 %T The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity %U /brokenurl#<Go to ISI>://WOS:000570130200001 %V 585 %X Perception of biotic and abiotic stresses often leads to stomatal closure in plants(1,2). Rapid influx of calcium ions (Ca2+) across the plasma membrane has an important role in this response, but the identity of the Ca(2+)channels involved has remained elusive(3,4). Here we report that theArabidopsis thalianaCa(2+)-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid-a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca(2+)channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca(2+)influx mechanisms in response to different stresses. A study inArabidopsis thalianashows that the immune receptor-associated cytosolic kinase BIK1 phosphorylates OSCA1.3 and identifies OSCA1.3 as the pathogen-responsive Ca2+-permeable channel that regulates stomatal closure.
• Photosynthetic cyclic electron transport provides ATP for homeostasis during trap closure in. Maurer, D.; Weber, D.; Ballering, E.; Alfarraj, S.; Albasher, G.; Hedrich, R.; Werner, C.; Rennenberg, H. In Annals of Botany, 125(3), pp. 485–494. 2020.
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  Background and Aims The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions. Methods We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey. Key Results The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents. Conclusions Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.

  @article{RN995, abstract = {Background and Aims The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions. Methods We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey. Key Results The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents. Conclusions Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.}, author = {Maurer, D. and Weber, D. and Ballering, E. and Alfarraj, S. and Albasher, G. and Hedrich, R. and Werner, C. and Rennenberg, H.}, journal = {Annals of Botany}, keywords = {atp}, note = {Ly1rp Times Cited:3 Cited References Count:72}, number = 3, pages = {485-494}, title = {Photosynthetic cyclic electron transport provides ATP for homeostasis during trap closure in}, type = {Journal Article}, volume = 125, year = 2020 }

  %0 Journal Article %1 RN995 %A Maurer, D. %A Weber, D. %A Ballering, E. %A Alfarraj, S. %A Albasher, G. %A Hedrich, R. %A Werner, C. %A Rennenberg, H. %D 2020 %J Annals of Botany %N 3 %P 485-494 %R 10.1093/aob/mcz185 %T Photosynthetic cyclic electron transport provides ATP for homeostasis during trap closure in %U /brokenurl#<Go to ISI>://WOS:000540299400010 %V 125 %X Background and Aims The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions. Methods We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey. Key Results The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents. Conclusions Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.
• The Venus flytrap trigger hair-specific potassium channel KDM1 can reestablish the K gradient required for hapto-electric signaling. Iosip, A. L.; Böhm, J.; Scherzer, S.; Al-Rasheid, K. A. S.; Dreyer, I.; Schultz, J.; Becker, D.; Kreuzer, I.; Hedrich, R. In Plos Biology, 18(12). 2020.
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  The carnivorous plant Dionaea muscipula harbors multicellular trigger hairs designed to sense mechanical stimuli upon contact with animal prey. At the base of the trigger hair, mechanosensation is transduced into an all-or-nothing action potential (AP) that spreads all over the trap, ultimately leading to trap closure and prey capture. To reveal the molecular basis for the unique functional repertoire of this mechanoresponsive plant structure, we determined the transcriptome of D. muscipula's trigger hair. Among the genes that were found to be highly specific to the trigger hair, the Shaker-type channel KDM1 was electrophysiologically characterized as a hyperpolarization- and acid-activated K+-selective channel, thus allowing the reuptake of K+ ions into the trigger hair's sensory cells during the hyperpolarization phase of the AP. During trap development, the increased electrical excitability of the trigger hair is associated with the transcriptional induction of KDM1. Conversely, when KDM1 is blocked by Cs+ in adult traps, the initiation of APs in response to trigger hair deflection is reduced, and trap closure is suppressed. KDM1 thus plays a dominant role in K+ homeostasis in the context of AP and turgor formation underlying the mechanosensation of trigger hair cells and thus D. muscipula's hapto-electric signaling.

  @article{RN997, abstract = {The carnivorous plant Dionaea muscipula harbors multicellular trigger hairs designed to sense mechanical stimuli upon contact with animal prey. At the base of the trigger hair, mechanosensation is transduced into an all-or-nothing action potential (AP) that spreads all over the trap, ultimately leading to trap closure and prey capture. To reveal the molecular basis for the unique functional repertoire of this mechanoresponsive plant structure, we determined the transcriptome of D. muscipula's trigger hair. Among the genes that were found to be highly specific to the trigger hair, the Shaker-type channel KDM1 was electrophysiologically characterized as a hyperpolarization- and acid-activated K+-selective channel, thus allowing the reuptake of K+ ions into the trigger hair's sensory cells during the hyperpolarization phase of the AP. During trap development, the increased electrical excitability of the trigger hair is associated with the transcriptional induction of KDM1. Conversely, when KDM1 is blocked by Cs+ in adult traps, the initiation of APs in response to trigger hair deflection is reduced, and trap closure is suppressed. KDM1 thus plays a dominant role in K+ homeostasis in the context of AP and turgor formation underlying the mechanosensation of trigger hair cells and thus D. muscipula's hapto-electric signaling.}, author = {Iosip, A. L. and Böhm, J. and Scherzer, S. and Al-Rasheid, K. A. S. and Dreyer, I. and Schultz, J. and Becker, D. and Kreuzer, I. and Hedrich, R.}, journal = {Plos Biology}, keywords = {sensitivity}, note = {Pd8xq Times Cited:27 Cited References Count:77}, number = 12, title = {The Venus flytrap trigger hair-specific potassium channel KDM1 can reestablish the K gradient required for hapto-electric signaling}, type = {Journal Article}, volume = 18, year = 2020 }

  %0 Journal Article %1 RN997 %A Iosip, A. L. %A Böhm, J. %A Scherzer, S. %A Al-Rasheid, K. A. S. %A Dreyer, I. %A Schultz, J. %A Becker, D. %A Kreuzer, I. %A Hedrich, R. %D 2020 %J Plos Biology %N 12 %R ARTN e3000964 10.1371/journal.pbio.3000964 %T The Venus flytrap trigger hair-specific potassium channel KDM1 can reestablish the K gradient required for hapto-electric signaling %U /brokenurl#<Go to ISI>://WOS:000597961200001 %V 18 %X The carnivorous plant Dionaea muscipula harbors multicellular trigger hairs designed to sense mechanical stimuli upon contact with animal prey. At the base of the trigger hair, mechanosensation is transduced into an all-or-nothing action potential (AP) that spreads all over the trap, ultimately leading to trap closure and prey capture. To reveal the molecular basis for the unique functional repertoire of this mechanoresponsive plant structure, we determined the transcriptome of D. muscipula's trigger hair. Among the genes that were found to be highly specific to the trigger hair, the Shaker-type channel KDM1 was electrophysiologically characterized as a hyperpolarization- and acid-activated K+-selective channel, thus allowing the reuptake of K+ ions into the trigger hair's sensory cells during the hyperpolarization phase of the AP. During trap development, the increased electrical excitability of the trigger hair is associated with the transcriptional induction of KDM1. Conversely, when KDM1 is blocked by Cs+ in adult traps, the initiation of APs in response to trigger hair deflection is reduced, and trap closure is suppressed. KDM1 thus plays a dominant role in K+ homeostasis in the context of AP and turgor formation underlying the mechanosensation of trigger hair cells and thus D. muscipula's hapto-electric signaling.

• Auxin-Induced Plasma Membrane Depolarization Is Regulated by Auxin Transport and Not by AUXIN BINDING PROTEIN1. Paponov, I. A.; Dindas, J.; Król, E.; Friz, T.; Budnyk, V.; Teale, W.; Paponov, M.; Hedrich, R.; Palme, K. In Frontiers in Plant Science, 9. 2019.
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  Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling.

  @article{RN1004, abstract = {Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling.}, author = {Paponov, I. A. and Dindas, J. and Król, E. and Friz, T. and Budnyk, V. and Teale, W. and Paponov, M. and Hedrich, R. and Palme, K.}, journal = {Frontiers in Plant Science}, keywords = {auxin}, note = {Hh8il Times Cited:17 Cited References Count:23}, title = {Auxin-Induced Plasma Membrane Depolarization Is Regulated by Auxin Transport and Not by AUXIN BINDING PROTEIN1}, type = {Journal Article}, volume = 9, year = 2019 }

  %0 Journal Article %1 RN1004 %A Paponov, I. A. %A Dindas, J. %A Król, E. %A Friz, T. %A Budnyk, V. %A Teale, W. %A Paponov, M. %A Hedrich, R. %A Palme, K. %D 2019 %J Frontiers in Plant Science %R ARTN 1953 10.3389/fpls.2018.01953 %T Auxin-Induced Plasma Membrane Depolarization Is Regulated by Auxin Transport and Not by AUXIN BINDING PROTEIN1 %U /brokenurl#<Go to ISI>://WOS:000455975000001 %V 9 %X Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling.
• Climate and development modulate the metabolome and antioxidative system of date palm leaves. Du, B. G.; Kruse, J.; Winkler, J. B.; Alfarray, S.; Schnitzler, J. P.; Ache, P.; Hedrich, R.; Rennenberg, H. In Journal of Experimental Botany, 70(20), pp. 5959–5969. 2019.
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  Date palms are remarkably tolerant to environmental stresses, but the mechanisms involved remain poorly characterized. Leaf metabolome profiling was therefore performed on mature (ML) and young (YL) leaves of 2-year-old date palm seedlings that had been grown in climate chambers that simulate summer and winter conditions in eastern Saudi Arabia. Cultivation under high temperature (summer climate) resulted in higher YL H2O2 leaf levels despite increases in dehydroascorbate reductase (DHAR) activities. The levels of raffinose and galactinol, tricarboxylic acid cycle intermediates, and total amino acids were higher under these conditions, particularly in YL. The accumulation of unsaturated fatty acids, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid, was lower in ML. In contrast, the amounts of saturated tetradecanoic acid and heptadecanoic acid were increased in YL under summer climate conditions. The accumulation of phenolic compounds was favored under summer conditions, while flavonoids accumulated under lower temperature (winter climate) conditions. YL displayed stronger hydration, lower H2O2 levels, and more negative delta C-13 values, indicating effective reactive oxygen species scavenging. These findings, which demonstrate the substantial metabolic adjustments that facilitate tolerance to the high temperatures in YL and ML, suggest that YL may be more responsive to climate change.

  @article{RN1011, abstract = {Date palms are remarkably tolerant to environmental stresses, but the mechanisms involved remain poorly characterized. Leaf metabolome profiling was therefore performed on mature (ML) and young (YL) leaves of 2-year-old date palm seedlings that had been grown in climate chambers that simulate summer and winter conditions in eastern Saudi Arabia. Cultivation under high temperature (summer climate) resulted in higher YL H2O2 leaf levels despite increases in dehydroascorbate reductase (DHAR) activities. The levels of raffinose and galactinol, tricarboxylic acid cycle intermediates, and total amino acids were higher under these conditions, particularly in YL. The accumulation of unsaturated fatty acids, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid, was lower in ML. In contrast, the amounts of saturated tetradecanoic acid and heptadecanoic acid were increased in YL under summer climate conditions. The accumulation of phenolic compounds was favored under summer conditions, while flavonoids accumulated under lower temperature (winter climate) conditions. YL displayed stronger hydration, lower H2O2 levels, and more negative delta C-13 values, indicating effective reactive oxygen species scavenging. These findings, which demonstrate the substantial metabolic adjustments that facilitate tolerance to the high temperatures in YL and ML, suggest that YL may be more responsive to climate change.}, author = {Du, B. G. and Kruse, J. and Winkler, J. B. and Alfarray, S. and Schnitzler, J. P. and Ache, P. and Hedrich, R. and Rennenberg, H.}, journal = {Journal of Experimental Botany}, keywords = {amino}, note = {Jw4kr Times Cited:17 Cited References Count:82}, number = 20, pages = {5959-5969}, title = {Climate and development modulate the metabolome and antioxidative system of date palm leaves}, type = {Journal Article}, volume = 70, year = 2019 }

  %0 Journal Article %1 RN1011 %A Du, B. G. %A Kruse, J. %A Winkler, J. B. %A Alfarray, S. %A Schnitzler, J. P. %A Ache, P. %A Hedrich, R. %A Rennenberg, H. %D 2019 %J Journal of Experimental Botany %N 20 %P 5959-5969 %R 10.1093/jxb/erz361 %T Climate and development modulate the metabolome and antioxidative system of date palm leaves %U /brokenurl#<Go to ISI>://WOS:000503022600035 %V 70 %X Date palms are remarkably tolerant to environmental stresses, but the mechanisms involved remain poorly characterized. Leaf metabolome profiling was therefore performed on mature (ML) and young (YL) leaves of 2-year-old date palm seedlings that had been grown in climate chambers that simulate summer and winter conditions in eastern Saudi Arabia. Cultivation under high temperature (summer climate) resulted in higher YL H2O2 leaf levels despite increases in dehydroascorbate reductase (DHAR) activities. The levels of raffinose and galactinol, tricarboxylic acid cycle intermediates, and total amino acids were higher under these conditions, particularly in YL. The accumulation of unsaturated fatty acids, 9,12-octadecadienoic acid and 9,12,15-octadecatrienoic acid, was lower in ML. In contrast, the amounts of saturated tetradecanoic acid and heptadecanoic acid were increased in YL under summer climate conditions. The accumulation of phenolic compounds was favored under summer conditions, while flavonoids accumulated under lower temperature (winter climate) conditions. YL displayed stronger hydration, lower H2O2 levels, and more negative delta C-13 values, indicating effective reactive oxygen species scavenging. These findings, which demonstrate the substantial metabolic adjustments that facilitate tolerance to the high temperatures in YL and ML, suggest that YL may be more responsive to climate change.
• Voltage-dependent gating of SV channel TPC1 confers vacuole excitability. Jaslan, D.; Dreyer, I.; Lu, J. P.; O’Malley, R.; Dindas, J.; Marten, I.; Hedrich, R. In Nature Communications, 10. 2019.
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  In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K+-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds. Electrical excitability is suppressed by increased vacuolar Ca2+ levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca2+, can be excited fully by even weak electrical stimuli. The TPC1-loss-of-function mutant tpc1-2 does not respond to electrical stimulation at all, and the loss of TPK1/TPK3-mediated K+ transport affects the duration of TPC1-dependent membrane depolarization. In combination with mathematical modeling, these results show that the vacuolar K+-conducting TPC1 and TPK1/TPK3 channels act in concert to provide for Ca2+- and voltage-induced electrical excitability to the central organelle of plant cells.

  @article{RN1009, abstract = {In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K+-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds. Electrical excitability is suppressed by increased vacuolar Ca2+ levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca2+, can be excited fully by even weak electrical stimuli. The TPC1-loss-of-function mutant tpc1-2 does not respond to electrical stimulation at all, and the loss of TPK1/TPK3-mediated K+ transport affects the duration of TPC1-dependent membrane depolarization. In combination with mathematical modeling, these results show that the vacuolar K+-conducting TPC1 and TPK1/TPK3 channels act in concert to provide for Ca2+- and voltage-induced electrical excitability to the central organelle of plant cells.}, author = {Jaslan, D. and Dreyer, I. and Lu, J. P. and O'Malley, R. and Dindas, J. and Marten, I. and Hedrich, R.}, journal = {Nature Communications}, keywords = {mobile}, note = {Id3ot Times Cited:30 Cited References Count:50}, title = {Voltage-dependent gating of SV channel TPC1 confers vacuole excitability}, type = {Journal Article}, volume = 10, year = 2019 }

  %0 Journal Article %1 RN1009 %A Jaslan, D. %A Dreyer, I. %A Lu, J. P. %A O'Malley, R. %A Dindas, J. %A Marten, I. %A Hedrich, R. %D 2019 %J Nature Communications %R ARTN 2659 10.1038/s41467-019-10599-x %T Voltage-dependent gating of SV channel TPC1 confers vacuole excitability %U /brokenurl#<Go to ISI>://WOS:000471586800015 %V 10 %X In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K+-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds. Electrical excitability is suppressed by increased vacuolar Ca2+ levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca2+, can be excited fully by even weak electrical stimuli. The TPC1-loss-of-function mutant tpc1-2 does not respond to electrical stimulation at all, and the loss of TPK1/TPK3-mediated K+ transport affects the duration of TPC1-dependent membrane depolarization. In combination with mathematical modeling, these results show that the vacuolar K+-conducting TPC1 and TPK1/TPK3 channels act in concert to provide for Ca2+- and voltage-induced electrical excitability to the central organelle of plant cells.
• A large-scale screening of quinoa accessions reveals an important role of epidermal bladder cells and stomata! patterning in salinity tolerance. Kiani-Pouya, A.; Rasouli, F.; Bazihizina, N.; Zhang, H.; Hedrich, R.; Shabala, S. In Environmental and Experimental Botany, 168. 2019.
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  The presence of epidermal bladder cells (EBCs) in halophytes allows considerable amount of Na+ being accumulated in these external structures, away from the metabolically active mesophile cells. Also, stomatal patterning may represent a primary mechanism by which plants can optimise its water-use efficiency under saline condition. This investigation was aimed to explore the varietal differences in a salinity tolerance of quinoa (Chenopodium guinea) by evaluating a broad range of accessions and linking the overall salinity tolerance with changes in stomatal characteristics and EBC parameters. One hundred and fourteen accessions were grown under temperature-controlled glasshouse under non-saline and 400 mM NaCl conditions, and different physiological and anatomical characteristics were measured. Accessions were classified into three classes (sensitive, intermediate and tolerant) based on a relative dry weight defined as salinity tolerance index (STI). Results showed a large variability in STI indicating a strong genetic variation in salinity tolerance in quinoa. Bladders density was increased in a majority of accessions under saline condition while the bladder's diameter remained unchanged; this resulted in a large variability in a bladder's volume as a dependant variable. Stomata density remained unchanged between saline and non-saline conditions while the stomata length declined between 3% to 43% amongst accessions. Leaf Na+ concentration varied from 669 mu mol/gDW to 3155 mu mol/gDW under saline condition and, with an exception of a few accessions, leaf K+ concentration increased under saline conditions. Correlation analysis indicated a significant positive association between EBC diameter and STI on one hand and EBC volume and STI on the other hand, in a salt-tolerant group. These observations are consistent with the role of EBCs in sequestration of toxic Na+ in the external structures, away from the cytosol. A negative association was found between EBC density and diameter in salt-sensitive plants. A negative association between STI and stomata length was also found in a salt-tolerant group, suggesting that these plants were able to efficiently regulate stomatal patterning to balance water loss and CO2 assimilation under saline conditions. Both salt-sensitive and salt-tolerant groups had the same Na+ concentration in the shoot under saline conditions; however, a negative association between leaf Na+ concentration and STI in salt-sensitive plants indicated a more efficient Na+ sequestration process into the EBCs in salt-tolerant plants.

  @article{RN1008, abstract = {The presence of epidermal bladder cells (EBCs) in halophytes allows considerable amount of Na+ being accumulated in these external structures, away from the metabolically active mesophile cells. Also, stomatal patterning may represent a primary mechanism by which plants can optimise its water-use efficiency under saline condition. This investigation was aimed to explore the varietal differences in a salinity tolerance of quinoa (Chenopodium guinea) by evaluating a broad range of accessions and linking the overall salinity tolerance with changes in stomatal characteristics and EBC parameters. One hundred and fourteen accessions were grown under temperature-controlled glasshouse under non-saline and 400 mM NaCl conditions, and different physiological and anatomical characteristics were measured. Accessions were classified into three classes (sensitive, intermediate and tolerant) based on a relative dry weight defined as salinity tolerance index (STI). Results showed a large variability in STI indicating a strong genetic variation in salinity tolerance in quinoa. Bladders density was increased in a majority of accessions under saline condition while the bladder's diameter remained unchanged; this resulted in a large variability in a bladder's volume as a dependant variable. Stomata density remained unchanged between saline and non-saline conditions while the stomata length declined between 3% to 43% amongst accessions. Leaf Na+ concentration varied from 669 mu mol/gDW to 3155 mu mol/gDW under saline condition and, with an exception of a few accessions, leaf K+ concentration increased under saline conditions. Correlation analysis indicated a significant positive association between EBC diameter and STI on one hand and EBC volume and STI on the other hand, in a salt-tolerant group. These observations are consistent with the role of EBCs in sequestration of toxic Na+ in the external structures, away from the cytosol. A negative association was found between EBC density and diameter in salt-sensitive plants. A negative association between STI and stomata length was also found in a salt-tolerant group, suggesting that these plants were able to efficiently regulate stomatal patterning to balance water loss and CO2 assimilation under saline conditions. Both salt-sensitive and salt-tolerant groups had the same Na+ concentration in the shoot under saline conditions; however, a negative association between leaf Na+ concentration and STI in salt-sensitive plants indicated a more efficient Na+ sequestration process into the EBCs in salt-tolerant plants.}, author = {Kiani-Pouya, A. and Rasouli, F. and Bazihizina, N. and Zhang, H. and Hedrich, R. and Shabala, S.}, journal = {Environmental and Experimental Botany}, keywords = {quinoa}, note = {Ji1fz Times Cited:34 Cited References Count:38}, title = {A large-scale screening of quinoa accessions reveals an important role of epidermal bladder cells and stomata! patterning in salinity tolerance}, type = {Journal Article}, volume = 168, year = 2019 }

  %0 Journal Article %1 RN1008 %A Kiani-Pouya, A. %A Rasouli, F. %A Bazihizina, N. %A Zhang, H. %A Hedrich, R. %A Shabala, S. %D 2019 %J Environmental and Experimental Botany %R ARTN 103885 10.1016/j.envexpbot.2019.103885 %T A large-scale screening of quinoa accessions reveals an important role of epidermal bladder cells and stomata! patterning in salinity tolerance %U /brokenurl#<Go to ISI>://WOS:000493212600001 %V 168 %X The presence of epidermal bladder cells (EBCs) in halophytes allows considerable amount of Na+ being accumulated in these external structures, away from the metabolically active mesophile cells. Also, stomatal patterning may represent a primary mechanism by which plants can optimise its water-use efficiency under saline condition. This investigation was aimed to explore the varietal differences in a salinity tolerance of quinoa (Chenopodium guinea) by evaluating a broad range of accessions and linking the overall salinity tolerance with changes in stomatal characteristics and EBC parameters. One hundred and fourteen accessions were grown under temperature-controlled glasshouse under non-saline and 400 mM NaCl conditions, and different physiological and anatomical characteristics were measured. Accessions were classified into three classes (sensitive, intermediate and tolerant) based on a relative dry weight defined as salinity tolerance index (STI). Results showed a large variability in STI indicating a strong genetic variation in salinity tolerance in quinoa. Bladders density was increased in a majority of accessions under saline condition while the bladder's diameter remained unchanged; this resulted in a large variability in a bladder's volume as a dependant variable. Stomata density remained unchanged between saline and non-saline conditions while the stomata length declined between 3% to 43% amongst accessions. Leaf Na+ concentration varied from 669 mu mol/gDW to 3155 mu mol/gDW under saline condition and, with an exception of a few accessions, leaf K+ concentration increased under saline conditions. Correlation analysis indicated a significant positive association between EBC diameter and STI on one hand and EBC volume and STI on the other hand, in a salt-tolerant group. These observations are consistent with the role of EBCs in sequestration of toxic Na+ in the external structures, away from the cytosol. A negative association was found between EBC density and diameter in salt-sensitive plants. A negative association between STI and stomata length was also found in a salt-tolerant group, suggesting that these plants were able to efficiently regulate stomatal patterning to balance water loss and CO2 assimilation under saline conditions. Both salt-sensitive and salt-tolerant groups had the same Na+ concentration in the shoot under saline conditions; however, a negative association between leaf Na+ concentration and STI in salt-sensitive plants indicated a more efficient Na+ sequestration process into the EBCs in salt-tolerant plants.
• Calcium signals in guard cells enhance the efficiency by which abscisic acid triggers stomatal closure. Huang, S. G.; Waadt, R.; Nuhkat, M.; Kollist, H.; Hedrich, R.; Roelfsema, M. R. G. In New Phytologist, 224(1), pp. 177–187. 2019.
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  During drought, abscisic acid (ABA) induces closure of stomata via a signaling pathway that involves the calcium (Ca2+)-independent protein kinase OST1, as well as Ca2+-dependent protein kinases. However, the interconnection between OST1 and Ca2+ signaling in ABA-induced stomatal closure has not been fully resolved. ABA-induced Ca2+ signals were monitored in intact Arabidopsis leaves, which express the ratiometric Ca2+ reporter R-GECO1-mTurquoise and the Ca2+-dependent activation of S-type anion channels was recorded with intracellular double-barreled microelectrodes. ABA triggered Ca2+ signals that occurred during the initiation period, as well as in the acceleration phase of stomatal closure. However, a subset of stomata closed in the absence of Ca2+ signals. On average, stomata closed faster if Ca2+ signals were elicited during the ABA response. Loss of OST1 prevented ABA-induced stomatal closure and repressed Ca2+ signals, whereas elevation of the cytosolic Ca2+ concentration caused a rapid activation of SLAC1 and SLAH3 anion channels. Our data show that the majority of Ca2+ signals are evoked during the acceleration phase of stomatal closure, which is initiated by OST1. These Ca2+ signals are likely to activate Ca2+-dependent protein kinases, which enhance the activity of S-type anion channels and boost stomatal closure.

  @article{RN1010, abstract = {During drought, abscisic acid (ABA) induces closure of stomata via a signaling pathway that involves the calcium (Ca2+)-independent protein kinase OST1, as well as Ca2+-dependent protein kinases. However, the interconnection between OST1 and Ca2+ signaling in ABA-induced stomatal closure has not been fully resolved. ABA-induced Ca2+ signals were monitored in intact Arabidopsis leaves, which express the ratiometric Ca2+ reporter R-GECO1-mTurquoise and the Ca2+-dependent activation of S-type anion channels was recorded with intracellular double-barreled microelectrodes. ABA triggered Ca2+ signals that occurred during the initiation period, as well as in the acceleration phase of stomatal closure. However, a subset of stomata closed in the absence of Ca2+ signals. On average, stomata closed faster if Ca2+ signals were elicited during the ABA response. Loss of OST1 prevented ABA-induced stomatal closure and repressed Ca2+ signals, whereas elevation of the cytosolic Ca2+ concentration caused a rapid activation of SLAC1 and SLAH3 anion channels. Our data show that the majority of Ca2+ signals are evoked during the acceleration phase of stomatal closure, which is initiated by OST1. These Ca2+ signals are likely to activate Ca2+-dependent protein kinases, which enhance the activity of S-type anion channels and boost stomatal closure.}, author = {Huang, S. G. and Waadt, R. and Nuhkat, M. and Kollist, H. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {abscisic}, note = {It5ti Times Cited:50 Cited References Count:73}, number = 1, pages = {177-187}, title = {Calcium signals in guard cells enhance the efficiency by which abscisic acid triggers stomatal closure}, type = {Journal Article}, volume = 224, year = 2019 }

  %0 Journal Article %1 RN1010 %A Huang, S. G. %A Waadt, R. %A Nuhkat, M. %A Kollist, H. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2019 %J New Phytologist %N 1 %P 177-187 %R 10.1111/nph.15985 %T Calcium signals in guard cells enhance the efficiency by which abscisic acid triggers stomatal closure %U /brokenurl#<Go to ISI>://WOS:000477211200001 %V 224 %X During drought, abscisic acid (ABA) induces closure of stomata via a signaling pathway that involves the calcium (Ca2+)-independent protein kinase OST1, as well as Ca2+-dependent protein kinases. However, the interconnection between OST1 and Ca2+ signaling in ABA-induced stomatal closure has not been fully resolved. ABA-induced Ca2+ signals were monitored in intact Arabidopsis leaves, which express the ratiometric Ca2+ reporter R-GECO1-mTurquoise and the Ca2+-dependent activation of S-type anion channels was recorded with intracellular double-barreled microelectrodes. ABA triggered Ca2+ signals that occurred during the initiation period, as well as in the acceleration phase of stomatal closure. However, a subset of stomata closed in the absence of Ca2+ signals. On average, stomata closed faster if Ca2+ signals were elicited during the ABA response. Loss of OST1 prevented ABA-induced stomatal closure and repressed Ca2+ signals, whereas elevation of the cytosolic Ca2+ concentration caused a rapid activation of SLAC1 and SLAH3 anion channels. Our data show that the majority of Ca2+ signals are evoked during the acceleration phase of stomatal closure, which is initiated by OST1. These Ca2+ signals are likely to activate Ca2+-dependent protein kinases, which enhance the activity of S-type anion channels and boost stomatal closure.
• On the origins of osmotically driven stomatal movements. Sussmilch, F. C.; Roelfsema, M. R. G.; Hedrich, R. In New Phytologist, 222(1), pp. 84–90. 2019.
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  Stomatal pores with apertures that can be adjusted by changes in guard cell turgor have facilitated plant success in dry environments. We explore their evolutionary origins, considering recent findings from bryophytes. Unlike vascular plant stomata, which close to prevent water loss, bryophyte stomata become locked open to promote spore desiccation. We find that the families of ion channels, known to control stomatal movements in angiosperms, are ancient and represented across extant land plants. However, although angiosperm guard cells express specific ion channel genes, none appear specifically expressed in stomata-bearing moss tissues. Given the evolutionary shift in stomatal function from promotion to prevention of water loss, we postulate that ion channels adopted guard cell-specific functions after the divergence of bryophytes.

  @article{RN1002, abstract = {Stomatal pores with apertures that can be adjusted by changes in guard cell turgor have facilitated plant success in dry environments. We explore their evolutionary origins, considering recent findings from bryophytes. Unlike vascular plant stomata, which close to prevent water loss, bryophyte stomata become locked open to promote spore desiccation. We find that the families of ion channels, known to control stomatal movements in angiosperms, are ancient and represented across extant land plants. However, although angiosperm guard cells express specific ion channel genes, none appear specifically expressed in stomata-bearing moss tissues. Given the evolutionary shift in stomatal function from promotion to prevention of water loss, we postulate that ion channels adopted guard cell-specific functions after the divergence of bryophytes.}, author = {Sussmilch, F. C. and Roelfsema, M. R. G. and Hedrich, R.}, journal = {New Phytologist}, keywords = {evolution}, note = {Hn1dx Times Cited:21 Cited References Count:48}, number = 1, pages = {84-90}, title = {On the origins of osmotically driven stomatal movements}, type = {Journal Article}, volume = 222, year = 2019 }

  %0 Journal Article %1 RN1002 %A Sussmilch, F. C. %A Roelfsema, M. R. G. %A Hedrich, R. %D 2019 %J New Phytologist %N 1 %P 84-90 %R 10.1111/nph.15593 %T On the origins of osmotically driven stomatal movements %U /brokenurl#<Go to ISI>://WOS:000459928400011 %V 222 %X Stomatal pores with apertures that can be adjusted by changes in guard cell turgor have facilitated plant success in dry environments. We explore their evolutionary origins, considering recent findings from bryophytes. Unlike vascular plant stomata, which close to prevent water loss, bryophyte stomata become locked open to promote spore desiccation. We find that the families of ion channels, known to control stomatal movements in angiosperms, are ancient and represented across extant land plants. However, although angiosperm guard cells express specific ion channel genes, none appear specifically expressed in stomata-bearing moss tissues. Given the evolutionary shift in stomatal function from promotion to prevention of water loss, we postulate that ion channels adopted guard cell-specific functions after the divergence of bryophytes.
• How PRR signaling regulates immunity. Kopischke, M.; Liu, Y.; Hawkins, T.; Maierhofer, T.; Sklenar, J.; Menke, F.; Geiger, D.; Hussey, P.; Hedrich, R.; Robatzek, S. In Molecular Plant-Microbe Interactions, 32(10), pp. 227–228. 2019.
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  @article{RN1007, author = {Kopischke, M. and Liu, Y. and Hawkins, T. and Maierhofer, T. and Sklenar, J. and Menke, F. and Geiger, D. and Hussey, P. and Hedrich, R. and Robatzek, S.}, journal = {Molecular Plant-Microbe Interactions}, keywords = {myOwn}, note = {Suppl. S Jb7wu Times Cited:0 Cited References Count:0}, number = 10, pages = {227-228}, title = {How PRR signaling regulates immunity}, type = {Journal Article}, volume = 32, year = 2019 }

  %0 Journal Article %1 RN1007 %A Kopischke, M. %A Liu, Y. %A Hawkins, T. %A Maierhofer, T. %A Sklenar, J. %A Menke, F. %A Geiger, D. %A Hussey, P. %A Hedrich, R. %A Robatzek, S. %D 2019 %J Molecular Plant-Microbe Interactions %N 10 %P 227-228 %T How PRR signaling regulates immunity %U /brokenurl#<Go to ISI>://WOS:000488776906060 %V 32
• Optimization of photosynthesis and stomatal conductance in the date palm during acclimation to heat and drought. Kruse, J.; Adams, M.; Winkler, B.; Ghirardo, A.; Alfarraj, S.; Kreuzwieser, J.; Hedrich, R.; Schnitzler, J. P.; Rennenberg, H. In New Phytologist, 223(4), pp. 1973–1988. 2019.
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  We studied acclimation of leaf gas exchange to differing seasonal climate and soil water availability in slow-growing date palm (Phoenix dactylifera) seedlings. We used an extended Arrhenius equation to describe instantaneous temperature responses of leaf net photosynthesis (A) and stomatal conductance (G), and derived physiological parameters suitable for characterization of acclimation (T-opt, A(opt) and T-equ). Optimum temperature of A (T-opt) ranged between 20-33 degrees C in winter and 28-45 degrees C in summer. Growth temperature (T-growth) explained c. 50% of the variation in T-opt, which additionally depended on leaf water status at the time of measurement. During water stress, light-saturated rates of A at T-opt (i.e. A(opt)) were reduced to 30-80% of control levels, albeit not limited by CO2 supply per se. Equilibrium temperature (T-equ), around which A/G and substomatal [CO2] are constant, remained tightly coupled with T-opt. Our results suggest that acclimatory shifts in T-opt and A(opt) reflect a balance between maximization of photosynthesis and minimization of the risk of metabolic perturbations caused by imbalances in cellular [CO2]. This novel perspective on acclimation of leaf gas exchange is compatible with optimization theory, and might help to elucidate other acclimation and growth strategies in species adapted to differing climates.

  @article{RN1006, abstract = {We studied acclimation of leaf gas exchange to differing seasonal climate and soil water availability in slow-growing date palm (Phoenix dactylifera) seedlings. We used an extended Arrhenius equation to describe instantaneous temperature responses of leaf net photosynthesis (A) and stomatal conductance (G), and derived physiological parameters suitable for characterization of acclimation (T-opt, A(opt) and T-equ). Optimum temperature of A (T-opt) ranged between 20-33 degrees C in winter and 28-45 degrees C in summer. Growth temperature (T-growth) explained c. 50% of the variation in T-opt, which additionally depended on leaf water status at the time of measurement. During water stress, light-saturated rates of A at T-opt (i.e. A(opt)) were reduced to 30-80% of control levels, albeit not limited by CO2 supply per se. Equilibrium temperature (T-equ), around which A/G and substomatal [CO2] are constant, remained tightly coupled with T-opt. Our results suggest that acclimatory shifts in T-opt and A(opt) reflect a balance between maximization of photosynthesis and minimization of the risk of metabolic perturbations caused by imbalances in cellular [CO2]. This novel perspective on acclimation of leaf gas exchange is compatible with optimization theory, and might help to elucidate other acclimation and growth strategies in species adapted to differing climates.}, author = {Kruse, J. and Adams, M. and Winkler, B. and Ghirardo, A. and Alfarraj, S. and Kreuzwieser, J. and Hedrich, R. and Schnitzler, J. P. and Rennenberg, H.}, journal = {New Phytologist}, keywords = {acclimation}, note = {In8da Times Cited:15 Cited References Count:104}, number = 4, pages = {1973-1988}, title = {Optimization of photosynthesis and stomatal conductance in the date palm during acclimation to heat and drought}, type = {Journal Article}, volume = 223, year = 2019 }

  %0 Journal Article %1 RN1006 %A Kruse, J. %A Adams, M. %A Winkler, B. %A Ghirardo, A. %A Alfarraj, S. %A Kreuzwieser, J. %A Hedrich, R. %A Schnitzler, J. P. %A Rennenberg, H. %D 2019 %J New Phytologist %N 4 %P 1973-1988 %R 10.1111/nph.15923 %T Optimization of photosynthesis and stomatal conductance in the date palm during acclimation to heat and drought %U /brokenurl#<Go to ISI>://WOS:000478146300001 %V 223 %X We studied acclimation of leaf gas exchange to differing seasonal climate and soil water availability in slow-growing date palm (Phoenix dactylifera) seedlings. We used an extended Arrhenius equation to describe instantaneous temperature responses of leaf net photosynthesis (A) and stomatal conductance (G), and derived physiological parameters suitable for characterization of acclimation (T-opt, A(opt) and T-equ). Optimum temperature of A (T-opt) ranged between 20-33 degrees C in winter and 28-45 degrees C in summer. Growth temperature (T-growth) explained c. 50% of the variation in T-opt, which additionally depended on leaf water status at the time of measurement. During water stress, light-saturated rates of A at T-opt (i.e. A(opt)) were reduced to 30-80% of control levels, albeit not limited by CO2 supply per se. Equilibrium temperature (T-equ), around which A/G and substomatal [CO2] are constant, remained tightly coupled with T-opt. Our results suggest that acclimatory shifts in T-opt and A(opt) reflect a balance between maximization of photosynthesis and minimization of the risk of metabolic perturbations caused by imbalances in cellular [CO2]. This novel perspective on acclimation of leaf gas exchange is compatible with optimization theory, and might help to elucidate other acclimation and growth strategies in species adapted to differing climates.
• Effects of temperature on the cuticular transpiration barrier of two desert plants with water-spender and water-saver strategies. Bueno, A.; Alfarhan, A.; Arand, K.; Burghardt, M.; Deininger, A. C.; Hedrich, R.; Leide, J.; Seufert, P.; Staiger, S.; Riederer, M. In Journal of Experimental Botany, 70(5), pp. 1613–1625. 2019.
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  Water-saver and water-spender strategies are successful adaptations allowing plants to cope with the limitations of hot desert habitats. We investigated whether the efficacy of the cuticular transpiration barrier and its susceptibility to high temperatures are ecophysiological traits differentially developed in the water-spender Citrullus colocynthis and the water-saver Phoenix dactylifera. Minimum leaf conductance (g(min)) at 25 degrees C was six times lower in P. dactylifera (1.1x10(-5) m s(-1)) than in C. colocynthis (6.9x10(-5) m s(-1)). Additionally, g(min) in the range 25-50 degrees C did not change in P. dactylifera but increased by a factor of 3.2 in C. colocynthis. Arrhenius formalism applied to the C. colocynthis g(min) led to a biphasic graph with a steep increase at temperatures 35 degrees C, whereas for P. dactylifera the graph was linear over all temperatures. Leaf cuticular wax coverage amounted to 4.2 +/- 0.4 mu g cm(-2) for C. colocynthis and 29.4 +/- 4.2 mu g cm(-2) for P. dactylifera. In both species, waxes were mainly composed of very-long-chain aliphatics. Midpoints of the wax melting ranges of P. dactylifera and C. colocynthis were 80 degrees C and 73 degrees C, respectively. We conclude that in P. dactylifera a particular wax and cutin chemistry prevents the rise of g(min) at elevated temperatures.

  @article{RN1013, abstract = {Water-saver and water-spender strategies are successful adaptations allowing plants to cope with the limitations of hot desert habitats. We investigated whether the efficacy of the cuticular transpiration barrier and its susceptibility to high temperatures are ecophysiological traits differentially developed in the water-spender Citrullus colocynthis and the water-saver Phoenix dactylifera. Minimum leaf conductance (g(min)) at 25 degrees C was six times lower in P. dactylifera (1.1x10(-5) m s(-1)) than in C. colocynthis (6.9x10(-5) m s(-1)). Additionally, g(min) in the range 25-50 degrees C did not change in P. dactylifera but increased by a factor of 3.2 in C. colocynthis. Arrhenius formalism applied to the C. colocynthis g(min) led to a biphasic graph with a steep increase at temperatures 35 degrees C, whereas for P. dactylifera the graph was linear over all temperatures. Leaf cuticular wax coverage amounted to 4.2 +/- 0.4 mu g cm(-2) for C. colocynthis and 29.4 +/- 4.2 mu g cm(-2) for P. dactylifera. In both species, waxes were mainly composed of very-long-chain aliphatics. Midpoints of the wax melting ranges of P. dactylifera and C. colocynthis were 80 degrees C and 73 degrees C, respectively. We conclude that in P. dactylifera a particular wax and cutin chemistry prevents the rise of g(min) at elevated temperatures.}, author = {Bueno, A. and Alfarhan, A. and Arand, K. and Burghardt, M. and Deininger, A. C. and Hedrich, R. and Leide, J. and Seufert, P. and Staiger, S. and Riederer, M.}, journal = {Journal of Experimental Botany}, keywords = {citrullus}, note = {Ho7re Times Cited:63 Cited References Count:56}, number = 5, pages = {1613-1625}, title = {Effects of temperature on the cuticular transpiration barrier of two desert plants with water-spender and water-saver strategies}, type = {Journal Article}, volume = 70, year = 2019 }

  %0 Journal Article %1 RN1013 %A Bueno, A. %A Alfarhan, A. %A Arand, K. %A Burghardt, M. %A Deininger, A. C. %A Hedrich, R. %A Leide, J. %A Seufert, P. %A Staiger, S. %A Riederer, M. %D 2019 %J Journal of Experimental Botany %N 5 %P 1613-1625 %R 10.1093/jxb/erz018 %T Effects of temperature on the cuticular transpiration barrier of two desert plants with water-spender and water-saver strategies %U /brokenurl#<Go to ISI>://WOS:000461145400016 %V 70 %X Water-saver and water-spender strategies are successful adaptations allowing plants to cope with the limitations of hot desert habitats. We investigated whether the efficacy of the cuticular transpiration barrier and its susceptibility to high temperatures are ecophysiological traits differentially developed in the water-spender Citrullus colocynthis and the water-saver Phoenix dactylifera. Minimum leaf conductance (g(min)) at 25 degrees C was six times lower in P. dactylifera (1.1x10(-5) m s(-1)) than in C. colocynthis (6.9x10(-5) m s(-1)). Additionally, g(min) in the range 25-50 degrees C did not change in P. dactylifera but increased by a factor of 3.2 in C. colocynthis. Arrhenius formalism applied to the C. colocynthis g(min) led to a biphasic graph with a steep increase at temperatures 35 degrees C, whereas for P. dactylifera the graph was linear over all temperatures. Leaf cuticular wax coverage amounted to 4.2 +/- 0.4 mu g cm(-2) for C. colocynthis and 29.4 +/- 4.2 mu g cm(-2) for P. dactylifera. In both species, waxes were mainly composed of very-long-chain aliphatics. Midpoints of the wax melting ranges of P. dactylifera and C. colocynthis were 80 degrees C and 73 degrees C, respectively. We conclude that in P. dactylifera a particular wax and cutin chemistry prevents the rise of g(min) at elevated temperatures.
• Acquiring Control: The Evolution of Stomatal Signalling Pathways. Sussmilch, F. C.; Schultz, J.; Hedrich, R.; Roelfsema, M. R. G. In Trends in Plant Science, 24(4), pp. 342–351. 2019.
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  In vascular plants, stomata balance two opposing functions: they open to facilitate CO2 uptake and close to prevent excessive water loss. Here, we discuss the evolution of three major signalling pathways that are known to control stomatal movements in angiosperms in response to light, CO2, and abscisic acid (ABA). We examine the evolutionary origins of key signalling genes involved in these pathways, and compare their expression patterns between an angiosperm and moss. We propose that variation in stomatal sensitivity to stimuli between plant groups are rooted in differences in: (i) gene presence/absence, (ii) specificity of gene spatial expression pattern, and (iii) protein characteristics and functional interactions.

  @article{RN1001, abstract = {In vascular plants, stomata balance two opposing functions: they open to facilitate CO2 uptake and close to prevent excessive water loss. Here, we discuss the evolution of three major signalling pathways that are known to control stomatal movements in angiosperms in response to light, CO2, and abscisic acid (ABA). We examine the evolutionary origins of key signalling genes involved in these pathways, and compare their expression patterns between an angiosperm and moss. We propose that variation in stomatal sensitivity to stimuli between plant groups are rooted in differences in: (i) gene presence/absence, (ii) specificity of gene spatial expression pattern, and (iii) protein characteristics and functional interactions.}, author = {Sussmilch, F. C. and Schultz, J. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Trends in Plant Science}, keywords = {h+-atpase}, note = {Hp6fe Times Cited:47 Cited References Count:113}, number = 4, pages = {342-351}, title = {Acquiring Control: The Evolution of Stomatal Signalling Pathways}, type = {Journal Article}, volume = 24, year = 2019 }

  %0 Journal Article %1 RN1001 %A Sussmilch, F. C. %A Schultz, J. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2019 %J Trends in Plant Science %N 4 %P 342-351 %R 10.1016/j.tplants.2019.01.002 %T Acquiring Control: The Evolution of Stomatal Signalling Pathways %U /brokenurl#<Go to ISI>://WOS:000461778000009 %V 24 %X In vascular plants, stomata balance two opposing functions: they open to facilitate CO2 uptake and close to prevent excessive water loss. Here, we discuss the evolution of three major signalling pathways that are known to control stomatal movements in angiosperms in response to light, CO2, and abscisic acid (ABA). We examine the evolutionary origins of key signalling genes involved in these pathways, and compare their expression patterns between an angiosperm and moss. We propose that variation in stomatal sensitivity to stimuli between plant groups are rooted in differences in: (i) gene presence/absence, (ii) specificity of gene spatial expression pattern, and (iii) protein characteristics and functional interactions.
• Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure. Liu, Y.; Maierhofer, T.; Rybak, K.; Sklenar, J.; Breakspear, A.; Johnston, M. G.; Fliegmann, J.; Huang, S. G.; Roelfsema, M. R. G.; Felix, G.; Faulkner, C.; Menke, F. L. H.; Geiger, D.; Hedrich, R.; Robatzek, S. In Elife, 8. 2019.
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  In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation.

  @article{RN1005, abstract = {In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation.}, author = {Liu, Y. and Maierhofer, T. and Rybak, K. and Sklenar, J. and Breakspear, A. and Johnston, M. G. and Fliegmann, J. and Huang, S. G. and Roelfsema, M. R. G. and Felix, G. and Faulkner, C. and Menke, F. L. H. and Geiger, D. and Hedrich, R. and Robatzek, S.}, journal = {Elife}, keywords = {receptors}, note = {Jc0qk Times Cited:39 Cited References Count:64}, title = {Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure}, type = {Journal Article}, volume = 8, year = 2019 }

  %0 Journal Article %1 RN1005 %A Liu, Y. %A Maierhofer, T. %A Rybak, K. %A Sklenar, J. %A Breakspear, A. %A Johnston, M. G. %A Fliegmann, J. %A Huang, S. G. %A Roelfsema, M. R. G. %A Felix, G. %A Faulkner, C. %A Menke, F. L. H. %A Geiger, D. %A Hedrich, R. %A Robatzek, S. %D 2019 %J Elife %R ARTN e44474 10.7554/eLife.44474 %T Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure %U /brokenurl#<Go to ISI>://WOS:000488984300001 %V 8 %X In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation.
• The role of ABA receptors from the PYR/PYL/RCAR family in stomatal acclimation and closure signal integration. Dittrich, M.; Mueller, H. M.; Bauer, H.; Peirats-Llobet, M.; Rodriguez, P. L.; Geilfus, C. M.; Carpentier, S. C.; Al Rasheid, K. A. S.; Kollist, H.; Merilo, E.; Herrmann, J.; Müller, T.; Ache, P.; Hetherington, A. M.; Hedrich, R. In Nature Plants, 5(9), pp. 1002–1011. 2019.
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  Stomata are microscopic pores found on the surfaces of leaves that act to control CO2 uptake and water loss. By integrating information derived from endogenous signals with cues from the surrounding environment, the guard cells, which surround the pore, 'set' the stomatal aperture to suit the prevailing conditions. Much research has concentrated on understanding the rapid intracellular changes that result in immediate changes to the stomatal aperture. In this study, we look instead at how stomatal acclimate to longer timescale variations in their environment. We show that the closure-inducing signals abscisic acid (ABA), increased CO2, decreased relative air humidity and darkness each access a unique gene network made up of clusters (or modules) of common cellular processes. However, within these networks some gene clusters are shared amongst all four stimuli. All stimuli modulate the expression of members of the PYR/PYL/RCAR family of ABA receptors. However, they are modulated differentially in a stimulus-specific manner. Of the six members of the PYR/PYL/RCAR family expressed in guard cells, PYL2 is sufficient for guard cell ABA-induced responses, whereas in the responses to CO2, PYL4 and PYL5 are essential. Overall, our work shows the importance of ABA as a central regulator and integrator of long-term changes in stomatal behaviour, including sensitivity, elicited by external signals. Understanding this architecture may aid in breeding crops with improved water and nutrient efficiency.

  @article{RN1012, abstract = {Stomata are microscopic pores found on the surfaces of leaves that act to control CO2 uptake and water loss. By integrating information derived from endogenous signals with cues from the surrounding environment, the guard cells, which surround the pore, 'set' the stomatal aperture to suit the prevailing conditions. Much research has concentrated on understanding the rapid intracellular changes that result in immediate changes to the stomatal aperture. In this study, we look instead at how stomatal acclimate to longer timescale variations in their environment. We show that the closure-inducing signals abscisic acid (ABA), increased CO2, decreased relative air humidity and darkness each access a unique gene network made up of clusters (or modules) of common cellular processes. However, within these networks some gene clusters are shared amongst all four stimuli. All stimuli modulate the expression of members of the PYR/PYL/RCAR family of ABA receptors. However, they are modulated differentially in a stimulus-specific manner. Of the six members of the PYR/PYL/RCAR family expressed in guard cells, PYL2 is sufficient for guard cell ABA-induced responses, whereas in the responses to CO2, PYL4 and PYL5 are essential. Overall, our work shows the importance of ABA as a central regulator and integrator of long-term changes in stomatal behaviour, including sensitivity, elicited by external signals. Understanding this architecture may aid in breeding crops with improved water and nutrient efficiency.}, author = {Dittrich, M. and Mueller, H. M. and Bauer, H. and Peirats-Llobet, M. and Rodriguez, P. L. and Geilfus, C. M. and Carpentier, S. C. and Al Rasheid, K. A. S. and Kollist, H. and Merilo, E. and Herrmann, J. and Müller, T. and Ache, P. and Hetherington, A. M. and Hedrich, R.}, journal = {Nature Plants}, keywords = {abscisic-acid}, note = {Iw7gx Times Cited:93 Cited References Count:62}, number = 9, pages = {1002-1011}, title = {The role of ABA receptors from the PYR/PYL/RCAR family in stomatal acclimation and closure signal integration}, type = {Journal Article}, volume = 5, year = 2019 }

  %0 Journal Article %1 RN1012 %A Dittrich, M. %A Mueller, H. M. %A Bauer, H. %A Peirats-Llobet, M. %A Rodriguez, P. L. %A Geilfus, C. M. %A Carpentier, S. C. %A Al Rasheid, K. A. S. %A Kollist, H. %A Merilo, E. %A Herrmann, J. %A Müller, T. %A Ache, P. %A Hetherington, A. M. %A Hedrich, R. %D 2019 %J Nature Plants %N 9 %P 1002-1011 %R 10.1038/s41477-019-0490-0 %T The role of ABA receptors from the PYR/PYL/RCAR family in stomatal acclimation and closure signal integration %U /brokenurl#<Go to ISI>://WOS:000485155000018 %V 5 %X Stomata are microscopic pores found on the surfaces of leaves that act to control CO2 uptake and water loss. By integrating information derived from endogenous signals with cues from the surrounding environment, the guard cells, which surround the pore, 'set' the stomatal aperture to suit the prevailing conditions. Much research has concentrated on understanding the rapid intracellular changes that result in immediate changes to the stomatal aperture. In this study, we look instead at how stomatal acclimate to longer timescale variations in their environment. We show that the closure-inducing signals abscisic acid (ABA), increased CO2, decreased relative air humidity and darkness each access a unique gene network made up of clusters (or modules) of common cellular processes. However, within these networks some gene clusters are shared amongst all four stimuli. All stimuli modulate the expression of members of the PYR/PYL/RCAR family of ABA receptors. However, they are modulated differentially in a stimulus-specific manner. Of the six members of the PYR/PYL/RCAR family expressed in guard cells, PYL2 is sufficient for guard cell ABA-induced responses, whereas in the responses to CO2, PYL4 and PYL5 are essential. Overall, our work shows the importance of ABA as a central regulator and integrator of long-term changes in stomatal behaviour, including sensitivity, elicited by external signals. Understanding this architecture may aid in breeding crops with improved water and nutrient efficiency.
• Comparing Arabidopsis receptor kinase and receptor protein-mediated immune signaling reveals BIK1-dependent differences. Wan, W. L.; Zhang, L. S.; Pruitt, R.; Zaidem, M.; Brugman, R.; Ma, X. Y.; Krol, E.; Perraki, A.; Kilian, J.; Grossmann, G.; Stahl, M.; Shan, L. B.; Zipfel, C.; van Kan, J. A. L.; Hedrich, R.; Weigel, D.; Gust, A. A.; Nürnberger, T. In New Phytologist, 221(4), pp. 2080–2095. 2019.
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  Pattern recognition receptors (PRRs) sense microbial patterns and activate innate immunity against attempted microbial invasions. The leucine-rich repeat receptor kinases (LRR-RK) FLS2 and EFR, and the LRR receptor protein (LRR-RP) receptors RLP23 and RLP42, respectively, represent prototypical members of these two prominent and closely related PRR families. We conducted a survey of Arabidopsis thaliana immune signaling mediated by these receptors to address the question of commonalities and differences between LRR-RK and LRR-RP signaling. Quantitative differences in timing and amplitude were observed for several early immune responses, with RP-mediated responses typically being slower and more prolonged than those mediated by RKs. Activation of RLP23, but not FLS2, induced the production of camalexin. Transcriptomic analysis revealed that RLP23-regulated genes represent only a fraction of those genes differentially expressed upon FLS2 activation. Several positive and negative regulators of FLS2-signaling play similar roles in RLP23 signaling. Intriguingly, the cytoplasmic receptor kinase BIK1, a positive regulator of RK signaling, acts as a negative regulator of RP-type immune receptors in a manner dependent on BIK1 kinase activity. Our study unveiled unexpected differences in two closely related receptor systems and reports a new negative role of BIK1 in plant immunity.

  @article{RN1000, abstract = {Pattern recognition receptors (PRRs) sense microbial patterns and activate innate immunity against attempted microbial invasions. The leucine-rich repeat receptor kinases (LRR-RK) FLS2 and EFR, and the LRR receptor protein (LRR-RP) receptors RLP23 and RLP42, respectively, represent prototypical members of these two prominent and closely related PRR families. We conducted a survey of Arabidopsis thaliana immune signaling mediated by these receptors to address the question of commonalities and differences between LRR-RK and LRR-RP signaling. Quantitative differences in timing and amplitude were observed for several early immune responses, with RP-mediated responses typically being slower and more prolonged than those mediated by RKs. Activation of RLP23, but not FLS2, induced the production of camalexin. Transcriptomic analysis revealed that RLP23-regulated genes represent only a fraction of those genes differentially expressed upon FLS2 activation. Several positive and negative regulators of FLS2-signaling play similar roles in RLP23 signaling. Intriguingly, the cytoplasmic receptor kinase BIK1, a positive regulator of RK signaling, acts as a negative regulator of RP-type immune receptors in a manner dependent on BIK1 kinase activity. Our study unveiled unexpected differences in two closely related receptor systems and reports a new negative role of BIK1 in plant immunity.}, author = {Wan, W. L. and Zhang, L. S. and Pruitt, R. and Zaidem, M. and Brugman, R. and Ma, X. Y. and Krol, E. and Perraki, A. and Kilian, J. and Grossmann, G. and Stahl, M. and Shan, L. B. and Zipfel, C. and van Kan, J. A. L. and Hedrich, R. and Weigel, D. and Gust, A. A. and Nürnberger, T.}, journal = {New Phytologist}, keywords = {arabidopsis}, note = {Hk8si Times Cited:48 Cited References Count:69}, number = 4, pages = {2080-2095}, title = {Comparing Arabidopsis receptor kinase and receptor protein-mediated immune signaling reveals BIK1-dependent differences}, type = {Journal Article}, volume = 221, year = 2019 }

  %0 Journal Article %1 RN1000 %A Wan, W. L. %A Zhang, L. S. %A Pruitt, R. %A Zaidem, M. %A Brugman, R. %A Ma, X. Y. %A Krol, E. %A Perraki, A. %A Kilian, J. %A Grossmann, G. %A Stahl, M. %A Shan, L. B. %A Zipfel, C. %A van Kan, J. A. L. %A Hedrich, R. %A Weigel, D. %A Gust, A. A. %A Nürnberger, T. %D 2019 %J New Phytologist %N 4 %P 2080-2095 %R 10.1111/nph.15497 %T Comparing Arabidopsis receptor kinase and receptor protein-mediated immune signaling reveals BIK1-dependent differences %U /brokenurl#<Go to ISI>://WOS:000458259600036 %V 221 %X Pattern recognition receptors (PRRs) sense microbial patterns and activate innate immunity against attempted microbial invasions. The leucine-rich repeat receptor kinases (LRR-RK) FLS2 and EFR, and the LRR receptor protein (LRR-RP) receptors RLP23 and RLP42, respectively, represent prototypical members of these two prominent and closely related PRR families. We conducted a survey of Arabidopsis thaliana immune signaling mediated by these receptors to address the question of commonalities and differences between LRR-RK and LRR-RP signaling. Quantitative differences in timing and amplitude were observed for several early immune responses, with RP-mediated responses typically being slower and more prolonged than those mediated by RKs. Activation of RLP23, but not FLS2, induced the production of camalexin. Transcriptomic analysis revealed that RLP23-regulated genes represent only a fraction of those genes differentially expressed upon FLS2 activation. Several positive and negative regulators of FLS2-signaling play similar roles in RLP23 signaling. Intriguingly, the cytoplasmic receptor kinase BIK1, a positive regulator of RK signaling, acts as a negative regulator of RP-type immune receptors in a manner dependent on BIK1 kinase activity. Our study unveiled unexpected differences in two closely related receptor systems and reports a new negative role of BIK1 in plant immunity.
• Venus flytrap trigger hairs are micronewton mechano-sensors that can detect small insect prey. Scherzer, S.; Federle, W.; Al-Rasheid, K. A. S.; Hedrich, R. In Nature Plants, 5(7), pp. 670–675. 2019.
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  Venus flytraps detect moving insects via highly sensitive, action potential (AP)-producing trigger hairs, which act as high-sensitivity levers, crucial for prey capture and digestion. Controlled stimulation revealed that they can trigger APs for deflections >2.9 degrees, angular velocities >3.4 degrees s(-1) and forces >29 mu N. Hairs became desensitized and subsequently responded to fast consecutive stimulations; desensitization increased at lower temperatures. Recording of ant trigger hair contact events revealed that even small insects exceed the hairs' sensitivity threshold.

  @article{RN1003, abstract = {Venus flytraps detect moving insects via highly sensitive, action potential (AP)-producing trigger hairs, which act as high-sensitivity levers, crucial for prey capture and digestion. Controlled stimulation revealed that they can trigger APs for deflections >2.9 degrees, angular velocities >3.4 degrees s(-1) and forces >29 mu N. Hairs became desensitized and subsequently responded to fast consecutive stimulations; desensitization increased at lower temperatures. Recording of ant trigger hair contact events revealed that even small insects exceed the hairs' sensitivity threshold.}, author = {Scherzer, S. and Federle, W. and Al-Rasheid, K. A. S. and Hedrich, R.}, journal = {Nature Plants}, keywords = {desensitization}, note = {Ih4ih Times Cited:46 Cited References Count:24}, number = 7, pages = {670-675}, title = {Venus flytrap trigger hairs are micronewton mechano-sensors that can detect small insect prey}, type = {Journal Article}, volume = 5, year = 2019 }

  %0 Journal Article %1 RN1003 %A Scherzer, S. %A Federle, W. %A Al-Rasheid, K. A. S. %A Hedrich, R. %D 2019 %J Nature Plants %N 7 %P 670-675 %R 10.1038/s41477-019-0465-1 %T Venus flytrap trigger hairs are micronewton mechano-sensors that can detect small insect prey %U /brokenurl#<Go to ISI>://WOS:000474454600012 %V 5 %X Venus flytraps detect moving insects via highly sensitive, action potential (AP)-producing trigger hairs, which act as high-sensitivity levers, crucial for prey capture and digestion. Controlled stimulation revealed that they can trigger APs for deflections >2.9 degrees, angular velocities >3.4 degrees s(-1) and forces >29 mu N. Hairs became desensitized and subsequently responded to fast consecutive stimulations; desensitization increased at lower temperatures. Recording of ant trigger hair contact events revealed that even small insects exceed the hairs' sensitivity threshold.

• Venus flytrap - a plant on an animal diet. Hedrich, R. In Febs Open Bio, 8, pp. 62–62. 2018.
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  @article{RN1025, author = {Hedrich, R.}, journal = {Febs Open Bio}, keywords = {myOwn}, note = {Suppl. 1 Gl9rl S.30-5 Times Cited:0 Cited References Count:0}, pages = {62-62}, title = {Venus flytrap - a plant on an animal diet}, type = {Journal Article}, volume = 8, year = 2018 }

  %0 Journal Article %1 RN1025 %A Hedrich, R. %D 2018 %J Febs Open Bio %P 62-62 %T Venus flytrap - a plant on an animal diet %U /brokenurl#<Go to ISI>://WOS:000437674100200 %V 8
• Advances and current challenges in calcium signaling. Kudla, J.; Becker, D.; Grill, E.; Hedrich, R.; Hippler, M.; Kummer, U.; Parniske, M.; Romeis, T.; Schumacher, K. In New Phytologist, 218(2), pp. 414–431. 2018.
  • [ Abstract ]
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  Temporally and spatially defined changes in Ca2+ concentration in distinct compartments of cells represent a universal information code in plants. Recently, it has become evident that Ca2+ signals not only govern intracellular regulation but also appear to contribute to long distance or even organismic signal propagation and physiological response regulation. Ca2+ signals are shaped by an intimate interplay of channels and transporters, and during past years important contributing individual components have been identified and characterized. Ca2+ signals are translated by an elaborate toolkit of Ca2+-binding proteins, many of which function as Ca2+ sensors, into defined downstream responses. Intriguing progress has been achieved in identifying specific modules that interconnect Ca2+ decoding proteins and protein kinases with downstream target effectors, and in characterizing molecular details of these processes. In this review, we reflect on recent major advances in our understanding of Ca2+ signaling and cover emerging concepts and existing open questions that should be informative also for scientists that are currently entering this field of ever-increasing breath and impact.

  @article{RN1018, abstract = {Temporally and spatially defined changes in Ca2+ concentration in distinct compartments of cells represent a universal information code in plants. Recently, it has become evident that Ca2+ signals not only govern intracellular regulation but also appear to contribute to long distance or even organismic signal propagation and physiological response regulation. Ca2+ signals are shaped by an intimate interplay of channels and transporters, and during past years important contributing individual components have been identified and characterized. Ca2+ signals are translated by an elaborate toolkit of Ca2+-binding proteins, many of which function as Ca2+ sensors, into defined downstream responses. Intriguing progress has been achieved in identifying specific modules that interconnect Ca2+ decoding proteins and protein kinases with downstream target effectors, and in characterizing molecular details of these processes. In this review, we reflect on recent major advances in our understanding of Ca2+ signaling and cover emerging concepts and existing open questions that should be informative also for scientists that are currently entering this field of ever-increasing breath and impact.}, author = {Kudla, J. and Becker, D. and Grill, E. and Hedrich, R. and Hippler, M. and Kummer, U. and Parniske, M. and Romeis, T. and Schumacher, K.}, journal = {New Phytologist}, keywords = {abscisic}, note = {Ga1iy Times Cited:365 Cited References Count:239}, number = 2, pages = {414-431}, title = {Advances and current challenges in calcium signaling}, type = {Journal Article}, volume = 218, year = 2018 }

  %0 Journal Article %1 RN1018 %A Kudla, J. %A Becker, D. %A Grill, E. %A Hedrich, R. %A Hippler, M. %A Kummer, U. %A Parniske, M. %A Romeis, T. %A Schumacher, K. %D 2018 %J New Phytologist %N 2 %P 414-431 %R 10.1111/nph.14966 %T Advances and current challenges in calcium signaling %U /brokenurl#<Go to ISI>://WOS:000428070100006 %V 218 %X Temporally and spatially defined changes in Ca2+ concentration in distinct compartments of cells represent a universal information code in plants. Recently, it has become evident that Ca2+ signals not only govern intracellular regulation but also appear to contribute to long distance or even organismic signal propagation and physiological response regulation. Ca2+ signals are shaped by an intimate interplay of channels and transporters, and during past years important contributing individual components have been identified and characterized. Ca2+ signals are translated by an elaborate toolkit of Ca2+-binding proteins, many of which function as Ca2+ sensors, into defined downstream responses. Intriguing progress has been achieved in identifying specific modules that interconnect Ca2+ decoding proteins and protein kinases with downstream target effectors, and in characterizing molecular details of these processes. In this review, we reflect on recent major advances in our understanding of Ca2+ signaling and cover emerging concepts and existing open questions that should be informative also for scientists that are currently entering this field of ever-increasing breath and impact.
• Spatio-temporal aspects of Ca signalling: lessons from guard cells and pollen tubes. Konrad, K. R.; Maierhofer, T.; Hedrich, R. In Journal of Experimental Botany, 69(17), pp. 4195–4214. 2018.
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  Changes in cytosolic Ca2+ concentration ([Ca2+](cyt)) serve to transmit information in eukaryotic cells. The involvement of this second messenger in plant cell growth as well as osmotic and water relations is well established. After almost 40 years of intense research on the coding and decoding of plant Ca2+ signals, numerous proteins involved in Ca2+ action have been identified. However, we are still far from understanding the complexity of Ca2+ networks. New in vivo Ca2+ imaging techniques combined with molecular genetics allow visualization of spatio-temporal aspects of Ca2+ signalling. In parallel, cell biology together with protein biochemistry and electrophysiology are able to dissect information processing by this second messenger in space and time. Here, we focus on the time-resolved changes in cellular events upon Ca2+ signals, concentrating on the two best-studied cell types, pollen tubes and guard cells. We put their signalling networks side by side, compare them with those of other cell types, and discuss rapid signalling in the context of Ca2+ transients and oscillations to regulate ion homeostasis.

  @article{RN1019, abstract = {Changes in cytosolic Ca2+ concentration ([Ca2+](cyt)) serve to transmit information in eukaryotic cells. The involvement of this second messenger in plant cell growth as well as osmotic and water relations is well established. After almost 40 years of intense research on the coding and decoding of plant Ca2+ signals, numerous proteins involved in Ca2+ action have been identified. However, we are still far from understanding the complexity of Ca2+ networks. New in vivo Ca2+ imaging techniques combined with molecular genetics allow visualization of spatio-temporal aspects of Ca2+ signalling. In parallel, cell biology together with protein biochemistry and electrophysiology are able to dissect information processing by this second messenger in space and time. Here, we focus on the time-resolved changes in cellular events upon Ca2+ signals, concentrating on the two best-studied cell types, pollen tubes and guard cells. We put their signalling networks side by side, compare them with those of other cell types, and discuss rapid signalling in the context of Ca2+ transients and oscillations to regulate ion homeostasis.}, author = {Konrad, K. R. and Maierhofer, T. and Hedrich, R.}, journal = {Journal of Experimental Botany}, keywords = {channel}, note = {Sp. Iss. SI Go8es Times Cited:19 Cited References Count:258}, number = 17, pages = {4195-4214}, title = {Spatio-temporal aspects of Ca signalling: lessons from guard cells and pollen tubes}, type = {Journal Article}, volume = 69, year = 2018 }

  %0 Journal Article %1 RN1019 %A Konrad, K. R. %A Maierhofer, T. %A Hedrich, R. %D 2018 %J Journal of Experimental Botany %N 17 %P 4195-4214 %R 10.1093/jxb/ery154 %T Spatio-temporal aspects of Ca signalling: lessons from guard cells and pollen tubes %U /brokenurl#<Go to ISI>://WOS:000440318400005 %V 69 %X Changes in cytosolic Ca2+ concentration ([Ca2+](cyt)) serve to transmit information in eukaryotic cells. The involvement of this second messenger in plant cell growth as well as osmotic and water relations is well established. After almost 40 years of intense research on the coding and decoding of plant Ca2+ signals, numerous proteins involved in Ca2+ action have been identified. However, we are still far from understanding the complexity of Ca2+ networks. New in vivo Ca2+ imaging techniques combined with molecular genetics allow visualization of spatio-temporal aspects of Ca2+ signalling. In parallel, cell biology together with protein biochemistry and electrophysiology are able to dissect information processing by this second messenger in space and time. Here, we focus on the time-resolved changes in cellular events upon Ca2+ signals, concentrating on the two best-studied cell types, pollen tubes and guard cells. We put their signalling networks side by side, compare them with those of other cell types, and discuss rapid signalling in the context of Ca2+ transients and oscillations to regulate ion homeostasis.
• Physiological responses of date palm ( ) seedlings to acute ozone exposure at high temperature. Du, B. G.; Kreuzwieser, J.; Winkler, J. B.; Ghirardo, A.; Schnitzler, J. P.; Ache, P.; Alfarraj, S.; Hedrich, R.; White, P.; Rennenberg, H. In Environmental Pollution, 242, pp. 905–913. 2018.
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  Vegetation in the Arabian Peninsula is facing high and steadily rising tropospheric ozone pollution. However, little is known about the impacts of elevated ozone on date palms, one of the most important indigenous economic species. To elucidate the physiological responses of date palm to peak levels of acute ozone exposure, seedlings were fumigated with 200 ppb ozone for 8 h. Net CO2 assimilation rate, stomatal conduction, total carbon, its isotope signature and total sugar contents in leaves and roots were not significantly affected by the treatment and visible symptoms of foliar damage were not induced. Ozone exposure did not affect hydrogen peroxide and thiol contents but diminished the activities of glutathione reductase and dehydroascorbate reductase, stimulated the oxidation of ascorbate, and resulted in elevated total ascorbate contents. Total nitrogen, soluble protein and lignin contents remained unchanged upon ozone exposure, but the abundance of low molecular weight nitrogen (LMWN) compounds such as amino acids and nitrate as well as other anions were strongly diminished in leaves and roots. Other nitrogen pools did not benefit from the decline of LMWN, indicating reduced uptake and/or enhanced release of these compounds into the soil as a systemic response to aboveground ozone exposure. Several phenolic compounds, concurrent with fatty acids and stearyl alcohol, accumulated in leaves, but declined in roots, whereas total phenol contents significantly increased in the roots. Together these results indicate that local and systemic changes in both, primary and secondary metabolism contribute to the high tolerance of date palms to short-term acute ozone exposure. (C) 2018 Elsevier Ltd. All rights reserved.

  @article{RN1028, abstract = {Vegetation in the Arabian Peninsula is facing high and steadily rising tropospheric ozone pollution. However, little is known about the impacts of elevated ozone on date palms, one of the most important indigenous economic species. To elucidate the physiological responses of date palm to peak levels of acute ozone exposure, seedlings were fumigated with 200 ppb ozone for 8 h. Net CO2 assimilation rate, stomatal conduction, total carbon, its isotope signature and total sugar contents in leaves and roots were not significantly affected by the treatment and visible symptoms of foliar damage were not induced. Ozone exposure did not affect hydrogen peroxide and thiol contents but diminished the activities of glutathione reductase and dehydroascorbate reductase, stimulated the oxidation of ascorbate, and resulted in elevated total ascorbate contents. Total nitrogen, soluble protein and lignin contents remained unchanged upon ozone exposure, but the abundance of low molecular weight nitrogen (LMWN) compounds such as amino acids and nitrate as well as other anions were strongly diminished in leaves and roots. Other nitrogen pools did not benefit from the decline of LMWN, indicating reduced uptake and/or enhanced release of these compounds into the soil as a systemic response to aboveground ozone exposure. Several phenolic compounds, concurrent with fatty acids and stearyl alcohol, accumulated in leaves, but declined in roots, whereas total phenol contents significantly increased in the roots. Together these results indicate that local and systemic changes in both, primary and secondary metabolism contribute to the high tolerance of date palms to short-term acute ozone exposure. (C) 2018 Elsevier Ltd. All rights reserved.}, author = {Du, B. G. and Kreuzwieser, J. and Winkler, J. B. and Ghirardo, A. and Schnitzler, J. P. and Ache, P. and Alfarraj, S. and Hedrich, R. and White, P. and Rennenberg, H.}, journal = {Environmental Pollution}, keywords = {sugars}, note = {A Gv5nx Times Cited:21 Cited References Count:59}, pages = {905-913}, title = {Physiological responses of date palm ( ) seedlings to acute ozone exposure at high temperature}, type = {Journal Article}, volume = 242, year = 2018 }

  %0 Journal Article %1 RN1028 %A Du, B. G. %A Kreuzwieser, J. %A Winkler, J. B. %A Ghirardo, A. %A Schnitzler, J. P. %A Ache, P. %A Alfarraj, S. %A Hedrich, R. %A White, P. %A Rennenberg, H. %D 2018 %J Environmental Pollution %P 905-913 %R 10.1016/j.envpol.2018.07.059 %T Physiological responses of date palm ( ) seedlings to acute ozone exposure at high temperature %U /brokenurl#<Go to ISI>://WOS:000446150300097 %V 242 %X Vegetation in the Arabian Peninsula is facing high and steadily rising tropospheric ozone pollution. However, little is known about the impacts of elevated ozone on date palms, one of the most important indigenous economic species. To elucidate the physiological responses of date palm to peak levels of acute ozone exposure, seedlings were fumigated with 200 ppb ozone for 8 h. Net CO2 assimilation rate, stomatal conduction, total carbon, its isotope signature and total sugar contents in leaves and roots were not significantly affected by the treatment and visible symptoms of foliar damage were not induced. Ozone exposure did not affect hydrogen peroxide and thiol contents but diminished the activities of glutathione reductase and dehydroascorbate reductase, stimulated the oxidation of ascorbate, and resulted in elevated total ascorbate contents. Total nitrogen, soluble protein and lignin contents remained unchanged upon ozone exposure, but the abundance of low molecular weight nitrogen (LMWN) compounds such as amino acids and nitrate as well as other anions were strongly diminished in leaves and roots. Other nitrogen pools did not benefit from the decline of LMWN, indicating reduced uptake and/or enhanced release of these compounds into the soil as a systemic response to aboveground ozone exposure. Several phenolic compounds, concurrent with fatty acids and stearyl alcohol, accumulated in leaves, but declined in roots, whereas total phenol contents significantly increased in the roots. Together these results indicate that local and systemic changes in both, primary and secondary metabolism contribute to the high tolerance of date palms to short-term acute ozone exposure. (C) 2018 Elsevier Ltd. All rights reserved.
• Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca levels autonomously. Voss, L. J.; McAdam, S. A. M.; Knoblauch, M.; Rathje, J. M.; Brodribb, T.; Hedrich, R.; Roelfsema, M. R. G. In New Phytologist, 219(1), pp. 206–215. 2018.
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  Recent studies have revealed that some responses of fern stomata to environmental signals differ from those of their relatives in seed plants. However, it is unknown whether the biophysical properties of guard cells differ fundamentally between species of both clades. Intracellular micro-electrodes and the fluorescent Ca2+ reporter FURA2 were used to study voltage-dependent cation channels and Ca2+ signals in guard cells of the ferns Polypodium vulgare and Asplenium scolopendrium. Voltage clamp experiments with fern guard cells revealed similar properties of voltage-dependent K+ channels as found in seed plants. However, fluorescent dyes moved within the fern stomata, from one guard cell to the other, which does not occur in most seed plants. Despite the presence of plasmodesmata, which interconnect fern guard cells, Ca2+ signals could be elicited in each of the cells individually. Based on the common properties of voltage-dependent channels in ferns and seed plants, it is likely that these key transport proteins are conserved in vascular plants. However, the symplastic connections between fern guard cells in mature stomata indicate that the biophysical mechanisms that control stomatal movements differ between ferns and seed plants.

  @article{RN1014, abstract = {Recent studies have revealed that some responses of fern stomata to environmental signals differ from those of their relatives in seed plants. However, it is unknown whether the biophysical properties of guard cells differ fundamentally between species of both clades. Intracellular micro-electrodes and the fluorescent Ca2+ reporter FURA2 were used to study voltage-dependent cation channels and Ca2+ signals in guard cells of the ferns Polypodium vulgare and Asplenium scolopendrium. Voltage clamp experiments with fern guard cells revealed similar properties of voltage-dependent K+ channels as found in seed plants. However, fluorescent dyes moved within the fern stomata, from one guard cell to the other, which does not occur in most seed plants. Despite the presence of plasmodesmata, which interconnect fern guard cells, Ca2+ signals could be elicited in each of the cells individually. Based on the common properties of voltage-dependent channels in ferns and seed plants, it is likely that these key transport proteins are conserved in vascular plants. However, the symplastic connections between fern guard cells in mature stomata indicate that the biophysical mechanisms that control stomatal movements differ between ferns and seed plants.}, author = {Voss, L. J. and McAdam, S. A. M. and Knoblauch, M. and Rathje, J. M. and Brodribb, T. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {calcium}, note = {Gi1tj Times Cited:13 Cited References Count:65}, number = 1, pages = {206-215}, title = {Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca levels autonomously}, type = {Journal Article}, volume = 219, year = 2018 }

  %0 Journal Article %1 RN1014 %A Voss, L. J. %A McAdam, S. A. M. %A Knoblauch, M. %A Rathje, J. M. %A Brodribb, T. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2018 %J New Phytologist %N 1 %P 206-215 %R 10.1111/nph.15153 %T Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca levels autonomously %U /brokenurl#<Go to ISI>://WOS:000434153200024 %V 219 %X Recent studies have revealed that some responses of fern stomata to environmental signals differ from those of their relatives in seed plants. However, it is unknown whether the biophysical properties of guard cells differ fundamentally between species of both clades. Intracellular micro-electrodes and the fluorescent Ca2+ reporter FURA2 were used to study voltage-dependent cation channels and Ca2+ signals in guard cells of the ferns Polypodium vulgare and Asplenium scolopendrium. Voltage clamp experiments with fern guard cells revealed similar properties of voltage-dependent K+ channels as found in seed plants. However, fluorescent dyes moved within the fern stomata, from one guard cell to the other, which does not occur in most seed plants. Despite the presence of plasmodesmata, which interconnect fern guard cells, Ca2+ signals could be elicited in each of the cells individually. Based on the common properties of voltage-dependent channels in ferns and seed plants, it is likely that these key transport proteins are conserved in vascular plants. However, the symplastic connections between fern guard cells in mature stomata indicate that the biophysical mechanisms that control stomatal movements differ between ferns and seed plants.
• Sulfate is Incorporated into Cysteine to Trigger ABA Production and Stomatal Closure. Batool, S.; Uslu, V. V.; Rajab, H.; Ahmad, N.; Waadt, R.; Geiger, D.; Malagoli, M.; Xiang, C. B.; Hedrich, R.; Rennenberg, H.; Herschbach, C.; Hell, R.; Wirtz, M. In Plant Cell, 30(12), pp. 2973–2987. 2018.
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  Plants close stomata when root water availability becomes limiting. Recent studies have demonstrated that soil-drying induces root-to-shoot sulfate transport via the xylem and that sulfate closes stomata. Here we provide evidence for a physiologically relevant signaling pathway that underlies sulfate-induced stomatal closure in Arabidopsis (Arabidopsis thaliana). We uncovered that, in the guard cells, sulfate activates NADPH oxidases to produce reactive oxygen species (ROS) and that this ROS induction is essential for sulfate-induced stomata closure. In line with the function of ROS as the second-messenger of abscisic acid (ABA) signaling, sulfate does not induce ROS in the ABA-synthesis mutant, aba3-1, and sulfate-induced ROS were ineffective at closing stomata in the ABA-insensitive mutant abi2-1 and a SLOW ANION CHANNEL1 loss-of-function mutant. We provided direct evidence for sulfate-induced accumulation of ABA in the cytosol of guard cells by application of the ABAleon2.1 ABA sensor, the ABA signaling reporter ProRAB18: GFP, and quantification of endogenous ABA marker genes. In concordance with previous studies, showing that ABA DEFICIENT3 uses Cys as the substrate for activation of the ABSCISIC ALDEHYDE OXIDASE3 (AAO3) enzyme catalyzing the last step of ABA production, we demonstrated that assimilation of sulfate into Cys is necessary for sulfate-induced stomatal closure and that sulfate-feeding or Cys-feeding induces transcription of NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3, limiting the synthesis of the AAO3 substrate. Consequently, Cys synthesis-depleted mutants are sensitive to soil-drying due to enhanced water loss. Our data demonstrate that sulfate is incorporated into Cys and tunes ABA biosynthesis in leaves, promoting stomatal closure, and that this mechanism contributes to the physiological water limitation response.

  @article{RN1031, abstract = {Plants close stomata when root water availability becomes limiting. Recent studies have demonstrated that soil-drying induces root-to-shoot sulfate transport via the xylem and that sulfate closes stomata. Here we provide evidence for a physiologically relevant signaling pathway that underlies sulfate-induced stomatal closure in Arabidopsis (Arabidopsis thaliana). We uncovered that, in the guard cells, sulfate activates NADPH oxidases to produce reactive oxygen species (ROS) and that this ROS induction is essential for sulfate-induced stomata closure. In line with the function of ROS as the second-messenger of abscisic acid (ABA) signaling, sulfate does not induce ROS in the ABA-synthesis mutant, aba3-1, and sulfate-induced ROS were ineffective at closing stomata in the ABA-insensitive mutant abi2-1 and a SLOW ANION CHANNEL1 loss-of-function mutant. We provided direct evidence for sulfate-induced accumulation of ABA in the cytosol of guard cells by application of the ABAleon2.1 ABA sensor, the ABA signaling reporter ProRAB18: GFP, and quantification of endogenous ABA marker genes. In concordance with previous studies, showing that ABA DEFICIENT3 uses Cys as the substrate for activation of the ABSCISIC ALDEHYDE OXIDASE3 (AAO3) enzyme catalyzing the last step of ABA production, we demonstrated that assimilation of sulfate into Cys is necessary for sulfate-induced stomatal closure and that sulfate-feeding or Cys-feeding induces transcription of NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3, limiting the synthesis of the AAO3 substrate. Consequently, Cys synthesis-depleted mutants are sensitive to soil-drying due to enhanced water loss. Our data demonstrate that sulfate is incorporated into Cys and tunes ABA biosynthesis in leaves, promoting stomatal closure, and that this mechanism contributes to the physiological water limitation response.}, author = {Batool, S. and Uslu, V. V. and Rajab, H. and Ahmad, N. and Waadt, R. and Geiger, D. and Malagoli, M. and Xiang, C. B. and Hedrich, R. and Rennenberg, H. and Herschbach, C. and Hell, R. and Wirtz, M.}, journal = {Plant Cell}, keywords = {molybdenum}, note = {Hj0ep Times Cited:75 Cited References Count:66}, number = 12, pages = {2973-2987}, title = {Sulfate is Incorporated into Cysteine to Trigger ABA Production and Stomatal Closure}, type = {Journal Article}, volume = 30, year = 2018 }

  %0 Journal Article %1 RN1031 %A Batool, S. %A Uslu, V. V. %A Rajab, H. %A Ahmad, N. %A Waadt, R. %A Geiger, D. %A Malagoli, M. %A Xiang, C. B. %A Hedrich, R. %A Rennenberg, H. %A Herschbach, C. %A Hell, R. %A Wirtz, M. %D 2018 %J Plant Cell %N 12 %P 2973-2987 %R 10.1105/tpc.18.00612 %T Sulfate is Incorporated into Cysteine to Trigger ABA Production and Stomatal Closure %U /brokenurl#<Go to ISI>://WOS:000456830600017 %V 30 %X Plants close stomata when root water availability becomes limiting. Recent studies have demonstrated that soil-drying induces root-to-shoot sulfate transport via the xylem and that sulfate closes stomata. Here we provide evidence for a physiologically relevant signaling pathway that underlies sulfate-induced stomatal closure in Arabidopsis (Arabidopsis thaliana). We uncovered that, in the guard cells, sulfate activates NADPH oxidases to produce reactive oxygen species (ROS) and that this ROS induction is essential for sulfate-induced stomata closure. In line with the function of ROS as the second-messenger of abscisic acid (ABA) signaling, sulfate does not induce ROS in the ABA-synthesis mutant, aba3-1, and sulfate-induced ROS were ineffective at closing stomata in the ABA-insensitive mutant abi2-1 and a SLOW ANION CHANNEL1 loss-of-function mutant. We provided direct evidence for sulfate-induced accumulation of ABA in the cytosol of guard cells by application of the ABAleon2.1 ABA sensor, the ABA signaling reporter ProRAB18: GFP, and quantification of endogenous ABA marker genes. In concordance with previous studies, showing that ABA DEFICIENT3 uses Cys as the substrate for activation of the ABSCISIC ALDEHYDE OXIDASE3 (AAO3) enzyme catalyzing the last step of ABA production, we demonstrated that assimilation of sulfate into Cys is necessary for sulfate-induced stomatal closure and that sulfate-feeding or Cys-feeding induces transcription of NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3, limiting the synthesis of the AAO3 substrate. Consequently, Cys synthesis-depleted mutants are sensitive to soil-drying due to enhanced water loss. Our data demonstrate that sulfate is incorporated into Cys and tunes ABA biosynthesis in leaves, promoting stomatal closure, and that this mechanism contributes to the physiological water limitation response.
• Venus Flytrap: How an Excitable, Carnivorous Plant Works. Hedrich, R.; Neher, E. In Trends in Plant Science, 23(3), pp. 220–234. 2018.
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  The carnivorous plant Dionaea possesses very sensitive mechanoreceptors. Upon contact with prey an action potential is triggered which, via an electrical network - comparable to the nervous system of vertebrates - rapidly closes its bivalved trap. The 'hunting cycle' comprises a constitutively activated mechanism for the rapid capture of prey, followed by a well-orchestrated sequence of activation of genes responsible for tight trap closure, digestion of the prey, and uptake of nutrients. Decisions on the step-by-step activation are based on 'counting' the number of stimulations of sensory organs. These remarkable animal-like skills in the carnivore are achieved not by taking over genes from its prey but by modifying and rearranging the functions of genes that are ubiquitous in plants.

  @article{RN1023, abstract = {The carnivorous plant Dionaea possesses very sensitive mechanoreceptors. Upon contact with prey an action potential is triggered which, via an electrical network - comparable to the nervous system of vertebrates - rapidly closes its bivalved trap. The 'hunting cycle' comprises a constitutively activated mechanism for the rapid capture of prey, followed by a well-orchestrated sequence of activation of genes responsible for tight trap closure, digestion of the prey, and uptake of nutrients. Decisions on the step-by-step activation are based on 'counting' the number of stimulations of sensory organs. These remarkable animal-like skills in the carnivore are achieved not by taking over genes from its prey but by modifying and rearranging the functions of genes that are ubiquitous in plants.}, author = {Hedrich, R. and Neher, E.}, journal = {Trends in Plant Science}, keywords = {channels}, note = {Fx0dz Times Cited:72 Cited References Count:86}, number = 3, pages = {220-234}, title = {Venus Flytrap: How an Excitable, Carnivorous Plant Works}, type = {Journal Article}, volume = 23, year = 2018 }

  %0 Journal Article %1 RN1023 %A Hedrich, R. %A Neher, E. %D 2018 %J Trends in Plant Science %N 3 %P 220-234 %R 10.1016/j.tplants.2017.12.004 %T Venus Flytrap: How an Excitable, Carnivorous Plant Works %U /brokenurl#<Go to ISI>://WOS:000425712300007 %V 23 %X The carnivorous plant Dionaea possesses very sensitive mechanoreceptors. Upon contact with prey an action potential is triggered which, via an electrical network - comparable to the nervous system of vertebrates - rapidly closes its bivalved trap. The 'hunting cycle' comprises a constitutively activated mechanism for the rapid capture of prey, followed by a well-orchestrated sequence of activation of genes responsible for tight trap closure, digestion of the prey, and uptake of nutrients. Decisions on the step-by-step activation are based on 'counting' the number of stimulations of sensory organs. These remarkable animal-like skills in the carnivore are achieved not by taking over genes from its prey but by modifying and rearranging the functions of genes that are ubiquitous in plants.
• Understanding the Molecular Basis of Salt Sequestration in Epidermal Bladder Cells of. Böhm, J.; Messerer, M.; Müller, H. M.; Scholz-Starke, J.; Gradogna, A.; Scherzer, S.; Maierhofer, T.; Bazihizina, N.; Zhang, H.; Stigloher, C.; Ache, P.; Al-Rasheid, K. A. S.; Mayer, K. F. X.; Shabala, S.; Carpaneto, A.; Haberer, G.; Zhu, J. K.; Hedrich, R. In Current Biology, 28(19), p. 3075-+. 2018.
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  Soil salinity is destroying arable land and is considered to be one of the major threats to global food security in the 21st century. Therefore, the ability of naturally salt-tolerant halophyte plants to sequester large quantities of salt in external structures, such as epidermal bladder cells (EBCs), is of great interest. Using Chenopodium quinoa, a pseudo-cereal halophyte of great economic potential, we have shown previously that, upon removal of salt bladders, quinoa becomes salt sensitive. In this work, we analyzed the molecular mechanism underlying the unique salt dumping capabilities of bladder cells in quinoa. The transporters differentially expressed in the EBC transcriptome and functional electrophysiological testing of key EBC transporters in Xenopus oocytes revealed that loading of Na+ and Cl- into EBCs is mediated by a set of tailored plasma and vacuole membrane-based sodium-selective channel and chloride-permeable transporter.

  @article{RN1030, abstract = {Soil salinity is destroying arable land and is considered to be one of the major threats to global food security in the 21st century. Therefore, the ability of naturally salt-tolerant halophyte plants to sequester large quantities of salt in external structures, such as epidermal bladder cells (EBCs), is of great interest. Using Chenopodium quinoa, a pseudo-cereal halophyte of great economic potential, we have shown previously that, upon removal of salt bladders, quinoa becomes salt sensitive. In this work, we analyzed the molecular mechanism underlying the unique salt dumping capabilities of bladder cells in quinoa. The transporters differentially expressed in the EBC transcriptome and functional electrophysiological testing of key EBC transporters in Xenopus oocytes revealed that loading of Na+ and Cl- into EBCs is mediated by a set of tailored plasma and vacuole membrane-based sodium-selective channel and chloride-permeable transporter.}, author = {Böhm, J. and Messerer, M. and Müller, H. M. and Scholz-Starke, J. and Gradogna, A. and Scherzer, S. and Maierhofer, T. and Bazihizina, N. and Zhang, H. and Stigloher, C. and Ache, P. and Al-Rasheid, K. A. S. and Mayer, K. F. X. and Shabala, S. and Carpaneto, A. and Haberer, G. and Zhu, J. K. and Hedrich, R.}, journal = {Current Biology}, keywords = {k+}, note = {Gw2dq Times Cited:73 Cited References Count:85}, number = 19, pages = {3075-+}, title = {Understanding the Molecular Basis of Salt Sequestration in Epidermal Bladder Cells of}, type = {Journal Article}, volume = 28, year = 2018 }

  %0 Journal Article %1 RN1030 %A Böhm, J. %A Messerer, M. %A Müller, H. M. %A Scholz-Starke, J. %A Gradogna, A. %A Scherzer, S. %A Maierhofer, T. %A Bazihizina, N. %A Zhang, H. %A Stigloher, C. %A Ache, P. %A Al-Rasheid, K. A. S. %A Mayer, K. F. X. %A Shabala, S. %A Carpaneto, A. %A Haberer, G. %A Zhu, J. K. %A Hedrich, R. %D 2018 %J Current Biology %N 19 %P 3075-+ %R 10.1016/j.cub.2018.08.004 %T Understanding the Molecular Basis of Salt Sequestration in Epidermal Bladder Cells of %U /brokenurl#<Go to ISI>://WOS:000446693400023 %V 28 %X Soil salinity is destroying arable land and is considered to be one of the major threats to global food security in the 21st century. Therefore, the ability of naturally salt-tolerant halophyte plants to sequester large quantities of salt in external structures, such as epidermal bladder cells (EBCs), is of great interest. Using Chenopodium quinoa, a pseudo-cereal halophyte of great economic potential, we have shown previously that, upon removal of salt bladders, quinoa becomes salt sensitive. In this work, we analyzed the molecular mechanism underlying the unique salt dumping capabilities of bladder cells in quinoa. The transporters differentially expressed in the EBC transcriptome and functional electrophysiological testing of key EBC transporters in Xenopus oocytes revealed that loading of Na+ and Cl- into EBCs is mediated by a set of tailored plasma and vacuole membrane-based sodium-selective channel and chloride-permeable transporter.
• The Genome: Secondary Complexity and Implications for Plant Terrestrialization. Nishiyama, T.; Sakayama, H.; de Vries, J.; Buschmann, H.; Saint-Marcoux, D.; Ullrich, K. K.; Haas, F. B.; Vanderstraeten, L.; Becker, D.; Lang, D.; Vosolsobe, S.; Rombauts, S.; Wilhelmsson, P. K. I.; Janitza, P.; Kern, R.; Heyl, A.; Rümpler, F.; Villalobos, L. I. A. C.; Clay, J. M.; Skokan, R.; Toyoda, A.; Suzuki, Y.; Kagoshima, H.; Schijlen, E.; Tajeshwar, N.; Catarino, B.; Hetherington, A. J.; Saltykova, A.; Bonnot, C.; Breuninger, H.; Symeonidi, A.; Radhakrishnan, G. V.; Van Nieuwerburgh, F.; Deforce, D.; Chang, C.; Karol, K. G.; Hedrich, R.; Ulvskov, P.; Glöckner, G.; Delwiche, C. F.; Petrásek, J.; Van de Peer, Y.; Friml, J.; Beilby, M.; Dolan, L.; Kohara, Y.; Sugano, S.; Fujiyama, A.; Delaux, P. M.; Quint, M.; Theissen, G.; Hagemann, M.; Harholt, J.; Dunand, C.; Zachgo, S.; Langdale, J.; Maumus, F.; Van Der Straeten, D.; Gould, S. B.; Rensing, S. A. In Cell, 174(2), p. 448-+. 2018.
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  Land plants evolved from charophytic algae, among which Charophyceae possess the most complex body plans. We present the genome of Chara braunii; comparison of the genome to those of land plants identified evolutionary novelties for plant terrestrialization and land plant heritage genes. C. braunii employs unique xylan synthases for cell wall biosynthesis, a phragmoplast (cell separation) mechanism similar to that of land plants, and many phytohormones. C. braunii plastids are controlled via landplant- like retrograde signaling, and transcriptional regulation is more elaborate than in other algae. The morphological complexity of this organism may result from expanded gene families, with three cases of particular note: genes effecting tolerance to reactive oxygen species (ROS), LysM receptor-like kinases, and transcription factors (TFs). Transcriptomic analysis of sexual reproductive structures reveals intricate control by TFs, activity of the ROS gene network, and the ancestral use of plant-like storage and stress protection proteins in the zygote.

  @article{RN1017, abstract = {Land plants evolved from charophytic algae, among which Charophyceae possess the most complex body plans. We present the genome of Chara braunii; comparison of the genome to those of land plants identified evolutionary novelties for plant terrestrialization and land plant heritage genes. C. braunii employs unique xylan synthases for cell wall biosynthesis, a phragmoplast (cell separation) mechanism similar to that of land plants, and many phytohormones. C. braunii plastids are controlled via landplant- like retrograde signaling, and transcriptional regulation is more elaborate than in other algae. The morphological complexity of this organism may result from expanded gene families, with three cases of particular note: genes effecting tolerance to reactive oxygen species (ROS), LysM receptor-like kinases, and transcription factors (TFs). Transcriptomic analysis of sexual reproductive structures reveals intricate control by TFs, activity of the ROS gene network, and the ancestral use of plant-like storage and stress protection proteins in the zygote.}, author = {Nishiyama, T. and Sakayama, H. and de Vries, J. and Buschmann, H. and Saint-Marcoux, D. and Ullrich, K. K. and Haas, F. B. and Vanderstraeten, L. and Becker, D. and Lang, D. and Vosolsobe, S. and Rombauts, S. and Wilhelmsson, P. K. I. and Janitza, P. and Kern, R. and Heyl, A. and Rümpler, F. and Villalobos, L. I. A. C. and Clay, J. M. and Skokan, R. and Toyoda, A. and Suzuki, Y. and Kagoshima, H. and Schijlen, E. and Tajeshwar, N. and Catarino, B. and Hetherington, A. J. and Saltykova, A. and Bonnot, C. and Breuninger, H. and Symeonidi, A. and Radhakrishnan, G. V. and Van Nieuwerburgh, F. and Deforce, D. and Chang, C. and Karol, K. G. and Hedrich, R. and Ulvskov, P. and Glöckner, G. and Delwiche, C. F. and Petrásek, J. and Van de Peer, Y. and Friml, J. and Beilby, M. and Dolan, L. and Kohara, Y. and Sugano, S. and Fujiyama, A. and Delaux, P. M. and Quint, M. and Theissen, G. and Hagemann, M. and Harholt, J. and Dunand, C. and Zachgo, S. and Langdale, J. and Maumus, F. and Van Der Straeten, D. and Gould, S. B. and Rensing, S. A.}, journal = {Cell}, keywords = {alignment}, note = {Gm8mm Times Cited:292 Cited References Count:116}, number = 2, pages = {448-+}, title = {The Genome: Secondary Complexity and Implications for Plant Terrestrialization}, type = {Journal Article}, volume = 174, year = 2018 }

  %0 Journal Article %1 RN1017 %A Nishiyama, T. %A Sakayama, H. %A de Vries, J. %A Buschmann, H. %A Saint-Marcoux, D. %A Ullrich, K. K. %A Haas, F. B. %A Vanderstraeten, L. %A Becker, D. %A Lang, D. %A Vosolsobe, S. %A Rombauts, S. %A Wilhelmsson, P. K. I. %A Janitza, P. %A Kern, R. %A Heyl, A. %A Rümpler, F. %A Villalobos, L. I. A. C. %A Clay, J. M. %A Skokan, R. %A Toyoda, A. %A Suzuki, Y. %A Kagoshima, H. %A Schijlen, E. %A Tajeshwar, N. %A Catarino, B. %A Hetherington, A. J. %A Saltykova, A. %A Bonnot, C. %A Breuninger, H. %A Symeonidi, A. %A Radhakrishnan, G. V. %A Van Nieuwerburgh, F. %A Deforce, D. %A Chang, C. %A Karol, K. G. %A Hedrich, R. %A Ulvskov, P. %A Glöckner, G. %A Delwiche, C. F. %A Petrásek, J. %A Van de Peer, Y. %A Friml, J. %A Beilby, M. %A Dolan, L. %A Kohara, Y. %A Sugano, S. %A Fujiyama, A. %A Delaux, P. M. %A Quint, M. %A Theissen, G. %A Hagemann, M. %A Harholt, J. %A Dunand, C. %A Zachgo, S. %A Langdale, J. %A Maumus, F. %A Van Der Straeten, D. %A Gould, S. B. %A Rensing, S. A. %D 2018 %J Cell %N 2 %P 448-+ %R 10.1016/j.cell.2018.06.033 %T The Genome: Secondary Complexity and Implications for Plant Terrestrialization %U /brokenurl#<Go to ISI>://WOS:000438482800019 %V 174 %X Land plants evolved from charophytic algae, among which Charophyceae possess the most complex body plans. We present the genome of Chara braunii; comparison of the genome to those of land plants identified evolutionary novelties for plant terrestrialization and land plant heritage genes. C. braunii employs unique xylan synthases for cell wall biosynthesis, a phragmoplast (cell separation) mechanism similar to that of land plants, and many phytohormones. C. braunii plastids are controlled via landplant- like retrograde signaling, and transcriptional regulation is more elaborate than in other algae. The morphological complexity of this organism may result from expanded gene families, with three cases of particular note: genes effecting tolerance to reactive oxygen species (ROS), LysM receptor-like kinases, and transcription factors (TFs). Transcriptomic analysis of sexual reproductive structures reveals intricate control by TFs, activity of the ROS gene network, and the ancestral use of plant-like storage and stress protection proteins in the zygote.
• The Receptor-like Pseudokinase GHR1 Is Required for Stomatal Closure. Sierla, M.; Horak, H.; Overmyer, K.; Waszczak, C.; Yarmolinsky, D.; Maierhofer, T.; Vainonen, J. P.; Salojärvi, J.; Denessiouk, K.; Laanemets, K.; Toldsepp, K.; Vahisalu, T.; Gauthier, A.; Puukko, T.; Paulin, L.; Auvinen, P.; Geiger, D.; Hedrich, R.; Kollist, H.; Kangasjärvi, J. In Plant Cell, 30(11), pp. 2813–2837. 2018.
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  Guard cells control the aperture of stomatal pores to balance photosynthetic carbon dioxide uptake with evaporative water loss. Stomatal closure is triggered by several stimuli that initiate complex signaling networks to govern the activity of ion channels. Activation of SLOW ANION CHANNEL1 (SLAC1) is central to the process of stomatal closure and requires the leucine-rich repeat receptor-like kinase (LRR-RLK) GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1), among other signaling components. Here, based on functional analysis of nine Arabidopsis thaliana ghr1 mutant alleles identified in two independent forward-genetic ozone-sensitivity screens, we found that GHR1 is required for stomatal responses to apoplastic reactive oxygen species, abscisic acid, high CO2 concentrations, and diurnal light/dark transitions. Furthermore, we show that the amino acid residues of GHR1 involved in ATP binding are not required for stomatal closure in Arabidopsis or the activation of SLAC1 anion currents in Xenopus laevis oocytes and present supporting in silico and in vitro evidence suggesting that GHR1 is an inactive pseudokinase. Biochemical analyses suggested that GHR1-mediated activation of SLAC1 occurs via interacting proteins and that CALCIUM-DEPENDENT PROTEIN KINASE3 interacts with GHR1. We propose that GHR1 acts in stomatal closure as a scaffolding component.

  @article{RN1015, abstract = {Guard cells control the aperture of stomatal pores to balance photosynthetic carbon dioxide uptake with evaporative water loss. Stomatal closure is triggered by several stimuli that initiate complex signaling networks to govern the activity of ion channels. Activation of SLOW ANION CHANNEL1 (SLAC1) is central to the process of stomatal closure and requires the leucine-rich repeat receptor-like kinase (LRR-RLK) GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1), among other signaling components. Here, based on functional analysis of nine Arabidopsis thaliana ghr1 mutant alleles identified in two independent forward-genetic ozone-sensitivity screens, we found that GHR1 is required for stomatal responses to apoplastic reactive oxygen species, abscisic acid, high CO2 concentrations, and diurnal light/dark transitions. Furthermore, we show that the amino acid residues of GHR1 involved in ATP binding are not required for stomatal closure in Arabidopsis or the activation of SLAC1 anion currents in Xenopus laevis oocytes and present supporting in silico and in vitro evidence suggesting that GHR1 is an inactive pseudokinase. Biochemical analyses suggested that GHR1-mediated activation of SLAC1 occurs via interacting proteins and that CALCIUM-DEPENDENT PROTEIN KINASE3 interacts with GHR1. We propose that GHR1 acts in stomatal closure as a scaffolding component.}, author = {Sierla, M. and Horak, H. and Overmyer, K. and Waszczak, C. and Yarmolinsky, D. and Maierhofer, T. and Vainonen, J. P. and Salojärvi, J. and Denessiouk, K. and Laanemets, K. and Toldsepp, K. and Vahisalu, T. and Gauthier, A. and Puukko, T. and Paulin, L. and Auvinen, P. and Geiger, D. and Hedrich, R. and Kollist, H. and Kangasjärvi, J.}, journal = {Plant Cell}, keywords = {phosphatases}, note = {Hf3gp Times Cited:75 Cited References Count:117}, number = 11, pages = {2813-2837}, title = {The Receptor-like Pseudokinase GHR1 Is Required for Stomatal Closure}, type = {Journal Article}, volume = 30, year = 2018 }

  %0 Journal Article %1 RN1015 %A Sierla, M. %A Horak, H. %A Overmyer, K. %A Waszczak, C. %A Yarmolinsky, D. %A Maierhofer, T. %A Vainonen, J. P. %A Salojärvi, J. %A Denessiouk, K. %A Laanemets, K. %A Toldsepp, K. %A Vahisalu, T. %A Gauthier, A. %A Puukko, T. %A Paulin, L. %A Auvinen, P. %A Geiger, D. %A Hedrich, R. %A Kollist, H. %A Kangasjärvi, J. %D 2018 %J Plant Cell %N 11 %P 2813-2837 %R 10.1105/tpc.18.00441 %T The Receptor-like Pseudokinase GHR1 Is Required for Stomatal Closure %U /brokenurl#<Go to ISI>://WOS:000454123800015 %V 30 %X Guard cells control the aperture of stomatal pores to balance photosynthetic carbon dioxide uptake with evaporative water loss. Stomatal closure is triggered by several stimuli that initiate complex signaling networks to govern the activity of ion channels. Activation of SLOW ANION CHANNEL1 (SLAC1) is central to the process of stomatal closure and requires the leucine-rich repeat receptor-like kinase (LRR-RLK) GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1), among other signaling components. Here, based on functional analysis of nine Arabidopsis thaliana ghr1 mutant alleles identified in two independent forward-genetic ozone-sensitivity screens, we found that GHR1 is required for stomatal responses to apoplastic reactive oxygen species, abscisic acid, high CO2 concentrations, and diurnal light/dark transitions. Furthermore, we show that the amino acid residues of GHR1 involved in ATP binding are not required for stomatal closure in Arabidopsis or the activation of SLAC1 anion currents in Xenopus laevis oocytes and present supporting in silico and in vitro evidence suggesting that GHR1 is an inactive pseudokinase. Biochemical analyses suggested that GHR1-mediated activation of SLAC1 occurs via interacting proteins and that CALCIUM-DEPENDENT PROTEIN KINASE3 interacts with GHR1. We propose that GHR1 acts in stomatal closure as a scaffolding component.
• Mycorrhizal lipochitinoligosaccharides (LCOs) depolarize root hairs of. Hürter, A. L.; Fort, S.; Cottaz, S.; Hedrich, R.; Geiger, D.; Roelfsema, M. R. G. In Plos One, 13(5). 2018.
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  Arbuscular Mycorrhiza and Root Nodule Symbiosis are symbiotic interactions with a high benefit for plant growth and crop production. Thus, it is of great interest to understand the developmental process of these symbioses in detail. We analysed very early symbiotic responses of Medicago truncatula root hair cells, by stimulation with lipochitinoligosacchar-ides specific for the induction of nodules (Nod-LCOs), or the interaction with mycorrhiza (Myc-LCOs). Intracellular micro electrodes were used, in combination with Ca2+ sensitive reporter dyes, to study the relations between cytosolic Ca2+ signals and membrane potential changes. We found that sulfated Myc-as well as Nod-LCOs initiate a membrane depolarization, which depends on the chemical composition of these signaling molecules, as well as the genotype of the plants that were studied. A successive application of sulfated Myc-LCOs and Nod-LCOs resulted only in a single transient depolarization, indicating that Myc-LCOs can repress plasma membrane responses to Nod-LCOs. In contrast to current models, the Nod-LCO-induced depolarization precedes changes in the cytosolic Ca2+ level of root hair cells. The Nod-LCO induced membrane depolarization thus is most likely independent of cytosolic Ca2+ signals and nuclear Ca2+ spiking.

  @article{RN1021, abstract = {Arbuscular Mycorrhiza and Root Nodule Symbiosis are symbiotic interactions with a high benefit for plant growth and crop production. Thus, it is of great interest to understand the developmental process of these symbioses in detail. We analysed very early symbiotic responses of Medicago truncatula root hair cells, by stimulation with lipochitinoligosacchar-ides specific for the induction of nodules (Nod-LCOs), or the interaction with mycorrhiza (Myc-LCOs). Intracellular micro electrodes were used, in combination with Ca2+ sensitive reporter dyes, to study the relations between cytosolic Ca2+ signals and membrane potential changes. We found that sulfated Myc-as well as Nod-LCOs initiate a membrane depolarization, which depends on the chemical composition of these signaling molecules, as well as the genotype of the plants that were studied. A successive application of sulfated Myc-LCOs and Nod-LCOs resulted only in a single transient depolarization, indicating that Myc-LCOs can repress plasma membrane responses to Nod-LCOs. In contrast to current models, the Nod-LCO-induced depolarization precedes changes in the cytosolic Ca2+ level of root hair cells. The Nod-LCO induced membrane depolarization thus is most likely independent of cytosolic Ca2+ signals and nuclear Ca2+ spiking.}, author = {Hürter, A. L. and Fort, S. and Cottaz, S. and Hedrich, R. and Geiger, D. and Roelfsema, M. R. G.}, journal = {Plos One}, keywords = {symbiotic}, note = {Gh8cd Times Cited:2 Cited References Count:51}, number = 5, title = {Mycorrhizal lipochitinoligosaccharides (LCOs) depolarize root hairs of}, type = {Journal Article}, volume = 13, year = 2018 }

  %0 Journal Article %1 RN1021 %A Hürter, A. L. %A Fort, S. %A Cottaz, S. %A Hedrich, R. %A Geiger, D. %A Roelfsema, M. R. G. %D 2018 %J Plos One %N 5 %R ARTN e0198126 10.1371/journal.pone.0198126 %T Mycorrhizal lipochitinoligosaccharides (LCOs) depolarize root hairs of %U /brokenurl#<Go to ISI>://WOS:000433893200033 %V 13 %X Arbuscular Mycorrhiza and Root Nodule Symbiosis are symbiotic interactions with a high benefit for plant growth and crop production. Thus, it is of great interest to understand the developmental process of these symbioses in detail. We analysed very early symbiotic responses of Medicago truncatula root hair cells, by stimulation with lipochitinoligosacchar-ides specific for the induction of nodules (Nod-LCOs), or the interaction with mycorrhiza (Myc-LCOs). Intracellular micro electrodes were used, in combination with Ca2+ sensitive reporter dyes, to study the relations between cytosolic Ca2+ signals and membrane potential changes. We found that sulfated Myc-as well as Nod-LCOs initiate a membrane depolarization, which depends on the chemical composition of these signaling molecules, as well as the genotype of the plants that were studied. A successive application of sulfated Myc-LCOs and Nod-LCOs resulted only in a single transient depolarization, indicating that Myc-LCOs can repress plasma membrane responses to Nod-LCOs. In contrast to current models, the Nod-LCO-induced depolarization precedes changes in the cytosolic Ca2+ level of root hair cells. The Nod-LCO induced membrane depolarization thus is most likely independent of cytosolic Ca2+ signals and nuclear Ca2+ spiking.
• A Tandem Amino Acid Residue Motif in Guard Cell SLAC1 Anion Channel of Grasses Allows for the Control of Stomatal Aperture by Nitrate. Schäfer, N.; Maierhofer, T.; Herrmann, J.; Jorgensen, M. E.; Lind, C.; von Meyer, K.; Lautner, S.; Fromm, J.; Felder, M.; Hetherington, A. M.; Ache, P.; Geiger, D.; Hedrich, R. In Current Biology, 28(9), pp. 1370-U145. 2018.
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  The latest major group of plants to evolve were the grasses. These became important in the mid-Paleogene about 40 million years ago. During evolution, leaf CO 2 uptake and transpirational water loss were optimized by the acquisition of grass-specific stomatal complexes. In contrast to the kidney-shaped guard cells (GCs) typical of the dicots such as Arabidopsis, in the grasses and agronomically important cereals, the GCs are dumbbell shaped and are associated with morphologically distinct subsidiary cells (SCs). We studied the molecular basis of GC action in the major cereal crop barley. Upon feeding ABA to xylem sap of an intact barley leaf, stomata closed in a nitrate-dependent manner. This process was initiated by activation of GC SLAC-type anion channel currents. HvSLAC1 expressed in Xenopus oocytes gave rise to S-type anion currents that increased several-fold upon stimulation with >3 mM nitrate. We identified a tandem amino acid residue motif that within the SLAC1 channels differs fundamentally between monocots and dicots. When the motif of nitrate-insensitive dicot Arabidopsis SLAC1 was replaced by the monocot signature, AtSLAC1 converted into a grass-type like nitrate-sensitive channel. Our work reveals a fundamental difference between monocot and dicot GCs and prompts questions into the selective pressures during evolution that resulted in fundamental changes in the regulation of SLAC1 function.

  @article{RN1016, abstract = {The latest major group of plants to evolve were the grasses. These became important in the mid-Paleogene about 40 million years ago. During evolution, leaf CO 2 uptake and transpirational water loss were optimized by the acquisition of grass-specific stomatal complexes. In contrast to the kidney-shaped guard cells (GCs) typical of the dicots such as Arabidopsis, in the grasses and agronomically important cereals, the GCs are dumbbell shaped and are associated with morphologically distinct subsidiary cells (SCs). We studied the molecular basis of GC action in the major cereal crop barley. Upon feeding ABA to xylem sap of an intact barley leaf, stomata closed in a nitrate-dependent manner. This process was initiated by activation of GC SLAC-type anion channel currents. HvSLAC1 expressed in Xenopus oocytes gave rise to S-type anion currents that increased several-fold upon stimulation with >3 mM nitrate. We identified a tandem amino acid residue motif that within the SLAC1 channels differs fundamentally between monocots and dicots. When the motif of nitrate-insensitive dicot Arabidopsis SLAC1 was replaced by the monocot signature, AtSLAC1 converted into a grass-type like nitrate-sensitive channel. Our work reveals a fundamental difference between monocot and dicot GCs and prompts questions into the selective pressures during evolution that resulted in fundamental changes in the regulation of SLAC1 function.}, author = {Schäfer, N. and Maierhofer, T. and Herrmann, J. and Jorgensen, M. E. and Lind, C. and von Meyer, K. and Lautner, S. and Fromm, J. and Felder, M. and Hetherington, A. M. and Ache, P. and Geiger, D. and Hedrich, R.}, journal = {Current Biology}, keywords = {pair}, note = {Gg1jc Times Cited:37 Cited References Count:70}, number = 9, pages = {1370-U145}, title = {A Tandem Amino Acid Residue Motif in Guard Cell SLAC1 Anion Channel of Grasses Allows for the Control of Stomatal Aperture by Nitrate}, type = {Journal Article}, volume = 28, year = 2018 }

  %0 Journal Article %1 RN1016 %A Schäfer, N. %A Maierhofer, T. %A Herrmann, J. %A Jorgensen, M. E. %A Lind, C. %A von Meyer, K. %A Lautner, S. %A Fromm, J. %A Felder, M. %A Hetherington, A. M. %A Ache, P. %A Geiger, D. %A Hedrich, R. %D 2018 %J Current Biology %N 9 %P 1370-U145 %R 10.1016/j.cub.2018.03.027 %T A Tandem Amino Acid Residue Motif in Guard Cell SLAC1 Anion Channel of Grasses Allows for the Control of Stomatal Aperture by Nitrate %U /brokenurl#<Go to ISI>://WOS:000432442300021 %V 28 %X The latest major group of plants to evolve were the grasses. These became important in the mid-Paleogene about 40 million years ago. During evolution, leaf CO 2 uptake and transpirational water loss were optimized by the acquisition of grass-specific stomatal complexes. In contrast to the kidney-shaped guard cells (GCs) typical of the dicots such as Arabidopsis, in the grasses and agronomically important cereals, the GCs are dumbbell shaped and are associated with morphologically distinct subsidiary cells (SCs). We studied the molecular basis of GC action in the major cereal crop barley. Upon feeding ABA to xylem sap of an intact barley leaf, stomata closed in a nitrate-dependent manner. This process was initiated by activation of GC SLAC-type anion channel currents. HvSLAC1 expressed in Xenopus oocytes gave rise to S-type anion currents that increased several-fold upon stimulation with >3 mM nitrate. We identified a tandem amino acid residue motif that within the SLAC1 channels differs fundamentally between monocots and dicots. When the motif of nitrate-insensitive dicot Arabidopsis SLAC1 was replaced by the monocot signature, AtSLAC1 converted into a grass-type like nitrate-sensitive channel. Our work reveals a fundamental difference between monocot and dicot GCs and prompts questions into the selective pressures during evolution that resulted in fundamental changes in the regulation of SLAC1 function.
• High V-PPase activity is beneficial under high salt loads, but detrimental without salinity. Graus, D.; Konrad, K. R.; Bemm, F.; Nebioglu, M. G. P.; Lorey, C.; Duscha, K.; Güthoff, T.; Herrmann, J.; Ferjani, A.; Cuin, T. A.; Roelfsema, M. R. G.; Schumacher, K.; Neuhaus, H. E.; Marten, I.; Hedrich, R. In New Phytologist, 219(4), pp. 1421–1432. 2018.
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  The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the V-type H+-ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V-PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton-pumping functions has yet to be dissected. For a better understanding of the molecular processes underlying V-PPase-dependent salt tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch-clamp, impalement electrodes and pH imaging. NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants. The results indicate that under normal growth conditions, plants need to regulate the V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.

  @article{RN1027, abstract = {The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the V-type H+-ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V-PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton-pumping functions has yet to be dissected. For a better understanding of the molecular processes underlying V-PPase-dependent salt tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch-clamp, impalement electrodes and pH imaging. NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants. The results indicate that under normal growth conditions, plants need to regulate the V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.}, author = {Graus, D. and Konrad, K. R. and Bemm, F. and Nebioglu, M. G. P. and Lorey, C. and Duscha, K. and Güthoff, T. and Herrmann, J. and Ferjani, A. and Cuin, T. A. and Roelfsema, M. R. G. and Schumacher, K. and Neuhaus, H. E. and Marten, I. and Hedrich, R.}, journal = {New Phytologist}, keywords = {cell}, note = {Gp4os Times Cited:28 Cited References Count:65}, number = 4, pages = {1421-1432}, title = {High V-PPase activity is beneficial under high salt loads, but detrimental without salinity}, type = {Journal Article}, volume = 219, year = 2018 }

  %0 Journal Article %1 RN1027 %A Graus, D. %A Konrad, K. R. %A Bemm, F. %A Nebioglu, M. G. P. %A Lorey, C. %A Duscha, K. %A Güthoff, T. %A Herrmann, J. %A Ferjani, A. %A Cuin, T. A. %A Roelfsema, M. R. G. %A Schumacher, K. %A Neuhaus, H. E. %A Marten, I. %A Hedrich, R. %D 2018 %J New Phytologist %N 4 %P 1421-1432 %R 10.1111/nph.15280 %T High V-PPase activity is beneficial under high salt loads, but detrimental without salinity %U /brokenurl#<Go to ISI>://WOS:000440847600027 %V 219 %X The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the V-type H+-ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V-PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton-pumping functions has yet to be dissected. For a better understanding of the molecular processes underlying V-PPase-dependent salt tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch-clamp, impalement electrodes and pH imaging. NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants. The results indicate that under normal growth conditions, plants need to regulate the V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.
• A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between and Its Host Arabidopsis. Johnson, J. M.; Thürich, J.; Petutschnig, E. K.; Altschmied, L.; Meichsner, D.; Sherameti, I.; Dindas, J.; Mrozinska, A.; Paetz, C.; Scholz, S. S.; Furch, A. C. U.; Lipka, V.; Hedrich, R.; Schneider, B.; Svatos, A.; Oelmüller, R. In Plant Physiology, 176(3), pp. 2496–2514. 2018.
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  Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. P. indica fungal cell wall extract induces cytoplasmic calcium elevation in host plant roots. Here, we show that cellotriose (CT) is an elicitor-active cell wall moiety released by P. indica into the medium. CT induces a mild defense-like response, including the production of reactive oxygen species, changes in membrane potential, and the expression of genes involved in growth regulation and root development. CT-based cytoplasmic calcium elevation in Arabidopsis (Arabidopsis thaliana) roots does not require the BAK1 coreceptor or the putative Ca2+ channels TPC1, GLR3.3, GLR2.4, and GLR2.5 and operates synergistically with the elicitor chitin. We identified an ethyl methanesulfonate-induced mutant (cytoplasmic calcium elevation mutant) impaired in the response to CT and various other cellooligomers (n = 2-7), but not to chitooligomers (n = 4-8), in roots. The mutant contains a single nucleotide exchange in the gene encoding a poly(A) ribonuclease (AtPARN; At1g55870) that degrades the poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our identification of cellotriose as a novel chemical mediator casts light on the complex P. indica-plant mutualistic relationship.

  @article{RN1020, abstract = {Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. P. indica fungal cell wall extract induces cytoplasmic calcium elevation in host plant roots. Here, we show that cellotriose (CT) is an elicitor-active cell wall moiety released by P. indica into the medium. CT induces a mild defense-like response, including the production of reactive oxygen species, changes in membrane potential, and the expression of genes involved in growth regulation and root development. CT-based cytoplasmic calcium elevation in Arabidopsis (Arabidopsis thaliana) roots does not require the BAK1 coreceptor or the putative Ca2+ channels TPC1, GLR3.3, GLR2.4, and GLR2.5 and operates synergistically with the elicitor chitin. We identified an ethyl methanesulfonate-induced mutant (cytoplasmic calcium elevation mutant) impaired in the response to CT and various other cellooligomers (n = 2-7), but not to chitooligomers (n = 4-8), in roots. The mutant contains a single nucleotide exchange in the gene encoding a poly(A) ribonuclease (AtPARN; At1g55870) that degrades the poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our identification of cellotriose as a novel chemical mediator casts light on the complex P. indica-plant mutualistic relationship.}, author = {Johnson, J. M. and Thürich, J. and Petutschnig, E. K. and Altschmied, L. and Meichsner, D. and Sherameti, I. and Dindas, J. and Mrozinska, A. and Paetz, C. and Scholz, S. S. and Furch, A. C. U. and Lipka, V. and Hedrich, R. and Schneider, B. and Svatos, A. and Oelmüller, R.}, journal = {Plant Physiology}, keywords = {interactions}, note = {Fy5ed Times Cited:54 Cited References Count:111}, number = 3, pages = {2496-2514}, title = {A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between and Its Host Arabidopsis}, type = {Journal Article}, volume = 176, year = 2018 }

  %0 Journal Article %1 RN1020 %A Johnson, J. M. %A Thürich, J. %A Petutschnig, E. K. %A Altschmied, L. %A Meichsner, D. %A Sherameti, I. %A Dindas, J. %A Mrozinska, A. %A Paetz, C. %A Scholz, S. S. %A Furch, A. C. U. %A Lipka, V. %A Hedrich, R. %A Schneider, B. %A Svatos, A. %A Oelmüller, R. %D 2018 %J Plant Physiology %N 3 %P 2496-2514 %R 10.1104/pp.17.01423 %T A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between and Its Host Arabidopsis %U /brokenurl#<Go to ISI>://WOS:000426848300046 %V 176 %X Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. P. indica fungal cell wall extract induces cytoplasmic calcium elevation in host plant roots. Here, we show that cellotriose (CT) is an elicitor-active cell wall moiety released by P. indica into the medium. CT induces a mild defense-like response, including the production of reactive oxygen species, changes in membrane potential, and the expression of genes involved in growth regulation and root development. CT-based cytoplasmic calcium elevation in Arabidopsis (Arabidopsis thaliana) roots does not require the BAK1 coreceptor or the putative Ca2+ channels TPC1, GLR3.3, GLR2.4, and GLR2.5 and operates synergistically with the elicitor chitin. We identified an ethyl methanesulfonate-induced mutant (cytoplasmic calcium elevation mutant) impaired in the response to CT and various other cellooligomers (n = 2-7), but not to chitooligomers (n = 4-8), in roots. The mutant contains a single nucleotide exchange in the gene encoding a poly(A) ribonuclease (AtPARN; At1g55870) that degrades the poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our identification of cellotriose as a novel chemical mediator casts light on the complex P. indica-plant mutualistic relationship.
• Stomata in a saline world. Hedrich, R.; Shabala, S. In Current Opinion in Plant Biology, 46, pp. 87–95. 2018.
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  Salt stress results in a dramatic increase in ABA biosynthesis, H2O2 accumulation, and reduced K+ availability in the shoot. Each of these factors leads to stomata closure, so reducing CO2 assimilation and imposing yield penalties. However, halophytes, naturally salt tolerant plant species, flourish under saline conditions that would cause massive yield penalties in glycophytic crops. Is there anything special about the stomata of halophytes, why is guard cell function in these salt tolerant species not affected by the above factors? This opinion paper addresses these questions by providing a comprehensive assessment of the molecular identity and operational modes of major plasma membrane transporters that mediate stomata movements.

  @article{RN1022, abstract = {Salt stress results in a dramatic increase in ABA biosynthesis, H2O2 accumulation, and reduced K+ availability in the shoot. Each of these factors leads to stomata closure, so reducing CO2 assimilation and imposing yield penalties. However, halophytes, naturally salt tolerant plant species, flourish under saline conditions that would cause massive yield penalties in glycophytic crops. Is there anything special about the stomata of halophytes, why is guard cell function in these salt tolerant species not affected by the above factors? This opinion paper addresses these questions by providing a comprehensive assessment of the molecular identity and operational modes of major plasma membrane transporters that mediate stomata movements.}, author = {Hedrich, R. and Shabala, S.}, journal = {Current Opinion in Plant Biology}, keywords = {abscisic-acid}, note = {He6el Times Cited:76 Cited References Count:77}, pages = {87-95}, title = {Stomata in a saline world}, type = {Journal Article}, volume = 46, year = 2018 }

  %0 Journal Article %1 RN1022 %A Hedrich, R. %A Shabala, S. %D 2018 %J Current Opinion in Plant Biology %P 87-95 %R 10.1016/j.pbi.2018.07.015 %T Stomata in a saline world %U /brokenurl#<Go to ISI>://WOS:000453496000013 %V 46 %X Salt stress results in a dramatic increase in ABA biosynthesis, H2O2 accumulation, and reduced K+ availability in the shoot. Each of these factors leads to stomata closure, so reducing CO2 assimilation and imposing yield penalties. However, halophytes, naturally salt tolerant plant species, flourish under saline conditions that would cause massive yield penalties in glycophytic crops. Is there anything special about the stomata of halophytes, why is guard cell function in these salt tolerant species not affected by the above factors? This opinion paper addresses these questions by providing a comprehensive assessment of the molecular identity and operational modes of major plasma membrane transporters that mediate stomata movements.
• AUX1-mediated root hair auxin influx governs SCF -type Ca signaling. Dindas, J.; Scherzer, S.; Roelfsema, M. R. G.; von Meyer, K.; Müller, H. M.; Al-Rasheid, K. A. S.; Palme, K.; Dietrich, P.; Becker, D.; Bennett, M. J.; Hedrich, R. In Nature Communications, 9. 2018.
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  Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration-and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA(-) triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots.

  @article{RN1029, abstract = {Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration-and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA(-) triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots.}, author = {Dindas, J. and Scherzer, S. and Roelfsema, M. R. G. and von Meyer, K. and Müller, H. M. and Al-Rasheid, K. A. S. and Palme, K. and Dietrich, P. and Becker, D. and Bennett, M. J. and Hedrich, R.}, journal = {Nature Communications}, keywords = {arabidopsis}, note = {Fz9kk Times Cited:137 Cited References Count:52}, title = {AUX1-mediated root hair auxin influx governs SCF -type Ca signaling}, type = {Journal Article}, volume = 9, year = 2018 }

  %0 Journal Article %1 RN1029 %A Dindas, J. %A Scherzer, S. %A Roelfsema, M. R. G. %A von Meyer, K. %A Müller, H. M. %A Al-Rasheid, K. A. S. %A Palme, K. %A Dietrich, P. %A Becker, D. %A Bennett, M. J. %A Hedrich, R. %D 2018 %J Nature Communications %R ARTN 1174 10.1038/s41467-018-03582-5 %T AUX1-mediated root hair auxin influx governs SCF -type Ca signaling %U /brokenurl#<Go to ISI>://WOS:000427929200005 %V 9 %X Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration-and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA(-) triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots.
• Structure and Function of TPC1 Vacuole SV Channel Gains Shape. Hedrich, R.; Mueller, T. D.; Becker, D.; Marten, I. In Molecular Plant, 11(6), pp. 764–775. 2018.
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  Plants and animals in endosomes operate TPC1/SV-type cation channels. All plants harbor at least one TPC1 gene. Although the encoded SV channel was firstly discovered in the plant vacuole membrane two decades ago, its biological function has remained enigmatic. Recently, the structure of a plant TPC1/SV channel protein was determined. Insights into the 3D topology has now guided site-directed mutation approaches, enabling structure-function analyses of TPC1/SV channels to shed new light on earlier findings. Fou2 plants carrying a hyperactive mutant form of TPC1 develop wounding stress phenotypes. Recent studies with fou2 and mutants that lack functional TPC1 have revealed atypical features in local and long-distance stress signaling, providing new access to the previously mysterious biology of this vacuolar cation channel type in planta.

  @article{RN1024, abstract = {Plants and animals in endosomes operate TPC1/SV-type cation channels. All plants harbor at least one TPC1 gene. Although the encoded SV channel was firstly discovered in the plant vacuole membrane two decades ago, its biological function has remained enigmatic. Recently, the structure of a plant TPC1/SV channel protein was determined. Insights into the 3D topology has now guided site-directed mutation approaches, enabling structure-function analyses of TPC1/SV channels to shed new light on earlier findings. Fou2 plants carrying a hyperactive mutant form of TPC1 develop wounding stress phenotypes. Recent studies with fou2 and mutants that lack functional TPC1 have revealed atypical features in local and long-distance stress signaling, providing new access to the previously mysterious biology of this vacuolar cation channel type in planta.}, author = {Hedrich, R. and Mueller, T. D. and Becker, D. and Marten, I.}, journal = {Molecular Plant}, keywords = {ca2+}, note = {Gi5rt Times Cited:39 Cited References Count:81}, number = 6, pages = {764-775}, title = {Structure and Function of TPC1 Vacuole SV Channel Gains Shape}, type = {Journal Article}, volume = 11, year = 2018 }

  %0 Journal Article %1 RN1024 %A Hedrich, R. %A Mueller, T. D. %A Becker, D. %A Marten, I. %D 2018 %J Molecular Plant %N 6 %P 764-775 %R 10.1016/j.molp.2018.03.017 %T Structure and Function of TPC1 Vacuole SV Channel Gains Shape %U /brokenurl#<Go to ISI>://WOS:000434429000002 %V 11 %X Plants and animals in endosomes operate TPC1/SV-type cation channels. All plants harbor at least one TPC1 gene. Although the encoded SV channel was firstly discovered in the plant vacuole membrane two decades ago, its biological function has remained enigmatic. Recently, the structure of a plant TPC1/SV channel protein was determined. Insights into the 3D topology has now guided site-directed mutation approaches, enabling structure-function analyses of TPC1/SV channels to shed new light on earlier findings. Fou2 plants carrying a hyperactive mutant form of TPC1 develop wounding stress phenotypes. Recent studies with fou2 and mutants that lack functional TPC1 have revealed atypical features in local and long-distance stress signaling, providing new access to the previously mysterious biology of this vacuolar cation channel type in planta.
• Tip-localized Ca -permeable channels control pollen tube growth via kinase-dependent R- and S-type anion channel regulation. Gutermuth, T.; Herbell, S.; Lassig, R.; Brosché, M.; Romeis, T.; Feijó, J. A.; Hedrich, R.; Konrad, K. R. In New Phytologist, 218(3), pp. 1089–1105. 2018.
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  Pollen tubes (PTs) are characterized by having tip-focused cytosolic calcium ion (Ca2+) concentration ([Ca2+](cyt)) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca2+](cyt) orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live-cell Ca2+ and anion imaging. We triggered Ca2+-channel activation by applying hyperpolarizing voltage pulses and observed that the evoked [Ca2+](cyt) increases were paralleled by high anion channel activity and a decrease in the cytosolic anion concentration at the PT tip. We confirmed a functional correlation between these patterns by showing that inhibition of Ca2+-permeable channels eliminated the [Ca2+](cyt) increase, resulting in the abrogation of anion channel activity via Ca2+-dependent protein kinases (CPKs). Functional characterization of CPK and anion-channel mutants revealed a CPK2/20/6-dependent activation of SLAH3 and ALMT12/13/14 anion channels. The impaired growth phenotypes of anion channel and CPK mutants support the physiological significance of a kinase- and Ca2+-dependent pathway to control PT growth via anion channel activation. Other than unveiling this functional link, our membrane hyperpolarization method allows for unprecedented manipulation of the [Ca2+](cyt) gradient or oscillations in the PT tips and opens an array of opportunities for channel screenings.

  @article{RN1026, abstract = {Pollen tubes (PTs) are characterized by having tip-focused cytosolic calcium ion (Ca2+) concentration ([Ca2+](cyt)) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca2+](cyt) orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live-cell Ca2+ and anion imaging. We triggered Ca2+-channel activation by applying hyperpolarizing voltage pulses and observed that the evoked [Ca2+](cyt) increases were paralleled by high anion channel activity and a decrease in the cytosolic anion concentration at the PT tip. We confirmed a functional correlation between these patterns by showing that inhibition of Ca2+-permeable channels eliminated the [Ca2+](cyt) increase, resulting in the abrogation of anion channel activity via Ca2+-dependent protein kinases (CPKs). Functional characterization of CPK and anion-channel mutants revealed a CPK2/20/6-dependent activation of SLAH3 and ALMT12/13/14 anion channels. The impaired growth phenotypes of anion channel and CPK mutants support the physiological significance of a kinase- and Ca2+-dependent pathway to control PT growth via anion channel activation. Other than unveiling this functional link, our membrane hyperpolarization method allows for unprecedented manipulation of the [Ca2+](cyt) gradient or oscillations in the PT tips and opens an array of opportunities for channel screenings.}, author = {Gutermuth, T. and Herbell, S. and Lassig, R. and Brosché, M. and Romeis, T. and Feijó, J. A. and Hedrich, R. and Konrad, K. R.}, journal = {New Phytologist}, keywords = {almt12}, note = {Sp. Iss. SI Gc9of Times Cited:41 Cited References Count:76}, number = 3, pages = {1089-1105}, title = {Tip-localized Ca -permeable channels control pollen tube growth via kinase-dependent R- and S-type anion channel regulation}, type = {Journal Article}, volume = 218, year = 2018 }

  %0 Journal Article %1 RN1026 %A Gutermuth, T. %A Herbell, S. %A Lassig, R. %A Brosché, M. %A Romeis, T. %A Feijó, J. A. %A Hedrich, R. %A Konrad, K. R. %D 2018 %J New Phytologist %N 3 %P 1089-1105 %R 10.1111/nph.15067 %T Tip-localized Ca -permeable channels control pollen tube growth via kinase-dependent R- and S-type anion channel regulation %U /brokenurl#<Go to ISI>://WOS:000430127000023 %V 218 %X Pollen tubes (PTs) are characterized by having tip-focused cytosolic calcium ion (Ca2+) concentration ([Ca2+](cyt)) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca2+](cyt) orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live-cell Ca2+ and anion imaging. We triggered Ca2+-channel activation by applying hyperpolarizing voltage pulses and observed that the evoked [Ca2+](cyt) increases were paralleled by high anion channel activity and a decrease in the cytosolic anion concentration at the PT tip. We confirmed a functional correlation between these patterns by showing that inhibition of Ca2+-permeable channels eliminated the [Ca2+](cyt) increase, resulting in the abrogation of anion channel activity via Ca2+-dependent protein kinases (CPKs). Functional characterization of CPK and anion-channel mutants revealed a CPK2/20/6-dependent activation of SLAH3 and ALMT12/13/14 anion channels. The impaired growth phenotypes of anion channel and CPK mutants support the physiological significance of a kinase- and Ca2+-dependent pathway to control PT growth via anion channel activation. Other than unveiling this functional link, our membrane hyperpolarization method allows for unprecedented manipulation of the [Ca2+](cyt) gradient or oscillations in the PT tips and opens an array of opportunities for channel screenings.

• The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration. Fasbender, L.; Maurer, D.; Kreuzwieser, J.; Kreuzer, I.; Schulze, W. X.; Kruse, J.; Becker, D.; Alfarraj, S.; Hedrich, R.; Werner, C.; Rennenberg, H. In New Phytologist, 214(2), pp. 597–606. 2017.
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  The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed C-13/N-15-glutamine (Gln). The release of (CO2)-C-13 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by C-13-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.

  @article{RN1043, abstract = {The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed C-13/N-15-glutamine (Gln). The release of (CO2)-C-13 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by C-13-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.}, author = {Fasbender, L. and Maurer, D. and Kreuzwieser, J. and Kreuzer, I. and Schulze, W. X. and Kruse, J. and Becker, D. and Alfarraj, S. and Hedrich, R. and Werner, C. and Rennenberg, H.}, journal = {New Phytologist}, keywords = {catabolism}, note = {Eq5pi Times Cited:18 Cited References Count:51}, number = 2, pages = {597-606}, title = {The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration}, type = {Journal Article}, volume = 214, year = 2017 }

  %0 Journal Article %1 RN1043 %A Fasbender, L. %A Maurer, D. %A Kreuzwieser, J. %A Kreuzer, I. %A Schulze, W. X. %A Kruse, J. %A Becker, D. %A Alfarraj, S. %A Hedrich, R. %A Werner, C. %A Rennenberg, H. %D 2017 %J New Phytologist %N 2 %P 597-606 %R 10.1111/nph.14404 %T The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration %U /brokenurl#<Go to ISI>://WOS:000398134700015 %V 214 %X The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed C-13/N-15-glutamine (Gln). The release of (CO2)-C-13 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by C-13-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.
• Detecting early signs of heat and drought stress in (date palm). Safronov, O.; Kreuzwieser, J.; Haberer, G.; Alyousif, M. S.; Schulze, W.; Al-Harbi, N.; Arab, L.; Ache, P.; Stempfl, T.; Kruse, J.; Mayer, K. X.; Hedrich, R.; Rennenberg, H.; Salojärvi, J.; Kangasjärvi, J. In Plos One, 12(6). 2017.
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  Plants adapt to the environment by either long-term genome evolution or by acclimatization processes where the cellular processes and metabolism of the plant are adjusted within the existing potential in the genome. Here we studied the adaptation strategies in date palm, Phoenix dactylifera, under mild heat, drought and combined heat and drought by transcriptomic and metabolomic profiling. In transcriptomics data, combined heat and drought resembled heat response, whereas in metabolomics data it was more similar to drought. In both conditions, soluble carbohydrates, such as fucose, and glucose derivatives, were increased, suggesting a switch to carbohydrate metabolism and cell wall biogenesis. This result is consistent with the evidence from transcriptomics and cis-motif analysis. In addition, transcriptomics data showed transcriptional activation of genes related to reactive oxygen species in all three conditions (drought, heat, and combined heat and drought), suggesting increased activity of enzymatic antioxidant systems in cytosol, chloroplast and peroxisome. Finally, the genes that were differentially expressed in heat and combined heat and drought stresses were significantly enriched for circadian and diurnal rhythm motifs, suggesting new stress avoidance strategies.

  @article{RN1036, abstract = {Plants adapt to the environment by either long-term genome evolution or by acclimatization processes where the cellular processes and metabolism of the plant are adjusted within the existing potential in the genome. Here we studied the adaptation strategies in date palm, Phoenix dactylifera, under mild heat, drought and combined heat and drought by transcriptomic and metabolomic profiling. In transcriptomics data, combined heat and drought resembled heat response, whereas in metabolomics data it was more similar to drought. In both conditions, soluble carbohydrates, such as fucose, and glucose derivatives, were increased, suggesting a switch to carbohydrate metabolism and cell wall biogenesis. This result is consistent with the evidence from transcriptomics and cis-motif analysis. In addition, transcriptomics data showed transcriptional activation of genes related to reactive oxygen species in all three conditions (drought, heat, and combined heat and drought), suggesting increased activity of enzymatic antioxidant systems in cytosol, chloroplast and peroxisome. Finally, the genes that were differentially expressed in heat and combined heat and drought stresses were significantly enriched for circadian and diurnal rhythm motifs, suggesting new stress avoidance strategies.}, author = {Safronov, O. and Kreuzwieser, J. and Haberer, G. and Alyousif, M. S. and Schulze, W. and Al-Harbi, N. and Arab, L. and Ache, P. and Stempfl, T. and Kruse, J. and Mayer, K. X. and Hedrich, R. and Rennenberg, H. and Salojärvi, J. and Kangasjärvi, J.}, journal = {Plos One}, keywords = {factor}, note = {Ew6hz Times Cited:37 Cited References Count:55}, number = 6, title = {Detecting early signs of heat and drought stress in (date palm)}, type = {Journal Article}, volume = 12, year = 2017 }

  %0 Journal Article %1 RN1036 %A Safronov, O. %A Kreuzwieser, J. %A Haberer, G. %A Alyousif, M. S. %A Schulze, W. %A Al-Harbi, N. %A Arab, L. %A Ache, P. %A Stempfl, T. %A Kruse, J. %A Mayer, K. X. %A Hedrich, R. %A Rennenberg, H. %A Salojärvi, J. %A Kangasjärvi, J. %D 2017 %J Plos One %N 6 %R ARTN e0177883 10.1371/journal.pone.0177883 %T Detecting early signs of heat and drought stress in (date palm) %U /brokenurl#<Go to ISI>://WOS:000402611800019 %V 12 %X Plants adapt to the environment by either long-term genome evolution or by acclimatization processes where the cellular processes and metabolism of the plant are adjusted within the existing potential in the genome. Here we studied the adaptation strategies in date palm, Phoenix dactylifera, under mild heat, drought and combined heat and drought by transcriptomic and metabolomic profiling. In transcriptomics data, combined heat and drought resembled heat response, whereas in metabolomics data it was more similar to drought. In both conditions, soluble carbohydrates, such as fucose, and glucose derivatives, were increased, suggesting a switch to carbohydrate metabolism and cell wall biogenesis. This result is consistent with the evidence from transcriptomics and cis-motif analysis. In addition, transcriptomics data showed transcriptional activation of genes related to reactive oxygen species in all three conditions (drought, heat, and combined heat and drought), suggesting increased activity of enzymatic antioxidant systems in cytosol, chloroplast and peroxisome. Finally, the genes that were differentially expressed in heat and combined heat and drought stresses were significantly enriched for circadian and diurnal rhythm motifs, suggesting new stress avoidance strategies.
• A high-quality genome assembly of quinoa provides insights into the molecular basis of salt bladder-based salinity tolerance and the exceptional nutritional value. Zou, C. S.; Chen, A. J.; Xiao, L. H.; Muller, H. M.; Ache, P.; Haberer, G.; Zhang, M. L.; Jia, W.; Deng, P.; Huang, R.; Lang, D.; Li, F.; Zhan, D. L.; Wu, X. Y.; Zhang, H.; Bohm, J.; Liu, R. Y.; Shabala, S.; Hedrich, R.; Zhu, J. K.; Zhang, H. In Cell Research, 27(11), pp. 1327–1340. 2017.
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  Chenopodium quinoa is a halophytic pseudocereal crop that is being cultivated in an ever-growing number of countries. Because quinoa is highly resistant to multiple abiotic stresses and its seed has a better nutritional value than any other major cereals, it is regarded as a future crop to ensure global food security. We generated a high-quality genome draft using an inbred line of the quinoa cultivar Real. The quinoa genome experienced one recent genome duplication about 4.3 million years ago, likely reflecting the genome fusion of two Chenopodium parents, in addition to the. paleohexaploidization reported for most eudicots. The genome is highly repetitive (64.5% repeat content) and contains 54 438 protein-coding genes and 192 microRNA genes, with more than 99.3% having orthologous genes from glycophylic species. Stress tolerance in quinoa is associated with the expansion of genes involved in ion and nutrient transport, ABA homeostasis and signaling, and enhanced basal-level ABA responses. Epidermal salt bladder cells exhibit similar characteristics as trichomes, with a significantly higher expression of genes related to energy import and ABA biosynthesis compared with the leaf lamina. The quinoa genome sequence provides insights into its exceptional nutritional value and the evolution of halophytes, enabling the identification of genes involved in salinity tolerance, and providing the basis for molecular breeding in quinoa.

  @article{RN1032, abstract = {Chenopodium quinoa is a halophytic pseudocereal crop that is being cultivated in an ever-growing number of countries. Because quinoa is highly resistant to multiple abiotic stresses and its seed has a better nutritional value than any other major cereals, it is regarded as a future crop to ensure global food security. We generated a high-quality genome draft using an inbred line of the quinoa cultivar Real. The quinoa genome experienced one recent genome duplication about 4.3 million years ago, likely reflecting the genome fusion of two Chenopodium parents, in addition to the. paleohexaploidization reported for most eudicots. The genome is highly repetitive (64.5% repeat content) and contains 54 438 protein-coding genes and 192 microRNA genes, with more than 99.3% having orthologous genes from glycophylic species. Stress tolerance in quinoa is associated with the expansion of genes involved in ion and nutrient transport, ABA homeostasis and signaling, and enhanced basal-level ABA responses. Epidermal salt bladder cells exhibit similar characteristics as trichomes, with a significantly higher expression of genes related to energy import and ABA biosynthesis compared with the leaf lamina. The quinoa genome sequence provides insights into its exceptional nutritional value and the evolution of halophytes, enabling the identification of genes involved in salinity tolerance, and providing the basis for molecular breeding in quinoa.}, author = {Zou, C. S. and Chen, A. J. and Xiao, L. H. and Muller, H. M. and Ache, P. and Haberer, G. and Zhang, M. L. and Jia, W. and Deng, P. and Huang, R. and Lang, D. and Li, F. and Zhan, D. L. and Wu, X. Y. and Zhang, H. and Bohm, J. and Liu, R. Y. and Shabala, S. and Hedrich, R. and Zhu, J. K. and Zhang, H.}, journal = {Cell Research}, keywords = {quinoa}, note = {Fl5sh Times Cited:142 Cited References Count:58}, number = 11, pages = {1327-1340}, title = {A high-quality genome assembly of quinoa provides insights into the molecular basis of salt bladder-based salinity tolerance and the exceptional nutritional value}, type = {Journal Article}, volume = 27, year = 2017 }

  %0 Journal Article %1 RN1032 %A Zou, C. S. %A Chen, A. J. %A Xiao, L. H. %A Muller, H. M. %A Ache, P. %A Haberer, G. %A Zhang, M. L. %A Jia, W. %A Deng, P. %A Huang, R. %A Lang, D. %A Li, F. %A Zhan, D. L. %A Wu, X. Y. %A Zhang, H. %A Bohm, J. %A Liu, R. Y. %A Shabala, S. %A Hedrich, R. %A Zhu, J. K. %A Zhang, H. %D 2017 %J Cell Research %N 11 %P 1327-1340 %R 10.1038/cr.2017.124 %T A high-quality genome assembly of quinoa provides insights into the molecular basis of salt bladder-based salinity tolerance and the exceptional nutritional value %U /brokenurl#<Go to ISI>://WOS:000414305500007 %V 27 %X Chenopodium quinoa is a halophytic pseudocereal crop that is being cultivated in an ever-growing number of countries. Because quinoa is highly resistant to multiple abiotic stresses and its seed has a better nutritional value than any other major cereals, it is regarded as a future crop to ensure global food security. We generated a high-quality genome draft using an inbred line of the quinoa cultivar Real. The quinoa genome experienced one recent genome duplication about 4.3 million years ago, likely reflecting the genome fusion of two Chenopodium parents, in addition to the. paleohexaploidization reported for most eudicots. The genome is highly repetitive (64.5% repeat content) and contains 54 438 protein-coding genes and 192 microRNA genes, with more than 99.3% having orthologous genes from glycophylic species. Stress tolerance in quinoa is associated with the expansion of genes involved in ion and nutrient transport, ABA homeostasis and signaling, and enhanced basal-level ABA responses. Epidermal salt bladder cells exhibit similar characteristics as trichomes, with a significantly higher expression of genes related to energy import and ABA biosynthesis compared with the leaf lamina. The quinoa genome sequence provides insights into its exceptional nutritional value and the evolution of halophytes, enabling the identification of genes involved in salinity tolerance, and providing the basis for molecular breeding in quinoa.
• Coprophagous features in carnivorous Nepenthes plants: a task for ureases. Yilamujiang, A.; Zhu, A. T.; Ligabue-Braun, R.; Bartram, S.; Witte, C. P.; Hedrich, R.; Hasabe, M.; Schöner, C. R.; Schöner, M. G.; Kerth, G.; Carlini, C. R.; Mithöfer, A. In Scientific Reports, 7. 2017.
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  Most terrestrial carnivorous plants are specialized on insect prey digestion to obtain additional nutrients. Few species of the genus Nepenthes developed mutualistic relationships with mammals for nitrogen supplementation. Whether dietary changes require certain enzymatic composition to utilize new sources of nutrients has rarely been tested. Here, we investigated the role of urease for Nepenthes hemsleyana that gains nitrogen from the bat Kerivoula hardwickii while it roosts inside the pitchers. We hypothesized that N. hemsleyana is able to use urea from the bats' excrements. In fact, we demonstrate that N-15-enriched urea provided to Nepenthes pitchers is metabolized and its nitrogen is distributed within the plant. As ureases are necessary to degrade urea, these hydrolytic enzymes should be involved. We proved the presence and enzymatic activity of a urease for Nepenthes plant tissues. The corresponding urease cDNA from N. hemsleyana was isolated and functionally expressed. A comprehensive phylogenetic analysis for eukaryotic ureases, including Nepenthes and five other carnivorous plants' taxa, identified them as canonical ureases and reflects the plant phylogeny. Hence, this study reveals ureases as an emblematic example for an efficient, low-cost but high adaptive plasticity in plants while developing a further specialized lifestyle from carnivory to coprophagy.

  @article{RN1033, abstract = {Most terrestrial carnivorous plants are specialized on insect prey digestion to obtain additional nutrients. Few species of the genus Nepenthes developed mutualistic relationships with mammals for nitrogen supplementation. Whether dietary changes require certain enzymatic composition to utilize new sources of nutrients has rarely been tested. Here, we investigated the role of urease for Nepenthes hemsleyana that gains nitrogen from the bat Kerivoula hardwickii while it roosts inside the pitchers. We hypothesized that N. hemsleyana is able to use urea from the bats' excrements. In fact, we demonstrate that N-15-enriched urea provided to Nepenthes pitchers is metabolized and its nitrogen is distributed within the plant. As ureases are necessary to degrade urea, these hydrolytic enzymes should be involved. We proved the presence and enzymatic activity of a urease for Nepenthes plant tissues. The corresponding urease cDNA from N. hemsleyana was isolated and functionally expressed. A comprehensive phylogenetic analysis for eukaryotic ureases, including Nepenthes and five other carnivorous plants' taxa, identified them as canonical ureases and reflects the plant phylogeny. Hence, this study reveals ureases as an emblematic example for an efficient, low-cost but high adaptive plasticity in plants while developing a further specialized lifestyle from carnivory to coprophagy.}, author = {Yilamujiang, A. and Zhu, A. T. and Ligabue-Braun, R. and Bartram, S. and Witte, C. P. and Hedrich, R. and Hasabe, M. and Schöner, C. R. and Schöner, M. G. and Kerth, G. and Carlini, C. R. and Mithöfer, A.}, journal = {Scientific Reports}, keywords = {functional-characterization}, note = {Fg9dz Times Cited:12 Cited References Count:56}, title = {Coprophagous features in carnivorous Nepenthes plants: a task for ureases}, type = {Journal Article}, volume = 7, year = 2017 }

  %0 Journal Article %1 RN1033 %A Yilamujiang, A. %A Zhu, A. T. %A Ligabue-Braun, R. %A Bartram, S. %A Witte, C. P. %A Hedrich, R. %A Hasabe, M. %A Schöner, C. R. %A Schöner, M. G. %A Kerth, G. %A Carlini, C. R. %A Mithöfer, A. %D 2017 %J Scientific Reports %R ARTN 11647 10.1038/s41598-017-11999-z %T Coprophagous features in carnivorous Nepenthes plants: a task for ureases %U /brokenurl#<Go to ISI>://WOS:000410740300002 %V 7 %X Most terrestrial carnivorous plants are specialized on insect prey digestion to obtain additional nutrients. Few species of the genus Nepenthes developed mutualistic relationships with mammals for nitrogen supplementation. Whether dietary changes require certain enzymatic composition to utilize new sources of nutrients has rarely been tested. Here, we investigated the role of urease for Nepenthes hemsleyana that gains nitrogen from the bat Kerivoula hardwickii while it roosts inside the pitchers. We hypothesized that N. hemsleyana is able to use urea from the bats' excrements. In fact, we demonstrate that N-15-enriched urea provided to Nepenthes pitchers is metabolized and its nitrogen is distributed within the plant. As ureases are necessary to degrade urea, these hydrolytic enzymes should be involved. We proved the presence and enzymatic activity of a urease for Nepenthes plant tissues. The corresponding urease cDNA from N. hemsleyana was isolated and functionally expressed. A comprehensive phylogenetic analysis for eukaryotic ureases, including Nepenthes and five other carnivorous plants' taxa, identified them as canonical ureases and reflects the plant phylogeny. Hence, this study reveals ureases as an emblematic example for an efficient, low-cost but high adaptive plasticity in plants while developing a further specialized lifestyle from carnivory to coprophagy.
• Biology of SLAC1-type anion channels - from nutrient uptake to stomatal closure. Hedrich, R.; Geiger, D. In New Phytologist, 216(1), pp. 46–61. 2017.
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  Stomatal guard cells control leaf CO2 intake and concomitant water loss to the atmosphere. When photosynthetic CO2 assimilation is limited and the ratio of CO2 intake to transpiration becomes suboptimal, guard cells, sensing the rise in CO2 concentration in the substomatal cavity, deflate and the stomata close. Screens for mutants that do not close in response to experimentally imposed high CO2 atmospheres identified the guard cell-expressed Slowly activating anion channel, SLAC1, as the key player in the regulation of stomatal closure. SLAC1 evolved, though, before the emergence of guard cells. In Arabidopsis, SLAC1 is the founder member of a family of anion channels, which comprises four homologues. SLAC1 and SLAH3 mediate chloride and nitrate transport in guard cells, while SLAH1, SLAH2 and SLAH3 are engaged in root nitrate and chloride acquisition, and anion translocation to the shoot. The signal transduction pathways involved in CO2, water stress and nutrient-sensing activate SLAC/SLAH via distinct protein kinase/phosphatase pairs. In this review, we discuss the role that SLAC/SLAH channels play in guard cell closure, on the one hand, and in the root-shoot continuum on the other, along with the molecular basis of the channels' anion selectivity and gating.

  @article{RN1042, abstract = {Stomatal guard cells control leaf CO2 intake and concomitant water loss to the atmosphere. When photosynthetic CO2 assimilation is limited and the ratio of CO2 intake to transpiration becomes suboptimal, guard cells, sensing the rise in CO2 concentration in the substomatal cavity, deflate and the stomata close. Screens for mutants that do not close in response to experimentally imposed high CO2 atmospheres identified the guard cell-expressed Slowly activating anion channel, SLAC1, as the key player in the regulation of stomatal closure. SLAC1 evolved, though, before the emergence of guard cells. In Arabidopsis, SLAC1 is the founder member of a family of anion channels, which comprises four homologues. SLAC1 and SLAH3 mediate chloride and nitrate transport in guard cells, while SLAH1, SLAH2 and SLAH3 are engaged in root nitrate and chloride acquisition, and anion translocation to the shoot. The signal transduction pathways involved in CO2, water stress and nutrient-sensing activate SLAC/SLAH via distinct protein kinase/phosphatase pairs. In this review, we discuss the role that SLAC/SLAH channels play in guard cell closure, on the one hand, and in the root-shoot continuum on the other, along with the molecular basis of the channels' anion selectivity and gating.}, author = {Hedrich, R. and Geiger, D.}, journal = {New Phytologist}, keywords = {signalling}, note = {Ff0kv Times Cited:90 Cited References Count:139}, number = 1, pages = {46-61}, title = {Biology of SLAC1-type anion channels - from nutrient uptake to stomatal closure}, type = {Journal Article}, volume = 216, year = 2017 }

  %0 Journal Article %1 RN1042 %A Hedrich, R. %A Geiger, D. %D 2017 %J New Phytologist %N 1 %P 46-61 %R 10.1111/nph.14685 %T Biology of SLAC1-type anion channels - from nutrient uptake to stomatal closure %U /brokenurl#<Go to ISI>://WOS:000408591500008 %V 216 %X Stomatal guard cells control leaf CO2 intake and concomitant water loss to the atmosphere. When photosynthetic CO2 assimilation is limited and the ratio of CO2 intake to transpiration becomes suboptimal, guard cells, sensing the rise in CO2 concentration in the substomatal cavity, deflate and the stomata close. Screens for mutants that do not close in response to experimentally imposed high CO2 atmospheres identified the guard cell-expressed Slowly activating anion channel, SLAC1, as the key player in the regulation of stomatal closure. SLAC1 evolved, though, before the emergence of guard cells. In Arabidopsis, SLAC1 is the founder member of a family of anion channels, which comprises four homologues. SLAC1 and SLAH3 mediate chloride and nitrate transport in guard cells, while SLAH1, SLAH2 and SLAH3 are engaged in root nitrate and chloride acquisition, and anion translocation to the shoot. The signal transduction pathways involved in CO2, water stress and nutrient-sensing activate SLAC/SLAH via distinct protein kinase/phosphatase pairs. In this review, we discuss the role that SLAC/SLAH channels play in guard cell closure, on the one hand, and in the root-shoot continuum on the other, along with the molecular basis of the channels' anion selectivity and gating.
• Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells. Scherzer, S.; Shabala, L.; Hedrich, B.; Fromm, J.; Bauer, H.; Munz, E.; Jakob, P.; Al-Rasheid, K. A. S.; Kreuzer, I.; Becker, D.; Eiblmeier, M.; Rennenberg, H.; Shabala, S.; Bennett, M.; Neher, E.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 114(18), pp. 4822–4827. 2017.
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  The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin's pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimuluscoupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl- fuse with the plasma membrane, hyperacidifying the "green stomach"-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.

  @article{RN1035, abstract = {The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin's pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimuluscoupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl- fuse with the plasma membrane, hyperacidifying the "green stomach"-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.}, author = {Scherzer, S. and Shabala, L. and Hedrich, B. and Fromm, J. and Bauer, H. and Munz, E. and Jakob, P. and Al-Rasheid, K. A. S. and Kreuzer, I. and Becker, D. and Eiblmeier, M. and Rennenberg, H. and Shabala, S. and Bennett, M. and Neher, E. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {myOwn}, note = {Et5vv Times Cited:39 Cited References Count:56}, number = 18, pages = {4822-4827}, title = {Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells}, type = {Journal Article}, volume = 114, year = 2017 }

  %0 Journal Article %1 RN1035 %A Scherzer, S. %A Shabala, L. %A Hedrich, B. %A Fromm, J. %A Bauer, H. %A Munz, E. %A Jakob, P. %A Al-Rasheid, K. A. S. %A Kreuzer, I. %A Becker, D. %A Eiblmeier, M. %A Rennenberg, H. %A Shabala, S. %A Bennett, M. %A Neher, E. %A Hedrich, R. %D 2017 %J Proceedings of the National Academy of Sciences of the United States of America %N 18 %P 4822-4827 %R 10.1073/pnas.1701860114 %T Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells %U /brokenurl#<Go to ISI>://WOS:000400358000068 %V 114 %X The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin's pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimuluscoupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl- fuse with the plasma membrane, hyperacidifying the "green stomach"-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.
• The fungal UmSrt1 and maize ZmSUT1 sucrose transporters battle for plant sugar resources. Wittek, A.; Dreyer, I.; Al-Rasheid, K. A. S.; Sauer, N.; Hedrich, R.; Geiger, D. In Journal of Integrative Plant Biology, 59(6), pp. 422–435. 2017.
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  The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize cells, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrt1 and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathosystem. Here we biophysically characterized ZmSUT1 and UmSrt1 in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT1, UmSrt1 has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrt1 exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concentration in the phloem appeared disadvantageous for the ZmSUT1, preventing sucrose recovery from the apoplastic space in the fungus/plant interface.

  @article{RN1034, abstract = {The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize cells, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrt1 and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathosystem. Here we biophysically characterized ZmSUT1 and UmSrt1 in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT1, UmSrt1 has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrt1 exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concentration in the phloem appeared disadvantageous for the ZmSUT1, preventing sucrose recovery from the apoplastic space in the fungus/plant interface.}, author = {Wittek, A. and Dreyer, I. and Al-Rasheid, K. A. S. and Sauer, N. and Hedrich, R. and Geiger, D.}, journal = {Journal of Integrative Plant Biology}, keywords = {monosaccharide}, note = {Sp. Iss. SI Ex1ww Times Cited:17 Cited References Count:51}, number = 6, pages = {422-435}, title = {The fungal UmSrt1 and maize ZmSUT1 sucrose transporters battle for plant sugar resources}, type = {Journal Article}, volume = 59, year = 2017 }

  %0 Journal Article %1 RN1034 %A Wittek, A. %A Dreyer, I. %A Al-Rasheid, K. A. S. %A Sauer, N. %A Hedrich, R. %A Geiger, D. %D 2017 %J Journal of Integrative Plant Biology %N 6 %P 422-435 %R 10.1111/jipb.12535 %T The fungal UmSrt1 and maize ZmSUT1 sucrose transporters battle for plant sugar resources %U /brokenurl#<Go to ISI>://WOS:000403018500006 %V 59 %X The biotrophic fungus Ustilago maydis causes corn smut disease, inducing tumor formation in its host Zea mays. Upon infection, the fungal hyphae invaginate the plasma membrane of infected maize cells, establishing an interface where pathogen and host are separated only by their plasma membranes. At this interface the fungal and maize sucrose transporters, UmSrt1 and ZmSUT1, compete for extracellular sucrose in the corn smut/maize pathosystem. Here we biophysically characterized ZmSUT1 and UmSrt1 in Xenopus oocytes with respect to their voltage-, pH- and substrate-dependence and determined affinities toward protons and sucrose. In contrast to ZmSUT1, UmSrt1 has a high affinity for sucrose and is relatively pH- and voltage-independent. Using these quantitative parameters, we developed a mathematical model to simulate the competition for extracellular sucrose at the contact zone between the fungus and the host plant. This approach revealed that UmSrt1 exploits the apoplastic sucrose resource, which forces the plant transporter into a sucrose export mode providing the fungus with sugar from the phloem. Importantly, the high sucrose concentration in the phloem appeared disadvantageous for the ZmSUT1, preventing sucrose recovery from the apoplastic space in the fungus/plant interface.
• Drought-Enhanced Xylem Sap Sulfate Closes Stomata by Affecting ALMT12 and Guard Cell ABA Synthesis. Malcheska, F.; Ahmad, A.; Batool, S.; Müller, H. M.; Ludwig-Mueller, J.; Kreuzwieser, J.; Randewig, D.; Hänsch, R.; Mendel, R. R.; Hell, R.; Wirtz, M.; Geiger, D.; Ache, P.; Hedrich, R.; Herschbach, C.; Rennenberg, H. In Plant Physiology, 174(2), pp. 798–814. 2017.
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  Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants (Populus x canescens) were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter (SULTR) expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and NCED3 were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (Arabidopsis thaliana). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, Atalmt12, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of NCED3, a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.

  @article{RN1039, abstract = {Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants (Populus x canescens) were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter (SULTR) expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and NCED3 were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (Arabidopsis thaliana). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, Atalmt12, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of NCED3, a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.}, author = {Malcheska, F. and Ahmad, A. and Batool, S. and Müller, H. M. and Ludwig-Mueller, J. and Kreuzwieser, J. and Randewig, D. and Hänsch, R. and Mendel, R. R. and Hell, R. and Wirtz, M. and Geiger, D. and Ache, P. and Hedrich, R. and Herschbach, C. and Rennenberg, H.}, journal = {Plant Physiology}, keywords = {abscisic-acid}, note = {Ex3sh Times Cited:78 Cited References Count:90}, number = 2, pages = {798-814}, title = {Drought-Enhanced Xylem Sap Sulfate Closes Stomata by Affecting ALMT12 and Guard Cell ABA Synthesis}, type = {Journal Article}, volume = 174, year = 2017 }

  %0 Journal Article %1 RN1039 %A Malcheska, F. %A Ahmad, A. %A Batool, S. %A Müller, H. M. %A Ludwig-Mueller, J. %A Kreuzwieser, J. %A Randewig, D. %A Hänsch, R. %A Mendel, R. R. %A Hell, R. %A Wirtz, M. %A Geiger, D. %A Ache, P. %A Hedrich, R. %A Herschbach, C. %A Rennenberg, H. %D 2017 %J Plant Physiology %N 2 %P 798-814 %R 10.1104/pp.16.01784 %T Drought-Enhanced Xylem Sap Sulfate Closes Stomata by Affecting ALMT12 and Guard Cell ABA Synthesis %U /brokenurl#<Go to ISI>://WOS:000403152200029 %V 174 %X Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants (Populus x canescens) were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter (SULTR) expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and NCED3 were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (Arabidopsis thaliana). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, Atalmt12, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of NCED3, a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.
• Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity. Lenglet, A.; Jaslan, D.; Toyota, M.; Müller, M.; Müller, T.; Schönknecht, G.; Marten, I.; Gilroy, S.; Hedrich, R.; Farmer, E. E. In New Phytologist, 216(4), pp. 1161–1169. 2017.
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  Unknown mechanisms tightly regulate the basal activity of the wound-inducible defence mediator jasmonate (JA) in undamaged tissues. However, the Arabidopsis fatty acid oxygenation upregulated2 (fou2) mutant in vacuolar two-pore channel 1 (TPC1(D454N)) displays high JA pathway activity in undamaged leaves. This mutant was used to explore mechanisms controlling basal JA pathway regulation. fou2 was re-mutated to generate novel 'ouf' suppressor mutants. Patch-clamping was used to examine TPC1 cation channel characteristics in the ouf suppressor mutants and in fou2. Calcium (Ca2+) imaging was used to study the effects fou2 on cytosolic Ca2+ concentrations. Six intragenic ouf suppressors with near wild-type (WT) JA pathway activity were recovered and one mutant, ouf8, affected the channel pore. At low luminal calcium concentrations, ouf8 had little detectable effect on fou2. However, increased vacuolar Ca2+ concentrations caused channel occlusion, selectively blocking K+ fluxes towards the cytoplasm. Cytosolic Ca2+ concentrations in unwounded fou2 were found to be lower than in the unwounded WT, but they increased in a similar manner in both genotypes following wounding. Basal JA pathway activity can be controlled solely by manipulating endomembrane cation flux capacities. We suggest that changes in endomembrane potential affect JA pathway activity.

  @article{RN1040, abstract = {Unknown mechanisms tightly regulate the basal activity of the wound-inducible defence mediator jasmonate (JA) in undamaged tissues. However, the Arabidopsis fatty acid oxygenation upregulated2 (fou2) mutant in vacuolar two-pore channel 1 (TPC1(D454N)) displays high JA pathway activity in undamaged leaves. This mutant was used to explore mechanisms controlling basal JA pathway regulation. fou2 was re-mutated to generate novel 'ouf' suppressor mutants. Patch-clamping was used to examine TPC1 cation channel characteristics in the ouf suppressor mutants and in fou2. Calcium (Ca2+) imaging was used to study the effects fou2 on cytosolic Ca2+ concentrations. Six intragenic ouf suppressors with near wild-type (WT) JA pathway activity were recovered and one mutant, ouf8, affected the channel pore. At low luminal calcium concentrations, ouf8 had little detectable effect on fou2. However, increased vacuolar Ca2+ concentrations caused channel occlusion, selectively blocking K+ fluxes towards the cytoplasm. Cytosolic Ca2+ concentrations in unwounded fou2 were found to be lower than in the unwounded WT, but they increased in a similar manner in both genotypes following wounding. Basal JA pathway activity can be controlled solely by manipulating endomembrane cation flux capacities. We suggest that changes in endomembrane potential affect JA pathway activity.}, author = {Lenglet, A. and Jaslan, D. and Toyota, M. and Müller, M. and Müller, T. and Schönknecht, G. and Marten, I. and Gilroy, S. and Hedrich, R. and Farmer, E. E.}, journal = {New Phytologist}, keywords = {calcium}, note = {Fm0gf Times Cited:34 Cited References Count:35}, number = 4, pages = {1161-1169}, title = {Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity}, type = {Journal Article}, volume = 216, year = 2017 }

  %0 Journal Article %1 RN1040 %A Lenglet, A. %A Jaslan, D. %A Toyota, M. %A Müller, M. %A Müller, T. %A Schönknecht, G. %A Marten, I. %A Gilroy, S. %A Hedrich, R. %A Farmer, E. E. %D 2017 %J New Phytologist %N 4 %P 1161-1169 %R 10.1111/nph.14754 %T Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity %U /brokenurl#<Go to ISI>://WOS:000414639800022 %V 216 %X Unknown mechanisms tightly regulate the basal activity of the wound-inducible defence mediator jasmonate (JA) in undamaged tissues. However, the Arabidopsis fatty acid oxygenation upregulated2 (fou2) mutant in vacuolar two-pore channel 1 (TPC1(D454N)) displays high JA pathway activity in undamaged leaves. This mutant was used to explore mechanisms controlling basal JA pathway regulation. fou2 was re-mutated to generate novel 'ouf' suppressor mutants. Patch-clamping was used to examine TPC1 cation channel characteristics in the ouf suppressor mutants and in fou2. Calcium (Ca2+) imaging was used to study the effects fou2 on cytosolic Ca2+ concentrations. Six intragenic ouf suppressors with near wild-type (WT) JA pathway activity were recovered and one mutant, ouf8, affected the channel pore. At low luminal calcium concentrations, ouf8 had little detectable effect on fou2. However, increased vacuolar Ca2+ concentrations caused channel occlusion, selectively blocking K+ fluxes towards the cytoplasm. Cytosolic Ca2+ concentrations in unwounded fou2 were found to be lower than in the unwounded WT, but they increased in a similar manner in both genotypes following wounding. Basal JA pathway activity can be controlled solely by manipulating endomembrane cation flux capacities. We suggest that changes in endomembrane potential affect JA pathway activity.
• Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet ( L.) source leaves. Nieberl, P.; Ehrl, C.; Pommerrenig, B.; Graus, D.; Marten, I.; Jung, B.; Ludewig, F.; Koch, W.; Harms, K.; Flügge, U. I.; Neuhaus, H. E.; Hedrich, R.; Sauer, N. In Plant Biology, 19(3), pp. 315–326. 2017.
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  Sugar beet (Beta vulgaris L.) is one of the most important sugar-producing plants worldwide and provides about one third of the sugar consumed by humans. Here we report on molecular characterisation of the BvSUT1 gene and on the functional characterisation of the encoded transporter. In contrast to the recently identified tonoplast-localised sucrose transporter BvTST2.1 from sugar beet taproots, which evolved within the monosaccharide transporter (MST) superfamily, BvSUT1 represents a classical sucrose transporter and is a typical member of the disaccharide transporter (DST) superfamily. Transgenic Arabidopsis plants expressing the -GLUCURONIDASE (GUS) reporter gene under control of the BvSUT1-promoter showed GUS histochemical staining of their phloem; an anti-BvSUT1-antiserum identified the BvSUT1 transporter specifically in phloem companion cells. After expression of BvSUT1 cDNA in bakers' yeasts (Saccharomyces cerevisiae) uptake characteristics of the BvSUT1 protein were studied. Moreover, the sugar beet transporter was characterised as a proton-coupled sucrose symporter in Xenopus laevis oocytes. Our findings indicate that BvSUT1 is the sucrose transporter that is responsible for loading of sucrose into the phloem of sugar beet source leaves delivering sucrose to the storage tissue in sugar beet taproot sinks.

  @article{RN1037, abstract = {Sugar beet (Beta vulgaris L.) is one of the most important sugar-producing plants worldwide and provides about one third of the sugar consumed by humans. Here we report on molecular characterisation of the BvSUT1 gene and on the functional characterisation of the encoded transporter. In contrast to the recently identified tonoplast-localised sucrose transporter BvTST2.1 from sugar beet taproots, which evolved within the monosaccharide transporter (MST) superfamily, BvSUT1 represents a classical sucrose transporter and is a typical member of the disaccharide transporter (DST) superfamily. Transgenic Arabidopsis plants expressing the -GLUCURONIDASE (GUS) reporter gene under control of the BvSUT1-promoter showed GUS histochemical staining of their phloem; an anti-BvSUT1-antiserum identified the BvSUT1 transporter specifically in phloem companion cells. After expression of BvSUT1 cDNA in bakers' yeasts (Saccharomyces cerevisiae) uptake characteristics of the BvSUT1 protein were studied. Moreover, the sugar beet transporter was characterised as a proton-coupled sucrose symporter in Xenopus laevis oocytes. Our findings indicate that BvSUT1 is the sucrose transporter that is responsible for loading of sucrose into the phloem of sugar beet source leaves delivering sucrose to the storage tissue in sugar beet taproot sinks.}, author = {Nieberl, P. and Ehrl, C. and Pommerrenig, B. and Graus, D. and Marten, I. and Jung, B. and Ludewig, F. and Koch, W. and Harms, K. and Flügge, U. I. and Neuhaus, H. E. and Hedrich, R. and Sauer, N.}, journal = {Plant Biology}, keywords = {bvsut1}, note = {Er3zl Times Cited:26 Cited References Count:57}, number = 3, pages = {315-326}, title = {Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet ( L.) source leaves}, type = {Journal Article}, volume = 19, year = 2017 }

  %0 Journal Article %1 RN1037 %A Nieberl, P. %A Ehrl, C. %A Pommerrenig, B. %A Graus, D. %A Marten, I. %A Jung, B. %A Ludewig, F. %A Koch, W. %A Harms, K. %A Flügge, U. I. %A Neuhaus, H. E. %A Hedrich, R. %A Sauer, N. %D 2017 %J Plant Biology %N 3 %P 315-326 %R 10.1111/plb.12546 %T Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet ( L.) source leaves %U /brokenurl#<Go to ISI>://WOS:000398738700001 %V 19 %X Sugar beet (Beta vulgaris L.) is one of the most important sugar-producing plants worldwide and provides about one third of the sugar consumed by humans. Here we report on molecular characterisation of the BvSUT1 gene and on the functional characterisation of the encoded transporter. In contrast to the recently identified tonoplast-localised sucrose transporter BvTST2.1 from sugar beet taproots, which evolved within the monosaccharide transporter (MST) superfamily, BvSUT1 represents a classical sucrose transporter and is a typical member of the disaccharide transporter (DST) superfamily. Transgenic Arabidopsis plants expressing the -GLUCURONIDASE (GUS) reporter gene under control of the BvSUT1-promoter showed GUS histochemical staining of their phloem; an anti-BvSUT1-antiserum identified the BvSUT1 transporter specifically in phloem companion cells. After expression of BvSUT1 cDNA in bakers' yeasts (Saccharomyces cerevisiae) uptake characteristics of the BvSUT1 protein were studied. Moreover, the sugar beet transporter was characterised as a proton-coupled sucrose symporter in Xenopus laevis oocytes. Our findings indicate that BvSUT1 is the sucrose transporter that is responsible for loading of sucrose into the phloem of sugar beet source leaves delivering sucrose to the storage tissue in sugar beet taproot sinks.
• The desert plant closes stomata via nitrate-regulated SLAC1 anion channel. Müller, H. M.; Schäfer, N.; Bauer, H.; Geiger, D.; Lautner, S.; Fromm, J.; Riederer, M.; Bueno, A.; Nussbaumer, T.; Mayer, K.; Alquraishi, S. A.; Alfarhan, A. H.; Neher, E.; Al-Rasheid, K. A. S.; Ache, P.; Hedrich, R. In New Phytologist, 216(1), pp. 150–162. 2017.
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  Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss? Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera. To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid (ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The Phoenix SLAC1-type anion channel is regulated by ABA kinase PdOST1. Energy-dispersive X-ray analysis (EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl- medium, PdOST1 did not activate the desert plant anion channel PdSLAC1 per se. Only when nitrate was present at the extracellular face of the anion channel did the OST1-gated PdSLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure. Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major anion channel SLAC1. This initiates guard cell depolarization and the release of anions together with potassium.

  @article{RN1038, abstract = {Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss? Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera. To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid (ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The Phoenix SLAC1-type anion channel is regulated by ABA kinase PdOST1. Energy-dispersive X-ray analysis (EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl- medium, PdOST1 did not activate the desert plant anion channel PdSLAC1 per se. Only when nitrate was present at the extracellular face of the anion channel did the OST1-gated PdSLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure. Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major anion channel SLAC1. This initiates guard cell depolarization and the release of anions together with potassium.}, author = {Müller, H. M. and Schäfer, N. and Bauer, H. and Geiger, D. and Lautner, S. and Fromm, J. and Riederer, M. and Bueno, A. and Nussbaumer, T. and Mayer, K. and Alquraishi, S. A. and Alfarhan, A. H. and Neher, E. and Al-Rasheid, K. A. S. and Ache, P. and Hedrich, R.}, journal = {New Phytologist}, keywords = {signalling}, note = {Ff0kv Times Cited:34 Cited References Count:67}, number = 1, pages = {150-162}, title = {The desert plant closes stomata via nitrate-regulated SLAC1 anion channel}, type = {Journal Article}, volume = 216, year = 2017 }

  %0 Journal Article %1 RN1038 %A Müller, H. M. %A Schäfer, N. %A Bauer, H. %A Geiger, D. %A Lautner, S. %A Fromm, J. %A Riederer, M. %A Bueno, A. %A Nussbaumer, T. %A Mayer, K. %A Alquraishi, S. A. %A Alfarhan, A. H. %A Neher, E. %A Al-Rasheid, K. A. S. %A Ache, P. %A Hedrich, R. %D 2017 %J New Phytologist %N 1 %P 150-162 %R 10.1111/nph.14672 %T The desert plant closes stomata via nitrate-regulated SLAC1 anion channel %U /brokenurl#<Go to ISI>://WOS:000408591500017 %V 216 %X Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss? Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera. To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid (ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The Phoenix SLAC1-type anion channel is regulated by ABA kinase PdOST1. Energy-dispersive X-ray analysis (EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl- medium, PdOST1 did not activate the desert plant anion channel PdSLAC1 per se. Only when nitrate was present at the extracellular face of the anion channel did the OST1-gated PdSLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure. Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major anion channel SLAC1. This initiates guard cell depolarization and the release of anions together with potassium.
• Epidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species. Kiani-Pouya, A.; Roessner, U.; Jayasinghe, N. S.; Lutz, A.; Rupasinghe, T.; Bazihizina, N.; Bohm, J.; Alharbi, S.; Hedrich, R.; Shabala, S. In Plant Cell and Environment, 40(9), pp. 1900–1915. 2017.
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  Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations.

  @article{RN1041, abstract = {Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations.}, author = {Kiani-Pouya, A. and Roessner, U. and Jayasinghe, N. S. and Lutz, A. and Rupasinghe, T. and Bazihizina, N. and Bohm, J. and Alharbi, S. and Hedrich, R. and Shabala, S.}, journal = {Plant Cell and Environment}, keywords = {epidermal}, note = {Fd8ad Times Cited:82 Cited References Count:83}, number = 9, pages = {1900-1915}, title = {Epidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species}, type = {Journal Article}, volume = 40, year = 2017 }

  %0 Journal Article %1 RN1041 %A Kiani-Pouya, A. %A Roessner, U. %A Jayasinghe, N. S. %A Lutz, A. %A Rupasinghe, T. %A Bazihizina, N. %A Bohm, J. %A Alharbi, S. %A Hedrich, R. %A Shabala, S. %D 2017 %J Plant Cell and Environment %N 9 %P 1900-1915 %R 10.1111/pce.12995 %T Epidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species %U /brokenurl#<Go to ISI>://WOS:000407746600019 %V 40 %X Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations.

• Do stomata of evolutionary distant species differ in sensitivity to environmental signals?. Roelfsema, M. R. G.; Hedrich, R. In New Phytologist, 211(3), pp. 767–770. 2016.
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  @article{RN1046, author = {Roelfsema, M. R. G. and Hedrich, R.}, journal = {New Phytologist}, keywords = {abscisic}, note = {Dr5ir Times Cited:6 Cited References Count:29}, number = 3, pages = {767-770}, title = {Do stomata of evolutionary distant species differ in sensitivity to environmental signals?}, type = {Journal Article}, volume = 211, year = 2016 }

  %0 Journal Article %1 RN1046 %A Roelfsema, M. R. G. %A Hedrich, R. %D 2016 %J New Phytologist %N 3 %P 767-770 %R 10.1111/nph.14074 %T Do stomata of evolutionary distant species differ in sensitivity to environmental signals? %U /brokenurl#<Go to ISI>://WOS:000379937200002 %V 211
• The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Crown Galls. Deeken, R.; Saupe, S.; Klinkenberg, J.; Riedel, M.; Leide, J.; Hedrich, R.; Mueller, T. D. In Plant Physiology, 172(3), pp. 1911–1927. 2016.
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  Nonspecific lipid transfer proteins reversibly bind different types of lipid molecules in a hydrophobic cavity. They facilitate phospholipid transfer between membranes in vitro, play a role in cuticle and possibly in suberin formation, and might be involved in plant pathogen defense signaling. This study focuses on the role of the lipid transfer protein AtLTPI-4 in crown gall development. Arabidopsis (Arabidopsis thaliana) crown gall tumors, which develop upon infection with the virulent Agrobacterium tumefaciens strain C-58, highly expressed AtLTPI-4. Crown galls of the atltpI-4 loss-of-function mutant were much smaller compared with those of wild-type plants. The gene expression pattern and localization of the protein to the plasma membrane pointed to a function of AtLTPI-4 in cell wall suberization. Since Arabidopsis crown galls are covered by a suberin-containing periderm instead of a cuticle, we analyzed the suberin composition of crown galls and found a reduction in the amounts of long-chain fatty acids (C-18:0) in the atltpI-4 mutant. To demonstrate the impact of AtLtpI-4 on extracellular lipid composition, we expressed the protein in Arabidopsis epidermis cells. This led to a significant increase in the very-long-chain fatty acids C-24 and C-26 in the cuticular wax fraction. Homology modeling and lipid-protein-overlay assays showed that AtLtpI-4 protein can bind these very-long-chain fatty acids. Thus, AtLtpI-4 protein may facilitate the transfer of long-chain as well as very-long-chain fatty acids into the apoplast, depending on the cell type in which it is expressed. In crown galls, which endogenously express AtLtpI-4, it is involved in suberin formation.

  @article{RN1052, abstract = {Nonspecific lipid transfer proteins reversibly bind different types of lipid molecules in a hydrophobic cavity. They facilitate phospholipid transfer between membranes in vitro, play a role in cuticle and possibly in suberin formation, and might be involved in plant pathogen defense signaling. This study focuses on the role of the lipid transfer protein AtLTPI-4 in crown gall development. Arabidopsis (Arabidopsis thaliana) crown gall tumors, which develop upon infection with the virulent Agrobacterium tumefaciens strain C-58, highly expressed AtLTPI-4. Crown galls of the atltpI-4 loss-of-function mutant were much smaller compared with those of wild-type plants. The gene expression pattern and localization of the protein to the plasma membrane pointed to a function of AtLTPI-4 in cell wall suberization. Since Arabidopsis crown galls are covered by a suberin-containing periderm instead of a cuticle, we analyzed the suberin composition of crown galls and found a reduction in the amounts of long-chain fatty acids (C-18:0) in the atltpI-4 mutant. To demonstrate the impact of AtLtpI-4 on extracellular lipid composition, we expressed the protein in Arabidopsis epidermis cells. This led to a significant increase in the very-long-chain fatty acids C-24 and C-26 in the cuticular wax fraction. Homology modeling and lipid-protein-overlay assays showed that AtLtpI-4 protein can bind these very-long-chain fatty acids. Thus, AtLtpI-4 protein may facilitate the transfer of long-chain as well as very-long-chain fatty acids into the apoplast, depending on the cell type in which it is expressed. In crown galls, which endogenously express AtLtpI-4, it is involved in suberin formation.}, author = {Deeken, R. and Saupe, S. and Klinkenberg, J. and Riedel, M. and Leide, J. and Hedrich, R. and Mueller, T. D.}, journal = {Plant Physiology}, keywords = {expression}, note = {Eg6qz Times Cited:50 Cited References Count:95}, number = 3, pages = {1911-1927}, title = {The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Crown Galls}, type = {Journal Article}, volume = 172, year = 2016 }

  %0 Journal Article %1 RN1052 %A Deeken, R. %A Saupe, S. %A Klinkenberg, J. %A Riedel, M. %A Leide, J. %A Hedrich, R. %A Mueller, T. D. %D 2016 %J Plant Physiology %N 3 %P 1911-1927 %R 10.1104/pp.16.01486 %T The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Crown Galls %U /brokenurl#<Go to ISI>://WOS:000391172300041 %V 172 %X Nonspecific lipid transfer proteins reversibly bind different types of lipid molecules in a hydrophobic cavity. They facilitate phospholipid transfer between membranes in vitro, play a role in cuticle and possibly in suberin formation, and might be involved in plant pathogen defense signaling. This study focuses on the role of the lipid transfer protein AtLTPI-4 in crown gall development. Arabidopsis (Arabidopsis thaliana) crown gall tumors, which develop upon infection with the virulent Agrobacterium tumefaciens strain C-58, highly expressed AtLTPI-4. Crown galls of the atltpI-4 loss-of-function mutant were much smaller compared with those of wild-type plants. The gene expression pattern and localization of the protein to the plasma membrane pointed to a function of AtLTPI-4 in cell wall suberization. Since Arabidopsis crown galls are covered by a suberin-containing periderm instead of a cuticle, we analyzed the suberin composition of crown galls and found a reduction in the amounts of long-chain fatty acids (C-18:0) in the atltpI-4 mutant. To demonstrate the impact of AtLtpI-4 on extracellular lipid composition, we expressed the protein in Arabidopsis epidermis cells. This led to a significant increase in the very-long-chain fatty acids C-24 and C-26 in the cuticular wax fraction. Homology modeling and lipid-protein-overlay assays showed that AtLtpI-4 protein can bind these very-long-chain fatty acids. Thus, AtLtpI-4 protein may facilitate the transfer of long-chain as well as very-long-chain fatty acids into the apoplast, depending on the cell type in which it is expressed. In crown galls, which endogenously express AtLtpI-4, it is involved in suberin formation.
• Venus Flytrap HKT1-Type Channel Provides for Prey Sodium Uptake into Carnivorous Plant Without Conflicting with Electrical Excitability. Böhm, J.; Scherzer, S.; Shabala, S.; Krol, E.; Neher, E.; Mueller, T. D.; Hedrich, R. In Molecular Plant, 9(3), pp. 428–436. 2016.
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  The animal diet of the carnivorous Venus flytrap, Dionaea muscipula, contains a sodium load that enters the capture organ via an HKT1-type sodium channel, expressed in special epithelia cells on the inner trap lobe surface. DmHKT1 expression and sodium uptake activity is induced upon prey contact. Here, we analyzed the HKT1 properties required for prey sodium osmolyte management of carnivorous Dionaea. Analyses were based on homology modeling, generation of model-derived point mutants, and their functional testing in Xenopus oocytes. We showed that the wild-type HKT1 and its Na+- and K+-permeable mutants function as ion channels rather than K+ transporters driven by proton or sodium gradients. These structural and biophysical features of a high-capacity, Na+-selective ion channel enable Dionaea glands to manage prey-derived sodium loads without confounding the action potential-based information management of the flytrap.

  @article{RN1054, abstract = {The animal diet of the carnivorous Venus flytrap, Dionaea muscipula, contains a sodium load that enters the capture organ via an HKT1-type sodium channel, expressed in special epithelia cells on the inner trap lobe surface. DmHKT1 expression and sodium uptake activity is induced upon prey contact. Here, we analyzed the HKT1 properties required for prey sodium osmolyte management of carnivorous Dionaea. Analyses were based on homology modeling, generation of model-derived point mutants, and their functional testing in Xenopus oocytes. We showed that the wild-type HKT1 and its Na+- and K+-permeable mutants function as ion channels rather than K+ transporters driven by proton or sodium gradients. These structural and biophysical features of a high-capacity, Na+-selective ion channel enable Dionaea glands to manage prey-derived sodium loads without confounding the action potential-based information management of the flytrap.}, author = {Böhm, J. and Scherzer, S. and Shabala, S. and Krol, E. and Neher, E. and Mueller, T. D. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {channel}, note = {Dg3nc Times Cited:44 Cited References Count:40}, number = 3, pages = {428-436}, title = {Venus Flytrap HKT1-Type Channel Provides for Prey Sodium Uptake into Carnivorous Plant Without Conflicting with Electrical Excitability}, type = {Journal Article}, volume = 9, year = 2016 }

  %0 Journal Article %1 RN1054 %A Böhm, J. %A Scherzer, S. %A Shabala, S. %A Krol, E. %A Neher, E. %A Mueller, T. D. %A Hedrich, R. %D 2016 %J Molecular Plant %N 3 %P 428-436 %R 10.1016/j.molp.2015.09.017 %T Venus Flytrap HKT1-Type Channel Provides for Prey Sodium Uptake into Carnivorous Plant Without Conflicting with Electrical Excitability %U /brokenurl#<Go to ISI>://WOS:000371975400009 %V 9 %X The animal diet of the carnivorous Venus flytrap, Dionaea muscipula, contains a sodium load that enters the capture organ via an HKT1-type sodium channel, expressed in special epithelia cells on the inner trap lobe surface. DmHKT1 expression and sodium uptake activity is induced upon prey contact. Here, we analyzed the HKT1 properties required for prey sodium osmolyte management of carnivorous Dionaea. Analyses were based on homology modeling, generation of model-derived point mutants, and their functional testing in Xenopus oocytes. We showed that the wild-type HKT1 and its Na+- and K+-permeable mutants function as ion channels rather than K+ transporters driven by proton or sodium gradients. These structural and biophysical features of a high-capacity, Na+-selective ion channel enable Dionaea glands to manage prey-derived sodium loads without confounding the action potential-based information management of the flytrap.
• Current Injection Provokes Rapid Expansion of the Guard Cell Cytosolic Volume and Triggers Ca Signals. Voss, L. J.; Hedrich, R.; Roelfsema, M. R. G. In Molecular Plant, 9(3), pp. 471–480. 2016.
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  High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca2+ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K+ uptake channels with Cs+, strongly suppressed the cytosolic volume changes. Cs+ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca2+ concentration. A complete loss of voltage-induced Ca2+ signals occurred when Ca2+-permeable plasma membrane channels were simultaneously blocked with La3+. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca2+-concentration: (i) activation of voltage-dependent Ca2+-permeable channels, (ii) osmotically induced expansion of the cytosol, which leads to a release of Ca2+ from intracellular stores.

  @article{RN1044, abstract = {High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca2+ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K+ uptake channels with Cs+, strongly suppressed the cytosolic volume changes. Cs+ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca2+ concentration. A complete loss of voltage-induced Ca2+ signals occurred when Ca2+-permeable plasma membrane channels were simultaneously blocked with La3+. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca2+-concentration: (i) activation of voltage-dependent Ca2+-permeable channels, (ii) osmotically induced expansion of the cytosol, which leads to a release of Ca2+ from intracellular stores.}, author = {Voss, L. J. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Molecular Plant}, keywords = {cell}, note = {Dg3nc Times Cited:9 Cited References Count:47}, number = 3, pages = {471-480}, title = {Current Injection Provokes Rapid Expansion of the Guard Cell Cytosolic Volume and Triggers Ca Signals}, type = {Journal Article}, volume = 9, year = 2016 }

  %0 Journal Article %1 RN1044 %A Voss, L. J. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2016 %J Molecular Plant %N 3 %P 471-480 %R 10.1016/j.molp.2016.02.004 %T Current Injection Provokes Rapid Expansion of the Guard Cell Cytosolic Volume and Triggers Ca Signals %U /brokenurl#<Go to ISI>://WOS:000371975400013 %V 9 %X High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca2+ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K+ uptake channels with Cs+, strongly suppressed the cytosolic volume changes. Cs+ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca2+ concentration. A complete loss of voltage-induced Ca2+ signals occurred when Ca2+-permeable plasma membrane channels were simultaneously blocked with La3+. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca2+-concentration: (i) activation of voltage-dependent Ca2+-permeable channels, (ii) osmotically induced expansion of the cytosol, which leads to a release of Ca2+ from intracellular stores.
• Abscisic acid controlled sex before transpiration in vascular plants. McAdam, S. A. M.; Brodribb, T. J.; Banks, J. A.; Hedrich, R.; Atallah, N. M.; Cai, C.; Geringer, M. A.; Lind, C.; Nichols, D. S.; Stachowski, K.; Geiger, D.; Sussmilch, F. C. In Proceedings of the National Academy of Sciences of the United States of America, 113(45), pp. 12862–12867. 2016.
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  Sexual reproduction in animals and plants shares common elements, including spermand egg production, but unlike animals, little is known about the regulatory pathways that determine the sex of plants. Here we use mutants and gene silencing in a fern species to identify a core regulatory mechanism in plant sexual differentiation. A key player in fern sex differentiation is the phytohormone abscisic acid (ABA), which regulates the sex ratio of male to hermaphrodite tissues during the reproductive cycle. Our analysis shows that in the fern Ceratopteris richardii, a gene homologous to core ABA transduction genes in flowering plants [SNF1-related kinase2s (SnRK2s)] is primarily responsible for the hormonal control of sex determination. Furthermore, we provide evidence that this ABA-SnRK2 signaling pathway has transitioned from determining the sex of ferns to controlling seed dormancy in the earliest seed plants before being co-opted to control transpiration and CO2 exchange in derived seed plants. By tracing the evolutionary history of this ABA signaling pathway from plant reproduction through to its role in the global regulation of plant-atmosphere gas exchange during the last 450 million years, we highlight the extraordinary effect of the ABA-SnRK2 signaling pathway in plant evolution and vegetation function.

  @article{RN1047, abstract = {Sexual reproduction in animals and plants shares common elements, including spermand egg production, but unlike animals, little is known about the regulatory pathways that determine the sex of plants. Here we use mutants and gene silencing in a fern species to identify a core regulatory mechanism in plant sexual differentiation. A key player in fern sex differentiation is the phytohormone abscisic acid (ABA), which regulates the sex ratio of male to hermaphrodite tissues during the reproductive cycle. Our analysis shows that in the fern Ceratopteris richardii, a gene homologous to core ABA transduction genes in flowering plants [SNF1-related kinase2s (SnRK2s)] is primarily responsible for the hormonal control of sex determination. Furthermore, we provide evidence that this ABA-SnRK2 signaling pathway has transitioned from determining the sex of ferns to controlling seed dormancy in the earliest seed plants before being co-opted to control transpiration and CO2 exchange in derived seed plants. By tracing the evolutionary history of this ABA signaling pathway from plant reproduction through to its role in the global regulation of plant-atmosphere gas exchange during the last 450 million years, we highlight the extraordinary effect of the ABA-SnRK2 signaling pathway in plant evolution and vegetation function.}, author = {McAdam, S. A. M. and Brodribb, T. J. and Banks, J. A. and Hedrich, R. and Atallah, N. M. and Cai, C. and Geringer, M. A. and Lind, C. and Nichols, D. S. and Stachowski, K. and Geiger, D. and Sussmilch, F. C.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {ost1}, note = {Ec4cl Times Cited:69 Cited References Count:43}, number = 45, pages = {12862-12867}, title = {Abscisic acid controlled sex before transpiration in vascular plants}, type = {Journal Article}, volume = 113, year = 2016 }

  %0 Journal Article %1 RN1047 %A McAdam, S. A. M. %A Brodribb, T. J. %A Banks, J. A. %A Hedrich, R. %A Atallah, N. M. %A Cai, C. %A Geringer, M. A. %A Lind, C. %A Nichols, D. S. %A Stachowski, K. %A Geiger, D. %A Sussmilch, F. C. %D 2016 %J Proceedings of the National Academy of Sciences of the United States of America %N 45 %P 12862-12867 %R 10.1073/pnas.1606614113 %T Abscisic acid controlled sex before transpiration in vascular plants %U /brokenurl#<Go to ISI>://WOS:000388073300083 %V 113 %X Sexual reproduction in animals and plants shares common elements, including spermand egg production, but unlike animals, little is known about the regulatory pathways that determine the sex of plants. Here we use mutants and gene silencing in a fern species to identify a core regulatory mechanism in plant sexual differentiation. A key player in fern sex differentiation is the phytohormone abscisic acid (ABA), which regulates the sex ratio of male to hermaphrodite tissues during the reproductive cycle. Our analysis shows that in the fern Ceratopteris richardii, a gene homologous to core ABA transduction genes in flowering plants [SNF1-related kinase2s (SnRK2s)] is primarily responsible for the hormonal control of sex determination. Furthermore, we provide evidence that this ABA-SnRK2 signaling pathway has transitioned from determining the sex of ferns to controlling seed dormancy in the earliest seed plants before being co-opted to control transpiration and CO2 exchange in derived seed plants. By tracing the evolutionary history of this ABA signaling pathway from plant reproduction through to its role in the global regulation of plant-atmosphere gas exchange during the last 450 million years, we highlight the extraordinary effect of the ABA-SnRK2 signaling pathway in plant evolution and vegetation function.
• Rainer Hedrich. Hedrich, R. In Current Biology, 26(23), pp. R1210-R1212. 2016.
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  @article{RN1051, author = {Hedrich, R.}, journal = {Current Biology}, keywords = {myOwn}, note = {Ee4qs Times Cited:0 Cited References Count:0}, number = 23, pages = {R1210-R1212}, title = {Rainer Hedrich}, type = {Journal Article}, volume = 26, year = 2016 }

  %0 Journal Article %1 RN1051 %A Hedrich, R. %D 2016 %J Current Biology %N 23 %P R1210-R1212 %R DOI 10.1016/j.cub.2016.10.002 %T Rainer Hedrich %U /brokenurl#<Go to ISI>://WOS:000389590500002 %V 26
• Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain. Jaslan, D.; Mueller, T. D.; Becker, D.; Schultz, J.; Cuin, T. A.; Marten, I.; Dreyer, I.; Schönknecht, G.; Hedrich, R. In Plant Biology, 18(5), pp. 750–760. 2016.
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  The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.

  @article{RN1048, abstract = {The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.}, author = {Jaslan, D. and Mueller, T. D. and Becker, D. and Schultz, J. and Cuin, T. A. and Marten, I. and Dreyer, I. and Schönknecht, G. and Hedrich, R.}, journal = {Plant Biology}, keywords = {arabidopsis}, note = {Ds8it Times Cited:16 Cited References Count:40}, number = 5, pages = {750-760}, title = {Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain}, type = {Journal Article}, volume = 18, year = 2016 }

  %0 Journal Article %1 RN1048 %A Jaslan, D. %A Mueller, T. D. %A Becker, D. %A Schultz, J. %A Cuin, T. A. %A Marten, I. %A Dreyer, I. %A Schönknecht, G. %A Hedrich, R. %D 2016 %J Plant Biology %N 5 %P 750-760 %R 10.1111/plb.12478 %T Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain %U /brokenurl#<Go to ISI>://WOS:000381027400002 %V 18 %X The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.
• Electrical Wiring and Long-Distance Plant Communication. Hedrich, R.; Salvador-Recatalà, V.; Dreyer, I. In Trends in Plant Science, 21(5), pp. 376–387. 2016.
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  Electrical signalling over long distances is an efficient way of achieving cell-to-cell communication in living organisms. In plants, the phloem can be considered as a 'green cable' that allows the transmission of action potentials (APs) induced by stimuli such as wounding and cold. Measuring phloem potential changes and separating them from secondary responses of surrounding tissues can be achieved using living aphids as bioelectrodes. Two glutamate receptor-like genes (GLR3.3 and 3.6) were identified as being involved in the propagation of electrical activity from the damaged to undamaged leaves. However, phloem APs are initiated and propagated independently of these glutamate receptors. Here, we propose new screening approaches to obtain further information on the components required for electrical signalling in phloem cables.

  @article{RN1050, abstract = {Electrical signalling over long distances is an efficient way of achieving cell-to-cell communication in living organisms. In plants, the phloem can be considered as a 'green cable' that allows the transmission of action potentials (APs) induced by stimuli such as wounding and cold. Measuring phloem potential changes and separating them from secondary responses of surrounding tissues can be achieved using living aphids as bioelectrodes. Two glutamate receptor-like genes (GLR3.3 and 3.6) were identified as being involved in the propagation of electrical activity from the damaged to undamaged leaves. However, phloem APs are initiated and propagated independently of these glutamate receptors. Here, we propose new screening approaches to obtain further information on the components required for electrical signalling in phloem cables.}, author = {Hedrich, R. and Salvador-Recatalà, V. and Dreyer, I.}, journal = {Trends in Plant Science}, keywords = {k+}, note = {Dl7hc Times Cited:151 Cited References Count:78}, number = 5, pages = {376-387}, title = {Electrical Wiring and Long-Distance Plant Communication}, type = {Journal Article}, volume = 21, year = 2016 }

  %0 Journal Article %1 RN1050 %A Hedrich, R. %A Salvador-Recatalà, V. %A Dreyer, I. %D 2016 %J Trends in Plant Science %N 5 %P 376-387 %R 10.1016/j.tplants.2016.01.016 %T Electrical Wiring and Long-Distance Plant Communication %U /brokenurl#<Go to ISI>://WOS:000375810600005 %V 21 %X Electrical signalling over long distances is an efficient way of achieving cell-to-cell communication in living organisms. In plants, the phloem can be considered as a 'green cable' that allows the transmission of action potentials (APs) induced by stimuli such as wounding and cold. Measuring phloem potential changes and separating them from secondary responses of surrounding tissues can be achieved using living aphids as bioelectrodes. Two glutamate receptor-like genes (GLR3.3 and 3.6) were identified as being involved in the propagation of electrical activity from the damaged to undamaged leaves. However, phloem APs are initiated and propagated independently of these glutamate receptors. Here, we propose new screening approaches to obtain further information on the components required for electrical signalling in phloem cables.
• Effectiveness of cuticular transpiration barriers in a desert plant at controlling water loss at high temperatures. Schuster, A. C.; Burghardt, M.; Alfarhan, A.; Bueno, A.; Hedrich, R.; Leide, J.; Thomas, J.; Riederer, M. In Aob Plants, 8. 2016.
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  Maintaining the integrity of the cuticular transpiration barrier even at elevated temperatures is of vital importance especially for hot-desert plants. Currently, the temperature dependence of the leaf cuticular water permeability and its relationship with the chemistry of the cuticles are not known for a single desert plant. This study investigates whether (i) the cuticular permeability of a desert plant is lower than that of species from non-desert habitats, (ii) the temperature-dependent increase of permeability is less pronounced than in those species and (iii) whether the susceptibility of the cuticular permeability barrier to high temperatures is related to the amounts or properties of the cutin or the cuticular waxes. We test these questions with Rhazya stricta using the minimum leaf water vapour conductance (g(min)) as a proxy for cuticular water permeability. g(min) of R. stricta (5.41 x 10 x 5 m s(-1) at 25 degrees C) is in the upper range of all existing data for woody species from various non-desert habitats. At the same time, in R. stricta, the effect of temperature (15-50 degrees C) on g(min) (2.4-fold) is lower than in all other species (up to 12-fold). Rhazya stricta is also special since the temperature dependence of g(min) does not become steeper above a certain transition temperature. For identifying the chemical and physical foundation of this phenomenon, the amounts and the compositions of cuticular waxes and cutin were determined. The leaf cuticular wax (251.4 mu g cm(-2)) is mainly composed of pentacyclic triterpenoids (85.2% of total wax) while long-chain aliphatics contribute only 3.4%. In comparison with many other species, the triterpenoid-to-cutin ratio of R. stricta (0.63) is high. We propose that the triterpenoids deposited within the cutin matrix restrict the thermal expansion of the polymer and, thus, prevent thermal damage to the highly ordered aliphatic wax barrier even at high temperatures.

  @article{RN1045, abstract = {Maintaining the integrity of the cuticular transpiration barrier even at elevated temperatures is of vital importance especially for hot-desert plants. Currently, the temperature dependence of the leaf cuticular water permeability and its relationship with the chemistry of the cuticles are not known for a single desert plant. This study investigates whether (i) the cuticular permeability of a desert plant is lower than that of species from non-desert habitats, (ii) the temperature-dependent increase of permeability is less pronounced than in those species and (iii) whether the susceptibility of the cuticular permeability barrier to high temperatures is related to the amounts or properties of the cutin or the cuticular waxes. We test these questions with Rhazya stricta using the minimum leaf water vapour conductance (g(min)) as a proxy for cuticular water permeability. g(min) of R. stricta (5.41 x 10 x 5 m s(-1) at 25 degrees C) is in the upper range of all existing data for woody species from various non-desert habitats. At the same time, in R. stricta, the effect of temperature (15-50 degrees C) on g(min) (2.4-fold) is lower than in all other species (up to 12-fold). Rhazya stricta is also special since the temperature dependence of g(min) does not become steeper above a certain transition temperature. For identifying the chemical and physical foundation of this phenomenon, the amounts and the compositions of cuticular waxes and cutin were determined. The leaf cuticular wax (251.4 mu g cm(-2)) is mainly composed of pentacyclic triterpenoids (85.2% of total wax) while long-chain aliphatics contribute only 3.4%. In comparison with many other species, the triterpenoid-to-cutin ratio of R. stricta (0.63) is high. We propose that the triterpenoids deposited within the cutin matrix restrict the thermal expansion of the polymer and, thus, prevent thermal damage to the highly ordered aliphatic wax barrier even at high temperatures.}, author = {Schuster, A. C. and Burghardt, M. and Alfarhan, A. and Bueno, A. and Hedrich, R. and Leide, J. and Thomas, J. and Riederer, M.}, journal = {Aob Plants}, keywords = {compounds}, note = {Ei1dd Times Cited:78 Cited References Count:72}, title = {Effectiveness of cuticular transpiration barriers in a desert plant at controlling water loss at high temperatures}, type = {Journal Article}, volume = 8, year = 2016 }

  %0 Journal Article %1 RN1045 %A Schuster, A. C. %A Burghardt, M. %A Alfarhan, A. %A Bueno, A. %A Hedrich, R. %A Leide, J. %A Thomas, J. %A Riederer, M. %D 2016 %J Aob Plants %R ARTN plw027 10.1093/aobpla/plw027 %T Effectiveness of cuticular transpiration barriers in a desert plant at controlling water loss at high temperatures %U /brokenurl#<Go to ISI>://WOS:000392215100001 %V 8 %X Maintaining the integrity of the cuticular transpiration barrier even at elevated temperatures is of vital importance especially for hot-desert plants. Currently, the temperature dependence of the leaf cuticular water permeability and its relationship with the chemistry of the cuticles are not known for a single desert plant. This study investigates whether (i) the cuticular permeability of a desert plant is lower than that of species from non-desert habitats, (ii) the temperature-dependent increase of permeability is less pronounced than in those species and (iii) whether the susceptibility of the cuticular permeability barrier to high temperatures is related to the amounts or properties of the cutin or the cuticular waxes. We test these questions with Rhazya stricta using the minimum leaf water vapour conductance (g(min)) as a proxy for cuticular water permeability. g(min) of R. stricta (5.41 x 10 x 5 m s(-1) at 25 degrees C) is in the upper range of all existing data for woody species from various non-desert habitats. At the same time, in R. stricta, the effect of temperature (15-50 degrees C) on g(min) (2.4-fold) is lower than in all other species (up to 12-fold). Rhazya stricta is also special since the temperature dependence of g(min) does not become steeper above a certain transition temperature. For identifying the chemical and physical foundation of this phenomenon, the amounts and the compositions of cuticular waxes and cutin were determined. The leaf cuticular wax (251.4 mu g cm(-2)) is mainly composed of pentacyclic triterpenoids (85.2% of total wax) while long-chain aliphatics contribute only 3.4%. In comparison with many other species, the triterpenoid-to-cutin ratio of R. stricta (0.63) is high. We propose that the triterpenoids deposited within the cutin matrix restrict the thermal expansion of the polymer and, thus, prevent thermal damage to the highly ordered aliphatic wax barrier even at high temperatures.
• Venus flytrap carnivorous lifestyle builds on herbivore defense strategies. Bemm, F.; Becker, D.; Larisch, C.; Kreuzer, I.; Escalante-Perez, M.; Schulze, W. X.; Ankenbrand, M.; Van de Weyer, A. L.; Krol, E.; Al-Rasheid, K. A.; Mithöfer, A.; Weber, A. P.; Schultz, J.; Hedrich, R. In Genome Research, 26(6), pp. 812–825. 2016.
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  Although the concept of botanical carnivory has been known since Darwin's time, the molecular mechanisms that allow animal feeding remain unknown, primarily due to a complete lack of genomic information. Here, we show that the transcriptomic landscape of the Dionaea trap is dramatically shifted toward signal transduction and nutrient transport upon insect feeding, with touch hormone signaling and protein secretion prevailing. At the same time, a massive induction of general defense responses is accompanied by the repression of cell death-related genes/processes. We hypothesize that the carnivory syndrome of Dionaea evolved by exaptation of ancient defense pathways, replacing cell death with nutrient acquisition.

  @article{RN1056, abstract = {Although the concept of botanical carnivory has been known since Darwin's time, the molecular mechanisms that allow animal feeding remain unknown, primarily due to a complete lack of genomic information. Here, we show that the transcriptomic landscape of the Dionaea trap is dramatically shifted toward signal transduction and nutrient transport upon insect feeding, with touch hormone signaling and protein secretion prevailing. At the same time, a massive induction of general defense responses is accompanied by the repression of cell death-related genes/processes. We hypothesize that the carnivory syndrome of Dionaea evolved by exaptation of ancient defense pathways, replacing cell death with nutrient acquisition.}, author = {Bemm, F. and Becker, D. and Larisch, C. and Kreuzer, I. and Escalante-Perez, M. and Schulze, W. X. and Ankenbrand, M. and Van de Weyer, A. L. and Krol, E. and Al-Rasheid, K. A. and Mithöfer, A. and Weber, A. P. and Schultz, J. and Hedrich, R.}, journal = {Genome Research}, keywords = {ellis}, note = {Dn5ey Times Cited:73 Cited References Count:105}, number = 6, pages = {812-825}, title = {Venus flytrap carnivorous lifestyle builds on herbivore defense strategies}, type = {Journal Article}, volume = 26, year = 2016 }

  %0 Journal Article %1 RN1056 %A Bemm, F. %A Becker, D. %A Larisch, C. %A Kreuzer, I. %A Escalante-Perez, M. %A Schulze, W. X. %A Ankenbrand, M. %A Van de Weyer, A. L. %A Krol, E. %A Al-Rasheid, K. A. %A Mithöfer, A. %A Weber, A. P. %A Schultz, J. %A Hedrich, R. %D 2016 %J Genome Research %N 6 %P 812-825 %R 10.1101/gr.202200.115 %T Venus flytrap carnivorous lifestyle builds on herbivore defense strategies %U /brokenurl#<Go to ISI>://WOS:000377090400009 %V 26 %X Although the concept of botanical carnivory has been known since Darwin's time, the molecular mechanisms that allow animal feeding remain unknown, primarily due to a complete lack of genomic information. Here, we show that the transcriptomic landscape of the Dionaea trap is dramatically shifted toward signal transduction and nutrient transport upon insect feeding, with touch hormone signaling and protein secretion prevailing. At the same time, a massive induction of general defense responses is accompanied by the repression of cell death-related genes/processes. We hypothesize that the carnivory syndrome of Dionaea evolved by exaptation of ancient defense pathways, replacing cell death with nutrient acquisition.
• SLAH3-type anion channel expressed in poplar secretory epithelia operates in calcium kinase CPK-autonomous manner. Jaborsky, M.; Maierhofer, T.; Olbrich, A.; Escalante-Pérez, M.; Müller, H. M.; Simon, J.; Krol, E.; Cuin, T. A.; Fromm, J.; Ache, P.; Geiger, D.; Hedrich, R. In New Phytologist, 210(3), pp. 922–933. 2016.
  • [ Abstract ]
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  Extrafloral nectaries secrete a sweet sugar cocktail that lures predator insects for protection from foraging herbivores. Apart from sugars and amino acids, the nectar contains the anions chloride and nitrate. Recent studies with Populus have identified a type of nectary covered by apical bipolar epidermal cells, reminiscent of the secretory brush border epithelium in animals. Border epithelia operate transepithelial anion transport, which is required for membrane potential and/or osmotic adjustment of the secretory cells. In search of anion transporters expressed in extrafloral nectaries, we identified PttSLAH3 (Populus tremulaxPopulustremuloides SLAC1 Homologue3), an anion channel of the SLAC/SLAH family. When expressed in Xenopus oocytes, PttSLAH3 displayed the features of a voltage-dependent anion channel, permeable to both nitrate and chloride. In contrast to the Arabidopsis SLAC/SLAH family members, the poplar isoform PttSLAH3 is independent of phosphorylation activation by protein kinases. To understand the basis for the autonomous activity of the poplar SLAH3, we generated and expressed chimera between kinase-independent PttSLAH3 and kinase-dependent Arabidopsis AtSLAH3. We identified the N-terminal tail and, to a lesser extent, the C-terminal tail as responsible for PttSLAH3 kinase-(in)dependent action. This feature of PttSLAH3 may provide the secretory cell with a channel probably controlling long-term nectar secretion.

  @article{RN1049, abstract = {Extrafloral nectaries secrete a sweet sugar cocktail that lures predator insects for protection from foraging herbivores. Apart from sugars and amino acids, the nectar contains the anions chloride and nitrate. Recent studies with Populus have identified a type of nectary covered by apical bipolar epidermal cells, reminiscent of the secretory brush border epithelium in animals. Border epithelia operate transepithelial anion transport, which is required for membrane potential and/or osmotic adjustment of the secretory cells. In search of anion transporters expressed in extrafloral nectaries, we identified PttSLAH3 (Populus tremulaxPopulustremuloides SLAC1 Homologue3), an anion channel of the SLAC/SLAH family. When expressed in Xenopus oocytes, PttSLAH3 displayed the features of a voltage-dependent anion channel, permeable to both nitrate and chloride. In contrast to the Arabidopsis SLAC/SLAH family members, the poplar isoform PttSLAH3 is independent of phosphorylation activation by protein kinases. To understand the basis for the autonomous activity of the poplar SLAH3, we generated and expressed chimera between kinase-independent PttSLAH3 and kinase-dependent Arabidopsis AtSLAH3. We identified the N-terminal tail and, to a lesser extent, the C-terminal tail as responsible for PttSLAH3 kinase-(in)dependent action. This feature of PttSLAH3 may provide the secretory cell with a channel probably controlling long-term nectar secretion.}, author = {Jaborsky, M. and Maierhofer, T. and Olbrich, A. and Escalante-Pérez, M. and Müller, H. M. and Simon, J. and Krol, E. and Cuin, T. A. and Fromm, J. and Ache, P. and Geiger, D. and Hedrich, R.}, journal = {New Phytologist}, keywords = {channels}, note = {Dj5ym Times Cited:14 Cited References Count:45}, number = 3, pages = {922-933}, title = {SLAH3-type anion channel expressed in poplar secretory epithelia operates in calcium kinase CPK-autonomous manner}, type = {Journal Article}, volume = 210, year = 2016 }

  %0 Journal Article %1 RN1049 %A Jaborsky, M. %A Maierhofer, T. %A Olbrich, A. %A Escalante-Pérez, M. %A Müller, H. M. %A Simon, J. %A Krol, E. %A Cuin, T. A. %A Fromm, J. %A Ache, P. %A Geiger, D. %A Hedrich, R. %D 2016 %J New Phytologist %N 3 %P 922-933 %R 10.1111/nph.13841 %T SLAH3-type anion channel expressed in poplar secretory epithelia operates in calcium kinase CPK-autonomous manner %U /brokenurl#<Go to ISI>://WOS:000374286700017 %V 210 %X Extrafloral nectaries secrete a sweet sugar cocktail that lures predator insects for protection from foraging herbivores. Apart from sugars and amino acids, the nectar contains the anions chloride and nitrate. Recent studies with Populus have identified a type of nectary covered by apical bipolar epidermal cells, reminiscent of the secretory brush border epithelium in animals. Border epithelia operate transepithelial anion transport, which is required for membrane potential and/or osmotic adjustment of the secretory cells. In search of anion transporters expressed in extrafloral nectaries, we identified PttSLAH3 (Populus tremulaxPopulustremuloides SLAC1 Homologue3), an anion channel of the SLAC/SLAH family. When expressed in Xenopus oocytes, PttSLAH3 displayed the features of a voltage-dependent anion channel, permeable to both nitrate and chloride. In contrast to the Arabidopsis SLAC/SLAH family members, the poplar isoform PttSLAH3 is independent of phosphorylation activation by protein kinases. To understand the basis for the autonomous activity of the poplar SLAH3, we generated and expressed chimera between kinase-independent PttSLAH3 and kinase-dependent Arabidopsis AtSLAH3. We identified the N-terminal tail and, to a lesser extent, the C-terminal tail as responsible for PttSLAH3 kinase-(in)dependent action. This feature of PttSLAH3 may provide the secretory cell with a channel probably controlling long-term nectar secretion.
• The Venus Flytrap Counts Prey-Induced Action Potentials to Induce Sodium Uptake. Böhm, J.; Scherzer, S.; Krol, E.; Kreuzer, I.; von Meyer, K.; Lorey, C.; Mueller, T. D.; Shabala, L.; Monte, I.; Solano, R.; Al-Rasheid, K. A. S.; Rennenberg, H.; Shabala, S.; Neher, E.; Hedrich, R. In Current Biology, 26(3), pp. 286–295. 2016.
  • [ Abstract ]
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  Carnivorous plants, such as the Venus flytrap (Dionaea muscipula), depend on an animal diet when grown in nutrient-poor soils. When an insect visits the trap and tilts the mechanosensors on the inner surface, action potentials (APs) are fired. After a moving object elicits two APs, the trap snaps shut, encaging the victim. Panicking preys repeatedly touch the trigger hairs over the subsequent hours, leading to a hermetically closed trap, which via the gland-based endocrine system is flooded by a prey-decomposing acidic enzyme cocktail. Here, we asked the question as to how many times trigger hairs have to be stimulated (e.g., now many APs are required) for the flytrap to recognize an encaged object as potential food, thus making it worthwhile activating the glands. By applying a series of trigger-hair stimulations, we found that the touch hormone jasmonic acid (JA) signaling pathway is activated after the second stimulus, while more than three APs are required to trigger an expression of genes encoding prey-degrading hydrolases, and that this expression is proportional to the number of mechanical stimulations. A decomposing animal contains a sodium load, and we have found that these sodium ions enter the capture organ via glands. We identified a flytrap sodium channel DmHKT1 as responsible for this sodium acquisition, with the number of transcripts expressed being dependent on the number of mechano-electric stimulations. Hence, the number of APs a victim triggers while trying to break out of the trap identifies the moving prey as a struggling Na+-rich animal and nutrition for the plant.

  @article{RN1055, abstract = {Carnivorous plants, such as the Venus flytrap (Dionaea muscipula), depend on an animal diet when grown in nutrient-poor soils. When an insect visits the trap and tilts the mechanosensors on the inner surface, action potentials (APs) are fired. After a moving object elicits two APs, the trap snaps shut, encaging the victim. Panicking preys repeatedly touch the trigger hairs over the subsequent hours, leading to a hermetically closed trap, which via the gland-based endocrine system is flooded by a prey-decomposing acidic enzyme cocktail. Here, we asked the question as to how many times trigger hairs have to be stimulated (e.g., now many APs are required) for the flytrap to recognize an encaged object as potential food, thus making it worthwhile activating the glands. By applying a series of trigger-hair stimulations, we found that the touch hormone jasmonic acid (JA) signaling pathway is activated after the second stimulus, while more than three APs are required to trigger an expression of genes encoding prey-degrading hydrolases, and that this expression is proportional to the number of mechanical stimulations. A decomposing animal contains a sodium load, and we have found that these sodium ions enter the capture organ via glands. We identified a flytrap sodium channel DmHKT1 as responsible for this sodium acquisition, with the number of transcripts expressed being dependent on the number of mechano-electric stimulations. Hence, the number of APs a victim triggers while trying to break out of the trap identifies the moving prey as a struggling Na+-rich animal and nutrition for the plant.}, author = {Böhm, J. and Scherzer, S. and Krol, E. and Kreuzer, I. and von Meyer, K. and Lorey, C. and Mueller, T. D. and Shabala, L. and Monte, I. and Solano, R. and Al-Rasheid, K. A. S. and Rennenberg, H. and Shabala, S. and Neher, E. and Hedrich, R.}, journal = {Current Biology}, keywords = {jasmonic}, note = {Dc8xi Times Cited:106 Cited References Count:71}, number = 3, pages = {286-295}, title = {The Venus Flytrap Counts Prey-Induced Action Potentials to Induce Sodium Uptake}, type = {Journal Article}, volume = 26, year = 2016 }

  %0 Journal Article %1 RN1055 %A Böhm, J. %A Scherzer, S. %A Krol, E. %A Kreuzer, I. %A von Meyer, K. %A Lorey, C. %A Mueller, T. D. %A Shabala, L. %A Monte, I. %A Solano, R. %A Al-Rasheid, K. A. S. %A Rennenberg, H. %A Shabala, S. %A Neher, E. %A Hedrich, R. %D 2016 %J Current Biology %N 3 %P 286-295 %R 10.1016/j.cub.2015.11.057 %T The Venus Flytrap Counts Prey-Induced Action Potentials to Induce Sodium Uptake %U /brokenurl#<Go to ISI>://WOS:000369502900019 %V 26 %X Carnivorous plants, such as the Venus flytrap (Dionaea muscipula), depend on an animal diet when grown in nutrient-poor soils. When an insect visits the trap and tilts the mechanosensors on the inner surface, action potentials (APs) are fired. After a moving object elicits two APs, the trap snaps shut, encaging the victim. Panicking preys repeatedly touch the trigger hairs over the subsequent hours, leading to a hermetically closed trap, which via the gland-based endocrine system is flooded by a prey-decomposing acidic enzyme cocktail. Here, we asked the question as to how many times trigger hairs have to be stimulated (e.g., now many APs are required) for the flytrap to recognize an encaged object as potential food, thus making it worthwhile activating the glands. By applying a series of trigger-hair stimulations, we found that the touch hormone jasmonic acid (JA) signaling pathway is activated after the second stimulus, while more than three APs are required to trigger an expression of genes encoding prey-degrading hydrolases, and that this expression is proportional to the number of mechanical stimulations. A decomposing animal contains a sodium load, and we have found that these sodium ions enter the capture organ via glands. We identified a flytrap sodium channel DmHKT1 as responsible for this sodium acquisition, with the number of transcripts expressed being dependent on the number of mechano-electric stimulations. Hence, the number of APs a victim triggers while trying to break out of the trap identifies the moving prey as a struggling Na+-rich animal and nutrition for the plant.
• Acclimation to heat and drought-Lessons to learn from the date palm ( ). Arab, L.; Kreuzwieser, J.; Kruse, J.; Zimmer, I.; Ache, P.; Alfarraj, S.; Al-Rasheid, K. A. S.; Schnitzler, J. P.; Hedrich, R.; Rennenberg, H. In Environmental and Experimental Botany, 125, pp. 20–30. 2016.
  • [ Abstract ]
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  In the present study, we investigated the responses of date palm (Phoenix dactylifera) to drought and heat as single stressors and in combination. We tested the hypotheses (i) that heat and drought enhance the capacity of the antioxidative system, and (ii) that due to the high stress tolerance of date palm, the plants' redox state will be widely unaffected, and (iii) that heat but not drought changes the plants' fatty acid composition and biosynthesis of isoprene, both contributing to the stabilization of membrane integrity. Photosynthesis was only weakly affected by both stresses, whereas the levels of the antioxidants ascorbate and glutathione in leaves dropped. This drop was, however, over-compensated by increased activities of glutathione reductase, an important enzyme of the antioxidative system. The plants' redox state was unaffected by stress as indicated by unchanged H2O2 levels. Because we do not know the concentration of isoprene at its site of action, isoprene emission might provide indirect hints on its possible functions. Isoprene emission strongly increased due to heat indicating its possible role as an antioxidant and for stabilization of thylakoid membranes. Fatty acids only reacted in response to drought. We conclude that the high heat and drought tolerance of date palm is the consequence of a concerted action of the antioxidative system, mainly based on enzyme activities and the assumed antioxidative effects of isoprene as well as adjustments in the fatty acid composition. (C) 2016 Elsevier B.V. All rights reserved.

  @article{RN1057, abstract = {In the present study, we investigated the responses of date palm (Phoenix dactylifera) to drought and heat as single stressors and in combination. We tested the hypotheses (i) that heat and drought enhance the capacity of the antioxidative system, and (ii) that due to the high stress tolerance of date palm, the plants' redox state will be widely unaffected, and (iii) that heat but not drought changes the plants' fatty acid composition and biosynthesis of isoprene, both contributing to the stabilization of membrane integrity. Photosynthesis was only weakly affected by both stresses, whereas the levels of the antioxidants ascorbate and glutathione in leaves dropped. This drop was, however, over-compensated by increased activities of glutathione reductase, an important enzyme of the antioxidative system. The plants' redox state was unaffected by stress as indicated by unchanged H2O2 levels. Because we do not know the concentration of isoprene at its site of action, isoprene emission might provide indirect hints on its possible functions. Isoprene emission strongly increased due to heat indicating its possible role as an antioxidant and for stabilization of thylakoid membranes. Fatty acids only reacted in response to drought. We conclude that the high heat and drought tolerance of date palm is the consequence of a concerted action of the antioxidative system, mainly based on enzyme activities and the assumed antioxidative effects of isoprene as well as adjustments in the fatty acid composition. (C) 2016 Elsevier B.V. All rights reserved.}, author = {Arab, L. and Kreuzwieser, J. and Kruse, J. and Zimmer, I. and Ache, P. and Alfarraj, S. and Al-Rasheid, K. A. S. and Schnitzler, J. P. and Hedrich, R. and Rennenberg, H.}, journal = {Environmental and Experimental Botany}, keywords = {ascorbate}, note = {Dh3kg Times Cited:43 Cited References Count:50}, pages = {20-30}, title = {Acclimation to heat and drought-Lessons to learn from the date palm ( )}, type = {Journal Article}, volume = 125, year = 2016 }

  %0 Journal Article %1 RN1057 %A Arab, L. %A Kreuzwieser, J. %A Kruse, J. %A Zimmer, I. %A Ache, P. %A Alfarraj, S. %A Al-Rasheid, K. A. S. %A Schnitzler, J. P. %A Hedrich, R. %A Rennenberg, H. %D 2016 %J Environmental and Experimental Botany %P 20-30 %R 10.1016/j.envexpbot.2016.01.003 %T Acclimation to heat and drought-Lessons to learn from the date palm ( ) %U /brokenurl#<Go to ISI>://WOS:000372685300003 %V 125 %X In the present study, we investigated the responses of date palm (Phoenix dactylifera) to drought and heat as single stressors and in combination. We tested the hypotheses (i) that heat and drought enhance the capacity of the antioxidative system, and (ii) that due to the high stress tolerance of date palm, the plants' redox state will be widely unaffected, and (iii) that heat but not drought changes the plants' fatty acid composition and biosynthesis of isoprene, both contributing to the stabilization of membrane integrity. Photosynthesis was only weakly affected by both stresses, whereas the levels of the antioxidants ascorbate and glutathione in leaves dropped. This drop was, however, over-compensated by increased activities of glutathione reductase, an important enzyme of the antioxidative system. The plants' redox state was unaffected by stress as indicated by unchanged H2O2 levels. Because we do not know the concentration of isoprene at its site of action, isoprene emission might provide indirect hints on its possible functions. Isoprene emission strongly increased due to heat indicating its possible role as an antioxidant and for stabilization of thylakoid membranes. Fatty acids only reacted in response to drought. We conclude that the high heat and drought tolerance of date palm is the consequence of a concerted action of the antioxidative system, mainly based on enzyme activities and the assumed antioxidative effects of isoprene as well as adjustments in the fatty acid composition. (C) 2016 Elsevier B.V. All rights reserved.
• Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation. Cubero-Font, P.; Maierhofer, T.; Jaslan, J.; Rosales, M. A.; Espartero, J.; Diaz-Rueda, P.; Müller, H. M.; Hürter, A. L.; AL-Rasheid, K. A. S.; Marten, I.; Hedrich, R.; Colmenero-Flores, J. M.; Geiger, D. In Current Biology, 26(16), pp. 2213–2220. 2016.
  • [ Abstract ]
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  Higher plants take up nutrients via the roots and load them into xylem vessels for translocation to the shoot. After uptake, anions have to be channeled toward the root xylem vessels. Thereby, xylem parenchyma and pericycle cells control the anion composition of the root-shoot xylem sap [1-6]. The fact that salt-tolerant genotypes possess lower xylem-sap Cl- contents compared to salt-sensitive genotypes [7-10] indicates that membrane transport proteins at the sites of xylem loading contribute to plant salinity tolerance via selective chloride exclusion. However, the molecular mechanism of xylem loading that lies behind the balance between NO3- and Cl- loading remains largely unknown. Here we identify two root anion channels in Arabidopsis, SLAH1 and SLAH3, that control the shoot NO3-/Cl- ratio. The AtSLAH1 gene is expressed in the root xylem-pole pericycle, where it co-localizes with AtSLAH3. Under high soil salinity, AtSLAH1 expression markedly declined and the chloride content of the xylem sap in AtSLAH1 loss-of-function mutants was half of the wild-type level only. SLAH3 anion channels are not active per se but require extracellular nitrate and phosphorylation by calcium-dependent kinases (CPKs) [11-13]. When co-expressed in Xenopus oocytes, however, the electrically silent SLAH1 subunit gates SLAH3 open even in the absence of nitrate- and calcium-dependent kinases. Apparently, SLAH1/SLAH3 heteromerization facilitates SLAH3-mediated chloride efflux from pericycle cells into the root xylem vessels. Our results indicate that under salt stress, plants adjust the distribution of NO3- and Cl- between root and shoot via differential expression and assembly of SLAH1/SLAH3 anion channel subunits.

  @article{RN1053, abstract = {Higher plants take up nutrients via the roots and load them into xylem vessels for translocation to the shoot. After uptake, anions have to be channeled toward the root xylem vessels. Thereby, xylem parenchyma and pericycle cells control the anion composition of the root-shoot xylem sap [1-6]. The fact that salt-tolerant genotypes possess lower xylem-sap Cl- contents compared to salt-sensitive genotypes [7-10] indicates that membrane transport proteins at the sites of xylem loading contribute to plant salinity tolerance via selective chloride exclusion. However, the molecular mechanism of xylem loading that lies behind the balance between NO3- and Cl- loading remains largely unknown. Here we identify two root anion channels in Arabidopsis, SLAH1 and SLAH3, that control the shoot NO3-/Cl- ratio. The AtSLAH1 gene is expressed in the root xylem-pole pericycle, where it co-localizes with AtSLAH3. Under high soil salinity, AtSLAH1 expression markedly declined and the chloride content of the xylem sap in AtSLAH1 loss-of-function mutants was half of the wild-type level only. SLAH3 anion channels are not active per se but require extracellular nitrate and phosphorylation by calcium-dependent kinases (CPKs) [11-13]. When co-expressed in Xenopus oocytes, however, the electrically silent SLAH1 subunit gates SLAH3 open even in the absence of nitrate- and calcium-dependent kinases. Apparently, SLAH1/SLAH3 heteromerization facilitates SLAH3-mediated chloride efflux from pericycle cells into the root xylem vessels. Our results indicate that under salt stress, plants adjust the distribution of NO3- and Cl- between root and shoot via differential expression and assembly of SLAH1/SLAH3 anion channel subunits.}, author = {Cubero-Font, P. and Maierhofer, T. and Jaslan, J. and Rosales, M. A. and Espartero, J. and Diaz-Rueda, P. and Müller, H. M. and Hürter, A. L. and AL-Rasheid, K. A. S. and Marten, I. and Hedrich, R. and Colmenero-Flores, J. M. and Geiger, D.}, journal = {Current Biology}, keywords = {citrus}, note = {Du3fo Times Cited:80 Cited References Count:40}, number = 16, pages = {2213-2220}, title = {Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation}, type = {Journal Article}, volume = 26, year = 2016 }

  %0 Journal Article %1 RN1053 %A Cubero-Font, P. %A Maierhofer, T. %A Jaslan, J. %A Rosales, M. A. %A Espartero, J. %A Diaz-Rueda, P. %A Müller, H. M. %A Hürter, A. L. %A AL-Rasheid, K. A. S. %A Marten, I. %A Hedrich, R. %A Colmenero-Flores, J. M. %A Geiger, D. %D 2016 %J Current Biology %N 16 %P 2213-2220 %R 10.1016/j.cub.2016.06.045 %T Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation %U /brokenurl#<Go to ISI>://WOS:000382096400034 %V 26 %X Higher plants take up nutrients via the roots and load them into xylem vessels for translocation to the shoot. After uptake, anions have to be channeled toward the root xylem vessels. Thereby, xylem parenchyma and pericycle cells control the anion composition of the root-shoot xylem sap [1-6]. The fact that salt-tolerant genotypes possess lower xylem-sap Cl- contents compared to salt-sensitive genotypes [7-10] indicates that membrane transport proteins at the sites of xylem loading contribute to plant salinity tolerance via selective chloride exclusion. However, the molecular mechanism of xylem loading that lies behind the balance between NO3- and Cl- loading remains largely unknown. Here we identify two root anion channels in Arabidopsis, SLAH1 and SLAH3, that control the shoot NO3-/Cl- ratio. The AtSLAH1 gene is expressed in the root xylem-pole pericycle, where it co-localizes with AtSLAH3. Under high soil salinity, AtSLAH1 expression markedly declined and the chloride content of the xylem sap in AtSLAH1 loss-of-function mutants was half of the wild-type level only. SLAH3 anion channels are not active per se but require extracellular nitrate and phosphorylation by calcium-dependent kinases (CPKs) [11-13]. When co-expressed in Xenopus oocytes, however, the electrically silent SLAH1 subunit gates SLAH3 open even in the absence of nitrate- and calcium-dependent kinases. Apparently, SLAH1/SLAH3 heteromerization facilitates SLAH3-mediated chloride efflux from pericycle cells into the root xylem vessels. Our results indicate that under salt stress, plants adjust the distribution of NO3- and Cl- between root and shoot via differential expression and assembly of SLAH1/SLAH3 anion channel subunits.

• Stomatal Guard Cells Co-opted an Ancient ABA-Dependent Desiccation Survival System to Regulate Stomatal Closure. Lind, C.; Dreyer, I.; López-Sanjurjo, E. J.; von Meyer, K.; Ishizaki, K.; Kohchi, T.; Lang, D.; Zhao, Y.; Kreuzer, I.; Al-Rasheid, K. A. S.; Ronne, H.; Reski, R.; Zhu, J. K.; Geiger, D.; Hedrich, R. In Current Biology, 25(7), pp. 928–935. 2015.
  • [ Abstract ]
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  During the transition from water to land, plants had to cope with the loss of water through transpiration, the inevitable result of photosynthetic CO2 fixation on land [1, 2]. Control of transpiration became possible through the development of a new cell type: guard cells, which form stomata. In vascular plants, stomatal regulation is mediated by the stress hormone ABA, which triggers the opening of the SnR kinase OST1-activated anion channel SLAC1 [3, 4]. To understand the evolution of this regulatory circuit, we cloned both ABA-signaling elements, SLAC1 and OST1, from a charophyte alga, a liverwort, and a moss, and functionally analyzed the channel-kinase interactions. We were able to show that the emergence of stomata in the last common ancestor of mosses and vascular plants coincided with the origin of SLAC1-type channels capable of using the ancient ABA drought signaling kinase OST1 for regulation of stomatal closure.

  @article{RN1062, abstract = {During the transition from water to land, plants had to cope with the loss of water through transpiration, the inevitable result of photosynthetic CO2 fixation on land [1, 2]. Control of transpiration became possible through the development of a new cell type: guard cells, which form stomata. In vascular plants, stomatal regulation is mediated by the stress hormone ABA, which triggers the opening of the SnR kinase OST1-activated anion channel SLAC1 [3, 4]. To understand the evolution of this regulatory circuit, we cloned both ABA-signaling elements, SLAC1 and OST1, from a charophyte alga, a liverwort, and a moss, and functionally analyzed the channel-kinase interactions. We were able to show that the emergence of stomata in the last common ancestor of mosses and vascular plants coincided with the origin of SLAC1-type channels capable of using the ancient ABA drought signaling kinase OST1 for regulation of stomatal closure.}, author = {Lind, C. and Dreyer, I. and López-Sanjurjo, E. J. and von Meyer, K. and Ishizaki, K. and Kohchi, T. and Lang, D. and Zhao, Y. and Kreuzer, I. and Al-Rasheid, K. A. S. and Ronne, H. and Reski, R. and Zhu, J. K. and Geiger, D. and Hedrich, R.}, journal = {Current Biology}, keywords = {protein-kinases}, note = {Ce8kl Times Cited:113 Cited References Count:40}, number = 7, pages = {928-935}, title = {Stomatal Guard Cells Co-opted an Ancient ABA-Dependent Desiccation Survival System to Regulate Stomatal Closure}, type = {Journal Article}, volume = 25, year = 2015 }

  %0 Journal Article %1 RN1062 %A Lind, C. %A Dreyer, I. %A López-Sanjurjo, E. J. %A von Meyer, K. %A Ishizaki, K. %A Kohchi, T. %A Lang, D. %A Zhao, Y. %A Kreuzer, I. %A Al-Rasheid, K. A. S. %A Ronne, H. %A Reski, R. %A Zhu, J. K. %A Geiger, D. %A Hedrich, R. %D 2015 %J Current Biology %N 7 %P 928-935 %R 10.1016/j.cub.2015.01.067 %T Stomatal Guard Cells Co-opted an Ancient ABA-Dependent Desiccation Survival System to Regulate Stomatal Closure %U /brokenurl#<Go to ISI>://WOS:000352091100030 %V 25 %X During the transition from water to land, plants had to cope with the loss of water through transpiration, the inevitable result of photosynthetic CO2 fixation on land [1, 2]. Control of transpiration became possible through the development of a new cell type: guard cells, which form stomata. In vascular plants, stomatal regulation is mediated by the stress hormone ABA, which triggers the opening of the SnR kinase OST1-activated anion channel SLAC1 [3, 4]. To understand the evolution of this regulatory circuit, we cloned both ABA-signaling elements, SLAC1 and OST1, from a charophyte alga, a liverwort, and a moss, and functionally analyzed the channel-kinase interactions. We were able to show that the emergence of stomata in the last common ancestor of mosses and vascular plants coincided with the origin of SLAC1-type channels capable of using the ancient ABA drought signaling kinase OST1 for regulation of stomatal closure.
• Sugar transport across the plant vacuolar membrane: nature and regulation of carrier proteins. Hedrich, R.; Sauer, N.; Neuhaus, H. E. In Current Opinion in Plant Biology, 25, pp. 63–70. 2015.
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  The ability of higher plants to store sugars is of crucial importance for plant development, adaption to endogenous or environmental cues and for the economic value of crop species. Sugar storage and accumulation, and its homeostasis in plant cells are managed by the vacuole. Although transport of sugars across the vacuolar membrane has been monitored for about four decades, the molecular entities of the transporters involved have been identified in the last 10 years only. Thus, it is just recently that our pictures of the transporters that channel the sugar load across the tonoplast have gained real shape. Here we describe the molecular nature and regulation of an important group of tonoplast sugar transporter (TST) allowing accumulation of sugars against large concentration gradients. In addition, we report on proton-driven tonoplast sugar exporters and on facilitators, which are also involved in balancing cytosolic and vacuolar sugar levels.

  @article{RN1065, abstract = {The ability of higher plants to store sugars is of crucial importance for plant development, adaption to endogenous or environmental cues and for the economic value of crop species. Sugar storage and accumulation, and its homeostasis in plant cells are managed by the vacuole. Although transport of sugars across the vacuolar membrane has been monitored for about four decades, the molecular entities of the transporters involved have been identified in the last 10 years only. Thus, it is just recently that our pictures of the transporters that channel the sugar load across the tonoplast have gained real shape. Here we describe the molecular nature and regulation of an important group of tonoplast sugar transporter (TST) allowing accumulation of sugars against large concentration gradients. In addition, we report on proton-driven tonoplast sugar exporters and on facilitators, which are also involved in balancing cytosolic and vacuolar sugar levels.}, author = {Hedrich, R. and Sauer, N. and Neuhaus, H. E.}, journal = {Current Opinion in Plant Biology}, keywords = {proton}, note = {Cp4za Times Cited:94 Cited References Count:75}, pages = {63-70}, title = {Sugar transport across the plant vacuolar membrane: nature and regulation of carrier proteins}, type = {Journal Article}, volume = 25, year = 2015 }

  %0 Journal Article %1 RN1065 %A Hedrich, R. %A Sauer, N. %A Neuhaus, H. E. %D 2015 %J Current Opinion in Plant Biology %P 63-70 %R 10.1016/j.pbi.2015.04.008 %T Sugar transport across the plant vacuolar membrane: nature and regulation of carrier proteins %U /brokenurl#<Go to ISI>://WOS:000359889900010 %V 25 %X The ability of higher plants to store sugars is of crucial importance for plant development, adaption to endogenous or environmental cues and for the economic value of crop species. Sugar storage and accumulation, and its homeostasis in plant cells are managed by the vacuole. Although transport of sugars across the vacuolar membrane has been monitored for about four decades, the molecular entities of the transporters involved have been identified in the last 10 years only. Thus, it is just recently that our pictures of the transporters that channel the sugar load across the tonoplast have gained real shape. Here we describe the molecular nature and regulation of an important group of tonoplast sugar transporter (TST) allowing accumulation of sugars against large concentration gradients. In addition, we report on proton-driven tonoplast sugar exporters and on facilitators, which are also involved in balancing cytosolic and vacuolar sugar levels.
• Identification of the transporter responsible for sucrose accumulation in sugar beet taproots. Jung, B.; Ludewig, F.; Schulz, A.; Meissner, G.; Wöstefeld, N.; Flügge, U. I.; Pommerrenig, B.; Wirsching, P.; Sauer, N.; Koch, W.; Sommer, F.; Mühlhaus, T.; Schroda, M.; Cuin, T. A.; Graus, D.; Marten, I.; Hedrich, R.; Neuhaus, H. E. In Nature Plants, 1(1). 2015.
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  Sugar beet provides around one third of the sugar consumed worldwide and serves as a significant source of bioenergy in the form of ethanol. Sucrose accounts for up to 18% of plant fresh weight in sugar beet. Most of the sucrose is concentrated in the taproot, where it accumulates in the vacuoles. Despite 30 years of intensive research, the transporter that facilitates taproot sucrose accumulation has escaped identification. Here, we combine proteomic analyses of the taproot vacuolar membrane, the tonoplast, with electrophysiological analyses to show that the transporter BvTST2.1 is responsible for vacuolar sucrose uptake in sugar beet taproots. We show that BvTST2.1 is a sucrose-specific transporter, and present evidence to suggest that it operates as a proton antiporter, coupling the import of sucrose into the vacuole to the export of protons. BvTST2.1 exhibits a high amino acid sequence similarity to members of the tonoplast monosaccharide transporter family in Arabidopsis, prompting us to rename this group of proteins 'tonoplast sugar transporters'. The identification of BvTST2.1 could help to increase sugar yields from sugar beet and other sugar-storing plants in future breeding programs.

  @article{RN1064, abstract = {Sugar beet provides around one third of the sugar consumed worldwide and serves as a significant source of bioenergy in the form of ethanol. Sucrose accounts for up to 18% of plant fresh weight in sugar beet. Most of the sucrose is concentrated in the taproot, where it accumulates in the vacuoles. Despite 30 years of intensive research, the transporter that facilitates taproot sucrose accumulation has escaped identification. Here, we combine proteomic analyses of the taproot vacuolar membrane, the tonoplast, with electrophysiological analyses to show that the transporter BvTST2.1 is responsible for vacuolar sucrose uptake in sugar beet taproots. We show that BvTST2.1 is a sucrose-specific transporter, and present evidence to suggest that it operates as a proton antiporter, coupling the import of sucrose into the vacuole to the export of protons. BvTST2.1 exhibits a high amino acid sequence similarity to members of the tonoplast monosaccharide transporter family in Arabidopsis, prompting us to rename this group of proteins 'tonoplast sugar transporters'. The identification of BvTST2.1 could help to increase sugar yields from sugar beet and other sugar-storing plants in future breeding programs.}, author = {Jung, B. and Ludewig, F. and Schulz, A. and Meissner, G. and Wöstefeld, N. and Flügge, U. I. and Pommerrenig, B. and Wirsching, P. and Sauer, N. and Koch, W. and Sommer, F. and Mühlhaus, T. and Schroda, M. and Cuin, T. A. and Graus, D. and Marten, I. and Hedrich, R. and Neuhaus, H. E.}, journal = {Nature Plants}, keywords = {monosaccharide}, note = {Cv6ns Times Cited:123 Cited References Count:46}, number = 1, title = {Identification of the transporter responsible for sucrose accumulation in sugar beet taproots}, type = {Journal Article}, volume = 1, year = 2015 }

  %0 Journal Article %1 RN1064 %A Jung, B. %A Ludewig, F. %A Schulz, A. %A Meissner, G. %A Wöstefeld, N. %A Flügge, U. I. %A Pommerrenig, B. %A Wirsching, P. %A Sauer, N. %A Koch, W. %A Sommer, F. %A Mühlhaus, T. %A Schroda, M. %A Cuin, T. A. %A Graus, D. %A Marten, I. %A Hedrich, R. %A Neuhaus, H. E. %D 2015 %J Nature Plants %N 1 %R Artn 14001 10.1038/Nplants.2014.1 %T Identification of the transporter responsible for sucrose accumulation in sugar beet taproots %U /brokenurl#<Go to ISI>://WOS:000364387500001 %V 1 %X Sugar beet provides around one third of the sugar consumed worldwide and serves as a significant source of bioenergy in the form of ethanol. Sucrose accounts for up to 18% of plant fresh weight in sugar beet. Most of the sucrose is concentrated in the taproot, where it accumulates in the vacuoles. Despite 30 years of intensive research, the transporter that facilitates taproot sucrose accumulation has escaped identification. Here, we combine proteomic analyses of the taproot vacuolar membrane, the tonoplast, with electrophysiological analyses to show that the transporter BvTST2.1 is responsible for vacuolar sucrose uptake in sugar beet taproots. We show that BvTST2.1 is a sucrose-specific transporter, and present evidence to suggest that it operates as a proton antiporter, coupling the import of sucrose into the vacuole to the export of protons. BvTST2.1 exhibits a high amino acid sequence similarity to members of the tonoplast monosaccharide transporter family in Arabidopsis, prompting us to rename this group of proteins 'tonoplast sugar transporters'. The identification of BvTST2.1 could help to increase sugar yields from sugar beet and other sugar-storing plants in future breeding programs.
• Elevated CO -Induced Responses in Stomata Require ABA and ABA Signaling. Chater, C.; Peng, K.; Movahedi, M.; Dunn, J. A.; Walker, H. J.; Liang, Y. K.; McLachlan, D. H.; Casson, S.; Isner, J. C.; Wilson, I.; Neill, S. J.; Hedrich, R.; Gray, J. E.; Hetherington, A. M. In Current Biology, 25(20), pp. 2709–2716. 2015.
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  An integral part of global environment change is an increase in the atmospheric concentration of CO2 ([CO2]) [1]. Increased [CO2] reduces leaf stomatal apertures and density of stomata that plays out as reductions in evapotranspiration [2-4]. Surprisingly, given the importance of transpiration to the control of terrestrial water fluxes [5] and plant nutrient acquisition [6], we know comparatively little about the molecular components involved in the intracellular signaling pathways by which [CO2] controls stomatal development and function [7]. Here, we report that elevated [CO2]-induced closure and reductions in stomatal density require the generation of reactive oxygen species (ROS), thereby adding a new common element to these signaling pathways. We also show that the PYR/RCAR family of ABA receptors [8, 9] and ABA itself are required in both responses. Using genetic approaches, we show that ABA in guard cells or their precursors is sufficient to mediate the [CO2]-induced stomatal density response. Taken together, our results suggest that stomatal responses to increased [CO2] operate through the intermediacy of ABA. In the case of [CO2]-induced reductions in stomatal aperture, this occurs by accessing the guard cell ABA signaling pathway. In both [CO2]-mediated responses, our data are consistent with a mechanism in which ABA increases the sensitivity of the system to [CO2] but could also be explained by requirement for a CO2-induced increase in ABA biosynthesis specifically in the guard cell lineage. Furthermore, the dependency of stomatal [CO2] signaling on ABA suggests that the ABA pathway is, in evolutionary terms, likely to be ancestral.

  @article{RN1069, abstract = {An integral part of global environment change is an increase in the atmospheric concentration of CO2 ([CO2]) [1]. Increased [CO2] reduces leaf stomatal apertures and density of stomata that plays out as reductions in evapotranspiration [2-4]. Surprisingly, given the importance of transpiration to the control of terrestrial water fluxes [5] and plant nutrient acquisition [6], we know comparatively little about the molecular components involved in the intracellular signaling pathways by which [CO2] controls stomatal development and function [7]. Here, we report that elevated [CO2]-induced closure and reductions in stomatal density require the generation of reactive oxygen species (ROS), thereby adding a new common element to these signaling pathways. We also show that the PYR/RCAR family of ABA receptors [8, 9] and ABA itself are required in both responses. Using genetic approaches, we show that ABA in guard cells or their precursors is sufficient to mediate the [CO2]-induced stomatal density response. Taken together, our results suggest that stomatal responses to increased [CO2] operate through the intermediacy of ABA. In the case of [CO2]-induced reductions in stomatal aperture, this occurs by accessing the guard cell ABA signaling pathway. In both [CO2]-mediated responses, our data are consistent with a mechanism in which ABA increases the sensitivity of the system to [CO2] but could also be explained by requirement for a CO2-induced increase in ABA biosynthesis specifically in the guard cell lineage. Furthermore, the dependency of stomatal [CO2] signaling on ABA suggests that the ABA pathway is, in evolutionary terms, likely to be ancestral.}, author = {Chater, C. and Peng, K. and Movahedi, M. and Dunn, J. A. and Walker, H. J. and Liang, Y. K. and McLachlan, D. H. and Casson, S. and Isner, J. C. and Wilson, I. and Neill, S. J. and Hedrich, R. and Gray, J. E. and Hetherington, A. M.}, journal = {Current Biology}, keywords = {abscisic-acid}, note = {Cu2nf Times Cited:155 Cited References Count:60}, number = 20, pages = {2709-2716}, title = {Elevated CO -Induced Responses in Stomata Require ABA and ABA Signaling}, type = {Journal Article}, volume = 25, year = 2015 }

  %0 Journal Article %1 RN1069 %A Chater, C. %A Peng, K. %A Movahedi, M. %A Dunn, J. A. %A Walker, H. J. %A Liang, Y. K. %A McLachlan, D. H. %A Casson, S. %A Isner, J. C. %A Wilson, I. %A Neill, S. J. %A Hedrich, R. %A Gray, J. E. %A Hetherington, A. M. %D 2015 %J Current Biology %N 20 %P 2709-2716 %R 10.1016/j.cub.2015.09.013 %T Elevated CO -Induced Responses in Stomata Require ABA and ABA Signaling %U /brokenurl#<Go to ISI>://WOS:000363359500030 %V 25 %X An integral part of global environment change is an increase in the atmospheric concentration of CO2 ([CO2]) [1]. Increased [CO2] reduces leaf stomatal apertures and density of stomata that plays out as reductions in evapotranspiration [2-4]. Surprisingly, given the importance of transpiration to the control of terrestrial water fluxes [5] and plant nutrient acquisition [6], we know comparatively little about the molecular components involved in the intracellular signaling pathways by which [CO2] controls stomatal development and function [7]. Here, we report that elevated [CO2]-induced closure and reductions in stomatal density require the generation of reactive oxygen species (ROS), thereby adding a new common element to these signaling pathways. We also show that the PYR/RCAR family of ABA receptors [8, 9] and ABA itself are required in both responses. Using genetic approaches, we show that ABA in guard cells or their precursors is sufficient to mediate the [CO2]-induced stomatal density response. Taken together, our results suggest that stomatal responses to increased [CO2] operate through the intermediacy of ABA. In the case of [CO2]-induced reductions in stomatal aperture, this occurs by accessing the guard cell ABA signaling pathway. In both [CO2]-mediated responses, our data are consistent with a mechanism in which ABA increases the sensitivity of the system to [CO2] but could also be explained by requirement for a CO2-induced increase in ABA biosynthesis specifically in the guard cell lineage. Furthermore, the dependency of stomatal [CO2] signaling on ABA suggests that the ABA pathway is, in evolutionary terms, likely to be ancestral.
• Calcium sensor kinase activates potassium uptake systems in gland cells of Venus flytraps. Scherzer, S.; Böhm, J.; Krol, E.; Shabala, L.; Kreuzer, I.; Larisch, C.; Bemm, F.; Al-Rasheid, K. A. S.; Shabala, S.; Rennenberg, H.; Neher, E.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 112(23), pp. 7309–7314. 2015.
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  The Darwin plant Dionaea muscipula is able to grow on mineral-poor soil, because it gains essential nutrients from captured animal prey. Given that no nutrients remain in the trap when it opens after the consumption of an animal meal, we here asked the question of how Dionaea sequesters prey-derived potassium. We show that prey capture triggers expression of a K+ uptake system in the Venus flytrap. In search of K+ transporters endowed with adequate properties for this role, we screened a Dionaea expressed sequence tag (EST) database and identified DmKT1 and DmHAK5 as candidates. On insect and touch hormone stimulation, the number of transcripts of these transporters increased in flytraps. After cRNA injection of K+-transporter genes into Xenopus oocytes, however, both putative K+ transporters remained silent. Assuming that calcium sensor kinases are regulating Arabidopsis K+ transporter 1 (AKT1), we coexpressed the putative K+ transporters with a large set of kinases and identified the CBL9-CIPK23 pair as the major activating complex for both transporters in Dionaea K+ uptake. DmKT1 was found to be a K+-selective channel of voltage-dependent high capacity and low affinity, whereas DmHAK5 was identified as the first, to our knowledge, proton-driven, high-affinity potassium transporter with weak selectivity. When the Venus flytrap is processing its prey, the gland cell membrane potential is maintained around -120 mV, and the apoplast is acidified to pH 3. These conditions in the green stomach formed by the closed flytrap allow DmKT1 and DmHAK5 to acquire prey-derived K+, reducing its concentration from millimolar levels down to trace levels.

  @article{RN1059, abstract = {The Darwin plant Dionaea muscipula is able to grow on mineral-poor soil, because it gains essential nutrients from captured animal prey. Given that no nutrients remain in the trap when it opens after the consumption of an animal meal, we here asked the question of how Dionaea sequesters prey-derived potassium. We show that prey capture triggers expression of a K+ uptake system in the Venus flytrap. In search of K+ transporters endowed with adequate properties for this role, we screened a Dionaea expressed sequence tag (EST) database and identified DmKT1 and DmHAK5 as candidates. On insect and touch hormone stimulation, the number of transcripts of these transporters increased in flytraps. After cRNA injection of K+-transporter genes into Xenopus oocytes, however, both putative K+ transporters remained silent. Assuming that calcium sensor kinases are regulating Arabidopsis K+ transporter 1 (AKT1), we coexpressed the putative K+ transporters with a large set of kinases and identified the CBL9-CIPK23 pair as the major activating complex for both transporters in Dionaea K+ uptake. DmKT1 was found to be a K+-selective channel of voltage-dependent high capacity and low affinity, whereas DmHAK5 was identified as the first, to our knowledge, proton-driven, high-affinity potassium transporter with weak selectivity. When the Venus flytrap is processing its prey, the gland cell membrane potential is maintained around -120 mV, and the apoplast is acidified to pH 3. These conditions in the green stomach formed by the closed flytrap allow DmKT1 and DmHAK5 to acquire prey-derived K+, reducing its concentration from millimolar levels down to trace levels.}, author = {Scherzer, S. and Böhm, J. and Krol, E. and Shabala, L. and Kreuzer, I. and Larisch, C. and Bemm, F. and Al-Rasheid, K. A. S. and Shabala, S. and Rennenberg, H. and Neher, E. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {muscipula}, note = {Cj9lg Times Cited:81 Cited References Count:42}, number = 23, pages = {7309-7314}, title = {Calcium sensor kinase activates potassium uptake systems in gland cells of Venus flytraps}, type = {Journal Article}, volume = 112, year = 2015 }

  %0 Journal Article %1 RN1059 %A Scherzer, S. %A Böhm, J. %A Krol, E. %A Shabala, L. %A Kreuzer, I. %A Larisch, C. %A Bemm, F. %A Al-Rasheid, K. A. S. %A Shabala, S. %A Rennenberg, H. %A Neher, E. %A Hedrich, R. %D 2015 %J Proceedings of the National Academy of Sciences of the United States of America %N 23 %P 7309-7314 %R 10.1073/pnas.1507810112 %T Calcium sensor kinase activates potassium uptake systems in gland cells of Venus flytraps %U /brokenurl#<Go to ISI>://WOS:000355823200059 %V 112 %X The Darwin plant Dionaea muscipula is able to grow on mineral-poor soil, because it gains essential nutrients from captured animal prey. Given that no nutrients remain in the trap when it opens after the consumption of an animal meal, we here asked the question of how Dionaea sequesters prey-derived potassium. We show that prey capture triggers expression of a K+ uptake system in the Venus flytrap. In search of K+ transporters endowed with adequate properties for this role, we screened a Dionaea expressed sequence tag (EST) database and identified DmKT1 and DmHAK5 as candidates. On insect and touch hormone stimulation, the number of transcripts of these transporters increased in flytraps. After cRNA injection of K+-transporter genes into Xenopus oocytes, however, both putative K+ transporters remained silent. Assuming that calcium sensor kinases are regulating Arabidopsis K+ transporter 1 (AKT1), we coexpressed the putative K+ transporters with a large set of kinases and identified the CBL9-CIPK23 pair as the major activating complex for both transporters in Dionaea K+ uptake. DmKT1 was found to be a K+-selective channel of voltage-dependent high capacity and low affinity, whereas DmHAK5 was identified as the first, to our knowledge, proton-driven, high-affinity potassium transporter with weak selectivity. When the Venus flytrap is processing its prey, the gland cell membrane potential is maintained around -120 mV, and the apoplast is acidified to pH 3. These conditions in the green stomach formed by the closed flytrap allow DmKT1 and DmHAK5 to acquire prey-derived K+, reducing its concentration from millimolar levels down to trace levels.
• Cytosolic Ca Signals Enhance the Vacuolar Ion Conductivity of Bulging Root Hair Cells. Wang, Y.; Dindas, J.; Ller, F. R.; Krebs, M.; Waadt, R.; Schumacher, K.; Wu, W. H.; Hedrich, R.; Roelfsema, M. R. G. In Molecular Plant, 8(11), pp. 1665–1674. 2015.
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  Plant cell expansion depends on the uptake of solutes across the plasma membrane and their storage within the vacuole. In contrast to the well-studied plasma membrane, little is known about the regulation of ion transport at the vacuolar membrane. We therefore established an experimental approach to study vacuolar ion transport in intact Arabidopsis root cells, with multi-barreled microelectrodes. The subcellular position of electrodes was detected by imaging current-injected fluorescent dyes. Comparison of measurements with electrodes in the cytosol and vacuole revealed an average vacuolar membrane potential of -31 mV. Voltage clamp recordings of single vacuoles resolved the activity of voltage-independent and slowly deactivating channels. In bulging root hairs that express the Ca2+ sensor R-GECO1, rapid elevation of the cytosolic Ca2+ concentration was observed, after impalement with microelectrodes, or injection of the Ca2+ chelator BAPTA. Elevation of the cytosolic Ca2+ level stimulated the activity of voltage-independent channels in the vacuolar membrane. Likewise, the vacuolar ion conductance was enhanced during a sudden increase of the cytosolic Ca2+ level in cells injected with fluorescent Ca2+ indicator FURA-2. These data thus show that cytosolic Ca2+ signals can rapidly activate vacuolar ion channels, which may prevent rupture of the vacuolar membrane, when facing mechanical forces.

  @article{RN1058, abstract = {Plant cell expansion depends on the uptake of solutes across the plasma membrane and their storage within the vacuole. In contrast to the well-studied plasma membrane, little is known about the regulation of ion transport at the vacuolar membrane. We therefore established an experimental approach to study vacuolar ion transport in intact Arabidopsis root cells, with multi-barreled microelectrodes. The subcellular position of electrodes was detected by imaging current-injected fluorescent dyes. Comparison of measurements with electrodes in the cytosol and vacuole revealed an average vacuolar membrane potential of -31 mV. Voltage clamp recordings of single vacuoles resolved the activity of voltage-independent and slowly deactivating channels. In bulging root hairs that express the Ca2+ sensor R-GECO1, rapid elevation of the cytosolic Ca2+ concentration was observed, after impalement with microelectrodes, or injection of the Ca2+ chelator BAPTA. Elevation of the cytosolic Ca2+ level stimulated the activity of voltage-independent channels in the vacuolar membrane. Likewise, the vacuolar ion conductance was enhanced during a sudden increase of the cytosolic Ca2+ level in cells injected with fluorescent Ca2+ indicator FURA-2. These data thus show that cytosolic Ca2+ signals can rapidly activate vacuolar ion channels, which may prevent rupture of the vacuolar membrane, when facing mechanical forces.}, author = {Wang, Y. and Dindas, J. and Ller, F. R. and Krebs, M. and Waadt, R. and Schumacher, K. and Wu, W. H. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Molecular Plant}, keywords = {electrophysiology}, note = {Cw5pt Times Cited:23 Cited References Count:55}, number = 11, pages = {1665-1674}, title = {Cytosolic Ca Signals Enhance the Vacuolar Ion Conductivity of Bulging Root Hair Cells}, type = {Journal Article}, volume = 8, year = 2015 }

  %0 Journal Article %1 RN1058 %A Wang, Y. %A Dindas, J. %A Ller, F. R. %A Krebs, M. %A Waadt, R. %A Schumacher, K. %A Wu, W. H. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2015 %J Molecular Plant %N 11 %P 1665-1674 %R 10.1016/j.molp.2015.07.009 %T Cytosolic Ca Signals Enhance the Vacuolar Ion Conductivity of Bulging Root Hair Cells %U /brokenurl#<Go to ISI>://WOS:000365049200008 %V 8 %X Plant cell expansion depends on the uptake of solutes across the plasma membrane and their storage within the vacuole. In contrast to the well-studied plasma membrane, little is known about the regulation of ion transport at the vacuolar membrane. We therefore established an experimental approach to study vacuolar ion transport in intact Arabidopsis root cells, with multi-barreled microelectrodes. The subcellular position of electrodes was detected by imaging current-injected fluorescent dyes. Comparison of measurements with electrodes in the cytosol and vacuole revealed an average vacuolar membrane potential of -31 mV. Voltage clamp recordings of single vacuoles resolved the activity of voltage-independent and slowly deactivating channels. In bulging root hairs that express the Ca2+ sensor R-GECO1, rapid elevation of the cytosolic Ca2+ concentration was observed, after impalement with microelectrodes, or injection of the Ca2+ chelator BAPTA. Elevation of the cytosolic Ca2+ level stimulated the activity of voltage-independent channels in the vacuolar membrane. Likewise, the vacuolar ion conductance was enhanced during a sudden increase of the cytosolic Ca2+ level in cells injected with fluorescent Ca2+ indicator FURA-2. These data thus show that cytosolic Ca2+ signals can rapidly activate vacuolar ion channels, which may prevent rupture of the vacuolar membrane, when facing mechanical forces.
• Guard cell SLAC1-type anion channels mediate flagellin-induced stomatal closure. Deger, A. G.; Scherzer, S.; Nuhkat, M.; Kedzierska, J.; Kollist, H.; Brosché, M.; Unyayar, S.; Boudsocq, M.; Hedrich, R.; Roelfsema, M. R. G. In New Phytologist, 208(1), pp. 162–173. 2015.
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  During infection plants recognize microbe-associated molecular patterns (MAMPs), and this leads to stomatal closure. This study analyzes the molecular mechanisms underlying this MAMP response and its interrelation with ABA signaling. Stomata in intact Arabidopsis thaliana plants were stimulated with the bacterial MAMP flg22, or the stress hormone ABA, by using the noninvasive nanoinfusion technique. Intracellular double-barreled microelectrodes were applied to measure the activity of plasma membrane ion channels. Flg22 induced rapid stomatal closure and stimulated the SLAC1 and SLAH3 anion channels in guard cells. Loss of both channels resulted in cells that lacked flg22-induced anion channel activity and stomata that did not close in response to flg22 or ABA. Rapid flg22-dependent stomatal closure was impaired in plants that were flagellin receptor (FLS2)-deficient, as well as in the ost1-2 (Open Stomata 1) mutant, which lacks a key ABA-signaling protein kinase. By contrast, stomata of the ABA protein phosphatase mutant abi1-1 (ABscisic acid Insensitive 1) remained flg22-responsive. These data suggest that the initial steps in flg22 and ABA signaling are different, but that the pathways merge at the level of OST1 and lead to activation of SLAC1 and SLAH3 anion channels.

  @article{RN1068, abstract = {During infection plants recognize microbe-associated molecular patterns (MAMPs), and this leads to stomatal closure. This study analyzes the molecular mechanisms underlying this MAMP response and its interrelation with ABA signaling. Stomata in intact Arabidopsis thaliana plants were stimulated with the bacterial MAMP flg22, or the stress hormone ABA, by using the noninvasive nanoinfusion technique. Intracellular double-barreled microelectrodes were applied to measure the activity of plasma membrane ion channels. Flg22 induced rapid stomatal closure and stimulated the SLAC1 and SLAH3 anion channels in guard cells. Loss of both channels resulted in cells that lacked flg22-induced anion channel activity and stomata that did not close in response to flg22 or ABA. Rapid flg22-dependent stomatal closure was impaired in plants that were flagellin receptor (FLS2)-deficient, as well as in the ost1-2 (Open Stomata 1) mutant, which lacks a key ABA-signaling protein kinase. By contrast, stomata of the ABA protein phosphatase mutant abi1-1 (ABscisic acid Insensitive 1) remained flg22-responsive. These data suggest that the initial steps in flg22 and ABA signaling are different, but that the pathways merge at the level of OST1 and lead to activation of SLAC1 and SLAH3 anion channels.}, author = {Deger, A. G. and Scherzer, S. and Nuhkat, M. and Kedzierska, J. and Kollist, H. and Brosché, M. and Unyayar, S. and Boudsocq, M. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {New Phytologist}, keywords = {aba}, note = {Cq1rn Times Cited:116 Cited References Count:80}, number = 1, pages = {162-173}, title = {Guard cell SLAC1-type anion channels mediate flagellin-induced stomatal closure}, type = {Journal Article}, volume = 208, year = 2015 }

  %0 Journal Article %1 RN1068 %A Deger, A. G. %A Scherzer, S. %A Nuhkat, M. %A Kedzierska, J. %A Kollist, H. %A Brosché, M. %A Unyayar, S. %A Boudsocq, M. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2015 %J New Phytologist %N 1 %P 162-173 %R 10.1111/nph.13435 %T Guard cell SLAC1-type anion channels mediate flagellin-induced stomatal closure %U /brokenurl#<Go to ISI>://WOS:000360376400021 %V 208 %X During infection plants recognize microbe-associated molecular patterns (MAMPs), and this leads to stomatal closure. This study analyzes the molecular mechanisms underlying this MAMP response and its interrelation with ABA signaling. Stomata in intact Arabidopsis thaliana plants were stimulated with the bacterial MAMP flg22, or the stress hormone ABA, by using the noninvasive nanoinfusion technique. Intracellular double-barreled microelectrodes were applied to measure the activity of plasma membrane ion channels. Flg22 induced rapid stomatal closure and stimulated the SLAC1 and SLAH3 anion channels in guard cells. Loss of both channels resulted in cells that lacked flg22-induced anion channel activity and stomata that did not close in response to flg22 or ABA. Rapid flg22-dependent stomatal closure was impaired in plants that were flagellin receptor (FLS2)-deficient, as well as in the ost1-2 (Open Stomata 1) mutant, which lacks a key ABA-signaling protein kinase. By contrast, stomata of the ABA protein phosphatase mutant abi1-1 (ABscisic acid Insensitive 1) remained flg22-responsive. These data suggest that the initial steps in flg22 and ABA signaling are different, but that the pathways merge at the level of OST1 and lead to activation of SLAC1 and SLAH3 anion channels.
• The Venus flytrap attracts insects by the release of volatile organic compounds (vol 65, pg 755, 2014). Kreuzwieser, J.; Scheerer, U.; Kruse, J.; Burzlaff, T.; Honsel, A.; Alfarraj, S.; Georgiev, P.; Schnitzler, J. P.; Ghirardo, A.; Kreuzer, I.; Hedrich, R.; Rennenberg, H. In Journal of Experimental Botany, 66(11), pp. 3429–3429. 2015.
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  @article{RN1063, author = {Kreuzwieser, J. and Scheerer, U. and Kruse, J. and Burzlaff, T. and Honsel, A. and Alfarraj, S. and Georgiev, P. and Schnitzler, J. P. and Ghirardo, A. and Kreuzer, I. and Hedrich, R. and Rennenberg, H.}, journal = {Journal of Experimental Botany}, keywords = {myOwn}, note = {Ck4wz Times Cited:1 Cited References Count:1}, number = 11, pages = {3429-3429}, title = {The Venus flytrap attracts insects by the release of volatile organic compounds (vol 65, pg 755, 2014)}, type = {Journal Article}, volume = 66, year = 2015 }

  %0 Journal Article %1 RN1063 %A Kreuzwieser, J. %A Scheerer, U. %A Kruse, J. %A Burzlaff, T. %A Honsel, A. %A Alfarraj, S. %A Georgiev, P. %A Schnitzler, J. P. %A Ghirardo, A. %A Kreuzer, I. %A Hedrich, R. %A Rennenberg, H. %D 2015 %J Journal of Experimental Botany %N 11 %P 3429-3429 %R 10.1093/jxb/erv242 %T The Venus flytrap attracts insects by the release of volatile organic compounds (vol 65, pg 755, 2014) %U /brokenurl#<Go to ISI>://WOS:000356225400034 %V 66
• Carnivorous plants. Hedrich, R. In Current Biology, 25(3), pp. R99-R100. 2015.
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  @article{RN1066, author = {Hedrich, R.}, journal = {Current Biology}, keywords = {myOwn}, note = {Ca5sb Times Cited:5 Cited References Count:4}, number = 3, pages = {R99-R100}, title = {Carnivorous plants}, type = {Journal Article}, volume = 25, year = 2015 }

  %0 Journal Article %1 RN1066 %A Hedrich, R. %D 2015 %J Current Biology %N 3 %P R99-R100 %R DOI 10.1016/j.cub.2014.11.036 %T Carnivorous plants %U /brokenurl#<Go to ISI>://WOS:000348967000003 %V 25
• A mechanism of growth inhibition by abscisic acid in germinating seeds of based on inhibition of plasma membrane H -ATPase and decreased cytosolic pH, K , and anions. Planes, M. D.; Niñoles, R.; Rubio, L.; Bissoli, G.; Bueso, E.; García-Sánchez, M. J.; Alejandro, S.; Gonzalez-Guzmán, M.; Hedrich, R.; Rodriguez, P. L.; Fernández, J. A.; Serrano, R. In Journal of Experimental Botany, 66(3), pp. 813–825. 2015.
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  The stress hormone abscisic acid (ABA) induces expression of defence genes in many organs, modulates ion homeostasis and metabolism in guard cells, and inhibits germination and seedling growth. Concerning the latter effect, several mutants of Arabidopsis thaliana with improved capability for H+ efflux (wat1-1D, overexpression of AKT1 and ost2-1D) are less sensitive to inhibition by ABA than the wild type. This suggested that ABA could inhibit H+ efflux (H+-ATPase) and induce cytosolic acidification as a mechanism of growth inhibition. Measurements to test this hypothesis could not be done in germinating seeds and we used roots as the most convenient system. ABA inhibited the root plasma-membrane H+-ATPase measured in vitro (ATP hydrolysis by isolated vesicles) and in vivo (H+ efflux from seedling roots). This inhibition involved the core ABA signalling elements: PYR/PYL/RCAR ABA receptors, ABA-inhibited protein phosphatases (HAB1), and ABA-activated protein kinases (SnRK2.2 and SnRK2.3). Electrophysiological measurements in root epidermal cells indicated that ABA, acting through the PYR/PYL/RCAR receptors, induced membrane hyperpolarization (due to K+ efflux through the GORK channel) and cytosolic acidification. This acidification was not observed in the wat1-1D mutant. The mechanism of inhibition of the H+-ATPase by ABA and its effects on cytosolic pH and membrane potential in roots were different from those in guard cells. ABA did not affect the in vivo phosphorylation level of the known activating site (penultimate threonine) of H+-ATPase in roots, and SnRK2.2 phosphorylated in vitro the C-terminal regulatory domain of H+-ATPase while the guard-cell kinase SnRK2.6/OST1 did not.

  @article{RN1061, abstract = {The stress hormone abscisic acid (ABA) induces expression of defence genes in many organs, modulates ion homeostasis and metabolism in guard cells, and inhibits germination and seedling growth. Concerning the latter effect, several mutants of Arabidopsis thaliana with improved capability for H+ efflux (wat1-1D, overexpression of AKT1 and ost2-1D) are less sensitive to inhibition by ABA than the wild type. This suggested that ABA could inhibit H+ efflux (H+-ATPase) and induce cytosolic acidification as a mechanism of growth inhibition. Measurements to test this hypothesis could not be done in germinating seeds and we used roots as the most convenient system. ABA inhibited the root plasma-membrane H+-ATPase measured in vitro (ATP hydrolysis by isolated vesicles) and in vivo (H+ efflux from seedling roots). This inhibition involved the core ABA signalling elements: PYR/PYL/RCAR ABA receptors, ABA-inhibited protein phosphatases (HAB1), and ABA-activated protein kinases (SnRK2.2 and SnRK2.3). Electrophysiological measurements in root epidermal cells indicated that ABA, acting through the PYR/PYL/RCAR receptors, induced membrane hyperpolarization (due to K+ efflux through the GORK channel) and cytosolic acidification. This acidification was not observed in the wat1-1D mutant. The mechanism of inhibition of the H+-ATPase by ABA and its effects on cytosolic pH and membrane potential in roots were different from those in guard cells. ABA did not affect the in vivo phosphorylation level of the known activating site (penultimate threonine) of H+-ATPase in roots, and SnRK2.2 phosphorylated in vitro the C-terminal regulatory domain of H+-ATPase while the guard-cell kinase SnRK2.6/OST1 did not.}, author = {Planes, M. D. and Niñoles, R. and Rubio, L. and Bissoli, G. and Bueso, E. and García-Sánchez, M. J. and Alejandro, S. and Gonzalez-Guzmán, M. and Hedrich, R. and Rodriguez, P. L. and Fernández, J. A. and Serrano, R.}, journal = {Journal of Experimental Botany}, keywords = {aba}, note = {Ce2rd Times Cited:60 Cited References Count:75}, number = 3, pages = {813-825}, title = {A mechanism of growth inhibition by abscisic acid in germinating seeds of based on inhibition of plasma membrane H -ATPase and decreased cytosolic pH, K , and anions}, type = {Journal Article}, volume = 66, year = 2015 }

  %0 Journal Article %1 RN1061 %A Planes, M. D. %A Niñoles, R. %A Rubio, L. %A Bissoli, G. %A Bueso, E. %A García-Sánchez, M. J. %A Alejandro, S. %A Gonzalez-Guzmán, M. %A Hedrich, R. %A Rodriguez, P. L. %A Fernández, J. A. %A Serrano, R. %D 2015 %J Journal of Experimental Botany %N 3 %P 813-825 %R 10.1093/jxb/eru442 %T A mechanism of growth inhibition by abscisic acid in germinating seeds of based on inhibition of plasma membrane H -ATPase and decreased cytosolic pH, K , and anions %U /brokenurl#<Go to ISI>://WOS:000351662300017 %V 66 %X The stress hormone abscisic acid (ABA) induces expression of defence genes in many organs, modulates ion homeostasis and metabolism in guard cells, and inhibits germination and seedling growth. Concerning the latter effect, several mutants of Arabidopsis thaliana with improved capability for H+ efflux (wat1-1D, overexpression of AKT1 and ost2-1D) are less sensitive to inhibition by ABA than the wild type. This suggested that ABA could inhibit H+ efflux (H+-ATPase) and induce cytosolic acidification as a mechanism of growth inhibition. Measurements to test this hypothesis could not be done in germinating seeds and we used roots as the most convenient system. ABA inhibited the root plasma-membrane H+-ATPase measured in vitro (ATP hydrolysis by isolated vesicles) and in vivo (H+ efflux from seedling roots). This inhibition involved the core ABA signalling elements: PYR/PYL/RCAR ABA receptors, ABA-inhibited protein phosphatases (HAB1), and ABA-activated protein kinases (SnRK2.2 and SnRK2.3). Electrophysiological measurements in root epidermal cells indicated that ABA, acting through the PYR/PYL/RCAR receptors, induced membrane hyperpolarization (due to K+ efflux through the GORK channel) and cytosolic acidification. This acidification was not observed in the wat1-1D mutant. The mechanism of inhibition of the H+-ATPase by ABA and its effects on cytosolic pH and membrane potential in roots were different from those in guard cells. ABA did not affect the in vivo phosphorylation level of the known activating site (penultimate threonine) of H+-ATPase in roots, and SnRK2.2 phosphorylated in vitro the C-terminal regulatory domain of H+-ATPase while the guard-cell kinase SnRK2.6/OST1 did not.
• β-amylase1 mutant Arabidopsis plants show improved drought tolerance due to reduced starch breakdown in guard cells. Prasch, C. M.; Ott, K. V.; Bauer, H.; Ache, P.; Hedrich, R.; Sonnewald, U. In Journal of Experimental Botany, 66(19), pp. 6059–6067. 2015.
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  bam1 mutant plants impaired in stomatal starch degradation showed an improved drought tolerance associated with a down-regulation of guard cell-specific gene expression involved in water uptake and cell expansion.In plants, drought stress is a major growth limiting factor causing cell water loss through open stomata. In this study, guard cell-specific transcripts from drought-stressedArabidopsis plants were analysed and a down-regulation of beta-amylase 1 (BAM1) was found. In previous studies, BAM1 was shown to be involved in stomatal starch degradation under ambient conditions. Impaired starch breakdown ofbam1 mutant plants was accompanied by decreased stomatal opening. Here, it is shown that drought tolerance ofbam1 mutant plants is improved as compared with wild-type controls. Microarray analysis of stomata-specific transcripts frombam1 mutant plants revealed a significant down-regulation of genes encoding aquaporins, auxin- and ethylene-responsive factors, and cell-wall modifying enzymes. This expression pattern suggests that reduced water uptake and limited cell wall extension are associated with the closed state of stomata ofbam1 mutant plants. Together these data suggest that regulation of stomata-specific starch turnover is important for adapting stomata opening to environmental needs and its breeding manipulation may result in drought tolerant crop plants.

  @article{RN1060, abstract = {bam1 mutant plants impaired in stomatal starch degradation showed an improved drought tolerance associated with a down-regulation of guard cell-specific gene expression involved in water uptake and cell expansion.In plants, drought stress is a major growth limiting factor causing cell water loss through open stomata. In this study, guard cell-specific transcripts from drought-stressedArabidopsis plants were analysed and a down-regulation of beta-amylase 1 (BAM1) was found. In previous studies, BAM1 was shown to be involved in stomatal starch degradation under ambient conditions. Impaired starch breakdown ofbam1 mutant plants was accompanied by decreased stomatal opening. Here, it is shown that drought tolerance ofbam1 mutant plants is improved as compared with wild-type controls. Microarray analysis of stomata-specific transcripts frombam1 mutant plants revealed a significant down-regulation of genes encoding aquaporins, auxin- and ethylene-responsive factors, and cell-wall modifying enzymes. This expression pattern suggests that reduced water uptake and limited cell wall extension are associated with the closed state of stomata ofbam1 mutant plants. Together these data suggest that regulation of stomata-specific starch turnover is important for adapting stomata opening to environmental needs and its breeding manipulation may result in drought tolerant crop plants.}, author = {Prasch, C. M. and Ott, K. V. and Bauer, H. and Ache, P. and Hedrich, R. and Sonnewald, U.}, journal = {Journal of Experimental Botany}, keywords = {arabidopsis}, note = {Cs4vf Times Cited:51 Cited References Count:45}, number = 19, pages = {6059-6067}, title = {β-amylase1 mutant Arabidopsis plants show improved drought tolerance due to reduced starch breakdown in guard cells}, type = {Journal Article}, volume = 66, year = 2015 }

  %0 Journal Article %1 RN1060 %A Prasch, C. M. %A Ott, K. V. %A Bauer, H. %A Ache, P. %A Hedrich, R. %A Sonnewald, U. %D 2015 %J Journal of Experimental Botany %N 19 %P 6059-6067 %R 10.1093/jxb/erv323 %T β-amylase1 mutant Arabidopsis plants show improved drought tolerance due to reduced starch breakdown in guard cells %U /brokenurl#<Go to ISI>://WOS:000362073400032 %V 66 %X bam1 mutant plants impaired in stomatal starch degradation showed an improved drought tolerance associated with a down-regulation of guard cell-specific gene expression involved in water uptake and cell expansion.In plants, drought stress is a major growth limiting factor causing cell water loss through open stomata. In this study, guard cell-specific transcripts from drought-stressedArabidopsis plants were analysed and a down-regulation of beta-amylase 1 (BAM1) was found. In previous studies, BAM1 was shown to be involved in stomatal starch degradation under ambient conditions. Impaired starch breakdown ofbam1 mutant plants was accompanied by decreased stomatal opening. Here, it is shown that drought tolerance ofbam1 mutant plants is improved as compared with wild-type controls. Microarray analysis of stomata-specific transcripts frombam1 mutant plants revealed a significant down-regulation of genes encoding aquaporins, auxin- and ethylene-responsive factors, and cell-wall modifying enzymes. This expression pattern suggests that reduced water uptake and limited cell wall extension are associated with the closed state of stomata ofbam1 mutant plants. Together these data suggest that regulation of stomata-specific starch turnover is important for adapting stomata opening to environmental needs and its breeding manipulation may result in drought tolerant crop plants.
• Integration of trap- and root-derived nitrogen nutrition of carnivorous. Gao, P.; Loeffler, T. S.; Honsel, A.; Kruse, J.; Krol, E.; Scherzer, S.; Kreuzer, I.; Bemm, F.; Buegger, F.; Burzlaff, T.; Hedrich, R.; Rennenberg, H. In New Phytologist, 205(3), pp. 1320–1329. 2015.
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  Carnivorous Dionaea muscipula operates active snap traps for nutrient acquisition from prey; so what is the role of D. muscipula's reduced root system? We studied the capacity for nitrogen (N) acquisition via traps, and its effect on plant allometry; the capacity of roots to absorb NO3-, NH4+ and glutamine from the soil solution; and the fate and interaction of foliar- and root-acquired N. Feeding D. muscipula snap traps with insects had little effect on the root:shoot ratio, but promoted petiole relative to trap growth. Large amounts of NH4+ and glutamine were absorbed upon root feeding. The high capacity for root N uptake was maintained upon feeding traps with glutamine. High root acquisition of NH4+ was mediated by 2.5-fold higher expression of the NH4+ transporter DmAMT1 in the roots compared with the traps. Electrophysiological studies confirmed a high constitutive capacity for NH4+ uptake by roots. Glutamine feeding of traps inhibited the influx of N-15 from root-absorbed N-15/C-13-glutamine into these traps, but not that of C-13. Apparently, fed traps turned into carbon sinks that even acquired organic carbon from roots. N acquisition at the whole-plant level is fundamentally different in D. muscipula compared with noncarnivorous species, where foliar N influx down-regulates N uptake by roots.

  @article{RN1067, abstract = {Carnivorous Dionaea muscipula operates active snap traps for nutrient acquisition from prey; so what is the role of D. muscipula's reduced root system? We studied the capacity for nitrogen (N) acquisition via traps, and its effect on plant allometry; the capacity of roots to absorb NO3-, NH4+ and glutamine from the soil solution; and the fate and interaction of foliar- and root-acquired N. Feeding D. muscipula snap traps with insects had little effect on the root:shoot ratio, but promoted petiole relative to trap growth. Large amounts of NH4+ and glutamine were absorbed upon root feeding. The high capacity for root N uptake was maintained upon feeding traps with glutamine. High root acquisition of NH4+ was mediated by 2.5-fold higher expression of the NH4+ transporter DmAMT1 in the roots compared with the traps. Electrophysiological studies confirmed a high constitutive capacity for NH4+ uptake by roots. Glutamine feeding of traps inhibited the influx of N-15 from root-absorbed N-15/C-13-glutamine into these traps, but not that of C-13. Apparently, fed traps turned into carbon sinks that even acquired organic carbon from roots. N acquisition at the whole-plant level is fundamentally different in D. muscipula compared with noncarnivorous species, where foliar N influx down-regulates N uptake by roots.}, author = {Gao, P. and Loeffler, T. S. and Honsel, A. and Kruse, J. and Krol, E. and Scherzer, S. and Kreuzer, I. and Bemm, F. and Buegger, F. and Burzlaff, T. and Hedrich, R. and Rennenberg, H.}, journal = {New Phytologist}, keywords = {ammonium}, note = {Ca2hx Times Cited:21 Cited References Count:41}, number = 3, pages = {1320-1329}, title = {Integration of trap- and root-derived nitrogen nutrition of carnivorous}, type = {Journal Article}, volume = 205, year = 2015 }

  %0 Journal Article %1 RN1067 %A Gao, P. %A Loeffler, T. S. %A Honsel, A. %A Kruse, J. %A Krol, E. %A Scherzer, S. %A Kreuzer, I. %A Bemm, F. %A Buegger, F. %A Burzlaff, T. %A Hedrich, R. %A Rennenberg, H. %D 2015 %J New Phytologist %N 3 %P 1320-1329 %R 10.1111/nph.13120 %T Integration of trap- and root-derived nitrogen nutrition of carnivorous %U /brokenurl#<Go to ISI>://WOS:000348730600041 %V 205 %X Carnivorous Dionaea muscipula operates active snap traps for nutrient acquisition from prey; so what is the role of D. muscipula's reduced root system? We studied the capacity for nitrogen (N) acquisition via traps, and its effect on plant allometry; the capacity of roots to absorb NO3-, NH4+ and glutamine from the soil solution; and the fate and interaction of foliar- and root-acquired N. Feeding D. muscipula snap traps with insects had little effect on the root:shoot ratio, but promoted petiole relative to trap growth. Large amounts of NH4+ and glutamine were absorbed upon root feeding. The high capacity for root N uptake was maintained upon feeding traps with glutamine. High root acquisition of NH4+ was mediated by 2.5-fold higher expression of the NH4+ transporter DmAMT1 in the roots compared with the traps. Electrophysiological studies confirmed a high constitutive capacity for NH4+ uptake by roots. Glutamine feeding of traps inhibited the influx of N-15 from root-absorbed N-15/C-13-glutamine into these traps, but not that of C-13. Apparently, fed traps turned into carbon sinks that even acquired organic carbon from roots. N acquisition at the whole-plant level is fundamentally different in D. muscipula compared with noncarnivorous species, where foliar N influx down-regulates N uptake by roots.
• An RLP23-SOBIR1-BAK1 complex mediates NLP-triggered immunity. Albert, I.; Böhm, H.; Albert, M.; Feiler, C. E.; Imkampe, J.; Wallmeroth, N.; Brancato, C.; Raaymakers, T. M.; Oome, S.; Zhang, H. Q.; Krol, E.; Grefen, C.; Gust, A. A.; Chai, J. J.; Hedrich, R.; Van den Ackerveken, G.; Nürnberger, T. In Nature Plants, 1(10). 2015.
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  Plants and animals employ innate immune systems to cope with microbial infection. Pattern-triggered immunity relies on the recognition of microbe-derived patterns by pattern recognition receptors (PRRs). Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) constitute plant immunogenic patterns that are unique, as these proteins are produced by multiple prokaryotic (bacterial) and eukaryotic (fungal, oomycete) species. Here we show that the leucine-rich repeat receptor protein (LRR-RP) RLP23 binds in vivo to a conserved 20-amino-acid fragment found in most NLPs (nlp20), thereby mediating immune activation in Arabidopsis thaliana. RLP23 forms a constitutive, ligand-independent complex with the LRR receptor kinase (LRR-RK) SOBIR1 (Suppressor of Brassinosteroid insensitive 1 (BRI1)-associated kinase (BAK1)-interacting receptor kinase 1), and recruits a second LRR-RK, BAK1, into a tripartite complex upon ligand binding. Stable, ectopic expression of RLP23 in potato (Solanum tuberosum) confers nlp20 pattern recognition and enhanced immunity to destructive oomycete and fungal plant pathogens, such as Phytophthora infestans and Sclerotinia sclerotiorum. PRRs that recognize widespread microbial patterns might be particularly suited for engineering immunity in crop plants.

  @article{RN1070, abstract = {Plants and animals employ innate immune systems to cope with microbial infection. Pattern-triggered immunity relies on the recognition of microbe-derived patterns by pattern recognition receptors (PRRs). Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) constitute plant immunogenic patterns that are unique, as these proteins are produced by multiple prokaryotic (bacterial) and eukaryotic (fungal, oomycete) species. Here we show that the leucine-rich repeat receptor protein (LRR-RP) RLP23 binds in vivo to a conserved 20-amino-acid fragment found in most NLPs (nlp20), thereby mediating immune activation in Arabidopsis thaliana. RLP23 forms a constitutive, ligand-independent complex with the LRR receptor kinase (LRR-RK) SOBIR1 (Suppressor of Brassinosteroid insensitive 1 (BRI1)-associated kinase (BAK1)-interacting receptor kinase 1), and recruits a second LRR-RK, BAK1, into a tripartite complex upon ligand binding. Stable, ectopic expression of RLP23 in potato (Solanum tuberosum) confers nlp20 pattern recognition and enhanced immunity to destructive oomycete and fungal plant pathogens, such as Phytophthora infestans and Sclerotinia sclerotiorum. PRRs that recognize widespread microbial patterns might be particularly suited for engineering immunity in crop plants.}, author = {Albert, I. and Böhm, H. and Albert, M. and Feiler, C. E. and Imkampe, J. and Wallmeroth, N. and Brancato, C. and Raaymakers, T. M. and Oome, S. and Zhang, H. Q. and Krol, E. and Grefen, C. and Gust, A. A. and Chai, J. J. and Hedrich, R. and Van den Ackerveken, G. and Nürnberger, T.}, journal = {Nature Plants}, keywords = {pattern-recognition}, note = {Cv6xi Times Cited:281 Cited References Count:53}, number = 10, title = {An RLP23-SOBIR1-BAK1 complex mediates NLP-triggered immunity}, type = {Journal Article}, volume = 1, year = 2015 }

  %0 Journal Article %1 RN1070 %A Albert, I. %A Böhm, H. %A Albert, M. %A Feiler, C. E. %A Imkampe, J. %A Wallmeroth, N. %A Brancato, C. %A Raaymakers, T. M. %A Oome, S. %A Zhang, H. Q. %A Krol, E. %A Grefen, C. %A Gust, A. A. %A Chai, J. J. %A Hedrich, R. %A Van den Ackerveken, G. %A Nürnberger, T. %D 2015 %J Nature Plants %N 10 %R Artn 15140 10.1038/Nplants.2015.140 %T An RLP23-SOBIR1-BAK1 complex mediates NLP-triggered immunity %U /brokenurl#<Go to ISI>://WOS:000364414800001 %V 1 %X Plants and animals employ innate immune systems to cope with microbial infection. Pattern-triggered immunity relies on the recognition of microbe-derived patterns by pattern recognition receptors (PRRs). Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) constitute plant immunogenic patterns that are unique, as these proteins are produced by multiple prokaryotic (bacterial) and eukaryotic (fungal, oomycete) species. Here we show that the leucine-rich repeat receptor protein (LRR-RP) RLP23 binds in vivo to a conserved 20-amino-acid fragment found in most NLPs (nlp20), thereby mediating immune activation in Arabidopsis thaliana. RLP23 forms a constitutive, ligand-independent complex with the LRR receptor kinase (LRR-RK) SOBIR1 (Suppressor of Brassinosteroid insensitive 1 (BRI1)-associated kinase (BAK1)-interacting receptor kinase 1), and recruits a second LRR-RK, BAK1, into a tripartite complex upon ligand binding. Stable, ectopic expression of RLP23 in potato (Solanum tuberosum) confers nlp20 pattern recognition and enhanced immunity to destructive oomycete and fungal plant pathogens, such as Phytophthora infestans and Sclerotinia sclerotiorum. PRRs that recognize widespread microbial patterns might be particularly suited for engineering immunity in crop plants.

• Mechano-Stimulation Triggers Turgor Changes Associated with Trap Closure in the Darwin Plant. Escalante-Pérez, M.; Scherzer, S.; Al-Rasheid, K. A. S.; Döttinger, C.; Neher, E.; Hedrich, R. In Molecular Plant, 7(4), pp. 744–746. 2014.
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  @article{RN1081, author = {Escalante-Pérez, M. and Scherzer, S. and Al-Rasheid, K. A. S. and Döttinger, C. and Neher, E. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {myOwn}, note = {Ah1py Times Cited:9 Cited References Count:10}, number = 4, pages = {744-746}, title = {Mechano-Stimulation Triggers Turgor Changes Associated with Trap Closure in the Darwin Plant}, type = {Journal Article}, volume = 7, year = 2014 }

  %0 Journal Article %1 RN1081 %A Escalante-Pérez, M. %A Scherzer, S. %A Al-Rasheid, K. A. S. %A Döttinger, C. %A Neher, E. %A Hedrich, R. %D 2014 %J Molecular Plant %N 4 %P 744-746 %R 10.1093/mp/sst169 %T Mechano-Stimulation Triggers Turgor Changes Associated with Trap Closure in the Darwin Plant %U /brokenurl#<Go to ISI>://WOS:000335894600014 %V 7
• Two Fatty Acid Desaturases, STEAROYL-ACYL CARRIER PROTEIN Δ -DESATURASE6 and FATTY ACID DESATURASE3, Are Involved in Drought and Hypoxia Stress Signaling in Arabidopsis Crown Galls. Klinkenberg, J.; Faist, H.; Saupe, S.; Lambertz, S.; Krischke, M.; Stingl, N.; Fekete, A.; Mueller, M. J.; Feussner, I.; Hedrich, R.; Deeken, R. In Plant Physiology, 164(2), pp. 570–583. 2014.
  • [ Abstract ]
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  Agrobacterium tumefaciens-derived crown galls of Arabidopsis (Arabidopsis thaliana) contain elevated levels of unsaturated fatty acids and strongly express two fatty acid desaturase genes, omega 3 FATTY ACID DESATURASE3 (FAD3) and STEAROYL-ACYL CARRIER PROTEIN Delta(9)-DESATURASE6 (SAD6). The fad3-2 mutant with impaired alpha-linolenic acid synthesis developed significantly smaller crown galls under normal, but not under high, relative humidity. This strongly suggests that FAD3 plays a role in increasing drought stress tolerance of crown galls. SAD6 is a member of the SAD family of as yet unknown function. Expression of the SAD6 gene is limited to hypoxia, a physiological condition found in crown galls. As no sad6 mutant exists and to link the function of SAD6 with fatty acid desaturation in crown galls, the lipid pattern was analyzed of plants with constitutive SAD6 overexpression (SAD6-OE). SAD6-OE plants contained lower stearic acid and higher oleic acid levels, which upon reduction of SAD6 overexpression by RNA interference (SAD6-OE-RNAi) regained wild-type-like levels. The development of crown galls was not affected either in SAD6-OE or SAD6-OE-RNAi or by RNA interference in crown galls. Since biochemical analysis of SAD6 in yeast (Saccharomyces cerevisiae) and Escherichia coli failed, SAD6 was ectopically expressed in the background of the well-known suppressor of salicylic acid-insensitive2 (ssi2-2) mutant to confirm the desaturase function of SAD6. All known ssi2-2 phenotypes were rescued, including the high stearic acid level. Thus, our findings suggest that SAD6 functions as a Delta(9)-desaturase, and together with FAD3 it increases the levels of unsaturated fatty acids in crown galls under hypoxia and drought stress conditions.

  @article{RN1078, abstract = {Agrobacterium tumefaciens-derived crown galls of Arabidopsis (Arabidopsis thaliana) contain elevated levels of unsaturated fatty acids and strongly express two fatty acid desaturase genes, omega 3 FATTY ACID DESATURASE3 (FAD3) and STEAROYL-ACYL CARRIER PROTEIN Delta(9)-DESATURASE6 (SAD6). The fad3-2 mutant with impaired alpha-linolenic acid synthesis developed significantly smaller crown galls under normal, but not under high, relative humidity. This strongly suggests that FAD3 plays a role in increasing drought stress tolerance of crown galls. SAD6 is a member of the SAD family of as yet unknown function. Expression of the SAD6 gene is limited to hypoxia, a physiological condition found in crown galls. As no sad6 mutant exists and to link the function of SAD6 with fatty acid desaturation in crown galls, the lipid pattern was analyzed of plants with constitutive SAD6 overexpression (SAD6-OE). SAD6-OE plants contained lower stearic acid and higher oleic acid levels, which upon reduction of SAD6 overexpression by RNA interference (SAD6-OE-RNAi) regained wild-type-like levels. The development of crown galls was not affected either in SAD6-OE or SAD6-OE-RNAi or by RNA interference in crown galls. Since biochemical analysis of SAD6 in yeast (Saccharomyces cerevisiae) and Escherichia coli failed, SAD6 was ectopically expressed in the background of the well-known suppressor of salicylic acid-insensitive2 (ssi2-2) mutant to confirm the desaturase function of SAD6. All known ssi2-2 phenotypes were rescued, including the high stearic acid level. Thus, our findings suggest that SAD6 functions as a Delta(9)-desaturase, and together with FAD3 it increases the levels of unsaturated fatty acids in crown galls under hypoxia and drought stress conditions.}, author = {Klinkenberg, J. and Faist, H. and Saupe, S. and Lambertz, S. and Krischke, M. and Stingl, N. and Fekete, A. and Mueller, M. J. and Feussner, I. and Hedrich, R. and Deeken, R.}, journal = {Plant Physiology}, keywords = {desaturase}, note = {Aa5jn Times Cited:60 Cited References Count:69}, number = 2, pages = {570-583}, title = {Two Fatty Acid Desaturases, STEAROYL-ACYL CARRIER PROTEIN Δ -DESATURASE6 and FATTY ACID DESATURASE3, Are Involved in Drought and Hypoxia Stress Signaling in Arabidopsis Crown Galls}, type = {Journal Article}, volume = 164, year = 2014 }

  %0 Journal Article %1 RN1078 %A Klinkenberg, J. %A Faist, H. %A Saupe, S. %A Lambertz, S. %A Krischke, M. %A Stingl, N. %A Fekete, A. %A Mueller, M. J. %A Feussner, I. %A Hedrich, R. %A Deeken, R. %D 2014 %J Plant Physiology %N 2 %P 570-583 %R 10.1104/pp.113.230326 %T Two Fatty Acid Desaturases, STEAROYL-ACYL CARRIER PROTEIN Δ -DESATURASE6 and FATTY ACID DESATURASE3, Are Involved in Drought and Hypoxia Stress Signaling in Arabidopsis Crown Galls %U /brokenurl#<Go to ISI>://WOS:000331132300007 %V 164 %X Agrobacterium tumefaciens-derived crown galls of Arabidopsis (Arabidopsis thaliana) contain elevated levels of unsaturated fatty acids and strongly express two fatty acid desaturase genes, omega 3 FATTY ACID DESATURASE3 (FAD3) and STEAROYL-ACYL CARRIER PROTEIN Delta(9)-DESATURASE6 (SAD6). The fad3-2 mutant with impaired alpha-linolenic acid synthesis developed significantly smaller crown galls under normal, but not under high, relative humidity. This strongly suggests that FAD3 plays a role in increasing drought stress tolerance of crown galls. SAD6 is a member of the SAD family of as yet unknown function. Expression of the SAD6 gene is limited to hypoxia, a physiological condition found in crown galls. As no sad6 mutant exists and to link the function of SAD6 with fatty acid desaturation in crown galls, the lipid pattern was analyzed of plants with constitutive SAD6 overexpression (SAD6-OE). SAD6-OE plants contained lower stearic acid and higher oleic acid levels, which upon reduction of SAD6 overexpression by RNA interference (SAD6-OE-RNAi) regained wild-type-like levels. The development of crown galls was not affected either in SAD6-OE or SAD6-OE-RNAi or by RNA interference in crown galls. Since biochemical analysis of SAD6 in yeast (Saccharomyces cerevisiae) and Escherichia coli failed, SAD6 was ectopically expressed in the background of the well-known suppressor of salicylic acid-insensitive2 (ssi2-2) mutant to confirm the desaturase function of SAD6. All known ssi2-2 phenotypes were rescued, including the high stearic acid level. Thus, our findings suggest that SAD6 functions as a Delta(9)-desaturase, and together with FAD3 it increases the levels of unsaturated fatty acids in crown galls under hypoxia and drought stress conditions.
• Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid. Maierhofer, T.; Diekmann, M.; Offenborn, J. N.; Lind, C.; Bauer, H.; Hashimoto, K.; Al-Rasheid, K. A. S.; Luan, S.; Kudla, J.; Geiger, D.; Hedrich, R. In Science Signaling, 7(342). 2014.
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  Under drought stress, abscisic acid (ABA) triggers closure of leaf cell pores called stomata, which are formed by two specialized cells called guard cells in plant epidermis. Two pathways downstream of ABA stimulate phosphorylation of the S-type anion channels SLAC1 (slow anion channel associated 1) and SLAH3 (SLAC1 homolog 3), which causes these channels to open, reducing guard cell volume and triggering stomatal closure. One branch involves OST1 (open stomata 1), a calcium-independent SnRK2-type kinase, and the other branch involves calcium-dependent protein kinases of the CPK (calcium-dependent protein kinase) family. We used coexpression analyses in Xenopus oocytes to show that the calcineurin B-like (CBL) calcium sensors CBL1 and CBL9 and their interacting protein kinase CIPK23 also triggered SLAC1 and SLAH3 opening. We analyzed whether regulation of SLAC1 opening by these different families of kinases involved the same or different sites on SLAC1 by measuring channel conductance of SLAC1 with mutations in the putative phosphorylation sites in the amino or carboxyl termini coexpressed with specific kinases in Xenopus oocytes. SLAC1 mutants lacking the OST1-phosphorylated site were still activated by CPK or by CBL/CIPK complexes. Phosphorylation and activation of SLAC1 by any of the kinases were inhibited by the phosphatase ABI1 (ABA insensitive 1), which is inactivated in response to ABA signaling. These findings identified CBL/CIPK complexes as potential regulators of stomatal aperture through S-type anion channels and indicated that phosphorylation at distinct sites enables SLAC1 activation by both calcium-dependent and calcium-independent pathways downstream of ABA.

  @article{RN1074, abstract = {Under drought stress, abscisic acid (ABA) triggers closure of leaf cell pores called stomata, which are formed by two specialized cells called guard cells in plant epidermis. Two pathways downstream of ABA stimulate phosphorylation of the S-type anion channels SLAC1 (slow anion channel associated 1) and SLAH3 (SLAC1 homolog 3), which causes these channels to open, reducing guard cell volume and triggering stomatal closure. One branch involves OST1 (open stomata 1), a calcium-independent SnRK2-type kinase, and the other branch involves calcium-dependent protein kinases of the CPK (calcium-dependent protein kinase) family. We used coexpression analyses in Xenopus oocytes to show that the calcineurin B-like (CBL) calcium sensors CBL1 and CBL9 and their interacting protein kinase CIPK23 also triggered SLAC1 and SLAH3 opening. We analyzed whether regulation of SLAC1 opening by these different families of kinases involved the same or different sites on SLAC1 by measuring channel conductance of SLAC1 with mutations in the putative phosphorylation sites in the amino or carboxyl termini coexpressed with specific kinases in Xenopus oocytes. SLAC1 mutants lacking the OST1-phosphorylated site were still activated by CPK or by CBL/CIPK complexes. Phosphorylation and activation of SLAC1 by any of the kinases were inhibited by the phosphatase ABI1 (ABA insensitive 1), which is inactivated in response to ABA signaling. These findings identified CBL/CIPK complexes as potential regulators of stomatal aperture through S-type anion channels and indicated that phosphorylation at distinct sites enables SLAC1 activation by both calcium-dependent and calcium-independent pathways downstream of ABA.}, author = {Maierhofer, T. and Diekmann, M. and Offenborn, J. N. and Lind, C. and Bauer, H. and Hashimoto, K. and Al-Rasheid, K. A. S. and Luan, S. and Kudla, J. and Geiger, D. and Hedrich, R.}, journal = {Science Signaling}, keywords = {protein-kinases}, note = {Ap8yq Times Cited:150 Cited References Count:71}, number = 342, title = {Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid}, type = {Journal Article}, volume = 7, year = 2014 }

  %0 Journal Article %1 RN1074 %A Maierhofer, T. %A Diekmann, M. %A Offenborn, J. N. %A Lind, C. %A Bauer, H. %A Hashimoto, K. %A Al-Rasheid, K. A. S. %A Luan, S. %A Kudla, J. %A Geiger, D. %A Hedrich, R. %D 2014 %J Science Signaling %N 342 %R ARTN ra86 10.1126/scisignal.2005703 %T Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid %U /brokenurl#<Go to ISI>://WOS:000342365700001 %V 7 %X Under drought stress, abscisic acid (ABA) triggers closure of leaf cell pores called stomata, which are formed by two specialized cells called guard cells in plant epidermis. Two pathways downstream of ABA stimulate phosphorylation of the S-type anion channels SLAC1 (slow anion channel associated 1) and SLAH3 (SLAC1 homolog 3), which causes these channels to open, reducing guard cell volume and triggering stomatal closure. One branch involves OST1 (open stomata 1), a calcium-independent SnRK2-type kinase, and the other branch involves calcium-dependent protein kinases of the CPK (calcium-dependent protein kinase) family. We used coexpression analyses in Xenopus oocytes to show that the calcineurin B-like (CBL) calcium sensors CBL1 and CBL9 and their interacting protein kinase CIPK23 also triggered SLAC1 and SLAH3 opening. We analyzed whether regulation of SLAC1 opening by these different families of kinases involved the same or different sites on SLAC1 by measuring channel conductance of SLAC1 with mutations in the putative phosphorylation sites in the amino or carboxyl termini coexpressed with specific kinases in Xenopus oocytes. SLAC1 mutants lacking the OST1-phosphorylated site were still activated by CPK or by CBL/CIPK complexes. Phosphorylation and activation of SLAC1 by any of the kinases were inhibited by the phosphatase ABI1 (ABA insensitive 1), which is inactivated in response to ABA signaling. These findings identified CBL/CIPK complexes as potential regulators of stomatal aperture through S-type anion channels and indicated that phosphorylation at distinct sites enables SLAC1 activation by both calcium-dependent and calcium-independent pathways downstream of ABA.
• A Single-Pore Residue Renders the Root Anion Channel SLAH2 Highly Nitrate Selective. Maierhofer, T.; Lind, C.; Hüttl, S.; Scherzer, S.; Papenfuss, M.; Simon, J.; Al-Rasheid, K. A. S.; Ache, P.; Rennenberg, H.; Hedrich, R.; Müller, T. D.; Geiger, D. In Plant Cell, 26(6), pp. 2554–2567. 2014.
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  In contrast to animal cells, plants use nitrate as a major source of nitrogen. Following the uptake of nitrate, this major macronutrient is fed into the vasculature for long-distance transport. The Arabidopsis thaliana shoot expresses the anion channel SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAC1 HOMOLOGOUS3 (SLAH3), which prefer nitrate as substrate but cannot exclude chloride ions. By contrast, we identified SLAH2 as a nitrate-specific channel that is impermeable for chloride. To understand the molecular basis for nitrate selection in the SLAH2 channel, SLAC1 and SLAH2 were modeled to the structure of HiTehA, a distantly related bacterial member. Structure-guided site-directed mutations converted SLAC1 into a SLAH2-like nitrate-specific anion channel and vice versa. Our findings indicate that two pore-occluding phenylalanines constrict the pore. The selectivity filter of SLAC/SLAH anion channels is determined by the polarity of pore-lining residues located on alpha helix 3. Changing the polar character of a single amino acid side chain (Ser-228) to a nonpolar residue turned the nitrate-selective SLAH2 into a chloride/nitrate-permeable anion channel. Thus, the molecular basis of the anion specificity of SLAC/SLAH anion channels seems to be determined by the presence and constellation of polar side chains that act in concert with the two pore-occluding phenylalanines.

  @article{RN1073, abstract = {In contrast to animal cells, plants use nitrate as a major source of nitrogen. Following the uptake of nitrate, this major macronutrient is fed into the vasculature for long-distance transport. The Arabidopsis thaliana shoot expresses the anion channel SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAC1 HOMOLOGOUS3 (SLAH3), which prefer nitrate as substrate but cannot exclude chloride ions. By contrast, we identified SLAH2 as a nitrate-specific channel that is impermeable for chloride. To understand the molecular basis for nitrate selection in the SLAH2 channel, SLAC1 and SLAH2 were modeled to the structure of HiTehA, a distantly related bacterial member. Structure-guided site-directed mutations converted SLAC1 into a SLAH2-like nitrate-specific anion channel and vice versa. Our findings indicate that two pore-occluding phenylalanines constrict the pore. The selectivity filter of SLAC/SLAH anion channels is determined by the polarity of pore-lining residues located on alpha helix 3. Changing the polar character of a single amino acid side chain (Ser-228) to a nonpolar residue turned the nitrate-selective SLAH2 into a chloride/nitrate-permeable anion channel. Thus, the molecular basis of the anion specificity of SLAC/SLAH anion channels seems to be determined by the presence and constellation of polar side chains that act in concert with the two pore-occluding phenylalanines.}, author = {Maierhofer, T. and Lind, C. and Hüttl, S. and Scherzer, S. and Papenfuss, M. and Simon, J. and Al-Rasheid, K. A. S. and Ache, P. and Rennenberg, H. and Hedrich, R. and Müller, T. D. and Geiger, D.}, journal = {Plant Cell}, keywords = {channels}, note = {Ap2dz Times Cited:58 Cited References Count:53}, number = 6, pages = {2554-2567}, title = {A Single-Pore Residue Renders the Root Anion Channel SLAH2 Highly Nitrate Selective}, type = {Journal Article}, volume = 26, year = 2014 }

  %0 Journal Article %1 RN1073 %A Maierhofer, T. %A Lind, C. %A Hüttl, S. %A Scherzer, S. %A Papenfuss, M. %A Simon, J. %A Al-Rasheid, K. A. S. %A Ache, P. %A Rennenberg, H. %A Hedrich, R. %A Müller, T. D. %A Geiger, D. %D 2014 %J Plant Cell %N 6 %P 2554-2567 %R 10.1105/tpc.114.125849 %T A Single-Pore Residue Renders the Root Anion Channel SLAH2 Highly Nitrate Selective %U /brokenurl#<Go to ISI>://WOS:000341884000018 %V 26 %X In contrast to animal cells, plants use nitrate as a major source of nitrogen. Following the uptake of nitrate, this major macronutrient is fed into the vasculature for long-distance transport. The Arabidopsis thaliana shoot expresses the anion channel SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAC1 HOMOLOGOUS3 (SLAH3), which prefer nitrate as substrate but cannot exclude chloride ions. By contrast, we identified SLAH2 as a nitrate-specific channel that is impermeable for chloride. To understand the molecular basis for nitrate selection in the SLAH2 channel, SLAC1 and SLAH2 were modeled to the structure of HiTehA, a distantly related bacterial member. Structure-guided site-directed mutations converted SLAC1 into a SLAH2-like nitrate-specific anion channel and vice versa. Our findings indicate that two pore-occluding phenylalanines constrict the pore. The selectivity filter of SLAC/SLAH anion channels is determined by the polarity of pore-lining residues located on alpha helix 3. Changing the polar character of a single amino acid side chain (Ser-228) to a nonpolar residue turned the nitrate-selective SLAH2 into a chloride/nitrate-permeable anion channel. Thus, the molecular basis of the anion specificity of SLAC/SLAH anion channels seems to be determined by the presence and constellation of polar side chains that act in concert with the two pore-occluding phenylalanines.
• : large-scale high-accuracy PacBio correction through iterative short read consensus. Hackl, T.; Hedrich, R.; Schultz, J.; Förster, F. In Bioinformatics, 30(21), pp. 3004–3011. 2014.
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  Motivation: Today, the base code of DNA is mostly determined through sequencing by synthesis as provided by the Illumina sequencers. Although highly accurate, resulting reads are short, making their analyses challenging. Recently, a new technology, single molecule real-time (SMRT) sequencing, was developed that could address these challenges, as it generates reads of several thousand bases. But, their broad application has been hampered by a high error rate. Therefore, hybrid approaches that use high-quality short reads to correct erroneous SMRT long reads have been developed. Still, current implementations have great demands on hardware, work only in well-defined computing infrastructures and reject a substantial amount of reads. This limits their usability considerably, especially in the case of large sequencing projects. Results: Here we present proovread, a hybrid correction pipeline for SMRT reads, which can be flexibly adapted on existing hardware and infrastructure from a laptop to a high-performance computing cluster. On genomic and transcriptomic test cases covering Escherichia coli, Arabidopsis thaliana and human, proovread achieved accuracies up to 99.9% and outperformed the existing hybrid correction programs. Furthermore, proovread-corrected sequences were longer and the throughput was higher. Thus, proovread combines the most accurate correction results with an excellent adaptability to the available hardware. It will therefore increase the applicability and value of SMRT sequencing.

  @article{RN1080, abstract = {Motivation: Today, the base code of DNA is mostly determined through sequencing by synthesis as provided by the Illumina sequencers. Although highly accurate, resulting reads are short, making their analyses challenging. Recently, a new technology, single molecule real-time (SMRT) sequencing, was developed that could address these challenges, as it generates reads of several thousand bases. But, their broad application has been hampered by a high error rate. Therefore, hybrid approaches that use high-quality short reads to correct erroneous SMRT long reads have been developed. Still, current implementations have great demands on hardware, work only in well-defined computing infrastructures and reject a substantial amount of reads. This limits their usability considerably, especially in the case of large sequencing projects. Results: Here we present proovread, a hybrid correction pipeline for SMRT reads, which can be flexibly adapted on existing hardware and infrastructure from a laptop to a high-performance computing cluster. On genomic and transcriptomic test cases covering Escherichia coli, Arabidopsis thaliana and human, proovread achieved accuracies up to 99.9% and outperformed the existing hybrid correction programs. Furthermore, proovread-corrected sequences were longer and the throughput was higher. Thus, proovread combines the most accurate correction results with an excellent adaptability to the available hardware. It will therefore increase the applicability and value of SMRT sequencing.}, author = {Hackl, T. and Hedrich, R. and Schultz, J. and Förster, F.}, journal = {Bioinformatics}, keywords = {myOwn}, note = {At0sg Times Cited:350 Cited References Count:26}, number = 21, pages = {3004-3011}, title = {: large-scale high-accuracy PacBio correction through iterative short read consensus}, type = {Journal Article}, volume = 30, year = 2014 }

  %0 Journal Article %1 RN1080 %A Hackl, T. %A Hedrich, R. %A Schultz, J. %A Förster, F. %D 2014 %J Bioinformatics %N 21 %P 3004-3011 %R 10.1093/bioinformatics/btu392 %T : large-scale high-accuracy PacBio correction through iterative short read consensus %U /brokenurl#<Go to ISI>://WOS:000344644600003 %V 30 %X Motivation: Today, the base code of DNA is mostly determined through sequencing by synthesis as provided by the Illumina sequencers. Although highly accurate, resulting reads are short, making their analyses challenging. Recently, a new technology, single molecule real-time (SMRT) sequencing, was developed that could address these challenges, as it generates reads of several thousand bases. But, their broad application has been hampered by a high error rate. Therefore, hybrid approaches that use high-quality short reads to correct erroneous SMRT long reads have been developed. Still, current implementations have great demands on hardware, work only in well-defined computing infrastructures and reject a substantial amount of reads. This limits their usability considerably, especially in the case of large sequencing projects. Results: Here we present proovread, a hybrid correction pipeline for SMRT reads, which can be flexibly adapted on existing hardware and infrastructure from a laptop to a high-performance computing cluster. On genomic and transcriptomic test cases covering Escherichia coli, Arabidopsis thaliana and human, proovread achieved accuracies up to 99.9% and outperformed the existing hybrid correction programs. Furthermore, proovread-corrected sequences were longer and the throughput was higher. Thus, proovread combines the most accurate correction results with an excellent adaptability to the available hardware. It will therefore increase the applicability and value of SMRT sequencing.
• Strategy of nitrogen acquisition and utilization by carnivorous. Kruse, J.; Gao, P.; Honsel, A.; Kreuzwieser, J.; Burzlaff, T.; Alfarraj, S.; Hedrich, R.; Rennenberg, H. In Oecologia, 174(3), pp. 839–851. 2014.
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  Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using C-13/N-15-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of N-15 uptake on light-saturated photosynthesis (A (max)), dark respiration (R (D)) and growth. Depending on N status, insect capture briefly altered the dynamics of R (D)/A (max), reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea's strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea's success with regards to a carnivorous life style.

  @article{RN1076, abstract = {Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using C-13/N-15-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of N-15 uptake on light-saturated photosynthesis (A (max)), dark respiration (R (D)) and growth. Depending on N status, insect capture briefly altered the dynamics of R (D)/A (max), reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea's strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea's success with regards to a carnivorous life style.}, author = {Kruse, J. and Gao, P. and Honsel, A. and Kreuzwieser, J. and Burzlaff, T. and Alfarraj, S. and Hedrich, R. and Rennenberg, H.}, journal = {Oecologia}, keywords = {carnivory}, note = {Ab7ws Times Cited:28 Cited References Count:59}, number = 3, pages = {839-851}, title = {Strategy of nitrogen acquisition and utilization by carnivorous}, type = {Journal Article}, volume = 174, year = 2014 }

  %0 Journal Article %1 RN1076 %A Kruse, J. %A Gao, P. %A Honsel, A. %A Kreuzwieser, J. %A Burzlaff, T. %A Alfarraj, S. %A Hedrich, R. %A Rennenberg, H. %D 2014 %J Oecologia %N 3 %P 839-851 %R 10.1007/s00442-013-2802-9 %T Strategy of nitrogen acquisition and utilization by carnivorous %U /brokenurl#<Go to ISI>://WOS:000332002300021 %V 174 %X Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using C-13/N-15-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of N-15 uptake on light-saturated photosynthesis (A (max)), dark respiration (R (D)) and growth. Depending on N status, insect capture briefly altered the dynamics of R (D)/A (max), reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea's strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea's success with regards to a carnivorous life style.
• Salt bladders: do they matter?. Shabala, S.; Bose, J.; Hedrich, R. In Trends in Plant Science, 19(11), pp. 687–691. 2014.
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  Soil salinity is claiming about three hectares of arable land from conventional crop farming every minute. At the same time, the challenge of feeding 9.3 billion people by 2050 is forcing agricultural production into marginal areas, and providing sufficient food for this growing population cannot be achieved without a major breakthrough in crop breeding for salinity tolerance. In this Opinion article, we argue that the current trend of targeting Na+ exclusion mechanisms in breeding programmes for salinity tolerance in crops needs revising. We propose that progress in this area will be achieved by learning from halophytes, naturally salt-loving plants capable of surviving in harsh saline environments, by targeting the mechanisms conferring Na+ sequestration in external storage organs.

  @article{RN1071, abstract = {Soil salinity is claiming about three hectares of arable land from conventional crop farming every minute. At the same time, the challenge of feeding 9.3 billion people by 2050 is forcing agricultural production into marginal areas, and providing sufficient food for this growing population cannot be achieved without a major breakthrough in crop breeding for salinity tolerance. In this Opinion article, we argue that the current trend of targeting Na+ exclusion mechanisms in breeding programmes for salinity tolerance in crops needs revising. We propose that progress in this area will be achieved by learning from halophytes, naturally salt-loving plants capable of surviving in harsh saline environments, by targeting the mechanisms conferring Na+ sequestration in external storage organs.}, author = {Shabala, S. and Bose, J. and Hedrich, R.}, journal = {Trends in Plant Science}, keywords = {sodium-transport}, note = {At9pi Times Cited:209 Cited References Count:45}, number = 11, pages = {687-691}, title = {Salt bladders: do they matter?}, type = {Journal Article}, volume = 19, year = 2014 }

  %0 Journal Article %1 RN1071 %A Shabala, S. %A Bose, J. %A Hedrich, R. %D 2014 %J Trends in Plant Science %N 11 %P 687-691 %R 10.1016/j.tplants.2014.09.001 %T Salt bladders: do they matter? %U /brokenurl#<Go to ISI>://WOS:000345258500003 %V 19 %X Soil salinity is claiming about three hectares of arable land from conventional crop farming every minute. At the same time, the challenge of feeding 9.3 billion people by 2050 is forcing agricultural production into marginal areas, and providing sufficient food for this growing population cannot be achieved without a major breakthrough in crop breeding for salinity tolerance. In this Opinion article, we argue that the current trend of targeting Na+ exclusion mechanisms in breeding programmes for salinity tolerance in crops needs revising. We propose that progress in this area will be achieved by learning from halophytes, naturally salt-loving plants capable of surviving in harsh saline environments, by targeting the mechanisms conferring Na+ sequestration in external storage organs.
• The Venus flytrap attracts insects by the release of volatile organic compounds. Kreuzwieser, J.; Scheerer, U.; Kruse, J.; Burzlaff, T.; Honsel, A.; Alfarraj, S.; Georgiev, P.; Schnitzler, J. P.; Ghirardo, A.; Kreuzer, I.; Hedrich, R.; Rennenberg, H. In Journal of Experimental Botany, 65(2), pp. 755–766. 2014.
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  Does Dionaea muscipula, the Venus flytrap, use a particular mechanism to attract animal prey? This question was raised by Charles Darwin 140 years ago, but it remains unanswered. This study tested the hypothesis that Dionaea releases volatile organic compounds (VOCs) to allure prey insects. For this purpose, olfactory choice bioassays were performed to elucidate if Dionaea attracts Drosophila melanogaster. The VOCs emitted by the plant were further analysed by GC-MS and proton transfer reaction-mass spectrometry (PTR-MS). The bioassays documented that Drosophila was strongly attracted by the carnivorous plant. Over 60 VOCs, including terpenes, benzenoids, and aliphatics, were emitted by Dionaea, predominantly in the light. This work further tested whether attraction of animal prey is affected by the nutritional status of the plant. For this purpose, Dionaea plants were fed with insect biomass to improve plant N status. However, although such feeding altered the VOC emission pattern by reducing terpene release, the attraction of Drosophila was not affected. From these results it is concluded that Dionaea attracts insects on the basis of food smell mimicry because the scent released has strong similarity to the bouquet of fruits and plant flowers. Such a volatile blend is emitted to attract insects searching for food to visit the deadly capture organ of the Venus flytrap.

  @article{RN1077, abstract = {Does Dionaea muscipula, the Venus flytrap, use a particular mechanism to attract animal prey? This question was raised by Charles Darwin 140 years ago, but it remains unanswered. This study tested the hypothesis that Dionaea releases volatile organic compounds (VOCs) to allure prey insects. For this purpose, olfactory choice bioassays were performed to elucidate if Dionaea attracts Drosophila melanogaster. The VOCs emitted by the plant were further analysed by GC-MS and proton transfer reaction-mass spectrometry (PTR-MS). The bioassays documented that Drosophila was strongly attracted by the carnivorous plant. Over 60 VOCs, including terpenes, benzenoids, and aliphatics, were emitted by Dionaea, predominantly in the light. This work further tested whether attraction of animal prey is affected by the nutritional status of the plant. For this purpose, Dionaea plants were fed with insect biomass to improve plant N status. However, although such feeding altered the VOC emission pattern by reducing terpene release, the attraction of Drosophila was not affected. From these results it is concluded that Dionaea attracts insects on the basis of food smell mimicry because the scent released has strong similarity to the bouquet of fruits and plant flowers. Such a volatile blend is emitted to attract insects searching for food to visit the deadly capture organ of the Venus flytrap.}, author = {Kreuzwieser, J. and Scheerer, U. and Kruse, J. and Burzlaff, T. and Honsel, A. and Alfarraj, S. and Georgiev, P. and Schnitzler, J. P. and Ghirardo, A. and Kreuzer, I. and Hedrich, R. and Rennenberg, H.}, journal = {Journal of Experimental Botany}, keywords = {carnivorous}, note = {Aa5eq Times Cited:62 Cited References Count:71}, number = 2, pages = {755-766}, title = {The Venus flytrap attracts insects by the release of volatile organic compounds}, type = {Journal Article}, volume = 65, year = 2014 }

  %0 Journal Article %1 RN1077 %A Kreuzwieser, J. %A Scheerer, U. %A Kruse, J. %A Burzlaff, T. %A Honsel, A. %A Alfarraj, S. %A Georgiev, P. %A Schnitzler, J. P. %A Ghirardo, A. %A Kreuzer, I. %A Hedrich, R. %A Rennenberg, H. %D 2014 %J Journal of Experimental Botany %N 2 %P 755-766 %R 10.1093/jxb/ert455 %T The Venus flytrap attracts insects by the release of volatile organic compounds %U /brokenurl#<Go to ISI>://WOS:000331119300030 %V 65 %X Does Dionaea muscipula, the Venus flytrap, use a particular mechanism to attract animal prey? This question was raised by Charles Darwin 140 years ago, but it remains unanswered. This study tested the hypothesis that Dionaea releases volatile organic compounds (VOCs) to allure prey insects. For this purpose, olfactory choice bioassays were performed to elucidate if Dionaea attracts Drosophila melanogaster. The VOCs emitted by the plant were further analysed by GC-MS and proton transfer reaction-mass spectrometry (PTR-MS). The bioassays documented that Drosophila was strongly attracted by the carnivorous plant. Over 60 VOCs, including terpenes, benzenoids, and aliphatics, were emitted by Dionaea, predominantly in the light. This work further tested whether attraction of animal prey is affected by the nutritional status of the plant. For this purpose, Dionaea plants were fed with insect biomass to improve plant N status. However, although such feeding altered the VOC emission pattern by reducing terpene release, the attraction of Drosophila was not affected. From these results it is concluded that Dionaea attracts insects on the basis of food smell mimicry because the scent released has strong similarity to the bouquet of fruits and plant flowers. Such a volatile blend is emitted to attract insects searching for food to visit the deadly capture organ of the Venus flytrap.
• A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants. Léran, S.; Varala, K.; Boyer, J. C.; Chiurazzi, M.; Crawford, N.; Daniel-Vedele, F.; David, L.; Dickstein, R.; Fernandez, E.; Forde, B.; Gassmann, W.; Geiger, D.; Gojon, A.; Gong, J. M.; Halkier, B. A.; Harris, J. M.; Hedrich, R.; Limami, A. M.; Rentsch, D.; Seo, M.; Tsay, Y. F.; Zhang, M. Y.; Coruzzi, G.; Lacombe, B. In Trends in Plant Science, 19(1), pp. 5–9. 2014.
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  Members of the plant NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER (NRT1/PTR) family display protein sequence homology with the SLC15/PepT/PTR/POT family of peptide transporters in animals. In comparison to their animal and bacterial counterparts, these plant proteins transport a wide variety of substrates: nitrate, peptides, amino acids, dicarboxylates, glucosinolates, IAA, and ABA. The phylogenetic relationship of the members of the NRT1/PTR family in 31 fully sequenced plant genomes allowed the identification of unambiguous clades, defining eight subfamilies. The phylogenetic tree was used to determine a unified nomenclature of this family named NPF, for NRT1/PTR FAMILY. We propose that the members should be named accordingly: NPFX.Y, where X denotes the subfamily and Y the individual member within the species.

  @article{RN1075, abstract = {Members of the plant NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER (NRT1/PTR) family display protein sequence homology with the SLC15/PepT/PTR/POT family of peptide transporters in animals. In comparison to their animal and bacterial counterparts, these plant proteins transport a wide variety of substrates: nitrate, peptides, amino acids, dicarboxylates, glucosinolates, IAA, and ABA. The phylogenetic relationship of the members of the NRT1/PTR family in 31 fully sequenced plant genomes allowed the identification of unambiguous clades, defining eight subfamilies. The phylogenetic tree was used to determine a unified nomenclature of this family named NPF, for NRT1/PTR FAMILY. We propose that the members should be named accordingly: NPFX.Y, where X denotes the subfamily and Y the individual member within the species.}, author = {Léran, S. and Varala, K. and Boyer, J. C. and Chiurazzi, M. and Crawford, N. and Daniel-Vedele, F. and David, L. and Dickstein, R. and Fernandez, E. and Forde, B. and Gassmann, W. and Geiger, D. and Gojon, A. and Gong, J. M. and Halkier, B. A. and Harris, J. M. and Hedrich, R. and Limami, A. M. and Rentsch, D. and Seo, M. and Tsay, Y. F. and Zhang, M. Y. and Coruzzi, G. and Lacombe, B.}, journal = {Trends in Plant Science}, keywords = {arabidopsis}, note = {294ab Times Cited:445 Cited References Count:52}, number = 1, pages = {5-9}, title = {A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants}, type = {Journal Article}, volume = 19, year = 2014 }

  %0 Journal Article %1 RN1075 %A Léran, S. %A Varala, K. %A Boyer, J. C. %A Chiurazzi, M. %A Crawford, N. %A Daniel-Vedele, F. %A David, L. %A Dickstein, R. %A Fernandez, E. %A Forde, B. %A Gassmann, W. %A Geiger, D. %A Gojon, A. %A Gong, J. M. %A Halkier, B. A. %A Harris, J. M. %A Hedrich, R. %A Limami, A. M. %A Rentsch, D. %A Seo, M. %A Tsay, Y. F. %A Zhang, M. Y. %A Coruzzi, G. %A Lacombe, B. %D 2014 %J Trends in Plant Science %N 1 %P 5-9 %R 10.1016/j.tplants.2013.08.008 %T A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants %U /brokenurl#<Go to ISI>://WOS:000330013700002 %V 19 %X Members of the plant NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER (NRT1/PTR) family display protein sequence homology with the SLC15/PepT/PTR/POT family of peptide transporters in animals. In comparison to their animal and bacterial counterparts, these plant proteins transport a wide variety of substrates: nitrate, peptides, amino acids, dicarboxylates, glucosinolates, IAA, and ABA. The phylogenetic relationship of the members of the NRT1/PTR family in 31 fully sequenced plant genomes allowed the identification of unambiguous clades, defining eight subfamilies. The phylogenetic tree was used to determine a unified nomenclature of this family named NPF, for NRT1/PTR FAMILY. We propose that the members should be named accordingly: NPFX.Y, where X denotes the subfamily and Y the individual member within the species.
• Secreted major Venus flytrap chitinase enables digestion of Arthropod prey. Paszota, P.; Escalante-Perez, M.; Thomsen, L. R.; Risor, M. W.; Dembski, A.; Sanglas, L.; Nielsen, T. A.; Karring, H.; Thogersen, I. B.; Hedrich, R.; Enghild, J. J.; Kreuzer, I.; Sanggaard, K. W. In Biochimica Et Biophysica Acta-Proteins and Proteomics, 1844(2), pp. 374–383. 2014.
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  Predation plays a major role in energy and nutrient flow in the biological food chain. Plant carnivory has attracted much interest since Darwin's time, but many fundamental properties of the carnivorous lifestyle are largely unexplored. In particular, the chain of events leading from prey perception to its digestive utilization remains to be elucidated. One of the first steps after the capture of animal prey, i.e. the enzymatic breakup of the insects' chitin-based shell, is reflected by considerable chitinase activity in the secreted digestive fluid in the carnivorous plant Venus flytrap. This study addresses the molecular nature, function, and regulation of the underlying enzyme, VF chitinase-I. Using mass spectrometry based de novo sequencing, VF chitinase-I was identified in the secreted fluid. As anticipated for one of the most prominent proteins in the flytrap's "green stomach" during prey digestion, transcription of VF chitinase-I is restricted to glands and enhanced by secretion-inducing stimuli. In their natural habitat, Venus flytrap is exposed to high temperatures. We expressed and purified recombinant VF chitinase-I and show that the enzyme exhibits the hallmark properties expected from an enzyme active in the hot and acidic digestive fluid of Dionaea muscipula. Structural modeling revealed a relative compact globular form of VF chitinase-I, which might contribute to its overall stability and resistance to proteolysis. These peculiar characteristics could well serve industrial purposes, especially because of the ability to hydrolyze both soluble and crystalline chitin substrates including the commercially important cleavage of alpha-chitin. (C) 2013 Elsevier B.V. All rights reserved.

  @article{RN1072, abstract = {Predation plays a major role in energy and nutrient flow in the biological food chain. Plant carnivory has attracted much interest since Darwin's time, but many fundamental properties of the carnivorous lifestyle are largely unexplored. In particular, the chain of events leading from prey perception to its digestive utilization remains to be elucidated. One of the first steps after the capture of animal prey, i.e. the enzymatic breakup of the insects' chitin-based shell, is reflected by considerable chitinase activity in the secreted digestive fluid in the carnivorous plant Venus flytrap. This study addresses the molecular nature, function, and regulation of the underlying enzyme, VF chitinase-I. Using mass spectrometry based de novo sequencing, VF chitinase-I was identified in the secreted fluid. As anticipated for one of the most prominent proteins in the flytrap's "green stomach" during prey digestion, transcription of VF chitinase-I is restricted to glands and enhanced by secretion-inducing stimuli. In their natural habitat, Venus flytrap is exposed to high temperatures. We expressed and purified recombinant VF chitinase-I and show that the enzyme exhibits the hallmark properties expected from an enzyme active in the hot and acidic digestive fluid of Dionaea muscipula. Structural modeling revealed a relative compact globular form of VF chitinase-I, which might contribute to its overall stability and resistance to proteolysis. These peculiar characteristics could well serve industrial purposes, especially because of the ability to hydrolyze both soluble and crystalline chitin substrates including the commercially important cleavage of alpha-chitin. (C) 2013 Elsevier B.V. All rights reserved.}, author = {Paszota, P. and Escalante-Perez, M. and Thomsen, L. R. and Risor, M. W. and Dembski, A. and Sanglas, L. and Nielsen, T. A. and Karring, H. and Thogersen, I. B. and Hedrich, R. and Enghild, J. J. and Kreuzer, I. and Sanggaard, K. W.}, journal = {Biochimica Et Biophysica Acta-Proteins and Proteomics}, keywords = {carnivorous}, note = {300uh Times Cited:35 Cited References Count:73}, number = 2, pages = {374-383}, title = {Secreted major Venus flytrap chitinase enables digestion of Arthropod prey}, type = {Journal Article}, volume = 1844, year = 2014 }

  %0 Journal Article %1 RN1072 %A Paszota, P. %A Escalante-Perez, M. %A Thomsen, L. R. %A Risor, M. W. %A Dembski, A. %A Sanglas, L. %A Nielsen, T. A. %A Karring, H. %A Thogersen, I. B. %A Hedrich, R. %A Enghild, J. J. %A Kreuzer, I. %A Sanggaard, K. W. %D 2014 %J Biochimica Et Biophysica Acta-Proteins and Proteomics %N 2 %P 374-383 %R 10.1016/j.bbapap.2013.11.009 %T Secreted major Venus flytrap chitinase enables digestion of Arthropod prey %U /brokenurl#<Go to ISI>://WOS:000330489000010 %V 1844 %X Predation plays a major role in energy and nutrient flow in the biological food chain. Plant carnivory has attracted much interest since Darwin's time, but many fundamental properties of the carnivorous lifestyle are largely unexplored. In particular, the chain of events leading from prey perception to its digestive utilization remains to be elucidated. One of the first steps after the capture of animal prey, i.e. the enzymatic breakup of the insects' chitin-based shell, is reflected by considerable chitinase activity in the secreted digestive fluid in the carnivorous plant Venus flytrap. This study addresses the molecular nature, function, and regulation of the underlying enzyme, VF chitinase-I. Using mass spectrometry based de novo sequencing, VF chitinase-I was identified in the secreted fluid. As anticipated for one of the most prominent proteins in the flytrap's "green stomach" during prey digestion, transcription of VF chitinase-I is restricted to glands and enhanced by secretion-inducing stimuli. In their natural habitat, Venus flytrap is exposed to high temperatures. We expressed and purified recombinant VF chitinase-I and show that the enzyme exhibits the hallmark properties expected from an enzyme active in the hot and acidic digestive fluid of Dionaea muscipula. Structural modeling revealed a relative compact globular form of VF chitinase-I, which might contribute to its overall stability and resistance to proteolysis. These peculiar characteristics could well serve industrial purposes, especially because of the ability to hydrolyze both soluble and crystalline chitin substrates including the commercially important cleavage of alpha-chitin. (C) 2013 Elsevier B.V. All rights reserved.
• Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination. Klemens, P. A. W.; Patzke, K.; Trentmann, O.; Poschet, G.; Büttner, M.; Schulz, A.; Marten, I.; Hedrich, R.; Neuhaus, H. E. In New Phytologist, 202(1), pp. 188–197. 2014.
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  Arabidopsis vacuoles harbor, besides sugar transporter of the TMT-type, an early response to dehydration like 6 (ERDL6) protein involved in glucose export into the cytosol. However, the mode of transport of ERDL6 and the plant's feedback to overexpression of its activity on essential properties such as, for example, seed germination or freezing tolerance, remain unexplored. Using patch-clamp studies on vacuoles expressing AtERDL6 we demonstrated directly that this carrier operates as a proton-driven glucose exporter. Overexpression of BvIMP, the closest sugar beet (Beta vulgaris) homolog to AtERDL6, in Arabidopsis leads surprisingly to impaired seed germination under both conditions, sugar application and low environmental temperatures, but not under standard conditions. Upon cold treatment, BvIMP overexpressor plants accumulated lower quantities of monosaccharides than the wild-type, a response in line with the reduced frost tolerance of the transgenic Arabidopsis plants, and the fact that cold temperatures inhibits BvIMP transcription in sugar beet leaves. With these findings we show that the tight control of vacuolar sugar import and export is a key requisite for cold tolerance and seed germination of plants.

  @article{RN1079, abstract = {Arabidopsis vacuoles harbor, besides sugar transporter of the TMT-type, an early response to dehydration like 6 (ERDL6) protein involved in glucose export into the cytosol. However, the mode of transport of ERDL6 and the plant's feedback to overexpression of its activity on essential properties such as, for example, seed germination or freezing tolerance, remain unexplored. Using patch-clamp studies on vacuoles expressing AtERDL6 we demonstrated directly that this carrier operates as a proton-driven glucose exporter. Overexpression of BvIMP, the closest sugar beet (Beta vulgaris) homolog to AtERDL6, in Arabidopsis leads surprisingly to impaired seed germination under both conditions, sugar application and low environmental temperatures, but not under standard conditions. Upon cold treatment, BvIMP overexpressor plants accumulated lower quantities of monosaccharides than the wild-type, a response in line with the reduced frost tolerance of the transgenic Arabidopsis plants, and the fact that cold temperatures inhibits BvIMP transcription in sugar beet leaves. With these findings we show that the tight control of vacuolar sugar import and export is a key requisite for cold tolerance and seed germination of plants.}, author = {Klemens, P. A. W. and Patzke, K. and Trentmann, O. and Poschet, G. and Büttner, M. and Schulz, A. and Marten, I. and Hedrich, R. and Neuhaus, H. E.}, journal = {New Phytologist}, keywords = {arabidopsis}, note = {Ab4cx Times Cited:55 Cited References Count:50}, number = 1, pages = {188-197}, title = {Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination}, type = {Journal Article}, volume = 202, year = 2014 }

  %0 Journal Article %1 RN1079 %A Klemens, P. A. W. %A Patzke, K. %A Trentmann, O. %A Poschet, G. %A Büttner, M. %A Schulz, A. %A Marten, I. %A Hedrich, R. %A Neuhaus, H. E. %D 2014 %J New Phytologist %N 1 %P 188-197 %R 10.1111/nph.12642 %T Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination %U /brokenurl#<Go to ISI>://WOS:000331737900027 %V 202 %X Arabidopsis vacuoles harbor, besides sugar transporter of the TMT-type, an early response to dehydration like 6 (ERDL6) protein involved in glucose export into the cytosol. However, the mode of transport of ERDL6 and the plant's feedback to overexpression of its activity on essential properties such as, for example, seed germination or freezing tolerance, remain unexplored. Using patch-clamp studies on vacuoles expressing AtERDL6 we demonstrated directly that this carrier operates as a proton-driven glucose exporter. Overexpression of BvIMP, the closest sugar beet (Beta vulgaris) homolog to AtERDL6, in Arabidopsis leads surprisingly to impaired seed germination under both conditions, sugar application and low environmental temperatures, but not under standard conditions. Upon cold treatment, BvIMP overexpressor plants accumulated lower quantities of monosaccharides than the wild-type, a response in line with the reduced frost tolerance of the transgenic Arabidopsis plants, and the fact that cold temperatures inhibits BvIMP transcription in sugar beet leaves. With these findings we show that the tight control of vacuolar sugar import and export is a key requisite for cold tolerance and seed germination of plants.

• How Do Stomata Sense Reductions in Atmospheric Relative Humidity?. Bauer, H.; Ache, P.; Wohlfart, F.; Al-Rasheid, K. A. S.; Sonnewald, S.; Sonnewald, U.; Kneitz, S.; Hetherington, A. M.; Hedrich, R. In Molecular Plant, 6(5), pp. 1703–1706. 2013.
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  @article{RN1090, author = {Bauer, H. and Ache, P. and Wohlfart, F. and Al-Rasheid, K. A. S. and Sonnewald, S. and Sonnewald, U. and Kneitz, S. and Hetherington, A. M. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {pair}, note = {223sk Times Cited:26 Cited References Count:11}, number = 5, pages = {1703-1706}, title = {How Do Stomata Sense Reductions in Atmospheric Relative Humidity?}, type = {Journal Article}, volume = 6, year = 2013 }

  %0 Journal Article %1 RN1090 %A Bauer, H. %A Ache, P. %A Wohlfart, F. %A Al-Rasheid, K. A. S. %A Sonnewald, S. %A Sonnewald, U. %A Kneitz, S. %A Hetherington, A. M. %A Hedrich, R. %D 2013 %J Molecular Plant %N 5 %P 1703-1706 %R 10.1093/mp/sst055 %T How Do Stomata Sense Reductions in Atmospheric Relative Humidity? %U /brokenurl#<Go to ISI>://WOS:000324829400025 %V 6
• The Ammonium Channel Provides NH Uptake Associated with Venus Flytrap’s Prey Digestion. Scherzer, S.; Kro, E.; Kreuzer, I.; Kruse, J.; Karl, F.; von Rüden, M.; Escalante-Perez, M.; Müller, T.; Rennenberg, H.; Al-Rasheid, K. A. S.; Neher, E.; Hedrich, R. In Current Biology, 23(17), pp. 1649–1657. 2013.
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  Background: Ammonium transporter (AMT/MEP/Rh) superfamily members mediate ammonium uptake and retrieval. This pivotal transport system is conserved among all living organisms. For plants, nitrogen represents a macronutrient available in the soil as ammonium, nitrate, and organic nitrogen compounds. Plants living on extremely nutrient-poor soils have developed a number of adaptation mechanisms, including a carnivorous lifestyle. This study addresses the molecular nature, function, and regulation of prey-derived ammonium uptake in the Venus flytrap, Dionaea muscipula, one of the fastest active carnivores. Results: The Dionaea muscipula ammonium transporter DmAMT1 was localized in gland complexes where its expression was upregulated upon secretion. These clusters of cells decorating the inner trap surface are engaged in (1) secretion of an acidic digestive enzyme cocktail and (2) uptake of prey-derived nutrients. Voltage clamp of Xenopus oocytes expressing DmAMT1 and membrane potential recordings with DmAMT1-expressing Dionaea glands were used to monitor and compare electrophysiological properties of DmAMT1 in vitro and in planta. DmAMT1 exhibited the hallmark biophysical properties of a NH4+-selective channel. At depolarized membrane potentials (V-m = 0), the K-m (3.2 +/- 0.3 mM) indicated a low affinity of DmAMT1 for ammonium that increased systematically with negative going voltages. Upon hyperpolarization to, e.g., -200 mV, a K-m of 0.14 +/- 0.015 mM documents the voltage-dependent shift of DmAMT1 into a NH4+ transport system of high affinity. Conclusions: We suggest that regulation of glandular DmAMT1 and membrane potential readjustments of the endocrine cells provide for effective adaptation to varying, prey-derived ammonium sources.

  @article{RN1082, abstract = {Background: Ammonium transporter (AMT/MEP/Rh) superfamily members mediate ammonium uptake and retrieval. This pivotal transport system is conserved among all living organisms. For plants, nitrogen represents a macronutrient available in the soil as ammonium, nitrate, and organic nitrogen compounds. Plants living on extremely nutrient-poor soils have developed a number of adaptation mechanisms, including a carnivorous lifestyle. This study addresses the molecular nature, function, and regulation of prey-derived ammonium uptake in the Venus flytrap, Dionaea muscipula, one of the fastest active carnivores. Results: The Dionaea muscipula ammonium transporter DmAMT1 was localized in gland complexes where its expression was upregulated upon secretion. These clusters of cells decorating the inner trap surface are engaged in (1) secretion of an acidic digestive enzyme cocktail and (2) uptake of prey-derived nutrients. Voltage clamp of Xenopus oocytes expressing DmAMT1 and membrane potential recordings with DmAMT1-expressing Dionaea glands were used to monitor and compare electrophysiological properties of DmAMT1 in vitro and in planta. DmAMT1 exhibited the hallmark biophysical properties of a NH4+-selective channel. At depolarized membrane potentials (V-m = 0), the K-m (3.2 +/- 0.3 mM) indicated a low affinity of DmAMT1 for ammonium that increased systematically with negative going voltages. Upon hyperpolarization to, e.g., -200 mV, a K-m of 0.14 +/- 0.015 mM documents the voltage-dependent shift of DmAMT1 into a NH4+ transport system of high affinity. Conclusions: We suggest that regulation of glandular DmAMT1 and membrane potential readjustments of the endocrine cells provide for effective adaptation to varying, prey-derived ammonium sources.}, author = {Scherzer, S. and Kro, E. and Kreuzer, I. and Kruse, J. and Karl, F. and von Rüden, M. and Escalante-Perez, M. and Müller, T. and Rennenberg, H. and Al-Rasheid, K. A. S. and Neher, E. and Hedrich, R.}, journal = {Current Biology}, keywords = {arabidopsis-thaliana}, note = {295ea Times Cited:43 Cited References Count:50}, number = 17, pages = {1649-1657}, title = {The Ammonium Channel Provides NH Uptake Associated with Venus Flytrap's Prey Digestion}, type = {Journal Article}, volume = 23, year = 2013 }

  %0 Journal Article %1 RN1082 %A Scherzer, S. %A Kro, E. %A Kreuzer, I. %A Kruse, J. %A Karl, F. %A von Rüden, M. %A Escalante-Perez, M. %A Müller, T. %A Rennenberg, H. %A Al-Rasheid, K. A. S. %A Neher, E. %A Hedrich, R. %D 2013 %J Current Biology %N 17 %P 1649-1657 %R 10.1016/j.cub.2013.07.028 %T The Ammonium Channel Provides NH Uptake Associated with Venus Flytrap's Prey Digestion %U /brokenurl#<Go to ISI>://WOS:000330098200033 %V 23 %X Background: Ammonium transporter (AMT/MEP/Rh) superfamily members mediate ammonium uptake and retrieval. This pivotal transport system is conserved among all living organisms. For plants, nitrogen represents a macronutrient available in the soil as ammonium, nitrate, and organic nitrogen compounds. Plants living on extremely nutrient-poor soils have developed a number of adaptation mechanisms, including a carnivorous lifestyle. This study addresses the molecular nature, function, and regulation of prey-derived ammonium uptake in the Venus flytrap, Dionaea muscipula, one of the fastest active carnivores. Results: The Dionaea muscipula ammonium transporter DmAMT1 was localized in gland complexes where its expression was upregulated upon secretion. These clusters of cells decorating the inner trap surface are engaged in (1) secretion of an acidic digestive enzyme cocktail and (2) uptake of prey-derived nutrients. Voltage clamp of Xenopus oocytes expressing DmAMT1 and membrane potential recordings with DmAMT1-expressing Dionaea glands were used to monitor and compare electrophysiological properties of DmAMT1 in vitro and in planta. DmAMT1 exhibited the hallmark biophysical properties of a NH4+-selective channel. At depolarized membrane potentials (V-m = 0), the K-m (3.2 +/- 0.3 mM) indicated a low affinity of DmAMT1 for ammonium that increased systematically with negative going voltages. Upon hyperpolarization to, e.g., -200 mV, a K-m of 0.14 +/- 0.015 mM documents the voltage-dependent shift of DmAMT1 into a NH4+ transport system of high affinity. Conclusions: We suggest that regulation of glandular DmAMT1 and membrane potential readjustments of the endocrine cells provide for effective adaptation to varying, prey-derived ammonium sources.
• Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells. Imes, D.; Mumm, P.; Böhm, J.; Al-Rasheid, K. A. S.; Marten, I.; Geiger, D.; Hedrich, R. In Plant Journal, 74(3), pp. 372–382. 2013.
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  Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell Stype anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata phenotype. Given the fact that guard cells express both SLAC- and R/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi11 and ost12 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the Rtype anion channel. These studies indicate that OST1 is addressing both S/SLAC- and R/QUAC-type guard cell anion channels, and explain why the ost12 mutant is much more sensitive to drought than single slac1 or quac1 mutants.

  @article{RN1085, abstract = {Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell Stype anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata phenotype. Given the fact that guard cells express both SLAC- and R/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi11 and ost12 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the Rtype anion channel. These studies indicate that OST1 is addressing both S/SLAC- and R/QUAC-type guard cell anion channels, and explain why the ost12 mutant is much more sensitive to drought than single slac1 or quac1 mutants.}, author = {Imes, D. and Mumm, P. and Böhm, J. and Al-Rasheid, K. A. S. and Marten, I. and Geiger, D. and Hedrich, R.}, journal = {Plant Journal}, keywords = {r}, note = {134tu Times Cited:147 Cited References Count:64}, number = 3, pages = {372-382}, title = {Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells}, type = {Journal Article}, volume = 74, year = 2013 }

  %0 Journal Article %1 RN1085 %A Imes, D. %A Mumm, P. %A Böhm, J. %A Al-Rasheid, K. A. S. %A Marten, I. %A Geiger, D. %A Hedrich, R. %D 2013 %J Plant Journal %N 3 %P 372-382 %R 10.1111/tpj.12133 %T Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells %U /brokenurl#<Go to ISI>://WOS:000318238500002 %V 74 %X Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell Stype anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata phenotype. Given the fact that guard cells express both SLAC- and R/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi11 and ost12 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the Rtype anion channel. These studies indicate that OST1 is addressing both S/SLAC- and R/QUAC-type guard cell anion channels, and explain why the ost12 mutant is much more sensitive to drought than single slac1 or quac1 mutants.
• C-Terminus-Mediated Voltage Gating of Guard Cell Anion Channel QUAC1. Mumm, P.; Imes, D.; Martinoia, E.; Al-Rasheid, K. A. S.; Geiger, D.; Marten, I.; Hedrich, R. In Molecular Plant, 6(5), pp. 1550–1563. 2013.
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  Here, we compared the highly voltage- and malate-dependent gating kinetics of R-/QUAC-type currents of guard cell protoplasts with QUAC1 expressed in oocytes. Truncations and mutation of QUAC1 indicated that the C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel familiesuSLAC/SLAH and ALMTuare known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al-3-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In contrast, ALMT12/QUAC1 (QUickly activating Anion Channel1) is expressed in guard cells transporting malate in an Al-3-insensitive and highly voltage-dependent manner. So far, no information is available about the structure and mechanism of voltage-dependent gating with the QUAC1 channel protein. Here, we analyzed gating of QUAC1-type currents in the plasma membrane of guard cells and QUAC1-expressing oocytes revealing similar voltage dependencies and activationdeactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increasing extra- and intracellular malate concentrations. Thereby, malate additively stimulated the voltage-dependent QUAC1 activity. In search of structural determinants of the gating process, we could not identify transmembrane domains common for voltage-sensitive channels. However, site-directed mutations and deletions at the C-terminus of QUAC1 resulted in altered voltage-dependent channel activity. Interestingly, the replacement of a single glutamate residue, which is conserved in ALMT channels from different clades, by an alanine disrupted QUAC1 activity. Together with C- and N-terminal tagging, these results indicate that the cytosolic C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.

  @article{RN1083, abstract = {Here, we compared the highly voltage- and malate-dependent gating kinetics of R-/QUAC-type currents of guard cell protoplasts with QUAC1 expressed in oocytes. Truncations and mutation of QUAC1 indicated that the C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel familiesuSLAC/SLAH and ALMTuare known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al-3-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In contrast, ALMT12/QUAC1 (QUickly activating Anion Channel1) is expressed in guard cells transporting malate in an Al-3-insensitive and highly voltage-dependent manner. So far, no information is available about the structure and mechanism of voltage-dependent gating with the QUAC1 channel protein. Here, we analyzed gating of QUAC1-type currents in the plasma membrane of guard cells and QUAC1-expressing oocytes revealing similar voltage dependencies and activationdeactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increasing extra- and intracellular malate concentrations. Thereby, malate additively stimulated the voltage-dependent QUAC1 activity. In search of structural determinants of the gating process, we could not identify transmembrane domains common for voltage-sensitive channels. However, site-directed mutations and deletions at the C-terminus of QUAC1 resulted in altered voltage-dependent channel activity. Interestingly, the replacement of a single glutamate residue, which is conserved in ALMT channels from different clades, by an alanine disrupted QUAC1 activity. Together with C- and N-terminal tagging, these results indicate that the cytosolic C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.}, author = {Mumm, P. and Imes, D. and Martinoia, E. and Al-Rasheid, K. A. S. and Geiger, D. and Marten, I. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {deactivation}, note = {223sk Times Cited:43 Cited References Count:82}, number = 5, pages = {1550-1563}, title = {C-Terminus-Mediated Voltage Gating of Guard Cell Anion Channel QUAC1}, type = {Journal Article}, volume = 6, year = 2013 }

  %0 Journal Article %1 RN1083 %A Mumm, P. %A Imes, D. %A Martinoia, E. %A Al-Rasheid, K. A. S. %A Geiger, D. %A Marten, I. %A Hedrich, R. %D 2013 %J Molecular Plant %N 5 %P 1550-1563 %R 10.1093/mp/sst008 %T C-Terminus-Mediated Voltage Gating of Guard Cell Anion Channel QUAC1 %U /brokenurl#<Go to ISI>://WOS:000324829400014 %V 6 %X Here, we compared the highly voltage- and malate-dependent gating kinetics of R-/QUAC-type currents of guard cell protoplasts with QUAC1 expressed in oocytes. Truncations and mutation of QUAC1 indicated that the C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel familiesuSLAC/SLAH and ALMTuare known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al-3-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In contrast, ALMT12/QUAC1 (QUickly activating Anion Channel1) is expressed in guard cells transporting malate in an Al-3-insensitive and highly voltage-dependent manner. So far, no information is available about the structure and mechanism of voltage-dependent gating with the QUAC1 channel protein. Here, we analyzed gating of QUAC1-type currents in the plasma membrane of guard cells and QUAC1-expressing oocytes revealing similar voltage dependencies and activationdeactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increasing extra- and intracellular malate concentrations. Thereby, malate additively stimulated the voltage-dependent QUAC1 activity. In search of structural determinants of the gating process, we could not identify transmembrane domains common for voltage-sensitive channels. However, site-directed mutations and deletions at the C-terminus of QUAC1 resulted in altered voltage-dependent channel activity. Interestingly, the replacement of a single glutamate residue, which is conserved in ALMT channels from different clades, by an alanine disrupted QUAC1 activity. Together with C- and N-terminal tagging, these results indicate that the cytosolic C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.
• DNA Methylation Mediated Control of Gene Expression Is Critical for Development of Crown Gall Tumors. Gohlke, J.; Scholz, C. J.; Kneitz, S.; Weber, D.; Fuchs, J.; Hedrich, R.; Deeken, R. In Plos Genetics, 9(2). 2013.
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  Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA-encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes. High levels of abscisic acid (ABA) in crown galls regulate expression of drought stress responsive genes and mediate drought stress acclimation, which is essential for wild-type-like tumor growth. An impact of epigenetic processes such as DNA methylation on crown gall development has been suggested; however, it has not yet been investigated comprehensively. In this study, the methylation pattern of Arabidopsis thaliana crown galls was analyzed on a genome-wide scale as well as at the single gene level. Bisulfite sequencing analysis revealed that the oncogenes Ipt, IaaH, and IaaM were unmethylated in crown galls. Nevertheless, the oncogenes were susceptible to siRNA-mediated methylation, which inhibited their expression and subsequently crown gall growth. Genome arrays, hybridized with methylated DNA obtained by immunoprecipitation, revealed a globally hypermethylated crown gall genome, while promoters were rather hypomethylated. Mutants with reduced non-CG methylation developed larger tumors than the wild-type controls, indicating that hypermethylation inhibits plant tumor growth. The differential methylation pattern of crown galls and the stem tissue from which they originate correlated with transcriptional changes. Genes known to be transcriptionally inhibited by ABA and methylated in crown galls became promoter methylated upon treatment of A. thaliana with ABA. This suggests that the high ABA levels in crown galls may mediate DNA methylation and regulate expression of genes involved in drought stress protection. In summary, our studies provide evidence that epigenetic processes regulate gene expression, physiological processes, and the development of crown gall tumors.

  @article{RN1087, abstract = {Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA-encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes. High levels of abscisic acid (ABA) in crown galls regulate expression of drought stress responsive genes and mediate drought stress acclimation, which is essential for wild-type-like tumor growth. An impact of epigenetic processes such as DNA methylation on crown gall development has been suggested; however, it has not yet been investigated comprehensively. In this study, the methylation pattern of Arabidopsis thaliana crown galls was analyzed on a genome-wide scale as well as at the single gene level. Bisulfite sequencing analysis revealed that the oncogenes Ipt, IaaH, and IaaM were unmethylated in crown galls. Nevertheless, the oncogenes were susceptible to siRNA-mediated methylation, which inhibited their expression and subsequently crown gall growth. Genome arrays, hybridized with methylated DNA obtained by immunoprecipitation, revealed a globally hypermethylated crown gall genome, while promoters were rather hypomethylated. Mutants with reduced non-CG methylation developed larger tumors than the wild-type controls, indicating that hypermethylation inhibits plant tumor growth. The differential methylation pattern of crown galls and the stem tissue from which they originate correlated with transcriptional changes. Genes known to be transcriptionally inhibited by ABA and methylated in crown galls became promoter methylated upon treatment of A. thaliana with ABA. This suggests that the high ABA levels in crown galls may mediate DNA methylation and regulate expression of genes involved in drought stress protection. In summary, our studies provide evidence that epigenetic processes regulate gene expression, physiological processes, and the development of crown gall tumors.}, author = {Gohlke, J. and Scholz, C. J. and Kneitz, S. and Weber, D. and Fuchs, J. and Hedrich, R. and Deeken, R.}, journal = {Plos Genetics}, keywords = {agrobacterium-tumefaciens}, note = {099rg Times Cited:44 Cited References Count:64}, number = 2, title = {DNA Methylation Mediated Control of Gene Expression Is Critical for Development of Crown Gall Tumors}, type = {Journal Article}, volume = 9, year = 2013 }

  %0 Journal Article %1 RN1087 %A Gohlke, J. %A Scholz, C. J. %A Kneitz, S. %A Weber, D. %A Fuchs, J. %A Hedrich, R. %A Deeken, R. %D 2013 %J Plos Genetics %N 2 %R ARTN e1003267 10.1371/journal.pgen.1003267 %T DNA Methylation Mediated Control of Gene Expression Is Critical for Development of Crown Gall Tumors %U /brokenurl#<Go to ISI>://WOS:000315638300026 %V 9 %X Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA-encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes. High levels of abscisic acid (ABA) in crown galls regulate expression of drought stress responsive genes and mediate drought stress acclimation, which is essential for wild-type-like tumor growth. An impact of epigenetic processes such as DNA methylation on crown gall development has been suggested; however, it has not yet been investigated comprehensively. In this study, the methylation pattern of Arabidopsis thaliana crown galls was analyzed on a genome-wide scale as well as at the single gene level. Bisulfite sequencing analysis revealed that the oncogenes Ipt, IaaH, and IaaM were unmethylated in crown galls. Nevertheless, the oncogenes were susceptible to siRNA-mediated methylation, which inhibited their expression and subsequently crown gall growth. Genome arrays, hybridized with methylated DNA obtained by immunoprecipitation, revealed a globally hypermethylated crown gall genome, while promoters were rather hypomethylated. Mutants with reduced non-CG methylation developed larger tumors than the wild-type controls, indicating that hypermethylation inhibits plant tumor growth. The differential methylation pattern of crown galls and the stem tissue from which they originate correlated with transcriptional changes. Genes known to be transcriptionally inhibited by ABA and methylated in crown galls became promoter methylated upon treatment of A. thaliana with ABA. This suggests that the high ABA levels in crown galls may mediate DNA methylation and regulate expression of genes involved in drought stress protection. In summary, our studies provide evidence that epigenetic processes regulate gene expression, physiological processes, and the development of crown gall tumors.
• On the cellular site of two-pore channel TPC1 action in the Poaceae. Dadacz-Narloch, B.; Kimura, S.; Kurusu, T.; Farmer, E. E.; Becker, D.; Kuchitsu, K.; Hedrich, R. In New Phytologist, 200(3), pp. 663–674. 2013.
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  The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.

  @article{RN1089, abstract = {The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.}, author = {Dadacz-Narloch, B. and Kimura, S. and Kurusu, T. and Farmer, E. E. and Becker, D. and Kuchitsu, K. and Hedrich, R.}, journal = {New Phytologist}, keywords = {lysosome}, note = {233gi Times Cited:21 Cited References Count:69}, number = 3, pages = {663-674}, title = {On the cellular site of two-pore channel TPC1 action in the Poaceae}, type = {Journal Article}, volume = 200, year = 2013 }

  %0 Journal Article %1 RN1089 %A Dadacz-Narloch, B. %A Kimura, S. %A Kurusu, T. %A Farmer, E. E. %A Becker, D. %A Kuchitsu, K. %A Hedrich, R. %D 2013 %J New Phytologist %N 3 %P 663-674 %R 10.1111/nph.12402 %T On the cellular site of two-pore channel TPC1 action in the Poaceae %U /brokenurl#<Go to ISI>://WOS:000325555400011 %V 200 %X The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.
• Salt Stress Triggers Phosphorylation of the Vacuolar K Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs). Latz, A.; Mehlmer, N.; Zapf, S.; Mueller, T. D.; Wurzinger, B.; Pfister, B.; Csaszar, E.; Hedrich, R.; Teige, M.; Becker, D. In Molecular Plant, 6(4), pp. 1274–1289. 2013.
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  The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Here, we report that this interaction requires activation of the 1433 binding motif in TPK1 by the calcium-dependent protein kinase CPK3. Cpk3 and tpk1 mutants displayed salt-sensitive phenotypes, providing evidence for an essential role of the vacuolar potassium channel TPK1 in Ca-2-dependent salt-stress adaptation.1433 proteins play an important role in the regulation of many cellular processes. The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Upon phosphorylation of the putative binding motif in the N-terminus of TPK1, GRF6 binds to TPK1 and activates the potassium channel. In order to gain a deeper understanding of this 1433-mediated signal transduction, we set out to identify the respective kinases, which regulate the phosphorylation status of the 1433 binding motif in TPK1. Here, we report that the calcium-dependent protein kinases (CDPKs) can phosphorylate and thereby activate the 1433 binding motif in TPK1. Focusing on the stress-activated kinase CPK3, we visualized direct and specific interaction of TPK1 with the kinase at the tonoplast in vivo. In line with its proposed role in K homeostasis, TPK1 phosphorylation was found to be induced by salt stress in planta, and both cpk3 and tpk1 mutants displayed salt-sensitive phenotypes. Molecular modeling of the TPK1CPK3 interaction domain provided mechanistic insights into TPK1 stress-regulated phosphorylation responses and pinpointed two arginine residues in the N-terminal 1433 binding motif in TPK1 critical for kinase interaction. Taken together, our studies provide evidence for an essential role of the vacuolar potassium channel TPK1 in salt-stress adaptation as a target of calcium-regulated stress signaling pathways involving Ca-2, Ca-2-dependent kinases, and 1433 proteins.

  @article{RN1084, abstract = {The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Here, we report that this interaction requires activation of the 1433 binding motif in TPK1 by the calcium-dependent protein kinase CPK3. Cpk3 and tpk1 mutants displayed salt-sensitive phenotypes, providing evidence for an essential role of the vacuolar potassium channel TPK1 in Ca-2-dependent salt-stress adaptation.1433 proteins play an important role in the regulation of many cellular processes. The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Upon phosphorylation of the putative binding motif in the N-terminus of TPK1, GRF6 binds to TPK1 and activates the potassium channel. In order to gain a deeper understanding of this 1433-mediated signal transduction, we set out to identify the respective kinases, which regulate the phosphorylation status of the 1433 binding motif in TPK1. Here, we report that the calcium-dependent protein kinases (CDPKs) can phosphorylate and thereby activate the 1433 binding motif in TPK1. Focusing on the stress-activated kinase CPK3, we visualized direct and specific interaction of TPK1 with the kinase at the tonoplast in vivo. In line with its proposed role in K homeostasis, TPK1 phosphorylation was found to be induced by salt stress in planta, and both cpk3 and tpk1 mutants displayed salt-sensitive phenotypes. Molecular modeling of the TPK1CPK3 interaction domain provided mechanistic insights into TPK1 stress-regulated phosphorylation responses and pinpointed two arginine residues in the N-terminal 1433 binding motif in TPK1 critical for kinase interaction. Taken together, our studies provide evidence for an essential role of the vacuolar potassium channel TPK1 in salt-stress adaptation as a target of calcium-regulated stress signaling pathways involving Ca-2, Ca-2-dependent kinases, and 1433 proteins.}, author = {Latz, A. and Mehlmer, N. and Zapf, S. and Mueller, T. D. and Wurzinger, B. and Pfister, B. and Csaszar, E. and Hedrich, R. and Teige, M. and Becker, D.}, journal = {Molecular Plant}, keywords = {channel}, note = {191kb Times Cited:139 Cited References Count:82}, number = 4, pages = {1274-1289}, title = {Salt Stress Triggers Phosphorylation of the Vacuolar K Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs)}, type = {Journal Article}, volume = 6, year = 2013 }

  %0 Journal Article %1 RN1084 %A Latz, A. %A Mehlmer, N. %A Zapf, S. %A Mueller, T. D. %A Wurzinger, B. %A Pfister, B. %A Csaszar, E. %A Hedrich, R. %A Teige, M. %A Becker, D. %D 2013 %J Molecular Plant %N 4 %P 1274-1289 %R 10.1093/mp/sss158 %T Salt Stress Triggers Phosphorylation of the Vacuolar K Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs) %U /brokenurl#<Go to ISI>://WOS:000322410700020 %V 6 %X The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Here, we report that this interaction requires activation of the 1433 binding motif in TPK1 by the calcium-dependent protein kinase CPK3. Cpk3 and tpk1 mutants displayed salt-sensitive phenotypes, providing evidence for an essential role of the vacuolar potassium channel TPK1 in Ca-2-dependent salt-stress adaptation.1433 proteins play an important role in the regulation of many cellular processes. The Arabidopsis vacuolar two-pore K channel 1 (TPK1) interacts with the 1433 protein GRF6 (GF14-). Upon phosphorylation of the putative binding motif in the N-terminus of TPK1, GRF6 binds to TPK1 and activates the potassium channel. In order to gain a deeper understanding of this 1433-mediated signal transduction, we set out to identify the respective kinases, which regulate the phosphorylation status of the 1433 binding motif in TPK1. Here, we report that the calcium-dependent protein kinases (CDPKs) can phosphorylate and thereby activate the 1433 binding motif in TPK1. Focusing on the stress-activated kinase CPK3, we visualized direct and specific interaction of TPK1 with the kinase at the tonoplast in vivo. In line with its proposed role in K homeostasis, TPK1 phosphorylation was found to be induced by salt stress in planta, and both cpk3 and tpk1 mutants displayed salt-sensitive phenotypes. Molecular modeling of the TPK1CPK3 interaction domain provided mechanistic insights into TPK1 stress-regulated phosphorylation responses and pinpointed two arginine residues in the N-terminal 1433 binding motif in TPK1 critical for kinase interaction. Taken together, our studies provide evidence for an essential role of the vacuolar potassium channel TPK1 in salt-stress adaptation as a target of calcium-regulated stress signaling pathways involving Ca-2, Ca-2-dependent kinases, and 1433 proteins.
• Pollen Tube Growth Regulation by Free Anions Depends on the Interaction between the Anion Channel SLAH3 and Calcium-Dependent Protein Kinases CPK2 and CPK20. Gutermuth, T.; Lassig, R.; Portes, M. T.; Maierhofer, T.; Romeis, T.; Borst, J. W.; Hedrich, R.; Feijó, J. A.; Konrad, K. R. In Plant Cell, 25(11), pp. 4525–4543. 2013.
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  Apical growth in pollen tubes (PTs) is associated with the presence of tip-focused ion gradients and fluxes, implying polar localization or regulation of the underlying transporters. The molecular identity and regulation of anion transporters in PTs is unknown. Here we report a negative gradient of cytosolic anion concentration focused on the tip, in negative correlation with the cytosolic Ca2+ concentration. We hypothesized that a possible link between these two ions is based on the presence of Ca2+-dependent protein kinases (CPKs). We characterized anion channels and CPK transcripts in PTs and analyzed their localization. Yellow fluorescent protein (YFP) tagging of a homolog of SLOW ANION CHANNEL-ASSOCIATED1 (SLAH3: YFP) was widespread along PTs, but, in accordance with the anion efflux, CPK2/CPK20/CPK17/CPK34: YFP fluorescence was strictly localized at the tip plasma membrane. Expression of SLAH3 with either CPK2 or CPK20 (but not CPK17/CPK34) in Xenopus laevis oocytes elicited S-type anion channel currents. Interaction of SLAH3 with CPK2/CPK20 (but not CPK17/CPK34) was confirmed by Forster-resonance energy transfer fluorescence lifetime microscopy in Arabidopsis thaliana mesophyll protoplasts and bimolecular fluorescence complementation in living PTs. Compared with wild-type PTs, slah3-1 and slah3-2 as well as cpk2-1 cpk20-2 PTs had reduced anion currents. Double mutant cpk2-1 cpk20-2 and slah3-1 PTs had reduced extracellular anion fluxes at the tip. Our studies provide evidence for a Ca2+-dependent CPK2/CPK20 regulation of the anion channel SLAH3 to regulate PT growth.

  @article{RN1086, abstract = {Apical growth in pollen tubes (PTs) is associated with the presence of tip-focused ion gradients and fluxes, implying polar localization or regulation of the underlying transporters. The molecular identity and regulation of anion transporters in PTs is unknown. Here we report a negative gradient of cytosolic anion concentration focused on the tip, in negative correlation with the cytosolic Ca2+ concentration. We hypothesized that a possible link between these two ions is based on the presence of Ca2+-dependent protein kinases (CPKs). We characterized anion channels and CPK transcripts in PTs and analyzed their localization. Yellow fluorescent protein (YFP) tagging of a homolog of SLOW ANION CHANNEL-ASSOCIATED1 (SLAH3: YFP) was widespread along PTs, but, in accordance with the anion efflux, CPK2/CPK20/CPK17/CPK34: YFP fluorescence was strictly localized at the tip plasma membrane. Expression of SLAH3 with either CPK2 or CPK20 (but not CPK17/CPK34) in Xenopus laevis oocytes elicited S-type anion channel currents. Interaction of SLAH3 with CPK2/CPK20 (but not CPK17/CPK34) was confirmed by Forster-resonance energy transfer fluorescence lifetime microscopy in Arabidopsis thaliana mesophyll protoplasts and bimolecular fluorescence complementation in living PTs. Compared with wild-type PTs, slah3-1 and slah3-2 as well as cpk2-1 cpk20-2 PTs had reduced anion currents. Double mutant cpk2-1 cpk20-2 and slah3-1 PTs had reduced extracellular anion fluxes at the tip. Our studies provide evidence for a Ca2+-dependent CPK2/CPK20 regulation of the anion channel SLAH3 to regulate PT growth.}, author = {Gutermuth, T. and Lassig, R. and Portes, M. T. and Maierhofer, T. and Romeis, T. and Borst, J. W. and Hedrich, R. and Feijó, J. A. and Konrad, K. R.}, journal = {Plant Cell}, keywords = {yellow}, note = {282ly Times Cited:106 Cited References Count:100}, number = 11, pages = {4525-4543}, title = {Pollen Tube Growth Regulation by Free Anions Depends on the Interaction between the Anion Channel SLAH3 and Calcium-Dependent Protein Kinases CPK2 and CPK20}, type = {Journal Article}, volume = 25, year = 2013 }

  %0 Journal Article %1 RN1086 %A Gutermuth, T. %A Lassig, R. %A Portes, M. T. %A Maierhofer, T. %A Romeis, T. %A Borst, J. W. %A Hedrich, R. %A Feijó, J. A. %A Konrad, K. R. %D 2013 %J Plant Cell %N 11 %P 4525-4543 %R 10.1105/tpc.113.118463 %T Pollen Tube Growth Regulation by Free Anions Depends on the Interaction between the Anion Channel SLAH3 and Calcium-Dependent Protein Kinases CPK2 and CPK20 %U /brokenurl#<Go to ISI>://WOS:000329174400020 %V 25 %X Apical growth in pollen tubes (PTs) is associated with the presence of tip-focused ion gradients and fluxes, implying polar localization or regulation of the underlying transporters. The molecular identity and regulation of anion transporters in PTs is unknown. Here we report a negative gradient of cytosolic anion concentration focused on the tip, in negative correlation with the cytosolic Ca2+ concentration. We hypothesized that a possible link between these two ions is based on the presence of Ca2+-dependent protein kinases (CPKs). We characterized anion channels and CPK transcripts in PTs and analyzed their localization. Yellow fluorescent protein (YFP) tagging of a homolog of SLOW ANION CHANNEL-ASSOCIATED1 (SLAH3: YFP) was widespread along PTs, but, in accordance with the anion efflux, CPK2/CPK20/CPK17/CPK34: YFP fluorescence was strictly localized at the tip plasma membrane. Expression of SLAH3 with either CPK2 or CPK20 (but not CPK17/CPK34) in Xenopus laevis oocytes elicited S-type anion channel currents. Interaction of SLAH3 with CPK2/CPK20 (but not CPK17/CPK34) was confirmed by Forster-resonance energy transfer fluorescence lifetime microscopy in Arabidopsis thaliana mesophyll protoplasts and bimolecular fluorescence complementation in living PTs. Compared with wild-type PTs, slah3-1 and slah3-2 as well as cpk2-1 cpk20-2 PTs had reduced anion currents. Double mutant cpk2-1 cpk20-2 and slah3-1 PTs had reduced extracellular anion fluxes at the tip. Our studies provide evidence for a Ca2+-dependent CPK2/CPK20 regulation of the anion channel SLAH3 to regulate PT growth.
• nanodomain-delimited ABA signaling pathway regulates the anion channel SLAH3. Demir, F.; Horntrich, C.; Blachutzik, J. O.; Scherzer, S.; Reinders, Y.; Kierszniowska, S.; Schulze, W. X.; Harms, G. S.; Hedrich, R.; Geiger, D.; Kreuzer, I. In Proceedings of the National Academy of Sciences of the United States of America, 110(20), pp. 8296–8301. 2013.
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  The phytohormone abscisic acid (ABA) plays a key role in the plant response to drought stress. Hence, ABA-dependent gene transcription and ion transport is regulated by a variety of protein kinases and phosphatases. However, the nature of the membrane-delimited ABA signal transduction steps remains largely unknown. To gain insight into plasma membrane-bound ABA signaling, we identified sterol-dependent proteins associated with detergent resistant membranes from Arabidopsis thaliana mesophyll cells. Among those, we detected the central ABA signaling phosphatase ABI1 (abscisic-acid insensitive 1) and the calcium-dependent protein kinase 21 (CPK21). Using fluorescence microscopy, we found these proteins to localize in membrane nanodomains, as observed by colocalization with the nanodomain marker remorin Arabidopsis thaliana remorin 1.3 (AtRem 1.3). After transient coexpression, CPK21 interacted with SLAH3 [slow anion channel 1 (SLAC1) homolog 3] and activated this anion channel. Upon CPK21 stimulation, SLAH3 exhibited the hallmark properties of S-type anion channels. Coexpression of SLAH3/CPK21 with ABI1, however, prevented proper nanodomain localization of the SLAH3/CPK21 protein complex, and as a result anion channel activation failed. FRET studies revealed enhanced interaction of SLAH3 and CPK21 within the plasma membrane in response to ABA and thus confirmed our initial observations. Interestingly, the ABA-induced SLAH3/CPK21 interaction was modulated by ABI1 and the ABA receptor RCAR1/PYL9 [regulatory components of ABA receptor 1/PYR1 (pyrabactin resistance 1)-like protein 9]. We therefore propose that ABA signaling via inhibition of ABI1 modulates the apparent association of a signaling and transport complex within membrane domains that is necessary for phosphorylation and activation of the S-type anion channel SLAH3 by CPK21.

  @article{RN1088, abstract = {The phytohormone abscisic acid (ABA) plays a key role in the plant response to drought stress. Hence, ABA-dependent gene transcription and ion transport is regulated by a variety of protein kinases and phosphatases. However, the nature of the membrane-delimited ABA signal transduction steps remains largely unknown. To gain insight into plasma membrane-bound ABA signaling, we identified sterol-dependent proteins associated with detergent resistant membranes from Arabidopsis thaliana mesophyll cells. Among those, we detected the central ABA signaling phosphatase ABI1 (abscisic-acid insensitive 1) and the calcium-dependent protein kinase 21 (CPK21). Using fluorescence microscopy, we found these proteins to localize in membrane nanodomains, as observed by colocalization with the nanodomain marker remorin Arabidopsis thaliana remorin 1.3 (AtRem 1.3). After transient coexpression, CPK21 interacted with SLAH3 [slow anion channel 1 (SLAC1) homolog 3] and activated this anion channel. Upon CPK21 stimulation, SLAH3 exhibited the hallmark properties of S-type anion channels. Coexpression of SLAH3/CPK21 with ABI1, however, prevented proper nanodomain localization of the SLAH3/CPK21 protein complex, and as a result anion channel activation failed. FRET studies revealed enhanced interaction of SLAH3 and CPK21 within the plasma membrane in response to ABA and thus confirmed our initial observations. Interestingly, the ABA-induced SLAH3/CPK21 interaction was modulated by ABI1 and the ABA receptor RCAR1/PYL9 [regulatory components of ABA receptor 1/PYR1 (pyrabactin resistance 1)-like protein 9]. We therefore propose that ABA signaling via inhibition of ABI1 modulates the apparent association of a signaling and transport complex within membrane domains that is necessary for phosphorylation and activation of the S-type anion channel SLAH3 by CPK21.}, author = {Demir, F. and Horntrich, C. and Blachutzik, J. O. and Scherzer, S. and Reinders, Y. and Kierszniowska, S. and Schulze, W. X. and Harms, G. S. and Hedrich, R. and Geiger, D. and Kreuzer, I.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {myOwn}, note = {156eh Times Cited:153 Cited References Count:52}, number = 20, pages = {8296-8301}, title = {nanodomain-delimited ABA signaling pathway regulates the anion channel SLAH3}, type = {Journal Article}, volume = 110, year = 2013 }

  %0 Journal Article %1 RN1088 %A Demir, F. %A Horntrich, C. %A Blachutzik, J. O. %A Scherzer, S. %A Reinders, Y. %A Kierszniowska, S. %A Schulze, W. X. %A Harms, G. S. %A Hedrich, R. %A Geiger, D. %A Kreuzer, I. %D 2013 %J Proceedings of the National Academy of Sciences of the United States of America %N 20 %P 8296-8301 %R 10.1073/pnas.1211667110 %T nanodomain-delimited ABA signaling pathway regulates the anion channel SLAH3 %U /brokenurl#<Go to ISI>://WOS:000319803500067 %V 110 %X The phytohormone abscisic acid (ABA) plays a key role in the plant response to drought stress. Hence, ABA-dependent gene transcription and ion transport is regulated by a variety of protein kinases and phosphatases. However, the nature of the membrane-delimited ABA signal transduction steps remains largely unknown. To gain insight into plasma membrane-bound ABA signaling, we identified sterol-dependent proteins associated with detergent resistant membranes from Arabidopsis thaliana mesophyll cells. Among those, we detected the central ABA signaling phosphatase ABI1 (abscisic-acid insensitive 1) and the calcium-dependent protein kinase 21 (CPK21). Using fluorescence microscopy, we found these proteins to localize in membrane nanodomains, as observed by colocalization with the nanodomain marker remorin Arabidopsis thaliana remorin 1.3 (AtRem 1.3). After transient coexpression, CPK21 interacted with SLAH3 [slow anion channel 1 (SLAC1) homolog 3] and activated this anion channel. Upon CPK21 stimulation, SLAH3 exhibited the hallmark properties of S-type anion channels. Coexpression of SLAH3/CPK21 with ABI1, however, prevented proper nanodomain localization of the SLAH3/CPK21 protein complex, and as a result anion channel activation failed. FRET studies revealed enhanced interaction of SLAH3 and CPK21 within the plasma membrane in response to ABA and thus confirmed our initial observations. Interestingly, the ABA-induced SLAH3/CPK21 interaction was modulated by ABI1 and the ABA receptor RCAR1/PYL9 [regulatory components of ABA receptor 1/PYR1 (pyrabactin resistance 1)-like protein 9]. We therefore propose that ABA signaling via inhibition of ABI1 modulates the apparent association of a signaling and transport complex within membrane domains that is necessary for phosphorylation and activation of the S-type anion channel SLAH3 by CPK21.
• The Stomatal Response to Reduced Relative Humidity Requires Guard Cell-Autonomous ABA Synthesis. Bauer, H.; Ache, P.; Lautner, S.; Fromm, J.; Hartung, W.; Al-Rasheid, K. A. S.; Sonnewald, S.; Sonnewald, U.; Kneitz, S.; Lachmann, N.; Mendel, R. R.; Bittner, F.; Hetherington, A. M.; Hedrich, R. In Current Biology, 23(1), pp. 53–57. 2013.
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  Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO2 for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin [1] showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.

  @article{RN1091, abstract = {Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO2 for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin [1] showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.}, author = {Bauer, H. and Ache, P. and Lautner, S. and Fromm, J. and Hartung, W. and Al-Rasheid, K. A. S. and Sonnewald, S. and Sonnewald, U. and Kneitz, S. and Lachmann, N. and Mendel, R. R. and Bittner, F. and Hetherington, A. M. and Hedrich, R.}, journal = {Current Biology}, keywords = {abscisic-acid}, note = {068rk Times Cited:356 Cited References Count:27}, number = 1, pages = {53-57}, title = {The Stomatal Response to Reduced Relative Humidity Requires Guard Cell-Autonomous ABA Synthesis}, type = {Journal Article}, volume = 23, year = 2013 }

  %0 Journal Article %1 RN1091 %A Bauer, H. %A Ache, P. %A Lautner, S. %A Fromm, J. %A Hartung, W. %A Al-Rasheid, K. A. S. %A Sonnewald, S. %A Sonnewald, U. %A Kneitz, S. %A Lachmann, N. %A Mendel, R. R. %A Bittner, F. %A Hetherington, A. M. %A Hedrich, R. %D 2013 %J Current Biology %N 1 %P 53-57 %R 10.1016/j.cub.2012.11.022 %T The Stomatal Response to Reduced Relative Humidity Requires Guard Cell-Autonomous ABA Synthesis %U /brokenurl#<Go to ISI>://WOS:000313383700022 %V 23 %X Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO2 for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin [1] showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.

• Luminal and Cytosolic pH Feedback on Proton Pump Activity and ATP Affinity of V-type ATPase from. Rienmüller, F.; Dreyer, I.; Schönknecht, G.; Schulz, A.; Schumacher, K.; Nagy, R.; Martinoia, E.; Marten, I.; Hedrich, R. In Journal of Biological Chemistry, 287(12), pp. 8986–8993. 2012.
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  Proton pumping of the vacuolar-type H+-ATPase into the lumen of the central plant organelle generates a proton gradient of often 1-2 pH units or more. Although structural aspects of the V-type ATPase have been studied in great detail, the question of whether and how the proton pump action is controlled by the proton concentration on both sides of the membrane is not understood. Applying the patch clamp technique to isolated vacuoles from Arabidopsis mesophyll cells in the whole-vacuole mode, we studied the response of the V-ATPase to protons, voltage, and ATP. Current-voltage relationships at different luminal pH values indicated decreasing coupling ratios with acidification. A detailed study of ATP-dependent H+-pump currents at a variety of different pH conditions showed a complex regulation of V-ATPase activity by both cytosolic and vacuolar pH. At cytosolic pH 7.5, vacuolar pH changes had relative little effects. Yet, at cytosolic pH 5.5, a 100-fold increase in vacuolar proton concentration resulted in a 70-fold increase of the affinity for ATP binding on the cytosolic side. Changes in pH on either side of the membrane seem to be transferred by the V-ATPase to the other side. A mathematical model was developed that indicates a feedback of proton concentration on peak H+ current amplitude (v(max)) and ATP consumption (K-m) of the V-ATPase. It proposes that for efficient V-ATPase function dissociation of transported protons from the pump protein might become higher with increasing pH. This feature results in an optimization of H+ pumping by the V-ATPase according to existing H+ concentrations.

  @article{RN1098, abstract = {Proton pumping of the vacuolar-type H+-ATPase into the lumen of the central plant organelle generates a proton gradient of often 1-2 pH units or more. Although structural aspects of the V-type ATPase have been studied in great detail, the question of whether and how the proton pump action is controlled by the proton concentration on both sides of the membrane is not understood. Applying the patch clamp technique to isolated vacuoles from Arabidopsis mesophyll cells in the whole-vacuole mode, we studied the response of the V-ATPase to protons, voltage, and ATP. Current-voltage relationships at different luminal pH values indicated decreasing coupling ratios with acidification. A detailed study of ATP-dependent H+-pump currents at a variety of different pH conditions showed a complex regulation of V-ATPase activity by both cytosolic and vacuolar pH. At cytosolic pH 7.5, vacuolar pH changes had relative little effects. Yet, at cytosolic pH 5.5, a 100-fold increase in vacuolar proton concentration resulted in a 70-fold increase of the affinity for ATP binding on the cytosolic side. Changes in pH on either side of the membrane seem to be transferred by the V-ATPase to the other side. A mathematical model was developed that indicates a feedback of proton concentration on peak H+ current amplitude (v(max)) and ATP consumption (K-m) of the V-ATPase. It proposes that for efficient V-ATPase function dissociation of transported protons from the pump protein might become higher with increasing pH. This feature results in an optimization of H+ pumping by the V-ATPase according to existing H+ concentrations.}, author = {Rienmüller, F. and Dreyer, I. and Schönknecht, G. and Schulz, A. and Schumacher, K. and Nagy, R. and Martinoia, E. and Marten, I. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {h+-atpase}, note = {912kv Times Cited:30 Cited References Count:40}, number = 12, pages = {8986-8993}, title = {Luminal and Cytosolic pH Feedback on Proton Pump Activity and ATP Affinity of V-type ATPase from}, type = {Journal Article}, volume = 287, year = 2012 }

  %0 Journal Article %1 RN1098 %A Rienmüller, F. %A Dreyer, I. %A Schönknecht, G. %A Schulz, A. %A Schumacher, K. %A Nagy, R. %A Martinoia, E. %A Marten, I. %A Hedrich, R. %D 2012 %J Journal of Biological Chemistry %N 12 %P 8986-8993 %R 10.1074/jbc.M111.310367 %T Luminal and Cytosolic pH Feedback on Proton Pump Activity and ATP Affinity of V-type ATPase from %U /brokenurl#<Go to ISI>://WOS:000301797800029 %V 287 %X Proton pumping of the vacuolar-type H+-ATPase into the lumen of the central plant organelle generates a proton gradient of often 1-2 pH units or more. Although structural aspects of the V-type ATPase have been studied in great detail, the question of whether and how the proton pump action is controlled by the proton concentration on both sides of the membrane is not understood. Applying the patch clamp technique to isolated vacuoles from Arabidopsis mesophyll cells in the whole-vacuole mode, we studied the response of the V-ATPase to protons, voltage, and ATP. Current-voltage relationships at different luminal pH values indicated decreasing coupling ratios with acidification. A detailed study of ATP-dependent H+-pump currents at a variety of different pH conditions showed a complex regulation of V-ATPase activity by both cytosolic and vacuolar pH. At cytosolic pH 7.5, vacuolar pH changes had relative little effects. Yet, at cytosolic pH 5.5, a 100-fold increase in vacuolar proton concentration resulted in a 70-fold increase of the affinity for ATP binding on the cytosolic side. Changes in pH on either side of the membrane seem to be transferred by the V-ATPase to the other side. A mathematical model was developed that indicates a feedback of proton concentration on peak H+ current amplitude (v(max)) and ATP consumption (K-m) of the V-ATPase. It proposes that for efficient V-ATPase function dissociation of transported protons from the pump protein might become higher with increasing pH. This feature results in an optimization of H+ pumping by the V-ATPase according to existing H+ concentrations.
• Methods of staining and visualization of sphingolipid enriched and non-enriched plasma membrane regions of with fluorescent dyes and lipid analogues. Blachutzik, J. O.; Demir, F.; Kreuzer, I.; Hedrich, R.; Harms, G. S. In Plant Methods, 8. 2012.
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  Background: Sterols and Sphingolipids form lipid clusters in the plasma membranes of cell types throughout the animal and plant kingdoms. These lipid domains provide a medium for protein signaling complexes at the plasma membrane and are also observed to be principal regions of membrane contact at the inception of infection. We visualized different specific fluorescent lipophilic stains of the both sphingolipid enriched and non-sphingolipid enriched regions in the plasma membranes of live protoplasts of Arabidopsis thaliana. Results: Lipid staining protocols for several fluorescent lipid analogues in plants are presented. The most emphasis was placed on successful protocols for the single and dual staining of sphingolipid enriched regions and exclusion of sphingolipid enriched regions on the plasma membrane of Arabidopsis thaliana protoplasts. A secondary focus was placed to ensure that these staining protocols presented still maintain cell viability. Furthermore, the protocols were successfully tested with the spectrally sensitive dye Laurdan. Conclusion: Almost all existing staining procedures of the plasma membrane with fluorescent lipid analogues are specified for animal cells and tissues. In order to develop lipid staining protocols for plants, procedures were established with critical steps for the plasma membrane staining of Arabidopsis leaf tissue and protoplasts. The success of the plasma membrane staining protocols was additionally verified by measurements of lipid dynamics by the fluorescence recovery after photobleaching technique and by the observation of new phenomena such as time dependent lipid polarization events in living protoplasts, for which a putative physiological relevance is suggested.

  @article{RN1105, abstract = {Background: Sterols and Sphingolipids form lipid clusters in the plasma membranes of cell types throughout the animal and plant kingdoms. These lipid domains provide a medium for protein signaling complexes at the plasma membrane and are also observed to be principal regions of membrane contact at the inception of infection. We visualized different specific fluorescent lipophilic stains of the both sphingolipid enriched and non-sphingolipid enriched regions in the plasma membranes of live protoplasts of Arabidopsis thaliana. Results: Lipid staining protocols for several fluorescent lipid analogues in plants are presented. The most emphasis was placed on successful protocols for the single and dual staining of sphingolipid enriched regions and exclusion of sphingolipid enriched regions on the plasma membrane of Arabidopsis thaliana protoplasts. A secondary focus was placed to ensure that these staining protocols presented still maintain cell viability. Furthermore, the protocols were successfully tested with the spectrally sensitive dye Laurdan. Conclusion: Almost all existing staining procedures of the plasma membrane with fluorescent lipid analogues are specified for animal cells and tissues. In order to develop lipid staining protocols for plants, procedures were established with critical steps for the plasma membrane staining of Arabidopsis leaf tissue and protoplasts. The success of the plasma membrane staining protocols was additionally verified by measurements of lipid dynamics by the fluorescence recovery after photobleaching technique and by the observation of new phenomena such as time dependent lipid polarization events in living protoplasts, for which a putative physiological relevance is suggested.}, author = {Blachutzik, J. O. and Demir, F. and Kreuzer, I. and Hedrich, R. and Harms, G. S.}, journal = {Plant Methods}, keywords = {protoplasts}, note = {075vy Times Cited:22 Cited References Count:71}, title = {Methods of staining and visualization of sphingolipid enriched and non-enriched plasma membrane regions of with fluorescent dyes and lipid analogues}, type = {Journal Article}, volume = 8, year = 2012 }

  %0 Journal Article %1 RN1105 %A Blachutzik, J. O. %A Demir, F. %A Kreuzer, I. %A Hedrich, R. %A Harms, G. S. %D 2012 %J Plant Methods %R Artn 28 10.1186/1746-4811-8-28 %T Methods of staining and visualization of sphingolipid enriched and non-enriched plasma membrane regions of with fluorescent dyes and lipid analogues %U /brokenurl#<Go to ISI>://WOS:000313916500001 %V 8 %X Background: Sterols and Sphingolipids form lipid clusters in the plasma membranes of cell types throughout the animal and plant kingdoms. These lipid domains provide a medium for protein signaling complexes at the plasma membrane and are also observed to be principal regions of membrane contact at the inception of infection. We visualized different specific fluorescent lipophilic stains of the both sphingolipid enriched and non-sphingolipid enriched regions in the plasma membranes of live protoplasts of Arabidopsis thaliana. Results: Lipid staining protocols for several fluorescent lipid analogues in plants are presented. The most emphasis was placed on successful protocols for the single and dual staining of sphingolipid enriched regions and exclusion of sphingolipid enriched regions on the plasma membrane of Arabidopsis thaliana protoplasts. A secondary focus was placed to ensure that these staining protocols presented still maintain cell viability. Furthermore, the protocols were successfully tested with the spectrally sensitive dye Laurdan. Conclusion: Almost all existing staining procedures of the plasma membrane with fluorescent lipid analogues are specified for animal cells and tissues. In order to develop lipid staining protocols for plants, procedures were established with critical steps for the plasma membrane staining of Arabidopsis leaf tissue and protoplasts. The success of the plasma membrane staining protocols was additionally verified by measurements of lipid dynamics by the fluorescence recovery after photobleaching technique and by the observation of new phenomena such as time dependent lipid polarization events in living protoplasts, for which a putative physiological relevance is suggested.
• The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms. Schulze, W. X.; Sanggaard, K. W.; Kreuzer, I.; Knudsen, A. D.; Bemm, F.; Thogersen, I. B.; Bräutigam, A.; Thomsen, L. R.; Schliesky, S.; Dyrlund, T. F.; Escalante-Perez, M.; Becker, D.; Schultz, J.; Karring, H.; Weber, A.; Hojrup, P.; Hedrich, R.; Enghild, J. J. In Molecular & Cellular Proteomics, 11(11), pp. 1306–1319. 2012.
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  The Venus flytrap (Dionaea muscipula) is one of the most well-known carnivorous plants because of its unique ability to capture small animals, usually insects or spiders, through a unique snap-trapping mechanism. The animals are subsequently killed and digested so that the plants can assimilate nutrients, as they grow in mineral-deficient soils. We deep sequenced the cDNA from Dionaea traps to obtain transcript libraries, which were used in the mass spectrometry-based identification of the proteins secreted during digestion. The identified proteins consisted of peroxidases, nucleases, phosphatases, phospholipases, a glucanase, chitinases, and proteolytic enzymes, including four cysteine proteases, two aspartic proteases, and a serine carboxypeptidase. The majority of the most abundant proteins were categorized as pathogenesis-related proteins, suggesting that the plant's digestive system evolved from defense-related processes. This in-depth characterization of a highly specialized secreted fluid from a carnivorous plant provides new information about the plant's prey digestion mechanism and the evolutionary processes driving its defense pathways and nutrient acquisition. Molecular & Cellular Proteomics 11: 10.1074/mcp.M112.021006, 1306-1319, 2012.

  @article{RN1094, abstract = {The Venus flytrap (Dionaea muscipula) is one of the most well-known carnivorous plants because of its unique ability to capture small animals, usually insects or spiders, through a unique snap-trapping mechanism. The animals are subsequently killed and digested so that the plants can assimilate nutrients, as they grow in mineral-deficient soils. We deep sequenced the cDNA from Dionaea traps to obtain transcript libraries, which were used in the mass spectrometry-based identification of the proteins secreted during digestion. The identified proteins consisted of peroxidases, nucleases, phosphatases, phospholipases, a glucanase, chitinases, and proteolytic enzymes, including four cysteine proteases, two aspartic proteases, and a serine carboxypeptidase. The majority of the most abundant proteins were categorized as pathogenesis-related proteins, suggesting that the plant's digestive system evolved from defense-related processes. This in-depth characterization of a highly specialized secreted fluid from a carnivorous plant provides new information about the plant's prey digestion mechanism and the evolutionary processes driving its defense pathways and nutrient acquisition. Molecular & Cellular Proteomics 11: 10.1074/mcp.M112.021006, 1306-1319, 2012.}, author = {Schulze, W. X. and Sanggaard, K. W. and Kreuzer, I. and Knudsen, A. D. and Bemm, F. and Thogersen, I. B. and Bräutigam, A. and Thomsen, L. R. and Schliesky, S. and Dyrlund, T. F. and Escalante-Perez, M. and Becker, D. and Schultz, J. and Karring, H. and Weber, A. and Hojrup, P. and Hedrich, R. and Enghild, J. J.}, journal = {Molecular & Cellular Proteomics}, keywords = {ellis}, note = {067ep Times Cited:78 Cited References Count:57}, number = 11, pages = {1306-1319}, title = {The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms}, type = {Journal Article}, volume = 11, year = 2012 }

  %0 Journal Article %1 RN1094 %A Schulze, W. X. %A Sanggaard, K. W. %A Kreuzer, I. %A Knudsen, A. D. %A Bemm, F. %A Thogersen, I. B. %A Bräutigam, A. %A Thomsen, L. R. %A Schliesky, S. %A Dyrlund, T. F. %A Escalante-Perez, M. %A Becker, D. %A Schultz, J. %A Karring, H. %A Weber, A. %A Hojrup, P. %A Hedrich, R. %A Enghild, J. J. %D 2012 %J Molecular & Cellular Proteomics %N 11 %P 1306-1319 %R 10.1074/mcp.M112.021006 %T The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms %U /brokenurl#<Go to ISI>://WOS:000313277100016 %V 11 %X The Venus flytrap (Dionaea muscipula) is one of the most well-known carnivorous plants because of its unique ability to capture small animals, usually insects or spiders, through a unique snap-trapping mechanism. The animals are subsequently killed and digested so that the plants can assimilate nutrients, as they grow in mineral-deficient soils. We deep sequenced the cDNA from Dionaea traps to obtain transcript libraries, which were used in the mass spectrometry-based identification of the proteins secreted during digestion. The identified proteins consisted of peroxidases, nucleases, phosphatases, phospholipases, a glucanase, chitinases, and proteolytic enzymes, including four cysteine proteases, two aspartic proteases, and a serine carboxypeptidase. The majority of the most abundant proteins were categorized as pathogenesis-related proteins, suggesting that the plant's digestive system evolved from defense-related processes. This in-depth characterization of a highly specialized secreted fluid from a carnivorous plant provides new information about the plant's prey digestion mechanism and the evolutionary processes driving its defense pathways and nutrient acquisition. Molecular & Cellular Proteomics 11: 10.1074/mcp.M112.021006, 1306-1319, 2012.
• Anion channels: master switches of stress responses. Roelfsema, M. R. G.; Hedrich, R.; Geiger, D. In Trends in Plant Science, 17(4), pp. 221–229. 2012.
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  During stress, plant cells activate anion channels and trigger the release of anions across the plasma membrane. Recently, two new gene families have been identified that encode major groups of anion channels. The SLAC/SLAH channels are characterized by slow voltage-dependent activation (S-type), whereas ALMT genes encode rapid-activating channels (R-type). Both S- and R-type channels are stimulated in guard cells by the stress hormone ABA, which leads to stomatal closure. Besides their role in ABA-dependent stomatal movement, anion channels are also activated by biotic stress factors such as microbe-associated molecular patterns (MAMPs). Given that anion channels occur throughout the plant kingdom, they are likely to serve a general function as master switches of stress responses.

  @article{RN1097, abstract = {During stress, plant cells activate anion channels and trigger the release of anions across the plasma membrane. Recently, two new gene families have been identified that encode major groups of anion channels. The SLAC/SLAH channels are characterized by slow voltage-dependent activation (S-type), whereas ALMT genes encode rapid-activating channels (R-type). Both S- and R-type channels are stimulated in guard cells by the stress hormone ABA, which leads to stomatal closure. Besides their role in ABA-dependent stomatal movement, anion channels are also activated by biotic stress factors such as microbe-associated molecular patterns (MAMPs). Given that anion channels occur throughout the plant kingdom, they are likely to serve a general function as master switches of stress responses.}, author = {Roelfsema, M. R. G. and Hedrich, R. and Geiger, D.}, journal = {Trends in Plant Science}, keywords = {s-type}, note = {934dl Times Cited:113 Cited References Count:97}, number = 4, pages = {221-229}, title = {Anion channels: master switches of stress responses}, type = {Journal Article}, volume = 17, year = 2012 }

  %0 Journal Article %1 RN1097 %A Roelfsema, M. R. G. %A Hedrich, R. %A Geiger, D. %D 2012 %J Trends in Plant Science %N 4 %P 221-229 %R 10.1016/j.tplants.2012.01.009 %T Anion channels: master switches of stress responses %U /brokenurl#<Go to ISI>://WOS:000303423300005 %V 17 %X During stress, plant cells activate anion channels and trigger the release of anions across the plasma membrane. Recently, two new gene families have been identified that encode major groups of anion channels. The SLAC/SLAH channels are characterized by slow voltage-dependent activation (S-type), whereas ALMT genes encode rapid-activating channels (R-type). Both S- and R-type channels are stimulated in guard cells by the stress hormone ABA, which leads to stomatal closure. Besides their role in ABA-dependent stomatal movement, anion channels are also activated by biotic stress factors such as microbe-associated molecular patterns (MAMPs). Given that anion channels occur throughout the plant kingdom, they are likely to serve a general function as master switches of stress responses.
• Poplar Extrafloral Nectar Is Protected against Plant and Human Pathogenic Fungus. Escalante-Pérez, M.; Jaborsky, M.; Reinders, J.; Kurzai, O.; Hedrich, R.; Ache, P. In Molecular Plant, 5(5), pp. 1157–1159. 2012.
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  @article{RN1102, author = {Escalante-Pérez, M. and Jaborsky, M. and Reinders, J. and Kurzai, O. and Hedrich, R. and Ache, P.}, journal = {Molecular Plant}, keywords = {myOwn}, note = {008mm Times Cited:11 Cited References Count:11}, number = 5, pages = {1157-1159}, title = {Poplar Extrafloral Nectar Is Protected against Plant and Human Pathogenic Fungus}, type = {Journal Article}, volume = 5, year = 2012 }

  %0 Journal Article %1 RN1102 %A Escalante-Pérez, M. %A Jaborsky, M. %A Reinders, J. %A Kurzai, O. %A Hedrich, R. %A Ache, P. %D 2012 %J Molecular Plant %N 5 %P 1157-1159 %R 10.1093/mp/sss072 %T Poplar Extrafloral Nectar Is Protected against Plant and Human Pathogenic Fungus %U /brokenurl#<Go to ISI>://WOS:000308961100023 %V 5
• PHO1 expression in guard cells mediates the stomatal response to abscisic acid in Arabidopsis. Zimmerli, C.; Ribot, C.; Vavasseur, A.; Bauer, H.; Hedrich, R.; Poirier, Y. In Plant Journal, 72(2), pp. 199–211. 2012.
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  Stomatal opening and closing are driven by ion fluxes that cause changes in guard cell turgor and volume. This process is, in turn, regulated by environmental and hormonal signals, including light and the phytohormone abscisic acid (ABA). Here, we present genetic evidence that expression of PHO1 in guard cells of Arabidopsis thaliana is required for full stomatal responses to ABA. PHO1 is involved in the export of phosphate into the root xylem vessels and, as a result, the pho1 mutant is characterized by low shoot phosphate levels. In leaves, PHO1 was found expressed in guard cells and up-regulated following treatment with ABA. The pho1 mutant was unaffected in production of reactive oxygen species following ABA treatment, and in stomatal movements in response to light cues, high extracellular calcium, auxin, and fusicoccin. However, stomatal movements in response to ABA treatment were severely impaired, both in terms of induction of closure and inhibition of opening. Micro-grafting a pho1 shoot scion onto wild-type rootstock resulted in plants with normal shoot growth and phosphate content, but failed to restore normal stomatal response to ABA treatment. PHO1 knockdown using RNA interference specifically in guard cells of wild-type plants caused a reduced stomatal response to ABA. In agreement, specific expression of PHO1 in guard cells of pho1 plants complemented the mutant guard cell phenotype and re-established ABA sensitivity, although full functional complementation was dependent on shoot phosphate sufficiency. Together, these data reveal an important role for phosphate and the action of PHO1 in the stomatal response to ABA.

  @article{RN1092, abstract = {Stomatal opening and closing are driven by ion fluxes that cause changes in guard cell turgor and volume. This process is, in turn, regulated by environmental and hormonal signals, including light and the phytohormone abscisic acid (ABA). Here, we present genetic evidence that expression of PHO1 in guard cells of Arabidopsis thaliana is required for full stomatal responses to ABA. PHO1 is involved in the export of phosphate into the root xylem vessels and, as a result, the pho1 mutant is characterized by low shoot phosphate levels. In leaves, PHO1 was found expressed in guard cells and up-regulated following treatment with ABA. The pho1 mutant was unaffected in production of reactive oxygen species following ABA treatment, and in stomatal movements in response to light cues, high extracellular calcium, auxin, and fusicoccin. However, stomatal movements in response to ABA treatment were severely impaired, both in terms of induction of closure and inhibition of opening. Micro-grafting a pho1 shoot scion onto wild-type rootstock resulted in plants with normal shoot growth and phosphate content, but failed to restore normal stomatal response to ABA treatment. PHO1 knockdown using RNA interference specifically in guard cells of wild-type plants caused a reduced stomatal response to ABA. In agreement, specific expression of PHO1 in guard cells of pho1 plants complemented the mutant guard cell phenotype and re-established ABA sensitivity, although full functional complementation was dependent on shoot phosphate sufficiency. Together, these data reveal an important role for phosphate and the action of PHO1 in the stomatal response to ABA.}, author = {Zimmerli, C. and Ribot, C. and Vavasseur, A. and Bauer, H. and Hedrich, R. and Poirier, Y.}, journal = {Plant Journal}, keywords = {abscisic}, note = {021ug Times Cited:27 Cited References Count:51}, number = 2, pages = {199-211}, title = {PHO1 expression in guard cells mediates the stomatal response to abscisic acid in Arabidopsis}, type = {Journal Article}, volume = 72, year = 2012 }

  %0 Journal Article %1 RN1092 %A Zimmerli, C. %A Ribot, C. %A Vavasseur, A. %A Bauer, H. %A Hedrich, R. %A Poirier, Y. %D 2012 %J Plant Journal %N 2 %P 199-211 %R 10.1111/j.1365-313X.2012.05058.x %T PHO1 expression in guard cells mediates the stomatal response to abscisic acid in Arabidopsis %U /brokenurl#<Go to ISI>://WOS:000309910300004 %V 72 %X Stomatal opening and closing are driven by ion fluxes that cause changes in guard cell turgor and volume. This process is, in turn, regulated by environmental and hormonal signals, including light and the phytohormone abscisic acid (ABA). Here, we present genetic evidence that expression of PHO1 in guard cells of Arabidopsis thaliana is required for full stomatal responses to ABA. PHO1 is involved in the export of phosphate into the root xylem vessels and, as a result, the pho1 mutant is characterized by low shoot phosphate levels. In leaves, PHO1 was found expressed in guard cells and up-regulated following treatment with ABA. The pho1 mutant was unaffected in production of reactive oxygen species following ABA treatment, and in stomatal movements in response to light cues, high extracellular calcium, auxin, and fusicoccin. However, stomatal movements in response to ABA treatment were severely impaired, both in terms of induction of closure and inhibition of opening. Micro-grafting a pho1 shoot scion onto wild-type rootstock resulted in plants with normal shoot growth and phosphate content, but failed to restore normal stomatal response to ABA treatment. PHO1 knockdown using RNA interference specifically in guard cells of wild-type plants caused a reduced stomatal response to ABA. In agreement, specific expression of PHO1 in guard cells of pho1 plants complemented the mutant guard cell phenotype and re-established ABA sensitivity, although full functional complementation was dependent on shoot phosphate sufficiency. Together, these data reveal an important role for phosphate and the action of PHO1 in the stomatal response to ABA.
• Poplar Extrafloral Nectaries: Two Types, Two Strategies of Indirect Defenses against Herbivores. Escalante-Pérez, M.; Jaborsky, M.; Lautner, S.; Fromm, J.; Müller, T.; Dittrich, M.; Kunert, M.; Boland, W.; Hedrich, R.; Ache, P. In Plant Physiology, 159(3), pp. 1176–1191. 2012.
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  Many plant species grow extrafloral nectaries and produce nectar to attract carnivore arthropods as defenders against herbivores. Two nectary types that evolved with Populus trichocarpa (Ptr) and Populus tremula x Populus tremuloides (Ptt) were studied from their ecology down to the genes and molecules. Both nectary types strongly differ in morphology, nectar composition and mode of secretion, and defense strategy. In Ptt, nectaries represent constitutive organs with continuous merocrine nectar flow, nectary appearance, nectar production, and flow. In contrast, Ptr nectaries were found to be holocrine and inducible. Neither mechanical wounding nor the application of jasmonic acid, but infestation by sucking insects, induced Ptr nectar secretion. Thus, nectaries of Ptr and Ptt seem to answer the same threat by the use of different mechanisms.

  @article{RN1103, abstract = {Many plant species grow extrafloral nectaries and produce nectar to attract carnivore arthropods as defenders against herbivores. Two nectary types that evolved with Populus trichocarpa (Ptr) and Populus tremula x Populus tremuloides (Ptt) were studied from their ecology down to the genes and molecules. Both nectary types strongly differ in morphology, nectar composition and mode of secretion, and defense strategy. In Ptt, nectaries represent constitutive organs with continuous merocrine nectar flow, nectary appearance, nectar production, and flow. In contrast, Ptr nectaries were found to be holocrine and inducible. Neither mechanical wounding nor the application of jasmonic acid, but infestation by sucking insects, induced Ptr nectar secretion. Thus, nectaries of Ptr and Ptt seem to answer the same threat by the use of different mechanisms.}, author = {Escalante-Pérez, M. and Jaborsky, M. and Lautner, S. and Fromm, J. and Müller, T. and Dittrich, M. and Kunert, M. and Boland, W. and Hedrich, R. and Ache, P.}, journal = {Plant Physiology}, keywords = {malacosoma-disstria}, note = {968du Times Cited:39 Cited References Count:100}, number = 3, pages = {1176-1191}, title = {Poplar Extrafloral Nectaries: Two Types, Two Strategies of Indirect Defenses against Herbivores}, type = {Journal Article}, volume = 159, year = 2012 }

  %0 Journal Article %1 RN1103 %A Escalante-Pérez, M. %A Jaborsky, M. %A Lautner, S. %A Fromm, J. %A Müller, T. %A Dittrich, M. %A Kunert, M. %A Boland, W. %A Hedrich, R. %A Ache, P. %D 2012 %J Plant Physiology %N 3 %P 1176-1191 %R 10.1104/pp.112.196014 %T Poplar Extrafloral Nectaries: Two Types, Two Strategies of Indirect Defenses against Herbivores %U /brokenurl#<Go to ISI>://WOS:000305958000025 %V 159 %X Many plant species grow extrafloral nectaries and produce nectar to attract carnivore arthropods as defenders against herbivores. Two nectary types that evolved with Populus trichocarpa (Ptr) and Populus tremula x Populus tremuloides (Ptt) were studied from their ecology down to the genes and molecules. Both nectary types strongly differ in morphology, nectar composition and mode of secretion, and defense strategy. In Ptt, nectaries represent constitutive organs with continuous merocrine nectar flow, nectary appearance, nectar production, and flow. In contrast, Ptr nectaries were found to be holocrine and inducible. Neither mechanical wounding nor the application of jasmonic acid, but infestation by sucking insects, induced Ptr nectar secretion. Thus, nectaries of Ptr and Ptt seem to answer the same threat by the use of different mechanisms.
• Vacuoles release sucrose via tonoplast-localised SUC4-type transporters. Schneider, S.; Hulpke, S.; Schulz, A.; Yaron, I.; Höll, J.; Imlau, A.; Schmitt, B.; Batz, S.; Wolf, S.; Hedrich, R.; Sauer, N. In Plant Biology, 14(2), pp. 325–336. 2012.
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  Arabidopsis thaliana has seven genes for functionally active sucrose transporters. Together with sucrose transporters from other dicot and monocot plants, these proteins form four separate phylogenetic groups. Group-IV includes the Arabidopsis protein SUC4 (synonym SUT4) and related proteins from monocots and dicots. These Group-IV sucrose transporters were reported to be either tonoplast- or plasma membrane-localised, and in heterologous expression systems were shown to act as sucrose/H+ symporters. Here, we present comparative analyses of the subcellular localisation of the Arabidopsis SUC4 protein and of several other Group-IV sucrose transporters, studies on tissue specificity of the Arabidopsis SUC4 promoter, phenotypic characterisations of Atsuc4.1 mutants and AtSUC4 overexpressing (AtSUC4-OX) plants, and functional comparisons of Atsuc4.1 and AtSUC4-OX vacuoles. Our data show that SUC4-type sucrose transporters from different plant families (Brassicaceae, Cucurbitaceae and Solanaceae) localise exclusively to the tonoplast, demonstrating that vacuolar sucrose transport is a common theme of all SUC4-type proteins. AtSUC4 expression is confined to the stele of Arabidopsis roots, developing anthers and meristematic tissues in all aerial parts. Analyses of the carbohydrate content of WT and mutant seedlings revealed reduced sucrose content in AtSUC4-OX seedlings. This is in line with patch-clamp analyses of AtSUC4-OX vacuoles that characterise AtSUC4 as a sucrose/H+ symporter directly in the tonoplast membrane.

  @article{RN1095, abstract = {Arabidopsis thaliana has seven genes for functionally active sucrose transporters. Together with sucrose transporters from other dicot and monocot plants, these proteins form four separate phylogenetic groups. Group-IV includes the Arabidopsis protein SUC4 (synonym SUT4) and related proteins from monocots and dicots. These Group-IV sucrose transporters were reported to be either tonoplast- or plasma membrane-localised, and in heterologous expression systems were shown to act as sucrose/H+ symporters. Here, we present comparative analyses of the subcellular localisation of the Arabidopsis SUC4 protein and of several other Group-IV sucrose transporters, studies on tissue specificity of the Arabidopsis SUC4 promoter, phenotypic characterisations of Atsuc4.1 mutants and AtSUC4 overexpressing (AtSUC4-OX) plants, and functional comparisons of Atsuc4.1 and AtSUC4-OX vacuoles. Our data show that SUC4-type sucrose transporters from different plant families (Brassicaceae, Cucurbitaceae and Solanaceae) localise exclusively to the tonoplast, demonstrating that vacuolar sucrose transport is a common theme of all SUC4-type proteins. AtSUC4 expression is confined to the stele of Arabidopsis roots, developing anthers and meristematic tissues in all aerial parts. Analyses of the carbohydrate content of WT and mutant seedlings revealed reduced sucrose content in AtSUC4-OX seedlings. This is in line with patch-clamp analyses of AtSUC4-OX vacuoles that characterise AtSUC4 as a sucrose/H+ symporter directly in the tonoplast membrane.}, author = {Schneider, S. and Hulpke, S. and Schulz, A. and Yaron, I. and Höll, J. and Imlau, A. and Schmitt, B. and Batz, S. and Wolf, S. and Hedrich, R. and Sauer, N.}, journal = {Plant Biology}, keywords = {localisation}, note = {887lm Times Cited:108 Cited References Count:53}, number = 2, pages = {325-336}, title = {Vacuoles release sucrose via tonoplast-localised SUC4-type transporters}, type = {Journal Article}, volume = 14, year = 2012 }

  %0 Journal Article %1 RN1095 %A Schneider, S. %A Hulpke, S. %A Schulz, A. %A Yaron, I. %A Höll, J. %A Imlau, A. %A Schmitt, B. %A Batz, S. %A Wolf, S. %A Hedrich, R. %A Sauer, N. %D 2012 %J Plant Biology %N 2 %P 325-336 %R 10.1111/j.1438-8677.2011.00506.x %T Vacuoles release sucrose via tonoplast-localised SUC4-type transporters %U /brokenurl#<Go to ISI>://WOS:000299928900009 %V 14 %X Arabidopsis thaliana has seven genes for functionally active sucrose transporters. Together with sucrose transporters from other dicot and monocot plants, these proteins form four separate phylogenetic groups. Group-IV includes the Arabidopsis protein SUC4 (synonym SUT4) and related proteins from monocots and dicots. These Group-IV sucrose transporters were reported to be either tonoplast- or plasma membrane-localised, and in heterologous expression systems were shown to act as sucrose/H+ symporters. Here, we present comparative analyses of the subcellular localisation of the Arabidopsis SUC4 protein and of several other Group-IV sucrose transporters, studies on tissue specificity of the Arabidopsis SUC4 promoter, phenotypic characterisations of Atsuc4.1 mutants and AtSUC4 overexpressing (AtSUC4-OX) plants, and functional comparisons of Atsuc4.1 and AtSUC4-OX vacuoles. Our data show that SUC4-type sucrose transporters from different plant families (Brassicaceae, Cucurbitaceae and Solanaceae) localise exclusively to the tonoplast, demonstrating that vacuolar sucrose transport is a common theme of all SUC4-type proteins. AtSUC4 expression is confined to the stele of Arabidopsis roots, developing anthers and meristematic tissues in all aerial parts. Analyses of the carbohydrate content of WT and mutant seedlings revealed reduced sucrose content in AtSUC4-OX seedlings. This is in line with patch-clamp analyses of AtSUC4-OX vacuoles that characterise AtSUC4 as a sucrose/H+ symporter directly in the tonoplast membrane.
• Ion Channels in Plants. Hedrich, R. In Physiological Reviews, 92(4), pp. 1777–1811. 2012.
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  Hedrich R. Ion Channels in Plants. Physiol Rev 92: 1777-1811, 2012; doi:10.1152/physrev.00038.2011.-Since the first recordings of single potassium channel activities in the plasma membrane of guard cells more than 25 years ago, patch-clamp studies discovered a variety of ion channels in all cell types and plant species under inspection. Their properties differed in a cell type- and cell membrane-dependent manner. Guard cells, for which the existence of plant potassium channels was initially documented, advanced to a versatile model system for studying plant ion channel structure, function, and physiology. Interestingly, one of the first identified potassium-channel genes encoding the Shaker-type channel KAT1 was shown to be highly expressed in guard cells. KAT1-type channels from Arabidopsis thaliana and its homologs from other species were found to encode the K+-selective inward rectifiers that had already been recorded in early patch-clamp studies with guard cells. Within the genome era, additional Arabidopsis Shaker-type channels appeared. All nine members of the Arabidopsis Shaker family are localized at the plasma membrane, where they either operate as inward rectifiers, outward rectifiers, weak voltage-dependent channels, or electrically silent, but modulatory subunits. The vacuole membrane, in contrast, harbors a set of two-pore K+ channels. Just very recently, two plant anion channel families of the SLAC/SLAH and ALMT/QUAC type were identified. SLAC1/SLAH3 and QUAC1 are expressed in guard cells and mediate Slow- and Rapid-type anion currents, respectively, that are involved in volume and turgor regulation. Anion channels in guard cells and other plant cells are key targets within often complex signaling networks. Here, the present knowledge is reviewed for the plant ion channel biology. Special emphasis is drawn to the molecular mechanisms of channel regulation, in the context of model systems and in the light of evolution.

  @article{RN1101, abstract = {Hedrich R. Ion Channels in Plants. Physiol Rev 92: 1777-1811, 2012; doi:10.1152/physrev.00038.2011.-Since the first recordings of single potassium channel activities in the plasma membrane of guard cells more than 25 years ago, patch-clamp studies discovered a variety of ion channels in all cell types and plant species under inspection. Their properties differed in a cell type- and cell membrane-dependent manner. Guard cells, for which the existence of plant potassium channels was initially documented, advanced to a versatile model system for studying plant ion channel structure, function, and physiology. Interestingly, one of the first identified potassium-channel genes encoding the Shaker-type channel KAT1 was shown to be highly expressed in guard cells. KAT1-type channels from Arabidopsis thaliana and its homologs from other species were found to encode the K+-selective inward rectifiers that had already been recorded in early patch-clamp studies with guard cells. Within the genome era, additional Arabidopsis Shaker-type channels appeared. All nine members of the Arabidopsis Shaker family are localized at the plasma membrane, where they either operate as inward rectifiers, outward rectifiers, weak voltage-dependent channels, or electrically silent, but modulatory subunits. The vacuole membrane, in contrast, harbors a set of two-pore K+ channels. Just very recently, two plant anion channel families of the SLAC/SLAH and ALMT/QUAC type were identified. SLAC1/SLAH3 and QUAC1 are expressed in guard cells and mediate Slow- and Rapid-type anion currents, respectively, that are involved in volume and turgor regulation. Anion channels in guard cells and other plant cells are key targets within often complex signaling networks. Here, the present knowledge is reviewed for the plant ion channel biology. Special emphasis is drawn to the molecular mechanisms of channel regulation, in the context of model systems and in the light of evolution.}, author = {Hedrich, R.}, journal = {Physiological Reviews}, keywords = {channels}, note = {023so Times Cited:317 Cited References Count:359}, number = 4, pages = {1777-1811}, title = {Ion Channels in Plants}, type = {Journal Article}, volume = 92, year = 2012 }

  %0 Journal Article %1 RN1101 %A Hedrich, R. %D 2012 %J Physiological Reviews %N 4 %P 1777-1811 %R 10.1152/physrev.00038.2011 %T Ion Channels in Plants %U /brokenurl#<Go to ISI>://WOS:000310055900007 %V 92 %X Hedrich R. Ion Channels in Plants. Physiol Rev 92: 1777-1811, 2012; doi:10.1152/physrev.00038.2011.-Since the first recordings of single potassium channel activities in the plasma membrane of guard cells more than 25 years ago, patch-clamp studies discovered a variety of ion channels in all cell types and plant species under inspection. Their properties differed in a cell type- and cell membrane-dependent manner. Guard cells, for which the existence of plant potassium channels was initially documented, advanced to a versatile model system for studying plant ion channel structure, function, and physiology. Interestingly, one of the first identified potassium-channel genes encoding the Shaker-type channel KAT1 was shown to be highly expressed in guard cells. KAT1-type channels from Arabidopsis thaliana and its homologs from other species were found to encode the K+-selective inward rectifiers that had already been recorded in early patch-clamp studies with guard cells. Within the genome era, additional Arabidopsis Shaker-type channels appeared. All nine members of the Arabidopsis Shaker family are localized at the plasma membrane, where they either operate as inward rectifiers, outward rectifiers, weak voltage-dependent channels, or electrically silent, but modulatory subunits. The vacuole membrane, in contrast, harbors a set of two-pore K+ channels. Just very recently, two plant anion channel families of the SLAC/SLAH and ALMT/QUAC type were identified. SLAC1/SLAH3 and QUAC1 are expressed in guard cells and mediate Slow- and Rapid-type anion currents, respectively, that are involved in volume and turgor regulation. Anion channels in guard cells and other plant cells are key targets within often complex signaling networks. Here, the present knowledge is reviewed for the plant ion channel biology. Special emphasis is drawn to the molecular mechanisms of channel regulation, in the context of model systems and in the light of evolution.
• Multiple Calcium-Dependent Kinases Modulate ABA-Activated Guard Cell Anion Channels. Scherzer, S.; Maierhofer, T.; Al-Rasheid, K. A. S.; Geiger, D.; Hedrich, R. In Molecular Plant, 5(6), pp. 1409–1412. 2012.
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  @article{RN1096, author = {Scherzer, S. and Maierhofer, T. and Al-Rasheid, K. A. S. and Geiger, D. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {slac1}, note = {057os Times Cited:103 Cited References Count:9}, number = 6, pages = {1409-1412}, title = {Multiple Calcium-Dependent Kinases Modulate ABA-Activated Guard Cell Anion Channels}, type = {Journal Article}, volume = 5, year = 2012 }

  %0 Journal Article %1 RN1096 %A Scherzer, S. %A Maierhofer, T. %A Al-Rasheid, K. A. S. %A Geiger, D. %A Hedrich, R. %D 2012 %J Molecular Plant %N 6 %P 1409-1412 %R 10.1093/mp/sss084 %T Multiple Calcium-Dependent Kinases Modulate ABA-Activated Guard Cell Anion Channels %U /brokenurl#<Go to ISI>://WOS:000312573500023 %V 5
• Regulation of the V-type ATPase by redox modulation. Seidel, T.; Scholl, S.; Krebs, M.; Rienmüller, F.; Marten, I.; Hedrich, R.; Hanitzsch, M.; Janetzki, P.; Dietz, K. J.; Schumacher, K. In Biochemical Journal, 448, pp. 243–251. 2012.
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  ATP-hydrolysis and proton pumping by the V-ATPase (vacuolar proton-translocating ATPase) are subject to redox regulation in mammals, yeast and plants. Oxidative inhibition of the V-ATPase is ascribed to disulfide-bond formation between conserved cysteine residues at the catalytic site of subunit A. Subunits containing amino acid substitutions of one of three conserved cysteine residues of VHA-A were expressed in a vha-A null mutant background in Arabidopsis. In vitro activity measurements revealed a complete absence of oxidative inhibition in the transgenic line expressing VHA-A C256S, confirming that Cys(256) is necessary for redox regulation. In contrast, oxidative inhibition was unaffected in plants expressing VHA-A C279S and VHA-A C535S, indicating that disulfide bridges involving these cysteine residues are not essential for oxidative inhibition. hi vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.

  @article{RN1093, abstract = {ATP-hydrolysis and proton pumping by the V-ATPase (vacuolar proton-translocating ATPase) are subject to redox regulation in mammals, yeast and plants. Oxidative inhibition of the V-ATPase is ascribed to disulfide-bond formation between conserved cysteine residues at the catalytic site of subunit A. Subunits containing amino acid substitutions of one of three conserved cysteine residues of VHA-A were expressed in a vha-A null mutant background in Arabidopsis. In vitro activity measurements revealed a complete absence of oxidative inhibition in the transgenic line expressing VHA-A C256S, confirming that Cys(256) is necessary for redox regulation. In contrast, oxidative inhibition was unaffected in plants expressing VHA-A C279S and VHA-A C535S, indicating that disulfide bridges involving these cysteine residues are not essential for oxidative inhibition. hi vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.}, author = {Seidel, T. and Scholl, S. and Krebs, M. and Rienmüller, F. and Marten, I. and Hedrich, R. and Hanitzsch, M. and Janetzki, P. and Dietz, K. J. and Schumacher, K.}, journal = {Biochemical Journal}, keywords = {arabidopsis}, note = {2 047yu Times Cited:23 Cited References Count:44}, pages = {243-251}, title = {Regulation of the V-type ATPase by redox modulation}, type = {Journal Article}, volume = 448, year = 2012 }

  %0 Journal Article %1 RN1093 %A Seidel, T. %A Scholl, S. %A Krebs, M. %A Rienmüller, F. %A Marten, I. %A Hedrich, R. %A Hanitzsch, M. %A Janetzki, P. %A Dietz, K. J. %A Schumacher, K. %D 2012 %J Biochemical Journal %P 243-251 %R 10.1042/Bj20120976 %T Regulation of the V-type ATPase by redox modulation %U /brokenurl#<Go to ISI>://WOS:000311878200007 %V 448 %X ATP-hydrolysis and proton pumping by the V-ATPase (vacuolar proton-translocating ATPase) are subject to redox regulation in mammals, yeast and plants. Oxidative inhibition of the V-ATPase is ascribed to disulfide-bond formation between conserved cysteine residues at the catalytic site of subunit A. Subunits containing amino acid substitutions of one of three conserved cysteine residues of VHA-A were expressed in a vha-A null mutant background in Arabidopsis. In vitro activity measurements revealed a complete absence of oxidative inhibition in the transgenic line expressing VHA-A C256S, confirming that Cys(256) is necessary for redox regulation. In contrast, oxidative inhibition was unaffected in plants expressing VHA-A C279S and VHA-A C535S, indicating that disulfide bridges involving these cysteine residues are not essential for oxidative inhibition. hi vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.
• Poplar Wood Rays Are Involved in Seasonal Remodeling of Tree Physiology. Larisch, C.; Dittrich, M.; Wildhagen, H.; Lautner, S.; Fromm, J.; Polle, A.; Hedrich, R.; Rennenberg, H.; Müller, T.; Ache, P. In Plant Physiology, 160(3), pp. 1515–1529. 2012.
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  Understanding seasonality and longevity is a major challenge in tree biology. In woody species, growth phases and dormancy follow one another consecutively. In the oldest living individuals, the annual cycle may run for more than 1,000 years. So far, however, not much is known about the processes triggering reactivation from dormancy. In this study, we focused on wood rays, which are known to play an important role in tree development. The transition phase from dormancy to flowering in early spring was compared with the phase of active growth in summer. Rays from wood samples of poplar (Populus x canescens) were enriched by laser microdissection, and transcripts were monitored by poplar whole-genome microarrays. The resulting seasonally varying complex expression and metabolite patterns were subjected to pathway analyses. In February, the metabolic pathways related to flower induction were high, indicating that reactivation from dormancy was already taking place at this time of the year. In July, the pathways related to active growth, like lignin biosynthesis, nitrogen assimilation, and defense, were enriched. Based on "marker" genes identified in our pathway analyses, we were able to validate periodical changes in wood samples by quantitative polymerase chain reaction. These studies, and the resulting ray database, provide new insights into the steps underlying the seasonality of poplar trees.

  @article{RN1100, abstract = {Understanding seasonality and longevity is a major challenge in tree biology. In woody species, growth phases and dormancy follow one another consecutively. In the oldest living individuals, the annual cycle may run for more than 1,000 years. So far, however, not much is known about the processes triggering reactivation from dormancy. In this study, we focused on wood rays, which are known to play an important role in tree development. The transition phase from dormancy to flowering in early spring was compared with the phase of active growth in summer. Rays from wood samples of poplar (Populus x canescens) were enriched by laser microdissection, and transcripts were monitored by poplar whole-genome microarrays. The resulting seasonally varying complex expression and metabolite patterns were subjected to pathway analyses. In February, the metabolic pathways related to flower induction were high, indicating that reactivation from dormancy was already taking place at this time of the year. In July, the pathways related to active growth, like lignin biosynthesis, nitrogen assimilation, and defense, were enriched. Based on "marker" genes identified in our pathway analyses, we were able to validate periodical changes in wood samples by quantitative polymerase chain reaction. These studies, and the resulting ray database, provide new insights into the steps underlying the seasonality of poplar trees.}, author = {Larisch, C. and Dittrich, M. and Wildhagen, H. and Lautner, S. and Fromm, J. and Polle, A. and Hedrich, R. and Rennenberg, H. and Müller, T. and Ache, P.}, journal = {Plant Physiology}, keywords = {myOwn}, note = {030qc Times Cited:27 Cited References Count:84}, number = 3, pages = {1515-1529}, title = {Poplar Wood Rays Are Involved in Seasonal Remodeling of Tree Physiology}, type = {Journal Article}, volume = 160, year = 2012 }

  %0 Journal Article %1 RN1100 %A Larisch, C. %A Dittrich, M. %A Wildhagen, H. %A Lautner, S. %A Fromm, J. %A Polle, A. %A Hedrich, R. %A Rennenberg, H. %A Müller, T. %A Ache, P. %D 2012 %J Plant Physiology %N 3 %P 1515-1529 %R 10.1104/pp.112.202291 %T Poplar Wood Rays Are Involved in Seasonal Remodeling of Tree Physiology %U /brokenurl#<Go to ISI>://WOS:000310584200028 %V 160 %X Understanding seasonality and longevity is a major challenge in tree biology. In woody species, growth phases and dormancy follow one another consecutively. In the oldest living individuals, the annual cycle may run for more than 1,000 years. So far, however, not much is known about the processes triggering reactivation from dormancy. In this study, we focused on wood rays, which are known to play an important role in tree development. The transition phase from dormancy to flowering in early spring was compared with the phase of active growth in summer. Rays from wood samples of poplar (Populus x canescens) were enriched by laser microdissection, and transcripts were monitored by poplar whole-genome microarrays. The resulting seasonally varying complex expression and metabolite patterns were subjected to pathway analyses. In February, the metabolic pathways related to flower induction were high, indicating that reactivation from dormancy was already taking place at this time of the year. In July, the pathways related to active growth, like lignin biosynthesis, nitrogen assimilation, and defense, were enriched. Based on "marker" genes identified in our pathway analyses, we were able to validate periodical changes in wood samples by quantitative polymerase chain reaction. These studies, and the resulting ray database, provide new insights into the steps underlying the seasonality of poplar trees.
• Molecular evolution of slow and quick anion channels (SLACs and QUACs/ALMTs). Dreyer, I.; Gomez-Porras, J. L.; Riaño-Pachón, D. M.; Hedrich, R.; Geiger, D. In Frontiers in Plant Science, 3. 2012.
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  Electrophysiological analyses conducted about 25 years ago detected two types of anion channels in the plasma membrane of guard cells. One type of channel responds slowly to changes in membrane voltage while the other responds quickly. Consequently, they were named SLAC, for SLow Anion Channel, and QUAC, for QUick Anion Channel. Recently, genes SLAC1 and QUAC1/ALMT12, underlying the two different anion current components, could be identified in the model plant Arabidopsis thaliana. Expression of the gene products in Xenopus oocytes confirmed the quick and slow current kinetics. In this study we provide an overview on our current knowledge on slow and quick anion channels in plants and analyze the molecular evolution of ALMT/QUAC-like and SLAC-like channels. We discovered fingerprints that allow screening databases for these channel types and were able to identify 192 (177 non-redundant) SLAC-like and 422 (402 non-redundant) ALMT/QUAC-like proteins in the fully sequenced genomes of 32 plant species. Phylogenetic analyses provided new insights into the molecular evolution of these channel types. We also combined sequence alignment and clustering with predictions of protein features, leading to the identification of known conserved phosphorylation sites in SLAC1-like channels along with potential sites that have not been yet experimentally confirmed. Using a similar strategy to analyze the hydropathicity of ALMT/QUAC-like channels, we propose a modified topology with additional transmembrane regions that integrates structure and function of these membrane proteins. Our results suggest that cross-referencing phylogenetic analyses with position-specific protein properties and functional data could be a very powerful tool for genome research approaches in general.

  @article{RN1104, abstract = {Electrophysiological analyses conducted about 25 years ago detected two types of anion channels in the plasma membrane of guard cells. One type of channel responds slowly to changes in membrane voltage while the other responds quickly. Consequently, they were named SLAC, for SLow Anion Channel, and QUAC, for QUick Anion Channel. Recently, genes SLAC1 and QUAC1/ALMT12, underlying the two different anion current components, could be identified in the model plant Arabidopsis thaliana. Expression of the gene products in Xenopus oocytes confirmed the quick and slow current kinetics. In this study we provide an overview on our current knowledge on slow and quick anion channels in plants and analyze the molecular evolution of ALMT/QUAC-like and SLAC-like channels. We discovered fingerprints that allow screening databases for these channel types and were able to identify 192 (177 non-redundant) SLAC-like and 422 (402 non-redundant) ALMT/QUAC-like proteins in the fully sequenced genomes of 32 plant species. Phylogenetic analyses provided new insights into the molecular evolution of these channel types. We also combined sequence alignment and clustering with predictions of protein features, leading to the identification of known conserved phosphorylation sites in SLAC1-like channels along with potential sites that have not been yet experimentally confirmed. Using a similar strategy to analyze the hydropathicity of ALMT/QUAC-like channels, we propose a modified topology with additional transmembrane regions that integrates structure and function of these membrane proteins. Our results suggest that cross-referencing phylogenetic analyses with position-specific protein properties and functional data could be a very powerful tool for genome research approaches in general.}, author = {Dreyer, I. and Gomez-Porras, J. L. and Riaño-Pachón, D. M. and Hedrich, R. and Geiger, D.}, journal = {Frontiers in Plant Science}, keywords = {channel}, note = {V30ti Times Cited:86 Cited References Count:55}, title = {Molecular evolution of slow and quick anion channels (SLACs and QUACs/ALMTs)}, type = {Journal Article}, volume = 3, year = 2012 }

  %0 Journal Article %1 RN1104 %A Dreyer, I. %A Gomez-Porras, J. L. %A Riaño-Pachón, D. M. %A Hedrich, R. %A Geiger, D. %D 2012 %J Frontiers in Plant Science %R ARTN 263 10.3389/fpls.2012.00263 %T Molecular evolution of slow and quick anion channels (SLACs and QUACs/ALMTs) %U /brokenurl#<Go to ISI>://WOS:000208837900259 %V 3 %X Electrophysiological analyses conducted about 25 years ago detected two types of anion channels in the plasma membrane of guard cells. One type of channel responds slowly to changes in membrane voltage while the other responds quickly. Consequently, they were named SLAC, for SLow Anion Channel, and QUAC, for QUick Anion Channel. Recently, genes SLAC1 and QUAC1/ALMT12, underlying the two different anion current components, could be identified in the model plant Arabidopsis thaliana. Expression of the gene products in Xenopus oocytes confirmed the quick and slow current kinetics. In this study we provide an overview on our current knowledge on slow and quick anion channels in plants and analyze the molecular evolution of ALMT/QUAC-like and SLAC-like channels. We discovered fingerprints that allow screening databases for these channel types and were able to identify 192 (177 non-redundant) SLAC-like and 422 (402 non-redundant) ALMT/QUAC-like proteins in the fully sequenced genomes of 32 plant species. Phylogenetic analyses provided new insights into the molecular evolution of these channel types. We also combined sequence alignment and clustering with predictions of protein features, leading to the identification of known conserved phosphorylation sites in SLAC1-like channels along with potential sites that have not been yet experimentally confirmed. Using a similar strategy to analyze the hydropathicity of ALMT/QUAC-like channels, we propose a modified topology with additional transmembrane regions that integrates structure and function of these membrane proteins. Our results suggest that cross-referencing phylogenetic analyses with position-specific protein properties and functional data could be a very powerful tool for genome research approaches in general.
• NRT/PTR transporters are essential for translocation of glucosinolate defence compounds to seeds. Nour-Eldin, H. H.; Andersen, T. G.; Burow, M.; Madsen, S. R.; Jorgensen, M. E.; Olsen, C. E.; Dreyer, I.; Hedrich, R.; Geiger, D.; Halkier, B. A. In Nature, 488(7412), pp. 531–534. 2012.
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  In plants, transport processes are important for the reallocation of defence compounds to protect tissues of high value(1), as demonstrated in the plant model Arabidopsis, in which the major defence compounds, glucosinolates(2), are translocated to seeds on maturation(3). The molecular basis for long-distance transport of glucosinolates and other defence compounds, however, remains unknown. Here we identify and characterize two members of the nitrate/peptide transporter family, GTR1 and GTR2, as high-affinity, proton-dependent glucosinolate-specific transporters. The gtr1 gtr2 double mutant did not accumulate glucosinolates in seeds and had more than tenfold over-accumulation in source tissues such as leaves and silique walls, indicating that both plasma membrane-localized transporters are essential for long-distance transport of glucosinolates. We propose that GTR1 and GTR2 control the loading of glucosinolates from the apoplasm into the phloem. Identification of the glucosinolate transporters has agricultural potential as a means to control allocation of defence compounds in a tissue-specific manner.

  @article{RN1099, abstract = {In plants, transport processes are important for the reallocation of defence compounds to protect tissues of high value(1), as demonstrated in the plant model Arabidopsis, in which the major defence compounds, glucosinolates(2), are translocated to seeds on maturation(3). The molecular basis for long-distance transport of glucosinolates and other defence compounds, however, remains unknown. Here we identify and characterize two members of the nitrate/peptide transporter family, GTR1 and GTR2, as high-affinity, proton-dependent glucosinolate-specific transporters. The gtr1 gtr2 double mutant did not accumulate glucosinolates in seeds and had more than tenfold over-accumulation in source tissues such as leaves and silique walls, indicating that both plasma membrane-localized transporters are essential for long-distance transport of glucosinolates. We propose that GTR1 and GTR2 control the loading of glucosinolates from the apoplasm into the phloem. Identification of the glucosinolate transporters has agricultural potential as a means to control allocation of defence compounds in a tissue-specific manner.}, author = {Nour-Eldin, H. H. and Andersen, T. G. and Burow, M. and Madsen, S. R. and Jorgensen, M. E. and Olsen, C. E. and Dreyer, I. and Hedrich, R. and Geiger, D. and Halkier, B. A.}, journal = {Nature}, keywords = {arabidopsis-thaliana}, note = {992fs Times Cited:351 Cited References Count:30}, number = 7412, pages = {531-534}, title = {NRT/PTR transporters are essential for translocation of glucosinolate defence compounds to seeds}, type = {Journal Article}, volume = 488, year = 2012 }

  %0 Journal Article %1 RN1099 %A Nour-Eldin, H. H. %A Andersen, T. G. %A Burow, M. %A Madsen, S. R. %A Jorgensen, M. E. %A Olsen, C. E. %A Dreyer, I. %A Hedrich, R. %A Geiger, D. %A Halkier, B. A. %D 2012 %J Nature %N 7412 %P 531-534 %R 10.1038/nature11285 %T NRT/PTR transporters are essential for translocation of glucosinolate defence compounds to seeds %U /brokenurl#<Go to ISI>://WOS:000307761600041 %V 488 %X In plants, transport processes are important for the reallocation of defence compounds to protect tissues of high value(1), as demonstrated in the plant model Arabidopsis, in which the major defence compounds, glucosinolates(2), are translocated to seeds on maturation(3). The molecular basis for long-distance transport of glucosinolates and other defence compounds, however, remains unknown. Here we identify and characterize two members of the nitrate/peptide transporter family, GTR1 and GTR2, as high-affinity, proton-dependent glucosinolate-specific transporters. The gtr1 gtr2 double mutant did not accumulate glucosinolates in seeds and had more than tenfold over-accumulation in source tissues such as leaves and silique walls, indicating that both plasma membrane-localized transporters are essential for long-distance transport of glucosinolates. We propose that GTR1 and GTR2 control the loading of glucosinolates from the apoplasm into the phloem. Identification of the glucosinolate transporters has agricultural potential as a means to control allocation of defence compounds in a tissue-specific manner.

• A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap. Escalante-Pérez, M.; Krol, E.; Stange, A.; Geiger, D.; Al-Rasheid, K. A. S.; Hause, B.; Neher, E.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 108(37), pp. 15492–15497. 2011.
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  Venus flytrap's leaves can catch an insect in a fraction of a second. Since the time of Charles Darwin, scientists have struggled to understand the sensory biology and biomechanics of this plant, Dionaea muscipula. Here we show that insect-capture of Dionaea traps is modulated by the phytohormone abscisic acid (ABA) and jasmonates. Water-stressed Dionaea, as well as those exposed to the drought-stress hormone ABA, are less sensitive to mechanical stimulation. In contrast, application of 12-oxo-phytodienoic acid (OPDA), a precursor of the phytohormone jasmonic acid (JA), the methyl ester of JA (Me-JA), and coronatine (COR), the molecular mimic of the isoleucine conjugate of JA (JA-Ile), triggers secretion of digestive enzymes without any preceding mechanical stimulus. Such secretion is accompanied by slow trap closure. Under physiological conditions, insect-capture is associated with Ca(2+) signaling and a rise in OPDA, Apparently, jasmonates bypass hapto-electric processes associated with trap closure. However, ABA does not affect OPDA-dependent gland activity. Therefore, signals for trap movement and secretion seem to involve separate pathways. Jasmonates are systemically active because application to a single trap induces secretion and slow closure not only in the given trap but also in all others. Furthermore, formerly touch-insensitive trap sectors are converted into mechanosensitive ones. These findings demonstrate that prey-catching Dionaea combines plant-specific signaling pathways, involving OPDA and ABA with a rapidly acting trigger, which uses ion channels, action potentials, and Ca(2+) signals.

  @article{RN1110, abstract = {Venus flytrap's leaves can catch an insect in a fraction of a second. Since the time of Charles Darwin, scientists have struggled to understand the sensory biology and biomechanics of this plant, Dionaea muscipula. Here we show that insect-capture of Dionaea traps is modulated by the phytohormone abscisic acid (ABA) and jasmonates. Water-stressed Dionaea, as well as those exposed to the drought-stress hormone ABA, are less sensitive to mechanical stimulation. In contrast, application of 12-oxo-phytodienoic acid (OPDA), a precursor of the phytohormone jasmonic acid (JA), the methyl ester of JA (Me-JA), and coronatine (COR), the molecular mimic of the isoleucine conjugate of JA (JA-Ile), triggers secretion of digestive enzymes without any preceding mechanical stimulus. Such secretion is accompanied by slow trap closure. Under physiological conditions, insect-capture is associated with Ca(2+) signaling and a rise in OPDA, Apparently, jasmonates bypass hapto-electric processes associated with trap closure. However, ABA does not affect OPDA-dependent gland activity. Therefore, signals for trap movement and secretion seem to involve separate pathways. Jasmonates are systemically active because application to a single trap induces secretion and slow closure not only in the given trap but also in all others. Furthermore, formerly touch-insensitive trap sectors are converted into mechanosensitive ones. These findings demonstrate that prey-catching Dionaea combines plant-specific signaling pathways, involving OPDA and ABA with a rapidly acting trigger, which uses ion channels, action potentials, and Ca(2+) signals.}, author = {Escalante-Pérez, M. and Krol, E. and Stange, A. and Geiger, D. and Al-Rasheid, K. A. S. and Hause, B. and Neher, E. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {ellis}, note = {819df Times Cited:95 Cited References Count:51}, number = 37, pages = {15492-15497}, title = {A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap}, type = {Journal Article}, volume = 108, year = 2011 }

  %0 Journal Article %1 RN1110 %A Escalante-Pérez, M. %A Krol, E. %A Stange, A. %A Geiger, D. %A Al-Rasheid, K. A. S. %A Hause, B. %A Neher, E. %A Hedrich, R. %D 2011 %J Proceedings of the National Academy of Sciences of the United States of America %N 37 %P 15492-15497 %R 10.1073/pnas.1112535108 %T A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap %U /brokenurl#<Go to ISI>://WOS:000294804900095 %V 108 %X Venus flytrap's leaves can catch an insect in a fraction of a second. Since the time of Charles Darwin, scientists have struggled to understand the sensory biology and biomechanics of this plant, Dionaea muscipula. Here we show that insect-capture of Dionaea traps is modulated by the phytohormone abscisic acid (ABA) and jasmonates. Water-stressed Dionaea, as well as those exposed to the drought-stress hormone ABA, are less sensitive to mechanical stimulation. In contrast, application of 12-oxo-phytodienoic acid (OPDA), a precursor of the phytohormone jasmonic acid (JA), the methyl ester of JA (Me-JA), and coronatine (COR), the molecular mimic of the isoleucine conjugate of JA (JA-Ile), triggers secretion of digestive enzymes without any preceding mechanical stimulus. Such secretion is accompanied by slow trap closure. Under physiological conditions, insect-capture is associated with Ca(2+) signaling and a rise in OPDA, Apparently, jasmonates bypass hapto-electric processes associated with trap closure. However, ABA does not affect OPDA-dependent gland activity. Therefore, signals for trap movement and secretion seem to involve separate pathways. Jasmonates are systemically active because application to a single trap induces secretion and slow closure not only in the given trap but also in all others. Furthermore, formerly touch-insensitive trap sectors are converted into mechanosensitive ones. These findings demonstrate that prey-catching Dionaea combines plant-specific signaling pathways, involving OPDA and ABA with a rapidly acting trigger, which uses ion channels, action potentials, and Ca(2+) signals.
• Stomatal Closure by Fast Abscisic Acid Signaling Is Mediated by the Guard Cell Anion Channel SLAH3 and the Receptor RCAR1. Geiger, D.; Maierhofer, T.; AL-Rasheid, K. A. S.; Scherzer, S.; Mumm, P.; Liese, A.; Ache, P.; Wellmann, C.; Marten, I.; Grill, E.; Romeis, T.; Hedrich, R. In Science Signaling, 4(173). 2011.
  • [ Abstract ]
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  S-type anion channels are direct targets of abscisic acid (ABA) signaling and contribute to chloride and nitrate release from guard cells, which in turn initiates stomatal closure. SLAC1 was the first component of the guard cell S-type anion channel identified. However, we found that guard cells of Arabidopsis SLAC1 mutants exhibited nitrate conductance. SLAH3 (SLAC1 homolog 3) was also present in guard cells, and coexpression of SLAH3 with the calcium ion (Ca2+)-dependent kinase CPK21 in Xenopus oocytes mediated nitrate-induced anion currents. Nitrate, calcium, and phosphorylation regulated SLAH3 activity. CPK21-dependent SLAH3 phosphorylation and activation were blocked by ABI1, a PP2C-type protein phosphatase that is inhibited by ABA and inhibits the ABA signaling pathway in guard cells. We reconstituted the ABA-stimulated phosphorylation of the SLAH3 amino-terminal domain by CPK21 in vitro by including the ABA receptor-phosphatase complex RCAR1-ABI1 in the reactions. We propose that ABA perception by the complex consisting of ABA receptors of the RCAR/PYR/PYL family and ABI1 releases CPK21 from inhibition by ABI1, and then CPK21 is further activated by an increase in the cytosolic Ca2+ concentration, leading to its phosphorylation of SLAH3. Thus, the identification of SLAH3 as the nitrate-, calcium-, and ABA-sensitive guard cell anion channel provides insights into the relationship among stomatal response to drought, signaling by nitrate, and nitrate metabolism.

  @article{RN1109, abstract = {S-type anion channels are direct targets of abscisic acid (ABA) signaling and contribute to chloride and nitrate release from guard cells, which in turn initiates stomatal closure. SLAC1 was the first component of the guard cell S-type anion channel identified. However, we found that guard cells of Arabidopsis SLAC1 mutants exhibited nitrate conductance. SLAH3 (SLAC1 homolog 3) was also present in guard cells, and coexpression of SLAH3 with the calcium ion (Ca2+)-dependent kinase CPK21 in Xenopus oocytes mediated nitrate-induced anion currents. Nitrate, calcium, and phosphorylation regulated SLAH3 activity. CPK21-dependent SLAH3 phosphorylation and activation were blocked by ABI1, a PP2C-type protein phosphatase that is inhibited by ABA and inhibits the ABA signaling pathway in guard cells. We reconstituted the ABA-stimulated phosphorylation of the SLAH3 amino-terminal domain by CPK21 in vitro by including the ABA receptor-phosphatase complex RCAR1-ABI1 in the reactions. We propose that ABA perception by the complex consisting of ABA receptors of the RCAR/PYR/PYL family and ABI1 releases CPK21 from inhibition by ABI1, and then CPK21 is further activated by an increase in the cytosolic Ca2+ concentration, leading to its phosphorylation of SLAH3. Thus, the identification of SLAH3 as the nitrate-, calcium-, and ABA-sensitive guard cell anion channel provides insights into the relationship among stomatal response to drought, signaling by nitrate, and nitrate metabolism.}, author = {Geiger, D. and Maierhofer, T. and AL-Rasheid, K. A. S. and Scherzer, S. and Mumm, P. and Liese, A. and Ache, P. and Wellmann, C. and Marten, I. and Grill, E. and Romeis, T. and Hedrich, R.}, journal = {Science Signaling}, keywords = {calmodulin-like}, note = {764xc Times Cited:285 Cited References Count:61}, number = 173, title = {Stomatal Closure by Fast Abscisic Acid Signaling Is Mediated by the Guard Cell Anion Channel SLAH3 and the Receptor RCAR1}, type = {Journal Article}, volume = 4, year = 2011 }

  %0 Journal Article %1 RN1109 %A Geiger, D. %A Maierhofer, T. %A AL-Rasheid, K. A. S. %A Scherzer, S. %A Mumm, P. %A Liese, A. %A Ache, P. %A Wellmann, C. %A Marten, I. %A Grill, E. %A Romeis, T. %A Hedrich, R. %D 2011 %J Science Signaling %N 173 %R ARTN ra32 10.1126/scisignal.2001346 %T Stomatal Closure by Fast Abscisic Acid Signaling Is Mediated by the Guard Cell Anion Channel SLAH3 and the Receptor RCAR1 %U /brokenurl#<Go to ISI>://WOS:000290666900002 %V 4 %X S-type anion channels are direct targets of abscisic acid (ABA) signaling and contribute to chloride and nitrate release from guard cells, which in turn initiates stomatal closure. SLAC1 was the first component of the guard cell S-type anion channel identified. However, we found that guard cells of Arabidopsis SLAC1 mutants exhibited nitrate conductance. SLAH3 (SLAC1 homolog 3) was also present in guard cells, and coexpression of SLAH3 with the calcium ion (Ca2+)-dependent kinase CPK21 in Xenopus oocytes mediated nitrate-induced anion currents. Nitrate, calcium, and phosphorylation regulated SLAH3 activity. CPK21-dependent SLAH3 phosphorylation and activation were blocked by ABI1, a PP2C-type protein phosphatase that is inhibited by ABA and inhibits the ABA signaling pathway in guard cells. We reconstituted the ABA-stimulated phosphorylation of the SLAH3 amino-terminal domain by CPK21 in vitro by including the ABA receptor-phosphatase complex RCAR1-ABI1 in the reactions. We propose that ABA perception by the complex consisting of ABA receptors of the RCAR/PYR/PYL family and ABI1 releases CPK21 from inhibition by ABI1, and then CPK21 is further activated by an increase in the cytosolic Ca2+ concentration, leading to its phosphorylation of SLAH3. Thus, the identification of SLAH3 as the nitrate-, calcium-, and ABA-sensitive guard cell anion channel provides insights into the relationship among stomatal response to drought, signaling by nitrate, and nitrate metabolism.
• A member of the mitogen-activated protein 3-kinase family is involved in the regulation of plant vacuolar glucose uptake. Wingenter, K.; Trentmann, O.; Winschuh, I.; Hörmiller, I. I.; Heyer, A. G.; Reinders, J.; Schulz, A.; Geiger, D.; Hedrich, R.; Neuhaus, H. E. In Plant Journal, 68(5), pp. 890–900. 2011.
  • [ Abstract ]
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  Vacuolar solute accumulation is an important process during plant development, growth and stress responses. Although several vacuolar carriers have been identified recently, knowledge regarding the regulation of transport is still limited. Solute accumulation may be controlled by various factors, such as alterations in carrier abundance or activity. Phosphorylation via kinases is a well-known principle for activation or deactivation of proteins. Several phosphorylated proteins have been identified in the tonoplast proteome; however, kinases that catalyse the phosphorylation of tonoplast proteins are currently unknown. The tonoplast monosaccaride transporter from Arabidopsis (AtTMT1) and its homologue from barley have multiple phosphorylation sites in their extremely large loops. Here we demonstrate that the loop of AtTMT1 interacts with a mitogen-activated triple kinase-like protein kinase (VIK), that an aspartate-rich loop domain is required for effective interaction, and that the presence of VIK stimulates glucose import into isolated vacuoles. Furthermore, the phenotype of VIK loss-of-function plants strikingly resembles that of plants lacking AtTMT1/2. These data suggest that VIK-mediated phosphorylation of the AtTMT1 loop enhances carrier activity and consequently vacuolar sugar accumulation. As many phosphorylated proteins have been identified in the tonoplast, differential phosphorylation may be a general mechanism regulating vacuolar solute import.

  @article{RN1106, abstract = {Vacuolar solute accumulation is an important process during plant development, growth and stress responses. Although several vacuolar carriers have been identified recently, knowledge regarding the regulation of transport is still limited. Solute accumulation may be controlled by various factors, such as alterations in carrier abundance or activity. Phosphorylation via kinases is a well-known principle for activation or deactivation of proteins. Several phosphorylated proteins have been identified in the tonoplast proteome; however, kinases that catalyse the phosphorylation of tonoplast proteins are currently unknown. The tonoplast monosaccaride transporter from Arabidopsis (AtTMT1) and its homologue from barley have multiple phosphorylation sites in their extremely large loops. Here we demonstrate that the loop of AtTMT1 interacts with a mitogen-activated triple kinase-like protein kinase (VIK), that an aspartate-rich loop domain is required for effective interaction, and that the presence of VIK stimulates glucose import into isolated vacuoles. Furthermore, the phenotype of VIK loss-of-function plants strikingly resembles that of plants lacking AtTMT1/2. These data suggest that VIK-mediated phosphorylation of the AtTMT1 loop enhances carrier activity and consequently vacuolar sugar accumulation. As many phosphorylated proteins have been identified in the tonoplast, differential phosphorylation may be a general mechanism regulating vacuolar solute import.}, author = {Wingenter, K. and Trentmann, O. and Winschuh, I. and Hörmiller, I. I. and Heyer, A. G. and Reinders, J. and Schulz, A. and Geiger, D. and Hedrich, R. and Neuhaus, H. E.}, journal = {Plant Journal}, keywords = {myOwn}, note = {862lx Times Cited:51 Cited References Count:33}, number = 5, pages = {890-900}, title = {A member of the mitogen-activated protein 3-kinase family is involved in the regulation of plant vacuolar glucose uptake}, type = {Journal Article}, volume = 68, year = 2011 }

  %0 Journal Article %1 RN1106 %A Wingenter, K. %A Trentmann, O. %A Winschuh, I. %A Hörmiller, I. I. %A Heyer, A. G. %A Reinders, J. %A Schulz, A. %A Geiger, D. %A Hedrich, R. %A Neuhaus, H. E. %D 2011 %J Plant Journal %N 5 %P 890-900 %R 10.1111/j.1365-313X.2011.04739.x %T A member of the mitogen-activated protein 3-kinase family is involved in the regulation of plant vacuolar glucose uptake %U /brokenurl#<Go to ISI>://WOS:000298093800011 %V 68 %X Vacuolar solute accumulation is an important process during plant development, growth and stress responses. Although several vacuolar carriers have been identified recently, knowledge regarding the regulation of transport is still limited. Solute accumulation may be controlled by various factors, such as alterations in carrier abundance or activity. Phosphorylation via kinases is a well-known principle for activation or deactivation of proteins. Several phosphorylated proteins have been identified in the tonoplast proteome; however, kinases that catalyse the phosphorylation of tonoplast proteins are currently unknown. The tonoplast monosaccaride transporter from Arabidopsis (AtTMT1) and its homologue from barley have multiple phosphorylation sites in their extremely large loops. Here we demonstrate that the loop of AtTMT1 interacts with a mitogen-activated triple kinase-like protein kinase (VIK), that an aspartate-rich loop domain is required for effective interaction, and that the presence of VIK stimulates glucose import into isolated vacuoles. Furthermore, the phenotype of VIK loss-of-function plants strikingly resembles that of plants lacking AtTMT1/2. These data suggest that VIK-mediated phosphorylation of the AtTMT1 loop enhances carrier activity and consequently vacuolar sugar accumulation. As many phosphorylated proteins have been identified in the tonoplast, differential phosphorylation may be a general mechanism regulating vacuolar solute import.
• A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels. Dadacz-Narloch, B.; Beyhl, D.; Larisch, C.; López-Sanjurjo, E. J.; Reski, R.; Kuchitsu, K.; Müller, T. D.; Becker, D.; Schönknecht, G.; Hedrich, R. In Plant Cell, 23(7), pp. 2696–2707. 2011.
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  Cytosolic calcium homeostasis is pivotal for intracellular signaling and requires sensing of calcium concentrations in the cytosol and accessible stores. Numerous Ca2+ binding sites have been characterized in cytosolic proteins. However, little is known about Ca2+ binding inside organelles, like the vacuole. The slow vacuolar (SV) channel, encoded by Arabidopsis thaliana TPC1, is regulated by luminal Ca2+. However, the D454/fou2 mutation in TPC1 eliminates vacuolar calcium sensitivity and increases store calcium content. In a search for the luminal calcium binding site, structure modeling indicated a possible coordination site formed by residues Glu-450, Asp-454, Glu-456, and Glu-457 on the luminal side of TPC1. Each Glu residue was replaced by Gln, the modified genes were transiently expressed in loss-of-TPC1-function protoplasts, and SV channel responses to luminal calcium were recorded by patch clamp. SV channels lacking any of the four negatively charged residues appeared altered in calcium sensitivity of channel gating. Our results indicate that Glu-450 and Asp-454 are directly involved in Ca2+ binding, whereas Glu-456 and Glu-457 are probably involved in connecting the luminal Ca2+ binding site to the channel gate. This novel vacuolar calcium binding site represents a potential tool to address calcium storage in plants.

  @article{RN1111, abstract = {Cytosolic calcium homeostasis is pivotal for intracellular signaling and requires sensing of calcium concentrations in the cytosol and accessible stores. Numerous Ca2+ binding sites have been characterized in cytosolic proteins. However, little is known about Ca2+ binding inside organelles, like the vacuole. The slow vacuolar (SV) channel, encoded by Arabidopsis thaliana TPC1, is regulated by luminal Ca2+. However, the D454/fou2 mutation in TPC1 eliminates vacuolar calcium sensitivity and increases store calcium content. In a search for the luminal calcium binding site, structure modeling indicated a possible coordination site formed by residues Glu-450, Asp-454, Glu-456, and Glu-457 on the luminal side of TPC1. Each Glu residue was replaced by Gln, the modified genes were transiently expressed in loss-of-TPC1-function protoplasts, and SV channel responses to luminal calcium were recorded by patch clamp. SV channels lacking any of the four negatively charged residues appeared altered in calcium sensitivity of channel gating. Our results indicate that Glu-450 and Asp-454 are directly involved in Ca2+ binding, whereas Glu-456 and Glu-457 are probably involved in connecting the luminal Ca2+ binding site to the channel gate. This novel vacuolar calcium binding site represents a potential tool to address calcium storage in plants.}, author = {Dadacz-Narloch, B. and Beyhl, D. and Larisch, C. and López-Sanjurjo, E. J. and Reski, R. and Kuchitsu, K. and Müller, T. D. and Becker, D. and Schönknecht, G. and Hedrich, R.}, journal = {Plant Cell}, keywords = {of-function}, note = {810xu Times Cited:74 Cited References Count:47}, number = 7, pages = {2696-2707}, title = {A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels}, type = {Journal Article}, volume = 23, year = 2011 }

  %0 Journal Article %1 RN1111 %A Dadacz-Narloch, B. %A Beyhl, D. %A Larisch, C. %A López-Sanjurjo, E. J. %A Reski, R. %A Kuchitsu, K. %A Müller, T. D. %A Becker, D. %A Schönknecht, G. %A Hedrich, R. %D 2011 %J Plant Cell %N 7 %P 2696-2707 %R 10.1105/tpc.111.086751 %T A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels %U /brokenurl#<Go to ISI>://WOS:000294164300022 %V 23 %X Cytosolic calcium homeostasis is pivotal for intracellular signaling and requires sensing of calcium concentrations in the cytosol and accessible stores. Numerous Ca2+ binding sites have been characterized in cytosolic proteins. However, little is known about Ca2+ binding inside organelles, like the vacuole. The slow vacuolar (SV) channel, encoded by Arabidopsis thaliana TPC1, is regulated by luminal Ca2+. However, the D454/fou2 mutation in TPC1 eliminates vacuolar calcium sensitivity and increases store calcium content. In a search for the luminal calcium binding site, structure modeling indicated a possible coordination site formed by residues Glu-450, Asp-454, Glu-456, and Glu-457 on the luminal side of TPC1. Each Glu residue was replaced by Gln, the modified genes were transiently expressed in loss-of-TPC1-function protoplasts, and SV channel responses to luminal calcium were recorded by patch clamp. SV channels lacking any of the four negatively charged residues appeared altered in calcium sensitivity of channel gating. Our results indicate that Glu-450 and Asp-454 are directly involved in Ca2+ binding, whereas Glu-456 and Glu-457 are probably involved in connecting the luminal Ca2+ binding site to the channel gate. This novel vacuolar calcium binding site represents a potential tool to address calcium storage in plants.
• Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2. Schulz, A.; Beyhl, D.; Marten, I.; Wormit, A.; Neuhaus, E.; Poschet, G.; Büttner, M.; Schneider, S.; Sauer, N.; Hedrich, R. In Plant Journal, 68(1), pp. 129–136. 2011.
  • [ Abstract ]
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  The vacuolar membrane is involved in solute uptake into and release from the vacuole, which is the largest plant organelle. In addition to inorganic ions and metabolites, large quantities of protons and sugars are shuttled across this membrane. Current models suggest that the proton gradient across the membrane drives the accumulation and/or release of sugars. Recent studies have associated AtSUC4 with the vacuolar membrane. Some members of the SUC family are plasma membrane proton/sucrose symporters. In addition, the sugar transporters TMT1 and TMT2, which are localized to the vacuolar membrane, have been suggested to function in proton-driven glucose antiport. Here we used the patch-clamp technique to monitor carrier-mediated sucrose transport by AtSUC4 and AtTMTs in intact Arabidopsis thaliana mesophyll vacuoles. In the whole-vacuole configuration with wild-type material, cytosolic sucrose-induced proton currents were associated with a proton/sucrose antiport mechanism. To identify the related transporter on one hand, and to enable the recording of symporter-mediated currents on the other hand, we electrophysiologically characterized vacuolar proteins recognized by Arabidopsis mutants of partially impaired sugar compartmentation. To our surprise, the intrinsic sucrose/proton antiporter activity was greatly reduced when vacuoles were isolated from plants lacking the monosaccharide transporter AtTMT1/TMT2. Transient expression of AtSUC4 in this mutant background resulted in proton/sucrose symport activity. From these studies, we conclude that, in the natural environment within the Arabidopsis cell, AtSUC4 most likely catalyses proton-coupled sucrose export from the vacuole. However, TMT1/2 probably represents a proton-coupled antiporter capable of high-capacity loading of glucose and sucrose into the vacuole.

  @article{RN1107, abstract = {The vacuolar membrane is involved in solute uptake into and release from the vacuole, which is the largest plant organelle. In addition to inorganic ions and metabolites, large quantities of protons and sugars are shuttled across this membrane. Current models suggest that the proton gradient across the membrane drives the accumulation and/or release of sugars. Recent studies have associated AtSUC4 with the vacuolar membrane. Some members of the SUC family are plasma membrane proton/sucrose symporters. In addition, the sugar transporters TMT1 and TMT2, which are localized to the vacuolar membrane, have been suggested to function in proton-driven glucose antiport. Here we used the patch-clamp technique to monitor carrier-mediated sucrose transport by AtSUC4 and AtTMTs in intact Arabidopsis thaliana mesophyll vacuoles. In the whole-vacuole configuration with wild-type material, cytosolic sucrose-induced proton currents were associated with a proton/sucrose antiport mechanism. To identify the related transporter on one hand, and to enable the recording of symporter-mediated currents on the other hand, we electrophysiologically characterized vacuolar proteins recognized by Arabidopsis mutants of partially impaired sugar compartmentation. To our surprise, the intrinsic sucrose/proton antiporter activity was greatly reduced when vacuoles were isolated from plants lacking the monosaccharide transporter AtTMT1/TMT2. Transient expression of AtSUC4 in this mutant background resulted in proton/sucrose symport activity. From these studies, we conclude that, in the natural environment within the Arabidopsis cell, AtSUC4 most likely catalyses proton-coupled sucrose export from the vacuole. However, TMT1/2 probably represents a proton-coupled antiporter capable of high-capacity loading of glucose and sucrose into the vacuole.}, author = {Schulz, A. and Beyhl, D. and Marten, I. and Wormit, A. and Neuhaus, E. and Poschet, G. and Büttner, M. and Schneider, S. and Sauer, N. and Hedrich, R.}, journal = {Plant Journal}, keywords = {antiport}, note = {827ae Times Cited:182 Cited References Count:36}, number = 1, pages = {129-136}, title = {Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2}, type = {Journal Article}, volume = 68, year = 2011 }

  %0 Journal Article %1 RN1107 %A Schulz, A. %A Beyhl, D. %A Marten, I. %A Wormit, A. %A Neuhaus, E. %A Poschet, G. %A Büttner, M. %A Schneider, S. %A Sauer, N. %A Hedrich, R. %D 2011 %J Plant Journal %N 1 %P 129-136 %R 10.1111/j.1365-313X.2011.04672.x %T Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2 %U /brokenurl#<Go to ISI>://WOS:000295395900011 %V 68 %X The vacuolar membrane is involved in solute uptake into and release from the vacuole, which is the largest plant organelle. In addition to inorganic ions and metabolites, large quantities of protons and sugars are shuttled across this membrane. Current models suggest that the proton gradient across the membrane drives the accumulation and/or release of sugars. Recent studies have associated AtSUC4 with the vacuolar membrane. Some members of the SUC family are plasma membrane proton/sucrose symporters. In addition, the sugar transporters TMT1 and TMT2, which are localized to the vacuolar membrane, have been suggested to function in proton-driven glucose antiport. Here we used the patch-clamp technique to monitor carrier-mediated sucrose transport by AtSUC4 and AtTMTs in intact Arabidopsis thaliana mesophyll vacuoles. In the whole-vacuole configuration with wild-type material, cytosolic sucrose-induced proton currents were associated with a proton/sucrose antiport mechanism. To identify the related transporter on one hand, and to enable the recording of symporter-mediated currents on the other hand, we electrophysiologically characterized vacuolar proteins recognized by Arabidopsis mutants of partially impaired sugar compartmentation. To our surprise, the intrinsic sucrose/proton antiporter activity was greatly reduced when vacuoles were isolated from plants lacking the monosaccharide transporter AtTMT1/TMT2. Transient expression of AtSUC4 in this mutant background resulted in proton/sucrose symport activity. From these studies, we conclude that, in the natural environment within the Arabidopsis cell, AtSUC4 most likely catalyses proton-coupled sucrose export from the vacuole. However, TMT1/2 probably represents a proton-coupled antiporter capable of high-capacity loading of glucose and sucrose into the vacuole.
• TPC1-SV Channels Gain Shape. Hedrich, R.; Marten, I. In Molecular Plant, 4(3), pp. 428–441. 2011.
  • [ Abstract ]
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  The most prominent ion channel localized in plant vacuoles is the slow activating SV type. Slow vacuolar (SV) channels were discovered by patch clamp studies as early as 1986. In the following two decades, numerous studies revealed that these calcium- and voltage-activated, nonselective cation channels are expressed in the vacuoles of all plants and every plant tissue. The voltage-dependent properties of the SV channel are susceptible to modulation by calcium, pH, redox state, as well as regulatory proteins. In Arabidopsis, the SV channel is encoded by the AtTPC1 gene, and even though its gene product represents the by far largest conductance of the vacuolar membrane, tpc1-loss-of-function mutants appeared not to be impaired in major physiological functions such as growth, development, and reproduction. In contrast, the fou2 gain-of-function point mutation D454N within TPC1 leads to a pronounced growth phenotype and increased synthesis of the stress hormone jasmonate. Since the TPC1 gene is present in all land plants, it likely encodes a very general function. In this review, we will discuss major SV channel properties and their impact on plant cell physiology.

  @article{RN1108, abstract = {The most prominent ion channel localized in plant vacuoles is the slow activating SV type. Slow vacuolar (SV) channels were discovered by patch clamp studies as early as 1986. In the following two decades, numerous studies revealed that these calcium- and voltage-activated, nonselective cation channels are expressed in the vacuoles of all plants and every plant tissue. The voltage-dependent properties of the SV channel are susceptible to modulation by calcium, pH, redox state, as well as regulatory proteins. In Arabidopsis, the SV channel is encoded by the AtTPC1 gene, and even though its gene product represents the by far largest conductance of the vacuolar membrane, tpc1-loss-of-function mutants appeared not to be impaired in major physiological functions such as growth, development, and reproduction. In contrast, the fou2 gain-of-function point mutation D454N within TPC1 leads to a pronounced growth phenotype and increased synthesis of the stress hormone jasmonate. Since the TPC1 gene is present in all land plants, it likely encodes a very general function. In this review, we will discuss major SV channel properties and their impact on plant cell physiology.}, author = {Hedrich, R. and Marten, I.}, journal = {Molecular Plant}, keywords = {channel}, note = {766vc Times Cited:119 Cited References Count:127}, number = 3, pages = {428-441}, title = {TPC1-SV Channels Gain Shape}, type = {Journal Article}, volume = 4, year = 2011 }

  %0 Journal Article %1 RN1108 %A Hedrich, R. %A Marten, I. %D 2011 %J Molecular Plant %N 3 %P 428-441 %R 10.1093/mp/ssr017 %T TPC1-SV Channels Gain Shape %U /brokenurl#<Go to ISI>://WOS:000290813600005 %V 4 %X The most prominent ion channel localized in plant vacuoles is the slow activating SV type. Slow vacuolar (SV) channels were discovered by patch clamp studies as early as 1986. In the following two decades, numerous studies revealed that these calcium- and voltage-activated, nonselective cation channels are expressed in the vacuoles of all plants and every plant tissue. The voltage-dependent properties of the SV channel are susceptible to modulation by calcium, pH, redox state, as well as regulatory proteins. In Arabidopsis, the SV channel is encoded by the AtTPC1 gene, and even though its gene product represents the by far largest conductance of the vacuolar membrane, tpc1-loss-of-function mutants appeared not to be impaired in major physiological functions such as growth, development, and reproduction. In contrast, the fou2 gain-of-function point mutation D454N within TPC1 leads to a pronounced growth phenotype and increased synthesis of the stress hormone jasmonate. Since the TPC1 gene is present in all land plants, it likely encodes a very general function. In this review, we will discuss major SV channel properties and their impact on plant cell physiology.

• Making sense out of Ca2+signals: their role in regulating stomatal movements. Roelfsema, M. R. G.; Hedrich, R. In Plant Cell and Environment, 33(3), pp. 305–321. 2010.
  • [ Abstract ]
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  Plant cells maintain high Ca2+ concentration gradients between the cytosol and the extracellular matrix, as well as intracellular compartments. During evolution, the regulatory mechanisms, maintaining low cytosolic free Ca2+ concentrations, most likely provided the backbone for the development of Ca2+-dependent signalling pathways. In this review, the current understanding of molecular mechanisms involved in Ca2+ homeostasis of plants cells is evaluated. The question is addressed to which extent the mechanisms, controlling the cytosolic Ca2+ concentration, are linked to Ca2+-based signalling. A large number of environmental stimuli can evoke Ca2+ signals, but the Ca2+-induced responses are likely to differ depending on the stimulus applied. Two mechanisms are put forward to explain signal specificity of Ca2+-dependent responses. A signal may evoke a specific Ca2+ signature that is recognized by downstream signalling components. Alternatively, Ca2+ signals are accompanied by Ca2+-independent signalling events that determine the specificity of the response. The existence of such parallel-acting pathways explains why guard cell responses to abscisic acid (ABA) can occur in the absence, as well as in the presence, of Ca2+ signals. Future research may shed new light on the relation between parallel acting Ca2+-dependent and -independent events, and may provide insights in their evolutionary origin.

  @article{RN1116, abstract = {Plant cells maintain high Ca2+ concentration gradients between the cytosol and the extracellular matrix, as well as intracellular compartments. During evolution, the regulatory mechanisms, maintaining low cytosolic free Ca2+ concentrations, most likely provided the backbone for the development of Ca2+-dependent signalling pathways. In this review, the current understanding of molecular mechanisms involved in Ca2+ homeostasis of plants cells is evaluated. The question is addressed to which extent the mechanisms, controlling the cytosolic Ca2+ concentration, are linked to Ca2+-based signalling. A large number of environmental stimuli can evoke Ca2+ signals, but the Ca2+-induced responses are likely to differ depending on the stimulus applied. Two mechanisms are put forward to explain signal specificity of Ca2+-dependent responses. A signal may evoke a specific Ca2+ signature that is recognized by downstream signalling components. Alternatively, Ca2+ signals are accompanied by Ca2+-independent signalling events that determine the specificity of the response. The existence of such parallel-acting pathways explains why guard cell responses to abscisic acid (ABA) can occur in the absence, as well as in the presence, of Ca2+ signals. Future research may shed new light on the relation between parallel acting Ca2+-dependent and -independent events, and may provide insights in their evolutionary origin.}, author = {Roelfsema, M. R. G. and Hedrich, R.}, journal = {Plant Cell and Environment}, keywords = {abscisic}, note = {554cg Times Cited:55 Cited References Count:178}, number = 3, pages = {305-321}, title = {Making sense out of Ca2+signals: their role in regulating stomatal movements}, type = {Journal Article}, volume = 33, year = 2010 }

  %0 Journal Article %1 RN1116 %A Roelfsema, M. R. G. %A Hedrich, R. %D 2010 %J Plant Cell and Environment %N 3 %P 305-321 %R 10.1111/j.1365-3040.2009.02075.x %T Making sense out of Ca2+signals: their role in regulating stomatal movements %U /brokenurl#<Go to ISI>://WOS:000274412500001 %V 33 %X Plant cells maintain high Ca2+ concentration gradients between the cytosol and the extracellular matrix, as well as intracellular compartments. During evolution, the regulatory mechanisms, maintaining low cytosolic free Ca2+ concentrations, most likely provided the backbone for the development of Ca2+-dependent signalling pathways. In this review, the current understanding of molecular mechanisms involved in Ca2+ homeostasis of plants cells is evaluated. The question is addressed to which extent the mechanisms, controlling the cytosolic Ca2+ concentration, are linked to Ca2+-based signalling. A large number of environmental stimuli can evoke Ca2+ signals, but the Ca2+-induced responses are likely to differ depending on the stimulus applied. Two mechanisms are put forward to explain signal specificity of Ca2+-dependent responses. A signal may evoke a specific Ca2+ signature that is recognized by downstream signalling components. Alternatively, Ca2+ signals are accompanied by Ca2+-independent signalling events that determine the specificity of the response. The existence of such parallel-acting pathways explains why guard cell responses to abscisic acid (ABA) can occur in the absence, as well as in the presence, of Ca2+ signals. Future research may shed new light on the relation between parallel acting Ca2+-dependent and -independent events, and may provide insights in their evolutionary origin.
• Stomatal action directly feeds back on leaf turgor: new insights into the regulation of the plant water status from non-invasive pressure probe measurements. Ache, P.; Bauer, H.; Kollist, H.; Al-Rasheid, K. A. S.; Lautner, S.; Hartung, W.; Hedrich, R. In Plant Journal, 62(6), pp. 1072–1082. 2010.
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  P>Uptake of CO2 by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard-cell anion release channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard-cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non-invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long-term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild-type plants responded to CO2, light, humidity, ozone and abscisic acid (ABA) in a guard cell-specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild-type plants, leaves from well-watered ost1 plants exposed to a dry atmosphere wilted after light-induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root-shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.

  @article{RN1129, abstract = {P>Uptake of CO2 by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard-cell anion release channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard-cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non-invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long-term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild-type plants responded to CO2, light, humidity, ozone and abscisic acid (ABA) in a guard cell-specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild-type plants, leaves from well-watered ost1 plants exposed to a dry atmosphere wilted after light-induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root-shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.}, author = {Ache, P. and Bauer, H. and Kollist, H. and Al-Rasheid, K. A. S. and Lautner, S. and Hartung, W. and Hedrich, R.}, journal = {Plant Journal}, keywords = {pressure}, note = {608zo Times Cited:78 Cited References Count:56}, number = 6, pages = {1072-1082}, title = {Stomatal action directly feeds back on leaf turgor: new insights into the regulation of the plant water status from non-invasive pressure probe measurements}, type = {Journal Article}, volume = 62, year = 2010 }

  %0 Journal Article %1 RN1129 %A Ache, P. %A Bauer, H. %A Kollist, H. %A Al-Rasheid, K. A. S. %A Lautner, S. %A Hartung, W. %A Hedrich, R. %D 2010 %J Plant Journal %N 6 %P 1072-1082 %R 10.1111/j.1365-313X.2010.04213.x %T Stomatal action directly feeds back on leaf turgor: new insights into the regulation of the plant water status from non-invasive pressure probe measurements %U /brokenurl#<Go to ISI>://WOS:000278624700013 %V 62 %X P>Uptake of CO2 by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard-cell anion release channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard-cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non-invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long-term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild-type plants responded to CO2, light, humidity, ozone and abscisic acid (ABA) in a guard cell-specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild-type plants, leaves from well-watered ost1 plants exposed to a dry atmosphere wilted after light-induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root-shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.
• POLYOL/MONOSACCHARIDE TRANSPORTERS 1 and 2: fructose and xylitol/H symporters in pollen and young xylem cells. Klepek, Y. S.; Volke, M.; Konrad, K. R.; Wippel, K.; Hoth, S.; Hedrich, R.; Sauer, N. In Journal of Experimental Botany, 61(2), pp. 537–550. 2010.
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  The genome of Arabidopsis thaliana contains six genes, AtPMT1 to AtPMT6 (Arabidopsis thaliana POLYOL/MONOSACCHARIDE TRANSPORTER 1-6), which form a distinct subfamily within the large family of more than 50 monosaccharide transporter-like (MST-like) genes. So far, only AtPMT5 [formerly named AtPLT5 (At3g18830)] has been characterized and was shown to be a plasma membrane-localized H+-symporter with broad substrate specificity. The characterization of AtPMT1 (At2g16120) and AtPMT2 (At2g16130), two other, almost identical, members of this transporter subfamily, are presented here. Expression of the AtPMT1 and AtPMT2 cDNAs in baker's yeast (Saccharomyces cerevisiae) revealed that these proteins catalyse the energy-dependent, high-capacity transport of fructose and xylitol, and the transport of several other compounds with lower rates. Expression of their cRNAs in Xenopus laevis oocytes showed that both proteins are voltage-dependent and catalyse the symport of their substrates with protons. Fusions of AtPMT1 or AtPMT2 with the green fluorescent protein (GFP) localized to Arabidopsis plasma membranes. Analyses of reporter genes performed with AtPMT1 or AtPMT2 promoter sequences showed expression in mature (AtPMT2) or germinating (AtPMT1) pollen grains, as well as in growing pollen tubes, hydathodes, and young xylem cells (both genes). The expression was confirmed with an anti-AtPMT1/AtPMT2 antiserum (alpha AtPMT1/2) raised against peptides conserved in AtPMT1 and AtPMT2. The physiological roles of the proteins are discussed and related to plant cell wall modifications.

  @article{RN1124, abstract = {The genome of Arabidopsis thaliana contains six genes, AtPMT1 to AtPMT6 (Arabidopsis thaliana POLYOL/MONOSACCHARIDE TRANSPORTER 1-6), which form a distinct subfamily within the large family of more than 50 monosaccharide transporter-like (MST-like) genes. So far, only AtPMT5 [formerly named AtPLT5 (At3g18830)] has been characterized and was shown to be a plasma membrane-localized H+-symporter with broad substrate specificity. The characterization of AtPMT1 (At2g16120) and AtPMT2 (At2g16130), two other, almost identical, members of this transporter subfamily, are presented here. Expression of the AtPMT1 and AtPMT2 cDNAs in baker's yeast (Saccharomyces cerevisiae) revealed that these proteins catalyse the energy-dependent, high-capacity transport of fructose and xylitol, and the transport of several other compounds with lower rates. Expression of their cRNAs in Xenopus laevis oocytes showed that both proteins are voltage-dependent and catalyse the symport of their substrates with protons. Fusions of AtPMT1 or AtPMT2 with the green fluorescent protein (GFP) localized to Arabidopsis plasma membranes. Analyses of reporter genes performed with AtPMT1 or AtPMT2 promoter sequences showed expression in mature (AtPMT2) or germinating (AtPMT1) pollen grains, as well as in growing pollen tubes, hydathodes, and young xylem cells (both genes). The expression was confirmed with an anti-AtPMT1/AtPMT2 antiserum (alpha AtPMT1/2) raised against peptides conserved in AtPMT1 and AtPMT2. The physiological roles of the proteins are discussed and related to plant cell wall modifications.}, author = {Klepek, Y. S. and Volke, M. and Konrad, K. R. and Wippel, K. and Hoth, S. and Hedrich, R. and Sauer, N.}, journal = {Journal of Experimental Botany}, keywords = {atplt}, note = {542nq Times Cited:47 Cited References Count:46}, number = 2, pages = {537-550}, title = {POLYOL/MONOSACCHARIDE TRANSPORTERS 1 and 2: fructose and xylitol/H symporters in pollen and young xylem cells}, type = {Journal Article}, volume = 61, year = 2010 }

  %0 Journal Article %1 RN1124 %A Klepek, Y. S. %A Volke, M. %A Konrad, K. R. %A Wippel, K. %A Hoth, S. %A Hedrich, R. %A Sauer, N. %D 2010 %J Journal of Experimental Botany %N 2 %P 537-550 %R 10.1093/jxb/erp322 %T POLYOL/MONOSACCHARIDE TRANSPORTERS 1 and 2: fructose and xylitol/H symporters in pollen and young xylem cells %U /brokenurl#<Go to ISI>://WOS:000273501400020 %V 61 %X The genome of Arabidopsis thaliana contains six genes, AtPMT1 to AtPMT6 (Arabidopsis thaliana POLYOL/MONOSACCHARIDE TRANSPORTER 1-6), which form a distinct subfamily within the large family of more than 50 monosaccharide transporter-like (MST-like) genes. So far, only AtPMT5 [formerly named AtPLT5 (At3g18830)] has been characterized and was shown to be a plasma membrane-localized H+-symporter with broad substrate specificity. The characterization of AtPMT1 (At2g16120) and AtPMT2 (At2g16130), two other, almost identical, members of this transporter subfamily, are presented here. Expression of the AtPMT1 and AtPMT2 cDNAs in baker's yeast (Saccharomyces cerevisiae) revealed that these proteins catalyse the energy-dependent, high-capacity transport of fructose and xylitol, and the transport of several other compounds with lower rates. Expression of their cRNAs in Xenopus laevis oocytes showed that both proteins are voltage-dependent and catalyse the symport of their substrates with protons. Fusions of AtPMT1 or AtPMT2 with the green fluorescent protein (GFP) localized to Arabidopsis plasma membranes. Analyses of reporter genes performed with AtPMT1 or AtPMT2 promoter sequences showed expression in mature (AtPMT2) or germinating (AtPMT1) pollen grains, as well as in growing pollen tubes, hydathodes, and young xylem cells (both genes). The expression was confirmed with an anti-AtPMT1/AtPMT2 antiserum (alpha AtPMT1/2) raised against peptides conserved in AtPMT1 and AtPMT2. The physiological roles of the proteins are discussed and related to plant cell wall modifications.
• Dynamics and regulation of plant membrane transport. Sauer, N.; Hedrich, R. In Plant Biology, 12, pp. 1–2. 2010.
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  @article{RN1115, author = {Sauer, N. and Hedrich, R.}, journal = {Plant Biology}, keywords = {expression}, note = {Suppl. 1 639ue Times Cited:0 Cited References Count:15}, pages = {1-2}, title = {Dynamics and regulation of plant membrane transport}, type = {Journal Article}, volume = 12, year = 2010 }

  %0 Journal Article %1 RN1115 %A Sauer, N. %A Hedrich, R. %D 2010 %J Plant Biology %P 1-2 %R DOI 10.1111/j.1438-8677.2010.00390.x %T Dynamics and regulation of plant membrane transport %U /brokenurl#<Go to ISI>://WOS:000280999200001 %V 12
• Potassium-dependent wood formation in poplar: seasonal aspects and environmental limitations. Ache, P.; Fromm, J.; Hedrich, R. In Plant Biology, 12(2), pp. 259–267. 2010.
  • [ Abstract ]
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  Potassium availability and acquisition are pivotal for the generation of biomass and thus wood formation in growing poplar trees. Here, we focus on the role of potassium (K+) in wood production, transitions between dormancy and active growth, and limiting environmental conditions. Molecular mechanisms, such as expression and activity of K+ transporters and channels controlling seasonal changes in wood formation, are discussed.

  @article{RN1128, abstract = {Potassium availability and acquisition are pivotal for the generation of biomass and thus wood formation in growing poplar trees. Here, we focus on the role of potassium (K+) in wood production, transitions between dormancy and active growth, and limiting environmental conditions. Molecular mechanisms, such as expression and activity of K+ transporters and channels controlling seasonal changes in wood formation, are discussed.}, author = {Ache, P. and Fromm, J. and Hedrich, R.}, journal = {Plant Biology}, keywords = {biomass}, note = {554ci Times Cited:21 Cited References Count:83}, number = 2, pages = {259-267}, title = {Potassium-dependent wood formation in poplar: seasonal aspects and environmental limitations}, type = {Journal Article}, volume = 12, year = 2010 }

  %0 Journal Article %1 RN1128 %A Ache, P. %A Fromm, J. %A Hedrich, R. %D 2010 %J Plant Biology %N 2 %P 259-267 %R 10.1111/j.1438-8677.2009.00282.x %T Potassium-dependent wood formation in poplar: seasonal aspects and environmental limitations %U /brokenurl#<Go to ISI>://WOS:000274412700003 %V 12 %X Potassium availability and acquisition are pivotal for the generation of biomass and thus wood formation in growing poplar trees. Here, we focus on the role of potassium (K+) in wood production, transitions between dormancy and active growth, and limiting environmental conditions. Molecular mechanisms, such as expression and activity of K+ transporters and channels controlling seasonal changes in wood formation, are discussed.
• Perception of the Danger Signal Peptide 1 Involves the Pattern Recognition Receptor PEPR1 and Its Close Homologue PEPR2. Krol, E.; Mentzel, T.; Chinchilla, D.; Boller, T.; Felix, G.; Kemmerling, B.; Postel, S.; Arents, M.; Jeworutzki, E.; Al-Rasheid, K. A. S.; Becker, D.; Hedrich, R. In Journal of Biological Chemistry, 285(18), pp. 13471–13479. 2010.
  • [ Abstract ]
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  Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.

  @article{RN1122, abstract = {Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.}, author = {Krol, E. and Mentzel, T. and Chinchilla, D. and Boller, T. and Felix, G. and Kemmerling, B. and Postel, S. and Arents, M. and Jeworutzki, E. and Al-Rasheid, K. A. S. and Becker, D. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {cell-death}, note = {587jl Times Cited:264 Cited References Count:34}, number = 18, pages = {13471-13479}, title = {Perception of the Danger Signal Peptide 1 Involves the Pattern Recognition Receptor PEPR1 and Its Close Homologue PEPR2}, type = {Journal Article}, volume = 285, year = 2010 }

  %0 Journal Article %1 RN1122 %A Krol, E. %A Mentzel, T. %A Chinchilla, D. %A Boller, T. %A Felix, G. %A Kemmerling, B. %A Postel, S. %A Arents, M. %A Jeworutzki, E. %A Al-Rasheid, K. A. S. %A Becker, D. %A Hedrich, R. %D 2010 %J Journal of Biological Chemistry %N 18 %P 13471-13479 %R 10.1074/jbc.M109.097394 %T Perception of the Danger Signal Peptide 1 Involves the Pattern Recognition Receptor PEPR1 and Its Close Homologue PEPR2 %U /brokenurl#<Go to ISI>://WOS:000276987700019 %V 285 %X Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.
• Guard Cell-Specific Calcium Sensitivity of High Density and Activity SV/TPC1 Channels. Rienmüller, F.; Beyhl, D.; Lautner, S.; Fromm, J.; Al-Rasheid, K. A. S.; Ache, P.; Farmer, E. E.; Marten, I.; Hedrich, R. In Plant and Cell Physiology, 51(9), pp. 1548–1554. 2010.
  • [ Abstract ]
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  The slow vacuolar (SV) channel, a Ca(2)-regulated vacuolar cation conductance channel, in Arabidopsis thaliana is encoded by the single-copy gene AtTPC1. Although loss-of-function tpc1 mutants were reported to exhibit a stoma phenotype, knowledge about the underlying guard cell-specific features of SV/TPC1 channels is still lacking. Here we demonstrate that TPC1 transcripts and SV current density in guard cells were much more pronounced than in mesophyll cells. Furthermore, the SV channel in motor cells exhibited a higher cytosolic Ca(2) sensitivity than in mesophyll cells. These distinct features of the guard cell SV channel therefore probably account for the published stomatal phenotype of tpc1-2.

  @article{RN1117, abstract = {The slow vacuolar (SV) channel, a Ca(2)-regulated vacuolar cation conductance channel, in Arabidopsis thaliana is encoded by the single-copy gene AtTPC1. Although loss-of-function tpc1 mutants were reported to exhibit a stoma phenotype, knowledge about the underlying guard cell-specific features of SV/TPC1 channels is still lacking. Here we demonstrate that TPC1 transcripts and SV current density in guard cells were much more pronounced than in mesophyll cells. Furthermore, the SV channel in motor cells exhibited a higher cytosolic Ca(2) sensitivity than in mesophyll cells. These distinct features of the guard cell SV channel therefore probably account for the published stomatal phenotype of tpc1-2.}, author = {Rienmüller, F. and Beyhl, D. and Lautner, S. and Fromm, J. and Al-Rasheid, K. A. S. and Ache, P. and Farmer, E. E. and Marten, I. and Hedrich, R.}, journal = {Plant and Cell Physiology}, keywords = {ca(2)}, note = {651un Times Cited:31 Cited References Count:33}, number = 9, pages = {1548-1554}, title = {Guard Cell-Specific Calcium Sensitivity of High Density and Activity SV/TPC1 Channels}, type = {Journal Article}, volume = 51, year = 2010 }

  %0 Journal Article %1 RN1117 %A Rienmüller, F. %A Beyhl, D. %A Lautner, S. %A Fromm, J. %A Al-Rasheid, K. A. S. %A Ache, P. %A Farmer, E. E. %A Marten, I. %A Hedrich, R. %D 2010 %J Plant and Cell Physiology %N 9 %P 1548-1554 %R 10.1093/pcp/pcq102 %T Guard Cell-Specific Calcium Sensitivity of High Density and Activity SV/TPC1 Channels %U /brokenurl#<Go to ISI>://WOS:000281952800017 %V 51 %X The slow vacuolar (SV) channel, a Ca(2)-regulated vacuolar cation conductance channel, in Arabidopsis thaliana is encoded by the single-copy gene AtTPC1. Although loss-of-function tpc1 mutants were reported to exhibit a stoma phenotype, knowledge about the underlying guard cell-specific features of SV/TPC1 channels is still lacking. Here we demonstrate that TPC1 transcripts and SV current density in guard cells were much more pronounced than in mesophyll cells. Furthermore, the SV channel in motor cells exhibited a higher cytosolic Ca(2) sensitivity than in mesophyll cells. These distinct features of the guard cell SV channel therefore probably account for the published stomatal phenotype of tpc1-2.
• Sucrose- and H -Dependent Charge Movements Associated with the Gating of Sucrose Transporter ZmSUT1. Carpaneto, A.; Koepsell, H.; Bamberg, E.; Hedrich, R.; Geiger, D. In Plos One, 5(9). 2010.
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  Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (C-m). In addition to sucrose C-m was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these C-m changes, presteady-state currents (I-pre) of ZmSUT1 transport were analyzed. Decay of I-pre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to I-pre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed C-m changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/iota) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions: Taken together our results indicate that in the absence of sucrose, 'trapped' protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to C-m changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents.

  @article{RN1127, abstract = {Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (C-m). In addition to sucrose C-m was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these C-m changes, presteady-state currents (I-pre) of ZmSUT1 transport were analyzed. Decay of I-pre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to I-pre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed C-m changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/iota) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions: Taken together our results indicate that in the absence of sucrose, 'trapped' protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to C-m changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents.}, author = {Carpaneto, A. and Koepsell, H. and Bamberg, E. and Hedrich, R. and Geiger, D.}, journal = {Plos One}, keywords = {cotransporter}, note = {647po Times Cited:29 Cited References Count:37}, number = 9, title = {Sucrose- and H -Dependent Charge Movements Associated with the Gating of Sucrose Transporter ZmSUT1}, type = {Journal Article}, volume = 5, year = 2010 }

  %0 Journal Article %1 RN1127 %A Carpaneto, A. %A Koepsell, H. %A Bamberg, E. %A Hedrich, R. %A Geiger, D. %D 2010 %J Plos One %N 9 %R ARTN e12605 10.1371/journal.pone.0012605 %T Sucrose- and H -Dependent Charge Movements Associated with the Gating of Sucrose Transporter ZmSUT1 %U /brokenurl#<Go to ISI>://WOS:000281631300028 %V 5 %X Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (C-m). In addition to sucrose C-m was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these C-m changes, presteady-state currents (I-pre) of ZmSUT1 transport were analyzed. Decay of I-pre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to I-pre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed C-m changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/iota) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions: Taken together our results indicate that in the absence of sucrose, 'trapped' protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to C-m changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents.
• Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation. Krebs, M.; Beyhl, D.; Görlich, E.; Al-Rasheid, K. A. S.; Marten, I.; Stierhof, Y. D.; Hedrich, R.; Schumacher, K. In Proceedings of the National Academy of Sciences of the United States of America, 107(7), pp. 3251–3256. 2010.
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  The productivity of higher plants as a major source of food and energy is linked to their ability to buffer changes in the concentrations of essential and toxic ions. Transport across the tonoplast is energized by two proton pumps, the vacuolar H+-ATPase (V-ATPase) and the vacuolar H+-pyrophosphatase (V-PPase); however, their functional relation and relative contributions to ion storage and detoxification are unclear. We have identified an Arabidopsis mutant in which energization of vacuolar transport solely relies on the activity of the V-PPase. The vha-a2 vha-a3 double mutant, which lacks the two tonoplast-localized isoforms of the membrane-integral V-ATPase subunit VHA-a, is viable but shows day-length-dependent growth retardation. Nitrate content is reduced whereas nitrate assimilation is increased in the vha-a2 vha-a3 mutant, indicating that vacuolar nitrate storage represents a major growth-limiting factor. Zinc is an essential micronutrient that is toxic at excess concentrations and is detoxified via a vacuolar Zn2+/H+-antiport system. Accordingly, the double mutant shows reduced zinc tolerance. In the same way the vacuolar Na+/H+-antiport system is assumed to be an important component of the system that removes sodium from the cytosol. Unexpectedly, salt tolerance and accumulation are not affected in the vha-a2 vha-a3 double mutant. In contrast, reduction of V-ATPase activity in the trans-Golgi network/early endosome (TGN/EE) leads to increased salt sensitivity. Taken together, our results show that during gametophyte and embryo development V-PPase activity at the tonoplast is sufficient whereas tonoplast V-ATPase activity is limiting for nutrient storage but not for sodium tolerance during vegetative and reproductive growth.

  @article{RN1123, abstract = {The productivity of higher plants as a major source of food and energy is linked to their ability to buffer changes in the concentrations of essential and toxic ions. Transport across the tonoplast is energized by two proton pumps, the vacuolar H+-ATPase (V-ATPase) and the vacuolar H+-pyrophosphatase (V-PPase); however, their functional relation and relative contributions to ion storage and detoxification are unclear. We have identified an Arabidopsis mutant in which energization of vacuolar transport solely relies on the activity of the V-PPase. The vha-a2 vha-a3 double mutant, which lacks the two tonoplast-localized isoforms of the membrane-integral V-ATPase subunit VHA-a, is viable but shows day-length-dependent growth retardation. Nitrate content is reduced whereas nitrate assimilation is increased in the vha-a2 vha-a3 mutant, indicating that vacuolar nitrate storage represents a major growth-limiting factor. Zinc is an essential micronutrient that is toxic at excess concentrations and is detoxified via a vacuolar Zn2+/H+-antiport system. Accordingly, the double mutant shows reduced zinc tolerance. In the same way the vacuolar Na+/H+-antiport system is assumed to be an important component of the system that removes sodium from the cytosol. Unexpectedly, salt tolerance and accumulation are not affected in the vha-a2 vha-a3 double mutant. In contrast, reduction of V-ATPase activity in the trans-Golgi network/early endosome (TGN/EE) leads to increased salt sensitivity. Taken together, our results show that during gametophyte and embryo development V-PPase activity at the tonoplast is sufficient whereas tonoplast V-ATPase activity is limiting for nutrient storage but not for sodium tolerance during vegetative and reproductive growth.}, author = {Krebs, M. and Beyhl, D. and Görlich, E. and Al-Rasheid, K. A. S. and Marten, I. and Stierhof, Y. D. and Hedrich, R. and Schumacher, K.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {myOwn}, note = {556oc Times Cited:254 Cited References Count:41}, number = 7, pages = {3251-3256}, title = {Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation}, type = {Journal Article}, volume = 107, year = 2010 }

  %0 Journal Article %1 RN1123 %A Krebs, M. %A Beyhl, D. %A Görlich, E. %A Al-Rasheid, K. A. S. %A Marten, I. %A Stierhof, Y. D. %A Hedrich, R. %A Schumacher, K. %D 2010 %J Proceedings of the National Academy of Sciences of the United States of America %N 7 %P 3251-3256 %R 10.1073/pnas.0913035107 %T Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation %U /brokenurl#<Go to ISI>://WOS:000274599500097 %V 107 %X The productivity of higher plants as a major source of food and energy is linked to their ability to buffer changes in the concentrations of essential and toxic ions. Transport across the tonoplast is energized by two proton pumps, the vacuolar H+-ATPase (V-ATPase) and the vacuolar H+-pyrophosphatase (V-PPase); however, their functional relation and relative contributions to ion storage and detoxification are unclear. We have identified an Arabidopsis mutant in which energization of vacuolar transport solely relies on the activity of the V-PPase. The vha-a2 vha-a3 double mutant, which lacks the two tonoplast-localized isoforms of the membrane-integral V-ATPase subunit VHA-a, is viable but shows day-length-dependent growth retardation. Nitrate content is reduced whereas nitrate assimilation is increased in the vha-a2 vha-a3 mutant, indicating that vacuolar nitrate storage represents a major growth-limiting factor. Zinc is an essential micronutrient that is toxic at excess concentrations and is detoxified via a vacuolar Zn2+/H+-antiport system. Accordingly, the double mutant shows reduced zinc tolerance. In the same way the vacuolar Na+/H+-antiport system is assumed to be an important component of the system that removes sodium from the cytosol. Unexpectedly, salt tolerance and accumulation are not affected in the vha-a2 vha-a3 double mutant. In contrast, reduction of V-ATPase activity in the trans-Golgi network/early endosome (TGN/EE) leads to increased salt sensitivity. Taken together, our results show that during gametophyte and embryo development V-PPase activity at the tonoplast is sufficient whereas tonoplast V-ATPase activity is limiting for nutrient storage but not for sodium tolerance during vegetative and reproductive growth.
• Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca affinities. Geiger, D.; Scherzer, S.; Mumm, P.; Marten, I.; Ache, P.; Matschi, S.; Liese, A.; Wellmann, C.; Al-Rasheid, K. A. S.; Grill, E.; Romeis, T.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 107(17), pp. 8023–8028. 2010.
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  In response to drought stress, the phytohormone abscisic acid (ABA) induces stomatal closure. Thereby the stress hormone activates guard cell anion channels in a calcium-dependent, as well as -independent, manner. Open stomata 1 protein kinase (OST1) and ABI1 protein phosphatase (ABA insensitive 1) represent key components of calcium-independent ABA signaling. Recently, the guard cell anion channel SLAC1 was identified. When expressed heterologously SLAC1 remained electrically silent. Upon coexpression with Ca2+-independent OST1, however, SLAC1 anion channels appear activated in an ABI1-dependent manner. Mutants lacking distinct calcium-dependent protein kinases (CPKs) appeared impaired in ABA stimulation of guard cell ion channels, too. To study SLAC1 activation via the calcium-dependent ABA pathway, we studied the SLAC1 response to CPKs in the Xenopus laevis oocyte system. Split YFP-based protein-protein interaction assays, using SLAC1 as the bait, identified guard cell expressed CPK21 and 23 as major interacting partners. Upon coexpression of SLAC1 with CPK21 and 23, anion currents document SLAC1 stimulation by these guard cell protein kinases. Ca2+-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca2+-insensitive. In line with activation by OST1, CPK activation of the guard cell anion channel was suppressed by ABI1. Thus the CPK and OST1 branch of ABA signal transduction in guard cells seem to converge on the level of SLAC1 under the control of the ABI1/ABA-receptor complex.

  @article{RN1126, abstract = {In response to drought stress, the phytohormone abscisic acid (ABA) induces stomatal closure. Thereby the stress hormone activates guard cell anion channels in a calcium-dependent, as well as -independent, manner. Open stomata 1 protein kinase (OST1) and ABI1 protein phosphatase (ABA insensitive 1) represent key components of calcium-independent ABA signaling. Recently, the guard cell anion channel SLAC1 was identified. When expressed heterologously SLAC1 remained electrically silent. Upon coexpression with Ca2+-independent OST1, however, SLAC1 anion channels appear activated in an ABI1-dependent manner. Mutants lacking distinct calcium-dependent protein kinases (CPKs) appeared impaired in ABA stimulation of guard cell ion channels, too. To study SLAC1 activation via the calcium-dependent ABA pathway, we studied the SLAC1 response to CPKs in the Xenopus laevis oocyte system. Split YFP-based protein-protein interaction assays, using SLAC1 as the bait, identified guard cell expressed CPK21 and 23 as major interacting partners. Upon coexpression of SLAC1 with CPK21 and 23, anion currents document SLAC1 stimulation by these guard cell protein kinases. Ca2+-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca2+-insensitive. In line with activation by OST1, CPK activation of the guard cell anion channel was suppressed by ABI1. Thus the CPK and OST1 branch of ABA signal transduction in guard cells seem to converge on the level of SLAC1 under the control of the ABI1/ABA-receptor complex.}, author = {Geiger, D. and Scherzer, S. and Mumm, P. and Marten, I. and Ache, P. and Matschi, S. and Liese, A. and Wellmann, C. and Al-Rasheid, K. A. S. and Grill, E. and Romeis, T. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {abscisic}, note = {588qq Times Cited:422 Cited References Count:49}, number = 17, pages = {8023-8028}, title = {Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca affinities}, type = {Journal Article}, volume = 107, year = 2010 }

  %0 Journal Article %1 RN1126 %A Geiger, D. %A Scherzer, S. %A Mumm, P. %A Marten, I. %A Ache, P. %A Matschi, S. %A Liese, A. %A Wellmann, C. %A Al-Rasheid, K. A. S. %A Grill, E. %A Romeis, T. %A Hedrich, R. %D 2010 %J Proceedings of the National Academy of Sciences of the United States of America %N 17 %P 8023-8028 %R 10.1073/pnas.0912030107 %T Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca affinities %U /brokenurl#<Go to ISI>://WOS:000277088700075 %V 107 %X In response to drought stress, the phytohormone abscisic acid (ABA) induces stomatal closure. Thereby the stress hormone activates guard cell anion channels in a calcium-dependent, as well as -independent, manner. Open stomata 1 protein kinase (OST1) and ABI1 protein phosphatase (ABA insensitive 1) represent key components of calcium-independent ABA signaling. Recently, the guard cell anion channel SLAC1 was identified. When expressed heterologously SLAC1 remained electrically silent. Upon coexpression with Ca2+-independent OST1, however, SLAC1 anion channels appear activated in an ABI1-dependent manner. Mutants lacking distinct calcium-dependent protein kinases (CPKs) appeared impaired in ABA stimulation of guard cell ion channels, too. To study SLAC1 activation via the calcium-dependent ABA pathway, we studied the SLAC1 response to CPKs in the Xenopus laevis oocyte system. Split YFP-based protein-protein interaction assays, using SLAC1 as the bait, identified guard cell expressed CPK21 and 23 as major interacting partners. Upon coexpression of SLAC1 with CPK21 and 23, anion currents document SLAC1 stimulation by these guard cell protein kinases. Ca2+-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca2+-insensitive. In line with activation by OST1, CPK activation of the guard cell anion channel was suppressed by ABI1. Thus the CPK and OST1 branch of ABA signal transduction in guard cells seem to converge on the level of SLAC1 under the control of the ABI1/ABA-receptor complex.
• Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca2+-associated opening of plasma membrane anion channels. Jeworutzki, E.; Roelfsema, M. R. G.; Anschütz, U.; Krol, E.; Elzenga, J. T. M.; Felix, G.; Boller, T.; Hedrich, R.; Becker, D. In Plant Journal, 62(3), pp. 367–378. 2010.
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  P>The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.

  @article{RN1125, abstract = {P>The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.}, author = {Jeworutzki, E. and Roelfsema, M. R. G. and Anschütz, U. and Krol, E. and Elzenga, J. T. M. and Felix, G. and Boller, T. and Hedrich, R. and Becker, D.}, journal = {Plant Journal}, keywords = {immunity}, note = {583fr Times Cited:169 Cited References Count:52}, number = 3, pages = {367-378}, title = {Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca2+-associated opening of plasma membrane anion channels}, type = {Journal Article}, volume = 62, year = 2010 }

  %0 Journal Article %1 RN1125 %A Jeworutzki, E. %A Roelfsema, M. R. G. %A Anschütz, U. %A Krol, E. %A Elzenga, J. T. M. %A Felix, G. %A Boller, T. %A Hedrich, R. %A Becker, D. %D 2010 %J Plant Journal %N 3 %P 367-378 %R 10.1111/j.1365-313X.2010.04155.x %T Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca2+-associated opening of plasma membrane anion channels %U /brokenurl#<Go to ISI>://WOS:000276659400002 %V 62 %X P>The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.
• Light-induced modification of plant plasma membrane ion transport. Marten, I.; Deeken, R.; Hedrich, R.; Roelfsema, M. R. G. In Plant Biology, 12, pp. 64–79. 2010.
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  Light is not only the driving force for electron and ion transport in the thylakoid membrane, but also regulates ion transport in various other membranes of plant cells. Light-dependent changes in ion transport at the plasma membrane and associated membrane potential changes have been studied intensively over the last century. These studies, with various species and cell types, revealed that apart from regulation by chloroplasts, plasma membrane transport can be controlled by phytochromes, phototropins or channel rhodopsins. In this review, we compare light-dependent plasma membrane responses of unicellular algae (Eremosphaera and Chlamydomonas), with those of a multicellular alga (Chara), liverworts (Conocephalum), mosses (Physcomitrella) and several angiosperm cell types. Light-dependent plasma membrane responses of Eremosphaera and Chara are characterised by the dominant role of K+ channels during membrane potential changes. In most other species, the Ca2+-dependent activation of plasma membrane anion channels represents a general light-triggered event. Cell type-specific responses are likely to have evolved by modification of this general response or through the development of additional light-dependent signalling pathways. Future research to elucidate these light-activated signalling chains is likely to benefit from the recent identification of S-type anion channel genes and proteins capable of regulating these channels.

  @article{RN1119, abstract = {Light is not only the driving force for electron and ion transport in the thylakoid membrane, but also regulates ion transport in various other membranes of plant cells. Light-dependent changes in ion transport at the plasma membrane and associated membrane potential changes have been studied intensively over the last century. These studies, with various species and cell types, revealed that apart from regulation by chloroplasts, plasma membrane transport can be controlled by phytochromes, phototropins or channel rhodopsins. In this review, we compare light-dependent plasma membrane responses of unicellular algae (Eremosphaera and Chlamydomonas), with those of a multicellular alga (Chara), liverworts (Conocephalum), mosses (Physcomitrella) and several angiosperm cell types. Light-dependent plasma membrane responses of Eremosphaera and Chara are characterised by the dominant role of K+ channels during membrane potential changes. In most other species, the Ca2+-dependent activation of plasma membrane anion channels represents a general light-triggered event. Cell type-specific responses are likely to have evolved by modification of this general response or through the development of additional light-dependent signalling pathways. Future research to elucidate these light-activated signalling chains is likely to benefit from the recent identification of S-type anion channel genes and proteins capable of regulating these channels.}, author = {Marten, I. and Deeken, R. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Plant Biology}, keywords = {algae}, note = {Suppl. 1 639ue Times Cited:31 Cited References Count:172}, pages = {64-79}, title = {Light-induced modification of plant plasma membrane ion transport}, type = {Journal Article}, volume = 12, year = 2010 }

  %0 Journal Article %1 RN1119 %A Marten, I. %A Deeken, R. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2010 %J Plant Biology %P 64-79 %R 10.1111/j.1438-8677.2010.00384.x %T Light-induced modification of plant plasma membrane ion transport %U /brokenurl#<Go to ISI>://WOS:000280999200008 %V 12 %X Light is not only the driving force for electron and ion transport in the thylakoid membrane, but also regulates ion transport in various other membranes of plant cells. Light-dependent changes in ion transport at the plasma membrane and associated membrane potential changes have been studied intensively over the last century. These studies, with various species and cell types, revealed that apart from regulation by chloroplasts, plasma membrane transport can be controlled by phytochromes, phototropins or channel rhodopsins. In this review, we compare light-dependent plasma membrane responses of unicellular algae (Eremosphaera and Chlamydomonas), with those of a multicellular alga (Chara), liverworts (Conocephalum), mosses (Physcomitrella) and several angiosperm cell types. Light-dependent plasma membrane responses of Eremosphaera and Chara are characterised by the dominant role of K+ channels during membrane potential changes. In most other species, the Ca2+-dependent activation of plasma membrane anion channels represents a general light-triggered event. Cell type-specific responses are likely to have evolved by modification of this general response or through the development of additional light-dependent signalling pathways. Future research to elucidate these light-activated signalling chains is likely to benefit from the recent identification of S-type anion channel genes and proteins capable of regulating these channels.
• K transport characteristics of the plasma membrane tandem-pore channel TPK4 and pore chimeras with its vacuolar homologs. Marcel, D.; Müller, T.; Hedrich, R.; Geiger, D. In Febs Letters, 584(11), pp. 2433–2439. 2010.
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  Vacuolar tandem-pore channels could not be analysed in Xenopus oocytes so far, due to misguided translocation. Owing to the conservation of their pore regions, we were able to prepare functional pore-chimeras between the plasma membrane localised TPK4 and vacuolar TPKs. Thereby, we found evidence that TPK2, TPK3 and TPK5, just like TPK4, form potassium-selective channels with instantaneous current kinetics. Homology modelling and mutational analyses identified a pore-located aspartate residue (Asp110), which is involved in potassium permeation as well as in inward rectification of TPK4. Furthermore, dominant-negative mutations in the selectivity filter of either pore one or two (Asp86, Asp200) rendered TPK4 non-functional. This observation supports the notion that the functional TPK4 channel complex is formed by two subunits. (C) 2010 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.

  @article{RN1120, abstract = {Vacuolar tandem-pore channels could not be analysed in Xenopus oocytes so far, due to misguided translocation. Owing to the conservation of their pore regions, we were able to prepare functional pore-chimeras between the plasma membrane localised TPK4 and vacuolar TPKs. Thereby, we found evidence that TPK2, TPK3 and TPK5, just like TPK4, form potassium-selective channels with instantaneous current kinetics. Homology modelling and mutational analyses identified a pore-located aspartate residue (Asp110), which is involved in potassium permeation as well as in inward rectification of TPK4. Furthermore, dominant-negative mutations in the selectivity filter of either pore one or two (Asp86, Asp200) rendered TPK4 non-functional. This observation supports the notion that the functional TPK4 channel complex is formed by two subunits. (C) 2010 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.}, author = {Marcel, D. and Müller, T. and Hedrich, R. and Geiger, D.}, journal = {Febs Letters}, keywords = {potassium}, note = {597wn Times Cited:22 Cited References Count:51}, number = 11, pages = {2433-2439}, title = {K transport characteristics of the plasma membrane tandem-pore channel TPK4 and pore chimeras with its vacuolar homologs}, type = {Journal Article}, volume = 584, year = 2010 }

  %0 Journal Article %1 RN1120 %A Marcel, D. %A Müller, T. %A Hedrich, R. %A Geiger, D. %D 2010 %J Febs Letters %N 11 %P 2433-2439 %R 10.1016/j.febslet.2010.04.038 %T K transport characteristics of the plasma membrane tandem-pore channel TPK4 and pore chimeras with its vacuolar homologs %U /brokenurl#<Go to ISI>://WOS:000277793200044 %V 584 %X Vacuolar tandem-pore channels could not be analysed in Xenopus oocytes so far, due to misguided translocation. Owing to the conservation of their pore regions, we were able to prepare functional pore-chimeras between the plasma membrane localised TPK4 and vacuolar TPKs. Thereby, we found evidence that TPK2, TPK3 and TPK5, just like TPK4, form potassium-selective channels with instantaneous current kinetics. Homology modelling and mutational analyses identified a pore-located aspartate residue (Asp110), which is involved in potassium permeation as well as in inward rectification of TPK4. Furthermore, dominant-negative mutations in the selectivity filter of either pore one or two (Asp86, Asp200) rendered TPK4 non-functional. This observation supports the notion that the functional TPK4 channel complex is formed by two subunits. (C) 2010 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.
• ALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells. Meyer, S.; Mumm, P.; Imes, D.; Endler, A.; Weder, B.; Al-Rasheid, K. A. S.; Geiger, D.; Marten, I.; Martinoia, E.; Hedrich, R. In Plant Journal, 63(6), pp. 1054–1062. 2010.
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  Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells. Anion efflux from guard cells involves slow (S-type) and rapid (R-type) anion channels. Recently the SLAC1 gene has been shown to encode the slow, voltage-independent anion channel component in guard cells. In contrast, the R-type channel still awaits identification. Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R-type anion channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane. Plants lacking AtALMT12 are impaired in dark-and CO2-induced stomatal closure, as well as in response to the drought-stress hormone abscisic acid. Patch-clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R-type currents compared with wild-type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage-dependent anion currents reminiscent to R-type channels could be activated. In line with the features of the R-type channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials. R-Type channels, like voltage-dependent cation channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long-term anion and K+ efflux via SLAC1 and GORK, respectively.

  @article{RN1118, abstract = {Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells. Anion efflux from guard cells involves slow (S-type) and rapid (R-type) anion channels. Recently the SLAC1 gene has been shown to encode the slow, voltage-independent anion channel component in guard cells. In contrast, the R-type channel still awaits identification. Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R-type anion channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane. Plants lacking AtALMT12 are impaired in dark-and CO2-induced stomatal closure, as well as in response to the drought-stress hormone abscisic acid. Patch-clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R-type currents compared with wild-type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage-dependent anion currents reminiscent to R-type channels could be activated. In line with the features of the R-type channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials. R-Type channels, like voltage-dependent cation channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long-term anion and K+ efflux via SLAC1 and GORK, respectively.}, author = {Meyer, S. and Mumm, P. and Imes, D. and Endler, A. and Weder, B. and Al-Rasheid, K. A. S. and Geiger, D. and Marten, I. and Martinoia, E. and Hedrich, R.}, journal = {Plant Journal}, keywords = {atalmt12}, note = {651cn Times Cited:275 Cited References Count:38}, number = 6, pages = {1054-1062}, title = {ALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells}, type = {Journal Article}, volume = 63, year = 2010 }

  %0 Journal Article %1 RN1118 %A Meyer, S. %A Mumm, P. %A Imes, D. %A Endler, A. %A Weder, B. %A Al-Rasheid, K. A. S. %A Geiger, D. %A Marten, I. %A Martinoia, E. %A Hedrich, R. %D 2010 %J Plant Journal %N 6 %P 1054-1062 %R 10.1111/j.1365-313X.2010.04302.x %T ALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells %U /brokenurl#<Go to ISI>://WOS:000281902300014 %V 63 %X Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells. Anion efflux from guard cells involves slow (S-type) and rapid (R-type) anion channels. Recently the SLAC1 gene has been shown to encode the slow, voltage-independent anion channel component in guard cells. In contrast, the R-type channel still awaits identification. Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R-type anion channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane. Plants lacking AtALMT12 are impaired in dark-and CO2-induced stomatal closure, as well as in response to the drought-stress hormone abscisic acid. Patch-clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R-type currents compared with wild-type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage-dependent anion currents reminiscent to R-type channels could be activated. In line with the features of the R-type channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials. R-Type channels, like voltage-dependent cation channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long-term anion and K+ efflux via SLAC1 and GORK, respectively.
• Inverse pH Regulation of Plant and Fungal Sucrose Transporters: A Mechanism to Regulate Competition for Sucrose at the Host/Pathogen Interface?. Wippel, K.; Wittek, A.; Hedrich, R.; Sauer, N. In Plos One, 5(8). 2010.
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  Background: Plant sucrose transporter activities were shown to respond to changes in the extracellular pH and redox status, and oxidizing compounds like glutathione (GSSG) or H(2)O(2) were reported to effect the subcellular targeting of these proteins. We hypothesized that changes in both parameters might be used to modulate the activities of competing sucrose transporters at a plant/pathogen interface. We, therefore, compared the effects of redox-active compounds and of extracellular pH on the sucrose transporters UmSRT1 and ZmSUT1 known to compete for extracellular sucrose in the Ustilago maydis (corn smut)/Zea mays (maize) pathosystem. Methodology/Principal Findings: We present functional analyses of the U. maydis sucrose transporter UmSRT1 and of the plant sucrose transporters ZmSUT1 and StSUT1 in Saccharomyces cerevisiae or in Xenopus laevis oocytes in the presence of different extracellular pH-values and redox systems, and study the possible effects of these treatments on the subcellular targeting. We observed an inverse regulation of host and pathogen sucrose transporters by changes in the apoplastic pH. Under none of the conditions analyzed, we could confirm the reported effects of redox-active compounds. Conclusions/Significance: Our data suggest that changes in the extracellular pH but not of the extracellular redox status might be used to oppositely adjust the transport activities of plant and fungal sucrose transporters at the host/pathogen interface.

  @article{RN1112, abstract = {Background: Plant sucrose transporter activities were shown to respond to changes in the extracellular pH and redox status, and oxidizing compounds like glutathione (GSSG) or H(2)O(2) were reported to effect the subcellular targeting of these proteins. We hypothesized that changes in both parameters might be used to modulate the activities of competing sucrose transporters at a plant/pathogen interface. We, therefore, compared the effects of redox-active compounds and of extracellular pH on the sucrose transporters UmSRT1 and ZmSUT1 known to compete for extracellular sucrose in the Ustilago maydis (corn smut)/Zea mays (maize) pathosystem. Methodology/Principal Findings: We present functional analyses of the U. maydis sucrose transporter UmSRT1 and of the plant sucrose transporters ZmSUT1 and StSUT1 in Saccharomyces cerevisiae or in Xenopus laevis oocytes in the presence of different extracellular pH-values and redox systems, and study the possible effects of these treatments on the subcellular targeting. We observed an inverse regulation of host and pathogen sucrose transporters by changes in the apoplastic pH. Under none of the conditions analyzed, we could confirm the reported effects of redox-active compounds. Conclusions/Significance: Our data suggest that changes in the extracellular pH but not of the extracellular redox status might be used to oppositely adjust the transport activities of plant and fungal sucrose transporters at the host/pathogen interface.}, author = {Wippel, K. and Wittek, A. and Hedrich, R. and Sauer, N.}, journal = {Plos One}, keywords = {saccharomyces-cerevisiae}, note = {643jl Times Cited:17 Cited References Count:27}, number = 8, title = {Inverse pH Regulation of Plant and Fungal Sucrose Transporters: A Mechanism to Regulate Competition for Sucrose at the Host/Pathogen Interface?}, type = {Journal Article}, volume = 5, year = 2010 }

  %0 Journal Article %1 RN1112 %A Wippel, K. %A Wittek, A. %A Hedrich, R. %A Sauer, N. %D 2010 %J Plos One %N 8 %R ARTN e12429 10.1371/journal.pone.0012429 %T Inverse pH Regulation of Plant and Fungal Sucrose Transporters: A Mechanism to Regulate Competition for Sucrose at the Host/Pathogen Interface? %U /brokenurl#<Go to ISI>://WOS:000281292100024 %V 5 %X Background: Plant sucrose transporter activities were shown to respond to changes in the extracellular pH and redox status, and oxidizing compounds like glutathione (GSSG) or H(2)O(2) were reported to effect the subcellular targeting of these proteins. We hypothesized that changes in both parameters might be used to modulate the activities of competing sucrose transporters at a plant/pathogen interface. We, therefore, compared the effects of redox-active compounds and of extracellular pH on the sucrose transporters UmSRT1 and ZmSUT1 known to compete for extracellular sucrose in the Ustilago maydis (corn smut)/Zea mays (maize) pathosystem. Methodology/Principal Findings: We present functional analyses of the U. maydis sucrose transporter UmSRT1 and of the plant sucrose transporters ZmSUT1 and StSUT1 in Saccharomyces cerevisiae or in Xenopus laevis oocytes in the presence of different extracellular pH-values and redox systems, and study the possible effects of these treatments on the subcellular targeting. We observed an inverse regulation of host and pathogen sucrose transporters by changes in the apoplastic pH. Under none of the conditions analyzed, we could confirm the reported effects of redox-active compounds. Conclusions/Significance: Our data suggest that changes in the extracellular pH but not of the extracellular redox status might be used to oppositely adjust the transport activities of plant and fungal sucrose transporters at the host/pathogen interface.
• Ca2+-dependent activation of guard cell anion channels, triggered by hyperpolarization, is promoted by prolonged depolarization. Stange, A.; Hedrich, R.; Roelfsema, M. R. G. In Plant Journal, 62(2), pp. 265–276. 2010.
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  P>Rapid stomatal closure is driven by the activation of S-type anion channels in the plasma membrane of guard cells. This response has been linked to Ca2+ signalling, but the impact of transient Ca2+ signals on S-type anion channel activity remains unknown. In this study, transient elevation of the cytosolic Ca2+ level was provoked by voltage steps in guard cells of intact Nicotiana tabacum plants. Changes in the activity of S-type anion channels were monitored using intracellular triple-barrelled micro-electrodes. In cells kept at a holding potential of -100 mV, voltage steps to -180 mV triggered elevation of the cytosolic free Ca2+ concentration. The increase in the cytosolic Ca2+ level was accompanied by activation of S-type anion channels. Guard cell anion channels were activated by Ca2+ with a half maximum concentration of 515 nm (SE = 235) and a mean saturation value of -349 pA (SE = 107) at -100 mV. Ca2+ signals could also be evoked by prolonged (100 sec) depolarization of the plasma membrane to 0 mV. Upon returning to -100 mV, a transient increase in the cytosolic Ca2+ level was observed, activating S-type channels without measurable delay. These data show that cytosolic Ca2+ elevation can activate S-type anion channels in intact guard cells through a fast signalling pathway. Furthermore, prolonged depolarization to 0 mV alters the activity of Ca2+ transport proteins, resulting in an overshoot of the cytosolic Ca2+ level after returning the membrane potential to -100 mV.

  @article{RN1114, abstract = {P>Rapid stomatal closure is driven by the activation of S-type anion channels in the plasma membrane of guard cells. This response has been linked to Ca2+ signalling, but the impact of transient Ca2+ signals on S-type anion channel activity remains unknown. In this study, transient elevation of the cytosolic Ca2+ level was provoked by voltage steps in guard cells of intact Nicotiana tabacum plants. Changes in the activity of S-type anion channels were monitored using intracellular triple-barrelled micro-electrodes. In cells kept at a holding potential of -100 mV, voltage steps to -180 mV triggered elevation of the cytosolic free Ca2+ concentration. The increase in the cytosolic Ca2+ level was accompanied by activation of S-type anion channels. Guard cell anion channels were activated by Ca2+ with a half maximum concentration of 515 nm (SE = 235) and a mean saturation value of -349 pA (SE = 107) at -100 mV. Ca2+ signals could also be evoked by prolonged (100 sec) depolarization of the plasma membrane to 0 mV. Upon returning to -100 mV, a transient increase in the cytosolic Ca2+ level was observed, activating S-type channels without measurable delay. These data show that cytosolic Ca2+ elevation can activate S-type anion channels in intact guard cells through a fast signalling pathway. Furthermore, prolonged depolarization to 0 mV alters the activity of Ca2+ transport proteins, resulting in an overshoot of the cytosolic Ca2+ level after returning the membrane potential to -100 mV.}, author = {Stange, A. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Plant Journal}, keywords = {s-type}, note = {581bp Times Cited:30 Cited References Count:66}, number = 2, pages = {265-276}, title = {Ca2+-dependent activation of guard cell anion channels, triggered by hyperpolarization, is promoted by prolonged depolarization}, type = {Journal Article}, volume = 62, year = 2010 }

  %0 Journal Article %1 RN1114 %A Stange, A. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2010 %J Plant Journal %N 2 %P 265-276 %R 10.1111/j.1365-313X.2010.04141.x %T Ca2+-dependent activation of guard cell anion channels, triggered by hyperpolarization, is promoted by prolonged depolarization %U /brokenurl#<Go to ISI>://WOS:000276496300008 %V 62 %X P>Rapid stomatal closure is driven by the activation of S-type anion channels in the plasma membrane of guard cells. This response has been linked to Ca2+ signalling, but the impact of transient Ca2+ signals on S-type anion channel activity remains unknown. In this study, transient elevation of the cytosolic Ca2+ level was provoked by voltage steps in guard cells of intact Nicotiana tabacum plants. Changes in the activity of S-type anion channels were monitored using intracellular triple-barrelled micro-electrodes. In cells kept at a holding potential of -100 mV, voltage steps to -180 mV triggered elevation of the cytosolic free Ca2+ concentration. The increase in the cytosolic Ca2+ level was accompanied by activation of S-type anion channels. Guard cell anion channels were activated by Ca2+ with a half maximum concentration of 515 nm (SE = 235) and a mean saturation value of -349 pA (SE = 107) at -100 mV. Ca2+ signals could also be evoked by prolonged (100 sec) depolarization of the plasma membrane to 0 mV. Upon returning to -100 mV, a transient increase in the cytosolic Ca2+ level was observed, activating S-type channels without measurable delay. These data show that cytosolic Ca2+ elevation can activate S-type anion channels in intact guard cells through a fast signalling pathway. Furthermore, prolonged depolarization to 0 mV alters the activity of Ca2+ transport proteins, resulting in an overshoot of the cytosolic Ca2+ level after returning the membrane potential to -100 mV.
• A role for PSK signaling in wounding and microbial interactions in. Loivamäki, M.; Stührwohldt, N.; Deeken, R.; Steffens, B.; Roitsch, T.; Hedrich, R.; Sauter, M. In Physiologia Plantarum, 139(4), pp. 348–357. 2010.
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  PSK-alpha is a disulfated peptide that acts as a growth factor in plants. PSK-alpha is derived from preproproteins which are encoded by five PSK precursor genes in Arabidopsis thaliana (L.) Heynh and is perceived by leucine-rich repeat receptor kinases. Arabidopsis has two PSK receptor genes, PSKR1 and PSKR2. Although ligand and receptor are well characterized, the biological functions of PSK signaling are not well understood. Using reporter lines and receptor knockout mutants of Arabidopsis, a role for PSK signaling in biotic interactions and in wounding was analyzed. Treatment of Arabidopsis leaves with the fungal elicitor E-Fol, or the fungal pathogens Alternaria brassicicola and Sclerotinia sclerotiorum resulted in induction of PSK2 and PSKR1 as shown by promoter:GUS analysis. Wounding of hypocotyls or leaves induced PSK3:GUS, PSK5:GUS and PSKR1:GUS expression indicating that PSK precursor genes are differentially regulated in response to specific stresses. The receptor knockout lines pskr1-3 and pskr2-1 showed significantly reduced photosynthesis in response to the fungal elicitor E-Fol which indicates that fungal defence is impaired. pskr1-3 plants further showed reduced growth of crown galls after infection with Agrobacterium tumefaciens. A role for PSK signaling in Agrobacterium tumefaciens tumor growth was supported by the finding that PSK precursor genes and PSKR1 are expressed in crown galls. Overall, the results indicate that PSK signaling may play a previously undescribed role in pathogen or herbivore interactions and is crucial for Agrobacterium-induced cell proliferation in crown gall formation.

  @article{RN1121, abstract = {PSK-alpha is a disulfated peptide that acts as a growth factor in plants. PSK-alpha is derived from preproproteins which are encoded by five PSK precursor genes in Arabidopsis thaliana (L.) Heynh and is perceived by leucine-rich repeat receptor kinases. Arabidopsis has two PSK receptor genes, PSKR1 and PSKR2. Although ligand and receptor are well characterized, the biological functions of PSK signaling are not well understood. Using reporter lines and receptor knockout mutants of Arabidopsis, a role for PSK signaling in biotic interactions and in wounding was analyzed. Treatment of Arabidopsis leaves with the fungal elicitor E-Fol, or the fungal pathogens Alternaria brassicicola and Sclerotinia sclerotiorum resulted in induction of PSK2 and PSKR1 as shown by promoter:GUS analysis. Wounding of hypocotyls or leaves induced PSK3:GUS, PSK5:GUS and PSKR1:GUS expression indicating that PSK precursor genes are differentially regulated in response to specific stresses. The receptor knockout lines pskr1-3 and pskr2-1 showed significantly reduced photosynthesis in response to the fungal elicitor E-Fol which indicates that fungal defence is impaired. pskr1-3 plants further showed reduced growth of crown galls after infection with Agrobacterium tumefaciens. A role for PSK signaling in Agrobacterium tumefaciens tumor growth was supported by the finding that PSK precursor genes and PSKR1 are expressed in crown galls. Overall, the results indicate that PSK signaling may play a previously undescribed role in pathogen or herbivore interactions and is crucial for Agrobacterium-induced cell proliferation in crown gall formation.}, author = {Loivamäki, M. and Stührwohldt, N. and Deeken, R. and Steffens, B. and Roitsch, T. and Hedrich, R. and Sauter, M.}, journal = {Physiologia Plantarum}, keywords = {mesophyll-cells}, note = {624sf Times Cited:37 Cited References Count:29}, number = 4, pages = {348-357}, title = {A role for PSK signaling in wounding and microbial interactions in}, type = {Journal Article}, volume = 139, year = 2010 }

  %0 Journal Article %1 RN1121 %A Loivamäki, M. %A Stührwohldt, N. %A Deeken, R. %A Steffens, B. %A Roitsch, T. %A Hedrich, R. %A Sauter, M. %D 2010 %J Physiologia Plantarum %N 4 %P 348-357 %R 10.1111/j.1399-3054.2010.01371.x %T A role for PSK signaling in wounding and microbial interactions in %U /brokenurl#<Go to ISI>://WOS:000279840300002 %V 139 %X PSK-alpha is a disulfated peptide that acts as a growth factor in plants. PSK-alpha is derived from preproproteins which are encoded by five PSK precursor genes in Arabidopsis thaliana (L.) Heynh and is perceived by leucine-rich repeat receptor kinases. Arabidopsis has two PSK receptor genes, PSKR1 and PSKR2. Although ligand and receptor are well characterized, the biological functions of PSK signaling are not well understood. Using reporter lines and receptor knockout mutants of Arabidopsis, a role for PSK signaling in biotic interactions and in wounding was analyzed. Treatment of Arabidopsis leaves with the fungal elicitor E-Fol, or the fungal pathogens Alternaria brassicicola and Sclerotinia sclerotiorum resulted in induction of PSK2 and PSKR1 as shown by promoter:GUS analysis. Wounding of hypocotyls or leaves induced PSK3:GUS, PSK5:GUS and PSKR1:GUS expression indicating that PSK precursor genes are differentially regulated in response to specific stresses. The receptor knockout lines pskr1-3 and pskr2-1 showed significantly reduced photosynthesis in response to the fungal elicitor E-Fol which indicates that fungal defence is impaired. pskr1-3 plants further showed reduced growth of crown galls after infection with Agrobacterium tumefaciens. A role for PSK signaling in Agrobacterium tumefaciens tumor growth was supported by the finding that PSK precursor genes and PSKR1 are expressed in crown galls. Overall, the results indicate that PSK signaling may play a previously undescribed role in pathogen or herbivore interactions and is crucial for Agrobacterium-induced cell proliferation in crown gall formation.
• Increased Activity of the Vacuolar Monosaccharide Transporter TMT1 Alters Cellular Sugar Partitioning, Sugar Signaling, and Seed Yield in Arabidopsis. Wingenter, K.; Schulz, A.; Wormit, A.; Wic, S.; Trentmann, O.; Hoermiller, I. I.; Heyer, A. G.; Marten, I.; Hedrich, R.; Neuhaus, H. E. In Plant Physiology, 154(2), pp. 665–677. 2010.
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  The extent to which vacuolar sugar transport activity affects molecular, cellular, and developmental processes in Arabidopsis (Arabidopsis thaliana) is unknown. Electrophysiological analysis revealed that overexpression of the tonoplast monosaccharide transporter TMT1 in a tmt1-2::tDNA mutant led to increased proton-coupled monosaccharide import into isolated mesophyll vacuoles in comparison with wild-type vacuoles. TMT1 overexpressor mutants grew faster than wild-type plants on soil and in high-glucose (Glc)-containing liquid medium. These effects were correlated with increased vacuolar monosaccharide compartmentation, as revealed by nonaqueous fractionation and by chlorophyll(ab)-binding protein1 and nitrate reductase1 gene expression studies. Soil-grown TMT1 overexpressor plants respired less Glc than wild-type plants and only about half the amount of Glc respired by tmt1-2::tDNA mutants. In sum, these data show that TMT activity in wild-type plants limits vacuolar monosaccharide loading. Remarkably, TMT1 overexpressor mutants produced larger seeds and greater total seed yield, which was associated with increased lipid and protein content. These changes in seed properties were correlated with slightly decreased nocturnal CO2 release and increased sugar export rates from detached source leaves. The SUC2 gene, which codes for a sucrose transporter that may be critical for phloem loading in leaves, has been identified as Glc repressed. Thus, the observation that SUC2 mRNA increased slightly in TMT1 overexpressor leaves, characterized by lowered cytosolic Glc levels than wild-type leaves, provided further evidence of a stimulated source capacity. In summary, increased TMT activity in Arabidopsis induced modified subcellular sugar compartmentation, altered cellular sugar sensing, affected assimilate allocation, increased the biomass of Arabidopsis seeds, and accelerated early plant development.

  @article{RN1113, abstract = {The extent to which vacuolar sugar transport activity affects molecular, cellular, and developmental processes in Arabidopsis (Arabidopsis thaliana) is unknown. Electrophysiological analysis revealed that overexpression of the tonoplast monosaccharide transporter TMT1 in a tmt1-2::tDNA mutant led to increased proton-coupled monosaccharide import into isolated mesophyll vacuoles in comparison with wild-type vacuoles. TMT1 overexpressor mutants grew faster than wild-type plants on soil and in high-glucose (Glc)-containing liquid medium. These effects were correlated with increased vacuolar monosaccharide compartmentation, as revealed by nonaqueous fractionation and by chlorophyll(ab)-binding protein1 and nitrate reductase1 gene expression studies. Soil-grown TMT1 overexpressor plants respired less Glc than wild-type plants and only about half the amount of Glc respired by tmt1-2::tDNA mutants. In sum, these data show that TMT activity in wild-type plants limits vacuolar monosaccharide loading. Remarkably, TMT1 overexpressor mutants produced larger seeds and greater total seed yield, which was associated with increased lipid and protein content. These changes in seed properties were correlated with slightly decreased nocturnal CO2 release and increased sugar export rates from detached source leaves. The SUC2 gene, which codes for a sucrose transporter that may be critical for phloem loading in leaves, has been identified as Glc repressed. Thus, the observation that SUC2 mRNA increased slightly in TMT1 overexpressor leaves, characterized by lowered cytosolic Glc levels than wild-type leaves, provided further evidence of a stimulated source capacity. In summary, increased TMT activity in Arabidopsis induced modified subcellular sugar compartmentation, altered cellular sugar sensing, affected assimilate allocation, increased the biomass of Arabidopsis seeds, and accelerated early plant development.}, author = {Wingenter, K. and Schulz, A. and Wormit, A. and Wic, S. and Trentmann, O. and Hoermiller, I. I. and Heyer, A. G. and Marten, I. and Hedrich, R. and Neuhaus, H. E.}, journal = {Plant Physiology}, keywords = {protoplasts}, note = {658tm Times Cited:127 Cited References Count:57}, number = 2, pages = {665-677}, title = {Increased Activity of the Vacuolar Monosaccharide Transporter TMT1 Alters Cellular Sugar Partitioning, Sugar Signaling, and Seed Yield in Arabidopsis}, type = {Journal Article}, volume = 154, year = 2010 }

  %0 Journal Article %1 RN1113 %A Wingenter, K. %A Schulz, A. %A Wormit, A. %A Wic, S. %A Trentmann, O. %A Hoermiller, I. I. %A Heyer, A. G. %A Marten, I. %A Hedrich, R. %A Neuhaus, H. E. %D 2010 %J Plant Physiology %N 2 %P 665-677 %R 10.1104/pp.110.162040 %T Increased Activity of the Vacuolar Monosaccharide Transporter TMT1 Alters Cellular Sugar Partitioning, Sugar Signaling, and Seed Yield in Arabidopsis %U /brokenurl#<Go to ISI>://WOS:000282512300043 %V 154 %X The extent to which vacuolar sugar transport activity affects molecular, cellular, and developmental processes in Arabidopsis (Arabidopsis thaliana) is unknown. Electrophysiological analysis revealed that overexpression of the tonoplast monosaccharide transporter TMT1 in a tmt1-2::tDNA mutant led to increased proton-coupled monosaccharide import into isolated mesophyll vacuoles in comparison with wild-type vacuoles. TMT1 overexpressor mutants grew faster than wild-type plants on soil and in high-glucose (Glc)-containing liquid medium. These effects were correlated with increased vacuolar monosaccharide compartmentation, as revealed by nonaqueous fractionation and by chlorophyll(ab)-binding protein1 and nitrate reductase1 gene expression studies. Soil-grown TMT1 overexpressor plants respired less Glc than wild-type plants and only about half the amount of Glc respired by tmt1-2::tDNA mutants. In sum, these data show that TMT activity in wild-type plants limits vacuolar monosaccharide loading. Remarkably, TMT1 overexpressor mutants produced larger seeds and greater total seed yield, which was associated with increased lipid and protein content. These changes in seed properties were correlated with slightly decreased nocturnal CO2 release and increased sugar export rates from detached source leaves. The SUC2 gene, which codes for a sucrose transporter that may be critical for phloem loading in leaves, has been identified as Glc repressed. Thus, the observation that SUC2 mRNA increased slightly in TMT1 overexpressor leaves, characterized by lowered cytosolic Glc levels than wild-type leaves, provided further evidence of a stimulated source capacity. In summary, increased TMT activity in Arabidopsis induced modified subcellular sugar compartmentation, altered cellular sugar sensing, affected assimilate allocation, increased the biomass of Arabidopsis seeds, and accelerated early plant development.

• Outward-rectifying K channel activities regulate cell elongation and cell division of tobacco BY-2 cells. Sano, T.; Kutsuna, N.; Becker, D.; Hedrich, R.; Hasezawa, S. In Plant Journal, 57(1), pp. 55–64. 2009.
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  Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH4)(2)SO4 increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.

  @article{RN1130, abstract = {Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH4)(2)SO4 increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.}, author = {Sano, T. and Kutsuna, N. and Becker, D. and Hedrich, R. and Hasezawa, S.}, journal = {Plant Journal}, keywords = {cell}, note = {387oy Times Cited:27 Cited References Count:52}, number = 1, pages = {55-64}, title = {Outward-rectifying K channel activities regulate cell elongation and cell division of tobacco BY-2 cells}, type = {Journal Article}, volume = 57, year = 2009 }

  %0 Journal Article %1 RN1130 %A Sano, T. %A Kutsuna, N. %A Becker, D. %A Hedrich, R. %A Hasezawa, S. %D 2009 %J Plant Journal %N 1 %P 55-64 %R 10.1111/j.1365-313X.2008.03672.x %T Outward-rectifying K channel activities regulate cell elongation and cell division of tobacco BY-2 cells %U /brokenurl#<Go to ISI>://WOS:000261962700005 %V 57 %X Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH4)(2)SO4 increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.
• Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair. Geiger, D.; Scherzer, S.; Mumm, P.; Stange, A.; Marten, I.; Bauer, H.; Ache, P.; Matschi, S.; Liese, A.; Al-Rasheid, K. A. S.; Romeis, T.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 106(50), pp. 21425–21430. 2009.
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  In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.

  @article{RN1132, abstract = {In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.}, author = {Geiger, D. and Scherzer, S. and Mumm, P. and Stange, A. and Marten, I. and Bauer, H. and Ache, P. and Matschi, S. and Liese, A. and Al-Rasheid, K. A. S. and Romeis, T. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {aba}, note = {533aw Times Cited:644 Cited References Count:68}, number = 50, pages = {21425-21430}, title = {Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair}, type = {Journal Article}, volume = 106, year = 2009 }

  %0 Journal Article %1 RN1132 %A Geiger, D. %A Scherzer, S. %A Mumm, P. %A Stange, A. %A Marten, I. %A Bauer, H. %A Ache, P. %A Matschi, S. %A Liese, A. %A Al-Rasheid, K. A. S. %A Romeis, T. %A Hedrich, R. %D 2009 %J Proceedings of the National Academy of Sciences of the United States of America %N 50 %P 21425-21430 %R 10.1073/pnas.0912021106 %T Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair %U /brokenurl#<Go to ISI>://WOS:000272795300074 %V 106 %X In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.
• Promotes Tumor Induction by Modulating Pathogen Defense in. Lee, C. W.; Efetova, M.; Engelmann, J. C.; Kramell, R.; Wasternack, C.; Ludwig-Müller, J.; Hedrich, R.; Deeken, R. In Plant Cell, 21(9), pp. 2948–2962. 2009.
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  Agrobacterium tumefaciens causes crown gall disease by transferring and integrating bacterial DNA (T-DNA) into the plant genome. To examine the physiological changes and adaptations during Agrobacterium-induced tumor development, we compared the profiles of salicylic acid (SA), ethylene (ET), jasmonic acid (JA), and auxin (indole-3-acetic acid [IAA]) with changes in the Arabidopsis thaliana transcriptome. Our data indicate that host responses were much stronger toward the oncogenic strain C58 than to the disarmed strain GV3101 and that auxin acts as a key modulator of the Arabidopsis Agrobacterium interaction. At initiation of infection, elevated levels of IAA and ET were associated with the induction of host genes involved in IAA, but not ET signaling. After T-DNA integration, SA as well as IAA and ET accumulated, but JA did not. This did not correlate with SA-controlled pathogenesis-related gene expression in the host, although high SA levels in mutant plants prevented tumor development, while low levels promoted it. Our data are consistent with a scenario in which ET and later on SA control virulence of agrobacteria, whereas ET and auxin stimulate neovascularization during tumor formation. We suggest that crosstalk among IAA, ET, and SA balances pathogen defense launched by the host and tumor growth initiated by agrobacteria.

  @article{RN1131, abstract = {Agrobacterium tumefaciens causes crown gall disease by transferring and integrating bacterial DNA (T-DNA) into the plant genome. To examine the physiological changes and adaptations during Agrobacterium-induced tumor development, we compared the profiles of salicylic acid (SA), ethylene (ET), jasmonic acid (JA), and auxin (indole-3-acetic acid [IAA]) with changes in the Arabidopsis thaliana transcriptome. Our data indicate that host responses were much stronger toward the oncogenic strain C58 than to the disarmed strain GV3101 and that auxin acts as a key modulator of the Arabidopsis Agrobacterium interaction. At initiation of infection, elevated levels of IAA and ET were associated with the induction of host genes involved in IAA, but not ET signaling. After T-DNA integration, SA as well as IAA and ET accumulated, but JA did not. This did not correlate with SA-controlled pathogenesis-related gene expression in the host, although high SA levels in mutant plants prevented tumor development, while low levels promoted it. Our data are consistent with a scenario in which ET and later on SA control virulence of agrobacteria, whereas ET and auxin stimulate neovascularization during tumor formation. We suggest that crosstalk among IAA, ET, and SA balances pathogen defense launched by the host and tumor growth initiated by agrobacteria.}, author = {Lee, C. W. and Efetova, M. and Engelmann, J. C. and Kramell, R. and Wasternack, C. and Ludwig-Müller, J. and Hedrich, R. and Deeken, R.}, journal = {Plant Cell}, keywords = {salicylic-acid}, note = {512sp Times Cited:108 Cited References Count:77}, number = 9, pages = {2948-2962}, title = {Promotes Tumor Induction by Modulating Pathogen Defense in}, type = {Journal Article}, volume = 21, year = 2009 }

  %0 Journal Article %1 RN1131 %A Lee, C. W. %A Efetova, M. %A Engelmann, J. C. %A Kramell, R. %A Wasternack, C. %A Ludwig-Müller, J. %A Hedrich, R. %A Deeken, R. %D 2009 %J Plant Cell %N 9 %P 2948-2962 %R 10.1105/tpc.108.064576 %T Promotes Tumor Induction by Modulating Pathogen Defense in %U /brokenurl#<Go to ISI>://WOS:000271271200033 %V 21 %X Agrobacterium tumefaciens causes crown gall disease by transferring and integrating bacterial DNA (T-DNA) into the plant genome. To examine the physiological changes and adaptations during Agrobacterium-induced tumor development, we compared the profiles of salicylic acid (SA), ethylene (ET), jasmonic acid (JA), and auxin (indole-3-acetic acid [IAA]) with changes in the Arabidopsis thaliana transcriptome. Our data indicate that host responses were much stronger toward the oncogenic strain C58 than to the disarmed strain GV3101 and that auxin acts as a key modulator of the Arabidopsis Agrobacterium interaction. At initiation of infection, elevated levels of IAA and ET were associated with the induction of host genes involved in IAA, but not ET signaling. After T-DNA integration, SA as well as IAA and ET accumulated, but JA did not. This did not correlate with SA-controlled pathogenesis-related gene expression in the host, although high SA levels in mutant plants prevented tumor development, while low levels promoted it. Our data are consistent with a scenario in which ET and later on SA control virulence of agrobacteria, whereas ET and auxin stimulate neovascularization during tumor formation. We suggest that crosstalk among IAA, ET, and SA balances pathogen defense launched by the host and tumor growth initiated by agrobacteria.
• Salt stress affects xylem differentiation of grey poplar ( ). Escalante-Pérez, M.; Lautner, S.; Nehls, U.; Selle, A.; Teuber, M.; Schnitzler, J. P.; Teichmann, T.; Fayyaz, P.; Hartung, W.; Polle, A.; Fromm, J.; Hedrich, R.; Ache, P. In Planta, 229(2), pp. 299–309. 2009.
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  In this study the impact of salt stress on the physiology and wood structure of the salt-sensitive Populus x canescens was investigated. Two weeks of salt stress altered wood anatomy significantly. The xylem differentiation zone was reduced and the resulting vessels exhibited reduced lumina. To understand this phenomenon, ion composition, levels of corresponding transcripts and of the stress hormone ABA were analysed. With increasing sodium and chloride concentrations, a general reduction of potassium was found in roots and shoots, but not in leaves. Consequently, the corresponding K+ channel transcripts in roots favoured K+ release. The overall osmolarity in leaves was up to fourfold higher than in roots or shoots. Therefore, adjustment of the K+/Na+ balance seemed not to be required in leaves. Sodium increased gradually from roots to shoots and then to leaves indicating that sodium storage took place first in roots, then in shoots, and finally in leaves to protect photosynthesis from salt effects as long as possible. Since leaf abscisic acid levels markedly increased, stomatal closure seemed to limit CO2 uptake. As a consequence, diminished nutrient supply to the cambium in combination with lowered shoot K+ content led to decreased vessel lumina, and a reduction of the radial cambium was observed. Thus, xylem differentiation was curtailed and the development of full size vessels was impaired.

  @article{RN1134, abstract = {In this study the impact of salt stress on the physiology and wood structure of the salt-sensitive Populus x canescens was investigated. Two weeks of salt stress altered wood anatomy significantly. The xylem differentiation zone was reduced and the resulting vessels exhibited reduced lumina. To understand this phenomenon, ion composition, levels of corresponding transcripts and of the stress hormone ABA were analysed. With increasing sodium and chloride concentrations, a general reduction of potassium was found in roots and shoots, but not in leaves. Consequently, the corresponding K+ channel transcripts in roots favoured K+ release. The overall osmolarity in leaves was up to fourfold higher than in roots or shoots. Therefore, adjustment of the K+/Na+ balance seemed not to be required in leaves. Sodium increased gradually from roots to shoots and then to leaves indicating that sodium storage took place first in roots, then in shoots, and finally in leaves to protect photosynthesis from salt effects as long as possible. Since leaf abscisic acid levels markedly increased, stomatal closure seemed to limit CO2 uptake. As a consequence, diminished nutrient supply to the cambium in combination with lowered shoot K+ content led to decreased vessel lumina, and a reduction of the radial cambium was observed. Thus, xylem differentiation was curtailed and the development of full size vessels was impaired.}, author = {Escalante-Pérez, M. and Lautner, S. and Nehls, U. and Selle, A. and Teuber, M. and Schnitzler, J. P. and Teichmann, T. and Fayyaz, P. and Hartung, W. and Polle, A. and Fromm, J. and Hedrich, R. and Ache, P.}, journal = {Planta}, keywords = {aba}, note = {383sc Times Cited:61 Cited References Count:51}, number = 2, pages = {299-309}, title = {Salt stress affects xylem differentiation of grey poplar ( )}, type = {Journal Article}, volume = 229, year = 2009 }

  %0 Journal Article %1 RN1134 %A Escalante-Pérez, M. %A Lautner, S. %A Nehls, U. %A Selle, A. %A Teuber, M. %A Schnitzler, J. P. %A Teichmann, T. %A Fayyaz, P. %A Hartung, W. %A Polle, A. %A Fromm, J. %A Hedrich, R. %A Ache, P. %D 2009 %J Planta %N 2 %P 299-309 %R 10.1007/s00425-008-0829-7 %T Salt stress affects xylem differentiation of grey poplar ( ) %U /brokenurl#<Go to ISI>://WOS:000261692700007 %V 229 %X In this study the impact of salt stress on the physiology and wood structure of the salt-sensitive Populus x canescens was investigated. Two weeks of salt stress altered wood anatomy significantly. The xylem differentiation zone was reduced and the resulting vessels exhibited reduced lumina. To understand this phenomenon, ion composition, levels of corresponding transcripts and of the stress hormone ABA were analysed. With increasing sodium and chloride concentrations, a general reduction of potassium was found in roots and shoots, but not in leaves. Consequently, the corresponding K+ channel transcripts in roots favoured K+ release. The overall osmolarity in leaves was up to fourfold higher than in roots or shoots. Therefore, adjustment of the K+/Na+ balance seemed not to be required in leaves. Sodium increased gradually from roots to shoots and then to leaves indicating that sodium storage took place first in roots, then in shoots, and finally in leaves to protect photosynthesis from salt effects as long as possible. Since leaf abscisic acid levels markedly increased, stomatal closure seemed to limit CO2 uptake. As a consequence, diminished nutrient supply to the cambium in combination with lowered shoot K+ content led to decreased vessel lumina, and a reduction of the radial cambium was observed. Thus, xylem differentiation was curtailed and the development of full size vessels was impaired.
• Heteromeric AtKC1.AKT1 Channels in Roots Facilitate Growth under K -limiting Conditions. Geiger, D.; Becker, D.; Vosloh, D.; Gambale, F.; Palme, K.; Rehers, M.; Anschuetz, U.; Dreyer, I.; Kudla, J.; Hedrich, R. In Journal of Biological Chemistry, 284(32), pp. 21288–21295. 2009.
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  Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K+ uptake module consisting of the two K+ channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K+-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E-K a condition resulting in cellular K+ leakage. Although at submillimolar external potassium an intrinsic K+ sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K+ loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K+ uptake module to prevent K+ loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K+ dependence. Together, these two processes appear to represent a safety strategy preventing K+ loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K+ supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K+ uptake and K+ homeostasis when plants experience conditions of K+ limitation.

  @article{RN1133, abstract = {Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K+ uptake module consisting of the two K+ channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K+-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E-K a condition resulting in cellular K+ leakage. Although at submillimolar external potassium an intrinsic K+ sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K+ loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K+ uptake module to prevent K+ loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K+ dependence. Together, these two processes appear to represent a safety strategy preventing K+ loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K+ supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K+ uptake and K+ homeostasis when plants experience conditions of K+ limitation.}, author = {Geiger, D. and Becker, D. and Vosloh, D. and Gambale, F. and Palme, K. and Rehers, M. and Anschuetz, U. and Dreyer, I. and Kudla, J. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {potassium-transport}, note = {478cc Times Cited:132 Cited References Count:44}, number = 32, pages = {21288-21295}, title = {Heteromeric AtKC1.AKT1 Channels in Roots Facilitate Growth under K -limiting Conditions}, type = {Journal Article}, volume = 284, year = 2009 }

  %0 Journal Article %1 RN1133 %A Geiger, D. %A Becker, D. %A Vosloh, D. %A Gambale, F. %A Palme, K. %A Rehers, M. %A Anschuetz, U. %A Dreyer, I. %A Kudla, J. %A Hedrich, R. %D 2009 %J Journal of Biological Chemistry %N 32 %P 21288-21295 %R DOI 10.1074/jbc.M109.017574 %T Heteromeric AtKC1.AKT1 Channels in Roots Facilitate Growth under K -limiting Conditions %U /brokenurl#<Go to ISI>://WOS:000268564400023 %V 284 %X Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K+ uptake module consisting of the two K+ channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K+-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E-K a condition resulting in cellular K+ leakage. Although at submillimolar external potassium an intrinsic K+ sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K+ loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K+ uptake module to prevent K+ loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K+ dependence. Together, these two processes appear to represent a safety strategy preventing K+ loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K+ supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K+ uptake and K+ homeostasis when plants experience conditions of K+ limitation.
• The mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium. Beyhl, D.; Hörtensteiner, S.; Martinoia, E.; Farmer, E. E.; Fromm, J.; Marten, I.; Hedrich, R. In Plant Journal, 58(5), pp. 715–723. 2009.
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  The SV channel encoded by the TPC1 gene represents a Ca2+- and voltage-dependent vacuolar cation channel. Point mutation D454N within TPC1, named fou2 for fatty acid oxygenation upregulated 2, results in increased synthesis of the stress hormone jasmonate. As wounding causes Ca2+ signals and cytosolic Ca2+ is required for SV channel function, we here studied the Ca2+-dependent properties of this major vacuolar cation channel with Arabidopsis thaliana mesophyll vacuoles. In patch clamp measurements, wild-type and fou2 SV channels did not exhibit differences in cytosolic Ca2+ sensitivity and Ca2+, impermeability. K+ fluxes through wild-type TPC1 were reduced or even completely faded away when vacuolar Ca2+ reached the 0.1-mm level. The foul protein under these conditions, however, remained active. Thus, D454N seems to be part of a luminal Ca2+ recognition site. Thereby the SV channel mutant gains tolerance towards elevated luminal Ca2+. A three-fold higher vacuolar Ca/K ratio in the fou2 mutant relative to wild-type plants seems to indicate that fou2 can accumulate higher levels of vacuolar Ca2+ before SV channel activity vanishes and K+ homeostasis is impaired. In response to wounding fou2 plants might thus elicit strong vacuole-derived cytosolic Ca2+ signals resulting in overproduction of jasmonate.

  @article{RN1135, abstract = {The SV channel encoded by the TPC1 gene represents a Ca2+- and voltage-dependent vacuolar cation channel. Point mutation D454N within TPC1, named fou2 for fatty acid oxygenation upregulated 2, results in increased synthesis of the stress hormone jasmonate. As wounding causes Ca2+ signals and cytosolic Ca2+ is required for SV channel function, we here studied the Ca2+-dependent properties of this major vacuolar cation channel with Arabidopsis thaliana mesophyll vacuoles. In patch clamp measurements, wild-type and fou2 SV channels did not exhibit differences in cytosolic Ca2+ sensitivity and Ca2+, impermeability. K+ fluxes through wild-type TPC1 were reduced or even completely faded away when vacuolar Ca2+ reached the 0.1-mm level. The foul protein under these conditions, however, remained active. Thus, D454N seems to be part of a luminal Ca2+ recognition site. Thereby the SV channel mutant gains tolerance towards elevated luminal Ca2+. A three-fold higher vacuolar Ca/K ratio in the fou2 mutant relative to wild-type plants seems to indicate that fou2 can accumulate higher levels of vacuolar Ca2+ before SV channel activity vanishes and K+ homeostasis is impaired. In response to wounding fou2 plants might thus elicit strong vacuole-derived cytosolic Ca2+ signals resulting in overproduction of jasmonate.}, author = {Beyhl, D. and Hörtensteiner, S. and Martinoia, E. and Farmer, E. E. and Fromm, J. and Marten, I. and Hedrich, R.}, journal = {Plant Journal}, keywords = {two}, note = {473px Times Cited:96 Cited References Count:35}, number = 5, pages = {715-723}, title = {The mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium}, type = {Journal Article}, volume = 58, year = 2009 }

  %0 Journal Article %1 RN1135 %A Beyhl, D. %A Hörtensteiner, S. %A Martinoia, E. %A Farmer, E. E. %A Fromm, J. %A Marten, I. %A Hedrich, R. %D 2009 %J Plant Journal %N 5 %P 715-723 %R 10.1111/j.1365-313X.2009.03820.x %T The mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium %U /brokenurl#<Go to ISI>://WOS:000268221100001 %V 58 %X The SV channel encoded by the TPC1 gene represents a Ca2+- and voltage-dependent vacuolar cation channel. Point mutation D454N within TPC1, named fou2 for fatty acid oxygenation upregulated 2, results in increased synthesis of the stress hormone jasmonate. As wounding causes Ca2+ signals and cytosolic Ca2+ is required for SV channel function, we here studied the Ca2+-dependent properties of this major vacuolar cation channel with Arabidopsis thaliana mesophyll vacuoles. In patch clamp measurements, wild-type and fou2 SV channels did not exhibit differences in cytosolic Ca2+ sensitivity and Ca2+, impermeability. K+ fluxes through wild-type TPC1 were reduced or even completely faded away when vacuolar Ca2+ reached the 0.1-mm level. The foul protein under these conditions, however, remained active. Thus, D454N seems to be part of a luminal Ca2+ recognition site. Thereby the SV channel mutant gains tolerance towards elevated luminal Ca2+. A three-fold higher vacuolar Ca/K ratio in the fou2 mutant relative to wild-type plants seems to indicate that fou2 can accumulate higher levels of vacuolar Ca2+ before SV channel activity vanishes and K+ homeostasis is impaired. In response to wounding fou2 plants might thus elicit strong vacuole-derived cytosolic Ca2+ signals resulting in overproduction of jasmonate.

• Loss of the vacuolar cation channel, AtTPC1, does not impair Ca signals induced by abiotic and biotic stresses. Ranf, S.; Wünnenberg, P.; Lee, J.; Becker, D.; Dunkel, M.; Hedrich, R.; Scheel, D.; Dietrich, P. In Plant Journal, 53(2), pp. 287–299. 2008.
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  The putative two-pore Ca2+ channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K+-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca2+-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca2+-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO2-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K+-, and Ca2+-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca2+ entry into the cytosol. Ca2+ responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca2+ signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca2+ concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca2+-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca2+-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca2+ homeostasis.

  @article{RN1137, abstract = {The putative two-pore Ca2+ channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K+-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca2+-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca2+-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO2-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K+-, and Ca2+-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca2+ entry into the cytosol. Ca2+ responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca2+ signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca2+ concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca2+-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca2+-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca2+ homeostasis.}, author = {Ranf, S. and Wünnenberg, P. and Lee, J. and Becker, D. and Dunkel, M. and Hedrich, R. and Scheel, D. and Dietrich, P.}, journal = {Plant Journal}, keywords = {channel}, note = {247va Times Cited:141 Cited References Count:66}, number = 2, pages = {287-299}, title = {Loss of the vacuolar cation channel, AtTPC1, does not impair Ca signals induced by abiotic and biotic stresses}, type = {Journal Article}, volume = 53, year = 2008 }

  %0 Journal Article %1 RN1137 %A Ranf, S. %A Wünnenberg, P. %A Lee, J. %A Becker, D. %A Dunkel, M. %A Hedrich, R. %A Scheel, D. %A Dietrich, P. %D 2008 %J Plant Journal %N 2 %P 287-299 %R 10.1111/j.1365-313X.2007.03342.x %T Loss of the vacuolar cation channel, AtTPC1, does not impair Ca signals induced by abiotic and biotic stresses %U /brokenurl#<Go to ISI>://WOS:000252109500008 %V 53 %X The putative two-pore Ca2+ channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K+-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca2+-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca2+-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO2-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K+-, and Ca2+-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca2+ entry into the cytosol. Ca2+ responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca2+ signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca2+ concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca2+-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca2+-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca2+ homeostasis.
• Functional and physiological characterization of a novel tonoplast-localized transporter for -inositol. Schneider, S.; Beyhl, D.; Hedrich, R.; Sauer, N. In Plant Cell, 20(4), pp. 1073–1087. 2008.
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  Arabidopsis thaliana INOSITOL TRANSPORTER1 (INT1) is a member of a small gene family with only three more genes (INT2 to INT4). INT2 and INT4 were shown to encode plasma membrane-localized transporters for different inositol epimers, and INT3 was characterized as a pseudogene. Here, we present the functional and physiological characterization of the INT1 protein, analyses of the tissue-specific expression of the INT1 gene, and analyses of phenotypic differences observed between wild-type plants and mutant lines carrying the int1.1 and int1.2 alleles. INT1 is a ubiquitously expressed gene, and Arabidopsis lines with T-DNA insertions in INT1 showed increased intracellular myo-inositol concentrations and reduced root growth. In Arabidopsis, tobacco (Nicotiana tabacum), and Saccharomyces cerevisiae, fusions of the green fluorescent protein to the C terminus of INT1 were targeted to the tonoplast membranes. Finally, patch-clamp analyses were performed on vacuoles from wild-type plants and from both int1 mutant lines to study the transport properties of INT1 at the tonoplast. In summary, the presented molecular, physiological, and functional studies demonstrate that INT1 is a tonoplast-localized H+/inositol symporter that mediates the efflux of inositol that is generated during the degradation of inositol-containing compounds in the vacuolar lumen.

  @article{RN1136, abstract = {Arabidopsis thaliana INOSITOL TRANSPORTER1 (INT1) is a member of a small gene family with only three more genes (INT2 to INT4). INT2 and INT4 were shown to encode plasma membrane-localized transporters for different inositol epimers, and INT3 was characterized as a pseudogene. Here, we present the functional and physiological characterization of the INT1 protein, analyses of the tissue-specific expression of the INT1 gene, and analyses of phenotypic differences observed between wild-type plants and mutant lines carrying the int1.1 and int1.2 alleles. INT1 is a ubiquitously expressed gene, and Arabidopsis lines with T-DNA insertions in INT1 showed increased intracellular myo-inositol concentrations and reduced root growth. In Arabidopsis, tobacco (Nicotiana tabacum), and Saccharomyces cerevisiae, fusions of the green fluorescent protein to the C terminus of INT1 were targeted to the tonoplast membranes. Finally, patch-clamp analyses were performed on vacuoles from wild-type plants and from both int1 mutant lines to study the transport properties of INT1 at the tonoplast. In summary, the presented molecular, physiological, and functional studies demonstrate that INT1 is a tonoplast-localized H+/inositol symporter that mediates the efflux of inositol that is generated during the degradation of inositol-containing compounds in the vacuolar lumen.}, author = {Schneider, S. and Beyhl, D. and Hedrich, R. and Sauer, N.}, journal = {Plant Cell}, keywords = {h+-symport}, note = {308ut Times Cited:70 Cited References Count:86}, number = 4, pages = {1073-1087}, title = {Functional and physiological characterization of a novel tonoplast-localized transporter for -inositol}, type = {Journal Article}, volume = 20, year = 2008 }

  %0 Journal Article %1 RN1136 %A Schneider, S. %A Beyhl, D. %A Hedrich, R. %A Sauer, N. %D 2008 %J Plant Cell %N 4 %P 1073-1087 %R 10.1105/tpc.107.055632 %T Functional and physiological characterization of a novel tonoplast-localized transporter for -inositol %U /brokenurl#<Go to ISI>://WOS:000256416200022 %V 20 %X Arabidopsis thaliana INOSITOL TRANSPORTER1 (INT1) is a member of a small gene family with only three more genes (INT2 to INT4). INT2 and INT4 were shown to encode plasma membrane-localized transporters for different inositol epimers, and INT3 was characterized as a pseudogene. Here, we present the functional and physiological characterization of the INT1 protein, analyses of the tissue-specific expression of the INT1 gene, and analyses of phenotypic differences observed between wild-type plants and mutant lines carrying the int1.1 and int1.2 alleles. INT1 is a ubiquitously expressed gene, and Arabidopsis lines with T-DNA insertions in INT1 showed increased intracellular myo-inositol concentrations and reduced root growth. In Arabidopsis, tobacco (Nicotiana tabacum), and Saccharomyces cerevisiae, fusions of the green fluorescent protein to the C terminus of INT1 were targeted to the tonoplast membranes. Finally, patch-clamp analyses were performed on vacuoles from wild-type plants and from both int1 mutant lines to study the transport properties of INT1 at the tonoplast. In summary, the presented molecular, physiological, and functional studies demonstrate that INT1 is a tonoplast-localized H+/inositol symporter that mediates the efflux of inositol that is generated during the degradation of inositol-containing compounds in the vacuolar lumen.
• The use of voltage-sensitive dyes to monitor signal-induced changes in membrane potential-ABA triggered membrane depolarization in guard cells. Konrad, K. R.; Hedrich, R. In Plant Journal, 55(1), pp. 161–173. 2008.
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  The plant membrane potential reports on the activity of electrogenic plasma membrane transport processes. The membrane potential is widely used to report for early events associated with changes in light regime, hormone action or pathogen attacks. The membrane potentials of guard cells can be precisely measured with microelectrodes, but this technique is not well suited for rapid screens with large sample numbers. To provide the basis for large-scale membrane potential recordings, we took advantage of voltage-sensitive dyes. Using the fluorescent dyes bis-(1,3-dibutylbarbituric acid)-trimethine oxonol (DiBAC(4)(3)) and the FLIPR Membrane Potential Assay Kit (FMP) dye we followed changes in the membrane potential in guard cells and vacuoles. Based on the fluorescence of DiBAC(4)(3) a method was established for quantification of the membrane potential in guard cell protoplasts which should be considered as an excellent system for high-throughput screening of plant cells. In the absence of abscisic acid (ABA), one-third of the guard cell protoplast population spontaneously oscillated for periods of 5-6 min. Upon application of ABA the hyperpolarized fraction (similar to 50%) of the guard cell protoplast population depolarized within a few minutes. Membrane potential oscillations were terminated by ABA. Oscillations and ABA responses were found in cell populations with active anion channels. Thus time- and voltage-dependent anion channels likely represent the ABA-sensitive conductance and part of the membrane potential oscillator. The suitability of membrane potential dyes was tested on vacuoles, too. Dye-based vacuolar membrane polarization was monitored upon ATP exposure. We conclude that voltage-sensitive dyes provide an excellent tool for the study of changes in the membrane potential in vacuole as well as guard cell populations.

  @article{RN1141, abstract = {The plant membrane potential reports on the activity of electrogenic plasma membrane transport processes. The membrane potential is widely used to report for early events associated with changes in light regime, hormone action or pathogen attacks. The membrane potentials of guard cells can be precisely measured with microelectrodes, but this technique is not well suited for rapid screens with large sample numbers. To provide the basis for large-scale membrane potential recordings, we took advantage of voltage-sensitive dyes. Using the fluorescent dyes bis-(1,3-dibutylbarbituric acid)-trimethine oxonol (DiBAC(4)(3)) and the FLIPR Membrane Potential Assay Kit (FMP) dye we followed changes in the membrane potential in guard cells and vacuoles. Based on the fluorescence of DiBAC(4)(3) a method was established for quantification of the membrane potential in guard cell protoplasts which should be considered as an excellent system for high-throughput screening of plant cells. In the absence of abscisic acid (ABA), one-third of the guard cell protoplast population spontaneously oscillated for periods of 5-6 min. Upon application of ABA the hyperpolarized fraction (similar to 50%) of the guard cell protoplast population depolarized within a few minutes. Membrane potential oscillations were terminated by ABA. Oscillations and ABA responses were found in cell populations with active anion channels. Thus time- and voltage-dependent anion channels likely represent the ABA-sensitive conductance and part of the membrane potential oscillator. The suitability of membrane potential dyes was tested on vacuoles, too. Dye-based vacuolar membrane polarization was monitored upon ATP exposure. We conclude that voltage-sensitive dyes provide an excellent tool for the study of changes in the membrane potential in vacuole as well as guard cell populations.}, author = {Konrad, K. R. and Hedrich, R.}, journal = {Plant Journal}, keywords = {potential}, note = {325ev Times Cited:40 Cited References Count:69}, number = 1, pages = {161-173}, title = {The use of voltage-sensitive dyes to monitor signal-induced changes in membrane potential-ABA triggered membrane depolarization in guard cells}, type = {Journal Article}, volume = 55, year = 2008 }

  %0 Journal Article %1 RN1141 %A Konrad, K. R. %A Hedrich, R. %D 2008 %J Plant Journal %N 1 %P 161-173 %R 10.1111/j.1365-313X.2008.03498.x %T The use of voltage-sensitive dyes to monitor signal-induced changes in membrane potential-ABA triggered membrane depolarization in guard cells %U /brokenurl#<Go to ISI>://WOS:000257572300013 %V 55 %X The plant membrane potential reports on the activity of electrogenic plasma membrane transport processes. The membrane potential is widely used to report for early events associated with changes in light regime, hormone action or pathogen attacks. The membrane potentials of guard cells can be precisely measured with microelectrodes, but this technique is not well suited for rapid screens with large sample numbers. To provide the basis for large-scale membrane potential recordings, we took advantage of voltage-sensitive dyes. Using the fluorescent dyes bis-(1,3-dibutylbarbituric acid)-trimethine oxonol (DiBAC(4)(3)) and the FLIPR Membrane Potential Assay Kit (FMP) dye we followed changes in the membrane potential in guard cells and vacuoles. Based on the fluorescence of DiBAC(4)(3) a method was established for quantification of the membrane potential in guard cell protoplasts which should be considered as an excellent system for high-throughput screening of plant cells. In the absence of abscisic acid (ABA), one-third of the guard cell protoplast population spontaneously oscillated for periods of 5-6 min. Upon application of ABA the hyperpolarized fraction (similar to 50%) of the guard cell protoplast population depolarized within a few minutes. Membrane potential oscillations were terminated by ABA. Oscillations and ABA responses were found in cell populations with active anion channels. Thus time- and voltage-dependent anion channels likely represent the ABA-sensitive conductance and part of the membrane potential oscillator. The suitability of membrane potential dyes was tested on vacuoles, too. Dye-based vacuolar membrane polarization was monitored upon ATP exposure. We conclude that voltage-sensitive dyes provide an excellent tool for the study of changes in the membrane potential in vacuole as well as guard cell populations.
• Identification of phloem RNAs provides a search criterion for phloem-based transcripts hidden in complex datasets of microarray experiments. Deeken, R.; Ache, P.; Kajahn, I.; Klinkenberg, J.; Bringmann, G.; Hedrich, R. In Plant Journal, 55(5), pp. 746–759. 2008.
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  Phloem-mobile signals play a major role in plant nutrition, development and communication. In the latter context, phloem-mobile RNAs have been associated with signalling between plant tissues. In this study, we focused on the identification of transcripts in the shoot phloem of the model plant Arabidopsis thaliana. To isolate transcripts expressed in phloem parenchyma cells and in companion cell-sieve element complexes, we used laser microdissection coupled to laser pressure catapulting (LMPC). Mobile transcripts in sieve elements were isolated from leaf phloem exudates. After optimization of sampling and fixation, RNA of high quality was isolated from both sources. The modifications to the RNA amplification procedure described here were well suited to production of RNA of sufficient yield and quality for microarray experiments. Microarrays hybridized with LMPC-derived phloem tissue or phloem sap RNA allowed differentiation between phloem-expressed and mobile transcript species. Using this set of phloem transcripts and comparing them with microarrays derived from databases of light, hormone and nutrient treatment experiments, we identified phloem-derived RNAs as mobile, potential long-distance signals. Our dataset thus provides a search criterion for phloem-based signals hidden in the complex datasets of microarray experiments. The availability of these comprehensive phloem transcript profiles will facilitate reverse-genetic studies and forward-genetic screens for phloem and long-distance RNA signalling mutants.

  @article{RN1143, abstract = {Phloem-mobile signals play a major role in plant nutrition, development and communication. In the latter context, phloem-mobile RNAs have been associated with signalling between plant tissues. In this study, we focused on the identification of transcripts in the shoot phloem of the model plant Arabidopsis thaliana. To isolate transcripts expressed in phloem parenchyma cells and in companion cell-sieve element complexes, we used laser microdissection coupled to laser pressure catapulting (LMPC). Mobile transcripts in sieve elements were isolated from leaf phloem exudates. After optimization of sampling and fixation, RNA of high quality was isolated from both sources. The modifications to the RNA amplification procedure described here were well suited to production of RNA of sufficient yield and quality for microarray experiments. Microarrays hybridized with LMPC-derived phloem tissue or phloem sap RNA allowed differentiation between phloem-expressed and mobile transcript species. Using this set of phloem transcripts and comparing them with microarrays derived from databases of light, hormone and nutrient treatment experiments, we identified phloem-derived RNAs as mobile, potential long-distance signals. Our dataset thus provides a search criterion for phloem-based signals hidden in the complex datasets of microarray experiments. The availability of these comprehensive phloem transcript profiles will facilitate reverse-genetic studies and forward-genetic screens for phloem and long-distance RNA signalling mutants.}, author = {Deeken, R. and Ache, P. and Kajahn, I. and Klinkenberg, J. and Bringmann, G. and Hedrich, R.}, journal = {Plant Journal}, keywords = {arabidopsis}, note = {339ss Times Cited:136 Cited References Count:56}, number = 5, pages = {746-759}, title = {Identification of phloem RNAs provides a search criterion for phloem-based transcripts hidden in complex datasets of microarray experiments}, type = {Journal Article}, volume = 55, year = 2008 }

  %0 Journal Article %1 RN1143 %A Deeken, R. %A Ache, P. %A Kajahn, I. %A Klinkenberg, J. %A Bringmann, G. %A Hedrich, R. %D 2008 %J Plant Journal %N 5 %P 746-759 %R 10.1111/j.1365-313X.2008.03555.x %T Identification of phloem RNAs provides a search criterion for phloem-based transcripts hidden in complex datasets of microarray experiments %U /brokenurl#<Go to ISI>://WOS:000258598200003 %V 55 %X Phloem-mobile signals play a major role in plant nutrition, development and communication. In the latter context, phloem-mobile RNAs have been associated with signalling between plant tissues. In this study, we focused on the identification of transcripts in the shoot phloem of the model plant Arabidopsis thaliana. To isolate transcripts expressed in phloem parenchyma cells and in companion cell-sieve element complexes, we used laser microdissection coupled to laser pressure catapulting (LMPC). Mobile transcripts in sieve elements were isolated from leaf phloem exudates. After optimization of sampling and fixation, RNA of high quality was isolated from both sources. The modifications to the RNA amplification procedure described here were well suited to production of RNA of sufficient yield and quality for microarray experiments. Microarrays hybridized with LMPC-derived phloem tissue or phloem sap RNA allowed differentiation between phloem-expressed and mobile transcript species. Using this set of phloem transcripts and comparing them with microarrays derived from databases of light, hormone and nutrient treatment experiments, we identified phloem-derived RNAs as mobile, potential long-distance signals. Our dataset thus provides a search criterion for phloem-based signals hidden in the complex datasets of microarray experiments. The availability of these comprehensive phloem transcript profiles will facilitate reverse-genetic studies and forward-genetic screens for phloem and long-distance RNA signalling mutants.
• Silencing of MPK4 impairs CO -induced stomatal closure, activation of anion channels and cytosolic Ca signals in guard cells. Marten, H.; Hyun, T.; Gomi, K.; Seo, S.; Hedrich, R.; Roelfsema, M. R. G. In Plant Journal, 55(4), pp. 698–708. 2008.
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  Light-induced stomatal opening in C3 and C4 plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on photosyntheticaly active radiation (PAR). Here, the role of NtMPK4 in light-induced stomatal opening was studied, as silencing of this MAP kinase stimulates stomatal opening. Stomata of NtMPK4-silenced plants do not close in elevated atmospheric CO2, and show a reduced response to PAR. However, stomatal closure can still be induced by abscisic acid. Measurements using multi-barrelled intracellular micro-electrodes showed that CO2 activates plasma membrane anion channels in wild-type Nicotiana tabacum guard cells, but not in NtMPK4-silenced cells. Anion channels were also activated in wild-type guard cells after switching off PAR. In approximately half of these cells, activation of anion channels was accompanied by an increase in the cytosolic free Ca2+ concentration. The activity of anion channels was higher in cells showing a parallel increase in cytosolic Ca2+ than in those with steady Ca2+ levels. Both the darkness-induced anion channel activation and Ca2+ signals were repressed in NtMPK4-silenced guard cells. These data show that CO2 and darkness can activate anion channels in a Ca2+-independent manner, but the anion channel activity is enhanced by parallel increases in the cytosolic Ca2+ concentration. NtMPK4 plays an essential role in CO2- and darkness-induced activation of guard-cell anion channels, through Ca2+-independent as well as Ca2+-dependent signalling pathways.

  @article{RN1138, abstract = {Light-induced stomatal opening in C3 and C4 plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on photosyntheticaly active radiation (PAR). Here, the role of NtMPK4 in light-induced stomatal opening was studied, as silencing of this MAP kinase stimulates stomatal opening. Stomata of NtMPK4-silenced plants do not close in elevated atmospheric CO2, and show a reduced response to PAR. However, stomatal closure can still be induced by abscisic acid. Measurements using multi-barrelled intracellular micro-electrodes showed that CO2 activates plasma membrane anion channels in wild-type Nicotiana tabacum guard cells, but not in NtMPK4-silenced cells. Anion channels were also activated in wild-type guard cells after switching off PAR. In approximately half of these cells, activation of anion channels was accompanied by an increase in the cytosolic free Ca2+ concentration. The activity of anion channels was higher in cells showing a parallel increase in cytosolic Ca2+ than in those with steady Ca2+ levels. Both the darkness-induced anion channel activation and Ca2+ signals were repressed in NtMPK4-silenced guard cells. These data show that CO2 and darkness can activate anion channels in a Ca2+-independent manner, but the anion channel activity is enhanced by parallel increases in the cytosolic Ca2+ concentration. NtMPK4 plays an essential role in CO2- and darkness-induced activation of guard-cell anion channels, through Ca2+-independent as well as Ca2+-dependent signalling pathways.}, author = {Marten, H. and Hyun, T. and Gomi, K. and Seo, S. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Plant Journal}, keywords = {co2-response}, note = {335ju Times Cited:62 Cited References Count:48}, number = 4, pages = {698-708}, title = {Silencing of MPK4 impairs CO -induced stomatal closure, activation of anion channels and cytosolic Ca signals in guard cells}, type = {Journal Article}, volume = 55, year = 2008 }

  %0 Journal Article %1 RN1138 %A Marten, H. %A Hyun, T. %A Gomi, K. %A Seo, S. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2008 %J Plant Journal %N 4 %P 698-708 %R 10.1111/j.1365-313X.2008.03542.x %T Silencing of MPK4 impairs CO -induced stomatal closure, activation of anion channels and cytosolic Ca signals in guard cells %U /brokenurl#<Go to ISI>://WOS:000258287700013 %V 55 %X Light-induced stomatal opening in C3 and C4 plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on photosyntheticaly active radiation (PAR). Here, the role of NtMPK4 in light-induced stomatal opening was studied, as silencing of this MAP kinase stimulates stomatal opening. Stomata of NtMPK4-silenced plants do not close in elevated atmospheric CO2, and show a reduced response to PAR. However, stomatal closure can still be induced by abscisic acid. Measurements using multi-barrelled intracellular micro-electrodes showed that CO2 activates plasma membrane anion channels in wild-type Nicotiana tabacum guard cells, but not in NtMPK4-silenced cells. Anion channels were also activated in wild-type guard cells after switching off PAR. In approximately half of these cells, activation of anion channels was accompanied by an increase in the cytosolic free Ca2+ concentration. The activity of anion channels was higher in cells showing a parallel increase in cytosolic Ca2+ than in those with steady Ca2+ levels. Both the darkness-induced anion channel activation and Ca2+ signals were repressed in NtMPK4-silenced guard cells. These data show that CO2 and darkness can activate anion channels in a Ca2+-independent manner, but the anion channel activity is enhanced by parallel increases in the cytosolic Ca2+ concentration. NtMPK4 plays an essential role in CO2- and darkness-induced activation of guard-cell anion channels, through Ca2+-independent as well as Ca2+-dependent signalling pathways.
• Stringent control of cytoplasmic Ca in guard cells of intact plants compared to their counterparts in epidermal strips or guard cell protoplasts. Levchenko, V.; Guinot, D. R.; Klein, M.; Roelfsema, M. R. G.; Hedrich, R.; Dietrich, P. In Protoplasma, 233(1-2), pp. 61–72. 2008.
  • [ Abstract ]
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  Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca2+ signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca2+ homeostasis and stimulus-induced Ca2+ signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca2+-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca2+ concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca2+ concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca2+ concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca2+ concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca2+ concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.

  @article{RN1139, abstract = {Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca2+ signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca2+ homeostasis and stimulus-induced Ca2+ signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca2+-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca2+ concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca2+ concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca2+ concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca2+ concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca2+ concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.}, author = {Levchenko, V. and Guinot, D. R. and Klein, M. and Roelfsema, M. R. G. and Hedrich, R. and Dietrich, P.}, journal = {Protoplasma}, keywords = {calcium}, note = {348ch Times Cited:11 Cited References Count:53}, number = {1-2}, pages = {61-72}, title = {Stringent control of cytoplasmic Ca in guard cells of intact plants compared to their counterparts in epidermal strips or guard cell protoplasts}, type = {Journal Article}, volume = 233, year = 2008 }

  %0 Journal Article %1 RN1139 %A Levchenko, V. %A Guinot, D. R. %A Klein, M. %A Roelfsema, M. R. G. %A Hedrich, R. %A Dietrich, P. %D 2008 %J Protoplasma %N 1-2 %P 61-72 %R 10.1007/s00709-008-0307-x %T Stringent control of cytoplasmic Ca in guard cells of intact plants compared to their counterparts in epidermal strips or guard cell protoplasts %U /brokenurl#<Go to ISI>://WOS:000259188100007 %V 233 %X Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca2+ signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca2+ homeostasis and stimulus-induced Ca2+ signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca2+-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca2+ concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca2+ concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca2+ concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca2+ concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca2+ concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.
• Targeting of Vacuolar Membrane Localized Members of the TPK Channel Family. Dunkel, M.; Latz, A.; Schumacher, K.; Wüller, T.; Becker, D.; Hedrich, R. In Molecular Plant, 1(6), pp. 938–949. 2008.
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  Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K+-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (IDLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.

  @article{RN1142, abstract = {Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K+-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (IDLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.}, author = {Dunkel, M. and Latz, A. and Schumacher, K. and Wüller, T. and Becker, D. and Hedrich, R.}, journal = {Molecular Plant}, keywords = {protein}, note = {400hg Times Cited:67 Cited References Count:82}, number = 6, pages = {938-949}, title = {Targeting of Vacuolar Membrane Localized Members of the TPK Channel Family}, type = {Journal Article}, volume = 1, year = 2008 }

  %0 Journal Article %1 RN1142 %A Dunkel, M. %A Latz, A. %A Schumacher, K. %A Wüller, T. %A Becker, D. %A Hedrich, R. %D 2008 %J Molecular Plant %N 6 %P 938-949 %R 10.1093/mp/ssn064 %T Targeting of Vacuolar Membrane Localized Members of the TPK Channel Family %U /brokenurl#<Go to ISI>://WOS:000262858000006 %V 1 %X Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K+-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (IDLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.
• TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins (vol 52, pg 449, 2007). Latz, A.; Becker, D.; Hekman, M.; Müller, T.; Beyhl, D.; Marten, I.; Eing, C.; Bihler, H.; Fischer, A.; Dunkel, M.; Bertl, A.; Rapp, U. R.; Hedrich, R. In Plant Journal, 54(5), pp. 963–963. 2008.
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  @article{RN1140, author = {Latz, A. and Becker, D. and Hekman, M. and Müller, T. and Beyhl, D. and Marten, I. and Eing, C. and Bihler, H. and Fischer, A. and Dunkel, M. and Bertl, A. and Rapp, U. R. and Hedrich, R.}, journal = {Plant Journal}, keywords = {myOwn}, note = {304xk Times Cited:1 Cited References Count:1}, number = 5, pages = {963-963}, title = {TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins (vol 52, pg 449, 2007)}, type = {Journal Article}, volume = 54, year = 2008 }

  %0 Journal Article %1 RN1140 %A Latz, A. %A Becker, D. %A Hekman, M. %A Müller, T. %A Beyhl, D. %A Marten, I. %A Eing, C. %A Bihler, H. %A Fischer, A. %A Dunkel, M. %A Bertl, A. %A Rapp, U. R. %A Hedrich, R. %D 2008 %J Plant Journal %N 5 %P 963-963 %R 10.1111/j.1365-313X.2008.03537.x %T TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins (vol 52, pg 449, 2007) %U /brokenurl#<Go to ISI>://WOS:000256142200015 %V 54

• TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins. Latz, A.; Becker, D.; Hekman, M.; Müeller, T.; Beyhl, D.; Marten, I.; Eing, C.; Fischer, A.; Dunkel, M.; Bertl, A.; Rapp, U. R.; Hedrich, R. In Plant Journal, 52(3), pp. 449–459. 2007.
  • [ Abstract ]
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  The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K+ channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca2+-activated K+ channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca2+- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.

  @article{RN1151, abstract = {The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K+ channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca2+-activated K+ channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca2+- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.}, author = {Latz, A. and Becker, D. and Hekman, M. and Müeller, T. and Beyhl, D. and Marten, I. and Eing, C. and Fischer, A. and Dunkel, M. and Bertl, A. and Rapp, U. R. and Hedrich, R.}, journal = {Plant Journal}, keywords = {channel}, note = {222ln Times Cited:115 Cited References Count:45}, number = 3, pages = {449-459}, title = {TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins}, type = {Journal Article}, volume = 52, year = 2007 }

  %0 Journal Article %1 RN1151 %A Latz, A. %A Becker, D. %A Hekman, M. %A Müeller, T. %A Beyhl, D. %A Marten, I. %A Eing, C. %A Fischer, A. %A Dunkel, M. %A Bertl, A. %A Rapp, U. R. %A Hedrich, R. %D 2007 %J Plant Journal %N 3 %P 449-459 %R 10.1111/j.1365-313X.2007.03255.x %T TPK1, a Ca -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins %U /brokenurl#<Go to ISI>://WOS:000250298600005 %V 52 %X The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K+ channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca2+-activated K+ channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca2+- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.
• Foliar water supply of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact on pressure bomb measurements. Zimmermann, D.; Westhoff, M.; Zimmermann, G.; Gessner, P.; Gessner, A.; Wegner, L. H.; Rokitta, M.; Ache, P.; Schneider, H.; Vasquez, J. A.; Kruck, W.; Shirley, S.; Jakob, P.; Hedrich, R.; Bentrup, F. W.; Bamberg, E.; Zimmermann, U. In Protoplasma, 232(1-2), pp. 10–34. 2007.
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  The water supply to leaves of 25 to 60 m tall trees (including high-salinity-tolerant ones) was studied. The filling status of the xylem vessels was determined by xylem sap extraction (using jet-discharge, gravity-discharge, and centrifugation) and by H-1 nuclear magnetic resonance imaging of wood pieces. Simultaneously, pressure bomb experiments were performed along the entire trunk of the trees up to a height of 57 m. Clear-cut evidence was found that the balancing pressure (P-b) values of leafy twigs were dictated by the ambient relative humidity rather than by height. Refilling of xylem vessels of apical leaves (branches) obviously mainly occurred via moisture uptake from the atmosphere. These findings could be traced back to the hydration and rehydration of mucilage layers on the leaf surfaces and/or of epistomatal mucilage plugs. Xylem vessels also contained mucilage. Mucilage formation was apparently enforced by water stress. The observed mucilage-based foliar water uptake and humidity dependency of the P-b values are at variance with the cohesion-tension theory and with the hypothesis that P-b measurements yield information about the relationships between xylem pressure gradients and height.

  @article{RN1144, abstract = {The water supply to leaves of 25 to 60 m tall trees (including high-salinity-tolerant ones) was studied. The filling status of the xylem vessels was determined by xylem sap extraction (using jet-discharge, gravity-discharge, and centrifugation) and by H-1 nuclear magnetic resonance imaging of wood pieces. Simultaneously, pressure bomb experiments were performed along the entire trunk of the trees up to a height of 57 m. Clear-cut evidence was found that the balancing pressure (P-b) values of leafy twigs were dictated by the ambient relative humidity rather than by height. Refilling of xylem vessels of apical leaves (branches) obviously mainly occurred via moisture uptake from the atmosphere. These findings could be traced back to the hydration and rehydration of mucilage layers on the leaf surfaces and/or of epistomatal mucilage plugs. Xylem vessels also contained mucilage. Mucilage formation was apparently enforced by water stress. The observed mucilage-based foliar water uptake and humidity dependency of the P-b values are at variance with the cohesion-tension theory and with the hypothesis that P-b measurements yield information about the relationships between xylem pressure gradients and height.}, author = {Zimmermann, D. and Westhoff, M. and Zimmermann, G. and Gessner, P. and Gessner, A. and Wegner, L. H. and Rokitta, M. and Ache, P. and Schneider, H. and Vasquez, J. A. and Kruck, W. and Shirley, S. and Jakob, P. and Hedrich, R. and Bentrup, F. W. and Bamberg, E. and Zimmermann, U.}, journal = {Protoplasma}, keywords = {resonance}, note = {249jm Times Cited:45 Cited References Count:43}, number = {1-2}, pages = {10-34}, title = {Foliar water supply of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact on pressure bomb measurements}, type = {Journal Article}, volume = 232, year = 2007 }

  %0 Journal Article %1 RN1144 %A Zimmermann, D. %A Westhoff, M. %A Zimmermann, G. %A Gessner, P. %A Gessner, A. %A Wegner, L. H. %A Rokitta, M. %A Ache, P. %A Schneider, H. %A Vasquez, J. A. %A Kruck, W. %A Shirley, S. %A Jakob, P. %A Hedrich, R. %A Bentrup, F. W. %A Bamberg, E. %A Zimmermann, U. %D 2007 %J Protoplasma %N 1-2 %P 10-34 %R 10.1007/s00709-007-0279-2 %T Foliar water supply of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact on pressure bomb measurements %U /brokenurl#<Go to ISI>://WOS:000252224200002 %V 232 %X The water supply to leaves of 25 to 60 m tall trees (including high-salinity-tolerant ones) was studied. The filling status of the xylem vessels was determined by xylem sap extraction (using jet-discharge, gravity-discharge, and centrifugation) and by H-1 nuclear magnetic resonance imaging of wood pieces. Simultaneously, pressure bomb experiments were performed along the entire trunk of the trees up to a height of 57 m. Clear-cut evidence was found that the balancing pressure (P-b) values of leafy twigs were dictated by the ambient relative humidity rather than by height. Refilling of xylem vessels of apical leaves (branches) obviously mainly occurred via moisture uptake from the atmosphere. These findings could be traced back to the hydration and rehydration of mucilage layers on the leaf surfaces and/or of epistomatal mucilage plugs. Xylem vessels also contained mucilage. Mucilage formation was apparently enforced by water stress. The observed mucilage-based foliar water uptake and humidity dependency of the P-b values are at variance with the cohesion-tension theory and with the hypothesis that P-b measurements yield information about the relationships between xylem pressure gradients and height.
• AKT2 subunits constitute a pH- and Ca -sensitive inward rectifying K channel. Latz, A.; Ivashikina, N.; Fischer, S.; Ache, P.; Sano, T.; Becker, D.; Deeken, R.; Hedrich, R. In Planta, 225(5), pp. 1179–1191. 2007.
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  Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.

  @article{RN1150, abstract = {Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.}, author = {Latz, A. and Ivashikina, N. and Fischer, S. and Ache, P. and Sano, T. and Becker, D. and Deeken, R. and Hedrich, R.}, journal = {Planta}, keywords = {agrobacterium}, note = {147mg Times Cited:28 Cited References Count:49}, number = 5, pages = {1179-1191}, title = {AKT2 subunits constitute a pH- and Ca -sensitive inward rectifying K channel}, type = {Journal Article}, volume = 225, year = 2007 }

  %0 Journal Article %1 RN1150 %A Latz, A. %A Ivashikina, N. %A Fischer, S. %A Ache, P. %A Sano, T. %A Becker, D. %A Deeken, R. %A Hedrich, R. %D 2007 %J Planta %N 5 %P 1179-1191 %R 10.1007/s00425-006-0428-4 %T AKT2 subunits constitute a pH- and Ca -sensitive inward rectifying K channel %U /brokenurl#<Go to ISI>://WOS:000245006500009 %V 225 %X Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.
• Blue light inhibits guard cell plasma membrane anion channels in a phototropin-dependent manner. Marten, H.; Hedrich, R.; Roelfsema, M. R. G. In Plant Journal, 50(1), pp. 29–39. 2007.
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  Guard cells respond to light through two independent signalling pathways. The first pathway is initiated by photosynthetically active radiation and has been associated with changes in the intercellular CO2 concentration, leading to inhibition of plasma membrane anion channels. The second response is blue-light-specific and so far has been restricted to the activation of plasma membrane H+-ATPases. In a search for interactions of both signalling pathways, guard cells of Vicia faba and Arabidopsis thaliana were studied in intact plants. Vicia faba guard cells recorded in CO2-free air responded to blue light with a transient outward plasma membrane current that had an average peak value of 17 pA. In line with previous reports, changes in the current-voltage relation of the plasma membrane indicate that this outward current is based on the activation of H+-ATPases. However, when V. faba guard cells were blue-light-stimulated in air with 700 mu l l(-1) CO2, the outward current increased to 56 pA. The increase in current was linked to inhibition of S-type anion channels. Blue light also inhibited plasma membrane anion channels in A. thaliana guard cells, but not in the phot1 phot2 double mutant. These results show that blue light inhibits plasma membrane anion channels through a pathway involving phototropins, in addition to the stimulation of guard cell plasma membrane H+-ATPases.

  @article{RN1149, abstract = {Guard cells respond to light through two independent signalling pathways. The first pathway is initiated by photosynthetically active radiation and has been associated with changes in the intercellular CO2 concentration, leading to inhibition of plasma membrane anion channels. The second response is blue-light-specific and so far has been restricted to the activation of plasma membrane H+-ATPases. In a search for interactions of both signalling pathways, guard cells of Vicia faba and Arabidopsis thaliana were studied in intact plants. Vicia faba guard cells recorded in CO2-free air responded to blue light with a transient outward plasma membrane current that had an average peak value of 17 pA. In line with previous reports, changes in the current-voltage relation of the plasma membrane indicate that this outward current is based on the activation of H+-ATPases. However, when V. faba guard cells were blue-light-stimulated in air with 700 mu l l(-1) CO2, the outward current increased to 56 pA. The increase in current was linked to inhibition of S-type anion channels. Blue light also inhibited plasma membrane anion channels in A. thaliana guard cells, but not in the phot1 phot2 double mutant. These results show that blue light inhibits plasma membrane anion channels through a pathway involving phototropins, in addition to the stimulation of guard cell plasma membrane H+-ATPases.}, author = {Marten, H. and Hedrich, R. and Roelfsema, M. R. G.}, journal = {Plant Journal}, keywords = {stomata}, note = {150zo Times Cited:68 Cited References Count:56}, number = 1, pages = {29-39}, title = {Blue light inhibits guard cell plasma membrane anion channels in a phototropin-dependent manner}, type = {Journal Article}, volume = 50, year = 2007 }

  %0 Journal Article %1 RN1149 %A Marten, H. %A Hedrich, R. %A Roelfsema, M. R. G. %D 2007 %J Plant Journal %N 1 %P 29-39 %R 10.1111/j.1365-313X.2006.03026.x %T Blue light inhibits guard cell plasma membrane anion channels in a phototropin-dependent manner %U /brokenurl#<Go to ISI>://WOS:000245258300003 %V 50 %X Guard cells respond to light through two independent signalling pathways. The first pathway is initiated by photosynthetically active radiation and has been associated with changes in the intercellular CO2 concentration, leading to inhibition of plasma membrane anion channels. The second response is blue-light-specific and so far has been restricted to the activation of plasma membrane H+-ATPases. In a search for interactions of both signalling pathways, guard cells of Vicia faba and Arabidopsis thaliana were studied in intact plants. Vicia faba guard cells recorded in CO2-free air responded to blue light with a transient outward plasma membrane current that had an average peak value of 17 pA. In line with previous reports, changes in the current-voltage relation of the plasma membrane indicate that this outward current is based on the activation of H+-ATPases. However, when V. faba guard cells were blue-light-stimulated in air with 700 mu l l(-1) CO2, the outward current increased to 56 pA. The increase in current was linked to inhibition of S-type anion channels. Blue light also inhibited plasma membrane anion channels in A. thaliana guard cells, but not in the phot1 phot2 double mutant. These results show that blue light inhibits plasma membrane anion channels through a pathway involving phototropins, in addition to the stimulation of guard cell plasma membrane H+-ATPases.
• Cold transiently activates calcium-permeable channels in Arabidopsis mesophyll cells. Carpaneto, A.; Ivashikina, N.; Levchenko, V.; Krol, E.; Jeworutzki, E.; Zhu, J. K.; Hedrich, R. In Plant Physiology, 143(1), pp. 487–494. 2007.
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  Living organisms are capable of discriminating thermal stimuli from noxious cold to noxious heat. For more than 30 years, it has been known that plant cells respond to cold with a large and transient depolarization. Recently, using transgenic Arabidopsis (Arabidopsis thaliana) expressing the calcium-sensitive protein aequorin, an increase in cytosolic calcium following cold treatment was observed. Applying the patch-clamp technique to Arabidopsis mesophyll protoplasts, we could identify a transient plasma membrane conductance induced by rapid cooling. This cold-induced transient conductance was characterized as an outward rectifying 33 pS nonselective cation channel. The permeability ratio between calcium and cesium was 0.7, pointing to a permeation pore.3.34 angstrom (phi of cesium). Our experiments thus provide direct evidence for the predicted but not yet measured cold-activated calcium-permeable channel in plants.

  @article{RN1153, abstract = {Living organisms are capable of discriminating thermal stimuli from noxious cold to noxious heat. For more than 30 years, it has been known that plant cells respond to cold with a large and transient depolarization. Recently, using transgenic Arabidopsis (Arabidopsis thaliana) expressing the calcium-sensitive protein aequorin, an increase in cytosolic calcium following cold treatment was observed. Applying the patch-clamp technique to Arabidopsis mesophyll protoplasts, we could identify a transient plasma membrane conductance induced by rapid cooling. This cold-induced transient conductance was characterized as an outward rectifying 33 pS nonselective cation channel. The permeability ratio between calcium and cesium was 0.7, pointing to a permeation pore.3.34 angstrom (phi of cesium). Our experiments thus provide direct evidence for the predicted but not yet measured cold-activated calcium-permeable channel in plants.}, author = {Carpaneto, A. and Ivashikina, N. and Levchenko, V. and Krol, E. and Jeworutzki, E. and Zhu, J. K. and Hedrich, R.}, journal = {Plant Physiology}, keywords = {potential}, note = {124ep Times Cited:82 Cited References Count:42}, number = 1, pages = {487-494}, title = {Cold transiently activates calcium-permeable channels in Arabidopsis mesophyll cells}, type = {Journal Article}, volume = 143, year = 2007 }

  %0 Journal Article %1 RN1153 %A Carpaneto, A. %A Ivashikina, N. %A Levchenko, V. %A Krol, E. %A Jeworutzki, E. %A Zhu, J. K. %A Hedrich, R. %D 2007 %J Plant Physiology %N 1 %P 487-494 %R 10.1104/pp.106.090928 %T Cold transiently activates calcium-permeable channels in Arabidopsis mesophyll cells %U /brokenurl#<Go to ISI>://WOS:000243350600043 %V 143 %X Living organisms are capable of discriminating thermal stimuli from noxious cold to noxious heat. For more than 30 years, it has been known that plant cells respond to cold with a large and transient depolarization. Recently, using transgenic Arabidopsis (Arabidopsis thaliana) expressing the calcium-sensitive protein aequorin, an increase in cytosolic calcium following cold treatment was observed. Applying the patch-clamp technique to Arabidopsis mesophyll protoplasts, we could identify a transient plasma membrane conductance induced by rapid cooling. This cold-induced transient conductance was characterized as an outward rectifying 33 pS nonselective cation channel. The permeability ratio between calcium and cesium was 0.7, pointing to a permeation pore.3.34 angstrom (phi of cesium). Our experiments thus provide direct evidence for the predicted but not yet measured cold-activated calcium-permeable channel in plants.
• Plant cells must pass a K threshold to re-enter the cell cycle. Sano, T.; Becker, D.; Ivashikina, N.; Wegner, L. H.; Zimmermann, U.; Roelfsema, M. R. G.; Nagata, T.; Hedrich, R. In Plant Journal, 50(3), pp. 401–413. 2007.
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  Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K+ channels in plant cell division and cell-cycle progression, however, has not been determined so far. K+ channel blocker studies with synchronized tobacco BY-2 cells revealed that K+ uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K+ channel activities and reduced driving force for K+ uptake in dividing cells. Among the four Shaker-like K+ channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K+ channel that mediates K+ uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K+ level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K+ channel density in plant cell division and cell-cycle progression is discussed.

  @article{RN1147, abstract = {Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K+ channels in plant cell division and cell-cycle progression, however, has not been determined so far. K+ channel blocker studies with synchronized tobacco BY-2 cells revealed that K+ uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K+ channel activities and reduced driving force for K+ uptake in dividing cells. Among the four Shaker-like K+ channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K+ channel that mediates K+ uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K+ level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K+ channel density in plant cell division and cell-cycle progression is discussed.}, author = {Sano, T. and Becker, D. and Ivashikina, N. and Wegner, L. H. and Zimmermann, U. and Roelfsema, M. R. G. and Nagata, T. and Hedrich, R.}, journal = {Plant Journal}, keywords = {cell}, note = {160mj Times Cited:58 Cited References Count:47}, number = 3, pages = {401-413}, title = {Plant cells must pass a K threshold to re-enter the cell cycle}, type = {Journal Article}, volume = 50, year = 2007 }

  %0 Journal Article %1 RN1147 %A Sano, T. %A Becker, D. %A Ivashikina, N. %A Wegner, L. H. %A Zimmermann, U. %A Roelfsema, M. R. G. %A Nagata, T. %A Hedrich, R. %D 2007 %J Plant Journal %N 3 %P 401-413 %R 10.1111/j.1365-313X.2007.03071.x %T Plant cells must pass a K threshold to re-enter the cell cycle %U /brokenurl#<Go to ISI>://WOS:000245945300003 %V 50 %X Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K+ channels in plant cell division and cell-cycle progression, however, has not been determined so far. K+ channel blocker studies with synchronized tobacco BY-2 cells revealed that K+ uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K+ channel activities and reduced driving force for K+ uptake in dividing cells. Among the four Shaker-like K+ channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K+ channel that mediates K+ uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K+ level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K+ channel density in plant cell division and cell-cycle progression is discussed.
• Mechanisms of electrically mediated cytosolic Ca transients in Aequorin-Transformed tobacco cells. Sukhorukov, V. L.; Endter, J. M.; Zimmermann, D.; Shirakashi, R.; Fehrmann, S.; Kiesel, M.; Reuss, R.; Becker, D.; Hedrich, R.; Bamberg, E.; Roitsch, T.; Zimmermann, U. In Biophysical Journal, 93(9), pp. 3324–3337. 2007.
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  Cytosolic Ca2+ changes induced by electric. field pulses of 50-mu s duration and 200-800 V/cm strength were monitored by measuring chemiluminescence in aequorin-transformed BY-2 tobacco cells. In Ca2+-substituted media, electropulsing led to a very fast initial increase of the cytosolic Ca2+ concentration reaching a peak value within < 100-200 ms. Peaking of [Ca2+](cyt) was followed by a biphasic decay due to removal of Ca2+ (e. g., by binding and/or sequestration in the cytosol). The decay had fast and slow components, characterized by time constants of; similar to 0.5 and 3-5 s, respectively. Experiments with various external Ca2+ concentrations and conductivities showed that the fast decay arises from Ca2+ fluxes through the plasmalemma, whereas the slow decay must be assigned to Ca2+ fluxes through the tonoplast. The amplitude of the [Ca2+](cyt) transients increased with increasing. field strength, whereas the time constants of the decay kinetics remained invariant. Breakdown of the plasmalemma was achieved at a critical. field strength of similar to 450 V/cm, whereas breakdown of the tonoplast required similar to 580 V/cm. The above. finndings could be explained by the transient potential profiles generated across the two membranes in response to an exponentially decaying. field pulse. The dielectric data required for calculation of the tonoplast and plasmalemma potentials were derived from electrorotation experiments on isolated vacuolated and evacuolated BY-2 protoplasts. The electrorotation response of vacuolated protoplasts could be described in terms of a three-shell model (i.e., by assuming that the capacitances of tonoplast and plasmalemma are arranged in series). Among other things, the theoretical analysis together with the experimental data show that genetic manipulations of plant cells by electrotransfection or electrofusion must be performed in low-conductivity media to minimize release of vacuolar Ca2+ and presumably other vacuolar ingredients.

  @article{RN1145, abstract = {Cytosolic Ca2+ changes induced by electric. field pulses of 50-mu s duration and 200-800 V/cm strength were monitored by measuring chemiluminescence in aequorin-transformed BY-2 tobacco cells. In Ca2+-substituted media, electropulsing led to a very fast initial increase of the cytosolic Ca2+ concentration reaching a peak value within < 100-200 ms. Peaking of [Ca2+](cyt) was followed by a biphasic decay due to removal of Ca2+ (e. g., by binding and/or sequestration in the cytosol). The decay had fast and slow components, characterized by time constants of; similar to 0.5 and 3-5 s, respectively. Experiments with various external Ca2+ concentrations and conductivities showed that the fast decay arises from Ca2+ fluxes through the plasmalemma, whereas the slow decay must be assigned to Ca2+ fluxes through the tonoplast. The amplitude of the [Ca2+](cyt) transients increased with increasing. field strength, whereas the time constants of the decay kinetics remained invariant. Breakdown of the plasmalemma was achieved at a critical. field strength of similar to 450 V/cm, whereas breakdown of the tonoplast required similar to 580 V/cm. The above. finndings could be explained by the transient potential profiles generated across the two membranes in response to an exponentially decaying. field pulse. The dielectric data required for calculation of the tonoplast and plasmalemma potentials were derived from electrorotation experiments on isolated vacuolated and evacuolated BY-2 protoplasts. The electrorotation response of vacuolated protoplasts could be described in terms of a three-shell model (i.e., by assuming that the capacitances of tonoplast and plasmalemma are arranged in series). Among other things, the theoretical analysis together with the experimental data show that genetic manipulations of plant cells by electrotransfection or electrofusion must be performed in low-conductivity media to minimize release of vacuolar Ca2+ and presumably other vacuolar ingredients.}, author = {Sukhorukov, V. L. and Endter, J. M. and Zimmermann, D. and Shirakashi, R. and Fehrmann, S. and Kiesel, M. and Reuss, R. and Becker, D. and Hedrich, R. and Bamberg, E. and Roitsch, T. and Zimmermann, U.}, journal = {Biophysical Journal}, keywords = {free}, note = {221ar Times Cited:8 Cited References Count:52}, number = 9, pages = {3324-3337}, title = {Mechanisms of electrically mediated cytosolic Ca transients in Aequorin-Transformed tobacco cells}, type = {Journal Article}, volume = 93, year = 2007 }

  %0 Journal Article %1 RN1145 %A Sukhorukov, V. L. %A Endter, J. M. %A Zimmermann, D. %A Shirakashi, R. %A Fehrmann, S. %A Kiesel, M. %A Reuss, R. %A Becker, D. %A Hedrich, R. %A Bamberg, E. %A Roitsch, T. %A Zimmermann, U. %D 2007 %J Biophysical Journal %N 9 %P 3324-3337 %R DOI 10.1529/biophysj.107.110783 %T Mechanisms of electrically mediated cytosolic Ca transients in Aequorin-Transformed tobacco cells %U /brokenurl#<Go to ISI>://WOS:000250199300037 %V 93 %X Cytosolic Ca2+ changes induced by electric. field pulses of 50-mu s duration and 200-800 V/cm strength were monitored by measuring chemiluminescence in aequorin-transformed BY-2 tobacco cells. In Ca2+-substituted media, electropulsing led to a very fast initial increase of the cytosolic Ca2+ concentration reaching a peak value within < 100-200 ms. Peaking of [Ca2+](cyt) was followed by a biphasic decay due to removal of Ca2+ (e. g., by binding and/or sequestration in the cytosol). The decay had fast and slow components, characterized by time constants of; similar to 0.5 and 3-5 s, respectively. Experiments with various external Ca2+ concentrations and conductivities showed that the fast decay arises from Ca2+ fluxes through the plasmalemma, whereas the slow decay must be assigned to Ca2+ fluxes through the tonoplast. The amplitude of the [Ca2+](cyt) transients increased with increasing. field strength, whereas the time constants of the decay kinetics remained invariant. Breakdown of the plasmalemma was achieved at a critical. field strength of similar to 450 V/cm, whereas breakdown of the tonoplast required similar to 580 V/cm. The above. finndings could be explained by the transient potential profiles generated across the two membranes in response to an exponentially decaying. field pulse. The dielectric data required for calculation of the tonoplast and plasmalemma potentials were derived from electrorotation experiments on isolated vacuolated and evacuolated BY-2 protoplasts. The electrorotation response of vacuolated protoplasts could be described in terms of a three-shell model (i.e., by assuming that the capacitances of tonoplast and plasmalemma are arranged in series). Among other things, the theoretical analysis together with the experimental data show that genetic manipulations of plant cells by electrotransfection or electrofusion must be performed in low-conductivity media to minimize release of vacuolar Ca2+ and presumably other vacuolar ingredients.
• The role of potassium ion in cell division and cell cycle progression of tobacco BY-2 cells. Sano, T.; Ivashikina, N.; Hedrich, R.; Hasezawa, S. In Plant and Cell Physiology, 48, pp. S90-S90. 2007.
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  @article{RN1146, author = {Sano, T. and Ivashikina, N. and Hedrich, R. and Hasezawa, S.}, journal = {Plant and Cell Physiology}, keywords = {myOwn}, note = {Suppl. S 160ec Times Cited:0 Cited References Count:0}, pages = {S90-S90}, title = {The role of potassium ion in cell division and cell cycle progression of tobacco BY-2 cells}, type = {Journal Article}, volume = 48, year = 2007 }

  %0 Journal Article %1 RN1146 %A Sano, T. %A Ivashikina, N. %A Hedrich, R. %A Hasezawa, S. %D 2007 %J Plant and Cell Physiology %P S90-S90 %T The role of potassium ion in cell division and cell cycle progression of tobacco BY-2 cells %U /brokenurl#<Go to ISI>://WOS:000245922700355 %V 48
• Ca -dependent and -independent abscisic acid activation of plasma membrane anion channels in guard cells of. Marten, H.; Konrad, K. R.; Dietrich, P.; Roelfsema, M. R. G.; Hedrich, R. In Plant Physiology, 143(1), pp. 28–37. 2007.
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  Drought induces stomatal closure, a response that is associated with the activation of plasma membrane anion channels in guard cells, by the phytohormone abscisic acid (ABA). In several species, this response is associated with changes in the cytoplasmic free Ca2+ concentration. In Vicia faba, however, guard cell anion channels activate in a Ca2+-independent manner. Because of potential differences between species, Nicotiana tabacum guard cells were studied in intact plants, with simultaneous recordings of the plasma membrane conductance and the cytoplasmic free Ca2+ concentration. ABA triggered transient rises in cytoplasmic Ca2+ in the majority of the guard cells (14 out of 19). In seven out of 14 guard cells, the change in cytoplasmic free Ca2+ closely matched the activation of anion channels, while the Ca2+ rise was delayed in seven other cells. In the remaining five cells, ABA stimulated anion channels without a change in the cytoplasmic Ca2+ level. Even though ABA could activate anion channels in N. tabacum guard cells independent of a rise in the cytoplasmic Ca2+ concentration, patch clamp experiments showed that anion channels in these cells are stimulated by elevated Ca2+ in an ATP-dependent manner. Guard cells thus seem to have evolved both Ca2+-independent and -dependent ABA signaling pathways. Guard cells of N. tabacum apparently utilize both pathways, while ABA signaling in V. faba seems to be restricted to the Ca2+-independent pathway.

  @article{RN1148, abstract = {Drought induces stomatal closure, a response that is associated with the activation of plasma membrane anion channels in guard cells, by the phytohormone abscisic acid (ABA). In several species, this response is associated with changes in the cytoplasmic free Ca2+ concentration. In Vicia faba, however, guard cell anion channels activate in a Ca2+-independent manner. Because of potential differences between species, Nicotiana tabacum guard cells were studied in intact plants, with simultaneous recordings of the plasma membrane conductance and the cytoplasmic free Ca2+ concentration. ABA triggered transient rises in cytoplasmic Ca2+ in the majority of the guard cells (14 out of 19). In seven out of 14 guard cells, the change in cytoplasmic free Ca2+ closely matched the activation of anion channels, while the Ca2+ rise was delayed in seven other cells. In the remaining five cells, ABA stimulated anion channels without a change in the cytoplasmic Ca2+ level. Even though ABA could activate anion channels in N. tabacum guard cells independent of a rise in the cytoplasmic Ca2+ concentration, patch clamp experiments showed that anion channels in these cells are stimulated by elevated Ca2+ in an ATP-dependent manner. Guard cells thus seem to have evolved both Ca2+-independent and -dependent ABA signaling pathways. Guard cells of N. tabacum apparently utilize both pathways, while ABA signaling in V. faba seems to be restricted to the Ca2+-independent pathway.}, author = {Marten, H. and Konrad, K. R. and Dietrich, P. and Roelfsema, M. R. G. and Hedrich, R.}, journal = {Plant Physiology}, keywords = {protein-kinase}, note = {124ep Times Cited:68 Cited References Count:49}, number = 1, pages = {28-37}, title = {Ca -dependent and -independent abscisic acid activation of plasma membrane anion channels in guard cells of}, type = {Journal Article}, volume = 143, year = 2007 }

  %0 Journal Article %1 RN1148 %A Marten, H. %A Konrad, K. R. %A Dietrich, P. %A Roelfsema, M. R. G. %A Hedrich, R. %D 2007 %J Plant Physiology %N 1 %P 28-37 %R 10.1104/pp.106.092643 %T Ca -dependent and -independent abscisic acid activation of plasma membrane anion channels in guard cells of %U /brokenurl#<Go to ISI>://WOS:000243350600006 %V 143 %X Drought induces stomatal closure, a response that is associated with the activation of plasma membrane anion channels in guard cells, by the phytohormone abscisic acid (ABA). In several species, this response is associated with changes in the cytoplasmic free Ca2+ concentration. In Vicia faba, however, guard cell anion channels activate in a Ca2+-independent manner. Because of potential differences between species, Nicotiana tabacum guard cells were studied in intact plants, with simultaneous recordings of the plasma membrane conductance and the cytoplasmic free Ca2+ concentration. ABA triggered transient rises in cytoplasmic Ca2+ in the majority of the guard cells (14 out of 19). In seven out of 14 guard cells, the change in cytoplasmic free Ca2+ closely matched the activation of anion channels, while the Ca2+ rise was delayed in seven other cells. In the remaining five cells, ABA stimulated anion channels without a change in the cytoplasmic Ca2+ level. Even though ABA could activate anion channels in N. tabacum guard cells independent of a rise in the cytoplasmic Ca2+ concentration, patch clamp experiments showed that anion channels in these cells are stimulated by elevated Ca2+ in an ATP-dependent manner. Guard cells thus seem to have evolved both Ca2+-independent and -dependent ABA signaling pathways. Guard cells of N. tabacum apparently utilize both pathways, while ABA signaling in V. faba seems to be restricted to the Ca2+-independent pathway.
• A central role of abscisic acid in drought stress protection of -induced tumors on arabidopsis. Efetova, M.; Zeier, J.; Riederer, M.; Lee, C. W.; Stingl, N.; Mueller, M.; Hartung, W.; Hedrich, R.; Deeken, R. In Plant Physiology, 145(3), pp. 853–862. 2007.
  • [ Abstract ]
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  Crown gall tumors induced by Agrobacterium tumefaciens represent a sink that has to be provided with nutrients and water by the host plant. The lack of an intact epidermis or cuticle results in uncontrolled loss of water. However, neither the tumor nor the host plant displays wilting. This phenomenon points to drought adaptation in both tumors and the crown gall host plant. To understand the underlying molecular mechanisms of protection against desiccation the gene expression pattern of Arabidopsis ( Arabidopsis thaliana) tumors was integrated with the profile of stress metabolites: Arabidopsis tumors accumulated high amounts of abscisic acid ( ABA), the ethylene precursor aminocyclopropyl carboxylic acid, osmoprotectants, and form a suberized periderm- like protective layer. Suberization of the outer tumor cell layers most likely is mediated by ABA since external application of ABA induced suberization of Arabidopsis roots. However, the expression level of the classical marker genes, known to respond to drought stress and/ or ABA, was lower in tumors. Instead another set of drought and/ or ABA-inducible genes was more highly transcribed. Elevated transcription of several ABA- dependent aquaporin genes might indicate that ABA controls the water balance of the tumor. The retarded tumor growth on abi and aba mutant plants underlined the importance of a tumor- specific ABA signaling pathway. Taken together, we propose that ABA is an important signal for protection of tumors against desiccation and thus supports tumor development.

  @article{RN1152, abstract = {Crown gall tumors induced by Agrobacterium tumefaciens represent a sink that has to be provided with nutrients and water by the host plant. The lack of an intact epidermis or cuticle results in uncontrolled loss of water. However, neither the tumor nor the host plant displays wilting. This phenomenon points to drought adaptation in both tumors and the crown gall host plant. To understand the underlying molecular mechanisms of protection against desiccation the gene expression pattern of Arabidopsis ( Arabidopsis thaliana) tumors was integrated with the profile of stress metabolites: Arabidopsis tumors accumulated high amounts of abscisic acid ( ABA), the ethylene precursor aminocyclopropyl carboxylic acid, osmoprotectants, and form a suberized periderm- like protective layer. Suberization of the outer tumor cell layers most likely is mediated by ABA since external application of ABA induced suberization of Arabidopsis roots. However, the expression level of the classical marker genes, known to respond to drought stress and/ or ABA, was lower in tumors. Instead another set of drought and/ or ABA-inducible genes was more highly transcribed. Elevated transcription of several ABA- dependent aquaporin genes might indicate that ABA controls the water balance of the tumor. The retarded tumor growth on abi and aba mutant plants underlined the importance of a tumor- specific ABA signaling pathway. Taken together, we propose that ABA is an important signal for protection of tumors against desiccation and thus supports tumor development.}, author = {Efetova, M. and Zeier, J. and Riederer, M. and Lee, C. W. and Stingl, N. and Mueller, M. and Hartung, W. and Hedrich, R. and Deeken, R.}, journal = {Plant Physiology}, keywords = {protein}, note = {228fk Times Cited:62 Cited References Count:61}, number = 3, pages = {853-862}, title = {A central role of abscisic acid in drought stress protection of -induced tumors on arabidopsis}, type = {Journal Article}, volume = 145, year = 2007 }

  %0 Journal Article %1 RN1152 %A Efetova, M. %A Zeier, J. %A Riederer, M. %A Lee, C. W. %A Stingl, N. %A Mueller, M. %A Hartung, W. %A Hedrich, R. %A Deeken, R. %D 2007 %J Plant Physiology %N 3 %P 853-862 %R 10.1104/pp.107.104851 %T A central role of abscisic acid in drought stress protection of -induced tumors on arabidopsis %U /brokenurl#<Go to ISI>://WOS:000250712800024 %V 145 %X Crown gall tumors induced by Agrobacterium tumefaciens represent a sink that has to be provided with nutrients and water by the host plant. The lack of an intact epidermis or cuticle results in uncontrolled loss of water. However, neither the tumor nor the host plant displays wilting. This phenomenon points to drought adaptation in both tumors and the crown gall host plant. To understand the underlying molecular mechanisms of protection against desiccation the gene expression pattern of Arabidopsis ( Arabidopsis thaliana) tumors was integrated with the profile of stress metabolites: Arabidopsis tumors accumulated high amounts of abscisic acid ( ABA), the ethylene precursor aminocyclopropyl carboxylic acid, osmoprotectants, and form a suberized periderm- like protective layer. Suberization of the outer tumor cell layers most likely is mediated by ABA since external application of ABA induced suberization of Arabidopsis roots. However, the expression level of the classical marker genes, known to respond to drought stress and/ or ABA, was lower in tumors. Instead another set of drought and/ or ABA-inducible genes was more highly transcribed. Elevated transcription of several ABA- dependent aquaporin genes might indicate that ABA controls the water balance of the tumor. The retarded tumor growth on abi and aba mutant plants underlined the importance of a tumor- specific ABA signaling pathway. Taken together, we propose that ABA is an important signal for protection of tumors against desiccation and thus supports tumor development.

• Ion channels meet auxin action. Fuchs, I.; Philippar, K.; Hedrich, R. In Plant Biology, 8(3), pp. 353–359. 2006.
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  The regulation of cell division and elongation in plants is accomplished by the action of different phytohormones. Auxin as one of these growth regulators is known to stimulate cell elongation growth in the aerial parts of the plant. Here, auxin enhances cell enlargement by increasing the extensibility of the cell wall and by facilitating the uptake of osmolytes such as potassium ions into the cell. Starting in the late 1990s, the auxin regulation of ion channels mediating K+ import into the cell has been studied in great detail. In this article we will focus on the molecular mechanisms underlying the modulation of K+ transport by auxin and present a model to explain how the regulation of K+ channels is involved in auxin-induced cell elongation growth.

  @article{RN1161, abstract = {The regulation of cell division and elongation in plants is accomplished by the action of different phytohormones. Auxin as one of these growth regulators is known to stimulate cell elongation growth in the aerial parts of the plant. Here, auxin enhances cell enlargement by increasing the extensibility of the cell wall and by facilitating the uptake of osmolytes such as potassium ions into the cell. Starting in the late 1990s, the auxin regulation of ion channels mediating K+ import into the cell has been studied in great detail. In this article we will focus on the molecular mechanisms underlying the modulation of K+ transport by auxin and present a model to explain how the regulation of K+ channels is involved in auxin-induced cell elongation growth.}, author = {Fuchs, I. and Philippar, K. and Hedrich, R.}, journal = {Plant Biology}, keywords = {auxin}, note = {054ek Times Cited:22 Cited References Count:70}, number = 3, pages = {353-359}, title = {Ion channels meet auxin action}, type = {Journal Article}, volume = 8, year = 2006 }

  %0 Journal Article %1 RN1161 %A Fuchs, I. %A Philippar, K. %A Hedrich, R. %D 2006 %J Plant Biology %N 3 %P 353-359 %R 10.1055/s-2006-924121 %T Ion channels meet auxin action %U /brokenurl#<Go to ISI>://WOS:000238359400011 %V 8 %X The regulation of cell division and elongation in plants is accomplished by the action of different phytohormones. Auxin as one of these growth regulators is known to stimulate cell elongation growth in the aerial parts of the plant. Here, auxin enhances cell enlargement by increasing the extensibility of the cell wall and by facilitating the uptake of osmolytes such as potassium ions into the cell. Starting in the late 1990s, the auxin regulation of ion channels mediating K+ import into the cell has been studied in great detail. In this article we will focus on the molecular mechanisms underlying the modulation of K+ transport by auxin and present a model to explain how the regulation of K+ channels is involved in auxin-induced cell elongation growth.
• Calcium ions are involved in the delay of plant cell cycle progression by abiotic stresses. Sano, T.; Higaki, T.; Handa, K.; Kadota, Y.; Kuchitsu, K.; Hasezawa, S.; Hoffmann, A.; Endter, J.; Zimmermann, U.; Hedrich, R.; Roitsch, T. In Febs Letters, 580(2), pp. 597–602. 2006.
  • [ Abstract ]
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  Higher plants respond to environmental stresses by a sequence of reactions which include the reduction of growth by affecting cell division. It has been shown that calcium ions plays a role as a second messenger in mediating various defence responses under environmental stresses. In this study, the role of calcium ions on cell cycle progression under abiotic stresses has been examined in tobacco BY-2 suspension culture cells. Using synchronized BY-2 cells expressing the endogenous calcium sensor aequorin as experimental system, we could show that oxidative and hypoosmotic stress both induce an increase of intracellular calcium and cause a delay of the cell cycle. The inhibitory effect of these abiotic stress stimuli on cell cycle progression could be mimicked by increasing the intracellular calcium concentration via application of an external electrical field. Likewise, depletion of calcium ions in the culture medium suppressed the effect of the stimuli tested. These results demonstrate that calcium signalling is involved in the regulation of cell cycle progression in response to abiotic stress. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  @article{RN1156, abstract = {Higher plants respond to environmental stresses by a sequence of reactions which include the reduction of growth by affecting cell division. It has been shown that calcium ions plays a role as a second messenger in mediating various defence responses under environmental stresses. In this study, the role of calcium ions on cell cycle progression under abiotic stresses has been examined in tobacco BY-2 suspension culture cells. Using synchronized BY-2 cells expressing the endogenous calcium sensor aequorin as experimental system, we could show that oxidative and hypoosmotic stress both induce an increase of intracellular calcium and cause a delay of the cell cycle. The inhibitory effect of these abiotic stress stimuli on cell cycle progression could be mimicked by increasing the intracellular calcium concentration via application of an external electrical field. Likewise, depletion of calcium ions in the culture medium suppressed the effect of the stimuli tested. These results demonstrate that calcium signalling is involved in the regulation of cell cycle progression in response to abiotic stress. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.}, author = {Sano, T. and Higaki, T. and Handa, K. and Kadota, Y. and Kuchitsu, K. and Hasezawa, S. and Hoffmann, A. and Endter, J. and Zimmermann, U. and Hedrich, R. and Roitsch, T.}, journal = {Febs Letters}, keywords = {ion}, note = {006zu Times Cited:24 Cited References Count:20}, number = 2, pages = {597-602}, title = {Calcium ions are involved in the delay of plant cell cycle progression by abiotic stresses}, type = {Journal Article}, volume = 580, year = 2006 }

  %0 Journal Article %1 RN1156 %A Sano, T. %A Higaki, T. %A Handa, K. %A Kadota, Y. %A Kuchitsu, K. %A Hasezawa, S. %A Hoffmann, A. %A Endter, J. %A Zimmermann, U. %A Hedrich, R. %A Roitsch, T. %D 2006 %J Febs Letters %N 2 %P 597-602 %R 10.1016/j.febslet.2005.12.074 %T Calcium ions are involved in the delay of plant cell cycle progression by abiotic stresses %U /brokenurl#<Go to ISI>://WOS:000234937400039 %V 580 %X Higher plants respond to environmental stresses by a sequence of reactions which include the reduction of growth by affecting cell division. It has been shown that calcium ions plays a role as a second messenger in mediating various defence responses under environmental stresses. In this study, the role of calcium ions on cell cycle progression under abiotic stresses has been examined in tobacco BY-2 suspension culture cells. Using synchronized BY-2 cells expressing the endogenous calcium sensor aequorin as experimental system, we could show that oxidative and hypoosmotic stress both induce an increase of intracellular calcium and cause a delay of the cell cycle. The inhibitory effect of these abiotic stress stimuli on cell cycle progression could be mimicked by increasing the intracellular calcium concentration via application of an external electrical field. Likewise, depletion of calcium ions in the culture medium suppressed the effect of the stimuli tested. These results demonstrate that calcium signalling is involved in the regulation of cell cycle progression in response to abiotic stress. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
• Phosphorylation of SPICK2, an AKT2 channel homologue from motor cells. Yu, L.; Becker, D.; Levi, H.; Moshelion, M.; Hedrich, R.; Lotan, I.; Moran, A.; Pick, U.; Naveh, L.; Libal, Y.; Moran, N. In Journal of Experimental Botany, 57(14), pp. 3583–3594. 2006.
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  SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.

  @article{RN1154, abstract = {SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.}, author = {Yu, L. and Becker, D. and Levi, H. and Moshelion, M. and Hedrich, R. and Lotan, I. and Moran, A. and Pick, U. and Naveh, L. and Libal, Y. and Moran, N.}, journal = {Journal of Experimental Botany}, keywords = {akt2}, note = {108wp Times Cited:10 Cited References Count:57}, number = 14, pages = {3583-3594}, title = {Phosphorylation of SPICK2, an AKT2 channel homologue from motor cells}, type = {Journal Article}, volume = 57, year = 2006 }

  %0 Journal Article %1 RN1154 %A Yu, L. %A Becker, D. %A Levi, H. %A Moshelion, M. %A Hedrich, R. %A Lotan, I. %A Moran, A. %A Pick, U. %A Naveh, L. %A Libal, Y. %A Moran, N. %D 2006 %J Journal of Experimental Botany %N 14 %P 3583-3594 %R 10.1093/jxb/erl104 %T Phosphorylation of SPICK2, an AKT2 channel homologue from motor cells %U /brokenurl#<Go to ISI>://WOS:000242270200005 %V 57 %X SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.
• The auxin-induced K channel gene in maize functions in coleoptile growth and is required for embryo development. Philippar, K.; Büchsenschütz, K.; Edwards, D.; Löffler, J.; Lüthen, H.; Kranz, E.; Edwards, K. J.; Hedrich, R. In Plant Molecular Biology, 61(4-5), pp. 757–768. 2006.
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  The transcript level and in turn protein density of the K+-uptake channel ZMK1 in maize (Zea mays) coleoptiles is controlled by the phytohormone auxin. ZMK1 is involved in auxin-regulated coleoptile elongation as well as gravi- and phototropism. To provide unequivocal evidence for the role of ZMK1 in these elementary processes we screened for maize plants containing a Mutator-tagged Zmk1 gene. In a site-selected approach, we were able to identify three independent alleles of Mutator-transposon insertions in Zmk1. zmk1-m1::Mu1 plants were characterised by a Mu1 transposon inside intron 1 of ZMK1. When we analysed the Zmk1-transcript abundance in growing coleoptiles of these homozygous mutants, however, we found the K+-channel allele overexpressed. In consequence, elevated levels of K+-channel transcripts resulted in a growth phenotype as expected from more efficient K+-uptake, representing a central factor for turgor formation. Following Zmk1 expression during maize embryogenesis, we found this K+-channel gene constitutively expressed throughout embryo development and upregulated in late stages. In line with a vital role in embryogenesis, the mutations of exon 2 and intron 2 of Zmk1-zmk1-m2::Mu8 and zmk1-m3::MuA2-caused a lethal, defective-kernel phenotype. Thus, these results demonstrate the central role of the auxin-regulated K+-channel gene Zmk1 in coleoptile growth and embryo development.

  @article{RN1158, abstract = {The transcript level and in turn protein density of the K+-uptake channel ZMK1 in maize (Zea mays) coleoptiles is controlled by the phytohormone auxin. ZMK1 is involved in auxin-regulated coleoptile elongation as well as gravi- and phototropism. To provide unequivocal evidence for the role of ZMK1 in these elementary processes we screened for maize plants containing a Mutator-tagged Zmk1 gene. In a site-selected approach, we were able to identify three independent alleles of Mutator-transposon insertions in Zmk1. zmk1-m1::Mu1 plants were characterised by a Mu1 transposon inside intron 1 of ZMK1. When we analysed the Zmk1-transcript abundance in growing coleoptiles of these homozygous mutants, however, we found the K+-channel allele overexpressed. In consequence, elevated levels of K+-channel transcripts resulted in a growth phenotype as expected from more efficient K+-uptake, representing a central factor for turgor formation. Following Zmk1 expression during maize embryogenesis, we found this K+-channel gene constitutively expressed throughout embryo development and upregulated in late stages. In line with a vital role in embryogenesis, the mutations of exon 2 and intron 2 of Zmk1-zmk1-m2::Mu8 and zmk1-m3::MuA2-caused a lethal, defective-kernel phenotype. Thus, these results demonstrate the central role of the auxin-regulated K+-channel gene Zmk1 in coleoptile growth and embryo development.}, author = {Philippar, K. and Büchsenschütz, K. and Edwards, D. and Löffler, J. and Lüthen, H. and Kranz, E. and Edwards, K. J. and Hedrich, R.}, journal = {Plant Molecular Biology}, keywords = {auxin}, note = {070ut Times Cited:20 Cited References Count:58}, number = {4-5}, pages = {757-768}, title = {The auxin-induced K channel gene in maize functions in coleoptile growth and is required for embryo development}, type = {Journal Article}, volume = 61, year = 2006 }

  %0 Journal Article %1 RN1158 %A Philippar, K. %A Büchsenschütz, K. %A Edwards, D. %A Löffler, J. %A Lüthen, H. %A Kranz, E. %A Edwards, K. J. %A Hedrich, R. %D 2006 %J Plant Molecular Biology %N 4-5 %P 757-768 %R 10.1007/s11103-006-0047-2 %T The auxin-induced K channel gene in maize functions in coleoptile growth and is required for embryo development %U /brokenurl#<Go to ISI>://WOS:000239551300017 %V 61 %X The transcript level and in turn protein density of the K+-uptake channel ZMK1 in maize (Zea mays) coleoptiles is controlled by the phytohormone auxin. ZMK1 is involved in auxin-regulated coleoptile elongation as well as gravi- and phototropism. To provide unequivocal evidence for the role of ZMK1 in these elementary processes we screened for maize plants containing a Mutator-tagged Zmk1 gene. In a site-selected approach, we were able to identify three independent alleles of Mutator-transposon insertions in Zmk1. zmk1-m1::Mu1 plants were characterised by a Mu1 transposon inside intron 1 of ZMK1. When we analysed the Zmk1-transcript abundance in growing coleoptiles of these homozygous mutants, however, we found the K+-channel allele overexpressed. In consequence, elevated levels of K+-channel transcripts resulted in a growth phenotype as expected from more efficient K+-uptake, representing a central factor for turgor formation. Following Zmk1 expression during maize embryogenesis, we found this K+-channel gene constitutively expressed throughout embryo development and upregulated in late stages. In line with a vital role in embryogenesis, the mutations of exon 2 and intron 2 of Zmk1-zmk1-m2::Mu8 and zmk1-m3::MuA2-caused a lethal, defective-kernel phenotype. Thus, these results demonstrate the central role of the auxin-regulated K+-channel gene Zmk1 in coleoptile growth and embryo development.
• An integrated view of gene expression and solute profiles of tumors:: A genome-wide approach. Deeken, R.; Engelmann, J. C.; Efetova, M.; Czirjak, T.; Müller, T.; Kaiser, W. M.; Tietz, O.; Krischke, M.; Mueller, M. J.; Palme, K.; Dandekar, T.; Hedrich, R. In Plant Cell, 18(12), pp. 3617–3634. 2006.
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  Transformation of plant cells with T-DNA of virulent agrobacteria is one of the most extreme triggers of developmental changes in higher plants. For rapid growth and development of resulting tumors, specific changes in the gene expression profile and metabolic adaptations are required. Increased transport and metabolic fluxes are critical preconditions for growth and tumor development. A functional genomics approach, using the Affymetrix whole genome microarray (similar to 22,800 genes), was applied to measure changes in gene expression. The solute pattern of Arabidopsis thaliana tumors and uninfected plant tissues was compared with the respective gene expression profile. Increased levels of anions, sugars, and amino acids were correlated with changes in the gene expression of specific enzymes and solute transporters. The expression profile of genes pivotal for energy metabolism, such as those involved in photosynthesis, mitochondrial electron transport, and fermentation, suggested that tumors produce C and N compounds heterotrophically and gain energy mainly anaerobically. Thus, understanding of gene-to-metabolite networks in plant tumors promotes the identification of mechanisms that control tumor development.

  @article{RN1162, abstract = {Transformation of plant cells with T-DNA of virulent agrobacteria is one of the most extreme triggers of developmental changes in higher plants. For rapid growth and development of resulting tumors, specific changes in the gene expression profile and metabolic adaptations are required. Increased transport and metabolic fluxes are critical preconditions for growth and tumor development. A functional genomics approach, using the Affymetrix whole genome microarray (similar to 22,800 genes), was applied to measure changes in gene expression. The solute pattern of Arabidopsis thaliana tumors and uninfected plant tissues was compared with the respective gene expression profile. Increased levels of anions, sugars, and amino acids were correlated with changes in the gene expression of specific enzymes and solute transporters. The expression profile of genes pivotal for energy metabolism, such as those involved in photosynthesis, mitochondrial electron transport, and fermentation, suggested that tumors produce C and N compounds heterotrophically and gain energy mainly anaerobically. Thus, understanding of gene-to-metabolite networks in plant tumors promotes the identification of mechanisms that control tumor development.}, author = {Deeken, R. and Engelmann, J. C. and Efetova, M. and Czirjak, T. and Müller, T. and Kaiser, W. M. and Tietz, O. and Krischke, M. and Mueller, M. J. and Palme, K. and Dandekar, T. and Hedrich, R.}, journal = {Plant Cell}, keywords = {cell-wall}, note = {135tr Times Cited:87 Cited References Count:78}, number = 12, pages = {3617-3634}, title = {An integrated view of gene expression and solute profiles of tumors:: A genome-wide approach}, type = {Journal Article}, volume = 18, year = 2006 }

  %0 Journal Article %1 RN1162 %A Deeken, R. %A Engelmann, J. C. %A Efetova, M. %A Czirjak, T. %A Müller, T. %A Kaiser, W. M. %A Tietz, O. %A Krischke, M. %A Mueller, M. J. %A Palme, K. %A Dandekar, T. %A Hedrich, R. %D 2006 %J Plant Cell %N 12 %P 3617-3634 %R 10.1105/tpc.106.044743 %T An integrated view of gene expression and solute profiles of tumors:: A genome-wide approach %U /brokenurl#<Go to ISI>://WOS:000244177000021 %V 18 %X Transformation of plant cells with T-DNA of virulent agrobacteria is one of the most extreme triggers of developmental changes in higher plants. For rapid growth and development of resulting tumors, specific changes in the gene expression profile and metabolic adaptations are required. Increased transport and metabolic fluxes are critical preconditions for growth and tumor development. A functional genomics approach, using the Affymetrix whole genome microarray (similar to 22,800 genes), was applied to measure changes in gene expression. The solute pattern of Arabidopsis thaliana tumors and uninfected plant tissues was compared with the respective gene expression profile. Increased levels of anions, sugars, and amino acids were correlated with changes in the gene expression of specific enzymes and solute transporters. The expression profile of genes pivotal for energy metabolism, such as those involved in photosynthesis, mitochondrial electron transport, and fermentation, suggested that tumors produce C and N compounds heterotrophically and gain energy mainly anaerobically. Thus, understanding of gene-to-metabolite networks in plant tumors promotes the identification of mechanisms that control tumor development.
• Arabidopsis INOSITOL TRANSPORTER4 mediates high-affinity H symport of myoinositol across the plasma membrane. Schneider, S.; Schneidereit, A.; Konrad, K. R.; Hajirezaei, M. R.; Gramann, M.; Hedrich, R.; Sauer, N. In Plant Physiology, 141(2), pp. 565–577. 2006.
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  Four genes of the Arabidopsis ( Arabidopsis thaliana) monosaccharide transporter-like superfamily share significant homology with transporter genes previously identified in the common ice plant ( Mesembryanthemum crystallinum), a model system for studies on salt tolerance of higher plants. These ice plant transporters had been discussed as tonoplast proteins catalyzing the inositol-dependent efflux of Na+ ions from vacuoles. The subcellular localization and the physiological role of the homologous proteins in the glycophyte Arabidopsis were unclear. Here we describe Arabidopsis INOSITOL TRANSPORTER4 ( AtINT4), the first member of this subgroup of Arabidopsis monosaccharide transporter-like transporters. Functional analyses of the protein in yeast ( Saccharomyces cerevisiae) and Xenopus laevis oocytes characterize this protein as a highly specific H 1 symporter for myoinositol. These activities and analyses of the subcellular localization of an AtINT4 fusion protein in Arabidopsis and tobacco ( Nicotiana tabacum) reveal that AtINT4 is located in the plasma membrane. AtINT4 promoter-reporter gene plants demonstrate that AtINT4 is strongly expressed in Arabidopsis pollen and phloem companion cells. The potential physiological role of AtINT4 is discussed.

  @article{RN1155, abstract = {Four genes of the Arabidopsis ( Arabidopsis thaliana) monosaccharide transporter-like superfamily share significant homology with transporter genes previously identified in the common ice plant ( Mesembryanthemum crystallinum), a model system for studies on salt tolerance of higher plants. These ice plant transporters had been discussed as tonoplast proteins catalyzing the inositol-dependent efflux of Na+ ions from vacuoles. The subcellular localization and the physiological role of the homologous proteins in the glycophyte Arabidopsis were unclear. Here we describe Arabidopsis INOSITOL TRANSPORTER4 ( AtINT4), the first member of this subgroup of Arabidopsis monosaccharide transporter-like transporters. Functional analyses of the protein in yeast ( Saccharomyces cerevisiae) and Xenopus laevis oocytes characterize this protein as a highly specific H 1 symporter for myoinositol. These activities and analyses of the subcellular localization of an AtINT4 fusion protein in Arabidopsis and tobacco ( Nicotiana tabacum) reveal that AtINT4 is located in the plasma membrane. AtINT4 promoter-reporter gene plants demonstrate that AtINT4 is strongly expressed in Arabidopsis pollen and phloem companion cells. The potential physiological role of AtINT4 is discussed.}, author = {Schneider, S. and Schneidereit, A. and Konrad, K. R. and Hajirezaei, M. R. and Gramann, M. and Hedrich, R. and Sauer, N.}, journal = {Plant Physiology}, keywords = {monosaccharide}, note = {051nw Times Cited:62 Cited References Count:69}, number = 2, pages = {565-577}, title = {Arabidopsis INOSITOL TRANSPORTER4 mediates high-affinity H symport of myoinositol across the plasma membrane}, type = {Journal Article}, volume = 141, year = 2006 }

  %0 Journal Article %1 RN1155 %A Schneider, S. %A Schneidereit, A. %A Konrad, K. R. %A Hajirezaei, M. R. %A Gramann, M. %A Hedrich, R. %A Sauer, N. %D 2006 %J Plant Physiology %N 2 %P 565-577 %R 10.1104/pp.106.077123 %T Arabidopsis INOSITOL TRANSPORTER4 mediates high-affinity H symport of myoinositol across the plasma membrane %U /brokenurl#<Go to ISI>://WOS:000238168800032 %V 141 %X Four genes of the Arabidopsis ( Arabidopsis thaliana) monosaccharide transporter-like superfamily share significant homology with transporter genes previously identified in the common ice plant ( Mesembryanthemum crystallinum), a model system for studies on salt tolerance of higher plants. These ice plant transporters had been discussed as tonoplast proteins catalyzing the inositol-dependent efflux of Na+ ions from vacuoles. The subcellular localization and the physiological role of the homologous proteins in the glycophyte Arabidopsis were unclear. Here we describe Arabidopsis INOSITOL TRANSPORTER4 ( AtINT4), the first member of this subgroup of Arabidopsis monosaccharide transporter-like transporters. Functional analyses of the protein in yeast ( Saccharomyces cerevisiae) and Xenopus laevis oocytes characterize this protein as a highly specific H 1 symporter for myoinositol. These activities and analyses of the subcellular localization of an AtINT4 fusion protein in Arabidopsis and tobacco ( Nicotiana tabacum) reveal that AtINT4 is located in the plasma membrane. AtINT4 promoter-reporter gene plants demonstrate that AtINT4 is strongly expressed in Arabidopsis pollen and phloem companion cells. The potential physiological role of AtINT4 is discussed.
• 30-year progress of membrane transport in plants. Hedrich, R.; Marten, I. In Planta, 224(4), pp. 725–739. 2006.
  • [ Abstract ]
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  In the past 30 years enormous progress was made in plant membrane biology and transport physiology, a fact reflected in the appearance of textbooks. The first book dedicated to 'Membrane Transport in Plants' was published on the occasion of the 'International Workshop on Membrane Transport in Plants' held at the Nuclear Research Center, Julich, Germany [Zimmermann and Dainty (eds) 1974] and was followed in 1976 by a related volume 'Transport in plants II' in the 'Encyclopedia of plant physiology' [Luttge and Pitman (eds) 1976]. A broad spectrum of topics including thermodynamics of transport processes, water relations, primary reactions of photosynthesis, as well as more conventional aspects of membrane transport was presented. The aim of the editors of the first book was to bring advanced thermodynamical concepts to the attention of biologists and to show physical chemists and biophysicist what the more complex biological systems were like. To bundle known data on membrane transport in plants and relevant fields for mutual understanding, interdisciplinary research and clarification of problems were considered highly important for further progress in this scientific area of plant physiology. The present review will critically evaluate the progress in research in membrane transport in plants that was achieved during the past. How did 'Membrane Transport in Plants' progress within the 30 years between the publication of the first book about this topic (Zimmermann and Dainty 1974), a recent one with the same title (Blatt 2004), and today?

  @article{RN1159, abstract = {In the past 30 years enormous progress was made in plant membrane biology and transport physiology, a fact reflected in the appearance of textbooks. The first book dedicated to 'Membrane Transport in Plants' was published on the occasion of the 'International Workshop on Membrane Transport in Plants' held at the Nuclear Research Center, Julich, Germany [Zimmermann and Dainty (eds) 1974] and was followed in 1976 by a related volume 'Transport in plants II' in the 'Encyclopedia of plant physiology' [Luttge and Pitman (eds) 1976]. A broad spectrum of topics including thermodynamics of transport processes, water relations, primary reactions of photosynthesis, as well as more conventional aspects of membrane transport was presented. The aim of the editors of the first book was to bring advanced thermodynamical concepts to the attention of biologists and to show physical chemists and biophysicist what the more complex biological systems were like. To bundle known data on membrane transport in plants and relevant fields for mutual understanding, interdisciplinary research and clarification of problems were considered highly important for further progress in this scientific area of plant physiology. The present review will critically evaluate the progress in research in membrane transport in plants that was achieved during the past. How did 'Membrane Transport in Plants' progress within the 30 years between the publication of the first book about this topic (Zimmermann and Dainty 1974), a recent one with the same title (Blatt 2004), and today?}, author = {Hedrich, R. and Marten, I.}, journal = {Planta}, keywords = {channels}, note = {077wt Times Cited:17 Cited References Count:206}, number = 4, pages = {725-739}, title = {30-year progress of membrane transport in plants}, type = {Journal Article}, volume = 224, year = 2006 }

  %0 Journal Article %1 RN1159 %A Hedrich, R. %A Marten, I. %D 2006 %J Planta %N 4 %P 725-739 %R 10.1007/s00425-006-0341-x %T 30-year progress of membrane transport in plants %U /brokenurl#<Go to ISI>://WOS:000240063100001 %V 224 %X In the past 30 years enormous progress was made in plant membrane biology and transport physiology, a fact reflected in the appearance of textbooks. The first book dedicated to 'Membrane Transport in Plants' was published on the occasion of the 'International Workshop on Membrane Transport in Plants' held at the Nuclear Research Center, Julich, Germany [Zimmermann and Dainty (eds) 1974] and was followed in 1976 by a related volume 'Transport in plants II' in the 'Encyclopedia of plant physiology' [Luttge and Pitman (eds) 1976]. A broad spectrum of topics including thermodynamics of transport processes, water relations, primary reactions of photosynthesis, as well as more conventional aspects of membrane transport was presented. The aim of the editors of the first book was to bring advanced thermodynamical concepts to the attention of biologists and to show physical chemists and biophysicist what the more complex biological systems were like. To bundle known data on membrane transport in plants and relevant fields for mutual understanding, interdisciplinary research and clarification of problems were considered highly important for further progress in this scientific area of plant physiology. The present review will critically evaluate the progress in research in membrane transport in plants that was achieved during the past. How did 'Membrane Transport in Plants' progress within the 30 years between the publication of the first book about this topic (Zimmermann and Dainty 1974), a recent one with the same title (Blatt 2004), and today?
• Guard cells in albino leaf patches do not respond to photosynthetically active radiation, but are sensitive to blue light, CO and abscisic acid. Roelfsema, M. R. G.; Konrad, K. R.; Marten, H.; Psaras, G. K.; Hartung, W.; Hedrich, R. In Plant Cell and Environment, 29(8), pp. 1595–1605. 2006.
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  Stomatal openings can be stimulated by light through two signalling pathways. The first pathway is blue light specific and involves phototropins, while the second pathway mediates a response to photosynthetically active radiation (PAR). This second pathway was studied with the use of albino Vicia faba plants and variegated leaves of Chlorophytum comosum. Treatment of V. faba with norflurazon (Nf) inhibits the synthesis of carotenoids and leads to albino leaves with guard cells that lack functional green chloroplasts. Guard cells in albino leaf patches of C. comosum, however, do contain photosynthetically active chloroplasts. Stomata in albino leaf patches of both plants did not respond to red light, although blue light could still induce stomatal opening. This shows that the response to PAR is not functioning in albino leaf patches, even though guard cells of C. comosum harbour chloroplasts. Stomata of Nf-treated plants still responded to CO2 and abscisic acid (ABA). The size of Nf-treated guard cells was increased, but impalement studies with double-barrelled microelectrodes revealed no changes in ion-transport properties at the plasma membrane of guard cells. Blue light could hyperpolarize albino guard cells by triggering outward currents with peak values of 37 pA in albino plants and 51 pA in green control cells. Because of the inhibition of carotenoid biosynthesis, Nf-treated V. faba plants contained only 4% of the ABA content found in green control plants. The ABA dose dependence of anion channel activation in guard cells was shifted in these plants, causing a reduced response to 10 mu m ABA. These data show that despite the dramatic changes in physiology caused by Nf, the gross responsiveness of guard cells to blue light, CO2 and ABA remains unaltered. Stomata in albino leaf patches, however, do not respond to PAR, but require photosynthetically active mesophyll cells for this response.

  @article{RN1157, abstract = {Stomatal openings can be stimulated by light through two signalling pathways. The first pathway is blue light specific and involves phototropins, while the second pathway mediates a response to photosynthetically active radiation (PAR). This second pathway was studied with the use of albino Vicia faba plants and variegated leaves of Chlorophytum comosum. Treatment of V. faba with norflurazon (Nf) inhibits the synthesis of carotenoids and leads to albino leaves with guard cells that lack functional green chloroplasts. Guard cells in albino leaf patches of C. comosum, however, do contain photosynthetically active chloroplasts. Stomata in albino leaf patches of both plants did not respond to red light, although blue light could still induce stomatal opening. This shows that the response to PAR is not functioning in albino leaf patches, even though guard cells of C. comosum harbour chloroplasts. Stomata of Nf-treated plants still responded to CO2 and abscisic acid (ABA). The size of Nf-treated guard cells was increased, but impalement studies with double-barrelled microelectrodes revealed no changes in ion-transport properties at the plasma membrane of guard cells. Blue light could hyperpolarize albino guard cells by triggering outward currents with peak values of 37 pA in albino plants and 51 pA in green control cells. Because of the inhibition of carotenoid biosynthesis, Nf-treated V. faba plants contained only 4% of the ABA content found in green control plants. The ABA dose dependence of anion channel activation in guard cells was shifted in these plants, causing a reduced response to 10 mu m ABA. These data show that despite the dramatic changes in physiology caused by Nf, the gross responsiveness of guard cells to blue light, CO2 and ABA remains unaltered. Stomata in albino leaf patches, however, do not respond to PAR, but require photosynthetically active mesophyll cells for this response.}, author = {Roelfsema, M. R. G. and Konrad, K. R. and Marten, H. and Psaras, G. K. and Hartung, W. and Hedrich, R.}, journal = {Plant Cell and Environment}, keywords = {channel}, note = {057wc Times Cited:70 Cited References Count:66}, number = 8, pages = {1595-1605}, title = {Guard cells in albino leaf patches do not respond to photosynthetically active radiation, but are sensitive to blue light, CO and abscisic acid}, type = {Journal Article}, volume = 29, year = 2006 }

  %0 Journal Article %1 RN1157 %A Roelfsema, M. R. G. %A Konrad, K. R. %A Marten, H. %A Psaras, G. K. %A Hartung, W. %A Hedrich, R. %D 2006 %J Plant Cell and Environment %N 8 %P 1595-1605 %R 10.1111/j.1365-3040.2006.01536.x %T Guard cells in albino leaf patches do not respond to photosynthetically active radiation, but are sensitive to blue light, CO and abscisic acid %U /brokenurl#<Go to ISI>://WOS:000238624900011 %V 29 %X Stomatal openings can be stimulated by light through two signalling pathways. The first pathway is blue light specific and involves phototropins, while the second pathway mediates a response to photosynthetically active radiation (PAR). This second pathway was studied with the use of albino Vicia faba plants and variegated leaves of Chlorophytum comosum. Treatment of V. faba with norflurazon (Nf) inhibits the synthesis of carotenoids and leads to albino leaves with guard cells that lack functional green chloroplasts. Guard cells in albino leaf patches of C. comosum, however, do contain photosynthetically active chloroplasts. Stomata in albino leaf patches of both plants did not respond to red light, although blue light could still induce stomatal opening. This shows that the response to PAR is not functioning in albino leaf patches, even though guard cells of C. comosum harbour chloroplasts. Stomata of Nf-treated plants still responded to CO2 and abscisic acid (ABA). The size of Nf-treated guard cells was increased, but impalement studies with double-barrelled microelectrodes revealed no changes in ion-transport properties at the plasma membrane of guard cells. Blue light could hyperpolarize albino guard cells by triggering outward currents with peak values of 37 pA in albino plants and 51 pA in green control cells. Because of the inhibition of carotenoid biosynthesis, Nf-treated V. faba plants contained only 4% of the ABA content found in green control plants. The ABA dose dependence of anion channel activation in guard cells was shifted in these plants, causing a reduced response to 10 mu m ABA. These data show that despite the dramatic changes in physiology caused by Nf, the gross responsiveness of guard cells to blue light, CO2 and ABA remains unaltered. Stomata in albino leaf patches, however, do not respond to PAR, but require photosynthetically active mesophyll cells for this response.
• Calcium signaling plant K uptake networks channel. Hedrich, R.; Kudla, J. In Cell, 125(7), pp. 1221–1223. 2006.
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  Potassium channel function is fundamental to many physiological processes in plants. In this issue of Cell, Xu et al. (2006) identify a protein complex in Arabidopsis consisting of a potassium channel, a protein kinase, and a calcium sensor. This study reveals that plants cope with limited soil potassium by coupling potassium channel activation to a cellular calcium signaling network.

  @article{RN1160, abstract = {Potassium channel function is fundamental to many physiological processes in plants. In this issue of Cell, Xu et al. (2006) identify a protein complex in Arabidopsis consisting of a potassium channel, a protein kinase, and a calcium sensor. This study reveals that plants cope with limited soil potassium by coupling potassium channel activation to a cellular calcium signaling network.}, author = {Hedrich, R. and Kudla, J.}, journal = {Cell}, keywords = {arabidopsis}, note = {064qp Times Cited:40 Cited References Count:12}, number = 7, pages = {1221-1223}, title = {Calcium signaling plant K uptake networks channel}, type = {Journal Article}, volume = 125, year = 2006 }

  %0 Journal Article %1 RN1160 %A Hedrich, R. %A Kudla, J. %D 2006 %J Cell %N 7 %P 1221-1223 %R 10.1016/j.cell.2006.06.017 %T Calcium signaling plant K uptake networks channel %U /brokenurl#<Go to ISI>://WOS:000239104500002 %V 125 %X Potassium channel function is fundamental to many physiological processes in plants. In this issue of Cell, Xu et al. (2006) identify a protein complex in Arabidopsis consisting of a potassium channel, a protein kinase, and a calcium sensor. This study reveals that plants cope with limited soil potassium by coupling potassium channel activation to a cellular calcium signaling network.

• Arabidopsis POLYOL TRANSPORTER5, a new member of the monosaccharide transporter-like superfamily, mediates H -symport of numerous substrates, including -inositol, glycerol, and ribosele. Klepek, Y. S.; Geiger, D.; Stadler, R.; Klebl, F.; Landouar-Arsivaud, L.; Lemoine, R.; Hedrich, R.; Sauer, N. In Plant Cell, 17(1), pp. 204–218. 2005.
  • [ Abstract ]
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  Six genes of the Arabidopsis thaliana monosaccharide transporter-like (MST-like) superfamily share significant homology with polyol transporter genes previously identified in plants translocating polyols (mannitol or sorbitol) in their phloem (celery [Apium graveolens], common plantain [Plantago major], or sour cherry [Prunus cerasus]). The physiological role and the functional properties of this group of proteins were unclear in Arabidopsis, which translocates sucrose and small amounts of raffinose rather than polyols. Here, we describe POLYOL TRANSPORTER5 (AtPLT5), the first member of this subgroup of Arabidopsis MST-like transporters. Transient expression of an AtPLT5-green fluorescent protein fusion in plant cells and functional analyses of the AtPLT5 protein in yeast and Xenopus oocytes demonstrate that AtPLT5 is located in the plasma membrane and characterize this protein as a broad-spectrum H+-symporter for linear polyols, such as sorbitol, xylitol, erythritol, or glycerol. Unexpectedly, however, AtPLT5 catalyzes also the transport of the cyclic polyol myo-inositol and of different hexoses and pentoses, including ribose, a sugar that is not transported by any of the previously characterized plant sugar transporters. RT-PCR analyses and AtPLT5 promoter-reporter gene plants revealed that AtPLT5 is most strongly expressed in Arabidopsis roots, but also in the vascular tissue of leaves and in specific floral organs. The potential physiological role of AtPLT5 is discussed.

  @article{RN1167, abstract = {Six genes of the Arabidopsis thaliana monosaccharide transporter-like (MST-like) superfamily share significant homology with polyol transporter genes previously identified in plants translocating polyols (mannitol or sorbitol) in their phloem (celery [Apium graveolens], common plantain [Plantago major], or sour cherry [Prunus cerasus]). The physiological role and the functional properties of this group of proteins were unclear in Arabidopsis, which translocates sucrose and small amounts of raffinose rather than polyols. Here, we describe POLYOL TRANSPORTER5 (AtPLT5), the first member of this subgroup of Arabidopsis MST-like transporters. Transient expression of an AtPLT5-green fluorescent protein fusion in plant cells and functional analyses of the AtPLT5 protein in yeast and Xenopus oocytes demonstrate that AtPLT5 is located in the plasma membrane and characterize this protein as a broad-spectrum H+-symporter for linear polyols, such as sorbitol, xylitol, erythritol, or glycerol. Unexpectedly, however, AtPLT5 catalyzes also the transport of the cyclic polyol myo-inositol and of different hexoses and pentoses, including ribose, a sugar that is not transported by any of the previously characterized plant sugar transporters. RT-PCR analyses and AtPLT5 promoter-reporter gene plants revealed that AtPLT5 is most strongly expressed in Arabidopsis roots, but also in the vascular tissue of leaves and in specific floral organs. The potential physiological role of AtPLT5 is discussed.}, author = {Klepek, Y. S. and Geiger, D. and Stadler, R. and Klebl, F. and Landouar-Arsivaud, L. and Lemoine, R. and Hedrich, R. and Sauer, N.}, journal = {Plant Cell}, keywords = {escherichia-coli}, note = {887pc Times Cited:108 Cited References Count:49}, number = 1, pages = {204-218}, title = {Arabidopsis POLYOL TRANSPORTER5, a new member of the monosaccharide transporter-like superfamily, mediates H -symport of numerous substrates, including -inositol, glycerol, and ribosele}, type = {Journal Article}, volume = 17, year = 2005 }

  %0 Journal Article %1 RN1167 %A Klepek, Y. S. %A Geiger, D. %A Stadler, R. %A Klebl, F. %A Landouar-Arsivaud, L. %A Lemoine, R. %A Hedrich, R. %A Sauer, N. %D 2005 %J Plant Cell %N 1 %P 204-218 %R 10.1105/tpc.104.026641 %T Arabidopsis POLYOL TRANSPORTER5, a new member of the monosaccharide transporter-like superfamily, mediates H -symport of numerous substrates, including -inositol, glycerol, and ribosele %U /brokenurl#<Go to ISI>://WOS:000226317000016 %V 17 %X Six genes of the Arabidopsis thaliana monosaccharide transporter-like (MST-like) superfamily share significant homology with polyol transporter genes previously identified in plants translocating polyols (mannitol or sorbitol) in their phloem (celery [Apium graveolens], common plantain [Plantago major], or sour cherry [Prunus cerasus]). The physiological role and the functional properties of this group of proteins were unclear in Arabidopsis, which translocates sucrose and small amounts of raffinose rather than polyols. Here, we describe POLYOL TRANSPORTER5 (AtPLT5), the first member of this subgroup of Arabidopsis MST-like transporters. Transient expression of an AtPLT5-green fluorescent protein fusion in plant cells and functional analyses of the AtPLT5 protein in yeast and Xenopus oocytes demonstrate that AtPLT5 is located in the plasma membrane and characterize this protein as a broad-spectrum H+-symporter for linear polyols, such as sorbitol, xylitol, erythritol, or glycerol. Unexpectedly, however, AtPLT5 catalyzes also the transport of the cyclic polyol myo-inositol and of different hexoses and pentoses, including ribose, a sugar that is not transported by any of the previously characterized plant sugar transporters. RT-PCR analyses and AtPLT5 promoter-reporter gene plants revealed that AtPLT5 is most strongly expressed in Arabidopsis roots, but also in the vascular tissue of leaves and in specific floral organs. The potential physiological role of AtPLT5 is discussed.
• K currents through SV-type vacuolar channels are sensitive to elevated luminal sodium levels. Ivashikina, N.; Hedrich, R. In Plant Journal, 41(4), pp. 606–614. 2005.
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  Non-selective slow vacuolar (SV) channels mediate uptake of K+ and Na+ into vacuolar compartment. Under salt stress plant cells accumulate Na+ in the vacuole and release vacuolar K+ into the cytoplasm. It is, however, unclear how plants mediate transport of K+ from the vacuole without concomitant efflux of toxic Na+. Here we show by patch-clamp studies on isolated Arabidopsis thaliana cell culture vacuoles that SV channels do not mediate Na+ release from the vacuole as luminal Na+ blocks this channel. Gating of the SV channel is dependent on the K+ gradient across the vacuolar membrane. Under symmetrical K+ concentrations on both sides of the vacuolar membrane, SV channels mediate potassium uptake. When cytoplasmic K+ decreases, SV channels allow K+ release from the vacuole. In contrast to potassium, Na+ can be taken up by SV channels, but not released even in the presence of a 150-fold gradient (lumen to cytoplasm). Accumulation of Na+ in the vacuole shifts the activation potential of SV channels to more positive voltages and prevents gradient-driven efflux of K+. Similar to sodium, under physiological conditions, vacuolar Ca2+ is not released from vacuoles via SV channels. We suggest that a major Arabidopsis SV channel is equipped with a positively charged intrinsic gate located at the luminal side, which prevents release of Na+ and Ca2+, but permits efflux of K+. This property of the SV channel guarantees that K+ can shuttle across the vacuolar membrane while maintaining Na+ and Ca2+ stored in this organelle.

  @article{RN1168, abstract = {Non-selective slow vacuolar (SV) channels mediate uptake of K+ and Na+ into vacuolar compartment. Under salt stress plant cells accumulate Na+ in the vacuole and release vacuolar K+ into the cytoplasm. It is, however, unclear how plants mediate transport of K+ from the vacuole without concomitant efflux of toxic Na+. Here we show by patch-clamp studies on isolated Arabidopsis thaliana cell culture vacuoles that SV channels do not mediate Na+ release from the vacuole as luminal Na+ blocks this channel. Gating of the SV channel is dependent on the K+ gradient across the vacuolar membrane. Under symmetrical K+ concentrations on both sides of the vacuolar membrane, SV channels mediate potassium uptake. When cytoplasmic K+ decreases, SV channels allow K+ release from the vacuole. In contrast to potassium, Na+ can be taken up by SV channels, but not released even in the presence of a 150-fold gradient (lumen to cytoplasm). Accumulation of Na+ in the vacuole shifts the activation potential of SV channels to more positive voltages and prevents gradient-driven efflux of K+. Similar to sodium, under physiological conditions, vacuolar Ca2+ is not released from vacuoles via SV channels. We suggest that a major Arabidopsis SV channel is equipped with a positively charged intrinsic gate located at the luminal side, which prevents release of Na+ and Ca2+, but permits efflux of K+. This property of the SV channel guarantees that K+ can shuttle across the vacuolar membrane while maintaining Na+ and Ca2+ stored in this organelle.}, author = {Ivashikina, N. and Hedrich, R.}, journal = {Plant Journal}, keywords = {arabidopsis}, note = {893gy Times Cited:70 Cited References Count:54}, number = 4, pages = {606-614}, title = {K currents through SV-type vacuolar channels are sensitive to elevated luminal sodium levels}, type = {Journal Article}, volume = 41, year = 2005 }

  %0 Journal Article %1 RN1168 %A Ivashikina, N. %A Hedrich, R. %D 2005 %J Plant Journal %N 4 %P 606-614 %R 10.1111/j.1365-313X.2004.02324.x %T K currents through SV-type vacuolar channels are sensitive to elevated luminal sodium levels %U /brokenurl#<Go to ISI>://WOS:000226708500009 %V 41 %X Non-selective slow vacuolar (SV) channels mediate uptake of K+ and Na+ into vacuolar compartment. Under salt stress plant cells accumulate Na+ in the vacuole and release vacuolar K+ into the cytoplasm. It is, however, unclear how plants mediate transport of K+ from the vacuole without concomitant efflux of toxic Na+. Here we show by patch-clamp studies on isolated Arabidopsis thaliana cell culture vacuoles that SV channels do not mediate Na+ release from the vacuole as luminal Na+ blocks this channel. Gating of the SV channel is dependent on the K+ gradient across the vacuolar membrane. Under symmetrical K+ concentrations on both sides of the vacuolar membrane, SV channels mediate potassium uptake. When cytoplasmic K+ decreases, SV channels allow K+ release from the vacuole. In contrast to potassium, Na+ can be taken up by SV channels, but not released even in the presence of a 150-fold gradient (lumen to cytoplasm). Accumulation of Na+ in the vacuole shifts the activation potential of SV channels to more positive voltages and prevents gradient-driven efflux of K+. Similar to sodium, under physiological conditions, vacuolar Ca2+ is not released from vacuoles via SV channels. We suggest that a major Arabidopsis SV channel is equipped with a positively charged intrinsic gate located at the luminal side, which prevents release of Na+ and Ca2+, but permits efflux of K+. This property of the SV channel guarantees that K+ can shuttle across the vacuolar membrane while maintaining Na+ and Ca2+ stored in this organelle.
• Differential expression of K channels between guard cells and subsidiary cells within the maize stomatal complex. Büchsenschütz, K.; Marten, I.; Becker, D.; Philippar, K.; Ache, P.; Hedrich, R. In Planta, 222(6), pp. 968–976. 2005.
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  Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.

  @article{RN1173, abstract = {Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.}, author = {Büchsenschütz, K. and Marten, I. and Becker, D. and Philippar, K. and Ache, P. and Hedrich, R.}, journal = {Planta}, keywords = {guard}, note = {988vr Times Cited:41 Cited References Count:32}, number = 6, pages = {968-976}, title = {Differential expression of K channels between guard cells and subsidiary cells within the maize stomatal complex}, type = {Journal Article}, volume = 222, year = 2005 }

  %0 Journal Article %1 RN1173 %A Büchsenschütz, K. %A Marten, I. %A Becker, D. %A Philippar, K. %A Ache, P. %A Hedrich, R. %D 2005 %J Planta %N 6 %P 968-976 %R 10.1007/s00425-005-0038-6 %T Differential expression of K channels between guard cells and subsidiary cells within the maize stomatal complex %U /brokenurl#<Go to ISI>://WOS:000233629700004 %V 222 %X Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.
• , a glutamate receptor channel-like gene is sensitive to touch and cold. Meyerhoff, O.; Müller, K.; Roelfsema, M. R.; Latz, A.; Lacombe, B.; Hedrich, R.; Dietrich, P.; Becker, D. In Planta, 222(3), pp. 418–427. 2005.
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  The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca2+ -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca2+ -based, fast transmission of environmental stress.

  @article{RN1165, abstract = {The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca2+ -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca2+ -based, fast transmission of environmental stress.}, author = {Meyerhoff, O. and Müller, K. and Roelfsema, M. R. and Latz, A. and Lacombe, B. and Hedrich, R. and Dietrich, P. and Becker, D.}, journal = {Planta}, keywords = {calcium}, note = {974sl Times Cited:134 Cited References Count:24}, number = 3, pages = {418-427}, title = {, a glutamate receptor channel-like gene is sensitive to touch and cold}, type = {Journal Article}, volume = 222, year = 2005 }

  %0 Journal Article %1 RN1165 %A Meyerhoff, O. %A Müller, K. %A Roelfsema, M. R. %A Latz, A. %A Lacombe, B. %A Hedrich, R. %A Dietrich, P. %A Becker, D. %D 2005 %J Planta %N 3 %P 418-427 %R 10.1007/s00425-005-1551-3 %T , a glutamate receptor channel-like gene is sensitive to touch and cold %U /brokenurl#<Go to ISI>://WOS:000232611600003 %V 222 %X The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca2+ -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca2+ -based, fast transmission of environmental stress.
• AKT2/3 subunits render guard cell K channels Ca sensitive. Ivashikina, N.; Deeken, R.; Fischer, S.; Ache, P.; Hedrich, R. In Journal of General Physiology, 125(5), pp. 483–492. 2005.
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  Inward-rectifying K+ channels serve as a major pathway for Ca2+-sensitive K+ influx into guard cells. Arabidopsis thaliana guard cell inward-rectifying K+ channels are assembled from multiple K+ channel subunits. Following the recent isolation and characterization of an akt2/3-1 knockout mutant, we examined whether the AKT2/3 subunit carries the Ca2+ sensitivity of the guard cell inward rectifier. Quantification of RT-PCR products showed that despite the absence of AKT2 transcripts in guard cells of the knockout plant, expression levels of the other K+ channel subunits (KAT1, KAT2, AKT1, and AtKC1) remained largely unaffected. Patch-clamp experiments with guard cell protoplasts from wild type and akt2/3-1 mutant, however, revealed pronounced differences in Ca2+ sensitivity of the K+ inward rectifier. Wild-type channels were blocked by extracellular Ca2+ in a concentration- and voltage-dependent manner. Akt2/3-1 mutants lacked the voltage-dependent Ca2+ block, characteristic for the K+ inward rectifier. To confirm the akt2/3-1 phenotype, two independent knockout mutants, akt2-1 and akt2::En-1 were tested, demonstrating that the loss of AKT2/3 indeed affects the Ca2+ dependence of guard cell inward rectifier. In contrast to AKT2 knockout plants, AKT1, AtKC1, and KAT1 loss-of-function mutants retained Ca2+ block of the guard cell inward rectifier. When expressed in HEK293 cells, AKT2 channel displayed a pronounced susceptibility toward extracellular Ca2+, while the dominant guard cell K+ channel KAT2 was Ca2+ insensitive. Thus, we conclude that the AKT2/3 subunit constitutes the Ca2+ sensitivity of the guard cell K+ uptake channel.

  @article{RN1169, abstract = {Inward-rectifying K+ channels serve as a major pathway for Ca2+-sensitive K+ influx into guard cells. Arabidopsis thaliana guard cell inward-rectifying K+ channels are assembled from multiple K+ channel subunits. Following the recent isolation and characterization of an akt2/3-1 knockout mutant, we examined whether the AKT2/3 subunit carries the Ca2+ sensitivity of the guard cell inward rectifier. Quantification of RT-PCR products showed that despite the absence of AKT2 transcripts in guard cells of the knockout plant, expression levels of the other K+ channel subunits (KAT1, KAT2, AKT1, and AtKC1) remained largely unaffected. Patch-clamp experiments with guard cell protoplasts from wild type and akt2/3-1 mutant, however, revealed pronounced differences in Ca2+ sensitivity of the K+ inward rectifier. Wild-type channels were blocked by extracellular Ca2+ in a concentration- and voltage-dependent manner. Akt2/3-1 mutants lacked the voltage-dependent Ca2+ block, characteristic for the K+ inward rectifier. To confirm the akt2/3-1 phenotype, two independent knockout mutants, akt2-1 and akt2::En-1 were tested, demonstrating that the loss of AKT2/3 indeed affects the Ca2+ dependence of guard cell inward rectifier. In contrast to AKT2 knockout plants, AKT1, AtKC1, and KAT1 loss-of-function mutants retained Ca2+ block of the guard cell inward rectifier. When expressed in HEK293 cells, AKT2 channel displayed a pronounced susceptibility toward extracellular Ca2+, while the dominant guard cell K+ channel KAT2 was Ca2+ insensitive. Thus, we conclude that the AKT2/3 subunit constitutes the Ca2+ sensitivity of the guard cell K+ uptake channel.}, author = {Ivashikina, N. and Deeken, R. and Fischer, S. and Ache, P. and Hedrich, R.}, journal = {Journal of General Physiology}, keywords = {arabidopsis}, note = {919yp Times Cited:51 Cited References Count:60}, number = 5, pages = {483-492}, title = {AKT2/3 subunits render guard cell K channels Ca sensitive}, type = {Journal Article}, volume = 125, year = 2005 }

  %0 Journal Article %1 RN1169 %A Ivashikina, N. %A Deeken, R. %A Fischer, S. %A Ache, P. %A Hedrich, R. %D 2005 %J Journal of General Physiology %N 5 %P 483-492 %R 10.1085/jgp.200409211 %T AKT2/3 subunits render guard cell K channels Ca sensitive %U /brokenurl#<Go to ISI>://WOS:000228654000005 %V 125 %X Inward-rectifying K+ channels serve as a major pathway for Ca2+-sensitive K+ influx into guard cells. Arabidopsis thaliana guard cell inward-rectifying K+ channels are assembled from multiple K+ channel subunits. Following the recent isolation and characterization of an akt2/3-1 knockout mutant, we examined whether the AKT2/3 subunit carries the Ca2+ sensitivity of the guard cell inward rectifier. Quantification of RT-PCR products showed that despite the absence of AKT2 transcripts in guard cells of the knockout plant, expression levels of the other K+ channel subunits (KAT1, KAT2, AKT1, and AtKC1) remained largely unaffected. Patch-clamp experiments with guard cell protoplasts from wild type and akt2/3-1 mutant, however, revealed pronounced differences in Ca2+ sensitivity of the K+ inward rectifier. Wild-type channels were blocked by extracellular Ca2+ in a concentration- and voltage-dependent manner. Akt2/3-1 mutants lacked the voltage-dependent Ca2+ block, characteristic for the K+ inward rectifier. To confirm the akt2/3-1 phenotype, two independent knockout mutants, akt2-1 and akt2::En-1 were tested, demonstrating that the loss of AKT2/3 indeed affects the Ca2+ dependence of guard cell inward rectifier. In contrast to AKT2 knockout plants, AKT1, AtKC1, and KAT1 loss-of-function mutants retained Ca2+ block of the guard cell inward rectifier. When expressed in HEK293 cells, AKT2 channel displayed a pronounced susceptibility toward extracellular Ca2+, while the dominant guard cell K+ channel KAT2 was Ca2+ insensitive. Thus, we conclude that the AKT2/3 subunit constitutes the Ca2+ sensitivity of the guard cell K+ uptake channel.
• Gene expression pattern reflects metabolic adaptations of crown galls. Deeken, R.; Hedrich, R. In Phytopathology, 95(6), pp. S23-S23. 2005.
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  @article{RN1171, author = {Deeken, R. and Hedrich, R.}, journal = {Phytopathology}, keywords = {myOwn}, note = {Suppl. S V44go Times Cited:0 Cited References Count:0}, number = 6, pages = {S23-S23}, title = {Gene expression pattern reflects metabolic adaptations of crown galls}, type = {Journal Article}, volume = 95, year = 2005 }

  %0 Journal Article %1 RN1171 %A Deeken, R. %A Hedrich, R. %D 2005 %J Phytopathology %N 6 %P S23-S23 %T Gene expression pattern reflects metabolic adaptations of crown galls %U /brokenurl#<Go to ISI>://WOS:000202991400137 %V 95
• Nucleotides and Mg ions differentially regulate K channels and non-selective cation channels present in cells forming the stomatal complex. Wolf, T.; Guinot, D. R.; Hedrich, R.; Dietrich, P.; Marten, I. In Plant and Cell Physiology, 46(10), pp. 1682–1689. 2005.
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  Voltage-dependent inward-rectifying (Ki(in)) and outward-rectifying (K-out) K+ channels are capable of mediating K+ fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K+ channels provided evidence for the requirement of ATP to maintain K+ channel activity. Here, the nucleotide and Mg2+ dependencies of time-dependent Ki(in) and K-out channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K-out channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K-out, channels by fast activation kinetics, inhibition by elevated intracellular Mg2+ concentration, permeability for K+ as well as for Na+ and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K+ and Na+ transport in both cell types and species.

  @article{RN1163, abstract = {Voltage-dependent inward-rectifying (Ki(in)) and outward-rectifying (K-out) K+ channels are capable of mediating K+ fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K+ channels provided evidence for the requirement of ATP to maintain K+ channel activity. Here, the nucleotide and Mg2+ dependencies of time-dependent Ki(in) and K-out channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K-out channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K-out, channels by fast activation kinetics, inhibition by elevated intracellular Mg2+ concentration, permeability for K+ as well as for Na+ and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K+ and Na+ transport in both cell types and species.}, author = {Wolf, T. and Guinot, D. R. and Hedrich, R. and Dietrich, P. and Marten, I.}, journal = {Plant and Cell Physiology}, keywords = {cell}, note = {981jd Times Cited:10 Cited References Count:38}, number = 10, pages = {1682-1689}, title = {Nucleotides and Mg ions differentially regulate K channels and non-selective cation channels present in cells forming the stomatal complex}, type = {Journal Article}, volume = 46, year = 2005 }

  %0 Journal Article %1 RN1163 %A Wolf, T. %A Guinot, D. R. %A Hedrich, R. %A Dietrich, P. %A Marten, I. %D 2005 %J Plant and Cell Physiology %N 10 %P 1682-1689 %R 10.1093/pcp/pci184 %T Nucleotides and Mg ions differentially regulate K channels and non-selective cation channels present in cells forming the stomatal complex %U /brokenurl#<Go to ISI>://WOS:000233084000010 %V 46 %X Voltage-dependent inward-rectifying (Ki(in)) and outward-rectifying (K-out) K+ channels are capable of mediating K+ fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K+ channels provided evidence for the requirement of ATP to maintain K+ channel activity. Here, the nucleotide and Mg2+ dependencies of time-dependent Ki(in) and K-out channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K-out channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K-out, channels by fast activation kinetics, inhibition by elevated intracellular Mg2+ concentration, permeability for K+ as well as for Na+ and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K+ and Na+ transport in both cell types and species.
• In the light of stomatal opening: new insights into ’the Watergate’. Roelfsema, M. R. G.; Hedrich, R. In New Phytologist, 167(3), pp. 665–691. 2005.
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  Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.

  @article{RN1164, abstract = {Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.}, author = {Roelfsema, M. R. G. and Hedrich, R.}, journal = {New Phytologist}, keywords = {abscisic}, note = {952hq Times Cited:377 Cited References Count:270}, number = 3, pages = {665-691}, title = {In the light of stomatal opening: new insights into 'the Watergate'}, type = {Journal Article}, volume = 167, year = 2005 }

  %0 Journal Article %1 RN1164 %A Roelfsema, M. R. G. %A Hedrich, R. %D 2005 %J New Phytologist %N 3 %P 665-691 %R 10.1111/j.1469-8137.2005.01460.x %T In the light of stomatal opening: new insights into 'the Watergate' %U /brokenurl#<Go to ISI>://WOS:000230995000005 %V 167 %X Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.
• Cytosolic abscisic acid activates guard cell anion channels without preceding Ca signals. Levchenko, V.; Konrad, K. R.; Dietrich, P.; Roelfsema, M. R. G.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 102(11), pp. 4203–4208. 2005.
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  The phytohormone abscisic acid (ABA) reports on the water status of the plant and induces stomatal closure. Guard cell anion channels play a central role in this response, because they mediate anion efflux, and in turn, cause a depolarization-induced K+ release. We recorded early steps in ABA signaling, introducing multibarreled microelectrodes in guard cells of intact plants. Upon external ABA treatment, anion channels transiently activated after a lag phase of approximate to 2 min. As expected for a cytosolic ABA receptor, iontophoretic ABA loading into the cytoplasm initiated a rise in anion current without delay. These ABA responses could be elicited repetitively at resting and at largely depolarized potentials (e.g., 0 mV), ruling out signal transduction by means of hyperpolarization-activated calcium channels. Likewise, ABA stimulation did not induce a rise in the cytosolic free-calcium concentration. However, the presence of approximate to 100 nM background Ca2+ was required for anion channel function, because the action of ABA on anion channels was repressed after loading of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate. The chain of events appears very direct, because none of the tested putative ABA-signaling intermediates (inositol 1,4,5 trisphosphate, inositol hexakisphosphate, nicotinic acid adenine dinucleotide phosphate, and cyclic ADP-ribose), could mimic ABA as anion channel activator. In patch-clamp experiments, cytosolic ABA also evoked anion current transients carried by R- and S-type anion channels. The response was dose-dependent with half-maximum activation at 2.6 mu M ABA. Our studies point to an ABA pathway initiated by ABA binding to a cytosolic receptor that within seconds activates anion channels, and in turn, leads to depolarization of the plasma membrane.

  @article{RN1166, abstract = {The phytohormone abscisic acid (ABA) reports on the water status of the plant and induces stomatal closure. Guard cell anion channels play a central role in this response, because they mediate anion efflux, and in turn, cause a depolarization-induced K+ release. We recorded early steps in ABA signaling, introducing multibarreled microelectrodes in guard cells of intact plants. Upon external ABA treatment, anion channels transiently activated after a lag phase of approximate to 2 min. As expected for a cytosolic ABA receptor, iontophoretic ABA loading into the cytoplasm initiated a rise in anion current without delay. These ABA responses could be elicited repetitively at resting and at largely depolarized potentials (e.g., 0 mV), ruling out signal transduction by means of hyperpolarization-activated calcium channels. Likewise, ABA stimulation did not induce a rise in the cytosolic free-calcium concentration. However, the presence of approximate to 100 nM background Ca2+ was required for anion channel function, because the action of ABA on anion channels was repressed after loading of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate. The chain of events appears very direct, because none of the tested putative ABA-signaling intermediates (inositol 1,4,5 trisphosphate, inositol hexakisphosphate, nicotinic acid adenine dinucleotide phosphate, and cyclic ADP-ribose), could mimic ABA as anion channel activator. In patch-clamp experiments, cytosolic ABA also evoked anion current transients carried by R- and S-type anion channels. The response was dose-dependent with half-maximum activation at 2.6 mu M ABA. Our studies point to an ABA pathway initiated by ABA binding to a cytosolic receptor that within seconds activates anion channels, and in turn, leads to depolarization of the plasma membrane.}, author = {Levchenko, V. and Konrad, K. R. and Dietrich, P. and Roelfsema, M. R. G. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {stomatal}, note = {907pt Times Cited:133 Cited References Count:54}, number = 11, pages = {4203-4208}, title = {Cytosolic abscisic acid activates guard cell anion channels without preceding Ca signals}, type = {Journal Article}, volume = 102, year = 2005 }

  %0 Journal Article %1 RN1166 %A Levchenko, V. %A Konrad, K. R. %A Dietrich, P. %A Roelfsema, M. R. G. %A Hedrich, R. %D 2005 %J Proceedings of the National Academy of Sciences of the United States of America %N 11 %P 4203-4208 %R 10.1073/pnas.0500146102 %T Cytosolic abscisic acid activates guard cell anion channels without preceding Ca signals %U /brokenurl#<Go to ISI>://WOS:000227731000058 %V 102 %X The phytohormone abscisic acid (ABA) reports on the water status of the plant and induces stomatal closure. Guard cell anion channels play a central role in this response, because they mediate anion efflux, and in turn, cause a depolarization-induced K+ release. We recorded early steps in ABA signaling, introducing multibarreled microelectrodes in guard cells of intact plants. Upon external ABA treatment, anion channels transiently activated after a lag phase of approximate to 2 min. As expected for a cytosolic ABA receptor, iontophoretic ABA loading into the cytoplasm initiated a rise in anion current without delay. These ABA responses could be elicited repetitively at resting and at largely depolarized potentials (e.g., 0 mV), ruling out signal transduction by means of hyperpolarization-activated calcium channels. Likewise, ABA stimulation did not induce a rise in the cytosolic free-calcium concentration. However, the presence of approximate to 100 nM background Ca2+ was required for anion channel function, because the action of ABA on anion channels was repressed after loading of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate. The chain of events appears very direct, because none of the tested putative ABA-signaling intermediates (inositol 1,4,5 trisphosphate, inositol hexakisphosphate, nicotinic acid adenine dinucleotide phosphate, and cyclic ADP-ribose), could mimic ABA as anion channel activator. In patch-clamp experiments, cytosolic ABA also evoked anion current transients carried by R- and S-type anion channels. The response was dose-dependent with half-maximum activation at 2.6 mu M ABA. Our studies point to an ABA pathway initiated by ABA binding to a cytosolic receptor that within seconds activates anion channels, and in turn, leads to depolarization of the plasma membrane.
• Polar-localised poplar K channel capable of controlling electrical properties of wood-forming cells. Arend, M.; Stinzing, A.; Wind, C.; Langer, K.; Latz, A.; Ache, P.; Fromm, J.; Hedrich, R. In Planta, 223(1), pp. 140–148. 2005.
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  In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K+ -release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K+ channels as the major K+ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.

  @article{RN1174, abstract = {In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K+ -release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K+ channels as the major K+ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.}, author = {Arend, M. and Stinzing, A. and Wind, C. and Langer, K. and Latz, A. and Ache, P. and Fromm, J. and Hedrich, R.}, journal = {Planta}, keywords = {electrophysiology}, note = {990ec Times Cited:21 Cited References Count:38}, number = 1, pages = {140-148}, title = {Polar-localised poplar K channel capable of controlling electrical properties of wood-forming cells}, type = {Journal Article}, volume = 223, year = 2005 }

  %0 Journal Article %1 RN1174 %A Arend, M. %A Stinzing, A. %A Wind, C. %A Langer, K. %A Latz, A. %A Ache, P. %A Fromm, J. %A Hedrich, R. %D 2005 %J Planta %N 1 %P 140-148 %R 10.1007/s00425-005-0122-y %T Polar-localised poplar K channel capable of controlling electrical properties of wood-forming cells %U /brokenurl#<Go to ISI>://WOS:000233725000014 %V 223 %X In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K+ -release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K+ channels as the major K+ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.
• Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force. Carpaneto, A.; Geiger, D.; Bamberg, E.; Sauer, N.; Fromm, J.; Hedrich, R. In Journal of Biological Chemistry, 280(22), pp. 21437–21443. 2005.
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  The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole- free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Munch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Munch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/ proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves ( source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues ( sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.

  @article{RN1172, abstract = {The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole- free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Munch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Munch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/ proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves ( source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues ( sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.}, author = {Carpaneto, A. and Geiger, D. and Bamberg, E. and Sauer, N. and Fromm, J. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {transporter}, note = {930ta Times Cited:169 Cited References Count:32}, number = 22, pages = {21437-21443}, title = {Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force}, type = {Journal Article}, volume = 280, year = 2005 }

  %0 Journal Article %1 RN1172 %A Carpaneto, A. %A Geiger, D. %A Bamberg, E. %A Sauer, N. %A Fromm, J. %A Hedrich, R. %D 2005 %J Journal of Biological Chemistry %N 22 %P 21437-21443 %R 10.1074/jbc.M501785200 %T Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force %U /brokenurl#<Go to ISI>://WOS:000229438800064 %V 280 %X The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole- free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Munch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Munch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/ proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves ( source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues ( sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.
• Rice K uptake channel OsAKT1 is sensitive to salt stress. Fuchs, I.; Stölzle, S.; Ivashikina, N.; Hedrich, R. In Planta, 221(2), pp. 212–221. 2005.
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  Potassium ions constitute the most important macronutrients taken up by plants. To unravel the mechanisms of K+ uptake and its sensitivity to salt stress in the model plant rice, we isolated and functionally characterized OsAKT1, a potassium channel homologous to the Arabidopsis root inward recti. er AKT1. OsAKT1 transcripts were predominantly found in the coleoptile and in the roots of young rice seedlings. K+ channel mRNA decreases in response to salt stress, both in the shoot and in the root of 4-day-old rice seedlings. Following expression in HEK293 cells, we were able to characterize OsAKT1 as a voltage-dependent, inward-rectifying K+ channel regulated by extracellular Ca2+ and protons. Patch-clamp studies on rice root protoplasts identified a K+ inward rectifier with similar channel properties as heterologously expressed OsAKT1. In line with the transcriptional downregulation of OsAKT1 in response to salt stress, inward K+ currents were significantly reduced in root protoplasts. Thus, OsAKT1 seems to represent the dominant salt-sensitive K+ uptake channel in rice roots.

  @article{RN1170, abstract = {Potassium ions constitute the most important macronutrients taken up by plants. To unravel the mechanisms of K+ uptake and its sensitivity to salt stress in the model plant rice, we isolated and functionally characterized OsAKT1, a potassium channel homologous to the Arabidopsis root inward recti. er AKT1. OsAKT1 transcripts were predominantly found in the coleoptile and in the roots of young rice seedlings. K+ channel mRNA decreases in response to salt stress, both in the shoot and in the root of 4-day-old rice seedlings. Following expression in HEK293 cells, we were able to characterize OsAKT1 as a voltage-dependent, inward-rectifying K+ channel regulated by extracellular Ca2+ and protons. Patch-clamp studies on rice root protoplasts identified a K+ inward rectifier with similar channel properties as heterologously expressed OsAKT1. In line with the transcriptional downregulation of OsAKT1 in response to salt stress, inward K+ currents were significantly reduced in root protoplasts. Thus, OsAKT1 seems to represent the dominant salt-sensitive K+ uptake channel in rice roots.}, author = {Fuchs, I. and Stölzle, S. and Ivashikina, N. and Hedrich, R.}, journal = {Planta}, keywords = {akt1}, note = {923or Times Cited:116 Cited References Count:48}, number = 2, pages = {212-221}, title = {Rice K uptake channel OsAKT1 is sensitive to salt stress}, type = {Journal Article}, volume = 221, year = 2005 }

  %0 Journal Article %1 RN1170 %A Fuchs, I. %A Stölzle, S. %A Ivashikina, N. %A Hedrich, R. %D 2005 %J Planta %N 2 %P 212-221 %R 10.1007/s00425-004-1437-9 %T Rice K uptake channel OsAKT1 is sensitive to salt stress %U /brokenurl#<Go to ISI>://WOS:000228919700005 %V 221 %X Potassium ions constitute the most important macronutrients taken up by plants. To unravel the mechanisms of K+ uptake and its sensitivity to salt stress in the model plant rice, we isolated and functionally characterized OsAKT1, a potassium channel homologous to the Arabidopsis root inward recti. er AKT1. OsAKT1 transcripts were predominantly found in the coleoptile and in the roots of young rice seedlings. K+ channel mRNA decreases in response to salt stress, both in the shoot and in the root of 4-day-old rice seedlings. Following expression in HEK293 cells, we were able to characterize OsAKT1 as a voltage-dependent, inward-rectifying K+ channel regulated by extracellular Ca2+ and protons. Patch-clamp studies on rice root protoplasts identified a K+ inward rectifier with similar channel properties as heterologously expressed OsAKT1. In line with the transcriptional downregulation of OsAKT1 in response to salt stress, inward K+ currents were significantly reduced in root protoplasts. Thus, OsAKT1 seems to represent the dominant salt-sensitive K+ uptake channel in rice roots.

• Differential regulation of K channels in epidermal and stelar root cells. Diatloff, E.; Geiger, D.; Shang, L.; Hedrich, R.; Roberts, S. K. In Plant Cell and Environment, 27(8), pp. 980–990. 2004.
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  The patch clamp technique was applied to protoplasts isolated from the epidermis and pericycle of Arabidopsis roots and their plasma membrane currents investigated. In the whole cell configuration, all protoplasts from the epidermis exhibited depolarization-activated time-dependent outwardly rectifying (OR) currents whereas OR currents were present in only 50% of cells from the pericycle. The properties of the OR currents in the epidermis and pericycle were compared with respect to their selectivity, pharmacology and gating. The time-dependent activation kinetics, selectivity and sensitivity to extracellular tetraethyl ammonium of the OR current in each cell type were not significantly different. The reversal potential (E-rev) of the OR currents indicated that they were primarily due to the movement of K+. However, the gating properties of the OR currents from the epidermis differed markedly from those exhibited in the pericycle. Although both cell types displayed OR currents with voltage-dependent gating modulated in a potassium-dependent fashion [i.e. the activation threshold (V-0.5) was displaced to more positive voltages as extracellular K+ increased], the OR currents in the epidermis also displayed voltage-independent gating by extracellular K+ which dramatically regulated current density. In the present study, reducing extracellular K+ activity from 40 to 0.87 rum reduced the OR current density in epidermal cells by approximately 80%. The chord conductance of the OR current saturated as a function of extracellular K+ and could be fitted with a Michaelis-Menten function to yield a binding constant (K.) of 10.5 mm. The ability of other monovalent cations to substitute for K+-gating of the OR currents was also investigated and shown to exhibit a relative sequence of K+ greater than or equal to Rb+ > Cs+ > Na+ greater than or equal to Li+ (Eisenmann sequence IV) with respect to efficacy of gating. Furthermore, single channel recordings demonstrated that channel activity rather than the single channel conductance was modulated by extracellular W. In contrast, OR current density in the pericycle was largely independent of extracellular K+. It is suggested that the contrasting gating properties of the K+ channels in the epidermis and pericycle reflect their different physiological roles, particularly with respect to their role in K+ (nutrient) transport from the soil solution to the shoot.

  @article{RN1180, abstract = {The patch clamp technique was applied to protoplasts isolated from the epidermis and pericycle of Arabidopsis roots and their plasma membrane currents investigated. In the whole cell configuration, all protoplasts from the epidermis exhibited depolarization-activated time-dependent outwardly rectifying (OR) currents whereas OR currents were present in only 50% of cells from the pericycle. The properties of the OR currents in the epidermis and pericycle were compared with respect to their selectivity, pharmacology and gating. The time-dependent activation kinetics, selectivity and sensitivity to extracellular tetraethyl ammonium of the OR current in each cell type were not significantly different. The reversal potential (E-rev) of the OR currents indicated that they were primarily due to the movement of K+. However, the gating properties of the OR currents from the epidermis differed markedly from those exhibited in the pericycle. Although both cell types displayed OR currents with voltage-dependent gating modulated in a potassium-dependent fashion [i.e. the activation threshold (V-0.5) was displaced to more positive voltages as extracellular K+ increased], the OR currents in the epidermis also displayed voltage-independent gating by extracellular K+ which dramatically regulated current density. In the present study, reducing extracellular K+ activity from 40 to 0.87 rum reduced the OR current density in epidermal cells by approximately 80%. The chord conductance of the OR current saturated as a function of extracellular K+ and could be fitted with a Michaelis-Menten function to yield a binding constant (K.) of 10.5 mm. The ability of other monovalent cations to substitute for K+-gating of the OR currents was also investigated and shown to exhibit a relative sequence of K+ greater than or equal to Rb+ > Cs+ > Na+ greater than or equal to Li+ (Eisenmann sequence IV) with respect to efficacy of gating. Furthermore, single channel recordings demonstrated that channel activity rather than the single channel conductance was modulated by extracellular W. In contrast, OR current density in the pericycle was largely independent of extracellular K+. It is suggested that the contrasting gating properties of the K+ channels in the epidermis and pericycle reflect their different physiological roles, particularly with respect to their role in K+ (nutrient) transport from the soil solution to the shoot.}, author = {Diatloff, E. and Geiger, D. and Shang, L. and Hedrich, R. and Roberts, S. K.}, journal = {Plant Cell and Environment}, keywords = {arabidopsis}, note = {843fr Times Cited:3 Cited References Count:24}, number = 8, pages = {980-990}, title = {Differential regulation of K channels in epidermal and stelar root cells}, type = {Journal Article}, volume = 27, year = 2004 }

  %0 Journal Article %1 RN1180 %A Diatloff, E. %A Geiger, D. %A Shang, L. %A Hedrich, R. %A Roberts, S. K. %D 2004 %J Plant Cell and Environment %N 8 %P 980-990 %R DOI 10.1111/j.1365-3040.2004.01201.x %T Differential regulation of K channels in epidermal and stelar root cells %U /brokenurl#<Go to ISI>://WOS:000223064400003 %V 27 %X The patch clamp technique was applied to protoplasts isolated from the epidermis and pericycle of Arabidopsis roots and their plasma membrane currents investigated. In the whole cell configuration, all protoplasts from the epidermis exhibited depolarization-activated time-dependent outwardly rectifying (OR) currents whereas OR currents were present in only 50% of cells from the pericycle. The properties of the OR currents in the epidermis and pericycle were compared with respect to their selectivity, pharmacology and gating. The time-dependent activation kinetics, selectivity and sensitivity to extracellular tetraethyl ammonium of the OR current in each cell type were not significantly different. The reversal potential (E-rev) of the OR currents indicated that they were primarily due to the movement of K+. However, the gating properties of the OR currents from the epidermis differed markedly from those exhibited in the pericycle. Although both cell types displayed OR currents with voltage-dependent gating modulated in a potassium-dependent fashion [i.e. the activation threshold (V-0.5) was displaced to more positive voltages as extracellular K+ increased], the OR currents in the epidermis also displayed voltage-independent gating by extracellular K+ which dramatically regulated current density. In the present study, reducing extracellular K+ activity from 40 to 0.87 rum reduced the OR current density in epidermal cells by approximately 80%. The chord conductance of the OR current saturated as a function of extracellular K+ and could be fitted with a Michaelis-Menten function to yield a binding constant (K.) of 10.5 mm. The ability of other monovalent cations to substitute for K+-gating of the OR currents was also investigated and shown to exhibit a relative sequence of K+ greater than or equal to Rb+ > Cs+ > Na+ greater than or equal to Li+ (Eisenmann sequence IV) with respect to efficacy of gating. Furthermore, single channel recordings demonstrated that channel activity rather than the single channel conductance was modulated by extracellular W. In contrast, OR current density in the pericycle was largely independent of extracellular K+. It is suggested that the contrasting gating properties of the K+ channels in the epidermis and pericycle reflect their different physiological roles, particularly with respect to their role in K+ (nutrient) transport from the soil solution to the shoot.
• The poplar K channel KPT1 is associated with K uptake during stomatal opening and bud development. Langer, K.; Levchenko, V.; Fromm, J.; Geiger, D.; Steinmeyer, R.; Lautner, S.; Ache, P.; Hedrich, R. In Plant Journal, 37(6), pp. 828–838. 2004.
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  To gain insights into the performance of poplar guard cells, we have measured stomatal conductance and aperture, guard cell K+ content and K+-channel activity of the guard cell plasma membrane in intact poplar leaves. In contrast to Arabidopsis, broad bean and tobacco grown under same conditions, poplar stomata operated just in the dynamic range - any change in conductance altered the rate of photosynthesis. In response to light, CO2 and abscisic acid (ABA), the stomatal opening velocity was two to five times faster than that measured for Arabidopsis thaliana, Nicotiana tabacum and Vicia faba. When stomata opened, the K+ content of guard cells increased almost twofold, indicating that the very fast stomatal opening in this species is mediated via potassium uptake. Following impalement of single guard cells embedded in their natural environment of intact leaves with triple-barrelled microelectrodes, time-dependent inward and outward-rectifying K+-channel-mediated currents of large amplitude were recorded. To analyse the molecular nature of genes encoding guard cell K+-uptake channels, we cloned K+-transporter Populus tremula (KPT)1 and functionally expressed this potassium channel in a K+-uptake-deficient Escherichia coli mutant. In addition to guard cells, this K+-transporter gene was expressed in buds, where the KPT1 gene activity strongly correlated with bud break. Thus, KPT1 represents one of only few poplar genes associated with bud flush.

  @article{RN1179, abstract = {To gain insights into the performance of poplar guard cells, we have measured stomatal conductance and aperture, guard cell K+ content and K+-channel activity of the guard cell plasma membrane in intact poplar leaves. In contrast to Arabidopsis, broad bean and tobacco grown under same conditions, poplar stomata operated just in the dynamic range - any change in conductance altered the rate of photosynthesis. In response to light, CO2 and abscisic acid (ABA), the stomatal opening velocity was two to five times faster than that measured for Arabidopsis thaliana, Nicotiana tabacum and Vicia faba. When stomata opened, the K+ content of guard cells increased almost twofold, indicating that the very fast stomatal opening in this species is mediated via potassium uptake. Following impalement of single guard cells embedded in their natural environment of intact leaves with triple-barrelled microelectrodes, time-dependent inward and outward-rectifying K+-channel-mediated currents of large amplitude were recorded. To analyse the molecular nature of genes encoding guard cell K+-uptake channels, we cloned K+-transporter Populus tremula (KPT)1 and functionally expressed this potassium channel in a K+-uptake-deficient Escherichia coli mutant. In addition to guard cells, this K+-transporter gene was expressed in buds, where the KPT1 gene activity strongly correlated with bud break. Thus, KPT1 represents one of only few poplar genes associated with bud flush.}, author = {Langer, K. and Levchenko, V. and Fromm, J. and Geiger, D. and Steinmeyer, R. and Lautner, S. and Ache, P. and Hedrich, R.}, journal = {Plant Journal}, keywords = {k+}, note = {802aa Times Cited:39 Cited References Count:47}, number = 6, pages = {828-838}, title = {The poplar K channel KPT1 is associated with K uptake during stomatal opening and bud development}, type = {Journal Article}, volume = 37, year = 2004 }

  %0 Journal Article %1 RN1179 %A Langer, K. %A Levchenko, V. %A Fromm, J. %A Geiger, D. %A Steinmeyer, R. %A Lautner, S. %A Ache, P. %A Hedrich, R. %D 2004 %J Plant Journal %N 6 %P 828-838 %R 10.1111/j.0960-7412.2003.02008.x %T The poplar K channel KPT1 is associated with K uptake during stomatal opening and bud development %U /brokenurl#<Go to ISI>://WOS:000220135200004 %V 37 %X To gain insights into the performance of poplar guard cells, we have measured stomatal conductance and aperture, guard cell K+ content and K+-channel activity of the guard cell plasma membrane in intact poplar leaves. In contrast to Arabidopsis, broad bean and tobacco grown under same conditions, poplar stomata operated just in the dynamic range - any change in conductance altered the rate of photosynthesis. In response to light, CO2 and abscisic acid (ABA), the stomatal opening velocity was two to five times faster than that measured for Arabidopsis thaliana, Nicotiana tabacum and Vicia faba. When stomata opened, the K+ content of guard cells increased almost twofold, indicating that the very fast stomatal opening in this species is mediated via potassium uptake. Following impalement of single guard cells embedded in their natural environment of intact leaves with triple-barrelled microelectrodes, time-dependent inward and outward-rectifying K+-channel-mediated currents of large amplitude were recorded. To analyse the molecular nature of genes encoding guard cell K+-uptake channels, we cloned K+-transporter Populus tremula (KPT)1 and functionally expressed this potassium channel in a K+-uptake-deficient Escherichia coli mutant. In addition to guard cells, this K+-transporter gene was expressed in buds, where the KPT1 gene activity strongly correlated with bud break. Thus, KPT1 represents one of only few poplar genes associated with bud flush.
• Involvement of a potassium channel gene, , in the cell cycle progression of tobacco BY-2 cells. Sano, T.; Becker, D.; Hedrich, R. In Plant and Cell Physiology, 45, pp. S173-S173. 2004.
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  @article{RN1175, author = {Sano, T. and Becker, D. and Hedrich, R.}, journal = {Plant and Cell Physiology}, keywords = {myOwn}, note = {Suppl. S 808tz Times Cited:0 Cited References Count:0}, pages = {S173-S173}, title = {Involvement of a potassium channel gene, , in the cell cycle progression of tobacco BY-2 cells}, type = {Journal Article}, volume = 45, year = 2004 }

  %0 Journal Article %1 RN1175 %A Sano, T. %A Becker, D. %A Hedrich, R. %D 2004 %J Plant and Cell Physiology %P S173-S173 %T Involvement of a potassium channel gene, , in the cell cycle progression of tobacco BY-2 cells %U /brokenurl#<Go to ISI>://WOS:000220592700684 %V 45
• ABA depolarizes guard cells in intact plants, through a transient activation of R- and S-type anion channels. Roelfsema, M. R. G.; Levchenko, V.; Hedrich, R. In Plant Journal, 37(4), pp. 578–588. 2004.
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  During drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double-barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (DeltaG < 5 nS), ABA predominantly activated voltage-independent (slow (S)-type) anion channels. During strong responses (DeltaG > 5 nS), however, ABA activated voltage-dependent (rapid (R)-type) in addition to S-type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl- from guard cells and a rapid but confined reduction in stomatal aperture.

  @article{RN1176, abstract = {During drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double-barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (DeltaG < 5 nS), ABA predominantly activated voltage-independent (slow (S)-type) anion channels. During strong responses (DeltaG > 5 nS), however, ABA activated voltage-dependent (rapid (R)-type) in addition to S-type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl- from guard cells and a rapid but confined reduction in stomatal aperture.}, author = {Roelfsema, M. R. G. and Levchenko, V. and Hedrich, R.}, journal = {Plant Journal}, keywords = {abscisic}, note = {770jx Times Cited:92 Cited References Count:46}, number = 4, pages = {578-588}, title = {ABA depolarizes guard cells in intact plants, through a transient activation of R- and S-type anion channels}, type = {Journal Article}, volume = 37, year = 2004 }

  %0 Journal Article %1 RN1176 %A Roelfsema, M. R. G. %A Levchenko, V. %A Hedrich, R. %D 2004 %J Plant Journal %N 4 %P 578-588 %R 10.1111/j.1365-313X.2003.01985.x %T ABA depolarizes guard cells in intact plants, through a transient activation of R- and S-type anion channels %U /brokenurl#<Go to ISI>://WOS:000188720400011 %V 37 %X During drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double-barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (DeltaG < 5 nS), ABA predominantly activated voltage-independent (slow (S)-type) anion channels. During strong responses (DeltaG > 5 nS), however, ABA activated voltage-dependent (rapid (R)-type) in addition to S-type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl- from guard cells and a rapid but confined reduction in stomatal aperture.
• Differential expression of sucrose transporter and polyol transporter genes during maturation of common plantain companion cells. Ramsperger-Gleixner, M.; Geiger, D.; Hedrich, R.; Sauer, N. In Plant Physiology, 134(1), pp. 147–160. 2004.
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  The cDNAs of two sorbitol transporters, common plantain (Plantago major) polyol transporter (PLT) 1 and 2 (PmPLT1 and PmPLT2), were isolated from a vascular bundle-specific cDNA library from common plantain, a dicot plant transporting Suc plus sorbitol in its phloem. Here, we describe the kinetic characterization of these sorbitol transporters by functional expression in Brewer's yeast (Saccharomyces cerevisiae) and in Xenopus sp. oocytes and for the first time the localization of plant PLTs in specific cell types of the vascular tissue. In the yeast system, both proteins were shown to be uncoupler sensitive and could be characterized as low-affinity and low-specificity polyol symporters. The K-m value for the physiological substrate sorbitol is 12 mm for PmPLT1 and even higher for PmPLT2, which showed an almost linear increase in sorbitol transport rates up to 20 mm. These data were confirmed in the Xenopus sp. system, where PmPLT1 was analyzed in detail and characterized as a H+ symporter. Using peptide-specific polyclonal antisera against PmPLT1 or PmPLT2 and simultaneous labeling with the monoclonal antiserum 1A2 raised against the companion cell-specific PmSUC2 Suc transporter, both PLTs were localized to companion cells of the phloem in common plantain source leaves. These analyses revealed two different types of companion cells in the common plantain phloem: younger cells expressing PmSUC2 at higher levels and older cells expressing lower levels of PmSUC2 plus both PLT genes. The putative role of these low-affinity transporters in phloem loading is discussed.

  @article{RN1177, abstract = {The cDNAs of two sorbitol transporters, common plantain (Plantago major) polyol transporter (PLT) 1 and 2 (PmPLT1 and PmPLT2), were isolated from a vascular bundle-specific cDNA library from common plantain, a dicot plant transporting Suc plus sorbitol in its phloem. Here, we describe the kinetic characterization of these sorbitol transporters by functional expression in Brewer's yeast (Saccharomyces cerevisiae) and in Xenopus sp. oocytes and for the first time the localization of plant PLTs in specific cell types of the vascular tissue. In the yeast system, both proteins were shown to be uncoupler sensitive and could be characterized as low-affinity and low-specificity polyol symporters. The K-m value for the physiological substrate sorbitol is 12 mm for PmPLT1 and even higher for PmPLT2, which showed an almost linear increase in sorbitol transport rates up to 20 mm. These data were confirmed in the Xenopus sp. system, where PmPLT1 was analyzed in detail and characterized as a H+ symporter. Using peptide-specific polyclonal antisera against PmPLT1 or PmPLT2 and simultaneous labeling with the monoclonal antiserum 1A2 raised against the companion cell-specific PmSUC2 Suc transporter, both PLTs were localized to companion cells of the phloem in common plantain source leaves. These analyses revealed two different types of companion cells in the common plantain phloem: younger cells expressing PmSUC2 at higher levels and older cells expressing lower levels of PmSUC2 plus both PLT genes. The putative role of these low-affinity transporters in phloem loading is discussed.}, author = {Ramsperger-Gleixner, M. and Geiger, D. and Hedrich, R. and Sauer, N.}, journal = {Plant Physiology}, keywords = {l}, note = {767el Times Cited:66 Cited References Count:56}, number = 1, pages = {147-160}, title = {Differential expression of sucrose transporter and polyol transporter genes during maturation of common plantain companion cells}, type = {Journal Article}, volume = 134, year = 2004 }

  %0 Journal Article %1 RN1177 %A Ramsperger-Gleixner, M. %A Geiger, D. %A Hedrich, R. %A Sauer, N. %D 2004 %J Plant Physiology %N 1 %P 147-160 %R 10.1104/pp.103.027136 %T Differential expression of sucrose transporter and polyol transporter genes during maturation of common plantain companion cells %U /brokenurl#<Go to ISI>://WOS:000188427200017 %V 134 %X The cDNAs of two sorbitol transporters, common plantain (Plantago major) polyol transporter (PLT) 1 and 2 (PmPLT1 and PmPLT2), were isolated from a vascular bundle-specific cDNA library from common plantain, a dicot plant transporting Suc plus sorbitol in its phloem. Here, we describe the kinetic characterization of these sorbitol transporters by functional expression in Brewer's yeast (Saccharomyces cerevisiae) and in Xenopus sp. oocytes and for the first time the localization of plant PLTs in specific cell types of the vascular tissue. In the yeast system, both proteins were shown to be uncoupler sensitive and could be characterized as low-affinity and low-specificity polyol symporters. The K-m value for the physiological substrate sorbitol is 12 mm for PmPLT1 and even higher for PmPLT2, which showed an almost linear increase in sorbitol transport rates up to 20 mm. These data were confirmed in the Xenopus sp. system, where PmPLT1 was analyzed in detail and characterized as a H+ symporter. Using peptide-specific polyclonal antisera against PmPLT1 or PmPLT2 and simultaneous labeling with the monoclonal antiserum 1A2 raised against the companion cell-specific PmSUC2 Suc transporter, both PLTs were localized to companion cells of the phloem in common plantain source leaves. These analyses revealed two different types of companion cells in the common plantain phloem: younger cells expressing PmSUC2 at higher levels and older cells expressing lower levels of PmSUC2 plus both PLT genes. The putative role of these low-affinity transporters in phloem loading is discussed.
• AtTPK4, an tandem-pore K channel, poised to control the pollen membrane voltage in a pH- and Ca -dependent manner. Becker, D.; Geiger, D.; Dunkel, M.; Roller, A.; Bertl, A.; Latz, A.; Carpaneto, A.; Dietrich, P.; Roelfsema, M. R. G.; Voelker, C.; Schmidt, D.; Mueller-Roeber, B.; Czempinski, K.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 101(44), pp. 15621–15626. 2004.
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  The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.

  @article{RN1181, abstract = {The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.}, author = {Becker, D. and Geiger, D. and Dunkel, M. and Roller, A. and Bertl, A. and Latz, A. and Carpaneto, A. and Dietrich, P. and Roelfsema, M. R. G. and Voelker, C. and Schmidt, D. and Mueller-Roeber, B. and Czempinski, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {myOwn}, note = {868og Times Cited:122 Cited References Count:25}, number = 44, pages = {15621-15626}, title = {AtTPK4, an tandem-pore K channel, poised to control the pollen membrane voltage in a pH- and Ca -dependent manner}, type = {Journal Article}, volume = 101, year = 2004 }

  %0 Journal Article %1 RN1181 %A Becker, D. %A Geiger, D. %A Dunkel, M. %A Roller, A. %A Bertl, A. %A Latz, A. %A Carpaneto, A. %A Dietrich, P. %A Roelfsema, M. R. G. %A Voelker, C. %A Schmidt, D. %A Mueller-Roeber, B. %A Czempinski, K. %A Hedrich, R. %D 2004 %J Proceedings of the National Academy of Sciences of the United States of America %N 44 %P 15621-15626 %R 10.1073/pnas.0401502101 %T AtTPK4, an tandem-pore K channel, poised to control the pollen membrane voltage in a pH- and Ca -dependent manner %U /brokenurl#<Go to ISI>://WOS:000224922300015 %V 101 %X The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.
• Auxin activates and , two K -channel genes expressed in seedlings of. Philippar, K.; Ivashikina, N.; Ache, P.; Christian, M.; Lüthen, H.; Palme, K.; Hedrich, R. In Plant Journal, 37(6), pp. 815–827. 2004.
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  The transcript abundance of the K+-channel gene ZMK1 (Zea mays K+ channel 1) in maize coleoptiles is controlled by the phytohormone auxin. Thus, ZMK1 is thought to function in auxin-regulated coleoptile elongation, as well as during gravitropism and phototropism. To investigate related growth phenomena in the dicotyledonous plant Arabidopsis thaliana, we screened etiolated seedlings for auxin-induced K+-channel genes. Among the members of the Shaker-like K+ channels, we thereby identified transcripts of the inward rectifiers, KAT1 (K+ transporter of Arabidopsis thaliana) and KAT2, to be upregulated by auxin. The phloem-associated KAT2 was localised in cotyledons and the apical part of etiolated seedlings. In contrast, the K+-channel gene KAT1 was expressed in the cortex and epidermis of etiolated hypocotyls, as well as in flower stalks. Furthermore, KAT1 was induced by active auxins in auxin-sensitive tissues characterised by rapid cell elongation. Applying the patch-clamp technique to protoplasts of etiolated hypocotyls, we correlated the electrical properties of K+ currents with the expression profile of K+-channel genes. In KAT1-knockout mutants, K+ currents after auxin stimulation were characterised by reduced amplitudes. Thus, this change in the electrical properties of the K+-uptake channel in hypocotyl protoplasts resulted from an auxin-induced increase of active KAT1 proteins. The loss of KAT1-channel subunits, however, did not affect the auxin-induced growth rate of hypocotyls, pointing to compensation by residual, constitutive K+ transporters. From gene expression and electrophysiological data, we suggest that auxin regulation of KAT1 is involved in elongation growth of Arabidopsis. Furthermore, a role for KAT2 in the auxin-controlled vascular patterning of leaves is discussed.

  @article{RN1178, abstract = {The transcript abundance of the K+-channel gene ZMK1 (Zea mays K+ channel 1) in maize coleoptiles is controlled by the phytohormone auxin. Thus, ZMK1 is thought to function in auxin-regulated coleoptile elongation, as well as during gravitropism and phototropism. To investigate related growth phenomena in the dicotyledonous plant Arabidopsis thaliana, we screened etiolated seedlings for auxin-induced K+-channel genes. Among the members of the Shaker-like K+ channels, we thereby identified transcripts of the inward rectifiers, KAT1 (K+ transporter of Arabidopsis thaliana) and KAT2, to be upregulated by auxin. The phloem-associated KAT2 was localised in cotyledons and the apical part of etiolated seedlings. In contrast, the K+-channel gene KAT1 was expressed in the cortex and epidermis of etiolated hypocotyls, as well as in flower stalks. Furthermore, KAT1 was induced by active auxins in auxin-sensitive tissues characterised by rapid cell elongation. Applying the patch-clamp technique to protoplasts of etiolated hypocotyls, we correlated the electrical properties of K+ currents with the expression profile of K+-channel genes. In KAT1-knockout mutants, K+ currents after auxin stimulation were characterised by reduced amplitudes. Thus, this change in the electrical properties of the K+-uptake channel in hypocotyl protoplasts resulted from an auxin-induced increase of active KAT1 proteins. The loss of KAT1-channel subunits, however, did not affect the auxin-induced growth rate of hypocotyls, pointing to compensation by residual, constitutive K+ transporters. From gene expression and electrophysiological data, we suggest that auxin regulation of KAT1 is involved in elongation growth of Arabidopsis. Furthermore, a role for KAT2 in the auxin-controlled vascular patterning of leaves is discussed.}, author = {Philippar, K. and Ivashikina, N. and Ache, P. and Christian, M. and Lüthen, H. and Palme, K. and Hedrich, R.}, journal = {Plant Journal}, keywords = {arabidopsis}, note = {802aa Times Cited:79 Cited References Count:52}, number = 6, pages = {815-827}, title = {Auxin activates and , two K -channel genes expressed in seedlings of}, type = {Journal Article}, volume = 37, year = 2004 }

  %0 Journal Article %1 RN1178 %A Philippar, K. %A Ivashikina, N. %A Ache, P. %A Christian, M. %A Lüthen, H. %A Palme, K. %A Hedrich, R. %D 2004 %J Plant Journal %N 6 %P 815-827 %R 10.1111/j.1365-313X.2003.02006.x %T Auxin activates and , two K -channel genes expressed in seedlings of %U /brokenurl#<Go to ISI>://WOS:000220135200003 %V 37 %X The transcript abundance of the K+-channel gene ZMK1 (Zea mays K+ channel 1) in maize coleoptiles is controlled by the phytohormone auxin. Thus, ZMK1 is thought to function in auxin-regulated coleoptile elongation, as well as during gravitropism and phototropism. To investigate related growth phenomena in the dicotyledonous plant Arabidopsis thaliana, we screened etiolated seedlings for auxin-induced K+-channel genes. Among the members of the Shaker-like K+ channels, we thereby identified transcripts of the inward rectifiers, KAT1 (K+ transporter of Arabidopsis thaliana) and KAT2, to be upregulated by auxin. The phloem-associated KAT2 was localised in cotyledons and the apical part of etiolated seedlings. In contrast, the K+-channel gene KAT1 was expressed in the cortex and epidermis of etiolated hypocotyls, as well as in flower stalks. Furthermore, KAT1 was induced by active auxins in auxin-sensitive tissues characterised by rapid cell elongation. Applying the patch-clamp technique to protoplasts of etiolated hypocotyls, we correlated the electrical properties of K+ currents with the expression profile of K+-channel genes. In KAT1-knockout mutants, K+ currents after auxin stimulation were characterised by reduced amplitudes. Thus, this change in the electrical properties of the K+-uptake channel in hypocotyl protoplasts resulted from an auxin-induced increase of active KAT1 proteins. The loss of KAT1-channel subunits, however, did not affect the auxin-induced growth rate of hypocotyls, pointing to compensation by residual, constitutive K+ transporters. From gene expression and electrophysiological data, we suggest that auxin regulation of KAT1 is involved in elongation growth of Arabidopsis. Furthermore, a role for KAT2 in the auxin-controlled vascular patterning of leaves is discussed.

• Diurnal and light-regulated expression of AtSTP1 in guard cells of Arabidopsis. Stadler, R.; Büttner, M.; Ache, P.; Hedrich, R.; Ivashikina, N.; Melzer, M.; Shearson, S. M.; Smith, S. M.; Sauer, N. In Plant Physiology, 133(2), pp. 528–537. 2003.
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  Guard cell chloroplasts are unable to perform significant photosynthetic CO2 fixation via Rubisco. Therefore, guard cells depend on carbon supply from adjacent cells even during the light period. Due to their reversible turgor changes, this import cannot be mediated by plasmodesmata. Nevertheless, guard cells of several plants were shown to use extracellular sugars or to accumulate sucrose as an osmoticum that drives water influx to increase stomatal aperture. This paper describes the first localization of a guard cell-specific Arabidopsis sugar transporter involved in carbon acquisition of these symplastically isolated cells. Expression of the AtSTP1 H+-monosacharide symporter gene in guard cells was demonstrated by in situ hybridization and by immunolocalization with an AtSTP1-specific antiserum. Additional RNase protection analyses revealed a strong increase of AtSTP1 expression in the dark and a transient, diurnally regulated increase during the photoperiod around midday. This transient increase in AtSTP1 expression correlates in time with the described guard cell-specific accumulation of sucrose. Our data suggest a function of AtSTP1 in monosaccharide import into guard cells during the night and a possible role in osmoregulation during the day.

  @article{RN1183, abstract = {Guard cell chloroplasts are unable to perform significant photosynthetic CO2 fixation via Rubisco. Therefore, guard cells depend on carbon supply from adjacent cells even during the light period. Due to their reversible turgor changes, this import cannot be mediated by plasmodesmata. Nevertheless, guard cells of several plants were shown to use extracellular sugars or to accumulate sucrose as an osmoticum that drives water influx to increase stomatal aperture. This paper describes the first localization of a guard cell-specific Arabidopsis sugar transporter involved in carbon acquisition of these symplastically isolated cells. Expression of the AtSTP1 H+-monosacharide symporter gene in guard cells was demonstrated by in situ hybridization and by immunolocalization with an AtSTP1-specific antiserum. Additional RNase protection analyses revealed a strong increase of AtSTP1 expression in the dark and a transient, diurnally regulated increase during the photoperiod around midday. This transient increase in AtSTP1 expression correlates in time with the described guard cell-specific accumulation of sucrose. Our data suggest a function of AtSTP1 in monosaccharide import into guard cells during the night and a possible role in osmoregulation during the day.}, author = {Stadler, R. and Büttner, M. and Ache, P. and Hedrich, R. and Ivashikina, N. and Melzer, M. and Shearson, S. M. and Smith, S. M. and Sauer, N.}, journal = {Plant Physiology}, keywords = {myOwn}, note = {732ze Times Cited:101 Cited References Count:47}, number = 2, pages = {528-537}, title = {Diurnal and light-regulated expression of AtSTP1 in guard cells of Arabidopsis}, type = {Journal Article}, volume = 133, year = 2003 }

  %0 Journal Article %1 RN1183 %A Stadler, R. %A Büttner, M. %A Ache, P. %A Hedrich, R. %A Ivashikina, N. %A Melzer, M. %A Shearson, S. M. %A Smith, S. M. %A Sauer, N. %D 2003 %J Plant Physiology %N 2 %P 528-537 %R DOI 10.1104/pp.103.024240 %T Diurnal and light-regulated expression of AtSTP1 in guard cells of Arabidopsis %U /brokenurl#<Go to ISI>://WOS:000185974800015 %V 133 %X Guard cell chloroplasts are unable to perform significant photosynthetic CO2 fixation via Rubisco. Therefore, guard cells depend on carbon supply from adjacent cells even during the light period. Due to their reversible turgor changes, this import cannot be mediated by plasmodesmata. Nevertheless, guard cells of several plants were shown to use extracellular sugars or to accumulate sucrose as an osmoticum that drives water influx to increase stomatal aperture. This paper describes the first localization of a guard cell-specific Arabidopsis sugar transporter involved in carbon acquisition of these symplastically isolated cells. Expression of the AtSTP1 H+-monosacharide symporter gene in guard cells was demonstrated by in situ hybridization and by immunolocalization with an AtSTP1-specific antiserum. Additional RNase protection analyses revealed a strong increase of AtSTP1 expression in the dark and a transient, diurnally regulated increase during the photoperiod around midday. This transient increase in AtSTP1 expression correlates in time with the described guard cell-specific accumulation of sucrose. Our data suggest a function of AtSTP1 in monosaccharide import into guard cells during the night and a possible role in osmoregulation during the day.
• Isolation of promoter-GFP-marked companion cells for patch-clamp studies and expression profiling. Ivashikina, N.; Deeken, R.; Ache, P.; Kranz, E.; Pommerrenig, B.; Sauer, N.; Hedrich, R. In Plant Journal, 36(6), pp. 931–945. 2003.
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  K+ channels control K+ homeostasis and the membrane potential in the sieve element/companion cell complexes. K+ channels from Arabidopsis phloem cells expressing green fluorescent protein (GFP) under the control of the AtSUC2 promoter were analysed using the patch-clamp technique and quantitative RT-PCR. Single green fluorescent protoplasts were selected after being isolated enzymatically from vascular strands of rosette leaves. Companion cell protoplasts, which could be recognized by their nucleus, vacuole and chloroplasts, and by their expression of the phloem-specific marker genes SUC2 and AHA3, formed the basis for a cell-specific cDNA library and expressed sequence tag (EST) collection. Although we used primers for all members of the Shaker K+ channel family, we identified only AKT2, KAT1 and KCO6 transcripts. In addition, we also detected transcripts for AtPP2CA, a protein phosphatase, that interacts with AKT2/3. In line with the presence of the K+ channel transcripts, patch-clamp experiments identified distinct K+ channel types. Time-dependent inward rectifying K+ currents were activated upon hyperpolarization and were characterized by a pronounced Ca2+-sensitivity and inhibition by protons. Whole-cell inward currents were carried by single K+-selective channels with a unitary conductance of approximately 4 pS. Outward rectifying K+ channels (approximately 19 pS), with sigmoidal activation kinetics, were elicited upon depolarization. These two dominant phloem K+ channel types provide a versatile mechanism to mediate K+ fluxes required for phloem action and potassium cycling.

  @article{RN1185, abstract = {K+ channels control K+ homeostasis and the membrane potential in the sieve element/companion cell complexes. K+ channels from Arabidopsis phloem cells expressing green fluorescent protein (GFP) under the control of the AtSUC2 promoter were analysed using the patch-clamp technique and quantitative RT-PCR. Single green fluorescent protoplasts were selected after being isolated enzymatically from vascular strands of rosette leaves. Companion cell protoplasts, which could be recognized by their nucleus, vacuole and chloroplasts, and by their expression of the phloem-specific marker genes SUC2 and AHA3, formed the basis for a cell-specific cDNA library and expressed sequence tag (EST) collection. Although we used primers for all members of the Shaker K+ channel family, we identified only AKT2, KAT1 and KCO6 transcripts. In addition, we also detected transcripts for AtPP2CA, a protein phosphatase, that interacts with AKT2/3. In line with the presence of the K+ channel transcripts, patch-clamp experiments identified distinct K+ channel types. Time-dependent inward rectifying K+ currents were activated upon hyperpolarization and were characterized by a pronounced Ca2+-sensitivity and inhibition by protons. Whole-cell inward currents were carried by single K+-selective channels with a unitary conductance of approximately 4 pS. Outward rectifying K+ channels (approximately 19 pS), with sigmoidal activation kinetics, were elicited upon depolarization. These two dominant phloem K+ channel types provide a versatile mechanism to mediate K+ fluxes required for phloem action and potassium cycling.}, author = {Ivashikina, N. and Deeken, R. and Ache, P. and Kranz, E. and Pommerrenig, B. and Sauer, N. and Hedrich, R.}, journal = {Plant Journal}, keywords = {arabidopsis}, note = {753xt Times Cited:73 Cited References Count:63}, number = 6, pages = {931-945}, title = {Isolation of promoter-GFP-marked companion cells for patch-clamp studies and expression profiling}, type = {Journal Article}, volume = 36, year = 2003 }

  %0 Journal Article %1 RN1185 %A Ivashikina, N. %A Deeken, R. %A Ache, P. %A Kranz, E. %A Pommerrenig, B. %A Sauer, N. %A Hedrich, R. %D 2003 %J Plant Journal %N 6 %P 931-945 %R 10.1046/j.1365-313X.2003.01931.x %T Isolation of promoter-GFP-marked companion cells for patch-clamp studies and expression profiling %U /brokenurl#<Go to ISI>://WOS:000187257400017 %V 36 %X K+ channels control K+ homeostasis and the membrane potential in the sieve element/companion cell complexes. K+ channels from Arabidopsis phloem cells expressing green fluorescent protein (GFP) under the control of the AtSUC2 promoter were analysed using the patch-clamp technique and quantitative RT-PCR. Single green fluorescent protoplasts were selected after being isolated enzymatically from vascular strands of rosette leaves. Companion cell protoplasts, which could be recognized by their nucleus, vacuole and chloroplasts, and by their expression of the phloem-specific marker genes SUC2 and AHA3, formed the basis for a cell-specific cDNA library and expressed sequence tag (EST) collection. Although we used primers for all members of the Shaker K+ channel family, we identified only AKT2, KAT1 and KCO6 transcripts. In addition, we also detected transcripts for AtPP2CA, a protein phosphatase, that interacts with AKT2/3. In line with the presence of the K+ channel transcripts, patch-clamp experiments identified distinct K+ channel types. Time-dependent inward rectifying K+ currents were activated upon hyperpolarization and were characterized by a pronounced Ca2+-sensitivity and inhibition by protons. Whole-cell inward currents were carried by single K+-selective channels with a unitary conductance of approximately 4 pS. Outward rectifying K+ channels (approximately 19 pS), with sigmoidal activation kinetics, were elicited upon depolarization. These two dominant phloem K+ channel types provide a versatile mechanism to mediate K+ fluxes required for phloem action and potassium cycling.
• Regulation of the ABA-sensitive potassium channel gene in response to water stress. Becker, D.; Hoth, S.; Ache, P.; Wenkel, S.; Roelfsema, M. R. G.; Meyerhoff, O.; Hartung, W.; Hedrich, R. In Febs Letters, 554(1-2), pp. 119–126. 2003.
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  The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time-and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abil-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 1224 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, CORK expression as well as K-out(+) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately. 2003 Federation of European Biochemical Societies. (C) Published by Elsevier B.V. All rights reserved.

  @article{RN1190, abstract = {The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time-and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abil-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 1224 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, CORK expression as well as K-out(+) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately. 2003 Federation of European Biochemical Societies. (C) Published by Elsevier B.V. All rights reserved.}, author = {Becker, D. and Hoth, S. and Ache, P. and Wenkel, S. and Roelfsema, M. R. G. and Meyerhoff, O. and Hartung, W. and Hedrich, R.}, journal = {Febs Letters}, keywords = {cell}, note = {741dt Times Cited:117 Cited References Count:64}, number = {1-2}, pages = {119-126}, title = {Regulation of the ABA-sensitive potassium channel gene in response to water stress}, type = {Journal Article}, volume = 554, year = 2003 }

  %0 Journal Article %1 RN1190 %A Becker, D. %A Hoth, S. %A Ache, P. %A Wenkel, S. %A Roelfsema, M. R. G. %A Meyerhoff, O. %A Hartung, W. %A Hedrich, R. %D 2003 %J Febs Letters %N 1-2 %P 119-126 %R 10.1016/S0014-5793(03)01118-9 %T Regulation of the ABA-sensitive potassium channel gene in response to water stress %U /brokenurl#<Go to ISI>://WOS:000186444000022 %V 554 %X The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time-and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abil-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 1224 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, CORK expression as well as K-out(+) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately. 2003 Federation of European Biochemical Societies. (C) Published by Elsevier B.V. All rights reserved.
• Blue light activates calcium-permeable channels in mesophyll cells via the phototropin signaling pathway. Stoelzle, S.; Kagawa, T.; Wada, M.; Hedrich, R.; Dietrich, P. In Proceedings of the National Academy of Sciences of the United States of America, 100(3), pp. 1456–1461. 2003.
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  Light is a central regulator of plant growth and development. Among the processes triggered by blue and UV-A light, phototropism, stomatal movement, and chloroplast orientation rely on the activation of blue-light receptors known as phototropins. So far, these photoreceptors constitute a class of light receptor kinases unique to the plant kingdom. In Arabidopsis thaliana, the two members phot1 and phot2 have been shown to display partially overlapping functions. Up to now little is known about the signaling cascade, which links these phototropins to the physiological responses downstream of blue-light perception. Here, we show that on illumination with blue light, but not red light, voltage-dependent and calcium-permeable channels activate in the plasma membrane of mesophyll cells. Blue-light stimulation in the presence of the photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicates that blue-light receptors rather than photosynthesis control channel activity. Sensitivity toward the protein kinase inhibitor K252a further pointed to the possible involvement of light receptor kinases. In support of this hypothesis, in the photoreceptor mutant phot1-5, blue-light induction of calcium currents was dramatically reduced and was eliminated in the double mutant phot1-5 phot2-1. By contrast, in cry1-304 cry2-1, an Arabidopsis mutant lacking another class of plant blue-light receptors, the channel remained sensitive to blue light. We thus conclude that blue light triggers calcium fluxes via the phototropin-activated calcium-permeable channel.

  @article{RN1182, abstract = {Light is a central regulator of plant growth and development. Among the processes triggered by blue and UV-A light, phototropism, stomatal movement, and chloroplast orientation rely on the activation of blue-light receptors known as phototropins. So far, these photoreceptors constitute a class of light receptor kinases unique to the plant kingdom. In Arabidopsis thaliana, the two members phot1 and phot2 have been shown to display partially overlapping functions. Up to now little is known about the signaling cascade, which links these phototropins to the physiological responses downstream of blue-light perception. Here, we show that on illumination with blue light, but not red light, voltage-dependent and calcium-permeable channels activate in the plasma membrane of mesophyll cells. Blue-light stimulation in the presence of the photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicates that blue-light receptors rather than photosynthesis control channel activity. Sensitivity toward the protein kinase inhibitor K252a further pointed to the possible involvement of light receptor kinases. In support of this hypothesis, in the photoreceptor mutant phot1-5, blue-light induction of calcium currents was dramatically reduced and was eliminated in the double mutant phot1-5 phot2-1. By contrast, in cry1-304 cry2-1, an Arabidopsis mutant lacking another class of plant blue-light receptors, the channel remained sensitive to blue light. We thus conclude that blue light triggers calcium fluxes via the phototropin-activated calcium-permeable channel.}, author = {Stoelzle, S. and Kagawa, T. and Wada, M. and Hedrich, R. and Dietrich, P.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {ca2+}, note = {642zu Times Cited:124 Cited References Count:47}, number = 3, pages = {1456-1461}, title = {Blue light activates calcium-permeable channels in mesophyll cells via the phototropin signaling pathway}, type = {Journal Article}, volume = 100, year = 2003 }

  %0 Journal Article %1 RN1182 %A Stoelzle, S. %A Kagawa, T. %A Wada, M. %A Hedrich, R. %A Dietrich, P. %D 2003 %J Proceedings of the National Academy of Sciences of the United States of America %N 3 %P 1456-1461 %R 10.1073/pnas.0333408100 %T Blue light activates calcium-permeable channels in mesophyll cells via the phototropin signaling pathway %U /brokenurl#<Go to ISI>://WOS:000180838100122 %V 100 %X Light is a central regulator of plant growth and development. Among the processes triggered by blue and UV-A light, phototropism, stomatal movement, and chloroplast orientation rely on the activation of blue-light receptors known as phototropins. So far, these photoreceptors constitute a class of light receptor kinases unique to the plant kingdom. In Arabidopsis thaliana, the two members phot1 and phot2 have been shown to display partially overlapping functions. Up to now little is known about the signaling cascade, which links these phototropins to the physiological responses downstream of blue-light perception. Here, we show that on illumination with blue light, but not red light, voltage-dependent and calcium-permeable channels activate in the plasma membrane of mesophyll cells. Blue-light stimulation in the presence of the photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicates that blue-light receptors rather than photosynthesis control channel activity. Sensitivity toward the protein kinase inhibitor K252a further pointed to the possible involvement of light receptor kinases. In support of this hypothesis, in the photoreceptor mutant phot1-5, blue-light induction of calcium currents was dramatically reduced and was eliminated in the double mutant phot1-5 phot2-1. By contrast, in cry1-304 cry2-1, an Arabidopsis mutant lacking another class of plant blue-light receptors, the channel remained sensitive to blue light. We thus conclude that blue light triggers calcium fluxes via the phototropin-activated calcium-permeable channel.
• Energy-dependent solute uptake into the symplast of leaves:: ATP/KCl, ATP/sucrose, ATP/D-serine and H /ATP stoichiometries of transmembrane transport. Bukhov, N. G.; Hedrich, R.; Heber, U. In Plant Biology, 5(2), pp. 159–166. 2003.
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  KCl, sucrose, D-serine and some other solutes were fed through the petiole to leaflets of Solanum tuberosum and uptake into the symplast was monitored. Solute transport was accompanied by changes in membrane potential, apoplastic pH and respiration. After termination of solute feeding, membrane potential, apoplastic pH and respiration returned to initial steady state values. From transpiration, solute uptake was calculated and compared to ATIP production during stimulated respiration, assuming an ATIP/CO2 ratio of 5. On this basis, calculated ATP/KCl ratios of energized transport approached 0.5. Similar ATP/solute ratios were observed with sucrose, mannitol, methylglucose and D-serine. With glucose, many ratios were somewhat above 0.5, possibly because of some metabolization of imported glucose. We conclude that solute uptake is energized by the proton motive force across the plasma membrane. Low ATP/ substrate ratios suggest that the H+/ATP ratio of proton export by the plasma membrane ATPase is not 1 as presently assumed but 2 in potato leaves, and that the contribution of the alternative cyanide-resistant oxidase to leaf respiration is small, if not negligible, in the dark.

  @article{RN1189, abstract = {KCl, sucrose, D-serine and some other solutes were fed through the petiole to leaflets of Solanum tuberosum and uptake into the symplast was monitored. Solute transport was accompanied by changes in membrane potential, apoplastic pH and respiration. After termination of solute feeding, membrane potential, apoplastic pH and respiration returned to initial steady state values. From transpiration, solute uptake was calculated and compared to ATIP production during stimulated respiration, assuming an ATIP/CO2 ratio of 5. On this basis, calculated ATP/KCl ratios of energized transport approached 0.5. Similar ATP/solute ratios were observed with sucrose, mannitol, methylglucose and D-serine. With glucose, many ratios were somewhat above 0.5, possibly because of some metabolization of imported glucose. We conclude that solute uptake is energized by the proton motive force across the plasma membrane. Low ATP/ substrate ratios suggest that the H+/ATP ratio of proton export by the plasma membrane ATPase is not 1 as presently assumed but 2 in potato leaves, and that the contribution of the alternative cyanide-resistant oxidase to leaf respiration is small, if not negligible, in the dark.}, author = {Bukhov, N. G. and Hedrich, R. and Heber, U.}, journal = {Plant Biology}, keywords = {atipase}, note = {690cl Times Cited:3 Cited References Count:34}, number = 2, pages = {159-166}, title = {Energy-dependent solute uptake into the symplast of leaves:: ATP/KCl, ATP/sucrose, ATP/D-serine and H /ATP stoichiometries of transmembrane transport}, type = {Journal Article}, volume = 5, year = 2003 }

  %0 Journal Article %1 RN1189 %A Bukhov, N. G. %A Hedrich, R. %A Heber, U. %D 2003 %J Plant Biology %N 2 %P 159-166 %R DOI 10.1055/s-2003-40720 %T Energy-dependent solute uptake into the symplast of leaves:: ATP/KCl, ATP/sucrose, ATP/D-serine and H /ATP stoichiometries of transmembrane transport %U /brokenurl#<Go to ISI>://WOS:000183529700007 %V 5 %X KCl, sucrose, D-serine and some other solutes were fed through the petiole to leaflets of Solanum tuberosum and uptake into the symplast was monitored. Solute transport was accompanied by changes in membrane potential, apoplastic pH and respiration. After termination of solute feeding, membrane potential, apoplastic pH and respiration returned to initial steady state values. From transpiration, solute uptake was calculated and compared to ATIP production during stimulated respiration, assuming an ATIP/CO2 ratio of 5. On this basis, calculated ATP/KCl ratios of energized transport approached 0.5. Similar ATP/solute ratios were observed with sucrose, mannitol, methylglucose and D-serine. With glucose, many ratios were somewhat above 0.5, possibly because of some metabolization of imported glucose. We conclude that solute uptake is energized by the proton motive force across the plasma membrane. Low ATP/ substrate ratios suggest that the H+/ATP ratio of proton export by the plasma membrane ATPase is not 1 as presently assumed but 2 in potato leaves, and that the contribution of the alternative cyanide-resistant oxidase to leaf respiration is small, if not negligible, in the dark.
• Blue light regulates an auxin-induced K -channel gene in the maize coleoptile. Fuchs, I.; Philippar, K.; Ljung, K.; Sandberg, G.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 100(20), pp. 11795–11800. 2003.
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  Auxin redistribution along gravistimulated maize coleoptiles causes differential expression of the auxin-induced K+-channel gene ZMK1 (Zea mays K+ channel 1) and precedes the curvature response. To evaluate the role of ZMK1 during phototropism, we here investigated blue light-stimulated coleoptiles. Four hours of blue light stimulation resulted in phototropic bending (23degrees). Rotation on a clinostat, at nominally "zero" gravity, and simultaneous stimulation with unidirectional blue light, however, resulted in up to 510 bending toward the light. Differential ZMK1 transcription reached a maximum after 90 min of blue light stimulation under gravity, whereas ZMK1 expression remained asymmetric for at least 180 min in photostimulated coleoptiles on a clinostat. We therefore conclude that the stronger phototropic bending under nominally "zero" gravity results from prolonged differential expression of ZMK1. Under both conditions, asymmetric expression of ZMK1 could be superimposed on the lateral auxin gradient across the coleoptile tip, whereas the gene for the blue light receptor phototropin 1 (PHOT1), expressed in the tip only, was not differentially regulated in response to blue light. The activation of the two different receptors eliciting the photo- and gravitropic response of the coleoptile thus feeds into a common signaling pathway, resulting in auxin redistribution in the coleoptile tip and finally in differential transcription of ZMK1. In the process of signal integration, gravity transduction restricts the magnitude of the blue light-inducible ZMK1 gradient. The spatial and temporal distribution of ZMK1 transcripts and thus differential K+ uptake in both flanks of the coleoptile seem to limit the stimulus-induced bending of this sensory organ.

  @article{RN1187, abstract = {Auxin redistribution along gravistimulated maize coleoptiles causes differential expression of the auxin-induced K+-channel gene ZMK1 (Zea mays K+ channel 1) and precedes the curvature response. To evaluate the role of ZMK1 during phototropism, we here investigated blue light-stimulated coleoptiles. Four hours of blue light stimulation resulted in phototropic bending (23degrees). Rotation on a clinostat, at nominally "zero" gravity, and simultaneous stimulation with unidirectional blue light, however, resulted in up to 510 bending toward the light. Differential ZMK1 transcription reached a maximum after 90 min of blue light stimulation under gravity, whereas ZMK1 expression remained asymmetric for at least 180 min in photostimulated coleoptiles on a clinostat. We therefore conclude that the stronger phototropic bending under nominally "zero" gravity results from prolonged differential expression of ZMK1. Under both conditions, asymmetric expression of ZMK1 could be superimposed on the lateral auxin gradient across the coleoptile tip, whereas the gene for the blue light receptor phototropin 1 (PHOT1), expressed in the tip only, was not differentially regulated in response to blue light. The activation of the two different receptors eliciting the photo- and gravitropic response of the coleoptile thus feeds into a common signaling pathway, resulting in auxin redistribution in the coleoptile tip and finally in differential transcription of ZMK1. In the process of signal integration, gravity transduction restricts the magnitude of the blue light-inducible ZMK1 gradient. The spatial and temporal distribution of ZMK1 transcripts and thus differential K+ uptake in both flanks of the coleoptile seem to limit the stimulus-induced bending of this sensory organ.}, author = {Fuchs, I. and Philippar, K. and Ljung, K. and Sandberg, G. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {h+-atpase}, note = {727xg Times Cited:48 Cited References Count:43}, number = 20, pages = {11795-11800}, title = {Blue light regulates an auxin-induced K -channel gene in the maize coleoptile}, type = {Journal Article}, volume = 100, year = 2003 }

  %0 Journal Article %1 RN1187 %A Fuchs, I. %A Philippar, K. %A Ljung, K. %A Sandberg, G. %A Hedrich, R. %D 2003 %J Proceedings of the National Academy of Sciences of the United States of America %N 20 %P 11795-11800 %R 10.1073/pnas.2032704100 %T Blue light regulates an auxin-induced K -channel gene in the maize coleoptile %U /brokenurl#<Go to ISI>://WOS:000185685700110 %V 100 %X Auxin redistribution along gravistimulated maize coleoptiles causes differential expression of the auxin-induced K+-channel gene ZMK1 (Zea mays K+ channel 1) and precedes the curvature response. To evaluate the role of ZMK1 during phototropism, we here investigated blue light-stimulated coleoptiles. Four hours of blue light stimulation resulted in phototropic bending (23degrees). Rotation on a clinostat, at nominally "zero" gravity, and simultaneous stimulation with unidirectional blue light, however, resulted in up to 510 bending toward the light. Differential ZMK1 transcription reached a maximum after 90 min of blue light stimulation under gravity, whereas ZMK1 expression remained asymmetric for at least 180 min in photostimulated coleoptiles on a clinostat. We therefore conclude that the stronger phototropic bending under nominally "zero" gravity results from prolonged differential expression of ZMK1. Under both conditions, asymmetric expression of ZMK1 could be superimposed on the lateral auxin gradient across the coleoptile tip, whereas the gene for the blue light receptor phototropin 1 (PHOT1), expressed in the tip only, was not differentially regulated in response to blue light. The activation of the two different receptors eliciting the photo- and gravitropic response of the coleoptile thus feeds into a common signaling pathway, resulting in auxin redistribution in the coleoptile tip and finally in differential transcription of ZMK1. In the process of signal integration, gravity transduction restricts the magnitude of the blue light-inducible ZMK1 gradient. The spatial and temporal distribution of ZMK1 transcripts and thus differential K+ uptake in both flanks of the coleoptile seem to limit the stimulus-induced bending of this sensory organ.
• The K channel KZM1 mediates potassium uptake into the phloem and guard cells of the C grass. Philippar, K.; Büchsenschütz, K.; Abshagen, M.; Fuchs, I.; Geiger, D.; Lacombe, B.; Hedrich, R. In Journal of Biological Chemistry, 278(19), pp. 16973–16981. 2003.
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  In search of K+ channel genes expressed in the leaf of the C-4 plant Zea mays, we isolated the cDNA of KZM1 (for K+ channel Zea mays 1). KZM1 showed highest similarity to the Arabidopsis K+ channels KAT1 and KAT2, which are localized in guard cells and phloem. When expressed in Xenopus oocytes, KZM1 exhibited the characteristic features of an inward-rectifying, potassium-selective channel. In contrast to KAT1- and KAT2-type K+ channels, however, KZM1 currents were insensitive to external pH changes. Northern blot analyses identified the leaf, nodes, and silks as sites of KZM1 expression. Following the separation of maize leaves into epidermal, mesophyll, and vascular fractions, quantitative real-time reverse transcriptase-PCR allowed us to localize KZM1 transcripts predominantly in vascular strands and the epidermis. Cell tissue separation and KZM1 localization were followed with marker genes such as the bundle sheath-specific ribulose-1,5-bisphosphate carboxylase, the phloem K+ channel ZMK2, and the putative sucrose transporter ZmSUT1. When expressed in Xenopus oocytes, ZmSUT1 mediated proton-coupled sucrose symport. Coexpression of ZmSUT1 with the phloem K+ channels KZM1 and ZMK2 revealed that ZMK2 is able to stabilize the membrane potential during phloem loading/unloading processes and KZM1 to mediate K+ uptake. During leaf development, sink-source transitions, and diurnal changes, KZM1 is constitutively expressed, pointing to a housekeeping function of this channel in K+ homeostasis of the maize leaf. Therefore, the voltage-dependent K+-uptake channel KZM1 seems to mediate K+ retrieval and K+ loading into the phloem as well as K+-dependent stomatal opening.

  @article{RN1184, abstract = {In search of K+ channel genes expressed in the leaf of the C-4 plant Zea mays, we isolated the cDNA of KZM1 (for K+ channel Zea mays 1). KZM1 showed highest similarity to the Arabidopsis K+ channels KAT1 and KAT2, which are localized in guard cells and phloem. When expressed in Xenopus oocytes, KZM1 exhibited the characteristic features of an inward-rectifying, potassium-selective channel. In contrast to KAT1- and KAT2-type K+ channels, however, KZM1 currents were insensitive to external pH changes. Northern blot analyses identified the leaf, nodes, and silks as sites of KZM1 expression. Following the separation of maize leaves into epidermal, mesophyll, and vascular fractions, quantitative real-time reverse transcriptase-PCR allowed us to localize KZM1 transcripts predominantly in vascular strands and the epidermis. Cell tissue separation and KZM1 localization were followed with marker genes such as the bundle sheath-specific ribulose-1,5-bisphosphate carboxylase, the phloem K+ channel ZMK2, and the putative sucrose transporter ZmSUT1. When expressed in Xenopus oocytes, ZmSUT1 mediated proton-coupled sucrose symport. Coexpression of ZmSUT1 with the phloem K+ channels KZM1 and ZMK2 revealed that ZMK2 is able to stabilize the membrane potential during phloem loading/unloading processes and KZM1 to mediate K+ uptake. During leaf development, sink-source transitions, and diurnal changes, KZM1 is constitutively expressed, pointing to a housekeeping function of this channel in K+ homeostasis of the maize leaf. Therefore, the voltage-dependent K+-uptake channel KZM1 seems to mediate K+ retrieval and K+ loading into the phloem as well as K+-dependent stomatal opening.}, author = {Philippar, K. and Büchsenschütz, K. and Abshagen, M. and Fuchs, I. and Geiger, D. and Lacombe, B. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {sucrose-export}, note = {677qg Times Cited:76 Cited References Count:63}, number = 19, pages = {16973-16981}, title = {The K channel KZM1 mediates potassium uptake into the phloem and guard cells of the C grass}, type = {Journal Article}, volume = 278, year = 2003 }

  %0 Journal Article %1 RN1184 %A Philippar, K. %A Büchsenschütz, K. %A Abshagen, M. %A Fuchs, I. %A Geiger, D. %A Lacombe, B. %A Hedrich, R. %D 2003 %J Journal of Biological Chemistry %N 19 %P 16973-16981 %R 10.1074/jbc.M212720200 %T The K channel KZM1 mediates potassium uptake into the phloem and guard cells of the C grass %U /brokenurl#<Go to ISI>://WOS:000182818600072 %V 278 %X In search of K+ channel genes expressed in the leaf of the C-4 plant Zea mays, we isolated the cDNA of KZM1 (for K+ channel Zea mays 1). KZM1 showed highest similarity to the Arabidopsis K+ channels KAT1 and KAT2, which are localized in guard cells and phloem. When expressed in Xenopus oocytes, KZM1 exhibited the characteristic features of an inward-rectifying, potassium-selective channel. In contrast to KAT1- and KAT2-type K+ channels, however, KZM1 currents were insensitive to external pH changes. Northern blot analyses identified the leaf, nodes, and silks as sites of KZM1 expression. Following the separation of maize leaves into epidermal, mesophyll, and vascular fractions, quantitative real-time reverse transcriptase-PCR allowed us to localize KZM1 transcripts predominantly in vascular strands and the epidermis. Cell tissue separation and KZM1 localization were followed with marker genes such as the bundle sheath-specific ribulose-1,5-bisphosphate carboxylase, the phloem K+ channel ZMK2, and the putative sucrose transporter ZmSUT1. When expressed in Xenopus oocytes, ZmSUT1 mediated proton-coupled sucrose symport. Coexpression of ZmSUT1 with the phloem K+ channels KZM1 and ZMK2 revealed that ZMK2 is able to stabilize the membrane potential during phloem loading/unloading processes and KZM1 to mediate K+ uptake. During leaf development, sink-source transitions, and diurnal changes, KZM1 is constitutively expressed, pointing to a housekeeping function of this channel in K+ homeostasis of the maize leaf. Therefore, the voltage-dependent K+-uptake channel KZM1 seems to mediate K+ retrieval and K+ loading into the phloem as well as K+-dependent stomatal opening.
• Energized uptake of ascorbate and dehydroascorbate from the apoplast of intact leaves in relation to apoplastic steady state concentrations of ascorbate. Heber, U.; Bukhov, N. G.; Wiese, C.; Hedrich, R. In Plant Biology, 5(2), pp. 151–158. 2003.
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  Transport of ascorbate (AA) and dehydroascorbate (DHA) through the petiole into detached leaves of Lepidium sotivum and other plant species via the transpiration stream, and energized uptake into leaf tissue, were measured indirectly by recording changes in membrane potential and apoplastic pH simultaneously with substrate-stimulated respiration and transpiratory water loss. When 25 mM AA or DHA was fed to the leaves, steady state respiration at 25degreesC was transiently increased by more than 50% with AA and 70% with DHA. Stimulation of respiration was accompanied by a transient breakdown of membrane potential followed by alkalinization of the leaf apoplast suggesting energized uptake at the expense of the transmembrane proton motive force. The average CO2/AA ratio calculated from stimulated respiration during ascorbate uptake was 0.76 +/- 0.26 (n = 17). The corresponding ratio for DHA was 1.38 +/- 0.28 (n=11). Far lower CO2/substrate ratios were observed when NaCl or KCl were fed to leaves. The differences indicate either partial metabolism of AA and DHA in addition to energized transport, or less likely, higher energy requirement for transport of AA and DHA than for the inorganic salts. Maximum rates of energized AA transport into leaf tissue (deduced from maxima of extra respiration and calculated on the basis of CO2/AA = 0.76) were close to 650 nmol m(-2) leaf area s(-1), i.e. far higher than most previously reported rates of transport. When the apoplastic concentration of AA was decreased below steady state levels during infiltration/centrifugation experiments, AA was released from leaf cells into the apoplast. This suggests that AA oxidation to DHA in the apoplast (as occurs during extracellular ozone detoxification) triggers energized transport of the DHA into the symplast and simultaneously AA release from the symplast into the apoplast, perhaps together with protons in a reversal of the energized uptake process.

  @article{RN1186, abstract = {Transport of ascorbate (AA) and dehydroascorbate (DHA) through the petiole into detached leaves of Lepidium sotivum and other plant species via the transpiration stream, and energized uptake into leaf tissue, were measured indirectly by recording changes in membrane potential and apoplastic pH simultaneously with substrate-stimulated respiration and transpiratory water loss. When 25 mM AA or DHA was fed to the leaves, steady state respiration at 25degreesC was transiently increased by more than 50% with AA and 70% with DHA. Stimulation of respiration was accompanied by a transient breakdown of membrane potential followed by alkalinization of the leaf apoplast suggesting energized uptake at the expense of the transmembrane proton motive force. The average CO2/AA ratio calculated from stimulated respiration during ascorbate uptake was 0.76 +/- 0.26 (n = 17). The corresponding ratio for DHA was 1.38 +/- 0.28 (n=11). Far lower CO2/substrate ratios were observed when NaCl or KCl were fed to leaves. The differences indicate either partial metabolism of AA and DHA in addition to energized transport, or less likely, higher energy requirement for transport of AA and DHA than for the inorganic salts. Maximum rates of energized AA transport into leaf tissue (deduced from maxima of extra respiration and calculated on the basis of CO2/AA = 0.76) were close to 650 nmol m(-2) leaf area s(-1), i.e. far higher than most previously reported rates of transport. When the apoplastic concentration of AA was decreased below steady state levels during infiltration/centrifugation experiments, AA was released from leaf cells into the apoplast. This suggests that AA oxidation to DHA in the apoplast (as occurs during extracellular ozone detoxification) triggers energized transport of the DHA into the symplast and simultaneously AA release from the symplast into the apoplast, perhaps together with protons in a reversal of the energized uptake process.}, author = {Heber, U. and Bukhov, N. G. and Wiese, C. and Hedrich, R.}, journal = {Plant Biology}, keywords = {ph}, note = {690cl Times Cited:5 Cited References Count:37}, number = 2, pages = {151-158}, title = {Energized uptake of ascorbate and dehydroascorbate from the apoplast of intact leaves in relation to apoplastic steady state concentrations of ascorbate}, type = {Journal Article}, volume = 5, year = 2003 }

  %0 Journal Article %1 RN1186 %A Heber, U. %A Bukhov, N. G. %A Wiese, C. %A Hedrich, R. %D 2003 %J Plant Biology %N 2 %P 151-158 %R DOI 10.1055/s-2003-40721 %T Energized uptake of ascorbate and dehydroascorbate from the apoplast of intact leaves in relation to apoplastic steady state concentrations of ascorbate %U /brokenurl#<Go to ISI>://WOS:000183529700006 %V 5 %X Transport of ascorbate (AA) and dehydroascorbate (DHA) through the petiole into detached leaves of Lepidium sotivum and other plant species via the transpiration stream, and energized uptake into leaf tissue, were measured indirectly by recording changes in membrane potential and apoplastic pH simultaneously with substrate-stimulated respiration and transpiratory water loss. When 25 mM AA or DHA was fed to the leaves, steady state respiration at 25degreesC was transiently increased by more than 50% with AA and 70% with DHA. Stimulation of respiration was accompanied by a transient breakdown of membrane potential followed by alkalinization of the leaf apoplast suggesting energized uptake at the expense of the transmembrane proton motive force. The average CO2/AA ratio calculated from stimulated respiration during ascorbate uptake was 0.76 +/- 0.26 (n = 17). The corresponding ratio for DHA was 1.38 +/- 0.28 (n=11). Far lower CO2/substrate ratios were observed when NaCl or KCl were fed to leaves. The differences indicate either partial metabolism of AA and DHA in addition to energized transport, or less likely, higher energy requirement for transport of AA and DHA than for the inorganic salts. Maximum rates of energized AA transport into leaf tissue (deduced from maxima of extra respiration and calculated on the basis of CO2/AA = 0.76) were close to 650 nmol m(-2) leaf area s(-1), i.e. far higher than most previously reported rates of transport. When the apoplastic concentration of AA was decreased below steady state levels during infiltration/centrifugation experiments, AA was released from leaf cells into the apoplast. This suggests that AA oxidation to DHA in the apoplast (as occurs during extracellular ozone detoxification) triggers energized transport of the DHA into the symplast and simultaneously AA release from the symplast into the apoplast, perhaps together with protons in a reversal of the energized uptake process.
• Tumour development in involves the -like K channels AKT1 and AKT2/3. Deeken, R.; Ivashikina, N.; Czirjak, T.; Philippar, K.; Becker, D.; Ache, P.; Hedrich, R. In Plant Journal, 34(6), pp. 778–787. 2003.
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  After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker -like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.

  @article{RN1188, abstract = {After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker -like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.}, author = {Deeken, R. and Ivashikina, N. and Czirjak, T. and Philippar, K. and Becker, D. and Ache, P. and Hedrich, R.}, journal = {Plant Journal}, keywords = {arabidopsis}, note = {688nw Times Cited:31 Cited References Count:52}, number = 6, pages = {778-787}, title = {Tumour development in involves the -like K channels AKT1 and AKT2/3}, type = {Journal Article}, volume = 34, year = 2003 }

  %0 Journal Article %1 RN1188 %A Deeken, R. %A Ivashikina, N. %A Czirjak, T. %A Philippar, K. %A Becker, D. %A Ache, P. %A Hedrich, R. %D 2003 %J Plant Journal %N 6 %P 778-787 %R DOI 10.1046/j.1365-313X.2003.01766.x %T Tumour development in involves the -like K channels AKT1 and AKT2/3 %U /brokenurl#<Go to ISI>://WOS:000183443000004 %V 34 %X After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker -like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.

• AtKC1, a silent potassium channel α-subunit modulates root hair K influx. Reintanz, B.; Szyroki, A.; Ivashikina, N.; Ache, P.; Godde, M.; Becker, D.; Palme, K.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 99(6), pp. 4079–4084. 2002.
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  Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different alpha-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new alpha-subunit from the Arabidopsis shaker-like ion channel family. Promoter-beta-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels alpha-subunits in root cells, we performed real-time reverse transcription-PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel alpha-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 alpha-subunit represents an integral component of functional root hair K+ uptake channels.

  @article{RN1195, abstract = {Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different alpha-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new alpha-subunit from the Arabidopsis shaker-like ion channel family. Promoter-beta-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels alpha-subunits in root cells, we performed real-time reverse transcription-PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel alpha-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 alpha-subunit represents an integral component of functional root hair K+ uptake channels.}, author = {Reintanz, B. and Szyroki, A. and Ivashikina, N. and Ache, P. and Godde, M. and Becker, D. and Palme, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {expression}, note = {533cc Times Cited:183 Cited References Count:57}, number = 6, pages = {4079-4084}, title = {AtKC1, a silent potassium channel α-subunit modulates root hair K influx}, type = {Journal Article}, volume = 99, year = 2002 }

  %0 Journal Article %1 RN1195 %A Reintanz, B. %A Szyroki, A. %A Ivashikina, N. %A Ache, P. %A Godde, M. %A Becker, D. %A Palme, K. %A Hedrich, R. %D 2002 %J Proceedings of the National Academy of Sciences of the United States of America %N 6 %P 4079-4084 %R 10.1073/pnas.052677799 %T AtKC1, a silent potassium channel α-subunit modulates root hair K influx %U /brokenurl#<Go to ISI>://WOS:000174511000127 %V 99 %X Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different alpha-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new alpha-subunit from the Arabidopsis shaker-like ion channel family. Promoter-beta-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels alpha-subunits in root cells, we performed real-time reverse transcription-PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel alpha-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 alpha-subunit represents an integral component of functional root hair K+ uptake channels.
• Loss of the AKT2/3 potassium channel affects sugar loading into the phloem of. Deeken, R.; Geiger, D.; Fromm, J.; Koroleva, O.; Ache, P.; Langenfeld-Heyser, R.; Sauer, N.; May, S. T.; Hedrich, R. In Planta, 216(2), pp. 334–344. 2002.
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  Members of the AKT2/3 family have been identified as photosynthate-induced phloem K+ channels. Here we describe the isolation and characterisation of an AKT2/3 loss-of-function mutant (akt2/3-1) from Arabidopsis thaliana (L.) Heynh. Micro autoradiography following (CO2)-C-14 incubation in the light revealed that a major fraction of (CO2)-C-14-derived photosynthates leaking out of sieve tubes appears not to be effectively reloaded (retrieval) into the phloem of the mutant. Using the aphid stylectomy technique we showed that the phloem sap of the mutant, lacking the phloem channels of the AKT2/3 type, contained only half the sucrose content of the wild type. Furthermore, the akt2/3 mutant exhibited a reduced K+ dependence of the phloem potential. Xenopus oocytes expressing the phloem sucrose/proton symporter depolarise upon sucrose application. When, however, the phloem channel was co-expressed - mimicking the situation in the sieve tube/companion cell complex - depolarisation was prevented. From our studies we thus conclude that AKT2/3 regulates the sucrose/H+ symporters via the phloem potential.

  @article{RN1203, abstract = {Members of the AKT2/3 family have been identified as photosynthate-induced phloem K+ channels. Here we describe the isolation and characterisation of an AKT2/3 loss-of-function mutant (akt2/3-1) from Arabidopsis thaliana (L.) Heynh. Micro autoradiography following (CO2)-C-14 incubation in the light revealed that a major fraction of (CO2)-C-14-derived photosynthates leaking out of sieve tubes appears not to be effectively reloaded (retrieval) into the phloem of the mutant. Using the aphid stylectomy technique we showed that the phloem sap of the mutant, lacking the phloem channels of the AKT2/3 type, contained only half the sucrose content of the wild type. Furthermore, the akt2/3 mutant exhibited a reduced K+ dependence of the phloem potential. Xenopus oocytes expressing the phloem sucrose/proton symporter depolarise upon sucrose application. When, however, the phloem channel was co-expressed - mimicking the situation in the sieve tube/companion cell complex - depolarisation was prevented. From our studies we thus conclude that AKT2/3 regulates the sucrose/H+ symporters via the phloem potential.}, author = {Deeken, R. and Geiger, D. and Fromm, J. and Koroleva, O. and Ache, P. and Langenfeld-Heyser, R. and Sauer, N. and May, S. T. and Hedrich, R.}, journal = {Planta}, keywords = {arabidopsis}, note = {629ek Times Cited:193 Cited References Count:55}, number = 2, pages = {334-344}, title = {Loss of the AKT2/3 potassium channel affects sugar loading into the phloem of}, type = {Journal Article}, volume = 216, year = 2002 }

  %0 Journal Article %1 RN1203 %A Deeken, R. %A Geiger, D. %A Fromm, J. %A Koroleva, O. %A Ache, P. %A Langenfeld-Heyser, R. %A Sauer, N. %A May, S. T. %A Hedrich, R. %D 2002 %J Planta %N 2 %P 334-344 %R 10.1007/s00425-002-0895-1 %T Loss of the AKT2/3 potassium channel affects sugar loading into the phloem of %U /brokenurl#<Go to ISI>://WOS:000180037300017 %V 216 %X Members of the AKT2/3 family have been identified as photosynthate-induced phloem K+ channels. Here we describe the isolation and characterisation of an AKT2/3 loss-of-function mutant (akt2/3-1) from Arabidopsis thaliana (L.) Heynh. Micro autoradiography following (CO2)-C-14 incubation in the light revealed that a major fraction of (CO2)-C-14-derived photosynthates leaking out of sieve tubes appears not to be effectively reloaded (retrieval) into the phloem of the mutant. Using the aphid stylectomy technique we showed that the phloem sap of the mutant, lacking the phloem channels of the AKT2/3 type, contained only half the sucrose content of the wild type. Furthermore, the akt2/3 mutant exhibited a reduced K+ dependence of the phloem potential. Xenopus oocytes expressing the phloem sucrose/proton symporter depolarise upon sucrose application. When, however, the phloem channel was co-expressed - mimicking the situation in the sieve tube/companion cell complex - depolarisation was prevented. From our studies we thus conclude that AKT2/3 regulates the sucrose/H+ symporters via the phloem potential.
• Energy-dependent solute transport from the apoplast into the symplast of leaves during transpiration. Heber, U.; Wiese, C.; Neimanis, S.; Savchenko, G.; Bukhov, N. G.; Hedrich, R. In Russian Journal of Plant Physiology, 49(1), pp. 32–43. 2002.
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  Inorganic and organic salts, amino acids, sugars, and phosphate esters (concentrations usually 25 mM) were fed via the transpiration stream through the petiole into detached leaves of Lepidium sativum and Solanum tuberosum. While water was lost by transpiration, solutes did not accumulate in the apoplast. Uptake into leaf cells was indicated by stimulation of respiration and by changes of membrane potential and apoplastic pH. Apoplastic alkalinization (followed by transient acidification) and membrane depolarization (followed by repolarization) indicated energization of transport at the expense of the proton motive force (PMF) across the plasma membrane in all examined cases. Loss of ATP in the symplast during proton extrusion into the apoplast by the plasmalemma ATPase is thought to be responsible for stimulation of respiration. Even unphysiological solutes such as beta-morpholinoethane sulfonate (Mes), or potentially toxic salts such as CdCl2 or AlCl3, and metabolites involved in energy conservation such as AMP and NAD, were readily transported into leaf cells at the expense of metabolic energy. At the maximum stimulation of CO2 release by D-serine (which is unlikely to be metabolized) respiration exceeded basal respiration by an average of 33%. Occasionally, and with other solutes, basal respiration was almost doubled. The ratio of transported solute to released extra CO2 was 6.9 +/- 1.1 (n = 11) in the case of D-serine. From this, maximum energized transport of D-serine was calculated to be close to 500 nmol/(m(2) leaf area s). Solute/CO2 ratios similar to those observed with D-serine were also obtained for sucrose. Lower ones were observed with organic solutes such as L-glycine, pyruvate, malate or citrate where: secondary metabolic conversions may contribute to CO2 release.

  @article{RN1199, abstract = {Inorganic and organic salts, amino acids, sugars, and phosphate esters (concentrations usually 25 mM) were fed via the transpiration stream through the petiole into detached leaves of Lepidium sativum and Solanum tuberosum. While water was lost by transpiration, solutes did not accumulate in the apoplast. Uptake into leaf cells was indicated by stimulation of respiration and by changes of membrane potential and apoplastic pH. Apoplastic alkalinization (followed by transient acidification) and membrane depolarization (followed by repolarization) indicated energization of transport at the expense of the proton motive force (PMF) across the plasma membrane in all examined cases. Loss of ATP in the symplast during proton extrusion into the apoplast by the plasmalemma ATPase is thought to be responsible for stimulation of respiration. Even unphysiological solutes such as beta-morpholinoethane sulfonate (Mes), or potentially toxic salts such as CdCl2 or AlCl3, and metabolites involved in energy conservation such as AMP and NAD, were readily transported into leaf cells at the expense of metabolic energy. At the maximum stimulation of CO2 release by D-serine (which is unlikely to be metabolized) respiration exceeded basal respiration by an average of 33%. Occasionally, and with other solutes, basal respiration was almost doubled. The ratio of transported solute to released extra CO2 was 6.9 +/- 1.1 (n = 11) in the case of D-serine. From this, maximum energized transport of D-serine was calculated to be close to 500 nmol/(m(2) leaf area s). Solute/CO2 ratios similar to those observed with D-serine were also obtained for sucrose. Lower ones were observed with organic solutes such as L-glycine, pyruvate, malate or citrate where: secondary metabolic conversions may contribute to CO2 release.}, author = {Heber, U. and Wiese, C. and Neimanis, S. and Savchenko, G. and Bukhov, N. G. and Hedrich, R.}, journal = {Russian Journal of Plant Physiology}, keywords = {apoplast}, note = {517wu Times Cited:5 Cited References Count:35}, number = 1, pages = {32-43}, title = {Energy-dependent solute transport from the apoplast into the symplast of leaves during transpiration}, type = {Journal Article}, volume = 49, year = 2002 }

  %0 Journal Article %1 RN1199 %A Heber, U. %A Wiese, C. %A Neimanis, S. %A Savchenko, G. %A Bukhov, N. G. %A Hedrich, R. %D 2002 %J Russian Journal of Plant Physiology %N 1 %P 32-43 %R Doi 10.1023/A:1013704009903 %T Energy-dependent solute transport from the apoplast into the symplast of leaves during transpiration %U /brokenurl#<Go to ISI>://WOS:000173634100005 %V 49 %X Inorganic and organic salts, amino acids, sugars, and phosphate esters (concentrations usually 25 mM) were fed via the transpiration stream through the petiole into detached leaves of Lepidium sativum and Solanum tuberosum. While water was lost by transpiration, solutes did not accumulate in the apoplast. Uptake into leaf cells was indicated by stimulation of respiration and by changes of membrane potential and apoplastic pH. Apoplastic alkalinization (followed by transient acidification) and membrane depolarization (followed by repolarization) indicated energization of transport at the expense of the proton motive force (PMF) across the plasma membrane in all examined cases. Loss of ATP in the symplast during proton extrusion into the apoplast by the plasmalemma ATPase is thought to be responsible for stimulation of respiration. Even unphysiological solutes such as beta-morpholinoethane sulfonate (Mes), or potentially toxic salts such as CdCl2 or AlCl3, and metabolites involved in energy conservation such as AMP and NAD, were readily transported into leaf cells at the expense of metabolic energy. At the maximum stimulation of CO2 release by D-serine (which is unlikely to be metabolized) respiration exceeded basal respiration by an average of 33%. Occasionally, and with other solutes, basal respiration was almost doubled. The ratio of transported solute to released extra CO2 was 6.9 +/- 1.1 (n = 11) in the case of D-serine. From this, maximum energized transport of D-serine was calculated to be close to 500 nmol/(m(2) leaf area s). Solute/CO2 ratios similar to those observed with D-serine were also obtained for sucrose. Lower ones were observed with organic solutes such as L-glycine, pyruvate, malate or citrate where: secondary metabolic conversions may contribute to CO2 release.
• Plasma membrane aquaporins in the motor cells of :: Diurnal and circadian regulation. Moshelion, M.; Becker, D.; Biela, A.; Uehlein, N.; Hedrich, R.; Otto, B.; Levi, H.; Moran, N.; Kaldenhoff, R. In Plant Cell, 14(3), pp. 727–739. 2002.
  • [ Abstract ]
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  Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P-f) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl2 and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P-f of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P-f increases were inhibited by 50 muM HgCl2, by 2 mM cycloheximide, and by 250 muM phloretin to the noon P-f level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.

  @article{RN1197, abstract = {Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P-f) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl2 and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P-f of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P-f increases were inhibited by 50 muM HgCl2, by 2 mM cycloheximide, and by 250 muM phloretin to the noon P-f level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.}, author = {Moshelion, M. and Becker, D. and Biela, A. and Uehlein, N. and Hedrich, R. and Otto, B. and Levi, H. and Moran, N. and Kaldenhoff, R.}, journal = {Plant Cell}, keywords = {channels}, note = {537zc Times Cited:176 Cited References Count:57}, number = 3, pages = {727-739}, title = {Plasma membrane aquaporins in the motor cells of :: Diurnal and circadian regulation}, type = {Journal Article}, volume = 14, year = 2002 }

  %0 Journal Article %1 RN1197 %A Moshelion, M. %A Becker, D. %A Biela, A. %A Uehlein, N. %A Hedrich, R. %A Otto, B. %A Levi, H. %A Moran, N. %A Kaldenhoff, R. %D 2002 %J Plant Cell %N 3 %P 727-739 %R 10.1105/tpc.010351 %T Plasma membrane aquaporins in the motor cells of :: Diurnal and circadian regulation %U /brokenurl#<Go to ISI>://WOS:000174788700018 %V 14 %X Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P-f) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl2 and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P-f of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P-f increases were inhibited by 50 muM HgCl2, by 2 mM cycloheximide, and by 250 muM phloretin to the noon P-f level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.
• Expression of the NH -transporter gene is induced in tomato roots upon association with N -fixing bacteria. Becker, D.; Stanke, R.; Fendrik, I.; Frommer, W. B.; Vanderleyden, J.; Kaiser, W. M.; Hedrich, R. In Planta, 215(3), pp. 424–429. 2002.
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  Plants growing in close association with N-2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N-2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4+-transporter gene. LEAMT1:2 (L. esculentum ammonium transporter 1,2), indicating that bacterial NH4+ might be used as an N source under these conditions. Azospirillum brasilense (nif(-)) Mutants. which lack the structural nifDK genes, failed to induce LEAMT1:2 expression. This suggests that root-associated N-2-fixing bacteria do excrete NH4+ levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1:2 with as low as greater than or equal to1 muM external NH4+. While peak expression was obtained with 2-5 muM NH4+, a further increase in NH4+ reduced LEAMT1:2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4+ concentration or the plant N status. Since micromolar concentrations of NH4+ strongly increased the LEAMT1;2-mRNA levels, the transported NH4+ ion itself could represent a key signal in the associative interaction between higher plants and N-2-fixing micro-organisms.

  @article{RN1204, abstract = {Plants growing in close association with N-2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N-2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4+-transporter gene. LEAMT1:2 (L. esculentum ammonium transporter 1,2), indicating that bacterial NH4+ might be used as an N source under these conditions. Azospirillum brasilense (nif(-)) Mutants. which lack the structural nifDK genes, failed to induce LEAMT1:2 expression. This suggests that root-associated N-2-fixing bacteria do excrete NH4+ levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1:2 with as low as greater than or equal to1 muM external NH4+. While peak expression was obtained with 2-5 muM NH4+, a further increase in NH4+ reduced LEAMT1:2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4+ concentration or the plant N status. Since micromolar concentrations of NH4+ strongly increased the LEAMT1;2-mRNA levels, the transported NH4+ ion itself could represent a key signal in the associative interaction between higher plants and N-2-fixing micro-organisms.}, author = {Becker, D. and Stanke, R. and Fendrik, I. and Frommer, W. B. and Vanderleyden, J. and Kaiser, W. M. and Hedrich, R.}, journal = {Planta}, keywords = {transport}, note = {579lp Times Cited:38 Cited References Count:21}, number = 3, pages = {424-429}, title = {Expression of the NH -transporter gene is induced in tomato roots upon association with N -fixing bacteria}, type = {Journal Article}, volume = 215, year = 2002 }

  %0 Journal Article %1 RN1204 %A Becker, D. %A Stanke, R. %A Fendrik, I. %A Frommer, W. B. %A Vanderleyden, J. %A Kaiser, W. M. %A Hedrich, R. %D 2002 %J Planta %N 3 %P 424-429 %R 10.1007/s00425-002-0773-x %T Expression of the NH -transporter gene is induced in tomato roots upon association with N -fixing bacteria %U /brokenurl#<Go to ISI>://WOS:000177179700010 %V 215 %X Plants growing in close association with N-2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N-2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4+-transporter gene. LEAMT1:2 (L. esculentum ammonium transporter 1,2), indicating that bacterial NH4+ might be used as an N source under these conditions. Azospirillum brasilense (nif(-)) Mutants. which lack the structural nifDK genes, failed to induce LEAMT1:2 expression. This suggests that root-associated N-2-fixing bacteria do excrete NH4+ levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1:2 with as low as greater than or equal to1 muM external NH4+. While peak expression was obtained with 2-5 muM NH4+, a further increase in NH4+ reduced LEAMT1:2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4+ concentration or the plant N status. Since micromolar concentrations of NH4+ strongly increased the LEAMT1;2-mRNA levels, the transported NH4+ ion itself could represent a key signal in the associative interaction between higher plants and N-2-fixing micro-organisms.
• Laser scanning microscopy study on adsorption of biologically relevant proteins on implant materials. Schöller, M.; Hauck, A.; Thull, R.; Steinmeyer, R.; Hedrich, R.; Schneider, F. W.; Kiefer, W.; Popp, J. In Biopolymers, 67(4-5), pp. 344–348. 2002.
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  The adsorption of proteins at implant surfaces plays a key role in osscointegration and is therefore of great importance in biomaterial science. Laser scanning microscopy (LSM) is described, a method that is used here for the first study of the adsorption of proteins on implant surfaces. These LSM measurements provide information on the surface morphology, and the spatial distribution of adsorbed proteins can be deduced. (C) 2002 Wiley Periodicals, Inc.

  @article{RN1192, abstract = {The adsorption of proteins at implant surfaces plays a key role in osscointegration and is therefore of great importance in biomaterial science. Laser scanning microscopy (LSM) is described, a method that is used here for the first study of the adsorption of proteins on implant surfaces. These LSM measurements provide information on the surface morphology, and the spatial distribution of adsorbed proteins can be deduced. (C) 2002 Wiley Periodicals, Inc.}, author = {Schöller, M. and Hauck, A. and Thull, R. and Steinmeyer, R. and Hedrich, R. and Schneider, F. W. and Kiefer, W. and Popp, J.}, journal = {Biopolymers}, keywords = {microscopy}, note = {548ph Times Cited:0 Cited References Count:14}, number = {4-5}, pages = {344-348}, title = {Laser scanning microscopy study on adsorption of biologically relevant proteins on implant materials}, type = {Journal Article}, volume = 67, year = 2002 }

  %0 Journal Article %1 RN1192 %A Schöller, M. %A Hauck, A. %A Thull, R. %A Steinmeyer, R. %A Hedrich, R. %A Schneider, F. W. %A Kiefer, W. %A Popp, J. %D 2002 %J Biopolymers %N 4-5 %P 344-348 %R 10.1002/bip.10100 %T Laser scanning microscopy study on adsorption of biologically relevant proteins on implant materials %U /brokenurl#<Go to ISI>://WOS:000175397200033 %V 67 %X The adsorption of proteins at implant surfaces plays a key role in osscointegration and is therefore of great importance in biomaterial science. Laser scanning microscopy (LSM) is described, a method that is used here for the first study of the adsorption of proteins on implant surfaces. These LSM measurements provide information on the surface morphology, and the spatial distribution of adsorbed proteins can be deduced. (C) 2002 Wiley Periodicals, Inc.
• Evidence for the functional organization of chloroplasts in adaxial guard cells of leaves by single cell analysis. Goh, C. H.; Hedrich, R.; Nam, H. G. In Plant Science, 162(6), pp. 965–972. 2002.
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  The functional organization of chloroplasts in adaxial guard cells (GCs) of Vicia faba leaves was investigated by the saturation pulse method of chlorophyll fluorescence induction using single GC pairs. Quantitative imaging analysis of chlorophyll fluorescence performed on adaxial GCs upon dark-light transition revealed a large chlorophyll fluorescence transient. Adaxial GCs displayed PS II quantum yields and relative electron transport rates (ETR) comparable to the abaxial GCs. The slow chlorophyll fluorescence transients in the two cells provided further evidence for the activation of the Calvin cycle in GC chloroplasts on both sides of the leaf. The ETR upon increasing light intensity was, however, differentially expressed in the two cell types. When the rates were normalized to their maximum ETR activity, half-saturation was achieved at 76 and 45 mumol m(-2) s(-1) in adaxial and abaxial GCs, respectively. These results provide unequivocal evidence that the chloroplasts of adaxial GCs have a highly expressive functional organization and that the photosynthetic apparatus of adaxial GCs is well adapted to elevated light intensities. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

  @article{RN1200, abstract = {The functional organization of chloroplasts in adaxial guard cells (GCs) of Vicia faba leaves was investigated by the saturation pulse method of chlorophyll fluorescence induction using single GC pairs. Quantitative imaging analysis of chlorophyll fluorescence performed on adaxial GCs upon dark-light transition revealed a large chlorophyll fluorescence transient. Adaxial GCs displayed PS II quantum yields and relative electron transport rates (ETR) comparable to the abaxial GCs. The slow chlorophyll fluorescence transients in the two cells provided further evidence for the activation of the Calvin cycle in GC chloroplasts on both sides of the leaf. The ETR upon increasing light intensity was, however, differentially expressed in the two cell types. When the rates were normalized to their maximum ETR activity, half-saturation was achieved at 76 and 45 mumol m(-2) s(-1) in adaxial and abaxial GCs, respectively. These results provide unequivocal evidence that the chloroplasts of adaxial GCs have a highly expressive functional organization and that the photosynthetic apparatus of adaxial GCs is well adapted to elevated light intensities. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.}, author = {Goh, C. H. and Hedrich, R. and Nam, H. G.}, journal = {Plant Science}, keywords = {adaxial}, note = {573kp Times Cited:6 Cited References Count:32}, number = 6, pages = {965-972}, title = {Evidence for the functional organization of chloroplasts in adaxial guard cells of leaves by single cell analysis}, type = {Journal Article}, volume = 162, year = 2002 }

  %0 Journal Article %1 RN1200 %A Goh, C. H. %A Hedrich, R. %A Nam, H. G. %D 2002 %J Plant Science %N 6 %P 965-972 %R Pii S0168-9452(02)00047-X Doi 10.1016/S0168-9452(02)00047-X %T Evidence for the functional organization of chloroplasts in adaxial guard cells of leaves by single cell analysis %U /brokenurl#<Go to ISI>://WOS:000176829000013 %V 162 %X The functional organization of chloroplasts in adaxial guard cells (GCs) of Vicia faba leaves was investigated by the saturation pulse method of chlorophyll fluorescence induction using single GC pairs. Quantitative imaging analysis of chlorophyll fluorescence performed on adaxial GCs upon dark-light transition revealed a large chlorophyll fluorescence transient. Adaxial GCs displayed PS II quantum yields and relative electron transport rates (ETR) comparable to the abaxial GCs. The slow chlorophyll fluorescence transients in the two cells provided further evidence for the activation of the Calvin cycle in GC chloroplasts on both sides of the leaf. The ETR upon increasing light intensity was, however, differentially expressed in the two cell types. When the rates were normalized to their maximum ETR activity, half-saturation was achieved at 76 and 45 mumol m(-2) s(-1) in adaxial and abaxial GCs, respectively. These results provide unequivocal evidence that the chloroplasts of adaxial GCs have a highly expressive functional organization and that the photosynthetic apparatus of adaxial GCs is well adapted to elevated light intensities. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
• Outer pore residues control the H and K sensitivity of the Arabidopsis potassium channel AKT3. Geiger, D.; Becker, D.; Lacombe, B.; Hedrich, R. In Plant Cell, 14(8), pp. 1859–1868. 2002.
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  The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca2+ block, proton inhibition, and, as shown in this study, K+ sensitivity. In contrast to inward-rectifying, acid-activated K+ channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K+-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K+ selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H+ and K+ sensitivity of AKT3. Although in K+-free bath solutions outward K+ currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K+ efflux. We conclude that the pH- and K+-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H+ and K+ sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.

  @article{RN1202, abstract = {The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca2+ block, proton inhibition, and, as shown in this study, K+ sensitivity. In contrast to inward-rectifying, acid-activated K+ channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K+-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K+ selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H+ and K+ sensitivity of AKT3. Although in K+-free bath solutions outward K+ currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K+ efflux. We conclude that the pH- and K+-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H+ and K+ sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.}, author = {Geiger, D. and Becker, D. and Lacombe, B. and Hedrich, R.}, journal = {Plant Cell}, keywords = {outward}, note = {586uu Times Cited:34 Cited References Count:47}, number = 8, pages = {1859-1868}, title = {Outer pore residues control the H and K sensitivity of the Arabidopsis potassium channel AKT3}, type = {Journal Article}, volume = 14, year = 2002 }

  %0 Journal Article %1 RN1202 %A Geiger, D. %A Becker, D. %A Lacombe, B. %A Hedrich, R. %D 2002 %J Plant Cell %N 8 %P 1859-1868 %R 10.1105/tpc.003244 %T Outer pore residues control the H and K sensitivity of the Arabidopsis potassium channel AKT3 %U /brokenurl#<Go to ISI>://WOS:000177604700014 %V 14 %X The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca2+ block, proton inhibition, and, as shown in this study, K+ sensitivity. In contrast to inward-rectifying, acid-activated K+ channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K+-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K+ selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H+ and K+ sensitivity of AKT3. Although in K+-free bath solutions outward K+ currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K+ efflux. We conclude that the pH- and K+-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H+ and K+ sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.
• Parallel recordings of photosynthetic electron transport and K -channel activity in single guard cells. Goh, C. H.; Dietrich, P.; Steinmeyer, R.; Schreiber, U.; Nam, H. G.; Hedrich, R. In Plant Journal, 32(4), pp. 623–630. 2002.
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  Stomata open in response to red and blue light. Red light-induced stomatal movement is mediated by guard cell chloroplasts and related to K+-uptake into these motor cells. We have combined a new type of microchlorophyll fluorometer with the patch-clamp technique for parallel studies of the photosynthetic electron transport and activity of plasma membrane K+ channels in single guard cell protoplast. In the whole-cell configuration and presence of ATP in the patch-pipette, the activity of the K+-uptake channels remained constant throughout the course of an experiment (up to 30 min) while photosynthetic activity declined to about 50%. In the absence of ATP inward K+ currents declined in a time-dependent manner. Under these ATP-free conditions, photosynthetic electron transport was completely blocked within 8 min. ADP together with orthophosphate was able to prevent inhibition of photosynthetic electron transport and run-down of K+-channel activity. The results demonstrate that the combination of these two techniques is suited to directly study cytosolic factors as common regulators of photosynthesis and plasma membrane transport within a single-cell.

  @article{RN1201, abstract = {Stomata open in response to red and blue light. Red light-induced stomatal movement is mediated by guard cell chloroplasts and related to K+-uptake into these motor cells. We have combined a new type of microchlorophyll fluorometer with the patch-clamp technique for parallel studies of the photosynthetic electron transport and activity of plasma membrane K+ channels in single guard cell protoplast. In the whole-cell configuration and presence of ATP in the patch-pipette, the activity of the K+-uptake channels remained constant throughout the course of an experiment (up to 30 min) while photosynthetic activity declined to about 50%. In the absence of ATP inward K+ currents declined in a time-dependent manner. Under these ATP-free conditions, photosynthetic electron transport was completely blocked within 8 min. ADP together with orthophosphate was able to prevent inhibition of photosynthetic electron transport and run-down of K+-channel activity. The results demonstrate that the combination of these two techniques is suited to directly study cytosolic factors as common regulators of photosynthesis and plasma membrane transport within a single-cell.}, author = {Goh, C. H. and Dietrich, P. and Steinmeyer, R. and Schreiber, U. and Nam, H. G. and Hedrich, R.}, journal = {Plant Journal}, keywords = {atp}, note = {618jc Times Cited:23 Cited References Count:31}, number = 4, pages = {623-630}, title = {Parallel recordings of photosynthetic electron transport and K -channel activity in single guard cells}, type = {Journal Article}, volume = 32, year = 2002 }

  %0 Journal Article %1 RN1201 %A Goh, C. H. %A Dietrich, P. %A Steinmeyer, R. %A Schreiber, U. %A Nam, H. G. %A Hedrich, R. %D 2002 %J Plant Journal %N 4 %P 623-630 %R DOI 10.1046/j.1365-313X.2002.01451.x %T Parallel recordings of photosynthetic electron transport and K -channel activity in single guard cells %U /brokenurl#<Go to ISI>://WOS:000179414100018 %V 32 %X Stomata open in response to red and blue light. Red light-induced stomatal movement is mediated by guard cell chloroplasts and related to K+-uptake into these motor cells. We have combined a new type of microchlorophyll fluorometer with the patch-clamp technique for parallel studies of the photosynthetic electron transport and activity of plasma membrane K+ channels in single guard cell protoplast. In the whole-cell configuration and presence of ATP in the patch-pipette, the activity of the K+-uptake channels remained constant throughout the course of an experiment (up to 30 min) while photosynthetic activity declined to about 50%. In the absence of ATP inward K+ currents declined in a time-dependent manner. Under these ATP-free conditions, photosynthetic electron transport was completely blocked within 8 min. ADP together with orthophosphate was able to prevent inhibition of photosynthetic electron transport and run-down of K+-channel activity. The results demonstrate that the combination of these two techniques is suited to directly study cytosolic factors as common regulators of photosynthesis and plasma membrane transport within a single-cell.
• Poplar potassium transporters capable of controlling K homeostasis and K -dependent xylogenesis. Langer, K.; Ache, P.; Geiger, D.; Stinzing, A.; Arend, M.; Wind, C.; Regan, S.; Fromm, J.; Hedrich, R. In Plant Journal, 32(6), pp. 997–1009. 2002.
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  The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA(+) ), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de-polarization. PtKUP1 was expressed in a K+ uptake-deficient Escherichia coli strain, where this K+ transporter rescued K+ -dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+ -dependent wood production.

  @article{RN1198, abstract = {The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA(+) ), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de-polarization. PtKUP1 was expressed in a K+ uptake-deficient Escherichia coli strain, where this K+ transporter rescued K+ -dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+ -dependent wood production.}, author = {Langer, K. and Ache, P. and Geiger, D. and Stinzing, A. and Arend, M. and Wind, C. and Regan, S. and Fromm, J. and Hedrich, R.}, journal = {Plant Journal}, keywords = {k+}, note = {629rf Times Cited:80 Cited References Count:58}, number = 6, pages = {997-1009}, title = {Poplar potassium transporters capable of controlling K homeostasis and K -dependent xylogenesis}, type = {Journal Article}, volume = 32, year = 2002 }

  %0 Journal Article %1 RN1198 %A Langer, K. %A Ache, P. %A Geiger, D. %A Stinzing, A. %A Arend, M. %A Wind, C. %A Regan, S. %A Fromm, J. %A Hedrich, R. %D 2002 %J Plant Journal %N 6 %P 997-1009 %R DOI 10.1046/j.1365-313X.2002.01487.x %T Poplar potassium transporters capable of controlling K homeostasis and K -dependent xylogenesis %U /brokenurl#<Go to ISI>://WOS:000180062100012 %V 32 %X The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA(+) ), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de-polarization. PtKUP1 was expressed in a K+ uptake-deficient Escherichia coli strain, where this K+ transporter rescued K+ -dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+ -dependent wood production.
• KCO1 is a component of the slow-vacuolar (SV) ion channel. Schönknecht, G.; Spoormaker, P.; Steinmeyer, R.; Brüggeman, L.; Ache, P.; Dutta, R.; Reintanz, B.; Godde, M.; Hedrich, R.; Palme, K. In Febs Letters, 511(1-3), pp. 28–32. 2002.
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  The Arabidopsis double pore K+ channel KCO1 was fused to green fluorescent protein and expressed in tobacco protoplasts. Microscopic analysis revealed a bright green fluorescence at the vacuolar membrane. RT-PCR experiments showed that KCO1 is expressed in the mesophyll. Vacuoles; from Arabidopsis wild-type and kco1 knockout plants were isolated for patch-clamp analyses. Currents mediated by slow-activating vacuolar (SV) channels of mesophyll cell vacuoles were significantly smaller in kco1 plants compared to the wild-type. This shown that KCO1 is involved in the formation of SV channels. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

  @article{RN1191, abstract = {The Arabidopsis double pore K+ channel KCO1 was fused to green fluorescent protein and expressed in tobacco protoplasts. Microscopic analysis revealed a bright green fluorescence at the vacuolar membrane. RT-PCR experiments showed that KCO1 is expressed in the mesophyll. Vacuoles; from Arabidopsis wild-type and kco1 knockout plants were isolated for patch-clamp analyses. Currents mediated by slow-activating vacuolar (SV) channels of mesophyll cell vacuoles were significantly smaller in kco1 plants compared to the wild-type. This shown that KCO1 is involved in the formation of SV channels. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.}, author = {Schönknecht, G. and Spoormaker, P. and Steinmeyer, R. and Brüggeman, L. and Ache, P. and Dutta, R. and Reintanz, B. and Godde, M. and Hedrich, R. and Palme, K.}, journal = {Febs Letters}, keywords = {k+}, note = {517uf Times Cited:49 Cited References Count:27}, number = {1-3}, pages = {28-32}, title = {KCO1 is a component of the slow-vacuolar (SV) ion channel}, type = {Journal Article}, volume = 511, year = 2002 }

  %0 Journal Article %1 RN1191 %A Schönknecht, G. %A Spoormaker, P. %A Steinmeyer, R. %A Brüggeman, L. %A Ache, P. %A Dutta, R. %A Reintanz, B. %A Godde, M. %A Hedrich, R. %A Palme, K. %D 2002 %J Febs Letters %N 1-3 %P 28-32 %R Doi 10.1016/S0014-5793(01)03273-2 %T KCO1 is a component of the slow-vacuolar (SV) ion channel %U /brokenurl#<Go to ISI>://WOS:000173628000006 %V 511 %X The Arabidopsis double pore K+ channel KCO1 was fused to green fluorescent protein and expressed in tobacco protoplasts. Microscopic analysis revealed a bright green fluorescence at the vacuolar membrane. RT-PCR experiments showed that KCO1 is expressed in the mesophyll. Vacuoles; from Arabidopsis wild-type and kco1 knockout plants were isolated for patch-clamp analyses. Currents mediated by slow-activating vacuolar (SV) channels of mesophyll cell vacuoles were significantly smaller in kco1 plants compared to the wild-type. This shown that KCO1 is involved in the formation of SV channels. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.
• Channelling auxin action: modulation of ion transport by indole-3-acetic acid. Becker, D.; Hedrich, R. In Plant Molecular Biology, 49(3-4), pp. 349–356. 2002.
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  The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.

  @article{RN1205, abstract = {The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.}, author = {Becker, D. and Hedrich, R.}, journal = {Plant Molecular Biology}, keywords = {auxin}, note = {543mj Times Cited:47 Cited References Count:92}, number = {3-4}, pages = {349-356}, title = {Channelling auxin action: modulation of ion transport by indole-3-acetic acid}, type = {Journal Article}, volume = 49, year = 2002 }

  %0 Journal Article %1 RN1205 %A Becker, D. %A Hedrich, R. %D 2002 %J Plant Molecular Biology %N 3-4 %P 349-356 %R Doi 10.1023/A:1015211231864 %T Channelling auxin action: modulation of ion transport by indole-3-acetic acid %U /brokenurl#<Go to ISI>://WOS:000175105500007 %V 49 %X The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.
• Studying guard cells in the intact plant: modulation of stomatal movement by apoplastic factors. Roelfsema, M. R. G.; Hedrich, R. In New Phytologist, 153(3), pp. 425–431. 2002.
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  Here, we discuss why guard cells in intact plants respond to environmental signals in a different way than guard cells in epidermal strips, or protoplasts thereof. In intact leaves stomatal opening is counteracted by epidermal cells that press against the guard cells. Changes in the turgor of epidermal cells therefore can alter the stomatal aperture. In addition, stornatal opening may be modulated by the solute composition of the guard cell wall. Changes in apoplastic K-+,K- Cl- and Ca2+ occur after light-dark transitions, but not in such a way that it would support stomatal opening. Organic anions may play a role, since they enhance the open probability of anion channels in the plasma membrane. Furthermore, studies with auxin-resistant and abscisic acid-insensitive mutants show that light-induced stomatal opening is modulated by these hormones. Using the newly developed method in which guard cells in the intact plant are impaled with double-barreled electrodes, the role of these apoplastic factors now can be studied on single guard cells that are still in their natural environment. (C) New Phytologist (2002) 153: 425-431.

  @article{RN1193, abstract = {Here, we discuss why guard cells in intact plants respond to environmental signals in a different way than guard cells in epidermal strips, or protoplasts thereof. In intact leaves stomatal opening is counteracted by epidermal cells that press against the guard cells. Changes in the turgor of epidermal cells therefore can alter the stomatal aperture. In addition, stornatal opening may be modulated by the solute composition of the guard cell wall. Changes in apoplastic K-+,K- Cl- and Ca2+ occur after light-dark transitions, but not in such a way that it would support stomatal opening. Organic anions may play a role, since they enhance the open probability of anion channels in the plasma membrane. Furthermore, studies with auxin-resistant and abscisic acid-insensitive mutants show that light-induced stomatal opening is modulated by these hormones. Using the newly developed method in which guard cells in the intact plant are impaled with double-barreled electrodes, the role of these apoplastic factors now can be studied on single guard cells that are still in their natural environment. (C) New Phytologist (2002) 153: 425-431.}, author = {Roelfsema, M. R. G. and Hedrich, R.}, journal = {New Phytologist}, keywords = {cell}, note = {523zh Times Cited:48 Cited References Count:51}, number = 3, pages = {425-431}, title = {Studying guard cells in the intact plant: modulation of stomatal movement by apoplastic factors}, type = {Journal Article}, volume = 153, year = 2002 }

  %0 Journal Article %1 RN1193 %A Roelfsema, M. R. G. %A Hedrich, R. %D 2002 %J New Phytologist %N 3 %P 425-431 %R DOI 10.1046/j.1469-8137.2002.00344.x %T Studying guard cells in the intact plant: modulation of stomatal movement by apoplastic factors %U /brokenurl#<Go to ISI>://WOS:000173987100008 %V 153 %X Here, we discuss why guard cells in intact plants respond to environmental signals in a different way than guard cells in epidermal strips, or protoplasts thereof. In intact leaves stomatal opening is counteracted by epidermal cells that press against the guard cells. Changes in the turgor of epidermal cells therefore can alter the stomatal aperture. In addition, stornatal opening may be modulated by the solute composition of the guard cell wall. Changes in apoplastic K-+,K- Cl- and Ca2+ occur after light-dark transitions, but not in such a way that it would support stomatal opening. Organic anions may play a role, since they enhance the open probability of anion channels in the plasma membrane. Furthermore, studies with auxin-resistant and abscisic acid-insensitive mutants show that light-induced stomatal opening is modulated by these hormones. Using the newly developed method in which guard cells in the intact plant are impaled with double-barreled electrodes, the role of these apoplastic factors now can be studied on single guard cells that are still in their natural environment. (C) New Phytologist (2002) 153: 425-431.
• CO provides an intermediate link in the red light response of guard cells. Roelfsema, M. R. G.; Hanstein, S.; Felle, H. H.; Hedrich, R. In Plant Journal, 32(1), pp. 65–75. 2002.
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  Guard cells in intact leafs display light-induced membrane potential changes, which alter the direction of K+ -transport across the plasma membrane (Roelfsema et al ., 2001). A beam of blue light, but not red light, directed at the impaled guard cell triggers this response, while both light qualities induce opening of stomata. To gain insight into this apparent contradiction, we explored the possible interaction between red light and CO2 . Guard cells in the intact plant were impaled with double-barrelled electrodes and illuminated with red light. Cells that were hyperpolarized in CO2 -free air, depolarized after a switch to air with 700 mul l(-1) CO2 , in a reversible manner. As a result, K+ -fluxes across the plasma membrane changed direction, to favour K+ extrusion and stomatal closure in the presence of CO2 . Concurrent with the depolarization, an inward current across the plasma membrane appeared, most likely due to activation of anion channels. Guard cell responses to CO2 could be recorded in darkness as well as in red light. However, in darkness some cells spontaneously depolarized, these cells hyperpolarized again in red light. Here, red light was projected on a large area of the leaf and decreased the intracellular CO2 concentration by about 250 mul l(-1) , as measured with a miniature CO2 sensor placed in the substomatal cavity. We conclude, that in intact leaves the red light response of guard cells is mediated through a decrease of the intercellular CO2 concentration.

  @article{RN1194, abstract = {Guard cells in intact leafs display light-induced membrane potential changes, which alter the direction of K+ -transport across the plasma membrane (Roelfsema et al ., 2001). A beam of blue light, but not red light, directed at the impaled guard cell triggers this response, while both light qualities induce opening of stomata. To gain insight into this apparent contradiction, we explored the possible interaction between red light and CO2 . Guard cells in the intact plant were impaled with double-barrelled electrodes and illuminated with red light. Cells that were hyperpolarized in CO2 -free air, depolarized after a switch to air with 700 mul l(-1) CO2 , in a reversible manner. As a result, K+ -fluxes across the plasma membrane changed direction, to favour K+ extrusion and stomatal closure in the presence of CO2 . Concurrent with the depolarization, an inward current across the plasma membrane appeared, most likely due to activation of anion channels. Guard cell responses to CO2 could be recorded in darkness as well as in red light. However, in darkness some cells spontaneously depolarized, these cells hyperpolarized again in red light. Here, red light was projected on a large area of the leaf and decreased the intracellular CO2 concentration by about 250 mul l(-1) , as measured with a miniature CO2 sensor placed in the substomatal cavity. We conclude, that in intact leaves the red light response of guard cells is mediated through a decrease of the intercellular CO2 concentration.}, author = {Roelfsema, M. R. G. and Hanstein, S. and Felle, H. H. and Hedrich, R.}, journal = {Plant Journal}, keywords = {cell}, note = {600cy Times Cited:125 Cited References Count:38}, number = 1, pages = {65-75}, title = {CO provides an intermediate link in the red light response of guard cells}, type = {Journal Article}, volume = 32, year = 2002 }

  %0 Journal Article %1 RN1194 %A Roelfsema, M. R. G. %A Hanstein, S. %A Felle, H. H. %A Hedrich, R. %D 2002 %J Plant Journal %N 1 %P 65-75 %R DOI 10.1046/j.1365-313X.2002.01403.x %T CO provides an intermediate link in the red light response of guard cells %U /brokenurl#<Go to ISI>://WOS:000178374100006 %V 32 %X Guard cells in intact leafs display light-induced membrane potential changes, which alter the direction of K+ -transport across the plasma membrane (Roelfsema et al ., 2001). A beam of blue light, but not red light, directed at the impaled guard cell triggers this response, while both light qualities induce opening of stomata. To gain insight into this apparent contradiction, we explored the possible interaction between red light and CO2 . Guard cells in the intact plant were impaled with double-barrelled electrodes and illuminated with red light. Cells that were hyperpolarized in CO2 -free air, depolarized after a switch to air with 700 mul l(-1) CO2 , in a reversible manner. As a result, K+ -fluxes across the plasma membrane changed direction, to favour K+ extrusion and stomatal closure in the presence of CO2 . Concurrent with the depolarization, an inward current across the plasma membrane appeared, most likely due to activation of anion channels. Guard cell responses to CO2 could be recorded in darkness as well as in red light. However, in darkness some cells spontaneously depolarized, these cells hyperpolarized again in red light. Here, red light was projected on a large area of the leaf and decreased the intracellular CO2 concentration by about 250 mul l(-1) , as measured with a miniature CO2 sensor placed in the substomatal cavity. We conclude, that in intact leaves the red light response of guard cells is mediated through a decrease of the intercellular CO2 concentration.
• Diurnal and circadian regulation of putative potassium channels in a leaf moving organ. Moshelion, M.; Becker, D.; Czempinski, K.; Mueller-Roeber, B.; Attali, B.; Hedrich, R.; Moran, N. In Plant Physiology, 128(2), pp. 634–642. 2002.
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  In a search for potassium channels involved in light- and clock-regulated leaf movements, we cloned four putative K channel genes from the leaf-moving organs, pulvini, of the legume Samanea santan. The S. saman SPOCK1 is homologous to KCO1, an Arabidopsis two-pore-domain K channel, the S. saman SPORK1 is similar to SKOR and GORK, Arabidopsis outward-rectifying Shaker-like K channels, and the S. saman SPICK1 and SPICK2 are homologous to AKT2, a weakly-inward-rectifying Shaker-like Arabidopsis K channel. All four S. saman sequences possess the universal K-channel-specific pore signature, TXXTXGYG, strongly suggesting a role in transmembrane K+ transport. The four S. saman genes had different expression patterns within four leaf parts: 'extensor' and 'flexor' (the motor tissues), the leaf blades (mainly mesophyll), and the vascular bundle ('rachis'). Based on northern blot analysis, their transcript level was correlated with the rhythmic leaf movements: (a) all four genes were regulated diurnally (Spick2, Spork1, and Spock1 in extensor and flexor, Spick1 in extensor and rachis); (b) Spork1 and Spock1 rhythms were inverted upon the inversion of the day-night cycle; and (c) in extensor and/or flexor, the expression of Spork1, Spick1, and Spick2 was also under a circadian control. These findings parallel the circadian rhythm shown to govern the resting membrane K+ permeability in extensor and flexor protoplasts and the susceptibility of this permeability to light stimulation (Kim et al., 1993). Thus, Samanea pulvinar motor cells are the first described system combining light and circadian regulation of K channels at the level of transcript and membrane transport.

  @article{RN1196, abstract = {In a search for potassium channels involved in light- and clock-regulated leaf movements, we cloned four putative K channel genes from the leaf-moving organs, pulvini, of the legume Samanea santan. The S. saman SPOCK1 is homologous to KCO1, an Arabidopsis two-pore-domain K channel, the S. saman SPORK1 is similar to SKOR and GORK, Arabidopsis outward-rectifying Shaker-like K channels, and the S. saman SPICK1 and SPICK2 are homologous to AKT2, a weakly-inward-rectifying Shaker-like Arabidopsis K channel. All four S. saman sequences possess the universal K-channel-specific pore signature, TXXTXGYG, strongly suggesting a role in transmembrane K+ transport. The four S. saman genes had different expression patterns within four leaf parts: 'extensor' and 'flexor' (the motor tissues), the leaf blades (mainly mesophyll), and the vascular bundle ('rachis'). Based on northern blot analysis, their transcript level was correlated with the rhythmic leaf movements: (a) all four genes were regulated diurnally (Spick2, Spork1, and Spock1 in extensor and flexor, Spick1 in extensor and rachis); (b) Spork1 and Spock1 rhythms were inverted upon the inversion of the day-night cycle; and (c) in extensor and/or flexor, the expression of Spork1, Spick1, and Spick2 was also under a circadian control. These findings parallel the circadian rhythm shown to govern the resting membrane K+ permeability in extensor and flexor protoplasts and the susceptibility of this permeability to light stimulation (Kim et al., 1993). Thus, Samanea pulvinar motor cells are the first described system combining light and circadian regulation of K channels at the level of transcript and membrane transport.}, author = {Moshelion, M. and Becker, D. and Czempinski, K. and Mueller-Roeber, B. and Attali, B. and Hedrich, R. and Moran, N.}, journal = {Plant Physiology}, keywords = {myOwn}, note = {523vc Times Cited:74 Cited References Count:35}, number = 2, pages = {634-642}, title = {Diurnal and circadian regulation of putative potassium channels in a leaf moving organ}, type = {Journal Article}, volume = 128, year = 2002 }

  %0 Journal Article %1 RN1196 %A Moshelion, M. %A Becker, D. %A Czempinski, K. %A Mueller-Roeber, B. %A Attali, B. %A Hedrich, R. %A Moran, N. %D 2002 %J Plant Physiology %N 2 %P 634-642 %R 10.1104/pp.010549 %T Diurnal and circadian regulation of putative potassium channels in a leaf moving organ %U /brokenurl#<Go to ISI>://WOS:000173977100034 %V 128 %X In a search for potassium channels involved in light- and clock-regulated leaf movements, we cloned four putative K channel genes from the leaf-moving organs, pulvini, of the legume Samanea santan. The S. saman SPOCK1 is homologous to KCO1, an Arabidopsis two-pore-domain K channel, the S. saman SPORK1 is similar to SKOR and GORK, Arabidopsis outward-rectifying Shaker-like K channels, and the S. saman SPICK1 and SPICK2 are homologous to AKT2, a weakly-inward-rectifying Shaker-like Arabidopsis K channel. All four S. saman sequences possess the universal K-channel-specific pore signature, TXXTXGYG, strongly suggesting a role in transmembrane K+ transport. The four S. saman genes had different expression patterns within four leaf parts: 'extensor' and 'flexor' (the motor tissues), the leaf blades (mainly mesophyll), and the vascular bundle ('rachis'). Based on northern blot analysis, their transcript level was correlated with the rhythmic leaf movements: (a) all four genes were regulated diurnally (Spick2, Spork1, and Spock1 in extensor and flexor, Spick1 in extensor and rachis); (b) Spork1 and Spock1 rhythms were inverted upon the inversion of the day-night cycle; and (c) in extensor and/or flexor, the expression of Spork1, Spick1, and Spick2 was also under a circadian control. These findings parallel the circadian rhythm shown to govern the resting membrane K+ permeability in extensor and flexor protoplasts and the susceptibility of this permeability to light stimulation (Kim et al., 1993). Thus, Samanea pulvinar motor cells are the first described system combining light and circadian regulation of K channels at the level of transcript and membrane transport.

• Do drought-hardened plants suffer from fever?. Hedrich, R.; Steinmeyer, R. In Trends in Plant Science, 6(11), pp. 506–506. 2001.
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  @article{RN1214, author = {Hedrich, R. and Steinmeyer, R.}, journal = {Trends in Plant Science}, keywords = {leaf}, note = {493pc Times Cited:4 Cited References Count:6}, number = 11, pages = {506-506}, title = {Do drought-hardened plants suffer from fever?}, type = {Journal Article}, volume = 6, year = 2001 }

  %0 Journal Article %1 RN1214 %A Hedrich, R. %A Steinmeyer, R. %D 2001 %J Trends in Plant Science %N 11 %P 506-506 %R Doi 10.1016/S1360-1385(01)02089-1 %T Do drought-hardened plants suffer from fever? %U /brokenurl#<Go to ISI>://WOS:000172231000008 %V 6
• K channel profile and electrical properties of root hairs. Ivashikina, N.; Becker, D.; Ache, P.; Meyerhoff, O.; Felle, H. H.; Hedrich, R. In Febs Letters, 508(3), pp. 463–469. 2001.
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  Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K+-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K+ channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K+ uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K+ fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha -subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K+ outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

  @article{RN1212, abstract = {Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K+-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K+ channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K+ uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K+ fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha -subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K+ outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.}, author = {Ivashikina, N. and Becker, D. and Ache, P. and Meyerhoff, O. and Felle, H. H. and Hedrich, R.}, journal = {Febs Letters}, keywords = {hairs}, note = {496uw Times Cited:137 Cited References Count:33}, number = 3, pages = {463-469}, title = {K channel profile and electrical properties of root hairs}, type = {Journal Article}, volume = 508, year = 2001 }

  %0 Journal Article %1 RN1212 %A Ivashikina, N. %A Becker, D. %A Ache, P. %A Meyerhoff, O. %A Felle, H. H. %A Hedrich, R. %D 2001 %J Febs Letters %N 3 %P 463-469 %R Doi 10.1016/S0014-5793(01)03114-3 %T K channel profile and electrical properties of root hairs %U /brokenurl#<Go to ISI>://WOS:000172416300038 %V 508 %X Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K+-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K+ channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K+ uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K+ fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha -subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K+ outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
• The pore of plant K channels is involved in voltage and pH sensing:: Domain-swapping between different K channel α-subunits. Hoth, S.; Geiger, D.; Becker, D.; Hedrich, R. In Plant Cell, 13(4), pp. 943–952. 2001.
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  Plant K+ uptake channel types differ with respect to their voltage, Ca2+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3(P)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H+ and Ca2+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca2+ insensitive, extracellular protons and Ca2+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca2+ regulation and for the rectification of voltage-dependent K+ uptake channels are located within the channel pore.

  @article{RN1213, abstract = {Plant K+ uptake channel types differ with respect to their voltage, Ca2+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3(P)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H+ and Ca2+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca2+ insensitive, extracellular protons and Ca2+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca2+ regulation and for the rectification of voltage-dependent K+ uptake channels are located within the channel pore.}, author = {Hoth, S. and Geiger, D. and Becker, D. and Hedrich, R.}, journal = {Plant Cell}, keywords = {channel}, note = {424ek Times Cited:35 Cited References Count:40}, number = 4, pages = {943-952}, title = {The pore of plant K channels is involved in voltage and pH sensing:: Domain-swapping between different K channel α-subunits}, type = {Journal Article}, volume = 13, year = 2001 }

  %0 Journal Article %1 RN1213 %A Hoth, S. %A Geiger, D. %A Becker, D. %A Hedrich, R. %D 2001 %J Plant Cell %N 4 %P 943-952 %R DOI 10.1105/tpc.13.4.943 %T The pore of plant K channels is involved in voltage and pH sensing:: Domain-swapping between different K channel α-subunits %U /brokenurl#<Go to ISI>://WOS:000168219000017 %V 13 %X Plant K+ uptake channel types differ with respect to their voltage, Ca2+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3(P)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H+ and Ca2+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca2+ insensitive, extracellular protons and Ca2+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca2+ regulation and for the rectification of voltage-dependent K+ uptake channels are located within the channel pore.
• Discontinuous single electrode voltage-clamp measurements:: assessment of clamp accuracy in guard cells. Roelfsema, M. R. G.; Steinmeyer, R.; Hedrich, R. In Journal of Experimental Botany, 52(362), pp. 1933–1939. 2001.
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  The use of a discontinuous single electrode voltage-clamp (dSEVC) offers an attractive alternative to the patch-clamp technique, since whole-cell measurements can be performed with a single sharp electrode. Comparison of current-voltage relations, however, revealed a weaker voltage dependence of channels measured with the dSEVC compared to patch clamp. The accuracy of the dSEVC was tested on Vicia faba guard cells impaled with double-barrelled electrodes. The actual clamp potential was measured independently of the dSEVC, at the second barrel. The weaker voltage dependence of ion channels appeared to be due to an overestimation of the clamp potential by the dSEVC. The deviation between the intended and actual clamp potential showed a linear relationship with the injected current; on average a 126 mV deviation was found for a clamp current of 1 nA. The deviation was probably caused by a slow settling capacity at the electrode, not compensated by the dSEVC amplifier. It is concluded that the dSEVC method in its current state is only suited for the study of small ion conductances in plant cells.

  @article{RN1208, abstract = {The use of a discontinuous single electrode voltage-clamp (dSEVC) offers an attractive alternative to the patch-clamp technique, since whole-cell measurements can be performed with a single sharp electrode. Comparison of current-voltage relations, however, revealed a weaker voltage dependence of channels measured with the dSEVC compared to patch clamp. The accuracy of the dSEVC was tested on Vicia faba guard cells impaled with double-barrelled electrodes. The actual clamp potential was measured independently of the dSEVC, at the second barrel. The weaker voltage dependence of ion channels appeared to be due to an overestimation of the clamp potential by the dSEVC. The deviation between the intended and actual clamp potential showed a linear relationship with the injected current; on average a 126 mV deviation was found for a clamp current of 1 nA. The deviation was probably caused by a slow settling capacity at the electrode, not compensated by the dSEVC amplifier. It is concluded that the dSEVC method in its current state is only suited for the study of small ion conductances in plant cells.}, author = {Roelfsema, M. R. G. and Steinmeyer, R. and Hedrich, R.}, journal = {Journal of Experimental Botany}, keywords = {clamp}, note = {471aw Times Cited:6 Cited References Count:23}, number = 362, pages = {1933-1939}, title = {Discontinuous single electrode voltage-clamp measurements:: assessment of clamp accuracy in guard cells}, type = {Journal Article}, volume = 52, year = 2001 }

  %0 Journal Article %1 RN1208 %A Roelfsema, M. R. G. %A Steinmeyer, R. %A Hedrich, R. %D 2001 %J Journal of Experimental Botany %N 362 %P 1933-1939 %R DOI 10.1093/jexbot/52.362.1933 %T Discontinuous single electrode voltage-clamp measurements:: assessment of clamp accuracy in guard cells %U /brokenurl#<Go to ISI>://WOS:000170905500022 %V 52 %X The use of a discontinuous single electrode voltage-clamp (dSEVC) offers an attractive alternative to the patch-clamp technique, since whole-cell measurements can be performed with a single sharp electrode. Comparison of current-voltage relations, however, revealed a weaker voltage dependence of channels measured with the dSEVC compared to patch clamp. The accuracy of the dSEVC was tested on Vicia faba guard cells impaled with double-barrelled electrodes. The actual clamp potential was measured independently of the dSEVC, at the second barrel. The weaker voltage dependence of ion channels appeared to be due to an overestimation of the clamp potential by the dSEVC. The deviation between the intended and actual clamp potential showed a linear relationship with the injected current; on average a 126 mV deviation was found for a clamp current of 1 nA. The deviation was probably caused by a slow settling capacity at the electrode, not compensated by the dSEVC amplifier. It is concluded that the dSEVC method in its current state is only suited for the study of small ion conductances in plant cells.
• A novel K channel expressed in carrot roots with a low susceptibility toward metal ions. Paganetto, A.; Bregante, M.; Downey, P.; Lo Schiavo, F.; Hoth, S.; Hedrich, R.; Gambale, F. In Journal of Bioenergetics and Biomembranes, 33(1), pp. 63–71. 2001.
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  Kdc1 is a novel K(+)-channel gene cloned from carrot roots, and which is also present in cultured carrot cells. We investigated the characteristics of the ionic current elicited in Xenopus oocytes coinjected with KDC1 (K(+)-Daucus carota 1) and KAT1 (from Arabidopsis thaliana) RNA. Expressed hereromeric channels displayed inward-rectifying potassium currents whose kinetics, voltage characteristics, and inhibition by metal ions depended on KDC1:KAT1 ratios. At low KDC1:KAT1 ratios, Zn(2+) inhibition of heteromeric K(+) current was less pronounced compared to homomeric KAT1 channels, while at higher KDC1:KAT1 ratios, the addition of Zn(2+) even produced an increase in current. Under the same conditions, the Ni(2+) inhibition of the current was also reduced, but no current increase was observed. These effects might be explained by the unusual amino acid composition of the KDC1 protein in terms of histidine residues that are absent in the pore region, but abundant (four per subunit) in the proximity of the pore entrance. Channels like KDC1 could be at least partially responsible for the higher resistance of carrot cells in the presence of metals.

  @article{RN1209, abstract = {Kdc1 is a novel K(+)-channel gene cloned from carrot roots, and which is also present in cultured carrot cells. We investigated the characteristics of the ionic current elicited in Xenopus oocytes coinjected with KDC1 (K(+)-Daucus carota 1) and KAT1 (from Arabidopsis thaliana) RNA. Expressed hereromeric channels displayed inward-rectifying potassium currents whose kinetics, voltage characteristics, and inhibition by metal ions depended on KDC1:KAT1 ratios. At low KDC1:KAT1 ratios, Zn(2+) inhibition of heteromeric K(+) current was less pronounced compared to homomeric KAT1 channels, while at higher KDC1:KAT1 ratios, the addition of Zn(2+) even produced an increase in current. Under the same conditions, the Ni(2+) inhibition of the current was also reduced, but no current increase was observed. These effects might be explained by the unusual amino acid composition of the KDC1 protein in terms of histidine residues that are absent in the pore region, but abundant (four per subunit) in the proximity of the pore entrance. Channels like KDC1 could be at least partially responsible for the higher resistance of carrot cells in the presence of metals.}, author = {Paganetto, A. and Bregante, M. and Downey, P. and Lo Schiavo, F. and Hoth, S. and Hedrich, R. and Gambale, F.}, journal = {Journal of Bioenergetics and Biomembranes}, keywords = {channels}, note = {420uc Times Cited:14 Cited References Count:35}, number = 1, pages = {63-71}, title = {A novel K channel expressed in carrot roots with a low susceptibility toward metal ions}, type = {Journal Article}, volume = 33, year = 2001 }

  %0 Journal Article %1 RN1209 %A Paganetto, A. %A Bregante, M. %A Downey, P. %A Lo Schiavo, F. %A Hoth, S. %A Hedrich, R. %A Gambale, F. %D 2001 %J Journal of Bioenergetics and Biomembranes %N 1 %P 63-71 %R Doi 10.1023/A:1005676724618 %T A novel K channel expressed in carrot roots with a low susceptibility toward metal ions %U /brokenurl#<Go to ISI>://WOS:000168022800007 %V 33 %X Kdc1 is a novel K(+)-channel gene cloned from carrot roots, and which is also present in cultured carrot cells. We investigated the characteristics of the ionic current elicited in Xenopus oocytes coinjected with KDC1 (K(+)-Daucus carota 1) and KAT1 (from Arabidopsis thaliana) RNA. Expressed hereromeric channels displayed inward-rectifying potassium currents whose kinetics, voltage characteristics, and inhibition by metal ions depended on KDC1:KAT1 ratios. At low KDC1:KAT1 ratios, Zn(2+) inhibition of heteromeric K(+) current was less pronounced compared to homomeric KAT1 channels, while at higher KDC1:KAT1 ratios, the addition of Zn(2+) even produced an increase in current. Under the same conditions, the Ni(2+) inhibition of the current was also reduced, but no current increase was observed. These effects might be explained by the unusual amino acid composition of the KDC1 protein in terms of histidine residues that are absent in the pore region, but abundant (four per subunit) in the proximity of the pore entrance. Channels like KDC1 could be at least partially responsible for the higher resistance of carrot cells in the presence of metals.
• Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of leaves. Goh, C. H.; Hedrich, R.; Schreiber, U. In Plant and Cell Physiology, 42(10), pp. 1186–1191. 2001.
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  Guard cell protoplasts isolated from Vicia leaves showed a strong suppression of the photosynthesis under hypotonic conditions, as reflected by changes in the chlorophyll fluorescence characteristics. The response was reversible as well. Mesophyll cell protoplasts did not show any lowering of photosynthetic activity under hypo-osmotic conditions. This result indicates that the response was guard cell specific.

  @article{RN1216, abstract = {Guard cell protoplasts isolated from Vicia leaves showed a strong suppression of the photosynthesis under hypotonic conditions, as reflected by changes in the chlorophyll fluorescence characteristics. The response was reversible as well. Mesophyll cell protoplasts did not show any lowering of photosynthetic activity under hypo-osmotic conditions. This result indicates that the response was guard cell specific.}, author = {Goh, C. H. and Hedrich, R. and Schreiber, U.}, journal = {Plant and Cell Physiology}, keywords = {chlorophyll}, note = {484lw Times Cited:6 Cited References Count:21}, number = 10, pages = {1186-1191}, title = {Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of leaves}, type = {Journal Article}, volume = 42, year = 2001 }

  %0 Journal Article %1 RN1216 %A Goh, C. H. %A Hedrich, R. %A Schreiber, U. %D 2001 %J Plant and Cell Physiology %N 10 %P 1186-1191 %R DOI 10.1093/pcp/pce149 %T Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of leaves %U /brokenurl#<Go to ISI>://WOS:000171692700021 %V 42 %X Guard cell protoplasts isolated from Vicia leaves showed a strong suppression of the photosynthesis under hypotonic conditions, as reflected by changes in the chlorophyll fluorescence characteristics. The response was reversible as well. Mesophyll cell protoplasts did not show any lowering of photosynthetic activity under hypo-osmotic conditions. This result indicates that the response was guard cell specific.
• VFK1, a K channel involved in phloem unloading. Ache, P.; Becker, D.; Deeken, R.; Dreyer, I.; Weber, H.; Fromm, J.; Hedrich, R. In Plant Journal, 27(6), pp. 571–580. 2001.
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  In search of a K+ channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K+ uptake channels. We cloned VFK1 (for Vicia faba K+ channel 1) characterised by a structure known from the Shaker family of plant K+ channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K+ selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K+ channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K+ concentration. Under these conditions K+ channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K+ channel is involved in sugar unloading and K+ retrieval.

  @article{RN1219, abstract = {In search of a K+ channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K+ uptake channels. We cloned VFK1 (for Vicia faba K+ channel 1) characterised by a structure known from the Shaker family of plant K+ channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K+ selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K+ channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K+ concentration. Under these conditions K+ channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K+ channel is involved in sugar unloading and K+ retrieval.}, author = {Ache, P. and Becker, D. and Deeken, R. and Dreyer, I. and Weber, H. and Fromm, J. and Hedrich, R.}, journal = {Plant Journal}, keywords = {k+}, note = {477lx Times Cited:74 Cited References Count:48}, number = 6, pages = {571-580}, title = {VFK1, a K channel involved in phloem unloading}, type = {Journal Article}, volume = 27, year = 2001 }

  %0 Journal Article %1 RN1219 %A Ache, P. %A Becker, D. %A Deeken, R. %A Dreyer, I. %A Weber, H. %A Fromm, J. %A Hedrich, R. %D 2001 %J Plant Journal %N 6 %P 571-580 %R DOI 10.1046/j.1365-313X.2001.01116.x %T VFK1, a K channel involved in phloem unloading %U /brokenurl#<Go to ISI>://WOS:000171286000009 %V 27 %X In search of a K+ channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K+ uptake channels. We cloned VFK1 (for Vicia faba K+ channel 1) characterised by a structure known from the Shaker family of plant K+ channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K+ selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K+ channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K+ concentration. Under these conditions K+ channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K+ channel is involved in sugar unloading and K+ retrieval.
• Single guard cell recordings in intact plants: light-induced hyperpolarization of the plasma membrane. Roelfsema, M. R. G.; Steinmeyer, R.; Staal, M.; Hedrich, R. In Plant Journal, 26(1), pp. 1–13. 2001.
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  Guard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current- and voltage-clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double-barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far-depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage-dependent anion channels. All other cells displayed both outward and inward rectifying K+-channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of -41 mV (SD 16) and -112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+-efflux via outward rectifying channels to a K+-influx via inward rectifying channels.

  @article{RN1207, abstract = {Guard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current- and voltage-clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double-barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far-depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage-dependent anion channels. All other cells displayed both outward and inward rectifying K+-channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of -41 mV (SD 16) and -112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+-efflux via outward rectifying channels to a K+-influx via inward rectifying channels.}, author = {Roelfsema, M. R. G. and Steinmeyer, R. and Staal, M. and Hedrich, R.}, journal = {Plant Journal}, keywords = {cell}, note = {437bd Times Cited:72 Cited References Count:53}, number = 1, pages = {1-13}, title = {Single guard cell recordings in intact plants: light-induced hyperpolarization of the plasma membrane}, type = {Journal Article}, volume = 26, year = 2001 }

  %0 Journal Article %1 RN1207 %A Roelfsema, M. R. G. %A Steinmeyer, R. %A Staal, M. %A Hedrich, R. %D 2001 %J Plant Journal %N 1 %P 1-13 %R DOI 10.1046/j.1365-313x.2001.01000.x %T Single guard cell recordings in intact plants: light-induced hyperpolarization of the plasma membrane %U /brokenurl#<Go to ISI>://WOS:000168969600001 %V 26 %X Guard cells are electrically isolated from other plant cells and therefore offer the unique possibility to conduct current- and voltage-clamp recordings on single cells in an intact plant. Guard cells in their natural environment were impaled with double-barreled electrodes and found to exhibit three physiological states. A minority of cells were classified as far-depolarized cells. These cells exhibited positive membrane potentials and were dominated by the activity of voltage-dependent anion channels. All other cells displayed both outward and inward rectifying K+-channel activity. These cells were either depolarized or hyperpolarized, with average membrane potentials of -41 mV (SD 16) and -112 mV (SD 19), respectively. Depolarized guard cells extrude K+ through outward rectifying channels, while K+ is taken up via inward rectifying channels in hyperpolarized cells. Upon a light/dark transition, guard cells that were hyperpolarized in the light switched to the depolarized state. The depolarization was accompanied by a 35 pA decrease in pump current and an increase in the conductance of inward rectifying channels. Both an increase in pump current and a decrease in the conductance of the inward rectifier were triggered by blue light, while red light was ineffective. From these studies we conclude that light modulates plasma membrane transport through large membrane potential changes, reversing the K+-efflux via outward rectifying channels to a K+-influx via inward rectifying channels.
• Identification of a novel, multifunctional β-defensin (human β-defensin 3) with specific antimicrobial activity -: Its interaction with plasma membranes of and the induction of macrophage chemoattraction. García, J. R. C.; Jaumann, F.; Schulz, S.; Krause, A.; Rodríguez-Jiménez, J.; Forssmann, U.; Adermann, K.; Klüver, E.; Vogelmeier, C.; Becker, D.; Hedrich, R.; Forssmann, W. G.; Bals, R. In Cell and Tissue Research, 306(2), pp. 257–264. 2001.
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  Previous studies have shown the implication of beta -defensins in host defense of the human body. The human beta -defensins 1 and 2 (hBD-1, hBD-2) have been isolated by biochemical methods. Here we report the identification of a third human beta -defensin, called human beta -defensin 3 (hBD-3; cDNA sequence, Genbank accession no. AF295370), based on bioinformatics and functional genomic analysis. Expression of hBD-3 is detected throughout epithelia of many organs and in non-epithelial tissues. In contrast to hBD-2, which is upregulated by microorganisms or tumor necrosis factor-alpha (TNF-alpha), hBD-3 expression is increased particularly after stimulation by interferon-gamma. Synthetic hBD-3 exhibits a strong antimicrobial activity against gram-negative and grampositive bacteria and fungi, including Burkholderia cepacia. In addition, hBD-3 activates monocytes and elicits ion channel activity in biomembranes, specifically in oocytes of Xenopus laevis. This paper also shows that screening of genomic sequences is a valuable tool with which to identify novel regulatory peptides. Human beta -defensins represent a family of antimicrobial peptides differentially expressed in most tissues, regulated by specific mechanisms, and exerting physiological functions not only related to direct host defense.

  @article{RN1217, abstract = {Previous studies have shown the implication of beta -defensins in host defense of the human body. The human beta -defensins 1 and 2 (hBD-1, hBD-2) have been isolated by biochemical methods. Here we report the identification of a third human beta -defensin, called human beta -defensin 3 (hBD-3; cDNA sequence, Genbank accession no. AF295370), based on bioinformatics and functional genomic analysis. Expression of hBD-3 is detected throughout epithelia of many organs and in non-epithelial tissues. In contrast to hBD-2, which is upregulated by microorganisms or tumor necrosis factor-alpha (TNF-alpha), hBD-3 expression is increased particularly after stimulation by interferon-gamma. Synthetic hBD-3 exhibits a strong antimicrobial activity against gram-negative and grampositive bacteria and fungi, including Burkholderia cepacia. In addition, hBD-3 activates monocytes and elicits ion channel activity in biomembranes, specifically in oocytes of Xenopus laevis. This paper also shows that screening of genomic sequences is a valuable tool with which to identify novel regulatory peptides. Human beta -defensins represent a family of antimicrobial peptides differentially expressed in most tissues, regulated by specific mechanisms, and exerting physiological functions not only related to direct host defense.}, author = {García, J. R. C. and Jaumann, F. and Schulz, S. and Krause, A. and Rodríguez-Jiménez, J. and Forssmann, U. and Adermann, K. and Klüver, E. and Vogelmeier, C. and Becker, D. and Hedrich, R. and Forssmann, W. G. and Bals, R.}, journal = {Cell and Tissue Research}, keywords = {myOwn}, note = {488ur Times Cited:341 Cited References Count:29}, number = 2, pages = {257-264}, title = {Identification of a novel, multifunctional β-defensin (human β-defensin 3) with specific antimicrobial activity -: Its interaction with plasma membranes of and the induction of macrophage chemoattraction}, type = {Journal Article}, volume = 306, year = 2001 }

  %0 Journal Article %1 RN1217 %A García, J. R. C. %A Jaumann, F. %A Schulz, S. %A Krause, A. %A Rodríguez-Jiménez, J. %A Forssmann, U. %A Adermann, K. %A Klüver, E. %A Vogelmeier, C. %A Becker, D. %A Hedrich, R. %A Forssmann, W. G. %A Bals, R. %D 2001 %J Cell and Tissue Research %N 2 %P 257-264 %R DOI 10.1007/s004410100433 %T Identification of a novel, multifunctional β-defensin (human β-defensin 3) with specific antimicrobial activity -: Its interaction with plasma membranes of and the induction of macrophage chemoattraction %U /brokenurl#<Go to ISI>://WOS:000171954700009 %V 306 %X Previous studies have shown the implication of beta -defensins in host defense of the human body. The human beta -defensins 1 and 2 (hBD-1, hBD-2) have been isolated by biochemical methods. Here we report the identification of a third human beta -defensin, called human beta -defensin 3 (hBD-3; cDNA sequence, Genbank accession no. AF295370), based on bioinformatics and functional genomic analysis. Expression of hBD-3 is detected throughout epithelia of many organs and in non-epithelial tissues. In contrast to hBD-2, which is upregulated by microorganisms or tumor necrosis factor-alpha (TNF-alpha), hBD-3 expression is increased particularly after stimulation by interferon-gamma. Synthetic hBD-3 exhibits a strong antimicrobial activity against gram-negative and grampositive bacteria and fungi, including Burkholderia cepacia. In addition, hBD-3 activates monocytes and elicits ion channel activity in biomembranes, specifically in oocytes of Xenopus laevis. This paper also shows that screening of genomic sequences is a valuable tool with which to identify novel regulatory peptides. Human beta -defensins represent a family of antimicrobial peptides differentially expressed in most tissues, regulated by specific mechanisms, and exerting physiological functions not only related to direct host defense.
• Changes in apoplastic pH and membrane potential in leaves in relation to stomatal responses to CO , malate, abscisic acid or interruption of water supply. Hedrich, R.; Neimanis, S.; Savchenko, G.; Felle, H. H.; Kaiser, W. M.; Heber, U. In Planta, 213(4), pp. 594–601. 2001.
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  Low CO2 concentrations open CO2-sensitive stomata whereas elevated CO2 levels close them. This CO2 response is maintained in the dark. To elucidate mechanisms underlying the dark CO2 response we introduced pH- and potential-sensitive dyes into the apoplast of leaves. After mounting excised leaves in a gas-exchange chamber, changes in extracellular proton concentration and transmembrane potential differences as well as transpiration and respiration were simultaneously monitored. Upon an increase in CO2 concentration transient changes in apoplastic pH (occasionally brief acidification, but always followed by alkalinization) and in membrane potential (brief hyperpolarization followed by depolarization) accompanied stomatal closure. Alkalinization and depolarization were also observed when leaves were challenged with abscisic acid or when water flow was interrupted. During stomatal opening in response to CO2-free air the apoplastic pH increased while the membrane potential initially depolarized before it transiently hyperpolarized. To examine whether changes in apoplastic malate concentrations represent a closing signal for stomata, malate was fed into the transpiration stream. Although malate caused apoplastic alkalinization and membrane depolarization reminiscent of the effects observed with CO2 and abscisic acid, this dicarboxylate closed the stomata only partially and less effectively than CO2. Apoplastic alkalinization was also observed and stomata closed partially when KCI was fed to the leaves. Respiration increased on feeding of malate or KCl, or while abscisic acid closed the stomate. From these results we conclude that CO2 signals modulate the activity of plasma-membrane ion channels and of plasmalemma H-ATPases during changes in stomatal aperture. Responses to potassium malate and KCI are not restricted to guard cells and neighbouring cells.

  @article{RN1215, abstract = {Low CO2 concentrations open CO2-sensitive stomata whereas elevated CO2 levels close them. This CO2 response is maintained in the dark. To elucidate mechanisms underlying the dark CO2 response we introduced pH- and potential-sensitive dyes into the apoplast of leaves. After mounting excised leaves in a gas-exchange chamber, changes in extracellular proton concentration and transmembrane potential differences as well as transpiration and respiration were simultaneously monitored. Upon an increase in CO2 concentration transient changes in apoplastic pH (occasionally brief acidification, but always followed by alkalinization) and in membrane potential (brief hyperpolarization followed by depolarization) accompanied stomatal closure. Alkalinization and depolarization were also observed when leaves were challenged with abscisic acid or when water flow was interrupted. During stomatal opening in response to CO2-free air the apoplastic pH increased while the membrane potential initially depolarized before it transiently hyperpolarized. To examine whether changes in apoplastic malate concentrations represent a closing signal for stomata, malate was fed into the transpiration stream. Although malate caused apoplastic alkalinization and membrane depolarization reminiscent of the effects observed with CO2 and abscisic acid, this dicarboxylate closed the stomata only partially and less effectively than CO2. Apoplastic alkalinization was also observed and stomata closed partially when KCI was fed to the leaves. Respiration increased on feeding of malate or KCl, or while abscisic acid closed the stomate. From these results we conclude that CO2 signals modulate the activity of plasma-membrane ion channels and of plasmalemma H-ATPases during changes in stomatal aperture. Responses to potassium malate and KCI are not restricted to guard cells and neighbouring cells.}, author = {Hedrich, R. and Neimanis, S. and Savchenko, G. and Felle, H. H. and Kaiser, W. M. and Heber, U.}, journal = {Planta}, keywords = {abscisic}, note = {467bh Times Cited:72 Cited References Count:29}, number = 4, pages = {594-601}, title = {Changes in apoplastic pH and membrane potential in leaves in relation to stomatal responses to CO , malate, abscisic acid or interruption of water supply}, type = {Journal Article}, volume = 213, year = 2001 }

  %0 Journal Article %1 RN1215 %A Hedrich, R. %A Neimanis, S. %A Savchenko, G. %A Felle, H. H. %A Kaiser, W. M. %A Heber, U. %D 2001 %J Planta %N 4 %P 594-601 %R DOI 10.1007/s004250100524 %T Changes in apoplastic pH and membrane potential in leaves in relation to stomatal responses to CO , malate, abscisic acid or interruption of water supply %U /brokenurl#<Go to ISI>://WOS:000170680300012 %V 213 %X Low CO2 concentrations open CO2-sensitive stomata whereas elevated CO2 levels close them. This CO2 response is maintained in the dark. To elucidate mechanisms underlying the dark CO2 response we introduced pH- and potential-sensitive dyes into the apoplast of leaves. After mounting excised leaves in a gas-exchange chamber, changes in extracellular proton concentration and transmembrane potential differences as well as transpiration and respiration were simultaneously monitored. Upon an increase in CO2 concentration transient changes in apoplastic pH (occasionally brief acidification, but always followed by alkalinization) and in membrane potential (brief hyperpolarization followed by depolarization) accompanied stomatal closure. Alkalinization and depolarization were also observed when leaves were challenged with abscisic acid or when water flow was interrupted. During stomatal opening in response to CO2-free air the apoplastic pH increased while the membrane potential initially depolarized before it transiently hyperpolarized. To examine whether changes in apoplastic malate concentrations represent a closing signal for stomata, malate was fed into the transpiration stream. Although malate caused apoplastic alkalinization and membrane depolarization reminiscent of the effects observed with CO2 and abscisic acid, this dicarboxylate closed the stomata only partially and less effectively than CO2. Apoplastic alkalinization was also observed and stomata closed partially when KCI was fed to the leaves. Respiration increased on feeding of malate or KCl, or while abscisic acid closed the stomate. From these results we conclude that CO2 signals modulate the activity of plasma-membrane ion channels and of plasmalemma H-ATPases during changes in stomatal aperture. Responses to potassium malate and KCI are not restricted to guard cells and neighbouring cells.
• KAT1 is not essential for stomatal opening. Szyroki, A.; Ivashikina, N.; Dietrich, P.; Roelfsema, M. R. G.; Ache, P.; Reintanz, B.; Deeken, R.; Godde, M.; Felle, H.; Steinmeyer, R.; Palme, K.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 98(5), pp. 2917–2921. 2001.
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  It is generally accepted that Kf uptake into guard cells via inward-rectifying K+ channels is required for stomatal opening. To test whether the guard cell K+ channel KAT1 is essential for stomatal opening, a knockout mutant, KAT1::En-1, was isolated from an En-l mutagenized Arabidopsis thaliana population. Stomatal action and K+ uptake, however, were not impaired in KAT1-deficient plants. Reverse transcription-PCR experiments with isolated guard cell protoplasts showed that in addition to KAT1, the Kf channels AKT1, AKT2/3, AtKC1, and KAT2 were expressed in this cell type. In impalement measurements, intact guard cells exhibited inward-rectifying Kf currents across the plasma membrane of both wildtype and KAT1::En-1 plants. This study demonstrates that multiple K+ channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.

  @article{RN1206, abstract = {It is generally accepted that Kf uptake into guard cells via inward-rectifying K+ channels is required for stomatal opening. To test whether the guard cell K+ channel KAT1 is essential for stomatal opening, a knockout mutant, KAT1::En-1, was isolated from an En-l mutagenized Arabidopsis thaliana population. Stomatal action and K+ uptake, however, were not impaired in KAT1-deficient plants. Reverse transcription-PCR experiments with isolated guard cell protoplasts showed that in addition to KAT1, the Kf channels AKT1, AKT2/3, AtKC1, and KAT2 were expressed in this cell type. In impalement measurements, intact guard cells exhibited inward-rectifying Kf currents across the plasma membrane of both wildtype and KAT1::En-1 plants. This study demonstrates that multiple K+ channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.}, author = {Szyroki, A. and Ivashikina, N. and Dietrich, P. and Roelfsema, M. R. G. and Ache, P. and Reintanz, B. and Deeken, R. and Godde, M. and Felle, H. and Steinmeyer, R. and Palme, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {plant}, note = {407eh Times Cited:182 Cited References Count:47}, number = 5, pages = {2917-2921}, title = {KAT1 is not essential for stomatal opening}, type = {Journal Article}, volume = 98, year = 2001 }

  %0 Journal Article %1 RN1206 %A Szyroki, A. %A Ivashikina, N. %A Dietrich, P. %A Roelfsema, M. R. G. %A Ache, P. %A Reintanz, B. %A Deeken, R. %A Godde, M. %A Felle, H. %A Steinmeyer, R. %A Palme, K. %A Hedrich, R. %D 2001 %J Proceedings of the National Academy of Sciences of the United States of America %N 5 %P 2917-2921 %R DOI 10.1073/pnas.051616698 %T KAT1 is not essential for stomatal opening %U /brokenurl#<Go to ISI>://WOS:000167258900145 %V 98 %X It is generally accepted that Kf uptake into guard cells via inward-rectifying K+ channels is required for stomatal opening. To test whether the guard cell K+ channel KAT1 is essential for stomatal opening, a knockout mutant, KAT1::En-1, was isolated from an En-l mutagenized Arabidopsis thaliana population. Stomatal action and K+ uptake, however, were not impaired in KAT1-deficient plants. Reverse transcription-PCR experiments with isolated guard cell protoplasts showed that in addition to KAT1, the Kf channels AKT1, AKT2/3, AtKC1, and KAT2 were expressed in this cell type. In impalement measurements, intact guard cells exhibited inward-rectifying Kf currents across the plasma membrane of both wildtype and KAT1::En-1 plants. This study demonstrates that multiple K+ channel transcripts exist in guard cells and that KAT1 is not essential for stomatal action.
• The identity of plant glutamate receptors. Lacombe, B.; Becker, D.; Hedrich, R.; DeSalle, R.; Hollmann, M.; Kwak, J. M.; Schroeder, J. I.; Le Novère, N.; Nam, H. G.; Spalding, E. P.; Tester, M.; Turano, F. J.; Chiu, J.; Coruzzi, G. In Science, 292(5521), pp. 1486–1487. 2001.
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  @article{RN1210, author = {Lacombe, B. and Becker, D. and Hedrich, R. and DeSalle, R. and Hollmann, M. and Kwak, J. M. and Schroeder, J. I. and Le Novère, N. and Nam, H. G. and Spalding, E. P. and Tester, M. and Turano, F. J. and Chiu, J. and Coruzzi, G.}, journal = {Science}, keywords = {myOwn}, note = {436yq Times Cited:151 Cited References Count:6}, number = 5521, pages = {1486-1487}, title = {The identity of plant glutamate receptors}, type = {Journal Article}, volume = 292, year = 2001 }

  %0 Journal Article %1 RN1210 %A Lacombe, B. %A Becker, D. %A Hedrich, R. %A DeSalle, R. %A Hollmann, M. %A Kwak, J. M. %A Schroeder, J. I. %A Le Novère, N. %A Nam, H. G. %A Spalding, E. P. %A Tester, M. %A Turano, F. J. %A Chiu, J. %A Coruzzi, G. %D 2001 %J Science %N 5521 %P 1486-1487 %T The identity of plant glutamate receptors %U /brokenurl#<Go to ISI>://WOS:000168963800023 %V 292
• Aluminum activates a citrate-permeable anion channel in the aluminum-sensitive zone of the maize root apex. A comparison between an aluminum-sensitive and an aluminum-resistant cultivar. Kollmeier, M.; Dietrich, P.; Bauer, C. S.; Horst, W. J.; Hedrich, R. In Plant Physiology, 126(1), pp. 397–410. 2001.
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  In search for the cellular and molecular basis for differences in aluminum (Al) resistance between maize (Zea mays) cultivars we applied the patch-clamp technique to protoplasts isolated from the apical root cortex of two maize cultivars differing in Al resistance. Measurements were performed on protoplasts from two apical root zones: The 1- to 2-mm zone (DTZ), described as most Al-sensitive, and the main Elongation zone (3-5 mm), the site of Al-induced inhibition of cell elongation. Al stimulated citrate and malate efflux from intact root apices, revealing cultivar differences. In the elongation zone, anion channels were not observed in the absence and presence of Al. Preincubation of intact roots with 90 muM Al for 1 h induced a citrate- and malate-permeable, large conductance anion channel in 80% of the DTZ protoplasts from the resistant cultivar, but only 30% from the sensitive cultivar. When Al was applied to the protoplasts in the whole-cell configuration, anion currents were elicited within 10 min in the resistant cultivar only. La3+ was not able to replace or counteract with Al3+ in the activation of this channel. Ln the presence of the anion-channel blockers, niflumic acid and 4, 4 ' -dinitrostilbene-2, 2 ' disulfonic acid, anion currents as well as Exudation rates were strongly inhibited. Application of cycloheximide did not affect the Al response, suggesting that the channel is activated through post-translational modifications. We propose that the Al-activated large anion channel described here contributes to enhanced genotypical Al resistance by facilitating the exudation of organic acid anions from the DTZ of the maize root apex.

  @article{RN1211, abstract = {In search for the cellular and molecular basis for differences in aluminum (Al) resistance between maize (Zea mays) cultivars we applied the patch-clamp technique to protoplasts isolated from the apical root cortex of two maize cultivars differing in Al resistance. Measurements were performed on protoplasts from two apical root zones: The 1- to 2-mm zone (DTZ), described as most Al-sensitive, and the main Elongation zone (3-5 mm), the site of Al-induced inhibition of cell elongation. Al stimulated citrate and malate efflux from intact root apices, revealing cultivar differences. In the elongation zone, anion channels were not observed in the absence and presence of Al. Preincubation of intact roots with 90 muM Al for 1 h induced a citrate- and malate-permeable, large conductance anion channel in 80% of the DTZ protoplasts from the resistant cultivar, but only 30% from the sensitive cultivar. When Al was applied to the protoplasts in the whole-cell configuration, anion currents were elicited within 10 min in the resistant cultivar only. La3+ was not able to replace or counteract with Al3+ in the activation of this channel. Ln the presence of the anion-channel blockers, niflumic acid and 4, 4 ' -dinitrostilbene-2, 2 ' disulfonic acid, anion currents as well as Exudation rates were strongly inhibited. Application of cycloheximide did not affect the Al response, suggesting that the channel is activated through post-translational modifications. We propose that the Al-activated large anion channel described here contributes to enhanced genotypical Al resistance by facilitating the exudation of organic acid anions from the DTZ of the maize root apex.}, author = {Kollmeier, M. and Dietrich, P. and Bauer, C. S. and Horst, W. J. and Hedrich, R.}, journal = {Plant Physiology}, keywords = {myOwn}, note = {432ld Times Cited:136 Cited References Count:62}, number = 1, pages = {397-410}, title = {Aluminum activates a citrate-permeable anion channel in the aluminum-sensitive zone of the maize root apex. A comparison between an aluminum-sensitive and an aluminum-resistant cultivar}, type = {Journal Article}, volume = 126, year = 2001 }

  %0 Journal Article %1 RN1211 %A Kollmeier, M. %A Dietrich, P. %A Bauer, C. S. %A Horst, W. J. %A Hedrich, R. %D 2001 %J Plant Physiology %N 1 %P 397-410 %R DOI 10.1104/pp.126.1.397 %T Aluminum activates a citrate-permeable anion channel in the aluminum-sensitive zone of the maize root apex. A comparison between an aluminum-sensitive and an aluminum-resistant cultivar %U /brokenurl#<Go to ISI>://WOS:000168692300045 %V 126 %X In search for the cellular and molecular basis for differences in aluminum (Al) resistance between maize (Zea mays) cultivars we applied the patch-clamp technique to protoplasts isolated from the apical root cortex of two maize cultivars differing in Al resistance. Measurements were performed on protoplasts from two apical root zones: The 1- to 2-mm zone (DTZ), described as most Al-sensitive, and the main Elongation zone (3-5 mm), the site of Al-induced inhibition of cell elongation. Al stimulated citrate and malate efflux from intact root apices, revealing cultivar differences. In the elongation zone, anion channels were not observed in the absence and presence of Al. Preincubation of intact roots with 90 muM Al for 1 h induced a citrate- and malate-permeable, large conductance anion channel in 80% of the DTZ protoplasts from the resistant cultivar, but only 30% from the sensitive cultivar. When Al was applied to the protoplasts in the whole-cell configuration, anion currents were elicited within 10 min in the resistant cultivar only. La3+ was not able to replace or counteract with Al3+ in the activation of this channel. Ln the presence of the anion-channel blockers, niflumic acid and 4, 4 ' -dinitrostilbene-2, 2 ' disulfonic acid, anion currents as well as Exudation rates were strongly inhibited. Application of cycloheximide did not affect the Al response, suggesting that the channel is activated through post-translational modifications. We propose that the Al-activated large anion channel described here contributes to enhanced genotypical Al resistance by facilitating the exudation of organic acid anions from the DTZ of the maize root apex.
• The role of ion channels in light-dependent stomatal opening. Dietrich, P.; Sanders, D.; Hedrich, R. In Journal of Experimental Botany, 52(363), pp. 1959–1967. 2001.
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  Stomatal opening represents a major determinant of plant productivity and stress management. Because plants lose water essentially through open stomata, volume control of the pore-forming guard cells represents a key step in the regulation of plant water status. These sensory cells are able to integrate various signals such as light, auxin, abscisic acid, and CO2. Following signal perception, changes in membrane potential and activity of ion transporters finally lead to the accumulation of potassium salts and turgor pressure formation. This review analyses recent progress in molecular aspects of ion channel regulation and suggests how these developments impact on our understanding of light- and auxin-dependent stomatal action.

  @article{RN1218, abstract = {Stomatal opening represents a major determinant of plant productivity and stress management. Because plants lose water essentially through open stomata, volume control of the pore-forming guard cells represents a key step in the regulation of plant water status. These sensory cells are able to integrate various signals such as light, auxin, abscisic acid, and CO2. Following signal perception, changes in membrane potential and activity of ion transporters finally lead to the accumulation of potassium salts and turgor pressure formation. This review analyses recent progress in molecular aspects of ion channel regulation and suggests how these developments impact on our understanding of light- and auxin-dependent stomatal action.}, author = {Dietrich, P. and Sanders, D. and Hedrich, R.}, journal = {Journal of Experimental Botany}, keywords = {cell}, note = {478xa Times Cited:79 Cited References Count:104}, number = 363, pages = {1959-1967}, title = {The role of ion channels in light-dependent stomatal opening}, type = {Journal Article}, volume = 52, year = 2001 }

  %0 Journal Article %1 RN1218 %A Dietrich, P. %A Sanders, D. %A Hedrich, R. %D 2001 %J Journal of Experimental Botany %N 363 %P 1959-1967 %R DOI 10.1093/jexbot/52.363.1959 %T The role of ion channels in light-dependent stomatal opening %U /brokenurl#<Go to ISI>://WOS:000171372300003 %V 52 %X Stomatal opening represents a major determinant of plant productivity and stress management. Because plants lose water essentially through open stomata, volume control of the pore-forming guard cells represents a key step in the regulation of plant water status. These sensory cells are able to integrate various signals such as light, auxin, abscisic acid, and CO2. Following signal perception, changes in membrane potential and activity of ion transporters finally lead to the accumulation of potassium salts and turgor pressure formation. This review analyses recent progress in molecular aspects of ion channel regulation and suggests how these developments impact on our understanding of light- and auxin-dependent stomatal action.

• Developmental and light-dependent regulation of a phloem-localised K channel of. Deeken, R.; Sanders, C.; Ache, P.; Hedrich, R. In Plant Journal, 23(2), pp. 285–290. 2000.
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  K+ channels in plants can currently be classified into six families with individual members being involved in nutrient uptake, loading of the xylem and the physiology of stomatal movement. In this study we have focused on akt2/3. This K+ channel, as shown by GUS-expression analysis, is expressed in the phloem and xylem of the aerial parts of Arabidopsis thaliana. Northern blot analyses revealed the highest akt2/3-concentrations in the flower stalk, followed by the leaf, flower and stem. During the light period (8 am to 4 pm), transcripts reached a peak around noon (11 am), decayed to almost 50% in the afternoon and reached a low background level in the following dark period. In continuous darkness, however, the K+ channel mRNA content had already decreased beyond the background level by noon. In leaves and flower stalk, the light-induced transcription of akt2/3 was suppressed by CO2-free air, indicating that gene activity is under the control of photosynthates. Additionally, when rosette leaves were illuminated and flower stalks shaded, akt2/3-mRNA transcription was still inhibited in the shaded region. This indicates that channel gene activation is sensitive to photosynthesis-derived factors from neighboring cells rather than factors mobile in the phloem. We propose that the coupling between sugar production and allocation involves the photosynthate- and light-dependent phloem K+ channel AKT2/3.

  @article{RN1225, abstract = {K+ channels in plants can currently be classified into six families with individual members being involved in nutrient uptake, loading of the xylem and the physiology of stomatal movement. In this study we have focused on akt2/3. This K+ channel, as shown by GUS-expression analysis, is expressed in the phloem and xylem of the aerial parts of Arabidopsis thaliana. Northern blot analyses revealed the highest akt2/3-concentrations in the flower stalk, followed by the leaf, flower and stem. During the light period (8 am to 4 pm), transcripts reached a peak around noon (11 am), decayed to almost 50% in the afternoon and reached a low background level in the following dark period. In continuous darkness, however, the K+ channel mRNA content had already decreased beyond the background level by noon. In leaves and flower stalk, the light-induced transcription of akt2/3 was suppressed by CO2-free air, indicating that gene activity is under the control of photosynthates. Additionally, when rosette leaves were illuminated and flower stalks shaded, akt2/3-mRNA transcription was still inhibited in the shaded region. This indicates that channel gene activation is sensitive to photosynthesis-derived factors from neighboring cells rather than factors mobile in the phloem. We propose that the coupling between sugar production and allocation involves the photosynthate- and light-dependent phloem K+ channel AKT2/3.}, author = {Deeken, R. and Sanders, C. and Ache, P. and Hedrich, R.}, journal = {Plant Journal}, keywords = {k+}, note = {339aa Times Cited:67 Cited References Count:33}, number = 2, pages = {285-290}, title = {Developmental and light-dependent regulation of a phloem-localised K channel of}, type = {Journal Article}, volume = 23, year = 2000 }

  %0 Journal Article %1 RN1225 %A Deeken, R. %A Sanders, C. %A Ache, P. %A Hedrich, R. %D 2000 %J Plant Journal %N 2 %P 285-290 %R DOI 10.1046/j.1365-313x.2000.00791.x %T Developmental and light-dependent regulation of a phloem-localised K channel of %U /brokenurl#<Go to ISI>://WOS:000088454400013 %V 23 %X K+ channels in plants can currently be classified into six families with individual members being involved in nutrient uptake, loading of the xylem and the physiology of stomatal movement. In this study we have focused on akt2/3. This K+ channel, as shown by GUS-expression analysis, is expressed in the phloem and xylem of the aerial parts of Arabidopsis thaliana. Northern blot analyses revealed the highest akt2/3-concentrations in the flower stalk, followed by the leaf, flower and stem. During the light period (8 am to 4 pm), transcripts reached a peak around noon (11 am), decayed to almost 50% in the afternoon and reached a low background level in the following dark period. In continuous darkness, however, the K+ channel mRNA content had already decreased beyond the background level by noon. In leaves and flower stalk, the light-induced transcription of akt2/3 was suppressed by CO2-free air, indicating that gene activity is under the control of photosynthates. Additionally, when rosette leaves were illuminated and flower stalks shaded, akt2/3-mRNA transcription was still inhibited in the shaded region. This indicates that channel gene activation is sensitive to photosynthesis-derived factors from neighboring cells rather than factors mobile in the phloem. We propose that the coupling between sugar production and allocation involves the photosynthate- and light-dependent phloem K+ channel AKT2/3.
• Differential expression and regulation of K channels in the maize coleoptile:: molecular and biophysical analysis of cells isolated from cortex and vasculature. Bauer, C. S.; Hoth, S.; Haga, K.; Philippar, K.; Aoki, N.; Hedrich, R. In Plant Journal, 24(2), pp. 139–145. 2000.
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  Recently, two K+ channel genes, ZMK1 and ZMK2, were isolated from maize coleoptiles. They are expressed in the cortex and vasculature, respectively. Expression in Xenopus oocytes characterized ZMK1 as an inwardly rectifying K+ channel activated by external acidification, while ZMK2 mediates voltage-independent and proton-inhibited K+ currents. In search of the related gene products in planta, we applied the patch-clamp technique to protoplasts isolated from the cortex and vasculature of Zea mays coleoptiles and mesocotyls. In the cortex, a 6-8 pS K+ channel gave rise to inwardly rectifying K+ currents. Like ZMK1, this channel was activated by apoplastic acidification. In contrast, protoplasts from vascular tissue expressing the sucrose transporter ZmSUT1 were dominated by largely voltage-independent K+ currents with a single-channel conductance of 22 pS. The pronounced sensitivity to the extracellular protons Ca2+, Cs+ and Ba2+ is reminiscent of ZMK2 properties in oocytes. Thus, the dominant K+ channels in cortex and vasculature most likely represent the gene products of ZMK1 and ZMK2. Our studies on the ZMK2-like channels represent the first in planta analysis of a K+ channel that shares properties with the AKT3 K+ channel family.

  @article{RN1226, abstract = {Recently, two K+ channel genes, ZMK1 and ZMK2, were isolated from maize coleoptiles. They are expressed in the cortex and vasculature, respectively. Expression in Xenopus oocytes characterized ZMK1 as an inwardly rectifying K+ channel activated by external acidification, while ZMK2 mediates voltage-independent and proton-inhibited K+ currents. In search of the related gene products in planta, we applied the patch-clamp technique to protoplasts isolated from the cortex and vasculature of Zea mays coleoptiles and mesocotyls. In the cortex, a 6-8 pS K+ channel gave rise to inwardly rectifying K+ currents. Like ZMK1, this channel was activated by apoplastic acidification. In contrast, protoplasts from vascular tissue expressing the sucrose transporter ZmSUT1 were dominated by largely voltage-independent K+ currents with a single-channel conductance of 22 pS. The pronounced sensitivity to the extracellular protons Ca2+, Cs+ and Ba2+ is reminiscent of ZMK2 properties in oocytes. Thus, the dominant K+ channels in cortex and vasculature most likely represent the gene products of ZMK1 and ZMK2. Our studies on the ZMK2-like channels represent the first in planta analysis of a K+ channel that shares properties with the AKT3 K+ channel family.}, author = {Bauer, C. S. and Hoth, S. and Haga, K. and Philippar, K. and Aoki, N. and Hedrich, R.}, journal = {Plant Journal}, keywords = {k+}, note = {365er Times Cited:45 Cited References Count:22}, number = 2, pages = {139-145}, title = {Differential expression and regulation of K channels in the maize coleoptile:: molecular and biophysical analysis of cells isolated from cortex and vasculature}, type = {Journal Article}, volume = 24, year = 2000 }

  %0 Journal Article %1 RN1226 %A Bauer, C. S. %A Hoth, S. %A Haga, K. %A Philippar, K. %A Aoki, N. %A Hedrich, R. %D 2000 %J Plant Journal %N 2 %P 139-145 %R DOI 10.1046/j.1365-313X.2000.00844.x %T Differential expression and regulation of K channels in the maize coleoptile:: molecular and biophysical analysis of cells isolated from cortex and vasculature %U /brokenurl#<Go to ISI>://WOS:000089935900001 %V 24 %X Recently, two K+ channel genes, ZMK1 and ZMK2, were isolated from maize coleoptiles. They are expressed in the cortex and vasculature, respectively. Expression in Xenopus oocytes characterized ZMK1 as an inwardly rectifying K+ channel activated by external acidification, while ZMK2 mediates voltage-independent and proton-inhibited K+ currents. In search of the related gene products in planta, we applied the patch-clamp technique to protoplasts isolated from the cortex and vasculature of Zea mays coleoptiles and mesocotyls. In the cortex, a 6-8 pS K+ channel gave rise to inwardly rectifying K+ currents. Like ZMK1, this channel was activated by apoplastic acidification. In contrast, protoplasts from vascular tissue expressing the sucrose transporter ZmSUT1 were dominated by largely voltage-independent K+ currents with a single-channel conductance of 22 pS. The pronounced sensitivity to the extracellular protons Ca2+, Cs+ and Ba2+ is reminiscent of ZMK2 properties in oocytes. Thus, the dominant K+ channels in cortex and vasculature most likely represent the gene products of ZMK1 and ZMK2. Our studies on the ZMK2-like channels represent the first in planta analysis of a K+ channel that shares properties with the AKT3 K+ channel family.
• Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact leaves during stomatal closure evoked by ABA and darkness. Felle, H. H.; Hanstein, S.; Steinmeyer, R.; Hedrich, R. In Plant Journal, 24(3), pp. 297–304. 2000.
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  Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 muM (Ca2+) and 89 muM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.

  @article{RN1223, abstract = {Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 muM (Ca2+) and 89 muM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.}, author = {Felle, H. H. and Hanstein, S. and Steinmeyer, R. and Hedrich, R.}, journal = {Plant Journal}, keywords = {aba}, note = {377nb Times Cited:61 Cited References Count:40}, number = 3, pages = {297-304}, title = {Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact leaves during stomatal closure evoked by ABA and darkness}, type = {Journal Article}, volume = 24, year = 2000 }

  %0 Journal Article %1 RN1223 %A Felle, H. H. %A Hanstein, S. %A Steinmeyer, R. %A Hedrich, R. %D 2000 %J Plant Journal %N 3 %P 297-304 %R DOI 10.1046/j.1365-313x.2000.00878.x %T Dynamics of ionic activities in the apoplast of the sub-stomatal cavity of intact leaves during stomatal closure evoked by ABA and darkness %U /brokenurl#<Go to ISI>://WOS:000165518700002 %V 24 %X Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 muM (Ca2+) and 89 muM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.
• GORK, a delayed outward rectifier expressed in guard cells of , is a K -selective, K -sensing ion channel. Ache, P.; Becker, D.; Ivashikina, N.; Dietrich, P.; Roelfsema, M. R. G.; Hedrich, R. In Febs Letters, 486(2), pp. 93–98. 2000.
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  Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K+-channel. GORK represents a new member of the plant Shaker K+ channel superfamily.When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K+ currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

  @article{RN1227, abstract = {Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K+-channel. GORK represents a new member of the plant Shaker K+ channel superfamily.When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K+ currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.}, author = {Ache, P. and Becker, D. and Ivashikina, N. and Dietrich, P. and Roelfsema, M. R. G. and Hedrich, R.}, journal = {Febs Letters}, keywords = {transport}, note = {383rr Times Cited:256 Cited References Count:25}, number = 2, pages = {93-98}, title = {GORK, a delayed outward rectifier expressed in guard cells of , is a K -selective, K -sensing ion channel}, type = {Journal Article}, volume = 486, year = 2000 }

  %0 Journal Article %1 RN1227 %A Ache, P. %A Becker, D. %A Ivashikina, N. %A Dietrich, P. %A Roelfsema, M. R. G. %A Hedrich, R. %D 2000 %J Febs Letters %N 2 %P 93-98 %R Doi 10.1016/S0014-5793(00)02248-1 %T GORK, a delayed outward rectifier expressed in guard cells of , is a K -selective, K -sensing ion channel %U /brokenurl#<Go to ISI>://WOS:000165897100002 %V 486 %X Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K+-channel. GORK represents a new member of the plant Shaker K+ channel superfamily.When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K+ currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
• pH regulation in apoplastic and cytoplasmic cell compartments of leaves. Savchenko, G.; Wiese, C.; Neimanis, S.; Hedrich, R.; Heber, U. In Planta, 211(2), pp. 246–255. 2000.
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  The regulation of pH in the apoplast, cytosol and chloroplasts of intact leaves was studied by means of fluorescent pH indicators and as a response of photosynthesis to acid stress. The apoplastic pH increased under anaerobiosis. Aeration reversed this effect.. Apoplastic responses to CO2, HCl or NH3 differed considerably. Whereas HCl and ammonia caused rapid acidification or alkalinization, the return to initial pH values was slow after cessation of fumigation. Addition of CO2 either did not produce the acidification expected on the basis of known apoplastic buffering or even caused some alkalinization. Removal of CO2 shifted the apoplastic pH into the alkaline range before the pH returned to initial steady-state levels. In the presence of vanadate, the alkaline shift was absent and the apoplastic pH returned slowly to the initial level when CO2 was removed from the atmosphere. In contrast to the response of the apoplast, anaerobiosis acidified the cytosol or, in some species, had little effect on its pH. Acidification was rapidly reversed upon re-admission of oxygen. The CO2-dependent pH changes were very fast in the cytosol. Considerable alkalinization was observed after removal of CO2 under aerobic, but not under anaerobic conditions. Rates of the re-entry of protons into the cytosol during recovery from CO2 stress increased in the presence of oxygen with the length of previous exposure to high CO2. Effective pH regulation in the chloroplasts was indicated by the recovery of photosynthesis after the transient inhibition of photosynthetic electron flow when CO2 was increased from 0.038% to 16% in air. As photosynthesis became inhibited under high CO2, reduction of the electron transport chain increased transiently. The time required for recovery of photosynthesis from inhibition during persistent CO2 stress was similar to the time require. for establishing steady-state pH values in the cytosol under add stress. The high capacity of leaf cells for the rapid re-attainment of pH homeostasis in the apoplast and the cytoplasm under acid or alkaline stress suggested the rapid activation or deactivation of membrane-localised proton-transporting enzymes and corresponding ion channel regulation for co-transport of anions or counter-transport of cations together with proton fluxes. Acidification of the cytoplasm appeared to activate energy-dependent proton export primarily into the vacuoles whereas apoplastic alkalinization resulted in the pumping of protons into the apoplast. Proton export rates from the cytosol into the apoplast after anaerobiosis were about 100 nmol (m(2) leaf area)(-1) s(-1) or less. Proton export under acid stress into the vacuole was about 1200 nmol m(-2) s(-1). The kinetics of pH responses to the addition or withdrawal of CO2 indicated the presence of carbonic anhydrase in the cytosol, but not in the apoplast.

  @article{RN1221, abstract = {The regulation of pH in the apoplast, cytosol and chloroplasts of intact leaves was studied by means of fluorescent pH indicators and as a response of photosynthesis to acid stress. The apoplastic pH increased under anaerobiosis. Aeration reversed this effect.. Apoplastic responses to CO2, HCl or NH3 differed considerably. Whereas HCl and ammonia caused rapid acidification or alkalinization, the return to initial pH values was slow after cessation of fumigation. Addition of CO2 either did not produce the acidification expected on the basis of known apoplastic buffering or even caused some alkalinization. Removal of CO2 shifted the apoplastic pH into the alkaline range before the pH returned to initial steady-state levels. In the presence of vanadate, the alkaline shift was absent and the apoplastic pH returned slowly to the initial level when CO2 was removed from the atmosphere. In contrast to the response of the apoplast, anaerobiosis acidified the cytosol or, in some species, had little effect on its pH. Acidification was rapidly reversed upon re-admission of oxygen. The CO2-dependent pH changes were very fast in the cytosol. Considerable alkalinization was observed after removal of CO2 under aerobic, but not under anaerobic conditions. Rates of the re-entry of protons into the cytosol during recovery from CO2 stress increased in the presence of oxygen with the length of previous exposure to high CO2. Effective pH regulation in the chloroplasts was indicated by the recovery of photosynthesis after the transient inhibition of photosynthetic electron flow when CO2 was increased from 0.038% to 16% in air. As photosynthesis became inhibited under high CO2, reduction of the electron transport chain increased transiently. The time required for recovery of photosynthesis from inhibition during persistent CO2 stress was similar to the time require. for establishing steady-state pH values in the cytosol under add stress. The high capacity of leaf cells for the rapid re-attainment of pH homeostasis in the apoplast and the cytoplasm under acid or alkaline stress suggested the rapid activation or deactivation of membrane-localised proton-transporting enzymes and corresponding ion channel regulation for co-transport of anions or counter-transport of cations together with proton fluxes. Acidification of the cytoplasm appeared to activate energy-dependent proton export primarily into the vacuoles whereas apoplastic alkalinization resulted in the pumping of protons into the apoplast. Proton export rates from the cytosol into the apoplast after anaerobiosis were about 100 nmol (m(2) leaf area)(-1) s(-1) or less. Proton export under acid stress into the vacuole was about 1200 nmol m(-2) s(-1). The kinetics of pH responses to the addition or withdrawal of CO2 indicated the presence of carbonic anhydrase in the cytosol, but not in the apoplast.}, author = {Savchenko, G. and Wiese, C. and Neimanis, S. and Hedrich, R. and Heber, U.}, journal = {Planta}, keywords = {apoplast}, note = {338bg Times Cited:45 Cited References Count:35}, number = 2, pages = {246-255}, title = {pH regulation in apoplastic and cytoplasmic cell compartments of leaves}, type = {Journal Article}, volume = 211, year = 2000 }

  %0 Journal Article %1 RN1221 %A Savchenko, G. %A Wiese, C. %A Neimanis, S. %A Hedrich, R. %A Heber, U. %D 2000 %J Planta %N 2 %P 246-255 %R DOI 10.1007/s004250000280 %T pH regulation in apoplastic and cytoplasmic cell compartments of leaves %U /brokenurl#<Go to ISI>://WOS:000088397800010 %V 211 %X The regulation of pH in the apoplast, cytosol and chloroplasts of intact leaves was studied by means of fluorescent pH indicators and as a response of photosynthesis to acid stress. The apoplastic pH increased under anaerobiosis. Aeration reversed this effect.. Apoplastic responses to CO2, HCl or NH3 differed considerably. Whereas HCl and ammonia caused rapid acidification or alkalinization, the return to initial pH values was slow after cessation of fumigation. Addition of CO2 either did not produce the acidification expected on the basis of known apoplastic buffering or even caused some alkalinization. Removal of CO2 shifted the apoplastic pH into the alkaline range before the pH returned to initial steady-state levels. In the presence of vanadate, the alkaline shift was absent and the apoplastic pH returned slowly to the initial level when CO2 was removed from the atmosphere. In contrast to the response of the apoplast, anaerobiosis acidified the cytosol or, in some species, had little effect on its pH. Acidification was rapidly reversed upon re-admission of oxygen. The CO2-dependent pH changes were very fast in the cytosol. Considerable alkalinization was observed after removal of CO2 under aerobic, but not under anaerobic conditions. Rates of the re-entry of protons into the cytosol during recovery from CO2 stress increased in the presence of oxygen with the length of previous exposure to high CO2. Effective pH regulation in the chloroplasts was indicated by the recovery of photosynthesis after the transient inhibition of photosynthetic electron flow when CO2 was increased from 0.038% to 16% in air. As photosynthesis became inhibited under high CO2, reduction of the electron transport chain increased transiently. The time required for recovery of photosynthesis from inhibition during persistent CO2 stress was similar to the time require. for establishing steady-state pH values in the cytosol under add stress. The high capacity of leaf cells for the rapid re-attainment of pH homeostasis in the apoplast and the cytoplasm under acid or alkaline stress suggested the rapid activation or deactivation of membrane-localised proton-transporting enzymes and corresponding ion channel regulation for co-transport of anions or counter-transport of cations together with proton fluxes. Acidification of the cytoplasm appeared to activate energy-dependent proton export primarily into the vacuoles whereas apoplastic alkalinization resulted in the pumping of protons into the apoplast. Proton export rates from the cytosol into the apoplast after anaerobiosis were about 100 nmol (m(2) leaf area)(-1) s(-1) or less. Proton export under acid stress into the vacuole was about 1200 nmol m(-2) s(-1). The kinetics of pH responses to the addition or withdrawal of CO2 indicated the presence of carbonic anhydrase in the cytosol, but not in the apoplast.
• ... response: Living with gravity. Philippar, K.; Becker, D.; Hedrich, R. In Trends in Plant Science, 5(3), pp. 86–87. 2000.
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  @article{RN1222, author = {Philippar, K. and Becker, D. and Hedrich, R.}, journal = {Trends in Plant Science}, keywords = {myOwn}, note = {291ph Times Cited:4 Cited References Count:6}, number = 3, pages = {86-87}, title = {... response: Living with gravity}, type = {Journal Article}, volume = 5, year = 2000 }

  %0 Journal Article %1 RN1222 %A Philippar, K. %A Becker, D. %A Hedrich, R. %D 2000 %J Trends in Plant Science %N 3 %P 86-87 %R Doi 10.1016/S1360-1385(00)01568-5 %T ... response: Living with gravity %U /brokenurl#<Go to ISI>://WOS:000085744900002 %V 5
• , a novel carrot root hair K channel -: Cloning, characterization, and expression in mammalian cells. Downey, P.; Szabò, I.; Ivashikina, N.; Negro, A.; Guzzo, F.; Ache, P.; Hedrich, R.; Terzi, M.; Lo Schiavo, F. In Journal of Biological Chemistry, 275(50), pp. 39420–39426. 2000.
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  Potassium is an essential nutrient which plays an important role in many aspects of plant growth and development. Plants have developed a number of highly specific mechanisms to take up potassium from the soil; these include the expression of K+ transporters and potassium channels in root cells. Despite the fact that root epidermal and hair cells are in direct contact with the soil, the role of these tissues in K+ uptake is not well understood. Here we report the molecular cloning and functional characterization of a novel potassium channel KDC1 which forms part of a new subfamily of plant K-in channels. Kdc1 was isolated from carrot root RNA and in situ hybridization experiments show Kdc1 to be highly expressed in root hair cells. Expressing the KDC1 protein in Chinese hamster ovary cells identified it as a voltage and pH-dependent inwardly rectifying potassium channel. An electrophysiological analysis of carrot root hair protoplasts confirmed the biophysical properties of the Kdc1 gene product (KDC1) in the heterologous expression system. KDC1 thus represents a major K+ uptake channel in carrot root hair cells.

  @article{RN1224, abstract = {Potassium is an essential nutrient which plays an important role in many aspects of plant growth and development. Plants have developed a number of highly specific mechanisms to take up potassium from the soil; these include the expression of K+ transporters and potassium channels in root cells. Despite the fact that root epidermal and hair cells are in direct contact with the soil, the role of these tissues in K+ uptake is not well understood. Here we report the molecular cloning and functional characterization of a novel potassium channel KDC1 which forms part of a new subfamily of plant K-in channels. Kdc1 was isolated from carrot root RNA and in situ hybridization experiments show Kdc1 to be highly expressed in root hair cells. Expressing the KDC1 protein in Chinese hamster ovary cells identified it as a voltage and pH-dependent inwardly rectifying potassium channel. An electrophysiological analysis of carrot root hair protoplasts confirmed the biophysical properties of the Kdc1 gene product (KDC1) in the heterologous expression system. KDC1 thus represents a major K+ uptake channel in carrot root hair cells.}, author = {Downey, P. and Szabò, I. and Ivashikina, N. and Negro, A. and Guzzo, F. and Ache, P. and Hedrich, R. and Terzi, M. and Lo Schiavo, F.}, journal = {Journal of Biological Chemistry}, keywords = {protein}, note = {384pb Times Cited:41 Cited References Count:48}, number = 50, pages = {39420-39426}, title = {, a novel carrot root hair K channel -: Cloning, characterization, and expression in mammalian cells}, type = {Journal Article}, volume = 275, year = 2000 }

  %0 Journal Article %1 RN1224 %A Downey, P. %A Szabò, I. %A Ivashikina, N. %A Negro, A. %A Guzzo, F. %A Ache, P. %A Hedrich, R. %A Terzi, M. %A Lo Schiavo, F. %D 2000 %J Journal of Biological Chemistry %N 50 %P 39420-39426 %R DOI 10.1074/jbc.M002962200 %T , a novel carrot root hair K channel -: Cloning, characterization, and expression in mammalian cells %U /brokenurl#<Go to ISI>://WOS:000165953100066 %V 275 %X Potassium is an essential nutrient which plays an important role in many aspects of plant growth and development. Plants have developed a number of highly specific mechanisms to take up potassium from the soil; these include the expression of K+ transporters and potassium channels in root cells. Despite the fact that root epidermal and hair cells are in direct contact with the soil, the role of these tissues in K+ uptake is not well understood. Here we report the molecular cloning and functional characterization of a novel potassium channel KDC1 which forms part of a new subfamily of plant K-in channels. Kdc1 was isolated from carrot root RNA and in situ hybridization experiments show Kdc1 to be highly expressed in root hair cells. Expressing the KDC1 protein in Chinese hamster ovary cells identified it as a voltage and pH-dependent inwardly rectifying potassium channel. An electrophysiological analysis of carrot root hair protoplasts confirmed the biophysical properties of the Kdc1 gene product (KDC1) in the heterologous expression system. KDC1 thus represents a major K+ uptake channel in carrot root hair cells.
• Histidine in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in oocytes. Tang, X. D.; Marten, I.; Dietrich, P.; Ivashikina, N.; Hedrich, R.; Hoshi, T. In Biophysical Journal, 78(3), pp. 1255–1269. 2000.
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  The guard cell K+ channel KAT1, cloned from Arabidopsis thaliana, is activated by hyperpolarization and regulated by a variety of physiological factors. Low internal pH accelerated the activation kinetics of the KAT1 channel expressed in Xenopus oocytes with a pK of approximately 6, similar to guard cells in vivo. Mutations of histidine-118 located in the putative cytoplasmic linker between the S2 and S3 segments profoundly affected the gating behavior and pH dependence. At pH 7.2, substitution with a negatively charged amino acid (glutamate, aspartate) specifically slowed the activation time course, whereas that with a positively charged amino acid (lysine, arginine) accelerated. These mutations did not alter the channel's deactivation time course or the gating behavior after the first opening. Introducing an uncharged amino acid (alanine, asparagine) at position 118 did not have any obvious effect-bn the activation kinetics at pH 7.2. The charged substitutions markedly decreased the sensitivity of the KAT1 channel to internal pH in the physiological range. We propose a linear kinetic scheme to account for the KAT1 activation time course at the voltages where the opening transitions dominate. Changes in one forward rate constant in the model adequately account for the effects of the mutations at position 118 in the S2-S3 linker segment. These results provide a molecular and biophysical basis for the diversity in the activation kinetics of inward rectifiers among different plant species.

  @article{RN1220, abstract = {The guard cell K+ channel KAT1, cloned from Arabidopsis thaliana, is activated by hyperpolarization and regulated by a variety of physiological factors. Low internal pH accelerated the activation kinetics of the KAT1 channel expressed in Xenopus oocytes with a pK of approximately 6, similar to guard cells in vivo. Mutations of histidine-118 located in the putative cytoplasmic linker between the S2 and S3 segments profoundly affected the gating behavior and pH dependence. At pH 7.2, substitution with a negatively charged amino acid (glutamate, aspartate) specifically slowed the activation time course, whereas that with a positively charged amino acid (lysine, arginine) accelerated. These mutations did not alter the channel's deactivation time course or the gating behavior after the first opening. Introducing an uncharged amino acid (alanine, asparagine) at position 118 did not have any obvious effect-bn the activation kinetics at pH 7.2. The charged substitutions markedly decreased the sensitivity of the KAT1 channel to internal pH in the physiological range. We propose a linear kinetic scheme to account for the KAT1 activation time course at the voltages where the opening transitions dominate. Changes in one forward rate constant in the model adequately account for the effects of the mutations at position 118 in the S2-S3 linker segment. These results provide a molecular and biophysical basis for the diversity in the activation kinetics of inward rectifiers among different plant species.}, author = {Tang, X. D. and Marten, I. and Dietrich, P. and Ivashikina, N. and Hedrich, R. and Hoshi, T.}, journal = {Biophysical Journal}, keywords = {stomatal}, note = {290vd Times Cited:20 Cited References Count:53}, number = 3, pages = {1255-1269}, title = {Histidine in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in oocytes}, type = {Journal Article}, volume = 78, year = 2000 }

  %0 Journal Article %1 RN1220 %A Tang, X. D. %A Marten, I. %A Dietrich, P. %A Ivashikina, N. %A Hedrich, R. %A Hoshi, T. %D 2000 %J Biophysical Journal %N 3 %P 1255-1269 %R Doi 10.1016/S0006-3495(00)76682-3 %T Histidine in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in oocytes %U /brokenurl#<Go to ISI>://WOS:000085697800016 %V 78 %X The guard cell K+ channel KAT1, cloned from Arabidopsis thaliana, is activated by hyperpolarization and regulated by a variety of physiological factors. Low internal pH accelerated the activation kinetics of the KAT1 channel expressed in Xenopus oocytes with a pK of approximately 6, similar to guard cells in vivo. Mutations of histidine-118 located in the putative cytoplasmic linker between the S2 and S3 segments profoundly affected the gating behavior and pH dependence. At pH 7.2, substitution with a negatively charged amino acid (glutamate, aspartate) specifically slowed the activation time course, whereas that with a positively charged amino acid (lysine, arginine) accelerated. These mutations did not alter the channel's deactivation time course or the gating behavior after the first opening. Introducing an uncharged amino acid (alanine, asparagine) at position 118 did not have any obvious effect-bn the activation kinetics at pH 7.2. The charged substitutions markedly decreased the sensitivity of the KAT1 channel to internal pH in the physiological range. We propose a linear kinetic scheme to account for the KAT1 activation time course at the voltages where the opening transitions dominate. Changes in one forward rate constant in the model adequately account for the effects of the mutations at position 118 in the S2-S3 linker segment. These results provide a molecular and biophysical basis for the diversity in the activation kinetics of inward rectifiers among different plant species.

• Susceptibility of the guard-cell K -uptake channel KST1 to Zn requires histidine residues in the S3-S4 linker and in the channel pore. Hoth, S.; Hedrich, R. In Planta, 209(4), pp. 543–546. 1999.
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  Potassium channels are inhibited by several mono- and divalent cations. To identify sites involved in the interaction between K+ channels and cationic effecters, we expressed the potato (Solanum tuberosum L.) guard-cell K+-uptake channel KST1 in Xenopus oocytes. This channel was reversibly blocked by extracellular Zn2+ in the micromolar range. In the presence of this heavy metal, steady-state currents were reduced in a pH-dependent but voltage-independent manner. Since Zn2+-inhibition was less effective at elevated external proton concentrations, we generated alanine mutants with respect to both extracellular histidines in KST1. Whereas substitution of the pore histidine H271 resulted in a reduced blockade by Zn2+, the channel mutant KST1-H160A in the S3-S4 linker lost most of its Zn2+ sensitivity. Since both histidines alter the susceptibility of KST1 to Zn2+, the block may predominantly result from these two sites. We thus conclude that the S3-S4 linker is involved in the formation of the outer pore.

  @article{RN1231, abstract = {Potassium channels are inhibited by several mono- and divalent cations. To identify sites involved in the interaction between K+ channels and cationic effecters, we expressed the potato (Solanum tuberosum L.) guard-cell K+-uptake channel KST1 in Xenopus oocytes. This channel was reversibly blocked by extracellular Zn2+ in the micromolar range. In the presence of this heavy metal, steady-state currents were reduced in a pH-dependent but voltage-independent manner. Since Zn2+-inhibition was less effective at elevated external proton concentrations, we generated alanine mutants with respect to both extracellular histidines in KST1. Whereas substitution of the pore histidine H271 resulted in a reduced blockade by Zn2+, the channel mutant KST1-H160A in the S3-S4 linker lost most of its Zn2+ sensitivity. Since both histidines alter the susceptibility of KST1 to Zn2+, the block may predominantly result from these two sites. We thus conclude that the S3-S4 linker is involved in the formation of the outer pore.}, author = {Hoth, S. and Hedrich, R.}, journal = {Planta}, keywords = {kst1}, note = {252ln Times Cited:8 Cited References Count:28}, number = 4, pages = {543-546}, title = {Susceptibility of the guard-cell K -uptake channel KST1 to Zn requires histidine residues in the S3-S4 linker and in the channel pore}, type = {Journal Article}, volume = 209, year = 1999 }

  %0 Journal Article %1 RN1231 %A Hoth, S. %A Hedrich, R. %D 1999 %J Planta %N 4 %P 543-546 %R DOI 10.1007/s004250050759 %T Susceptibility of the guard-cell K -uptake channel KST1 to Zn requires histidine residues in the S3-S4 linker and in the channel pore %U /brokenurl#<Go to ISI>://WOS:000083503100020 %V 209 %X Potassium channels are inhibited by several mono- and divalent cations. To identify sites involved in the interaction between K+ channels and cationic effecters, we expressed the potato (Solanum tuberosum L.) guard-cell K+-uptake channel KST1 in Xenopus oocytes. This channel was reversibly blocked by extracellular Zn2+ in the micromolar range. In the presence of this heavy metal, steady-state currents were reduced in a pH-dependent but voltage-independent manner. Since Zn2+-inhibition was less effective at elevated external proton concentrations, we generated alanine mutants with respect to both extracellular histidines in KST1. Whereas substitution of the pore histidine H271 resulted in a reduced blockade by Zn2+, the channel mutant KST1-H160A in the S3-S4 linker lost most of its Zn2+ sensitivity. Since both histidines alter the susceptibility of KST1 to Zn2+, the block may predominantly result from these two sites. We thus conclude that the S3-S4 linker is involved in the formation of the outer pore.
• AKT3, a phloem-localized K channel, is blocked by protons. Marten, I.; Hoth, S.; Deeken, R.; Ache, P.; Ketchum, K. A.; Hoshi, T.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 96(13), pp. 7581–7586. 1999.
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  The potassium-channel gene, AKT3, has recently been isolated from an Arabidopsis thaliana cDNA library, By using the whole-mount and in situ hybridization techniques, we found AKT3 predominantly expressed in the phloem, To study the physiological role of this channel type, AKTS was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell Kt channels KAT1 and KST1, the AKT3 channels were only weakly; regulated by the membrane potential. Furthermore, AKT3 was blocked by physiological concentrations of external Ca2+ and showed an inverted pH regulation. Extracellular acidification decreased the macroscopic AKT3 currents by reducing the single-channel conductance. Because assimilate transport in the vascular tissue coincides with both Hf and Bf fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.

  @article{RN1229, abstract = {The potassium-channel gene, AKT3, has recently been isolated from an Arabidopsis thaliana cDNA library, By using the whole-mount and in situ hybridization techniques, we found AKT3 predominantly expressed in the phloem, To study the physiological role of this channel type, AKTS was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell Kt channels KAT1 and KST1, the AKT3 channels were only weakly; regulated by the membrane potential. Furthermore, AKT3 was blocked by physiological concentrations of external Ca2+ and showed an inverted pH regulation. Extracellular acidification decreased the macroscopic AKT3 currents by reducing the single-channel conductance. Because assimilate transport in the vascular tissue coincides with both Hf and Bf fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.}, author = {Marten, I. and Hoth, S. and Deeken, R. and Ache, P. and Ketchum, K. A. and Hoshi, T. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {channel}, note = {209pb Times Cited:144 Cited References Count:38}, number = 13, pages = {7581-7586}, title = {AKT3, a phloem-localized K channel, is blocked by protons}, type = {Journal Article}, volume = 96, year = 1999 }

  %0 Journal Article %1 RN1229 %A Marten, I. %A Hoth, S. %A Deeken, R. %A Ache, P. %A Ketchum, K. A. %A Hoshi, T. %A Hedrich, R. %D 1999 %J Proceedings of the National Academy of Sciences of the United States of America %N 13 %P 7581-7586 %R DOI 10.1073/pnas.96.13.7581 %T AKT3, a phloem-localized K channel, is blocked by protons %U /brokenurl#<Go to ISI>://WOS:000081056000084 %V 96 %X The potassium-channel gene, AKT3, has recently been isolated from an Arabidopsis thaliana cDNA library, By using the whole-mount and in situ hybridization techniques, we found AKT3 predominantly expressed in the phloem, To study the physiological role of this channel type, AKTS was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell Kt channels KAT1 and KST1, the AKT3 channels were only weakly; regulated by the membrane potential. Furthermore, AKT3 was blocked by physiological concentrations of external Ca2+ and showed an inverted pH regulation. Extracellular acidification decreased the macroscopic AKT3 currents by reducing the single-channel conductance. Because assimilate transport in the vascular tissue coincides with both Hf and Bf fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.
• Distinct molecular bases for pH sensitivity of the guard cell K channels KST1 and KAT1. Hoth, S.; Hedrich, R. In Journal of Biological Chemistry, 274(17), pp. 11599–11603. 1999.
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  Acid-induced potassium uptake through Kt channels is a prerequisite for stomatal opening. Our previous studies identified a pore histidine as a major component of the acid activation mechanism of the potato guard cell K+ channel KST1 (1), Although this histidine is highly conserved among all plant K+ uptake channels cloned so far, the pH-dependent gating of the Arabidopsis thaliana guard cell K+ channel KAT1 was not affected by mutations of this histidine, In both channels, KST1 and KAT1, aspartate mutants in the K+ channel consensus sequence GYGD adjacent to the histidine (KST1-D269N and KAT1-D265N) were inhibited by a rise in the extracellular proton concentration. pH changes affected the half-maximal activation voltage Vim of the KST1 mutant, whereas in the mutant channel KAT1-D265N an acid-induced decrease in the maximum conductance g(max) indicated the presence of a proton block. In contrast to the wild type KST1, the S4-mutant chan nel KST1-R181Q exhibited an activation upon alcalization of the extracellular solution. From our electrophysiological studies on channel mutants with respect to the pore histidine as well as the aspartate, we conclude that the common proton-supported shift in the voltage dependence of KST1 and KAT1 is based on distinct molecular elements.

  @article{RN1230, abstract = {Acid-induced potassium uptake through Kt channels is a prerequisite for stomatal opening. Our previous studies identified a pore histidine as a major component of the acid activation mechanism of the potato guard cell K+ channel KST1 (1), Although this histidine is highly conserved among all plant K+ uptake channels cloned so far, the pH-dependent gating of the Arabidopsis thaliana guard cell K+ channel KAT1 was not affected by mutations of this histidine, In both channels, KST1 and KAT1, aspartate mutants in the K+ channel consensus sequence GYGD adjacent to the histidine (KST1-D269N and KAT1-D265N) were inhibited by a rise in the extracellular proton concentration. pH changes affected the half-maximal activation voltage Vim of the KST1 mutant, whereas in the mutant channel KAT1-D265N an acid-induced decrease in the maximum conductance g(max) indicated the presence of a proton block. In contrast to the wild type KST1, the S4-mutant chan nel KST1-R181Q exhibited an activation upon alcalization of the extracellular solution. From our electrophysiological studies on channel mutants with respect to the pore histidine as well as the aspartate, we conclude that the common proton-supported shift in the voltage dependence of KST1 and KAT1 is based on distinct molecular elements.}, author = {Hoth, S. and Hedrich, R.}, journal = {Journal of Biological Chemistry}, keywords = {channel}, note = {188ex Times Cited:51 Cited References Count:35}, number = 17, pages = {11599-11603}, title = {Distinct molecular bases for pH sensitivity of the guard cell K channels KST1 and KAT1}, type = {Journal Article}, volume = 274, year = 1999 }

  %0 Journal Article %1 RN1230 %A Hoth, S. %A Hedrich, R. %D 1999 %J Journal of Biological Chemistry %N 17 %P 11599-11603 %R DOI 10.1074/jbc.274.17.11599 %T Distinct molecular bases for pH sensitivity of the guard cell K channels KST1 and KAT1 %U /brokenurl#<Go to ISI>://WOS:000079834800024 %V 274 %X Acid-induced potassium uptake through Kt channels is a prerequisite for stomatal opening. Our previous studies identified a pore histidine as a major component of the acid activation mechanism of the potato guard cell K+ channel KST1 (1), Although this histidine is highly conserved among all plant K+ uptake channels cloned so far, the pH-dependent gating of the Arabidopsis thaliana guard cell K+ channel KAT1 was not affected by mutations of this histidine, In both channels, KST1 and KAT1, aspartate mutants in the K+ channel consensus sequence GYGD adjacent to the histidine (KST1-D269N and KAT1-D265N) were inhibited by a rise in the extracellular proton concentration. pH changes affected the half-maximal activation voltage Vim of the KST1 mutant, whereas in the mutant channel KAT1-D265N an acid-induced decrease in the maximum conductance g(max) indicated the presence of a proton block. In contrast to the wild type KST1, the S4-mutant chan nel KST1-R181Q exhibited an activation upon alcalization of the extracellular solution. From our electrophysiological studies on channel mutants with respect to the pore histidine as well as the aspartate, we conclude that the common proton-supported shift in the voltage dependence of KST1 and KAT1 is based on distinct molecular elements.
• Pronounced differences between the native K channels and KAT1 and KST1 α-subunit homomers of guard cells. Brüggemann, L.; Dietrich, P.; Dreyer, I.; Hedrich, R. In Planta, 207(3), pp. 370–376. 1999.
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  Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.

  @article{RN1233, abstract = {Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.}, author = {Brüggemann, L. and Dietrich, P. and Dreyer, I. and Hedrich, R.}, journal = {Planta}, keywords = {arabidopsis}, note = {161ec Times Cited:33 Cited References Count:49}, number = 3, pages = {370-376}, title = {Pronounced differences between the native K channels and KAT1 and KST1 α-subunit homomers of guard cells}, type = {Journal Article}, volume = 207, year = 1999 }

  %0 Journal Article %1 RN1233 %A Brüggemann, L. %A Dietrich, P. %A Dreyer, I. %A Hedrich, R. %D 1999 %J Planta %N 3 %P 370-376 %R DOI 10.1007/s004250050494 %T Pronounced differences between the native K channels and KAT1 and KST1 α-subunit homomers of guard cells %U /brokenurl#<Go to ISI>://WOS:000078274900006 %V 207 %X Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.
• New approach of monitoring changes in chlorophyll fluorescence of single guard cells and protoplasts in response to physiological stimuli. Goh, C. H.; Schreiber, U.; Hedrich, R. In Plant Cell and Environment, 22(9), pp. 1057–1070. 1999.
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  A new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy-pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark-light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology.

  @article{RN1232, abstract = {A new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy-pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark-light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology.}, author = {Goh, C. H. and Schreiber, U. and Hedrich, R.}, journal = {Plant Cell and Environment}, keywords = {vicia}, note = {235hr Times Cited:67 Cited References Count:62}, number = 9, pages = {1057-1070}, title = {New approach of monitoring changes in chlorophyll fluorescence of single guard cells and protoplasts in response to physiological stimuli}, type = {Journal Article}, volume = 22, year = 1999 }

  %0 Journal Article %1 RN1232 %A Goh, C. H. %A Schreiber, U. %A Hedrich, R. %D 1999 %J Plant Cell and Environment %N 9 %P 1057-1070 %R DOI 10.1046/j.1365-3040.1999.00475.x %T New approach of monitoring changes in chlorophyll fluorescence of single guard cells and protoplasts in response to physiological stimuli %U /brokenurl#<Go to ISI>://WOS:000082536700002 %V 22 %X A new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy-pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark-light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology.
• Auxin-induced K channel expression represents an essential step in coleoptile growth and gravitropism. Philippar, K.; Fuchs, I.; Lüthen, H.; Hoth, S.; Bauer, C. S.; Haga, K.; Thiel, G.; Ljung, K.; Sandberg, G.; Böttger, M.; Becker, D.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 96(21), pp. 12186–12191. 1999.
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  @article{RN1228, author = {Philippar, K. and Fuchs, I. and Lüthen, H. and Hoth, S. and Bauer, C. S. and Haga, K. and Thiel, G. and Ljung, K. and Sandberg, G. and Böttger, M. and Becker, D. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {h+-atpase}, note = {246md Times Cited:230 Cited References Count:35}, number = 21, pages = {12186-12191}, title = {Auxin-induced K channel expression represents an essential step in coleoptile growth and gravitropism}, type = {Journal Article}, volume = 96, year = 1999 }

  %0 Journal Article %1 RN1228 %A Philippar, K. %A Fuchs, I. %A Lüthen, H. %A Hoth, S. %A Bauer, C. S. %A Haga, K. %A Thiel, G. %A Ljung, K. %A Sandberg, G. %A Böttger, M. %A Becker, D. %A Hedrich, R. %D 1999 %J Proceedings of the National Academy of Sciences of the United States of America %N 21 %P 12186-12191 %R DOI 10.1073/pnas.96.21.12186 %T Auxin-induced K channel expression represents an essential step in coleoptile growth and gravitropism %U /brokenurl#<Go to ISI>://WOS:000083166800090 %V 96
• Channel-mediated high-affinity K uptake into guard cells from. Brüggemann, L.; Dietrich, P.; Becker, D.; Dreyer, I.; Palme, K.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 96(6), pp. 3298–3302. 1999.
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  Potassium uptake bg higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton dependent K+ uptake system is still scant. Taking advantage of the high current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 mu M of external K+, Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a kif-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.

  @article{RN1234, abstract = {Potassium uptake bg higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton dependent K+ uptake system is still scant. Taking advantage of the high current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 mu M of external K+, Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a kif-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.}, author = {Brüggemann, L. and Dietrich, P. and Becker, D. and Dreyer, I. and Palme, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {uptake}, note = {177rh Times Cited:57 Cited References Count:34}, number = 6, pages = {3298-3302}, title = {Channel-mediated high-affinity K uptake into guard cells from}, type = {Journal Article}, volume = 96, year = 1999 }

  %0 Journal Article %1 RN1234 %A Brüggemann, L. %A Dietrich, P. %A Becker, D. %A Dreyer, I. %A Palme, K. %A Hedrich, R. %D 1999 %J Proceedings of the National Academy of Sciences of the United States of America %N 6 %P 3298-3302 %R DOI 10.1073/pnas.96.6.3298 %T Channel-mediated high-affinity K uptake into guard cells from %U /brokenurl#<Go to ISI>://WOS:000079224500132 %V 96 %X Potassium uptake bg higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton dependent K+ uptake system is still scant. Taking advantage of the high current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 mu M of external K+, Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a kif-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.
• The plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol. Biela, A.; Grote, K.; Otto, B.; Hoth, S.; Hedrich, R.; Kaldenhoff, R. In Plant Journal, 18(5), pp. 565–570. 1999.
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  A new aquaporin from Nicotiana tabacum (cv. Samsun) was characterized. It shares sequence homology to the Arabidopsis thaliana PIP1 protein family. By two-phase partitioning and immunoblot analysis, plasma membrane localization could be demonstrated. The corresponding mRNA is highly abundant in roots and flowers, while it is rarely expressed in leaves and stems. Functional expression in Xenopus oocytes revealed that NtAQP1 can mediate glycerol transport in addition to water flow. However, NtAQP1 is impermeable for Na+, K+ and Cl- ions. The water permeability and selectivity could not be modulated by addition of mercurials or the activity of cAMP-dependent protein kinases.

  @article{RN1235, abstract = {A new aquaporin from Nicotiana tabacum (cv. Samsun) was characterized. It shares sequence homology to the Arabidopsis thaliana PIP1 protein family. By two-phase partitioning and immunoblot analysis, plasma membrane localization could be demonstrated. The corresponding mRNA is highly abundant in roots and flowers, while it is rarely expressed in leaves and stems. Functional expression in Xenopus oocytes revealed that NtAQP1 can mediate glycerol transport in addition to water flow. However, NtAQP1 is impermeable for Na+, K+ and Cl- ions. The water permeability and selectivity could not be modulated by addition of mercurials or the activity of cAMP-dependent protein kinases.}, author = {Biela, A. and Grote, K. and Otto, B. and Hoth, S. and Hedrich, R. and Kaldenhoff, R.}, journal = {Plant Journal}, keywords = {water}, note = {212ty Times Cited:188 Cited References Count:32}, number = 5, pages = {565-570}, title = {The plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol}, type = {Journal Article}, volume = 18, year = 1999 }

  %0 Journal Article %1 RN1235 %A Biela, A. %A Grote, K. %A Otto, B. %A Hoth, S. %A Hedrich, R. %A Kaldenhoff, R. %D 1999 %J Plant Journal %N 5 %P 565-570 %R DOI 10.1046/j.1365-313X.1999.00474.x %T The plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol %U /brokenurl#<Go to ISI>://WOS:000081233900011 %V 18 %X A new aquaporin from Nicotiana tabacum (cv. Samsun) was characterized. It shares sequence homology to the Arabidopsis thaliana PIP1 protein family. By two-phase partitioning and immunoblot analysis, plasma membrane localization could be demonstrated. The corresponding mRNA is highly abundant in roots and flowers, while it is rarely expressed in leaves and stems. Functional expression in Xenopus oocytes revealed that NtAQP1 can mediate glycerol transport in addition to water flow. However, NtAQP1 is impermeable for Na+, K+ and Cl- ions. The water permeability and selectivity could not be modulated by addition of mercurials or the activity of cAMP-dependent protein kinases.

• Single mutations strongly alter the K -selective pore of the K channel KAT1. Dreyer, I.; Becker, D.; Bregante, M.; Gambale, F.; Lehnen, M.; Palme, K.; Hedrich, R. In Febs Letters, 430(3), pp. 370–376. 1998.
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  Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening, The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K-in channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K-in channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1, From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating. (C) 1998 Federation of European Biochemical Societies.

  @article{RN1237, abstract = {Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening, The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K-in channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K-in channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1, From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating. (C) 1998 Federation of European Biochemical Societies.}, author = {Dreyer, I. and Becker, D. and Bregante, M. and Gambale, F. and Lehnen, M. and Palme, K. and Hedrich, R.}, journal = {Febs Letters}, keywords = {gating}, note = {100cv Times Cited:24 Cited References Count:35}, number = 3, pages = {370-376}, title = {Single mutations strongly alter the K -selective pore of the K channel KAT1}, type = {Journal Article}, volume = 430, year = 1998 }

  %0 Journal Article %1 RN1237 %A Dreyer, I. %A Becker, D. %A Bregante, M. %A Gambale, F. %A Lehnen, M. %A Palme, K. %A Hedrich, R. %D 1998 %J Febs Letters %N 3 %P 370-376 %R Doi 10.1016/S0014-5793(98)00694-2 %T Single mutations strongly alter the K -selective pore of the K channel KAT1 %U /brokenurl#<Go to ISI>://WOS:000074797600047 %V 430 %X Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening, The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K-in channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K-in channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1, From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating. (C) 1998 Federation of European Biochemical Societies.
• Ion-selective flow-through sensors with solid-state contacts insensitive to light and oxygen for plant physiological on-line electroanalysis of transmembraneous ionic transports during photosynthesis. Schindler, J. G.; Herna, K.; Pfaff, S.; Schindler, M. M.; Hedrich, R.; Becker, D. In Journal Fur Praktische Chemie-Chemiker-Zeitung, 340(8), pp. 738–743. 1998.
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  A bioelectrochemical multiple measurement system with ion-selective flow-through sensors for determination of pH, ionic activities and concentrations of transmembraneous ionic transports is described. Non-invasive electroanalysis during photosynthesis was realized by development of new solid-state contacts insensitive to Light and oxygen. Continuous measurement of Ca2+, K+, Cl- and pH demonstrates the known intake of potassium ions by Vicia faba L. guard cells under the influence of light. Glucose intensifies the effect.

  @article{RN1236, abstract = {A bioelectrochemical multiple measurement system with ion-selective flow-through sensors for determination of pH, ionic activities and concentrations of transmembraneous ionic transports is described. Non-invasive electroanalysis during photosynthesis was realized by development of new solid-state contacts insensitive to Light and oxygen. Continuous measurement of Ca2+, K+, Cl- and pH demonstrates the known intake of potassium ions by Vicia faba L. guard cells under the influence of light. Glucose intensifies the effect.}, author = {Schindler, J. G. and Herna, K. and Pfaff, S. and Schindler, M. M. and Hedrich, R. and Becker, D.}, journal = {Journal Fur Praktische Chemie-Chemiker-Zeitung}, keywords = {carrier-pvc-membranes}, note = {142qb Times Cited:0 Cited References Count:30}, number = 8, pages = {738-743}, title = {Ion-selective flow-through sensors with solid-state contacts insensitive to light and oxygen for plant physiological on-line electroanalysis of transmembraneous ionic transports during photosynthesis}, type = {Journal Article}, volume = 340, year = 1998 }

  %0 Journal Article %1 RN1236 %A Schindler, J. G. %A Herna, K. %A Pfaff, S. %A Schindler, M. M. %A Hedrich, R. %A Becker, D. %D 1998 %J Journal Fur Praktische Chemie-Chemiker-Zeitung %N 8 %P 738-743 %R DOI 10.1002/prac.19983400806 %T Ion-selective flow-through sensors with solid-state contacts insensitive to light and oxygen for plant physiological on-line electroanalysis of transmembraneous ionic transports during photosynthesis %U /brokenurl#<Go to ISI>://WOS:000077210700005 %V 340 %X A bioelectrochemical multiple measurement system with ion-selective flow-through sensors for determination of pH, ionic activities and concentrations of transmembraneous ionic transports is described. Non-invasive electroanalysis during photosynthesis was realized by development of new solid-state contacts insensitive to Light and oxygen. Continuous measurement of Ca2+, K+, Cl- and pH demonstrates the known intake of potassium ions by Vicia faba L. guard cells under the influence of light. Glucose intensifies the effect.
• Cation sensitivity and kinetics of guard-cell potassium channels differ among species. Dietrich, P.; Dreyer, I.; Wiesner, P.; Hedrich, R. In Planta, 205(2), pp. 277–287. 1998.
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  In patch-clamp studies we compared the electrical properties of an inward rectifying guard cell K+ channel, GCKCl(in), from three major crop plants Solanum tuberosum L., Nicotiana tabacum L., and Vicia faba L. Selecting guard cells for our analyses we aimed to test whether K+ channels of the same cell type differ among species. The channels shared basic features including voltage-dependence, selectivity and single-channel conductance. They activated at hyperpolarization (V-1/2 approximate to -164 mV) with single channels of 7 pS underlying the whole-cell current. The channel density in S. tuberosum was higher than in V. faba and N. tabacum while the activation and deactivation kinetics were faster in the latter two species. Among different monovalent cations the K+ channels discriminated strongly against Na+. Li+, and Cs+. The sensitivity to Cs+ was similar for the three species. Extracellular Ca2+ blocked the V. faba K+ channel at concentrations greater than or equal to 1 mM but only affected its functional homologs in S. tuberosum and N. tabacum at higher concentrations and more-negative membrane potentials. Like the differences in Ca2+-sensitivity, protoplasts from the three species differed remarkably in their response towards extracellular pH changes. Whereas protons neither altered the open probability nor the kinetic parameters of the V. faba GCKCl(in), in S. tuberosum and N. tabacum this cation affected the voltage-dependent properties strongly. An increase in proton concentration from pH 8.5 to 4.5 shifted the potential of half-maximal open probability to less-negative values with a maximum effect around pH 6.2. The pH modulation of the K+ channels could be described assuming a two-state model where the open and closed channel can be protonated. The observed differences in cation-sensitivity and voltage-dependent kinetics between K+ channels reflect the diversification of guard-cell channels that may contribute to species-specific variations in the control of stomatal aperture.

  @article{RN1239, abstract = {In patch-clamp studies we compared the electrical properties of an inward rectifying guard cell K+ channel, GCKCl(in), from three major crop plants Solanum tuberosum L., Nicotiana tabacum L., and Vicia faba L. Selecting guard cells for our analyses we aimed to test whether K+ channels of the same cell type differ among species. The channels shared basic features including voltage-dependence, selectivity and single-channel conductance. They activated at hyperpolarization (V-1/2 approximate to -164 mV) with single channels of 7 pS underlying the whole-cell current. The channel density in S. tuberosum was higher than in V. faba and N. tabacum while the activation and deactivation kinetics were faster in the latter two species. Among different monovalent cations the K+ channels discriminated strongly against Na+. Li+, and Cs+. The sensitivity to Cs+ was similar for the three species. Extracellular Ca2+ blocked the V. faba K+ channel at concentrations greater than or equal to 1 mM but only affected its functional homologs in S. tuberosum and N. tabacum at higher concentrations and more-negative membrane potentials. Like the differences in Ca2+-sensitivity, protoplasts from the three species differed remarkably in their response towards extracellular pH changes. Whereas protons neither altered the open probability nor the kinetic parameters of the V. faba GCKCl(in), in S. tuberosum and N. tabacum this cation affected the voltage-dependent properties strongly. An increase in proton concentration from pH 8.5 to 4.5 shifted the potential of half-maximal open probability to less-negative values with a maximum effect around pH 6.2. The pH modulation of the K+ channels could be described assuming a two-state model where the open and closed channel can be protonated. The observed differences in cation-sensitivity and voltage-dependent kinetics between K+ channels reflect the diversification of guard-cell channels that may contribute to species-specific variations in the control of stomatal aperture.}, author = {Dietrich, P. and Dreyer, I. and Wiesner, P. and Hedrich, R.}, journal = {Planta}, keywords = {cation}, note = {Zr213 Times Cited:44 Cited References Count:62}, number = 2, pages = {277-287}, title = {Cation sensitivity and kinetics of guard-cell potassium channels differ among species}, type = {Journal Article}, volume = 205, year = 1998 }

  %0 Journal Article %1 RN1239 %A Dietrich, P. %A Dreyer, I. %A Wiesner, P. %A Hedrich, R. %D 1998 %J Planta %N 2 %P 277-287 %R DOI 10.1007/s004250050322 %T Cation sensitivity and kinetics of guard-cell potassium channels differ among species %U /brokenurl#<Go to ISI>://WOS:000073951600017 %V 205 %X In patch-clamp studies we compared the electrical properties of an inward rectifying guard cell K+ channel, GCKCl(in), from three major crop plants Solanum tuberosum L., Nicotiana tabacum L., and Vicia faba L. Selecting guard cells for our analyses we aimed to test whether K+ channels of the same cell type differ among species. The channels shared basic features including voltage-dependence, selectivity and single-channel conductance. They activated at hyperpolarization (V-1/2 approximate to -164 mV) with single channels of 7 pS underlying the whole-cell current. The channel density in S. tuberosum was higher than in V. faba and N. tabacum while the activation and deactivation kinetics were faster in the latter two species. Among different monovalent cations the K+ channels discriminated strongly against Na+. Li+, and Cs+. The sensitivity to Cs+ was similar for the three species. Extracellular Ca2+ blocked the V. faba K+ channel at concentrations greater than or equal to 1 mM but only affected its functional homologs in S. tuberosum and N. tabacum at higher concentrations and more-negative membrane potentials. Like the differences in Ca2+-sensitivity, protoplasts from the three species differed remarkably in their response towards extracellular pH changes. Whereas protons neither altered the open probability nor the kinetic parameters of the V. faba GCKCl(in), in S. tuberosum and N. tabacum this cation affected the voltage-dependent properties strongly. An increase in proton concentration from pH 8.5 to 4.5 shifted the potential of half-maximal open probability to less-negative values with a maximum effect around pH 6.2. The pH modulation of the K+ channels could be described assuming a two-state model where the open and closed channel can be protonated. The observed differences in cation-sensitivity and voltage-dependent kinetics between K+ channels reflect the diversification of guard-cell channels that may contribute to species-specific variations in the control of stomatal aperture.
• Anions permeate and gate GCAC1, a voltage-dependent guard cell anion channel. Dietrich, P.; Hedrich, R. In Plant Journal, 15(4), pp. 479–487. 1998.
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  GCAC1 is a strongly voltage-dependent anion channel in the guard-cell plasma membrane of Vicia faba. In patch-clamp experiments, we have investigated the permeation and gating properties of GCAC1 with respect to its anion dependence in the whole-cell and excised-patch configuration. The relative permeability followed the order SCN- > NO3- > Br- > Cl- while the single-channel conductances in symmetrical anionic solutions exhibited a nearly inverse sequence. The Cl- dependence of inward currents (Cl- release) is characterized by a maximum single-channel conductance of 89 pS half-saturating at 87 mM cytoplasmic chloride. In addition to this substrate saturation, anion release was also dependent on the external Cl- activity (K-m = 16 mM). In the presence of SCN- and Cl-, the single-channel conductance exhibited an anomalous mole-fraction dependence, identifying GCAC1 as a multi-ion single-file pore. Using anions with increasing ionic size, a minimum pore diameter of 0.5 nm was assumed from their relative permeabilities. In line with an anion-selective channel, a tenfold increase in the extracellular anion activity shifted the reversal potential by -59.8 mV. Simultaneously, the half-activation potential shifted negatively by about 23 mV. A further analysis of the anion dependence revealed that extracellular rather than cytosolic anions affect the gating process of GCAC1. From anion substitution experiments, we conclude that anion concentration and species determines both permeation and gating of the plant anion channel GCAC1.

  @article{RN1238, abstract = {GCAC1 is a strongly voltage-dependent anion channel in the guard-cell plasma membrane of Vicia faba. In patch-clamp experiments, we have investigated the permeation and gating properties of GCAC1 with respect to its anion dependence in the whole-cell and excised-patch configuration. The relative permeability followed the order SCN- > NO3- > Br- > Cl- while the single-channel conductances in symmetrical anionic solutions exhibited a nearly inverse sequence. The Cl- dependence of inward currents (Cl- release) is characterized by a maximum single-channel conductance of 89 pS half-saturating at 87 mM cytoplasmic chloride. In addition to this substrate saturation, anion release was also dependent on the external Cl- activity (K-m = 16 mM). In the presence of SCN- and Cl-, the single-channel conductance exhibited an anomalous mole-fraction dependence, identifying GCAC1 as a multi-ion single-file pore. Using anions with increasing ionic size, a minimum pore diameter of 0.5 nm was assumed from their relative permeabilities. In line with an anion-selective channel, a tenfold increase in the extracellular anion activity shifted the reversal potential by -59.8 mV. Simultaneously, the half-activation potential shifted negatively by about 23 mV. A further analysis of the anion dependence revealed that extracellular rather than cytosolic anions affect the gating process of GCAC1. From anion substitution experiments, we conclude that anion concentration and species determines both permeation and gating of the plant anion channel GCAC1.}, author = {Dietrich, P. and Hedrich, R.}, journal = {Plant Journal}, keywords = {myOwn}, note = {117kp Times Cited:44 Cited References Count:39}, number = 4, pages = {479-487}, title = {Anions permeate and gate GCAC1, a voltage-dependent guard cell anion channel}, type = {Journal Article}, volume = 15, year = 1998 }

  %0 Journal Article %1 RN1238 %A Dietrich, P. %A Hedrich, R. %D 1998 %J Plant Journal %N 4 %P 479-487 %R DOI 10.1046/j.1365-313X.1998.00225.x %T Anions permeate and gate GCAC1, a voltage-dependent guard cell anion channel %U /brokenurl#<Go to ISI>://WOS:000075780700004 %V 15 %X GCAC1 is a strongly voltage-dependent anion channel in the guard-cell plasma membrane of Vicia faba. In patch-clamp experiments, we have investigated the permeation and gating properties of GCAC1 with respect to its anion dependence in the whole-cell and excised-patch configuration. The relative permeability followed the order SCN- > NO3- > Br- > Cl- while the single-channel conductances in symmetrical anionic solutions exhibited a nearly inverse sequence. The Cl- dependence of inward currents (Cl- release) is characterized by a maximum single-channel conductance of 89 pS half-saturating at 87 mM cytoplasmic chloride. In addition to this substrate saturation, anion release was also dependent on the external Cl- activity (K-m = 16 mM). In the presence of SCN- and Cl-, the single-channel conductance exhibited an anomalous mole-fraction dependence, identifying GCAC1 as a multi-ion single-file pore. Using anions with increasing ionic size, a minimum pore diameter of 0.5 nm was assumed from their relative permeabilities. In line with an anion-selective channel, a tenfold increase in the extracellular anion activity shifted the reversal potential by -59.8 mV. Simultaneously, the half-activation potential shifted negatively by about 23 mV. A further analysis of the anion dependence revealed that extracellular rather than cytosolic anions affect the gating process of GCAC1. From anion substitution experiments, we conclude that anion concentration and species determines both permeation and gating of the plant anion channel GCAC1.

• Slowly activating vacuolar channels can not mediate Ca -induced Ca release. Pottosin, I. I.; Tikhonova, L. I.; Hedrich, R.; Schönknecht, G. In Plant Journal, 12(6), pp. 1387–1398. 1997.
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  In order to test the hypothesis that slowly activating vacuolar (SV) channels mediate Ca2+-induced Ca2+ release the voltage- and Ca2+-dependence of these K+ and Ca2+-permeable channels were studied in a quantitative manner. The patch-clamp technique was applied to barley (Hordeum vulgare L.) mesophyll vacuoles in the whole vacuole and vacuolar-free patch configuration. Under symmetrical ionic conditions the current-voltage relationship of the open SV channel was characterized by a pronounced inward rectification. The single channel current amplitude was not affected by changes in cytosolic Ca2+ whereas an increase in vacuolar Ca2+ decreased the unitary current in a voltage dependent manner. The SV channel open-probability increased with positive potentials and elevated cytosolic Ca2+, but not with elevated cytosolic Mg2+. An increase of cytosolic Ca2+ shifted the half-activation potential to more negative voltages, whereas an increase of vacuolar Ca2+ shifted the half-activation potential to more positive voltages. At physiological vacuolar Ca2+ activities (50 mu M to 2 mM) changes in cytosolic Ca2+ (5 mu M to 2 mM) revealed an exponential dependence of the SV channel open probability on the electrochemical potential gradient for Ca2+ (Delta mu(Ca)). At the Ca2+ equilibrium potential (Delta mu(Ca) = 0) the open-probability was as low as 0.4%. Higher open-probabilities required net Ca2+ motive forces which would drive Ca2+ influx into the vacuole. Under conditions favouring Ca2+ release from the vacuole, however, the open-probability further decreased. Based on quantitative analysis, it was concluded that the SV channel is not suited for Ca2+-induced Ca2+ release from the vacuole.

  @article{RN1240, abstract = {In order to test the hypothesis that slowly activating vacuolar (SV) channels mediate Ca2+-induced Ca2+ release the voltage- and Ca2+-dependence of these K+ and Ca2+-permeable channels were studied in a quantitative manner. The patch-clamp technique was applied to barley (Hordeum vulgare L.) mesophyll vacuoles in the whole vacuole and vacuolar-free patch configuration. Under symmetrical ionic conditions the current-voltage relationship of the open SV channel was characterized by a pronounced inward rectification. The single channel current amplitude was not affected by changes in cytosolic Ca2+ whereas an increase in vacuolar Ca2+ decreased the unitary current in a voltage dependent manner. The SV channel open-probability increased with positive potentials and elevated cytosolic Ca2+, but not with elevated cytosolic Mg2+. An increase of cytosolic Ca2+ shifted the half-activation potential to more negative voltages, whereas an increase of vacuolar Ca2+ shifted the half-activation potential to more positive voltages. At physiological vacuolar Ca2+ activities (50 mu M to 2 mM) changes in cytosolic Ca2+ (5 mu M to 2 mM) revealed an exponential dependence of the SV channel open probability on the electrochemical potential gradient for Ca2+ (Delta mu(Ca)). At the Ca2+ equilibrium potential (Delta mu(Ca) = 0) the open-probability was as low as 0.4%. Higher open-probabilities required net Ca2+ motive forces which would drive Ca2+ influx into the vacuole. Under conditions favouring Ca2+ release from the vacuole, however, the open-probability further decreased. Based on quantitative analysis, it was concluded that the SV channel is not suited for Ca2+-induced Ca2+ release from the vacuole.}, author = {Pottosin, I. I. and Tikhonova, L. I. and Hedrich, R. and Schönknecht, G.}, journal = {Plant Journal}, keywords = {eremosphaera-viridis}, note = {Yt069 Times Cited:96 Cited References Count:27}, number = 6, pages = {1387-1398}, title = {Slowly activating vacuolar channels can not mediate Ca -induced Ca release}, type = {Journal Article}, volume = 12, year = 1997 }

  %0 Journal Article %1 RN1240 %A Pottosin, I. I. %A Tikhonova, L. I. %A Hedrich, R. %A Schönknecht, G. %D 1997 %J Plant Journal %N 6 %P 1387-1398 %R DOI 10.1046/j.1365-313x.1997.12061387.x %T Slowly activating vacuolar channels can not mediate Ca -induced Ca release %U /brokenurl#<Go to ISI>://WOS:000071560900015 %V 12 %X In order to test the hypothesis that slowly activating vacuolar (SV) channels mediate Ca2+-induced Ca2+ release the voltage- and Ca2+-dependence of these K+ and Ca2+-permeable channels were studied in a quantitative manner. The patch-clamp technique was applied to barley (Hordeum vulgare L.) mesophyll vacuoles in the whole vacuole and vacuolar-free patch configuration. Under symmetrical ionic conditions the current-voltage relationship of the open SV channel was characterized by a pronounced inward rectification. The single channel current amplitude was not affected by changes in cytosolic Ca2+ whereas an increase in vacuolar Ca2+ decreased the unitary current in a voltage dependent manner. The SV channel open-probability increased with positive potentials and elevated cytosolic Ca2+, but not with elevated cytosolic Mg2+. An increase of cytosolic Ca2+ shifted the half-activation potential to more negative voltages, whereas an increase of vacuolar Ca2+ shifted the half-activation potential to more positive voltages. At physiological vacuolar Ca2+ activities (50 mu M to 2 mM) changes in cytosolic Ca2+ (5 mu M to 2 mM) revealed an exponential dependence of the SV channel open probability on the electrochemical potential gradient for Ca2+ (Delta mu(Ca)). At the Ca2+ equilibrium potential (Delta mu(Ca) = 0) the open-probability was as low as 0.4%. Higher open-probabilities required net Ca2+ motive forces which would drive Ca2+ influx into the vacuole. Under conditions favouring Ca2+ release from the vacuole, however, the open-probability further decreased. Based on quantitative analysis, it was concluded that the SV channel is not suited for Ca2+-induced Ca2+ release from the vacuole.
• Mutational analysis of functional domains within plant K+ uptake channels. Hoth, S.; Dreyer, I.; Hedrich, R. In Journal of Experimental Botany, 48, pp. 415–420. 1997.
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  Site-directed mutations have been generated in the pore and voltage sensor regions of the inwardly rectifying potassium channels KAT1 and KST1. The properties of mutant channels have been analysed in Xenopus oocytes, and give insights into the structure-function relations of these channels.

  @article{RN1255, abstract = {Site-directed mutations have been generated in the pore and voltage sensor regions of the inwardly rectifying potassium channels KAT1 and KST1. The properties of mutant channels have been analysed in Xenopus oocytes, and give insights into the structure-function relations of these channels.}, author = {Hoth, S. and Dreyer, I. and Hedrich, R.}, journal = {Journal of Experimental Botany}, keywords = {domains}, note = {Sp. Iss. SI Xb825 Times Cited:13 Cited References Count:37}, pages = {415-420}, title = {Mutational analysis of functional domains within plant K+ uptake channels}, type = {Journal Article}, volume = 48, year = 1997 }

  %0 Journal Article %1 RN1255 %A Hoth, S. %A Dreyer, I. %A Hedrich, R. %D 1997 %J Journal of Experimental Botany %P 415-420 %R DOI 10.1093/jxb/48.Special_Issue.415 %T Mutational analysis of functional domains within plant K+ uptake channels %U /brokenurl#<Go to ISI>://WOS:A1997XB82500008 %V 48 %X Site-directed mutations have been generated in the pore and voltage sensor regions of the inwardly rectifying potassium channels KAT1 and KST1. The properties of mutant channels have been analysed in Xenopus oocytes, and give insights into the structure-function relations of these channels.
• Molecular basis of plant-specific acid activation of K+ uptake channels. Hoth, S.; Dreyer, I.; Dietrich, P.; Becker, D.; MullerRober, B.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 94(9), pp. 4806–4810. 1997.
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  During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified, Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein, Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.

  @article{RN1253, abstract = {During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified, Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein, Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.}, author = {Hoth, S. and Dreyer, I. and Dietrich, P. and Becker, D. and MullerRober, B. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {channels}, note = {Wx362 Times Cited:111 Cited References Count:25}, number = 9, pages = {4806-4810}, title = {Molecular basis of plant-specific acid activation of K+ uptake channels}, type = {Journal Article}, volume = 94, year = 1997 }

  %0 Journal Article %1 RN1253 %A Hoth, S. %A Dreyer, I. %A Dietrich, P. %A Becker, D. %A MullerRober, B. %A Hedrich, R. %D 1997 %J Proceedings of the National Academy of Sciences of the United States of America %N 9 %P 4806-4810 %R DOI 10.1073/pnas.94.9.4806 %T Molecular basis of plant-specific acid activation of K+ uptake channels %U /brokenurl#<Go to ISI>://WOS:A1997WX36200103 %V 94 %X During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified, Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein, Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.
• Receptor-mediated activation of a plant Ca2+-permeable ion channel involved in pathogen defense. Zimmermann, S.; Nurnberger, T.; Frachisse, J. M.; Wirtz, W.; Guern, J.; Hedrich, R.; Scheel, D. In Proceedings of the National Academy of Sciences of the United States of America, 94(6), pp. 2751–2755. 1997.
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  Pathogen recognition at the plant cell surface typically results in the initiation of a multicomponent defense response. Transient influx of Ca2+ across the plasma membrane is postulated to be part of the signaling chain leading to pathogen resistance, Patch-clamp analysis of parsley protoplasts revealed a novel Ca2+-permeable, La3+- sensitive plasma membrane ion channel of large conductance (309 pS in 240 mM CaCl2), At an extracellular Ca2+ concentration of 1 mM, which is representative of the plant cell apoplast, unitary channel conductance was determined to be 80 pS, This ion channel (LEAC, for large conductance elicitor-activated ion channel) is reversibly activated upon treatment of parsley protoplasts with an oligopeptide elicitor derived from a cell wall protein of Phytophthora sojae, Structural features of the elicitor found previously to be essential for receptor binding, induction of defense-related gene expression, and phytoalexin formation are identical to those required for activation of LEAC, Thus, receptor-mediated stimulation of this channel appears to be causally involved in the signaling cascade triggering pathogen defense in parsley.

  @article{RN1254, abstract = {Pathogen recognition at the plant cell surface typically results in the initiation of a multicomponent defense response. Transient influx of Ca2+ across the plasma membrane is postulated to be part of the signaling chain leading to pathogen resistance, Patch-clamp analysis of parsley protoplasts revealed a novel Ca2+-permeable, La3+- sensitive plasma membrane ion channel of large conductance (309 pS in 240 mM CaCl2), At an extracellular Ca2+ concentration of 1 mM, which is representative of the plant cell apoplast, unitary channel conductance was determined to be 80 pS, This ion channel (LEAC, for large conductance elicitor-activated ion channel) is reversibly activated upon treatment of parsley protoplasts with an oligopeptide elicitor derived from a cell wall protein of Phytophthora sojae, Structural features of the elicitor found previously to be essential for receptor binding, induction of defense-related gene expression, and phytoalexin formation are identical to those required for activation of LEAC, Thus, receptor-mediated stimulation of this channel appears to be causally involved in the signaling cascade triggering pathogen defense in parsley.}, author = {Zimmermann, S. and Nurnberger, T. and Frachisse, J. M. and Wirtz, W. and Guern, J. and Hedrich, R. and Scheel, D.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {patch-clamp}, note = {Wp334 Times Cited:174 Cited References Count:41}, number = 6, pages = {2751-2755}, title = {Receptor-mediated activation of a plant Ca2+-permeable ion channel involved in pathogen defense}, type = {Journal Article}, volume = 94, year = 1997 }

  %0 Journal Article %1 RN1254 %A Zimmermann, S. %A Nurnberger, T. %A Frachisse, J. M. %A Wirtz, W. %A Guern, J. %A Hedrich, R. %A Scheel, D. %D 1997 %J Proceedings of the National Academy of Sciences of the United States of America %N 6 %P 2751-2755 %R DOI 10.1073/pnas.94.6.2751 %T Receptor-mediated activation of a plant Ca2+-permeable ion channel involved in pathogen defense %U /brokenurl#<Go to ISI>://WOS:A1997WP33400120 %V 94 %X Pathogen recognition at the plant cell surface typically results in the initiation of a multicomponent defense response. Transient influx of Ca2+ across the plasma membrane is postulated to be part of the signaling chain leading to pathogen resistance, Patch-clamp analysis of parsley protoplasts revealed a novel Ca2+-permeable, La3+- sensitive plasma membrane ion channel of large conductance (309 pS in 240 mM CaCl2), At an extracellular Ca2+ concentration of 1 mM, which is representative of the plant cell apoplast, unitary channel conductance was determined to be 80 pS, This ion channel (LEAC, for large conductance elicitor-activated ion channel) is reversibly activated upon treatment of parsley protoplasts with an oligopeptide elicitor derived from a cell wall protein of Phytophthora sojae, Structural features of the elicitor found previously to be essential for receptor binding, induction of defense-related gene expression, and phytoalexin formation are identical to those required for activation of LEAC, Thus, receptor-mediated stimulation of this channel appears to be causally involved in the signaling cascade triggering pathogen defense in parsley.
• Molecular basis of plant-specific acid activation of K+ uptake channels. Hoth, S.; Dreyer, I.; Dietrich, P.; Becker, D.; MullerRober, B.; Hedrich, R. In European Journal of Cell Biology, 72, pp. 51–51. 1997.
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  @article{RN1241, author = {Hoth, S. and Dreyer, I. and Dietrich, P. and Becker, D. and MullerRober, B. and Hedrich, R.}, journal = {European Journal of Cell Biology}, keywords = {myOwn}, note = {Suppl. 43 Wn584 Times Cited:0 Cited References Count:0}, pages = {51-51}, title = {Molecular basis of plant-specific acid activation of K+ uptake channels}, type = {Journal Article}, volume = 72, year = 1997 }

  %0 Journal Article %1 RN1241 %A Hoth, S. %A Dreyer, I. %A Dietrich, P. %A Becker, D. %A MullerRober, B. %A Hedrich, R. %D 1997 %J European Journal of Cell Biology %P 51-51 %T Molecular basis of plant-specific acid activation of K+ uptake channels %U /brokenurl#<Go to ISI>://WOS:A1997WN58400050 %V 72
• Plant K+ channel alpha-subunits assemble indiscriminately. Dreyer, I.; Antunes, S.; Hoshi, T.; MullerRober, B.; Palme, K.; Pongs, O.; Reintanz, B.; Hedrich, R. In Biophysical Journal, 72(5), pp. 2143–2150. 1997.
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  In plants a large diversity of inwardly rectifying K+ channels (K-in channels) has been observed between tissues and species. However, only three different types of voltage-dependent plant K+ uptake channel subfamilies have been cloned so tar. they relate either to KAT1, AKT1, or AtKC1. To explore the mechanisms underlying the channel diversity, we investigated the assembly of plant inwardly rectifying alpha-subunits. cRNA encoding five different K+ channel alpha-subunits of the three subfamilies (KAT1, KST1, AKT1, SKT1, and AtKC1) which were isolated from different tissues, species, and plant families (Arabidopsis thaliana and Solanum tuberosum) was reciprocally co-injected into Xenopus oocytes. We identified plant K+ channels as multimers. Moreover, using K+ channel mutants expressing different sensitivities to voltage, Cs+, Ca2+, and H+, we could prove heteromers on the basis of their altered voltage and modulator susceptibility. We discovered that, in contrast to animal K+ channel alpha-subunits, functional aggregates of plant K+, channel alpha-subunits assembled indiscriminately. Interestingly, AKT-type channels from A. thaliana and S. tuberosum, which as homomers were electrically silent in oocytes after co-expression, mediated K+ currents. Our findings suggest that K+ channel diversity in plants results from nonselective heteromerization of different alpha-subunits, and thus depends on the spatial segregation of individual alpha-subunit pools and the degree of temporal overlap and kinetics of expression.

  @article{RN1252, abstract = {In plants a large diversity of inwardly rectifying K+ channels (K-in channels) has been observed between tissues and species. However, only three different types of voltage-dependent plant K+ uptake channel subfamilies have been cloned so tar. they relate either to KAT1, AKT1, or AtKC1. To explore the mechanisms underlying the channel diversity, we investigated the assembly of plant inwardly rectifying alpha-subunits. cRNA encoding five different K+ channel alpha-subunits of the three subfamilies (KAT1, KST1, AKT1, SKT1, and AtKC1) which were isolated from different tissues, species, and plant families (Arabidopsis thaliana and Solanum tuberosum) was reciprocally co-injected into Xenopus oocytes. We identified plant K+ channels as multimers. Moreover, using K+ channel mutants expressing different sensitivities to voltage, Cs+, Ca2+, and H+, we could prove heteromers on the basis of their altered voltage and modulator susceptibility. We discovered that, in contrast to animal K+ channel alpha-subunits, functional aggregates of plant K+, channel alpha-subunits assembled indiscriminately. Interestingly, AKT-type channels from A. thaliana and S. tuberosum, which as homomers were electrically silent in oocytes after co-expression, mediated K+ currents. Our findings suggest that K+ channel diversity in plants results from nonselective heteromerization of different alpha-subunits, and thus depends on the spatial segregation of individual alpha-subunit pools and the degree of temporal overlap and kinetics of expression.}, author = {Dreyer, I. and Antunes, S. and Hoshi, T. and MullerRober, B. and Palme, K. and Pongs, O. and Reintanz, B. and Hedrich, R.}, journal = {Biophysical Journal}, keywords = {channel}, note = {Wv984 Times Cited:139 Cited References Count:44}, number = 5, pages = {2143-2150}, title = {Plant K+ channel alpha-subunits assemble indiscriminately}, type = {Journal Article}, volume = 72, year = 1997 }

  %0 Journal Article %1 RN1252 %A Dreyer, I. %A Antunes, S. %A Hoshi, T. %A MullerRober, B. %A Palme, K. %A Pongs, O. %A Reintanz, B. %A Hedrich, R. %D 1997 %J Biophysical Journal %N 5 %P 2143-2150 %R Doi 10.1016/S0006-3495(97)78857-X %T Plant K+ channel alpha-subunits assemble indiscriminately %U /brokenurl#<Go to ISI>://WOS:A1997WV98400021 %V 72 %X In plants a large diversity of inwardly rectifying K+ channels (K-in channels) has been observed between tissues and species. However, only three different types of voltage-dependent plant K+ uptake channel subfamilies have been cloned so tar. they relate either to KAT1, AKT1, or AtKC1. To explore the mechanisms underlying the channel diversity, we investigated the assembly of plant inwardly rectifying alpha-subunits. cRNA encoding five different K+ channel alpha-subunits of the three subfamilies (KAT1, KST1, AKT1, SKT1, and AtKC1) which were isolated from different tissues, species, and plant families (Arabidopsis thaliana and Solanum tuberosum) was reciprocally co-injected into Xenopus oocytes. We identified plant K+ channels as multimers. Moreover, using K+ channel mutants expressing different sensitivities to voltage, Cs+, Ca2+, and H+, we could prove heteromers on the basis of their altered voltage and modulator susceptibility. We discovered that, in contrast to animal K+ channel alpha-subunits, functional aggregates of plant K+, channel alpha-subunits assembled indiscriminately. Interestingly, AKT-type channels from A. thaliana and S. tuberosum, which as homomers were electrically silent in oocytes after co-expression, mediated K+ currents. Our findings suggest that K+ channel diversity in plants results from nonselective heteromerization of different alpha-subunits, and thus depends on the spatial segregation of individual alpha-subunit pools and the degree of temporal overlap and kinetics of expression.

• GCAC1 recognizes the pH gradient across the plasma membrane: A pH-sensitive and ATP-dependent anion channel links guard cell membrane potential to acid and energy metabolism. SchulzLessdorf, B.; Lohse, G.; Hedrich, R. In Plant Journal, 10(6), pp. 993–1004. 1996.
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  Ion channels in the plasma membrane of guard cells provide key mechanisms in signal perception and volume regulation during stomatal movement. Recent studies have suggested that the strongly voltage-dependent, inactivating guard cell onion channel (GCAC1) acts as a sensor of the ambient extracellular CO2 concentration and as a target of modulation by nucleotides and Ca2+ ions. Applying the patch-clamp technique it is demonstrated here that GCAC1 is activated by cytoplasmic ATP in a pH-dependent manner. When the apoplastic pH was buffered to 5.6 and the cytosolic pH dropped step-wise from 7.8 to 5.6, the single-channel activity increased as a function of proton concentration. This pH-sensitivity is characterized by a titratable site with an apparent pK value around 6.9. While the steepness and direction of the transmembrane pH gradient did not affect the kinetics of activation, deactivation and fast inactivation of the whole cell anion current, the kinetics of slow inactivation and reactivation were strongly influenced. When at a constant intracellular proton concentration of pH 7.2 the external pH decreased from 7.2 to 5.6 the time constants of slow inactivation and the half-times of reactivation increased two- and sevenfold, respectively. The mechanism of nucleotide activation of GCAC1 was quantitatively analysed on the level of single-channel events. Using inside-out, cell-free membrane patches, GCAC1 half-activated around 0.4 mM ATP. The sigmoidal dose dependence of anion channel activation could be well fitted with an apparent Hill coefficient of 3.6. This behaviour might indicate that the activation process involves a strongly cooperative interaction of four ATP binding sites. Neither ATP nor its non-hydrolysable analogue AMP-PMP, which also activated GCAC1, altered the voltage-dependent gating. AMP-PMP stimulation and the insensitivity of GCAC1 towards the phosphatase inhibitor, okadaic acid, and the kinase inhibitors, staurosporine and H-7, provided evidence that nucleotide binding rather than phosphorylation caused channel activation. Since the time- and voltage-dependent activity of GCAC1 is strongly modulated by ATP and protons, this channel is capable of sensing changes in the energy status, acid metabolism and the Hf ATPase activity of guard cells.

  @article{RN1242, abstract = {Ion channels in the plasma membrane of guard cells provide key mechanisms in signal perception and volume regulation during stomatal movement. Recent studies have suggested that the strongly voltage-dependent, inactivating guard cell onion channel (GCAC1) acts as a sensor of the ambient extracellular CO2 concentration and as a target of modulation by nucleotides and Ca2+ ions. Applying the patch-clamp technique it is demonstrated here that GCAC1 is activated by cytoplasmic ATP in a pH-dependent manner. When the apoplastic pH was buffered to 5.6 and the cytosolic pH dropped step-wise from 7.8 to 5.6, the single-channel activity increased as a function of proton concentration. This pH-sensitivity is characterized by a titratable site with an apparent pK value around 6.9. While the steepness and direction of the transmembrane pH gradient did not affect the kinetics of activation, deactivation and fast inactivation of the whole cell anion current, the kinetics of slow inactivation and reactivation were strongly influenced. When at a constant intracellular proton concentration of pH 7.2 the external pH decreased from 7.2 to 5.6 the time constants of slow inactivation and the half-times of reactivation increased two- and sevenfold, respectively. The mechanism of nucleotide activation of GCAC1 was quantitatively analysed on the level of single-channel events. Using inside-out, cell-free membrane patches, GCAC1 half-activated around 0.4 mM ATP. The sigmoidal dose dependence of anion channel activation could be well fitted with an apparent Hill coefficient of 3.6. This behaviour might indicate that the activation process involves a strongly cooperative interaction of four ATP binding sites. Neither ATP nor its non-hydrolysable analogue AMP-PMP, which also activated GCAC1, altered the voltage-dependent gating. AMP-PMP stimulation and the insensitivity of GCAC1 towards the phosphatase inhibitor, okadaic acid, and the kinase inhibitors, staurosporine and H-7, provided evidence that nucleotide binding rather than phosphorylation caused channel activation. Since the time- and voltage-dependent activity of GCAC1 is strongly modulated by ATP and protons, this channel is capable of sensing changes in the energy status, acid metabolism and the Hf ATPase activity of guard cells.}, author = {SchulzLessdorf, B. and Lohse, G. and Hedrich, R.}, journal = {Plant Journal}, keywords = {l}, note = {Wc591 Times Cited:61 Cited References Count:64}, number = 6, pages = {993-1004}, title = {GCAC1 recognizes the pH gradient across the plasma membrane: A pH-sensitive and ATP-dependent anion channel links guard cell membrane potential to acid and energy metabolism}, type = {Journal Article}, volume = 10, year = 1996 }

  %0 Journal Article %1 RN1242 %A SchulzLessdorf, B. %A Lohse, G. %A Hedrich, R. %D 1996 %J Plant Journal %N 6 %P 993-1004 %R DOI 10.1046/j.1365-313X.1996.10060993.x %T GCAC1 recognizes the pH gradient across the plasma membrane: A pH-sensitive and ATP-dependent anion channel links guard cell membrane potential to acid and energy metabolism %U /brokenurl#<Go to ISI>://WOS:A1996WC59100004 %V 10 %X Ion channels in the plasma membrane of guard cells provide key mechanisms in signal perception and volume regulation during stomatal movement. Recent studies have suggested that the strongly voltage-dependent, inactivating guard cell onion channel (GCAC1) acts as a sensor of the ambient extracellular CO2 concentration and as a target of modulation by nucleotides and Ca2+ ions. Applying the patch-clamp technique it is demonstrated here that GCAC1 is activated by cytoplasmic ATP in a pH-dependent manner. When the apoplastic pH was buffered to 5.6 and the cytosolic pH dropped step-wise from 7.8 to 5.6, the single-channel activity increased as a function of proton concentration. This pH-sensitivity is characterized by a titratable site with an apparent pK value around 6.9. While the steepness and direction of the transmembrane pH gradient did not affect the kinetics of activation, deactivation and fast inactivation of the whole cell anion current, the kinetics of slow inactivation and reactivation were strongly influenced. When at a constant intracellular proton concentration of pH 7.2 the external pH decreased from 7.2 to 5.6 the time constants of slow inactivation and the half-times of reactivation increased two- and sevenfold, respectively. The mechanism of nucleotide activation of GCAC1 was quantitatively analysed on the level of single-channel events. Using inside-out, cell-free membrane patches, GCAC1 half-activated around 0.4 mM ATP. The sigmoidal dose dependence of anion channel activation could be well fitted with an apparent Hill coefficient of 3.6. This behaviour might indicate that the activation process involves a strongly cooperative interaction of four ATP binding sites. Neither ATP nor its non-hydrolysable analogue AMP-PMP, which also activated GCAC1, altered the voltage-dependent gating. AMP-PMP stimulation and the insensitivity of GCAC1 towards the phosphatase inhibitor, okadaic acid, and the kinase inhibitors, staurosporine and H-7, provided evidence that nucleotide binding rather than phosphorylation caused channel activation. Since the time- and voltage-dependent activity of GCAC1 is strongly modulated by ATP and protons, this channel is capable of sensing changes in the energy status, acid metabolism and the Hf ATPase activity of guard cells.
• Functional expression of the plant K+ channel KAT1 in insect cells. Marten, I.; Gaymard, F.; Lemaillet, G.; Thibaud, J. B.; Sentenac, H.; Hedrich, R. In Febs Letters, 380(3), pp. 229–232. 1996.
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  Following the biophysical analysis of plant K+ channels in their natural environment, three members from the green branch of the evolutionary tree of life KAT1, AKT1 and KST1 have recently been identified on the molecular level, Among them, we focused on the expression and characterization of the Arabopsis thaliana K+ channel KAT1 in the insect cell line Sf9, The infection of Sf9 cells with KAT1-recombinant baculovirus resulted in functional expression of KAT1 channels, which was monitored by inward-rectifying, K+-selective (impermeable to Na+ and even NH4+) ionic conductance in whole-cell patch-clamp recordings, A voltage threshold as low as -60 to -80 mV for voltage activation compared to other plant inward rectifiers in vivo, and to in vitro expression of KAT1 in Xenopus oocytes or yeast, may be indicative for channel modulation by the expression system, A rise in cytoplasmic Ca2+ concentration (up to 1 mM), a regulator of the inward rectifier in Vicia faba guard cells, did not modify the voltage dependence of KAT1 in Sf9 cells, The access to channel function on one side and channel protein on the other make Sf9 cells a suitable heterologous system for studies on the biophysical properties, post-translational modification and assembly of a green inward rectifier.

  @article{RN1259, abstract = {Following the biophysical analysis of plant K+ channels in their natural environment, three members from the green branch of the evolutionary tree of life KAT1, AKT1 and KST1 have recently been identified on the molecular level, Among them, we focused on the expression and characterization of the Arabopsis thaliana K+ channel KAT1 in the insect cell line Sf9, The infection of Sf9 cells with KAT1-recombinant baculovirus resulted in functional expression of KAT1 channels, which was monitored by inward-rectifying, K+-selective (impermeable to Na+ and even NH4+) ionic conductance in whole-cell patch-clamp recordings, A voltage threshold as low as -60 to -80 mV for voltage activation compared to other plant inward rectifiers in vivo, and to in vitro expression of KAT1 in Xenopus oocytes or yeast, may be indicative for channel modulation by the expression system, A rise in cytoplasmic Ca2+ concentration (up to 1 mM), a regulator of the inward rectifier in Vicia faba guard cells, did not modify the voltage dependence of KAT1 in Sf9 cells, The access to channel function on one side and channel protein on the other make Sf9 cells a suitable heterologous system for studies on the biophysical properties, post-translational modification and assembly of a green inward rectifier.}, author = {Marten, I. and Gaymard, F. and Lemaillet, G. and Thibaud, J. B. and Sentenac, H. and Hedrich, R.}, journal = {Febs Letters}, keywords = {cell}, note = {Tw665 Times Cited:41 Cited References Count:29}, number = 3, pages = {229-232}, title = {Functional expression of the plant K+ channel KAT1 in insect cells}, type = {Journal Article}, volume = 380, year = 1996 }

  %0 Journal Article %1 RN1259 %A Marten, I. %A Gaymard, F. %A Lemaillet, G. %A Thibaud, J. B. %A Sentenac, H. %A Hedrich, R. %D 1996 %J Febs Letters %N 3 %P 229-232 %R Doi 10.1016/0014-5793(96)00042-7 %T Functional expression of the plant K+ channel KAT1 in insect cells %U /brokenurl#<Go to ISI>://WOS:A1996TW66500005 %V 380 %X Following the biophysical analysis of plant K+ channels in their natural environment, three members from the green branch of the evolutionary tree of life KAT1, AKT1 and KST1 have recently been identified on the molecular level, Among them, we focused on the expression and characterization of the Arabopsis thaliana K+ channel KAT1 in the insect cell line Sf9, The infection of Sf9 cells with KAT1-recombinant baculovirus resulted in functional expression of KAT1 channels, which was monitored by inward-rectifying, K+-selective (impermeable to Na+ and even NH4+) ionic conductance in whole-cell patch-clamp recordings, A voltage threshold as low as -60 to -80 mV for voltage activation compared to other plant inward rectifiers in vivo, and to in vitro expression of KAT1 in Xenopus oocytes or yeast, may be indicative for channel modulation by the expression system, A rise in cytoplasmic Ca2+ concentration (up to 1 mM), a regulator of the inward rectifier in Vicia faba guard cells, did not modify the voltage dependence of KAT1 in Sf9 cells, The access to channel function on one side and channel protein on the other make Sf9 cells a suitable heterologous system for studies on the biophysical properties, post-translational modification and assembly of a green inward rectifier.
• Plant K+ channels: Similarity and diversity. Hedrich, R.; Dietrich, P. In Botanica Acta, 109(2), pp. 94–101. 1996.
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  In this review we compared the electrophysiological properties of plant K+ uptake channels from different plants and tissues. Taking into account the detailed knowledge of K+ channel properties, which has emerged since the application of the patch-clamp technique on plant cells, as well as results from our recent studies we were able to extract features common among plant K+ channels. In addition, we focused on the diversity that could create plant or tissue-specificity. Functional fingerprints for the voltage-dependent K+ uptake channels were generated on the basis of their voltage-dependence, kinetics, permeability, conductance and pharmacology as well as regulation of K+ channels studied in their natural environment and cloned channels in heterologous expression systems. Finally, sequence information on plant and animal K+ channels cloned so far was used to identify structural motifs that may be related to functional phenotypes.

  @article{RN1258, abstract = {In this review we compared the electrophysiological properties of plant K+ uptake channels from different plants and tissues. Taking into account the detailed knowledge of K+ channel properties, which has emerged since the application of the patch-clamp technique on plant cells, as well as results from our recent studies we were able to extract features common among plant K+ channels. In addition, we focused on the diversity that could create plant or tissue-specificity. Functional fingerprints for the voltage-dependent K+ uptake channels were generated on the basis of their voltage-dependence, kinetics, permeability, conductance and pharmacology as well as regulation of K+ channels studied in their natural environment and cloned channels in heterologous expression systems. Finally, sequence information on plant and animal K+ channels cloned so far was used to identify structural motifs that may be related to functional phenotypes.}, author = {Hedrich, R. and Dietrich, P.}, journal = {Botanica Acta}, keywords = {k+}, note = {Ur545 Times Cited:37 Cited References Count:86}, number = 2, pages = {94-101}, title = {Plant K+ channels: Similarity and diversity}, type = {Journal Article}, volume = 109, year = 1996 }

  %0 Journal Article %1 RN1258 %A Hedrich, R. %A Dietrich, P. %D 1996 %J Botanica Acta %N 2 %P 94-101 %R DOI 10.1111/j.1438-8677.1996.tb00548.x %T Plant K+ channels: Similarity and diversity %U /brokenurl#<Go to ISI>://WOS:A1996UR54500004 %V 109 %X In this review we compared the electrophysiological properties of plant K+ uptake channels from different plants and tissues. Taking into account the detailed knowledge of K+ channel properties, which has emerged since the application of the patch-clamp technique on plant cells, as well as results from our recent studies we were able to extract features common among plant K+ channels. In addition, we focused on the diversity that could create plant or tissue-specificity. Functional fingerprints for the voltage-dependent K+ uptake channels were generated on the basis of their voltage-dependence, kinetics, permeability, conductance and pharmacology as well as regulation of K+ channels studied in their natural environment and cloned channels in heterologous expression systems. Finally, sequence information on plant and animal K+ channels cloned so far was used to identify structural motifs that may be related to functional phenotypes.
• Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1. Becker, D.; Dreyer, I.; Hoth, S.; Reid, J. D.; Busch, H.; Lehnen, M.; Palme, K.; Hedrich, R. In Proceedings of the National Academy of Sciences of the United States of America, 93(15), pp. 8123–8128. 1996.
  • [ Abstract ]
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  KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The H5 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in K4T1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U-1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.

  @article{RN1257, abstract = {KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The H5 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in K4T1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U-1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.}, author = {Becker, D. and Dreyer, I. and Hoth, S. and Reid, J. D. and Busch, H. and Lehnen, M. and Palme, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {cell-membrane}, note = {Uy930 Times Cited:106 Cited References Count:39}, number = 15, pages = {8123-8128}, title = {Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1}, type = {Journal Article}, volume = 93, year = 1996 }

  %0 Journal Article %1 RN1257 %A Becker, D. %A Dreyer, I. %A Hoth, S. %A Reid, J. D. %A Busch, H. %A Lehnen, M. %A Palme, K. %A Hedrich, R. %D 1996 %J Proceedings of the National Academy of Sciences of the United States of America %N 15 %P 8123-8128 %R DOI 10.1073/pnas.93.15.8123 %T Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1 %U /brokenurl#<Go to ISI>://WOS:A1996UY93000128 %V 93 %X KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The H5 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in K4T1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U-1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.

• Cloning and Electrophysiological Analysis of Kst1, an Inward Rectifying K+ Channel Expressed in Potato Guard-Cells. Mullerrober, B.; Ellenberg, J.; Provart, N.; Willmitzer, L.; Busch, H.; Becker, D.; Dietrich, P.; Hoth, S.; Hedrich, R. In Embo Journal, 14(11), pp. 2409–2416. 1995.
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  Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening, Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types, Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K+-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.

  @article{RN1265, abstract = {Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening, Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types, Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K+-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.}, author = {Mullerrober, B. and Ellenberg, J. and Provart, N. and Willmitzer, L. and Busch, H. and Becker, D. and Dietrich, P. and Hoth, S. and Hedrich, R.}, journal = {Embo Journal}, keywords = {guard}, note = {Rc664 Times Cited:181 Cited References Count:36}, number = 11, pages = {2409-2416}, title = {Cloning and Electrophysiological Analysis of Kst1, an Inward Rectifying K+ Channel Expressed in Potato Guard-Cells}, type = {Journal Article}, volume = 14, year = 1995 }

  %0 Journal Article %1 RN1265 %A Mullerrober, B. %A Ellenberg, J. %A Provart, N. %A Willmitzer, L. %A Busch, H. %A Becker, D. %A Dietrich, P. %A Hoth, S. %A Hedrich, R. %D 1995 %J Embo Journal %N 11 %P 2409-2416 %R DOI 10.1002/j.1460-2075.1995.tb07238.x %T Cloning and Electrophysiological Analysis of Kst1, an Inward Rectifying K+ Channel Expressed in Potato Guard-Cells %U /brokenurl#<Go to ISI>://WOS:A1995RC66400002 %V 14 %X Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening, Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types, Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K+-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.
• The Voltage-Dependent Potassium-Uptake Channel of Corn Coleoptiles Has Permeation Properties Different from Other K+ Channels. Hedrich, R.; Bregante, M.; Dreyer, I.; Gambale, F. In Planta, 197(1), pp. 193–199. 1995.
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  The initial response of coleoptile cells to growth hormones and light is a rapid change in plasmamembrane polarization. We have isolated protoplasts from the cortex of maize (Zea mays L.) coleoptiles to study the electrical properties of their plasma membrane by the patch-clamp technique. Using the whole-cell configuration and cell-free membrane patches we could identify an H+-ATPase, hyperpolarizing the membrane potential often more negative than -150 mV, and a voltage-dependent, inward-rectifying K+ channel (unit conductance approximate to 5-7 pS) as the major membrane conductances. Potassium currents through this channel named CKC1(in) (for Coleoptile K+ Channel inward rectifier) were elicited upon voltage steps negative to -80 mV, characterized by a half-activation potential of -112 mV. The kinetics of activation, well described by a double-exponential process, were strongly dependent on the degree of hyperpolarization and the cytoplasmic Ca2+ level. Whereas at nanomolar Ca2+ concentrations K+ currents increased with a t(1/2)=16 ms (at -180 mV), higher calcium levels slowed the activation process about four- to fivefold. Upon changes in the extracellular K+ concentration the reversal potential of the K+ channel followed the Nernst potential for potassium with a 56-mV shift for a tenfold increase. The absence of a measurable conductance for Na+, Rb+, Cs+ and a permeability ratio P-NH4+/P-K+ around 0.25 underlines the high selectivity of CKClin for K+. In contrast to Cs+, which at submillimolar concentration blocks the channel in a voltage-dependent manner, Rb+, often used as a tracer for K+, does not permeate this type of K+ channel. The lack of Rb+ permeability is unique with respect to other K+ transporters. Therefore, future molecular analysis of CKC1(in) considered as a unique variation of plant inward rectifiers, might help to understand the permeation properties of K+ channels in general.

  @article{RN1264, abstract = {The initial response of coleoptile cells to growth hormones and light is a rapid change in plasmamembrane polarization. We have isolated protoplasts from the cortex of maize (Zea mays L.) coleoptiles to study the electrical properties of their plasma membrane by the patch-clamp technique. Using the whole-cell configuration and cell-free membrane patches we could identify an H+-ATPase, hyperpolarizing the membrane potential often more negative than -150 mV, and a voltage-dependent, inward-rectifying K+ channel (unit conductance approximate to 5-7 pS) as the major membrane conductances. Potassium currents through this channel named CKC1(in) (for Coleoptile K+ Channel inward rectifier) were elicited upon voltage steps negative to -80 mV, characterized by a half-activation potential of -112 mV. The kinetics of activation, well described by a double-exponential process, were strongly dependent on the degree of hyperpolarization and the cytoplasmic Ca2+ level. Whereas at nanomolar Ca2+ concentrations K+ currents increased with a t(1/2)=16 ms (at -180 mV), higher calcium levels slowed the activation process about four- to fivefold. Upon changes in the extracellular K+ concentration the reversal potential of the K+ channel followed the Nernst potential for potassium with a 56-mV shift for a tenfold increase. The absence of a measurable conductance for Na+, Rb+, Cs+ and a permeability ratio P-NH4+/P-K+ around 0.25 underlines the high selectivity of CKClin for K+. In contrast to Cs+, which at submillimolar concentration blocks the channel in a voltage-dependent manner, Rb+, often used as a tracer for K+, does not permeate this type of K+ channel. The lack of Rb+ permeability is unique with respect to other K+ transporters. Therefore, future molecular analysis of CKC1(in) considered as a unique variation of plant inward rectifiers, might help to understand the permeation properties of K+ channels in general.}, author = {Hedrich, R. and Bregante, M. and Dreyer, I. and Gambale, F.}, journal = {Planta}, keywords = {uptake)}, note = {Rw200 Times Cited:42 Cited References Count:43}, number = 1, pages = {193-199}, title = {The Voltage-Dependent Potassium-Uptake Channel of Corn Coleoptiles Has Permeation Properties Different from Other K+ Channels}, type = {Journal Article}, volume = 197, year = 1995 }

  %0 Journal Article %1 RN1264 %A Hedrich, R. %A Bregante, M. %A Dreyer, I. %A Gambale, F. %D 1995 %J Planta %N 1 %P 193-199 %T The Voltage-Dependent Potassium-Uptake Channel of Corn Coleoptiles Has Permeation Properties Different from Other K+ Channels %U /brokenurl#<Go to ISI>://WOS:A1995RW20000024 %V 197 %X The initial response of coleoptile cells to growth hormones and light is a rapid change in plasmamembrane polarization. We have isolated protoplasts from the cortex of maize (Zea mays L.) coleoptiles to study the electrical properties of their plasma membrane by the patch-clamp technique. Using the whole-cell configuration and cell-free membrane patches we could identify an H+-ATPase, hyperpolarizing the membrane potential often more negative than -150 mV, and a voltage-dependent, inward-rectifying K+ channel (unit conductance approximate to 5-7 pS) as the major membrane conductances. Potassium currents through this channel named CKC1(in) (for Coleoptile K+ Channel inward rectifier) were elicited upon voltage steps negative to -80 mV, characterized by a half-activation potential of -112 mV. The kinetics of activation, well described by a double-exponential process, were strongly dependent on the degree of hyperpolarization and the cytoplasmic Ca2+ level. Whereas at nanomolar Ca2+ concentrations K+ currents increased with a t(1/2)=16 ms (at -180 mV), higher calcium levels slowed the activation process about four- to fivefold. Upon changes in the extracellular K+ concentration the reversal potential of the K+ channel followed the Nernst potential for potassium with a 56-mV shift for a tenfold increase. The absence of a measurable conductance for Na+, Rb+, Cs+ and a permeability ratio P-NH4+/P-K+ around 0.25 underlines the high selectivity of CKClin for K+. In contrast to Cs+, which at submillimolar concentration blocks the channel in a voltage-dependent manner, Rb+, often used as a tracer for K+, does not permeate this type of K+ channel. The lack of Rb+ permeability is unique with respect to other K+ transporters. Therefore, future molecular analysis of CKC1(in) considered as a unique variation of plant inward rectifiers, might help to understand the permeation properties of K+ channels in general.
• Hodgkin-Huxley Analysis of a Gcac1 Anion Channel in the Plasma-Membrane of Guard-Cells. Kolb, H. A.; Marten, I.; Hedrich, R. In Journal of Membrane Biology, 146(3), pp. 273–282. 1995.
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  A quantitative analysis of the time- and voltage-dependent kinetics of the guard cell anion channel (GCAC1) current in guard cell protoplasts from Vicia faba was analyzed using the whole-cell patch clamp technique. The voltage-dependent steady-state activation of GCAC1 current followed a Boltzmann distribution. For the corresponding steady-state value of the activation variable a power of two was derived which yielded suitable fits of the time course of voltage-dependent current activation. The GCAC1 mediated chloride current could successfully be described in terms of the Hodgkin-Huxley equations commonly evoked for the Na channel in nerve. After step depolarizations from a potential in the range of the resting potential to potentials above the equilibrium potential for chloride an activation and also an inactivation could be described. The gating of both processes exhibited an inverse relationship on the polarity of the applied step potentials in the order of milliseconds. Deactivating tail currents decline exponentially. The presented analysis contributes to the understanding of the rising phase of the observed action potentials in guard cells of V. faba. Evidence is presented that the voltage-dependent kinetic properties of the GCAC1 current are different from those properties described for the excitable anion currents in the plasmalemma of Chara corallina (Beilby & Coster, 1979a).

  @article{RN1263, abstract = {A quantitative analysis of the time- and voltage-dependent kinetics of the guard cell anion channel (GCAC1) current in guard cell protoplasts from Vicia faba was analyzed using the whole-cell patch clamp technique. The voltage-dependent steady-state activation of GCAC1 current followed a Boltzmann distribution. For the corresponding steady-state value of the activation variable a power of two was derived which yielded suitable fits of the time course of voltage-dependent current activation. The GCAC1 mediated chloride current could successfully be described in terms of the Hodgkin-Huxley equations commonly evoked for the Na channel in nerve. After step depolarizations from a potential in the range of the resting potential to potentials above the equilibrium potential for chloride an activation and also an inactivation could be described. The gating of both processes exhibited an inverse relationship on the polarity of the applied step potentials in the order of milliseconds. Deactivating tail currents decline exponentially. The presented analysis contributes to the understanding of the rising phase of the observed action potentials in guard cells of V. faba. Evidence is presented that the voltage-dependent kinetic properties of the GCAC1 current are different from those properties described for the excitable anion currents in the plasmalemma of Chara corallina (Beilby & Coster, 1979a).}, author = {Kolb, H. A. and Marten, I. and Hedrich, R.}, journal = {Journal of Membrane Biology}, keywords = {gcac1}, note = {Rq270 Times Cited:29 Cited References Count:36}, number = 3, pages = {273-282}, title = {Hodgkin-Huxley Analysis of a Gcac1 Anion Channel in the Plasma-Membrane of Guard-Cells}, type = {Journal Article}, volume = 146, year = 1995 }

  %0 Journal Article %1 RN1263 %A Kolb, H. A. %A Marten, I. %A Hedrich, R. %D 1995 %J Journal of Membrane Biology %N 3 %P 273-282 %T Hodgkin-Huxley Analysis of a Gcac1 Anion Channel in the Plasma-Membrane of Guard-Cells %U /brokenurl#<Go to ISI>://WOS:A1995RQ27000005 %V 146 %X A quantitative analysis of the time- and voltage-dependent kinetics of the guard cell anion channel (GCAC1) current in guard cell protoplasts from Vicia faba was analyzed using the whole-cell patch clamp technique. The voltage-dependent steady-state activation of GCAC1 current followed a Boltzmann distribution. For the corresponding steady-state value of the activation variable a power of two was derived which yielded suitable fits of the time course of voltage-dependent current activation. The GCAC1 mediated chloride current could successfully be described in terms of the Hodgkin-Huxley equations commonly evoked for the Na channel in nerve. After step depolarizations from a potential in the range of the resting potential to potentials above the equilibrium potential for chloride an activation and also an inactivation could be described. The gating of both processes exhibited an inverse relationship on the polarity of the applied step potentials in the order of milliseconds. Deactivating tail currents decline exponentially. The presented analysis contributes to the understanding of the rising phase of the observed action potentials in guard cells of V. faba. Evidence is presented that the voltage-dependent kinetic properties of the GCAC1 current are different from those properties described for the excitable anion currents in the plasmalemma of Chara corallina (Beilby & Coster, 1979a).
• Inward Rectifier Potassium Channels in Plants Differ from Their Animal Counterparts in Response to Voltage and Channel Modulators. Hedrich, R.; Moran, O.; Conti, F.; Busch, H.; Becker, D.; Gambale, F.; Dreyer, I.; Kuch, A.; Neuwinger, K.; Palme, K. In European Biophysics Journal, 24(2), pp. 107–115. 1995.
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  We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related Kf channels in the plasmamembrane of guard and root cells from Vicia faba and Zen mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H+-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg2+-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.

  @article{RN1262, abstract = {We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related Kf channels in the plasmamembrane of guard and root cells from Vicia faba and Zen mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H+-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg2+-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.}, author = {Hedrich, R. and Moran, O. and Conti, F. and Busch, H. and Becker, D. and Gambale, F. and Dreyer, I. and Kuch, A. and Neuwinger, K. and Palme, K.}, journal = {European Biophysics Journal}, keywords = {channel}, note = {Te482 Times Cited:85 Cited References Count:40}, number = 2, pages = {107-115}, title = {Inward Rectifier Potassium Channels in Plants Differ from Their Animal Counterparts in Response to Voltage and Channel Modulators}, type = {Journal Article}, volume = 24, year = 1995 }

  %0 Journal Article %1 RN1262 %A Hedrich, R. %A Moran, O. %A Conti, F. %A Busch, H. %A Becker, D. %A Gambale, F. %A Dreyer, I. %A Kuch, A. %A Neuwinger, K. %A Palme, K. %D 1995 %J European Biophysics Journal %N 2 %P 107-115 %T Inward Rectifier Potassium Channels in Plants Differ from Their Animal Counterparts in Response to Voltage and Channel Modulators %U /brokenurl#<Go to ISI>://WOS:A1995TE48200008 %V 24 %X We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related Kf channels in the plasmamembrane of guard and root cells from Vicia faba and Zen mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H+-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg2+-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.
• Protons and Calcium Modulate Sv-Type Channels in the Vacuolar-Lysosomal Compartment - Channel Interaction with Calmodulin Inhibitors. Schulzlessdorf, B.; Hedrich, R. In Planta, 197(4), pp. 655–671. 1995.
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  Slowly activating vacuolar (SV-type; Hedrich and Neher 1987, Nature 329: 833-835) ion channels provide the predominant membrane conductance of the vacuolar-lysosomal compartment of Vicia faba L. guard cells and sugar beet (Beta vulgaris L.) taproots. Applying the patch-clamp technique to isolated vacuoles of both tissues, the electrical and pharmacological properties of guard-cell SV-type currents were studied and compared to the sugar beet channel with regard to its modulation by cytoplasmic Ca2+ and pH. This outward rectifier of V. faba guard cells showed a half-maximum activation at 55-60 mV with an apparent gating charge equivalent of z approximate to 4. Studies on the single-channel and whole-vacuole level revealed an extremely high conductance of 280 pS for the guard-cell channels at a mean density of 0.37 mu m(-2) compared to taproots (120-140 pS at about 0.16 channels per mu m(2)) Guard-cell SV-type channels are weakly selective for cations over anions and lack saturation at KCl concentrations of up to 1 M. Since in the absence of physiological K+ concentrations, Ca2+ is the major permeable ion, relative changes in the amounts of the two ions might control the permeation process. In spite of their different origins and physiological functions, in guard cells and beet taproot cells, cytoplasmic Ca2+ and protons, both considered as candidates for intracellular signalling in plants, modulate the voltage dependence of SV-type channels. While the two effecters do not alter the single-channel conductance, they strongly interact with the voltage sensor. The calmodulin (CaM) antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), trifluoperazine (TFP) and calmidazolium hydrochloride (R 24571) effectively blocked the channel in an antagonist-specific manner. In agreement with the properties of a Ca2+-permeable channel, CaM could be involved in the modulation of the activation threshold of the SV-type channel. We therefore conclude that guard-cell SV-type channels, which might be responsible for the release of K+, Cl- and to a smaller extent Ca2+ during stomatal closure, could serve as an intracellular sensor for changes in cytosolic calcium (calcium-CaM) and pH.

  @article{RN1260, abstract = {Slowly activating vacuolar (SV-type; Hedrich and Neher 1987, Nature 329: 833-835) ion channels provide the predominant membrane conductance of the vacuolar-lysosomal compartment of Vicia faba L. guard cells and sugar beet (Beta vulgaris L.) taproots. Applying the patch-clamp technique to isolated vacuoles of both tissues, the electrical and pharmacological properties of guard-cell SV-type currents were studied and compared to the sugar beet channel with regard to its modulation by cytoplasmic Ca2+ and pH. This outward rectifier of V. faba guard cells showed a half-maximum activation at 55-60 mV with an apparent gating charge equivalent of z approximate to 4. Studies on the single-channel and whole-vacuole level revealed an extremely high conductance of 280 pS for the guard-cell channels at a mean density of 0.37 mu m(-2) compared to taproots (120-140 pS at about 0.16 channels per mu m(2)) Guard-cell SV-type channels are weakly selective for cations over anions and lack saturation at KCl concentrations of up to 1 M. Since in the absence of physiological K+ concentrations, Ca2+ is the major permeable ion, relative changes in the amounts of the two ions might control the permeation process. In spite of their different origins and physiological functions, in guard cells and beet taproot cells, cytoplasmic Ca2+ and protons, both considered as candidates for intracellular signalling in plants, modulate the voltage dependence of SV-type channels. While the two effecters do not alter the single-channel conductance, they strongly interact with the voltage sensor. The calmodulin (CaM) antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), trifluoperazine (TFP) and calmidazolium hydrochloride (R 24571) effectively blocked the channel in an antagonist-specific manner. In agreement with the properties of a Ca2+-permeable channel, CaM could be involved in the modulation of the activation threshold of the SV-type channel. We therefore conclude that guard-cell SV-type channels, which might be responsible for the release of K+, Cl- and to a smaller extent Ca2+ during stomatal closure, could serve as an intracellular sensor for changes in cytosolic calcium (calcium-CaM) and pH.}, author = {Schulzlessdorf, B. and Hedrich, R.}, journal = {Planta}, keywords = {calcium}, note = {Tj713 Times Cited:120 Cited References Count:83}, number = 4, pages = {655-671}, title = {Protons and Calcium Modulate Sv-Type Channels in the Vacuolar-Lysosomal Compartment - Channel Interaction with Calmodulin Inhibitors}, type = {Journal Article}, volume = 197, year = 1995 }

  %0 Journal Article %1 RN1260 %A Schulzlessdorf, B. %A Hedrich, R. %D 1995 %J Planta %N 4 %P 655-671 %T Protons and Calcium Modulate Sv-Type Channels in the Vacuolar-Lysosomal Compartment - Channel Interaction with Calmodulin Inhibitors %U /brokenurl#<Go to ISI>://WOS:A1995TJ71300014 %V 197 %X Slowly activating vacuolar (SV-type; Hedrich and Neher 1987, Nature 329: 833-835) ion channels provide the predominant membrane conductance of the vacuolar-lysosomal compartment of Vicia faba L. guard cells and sugar beet (Beta vulgaris L.) taproots. Applying the patch-clamp technique to isolated vacuoles of both tissues, the electrical and pharmacological properties of guard-cell SV-type currents were studied and compared to the sugar beet channel with regard to its modulation by cytoplasmic Ca2+ and pH. This outward rectifier of V. faba guard cells showed a half-maximum activation at 55-60 mV with an apparent gating charge equivalent of z approximate to 4. Studies on the single-channel and whole-vacuole level revealed an extremely high conductance of 280 pS for the guard-cell channels at a mean density of 0.37 mu m(-2) compared to taproots (120-140 pS at about 0.16 channels per mu m(2)) Guard-cell SV-type channels are weakly selective for cations over anions and lack saturation at KCl concentrations of up to 1 M. Since in the absence of physiological K+ concentrations, Ca2+ is the major permeable ion, relative changes in the amounts of the two ions might control the permeation process. In spite of their different origins and physiological functions, in guard cells and beet taproot cells, cytoplasmic Ca2+ and protons, both considered as candidates for intracellular signalling in plants, modulate the voltage dependence of SV-type channels. While the two effecters do not alter the single-channel conductance, they strongly interact with the voltage sensor. The calmodulin (CaM) antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), trifluoperazine (TFP) and calmidazolium hydrochloride (R 24571) effectively blocked the channel in an antagonist-specific manner. In agreement with the properties of a Ca2+-permeable channel, CaM could be involved in the modulation of the activation threshold of the SV-type channel. We therefore conclude that guard-cell SV-type channels, which might be responsible for the release of K+, Cl- and to a smaller extent Ca2+ during stomatal closure, could serve as an intracellular sensor for changes in cytosolic calcium (calcium-CaM) and pH.
• Anions Modify the Response of Guard-Cell Anion Channels to Auxin. Lohse, G.; Hedrich, R. In Planta, 197(3), pp. 546–552. 1995.
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  The anion channel in the guard-cell plasma membrane of Vicia faba, GCAC1, possesses recognition sites for the plant growth hormone auxin at the extracellular mouth of the channel (Marten et al. 1991, Nature 353:759-762). Using the patch-clamp technique we could demonstrate that auxins induced a shift of the voltage dependence of the anion channel to hyperpolarized potentials; the shift was attenuated during an increase in the extracellular chloride concentration, indicating that chloride shields the hormone-binding site. The auxin-induced shift was concentration-dependent, characterized by a Michaelis-Menten type of behaviour with a half-saturation constant (K-m) of about 10 mu M naphthalene-1-acetic acid (1-NAA) in the presence of 2 mM Cl- and 12 mu M in 80 mM Cl-. In the presence of malate, another gating modulator of GCAC1, auxins were less effective, indicating that both ligands compete for common sites. Inactive auxins with respect to stomatal opening or stimulation of the plasma membrane H+-ATPase, such as 2-NAA, modulated the activation threshold and kinetics of GCAC1 similar to the active form 1-NAA. At a concentration of 100 mu M 2-NAA the peak-current potential shifted by about 30 mV more negative.

  @article{RN1261, abstract = {The anion channel in the guard-cell plasma membrane of Vicia faba, GCAC1, possesses recognition sites for the plant growth hormone auxin at the extracellular mouth of the channel (Marten et al. 1991, Nature 353:759-762). Using the patch-clamp technique we could demonstrate that auxins induced a shift of the voltage dependence of the anion channel to hyperpolarized potentials; the shift was attenuated during an increase in the extracellular chloride concentration, indicating that chloride shields the hormone-binding site. The auxin-induced shift was concentration-dependent, characterized by a Michaelis-Menten type of behaviour with a half-saturation constant (K-m) of about 10 mu M naphthalene-1-acetic acid (1-NAA) in the presence of 2 mM Cl- and 12 mu M in 80 mM Cl-. In the presence of malate, another gating modulator of GCAC1, auxins were less effective, indicating that both ligands compete for common sites. Inactive auxins with respect to stomatal opening or stimulation of the plasma membrane H+-ATPase, such as 2-NAA, modulated the activation threshold and kinetics of GCAC1 similar to the active form 1-NAA. At a concentration of 100 mu M 2-NAA the peak-current potential shifted by about 30 mV more negative.}, author = {Lohse, G. and Hedrich, R.}, journal = {Planta}, keywords = {auxin}, note = {Te428 Times Cited:29 Cited References Count:30}, number = 3, pages = {546-552}, title = {Anions Modify the Response of Guard-Cell Anion Channels to Auxin}, type = {Journal Article}, volume = 197, year = 1995 }

  %0 Journal Article %1 RN1261 %A Lohse, G. %A Hedrich, R. %D 1995 %J Planta %N 3 %P 546-552 %T Anions Modify the Response of Guard-Cell Anion Channels to Auxin %U /brokenurl#<Go to ISI>://WOS:A1995TE42800015 %V 197 %X The anion channel in the guard-cell plasma membrane of Vicia faba, GCAC1, possesses recognition sites for the plant growth hormone auxin at the extracellular mouth of the channel (Marten et al. 1991, Nature 353:759-762). Using the patch-clamp technique we could demonstrate that auxins induced a shift of the voltage dependence of the anion channel to hyperpolarized potentials; the shift was attenuated during an increase in the extracellular chloride concentration, indicating that chloride shields the hormone-binding site. The auxin-induced shift was concentration-dependent, characterized by a Michaelis-Menten type of behaviour with a half-saturation constant (K-m) of about 10 mu M naphthalene-1-acetic acid (1-NAA) in the presence of 2 mM Cl- and 12 mu M in 80 mM Cl-. In the presence of malate, another gating modulator of GCAC1, auxins were less effective, indicating that both ligands compete for common sites. Inactive auxins with respect to stomatal opening or stimulation of the plasma membrane H+-ATPase, such as 2-NAA, modulated the activation threshold and kinetics of GCAC1 similar to the active form 1-NAA. At a concentration of 100 mu M 2-NAA the peak-current potential shifted by about 30 mV more negative.

• Interconversion of Fast and Slow Gating Modes of Gcac1, a Guard-Cell Anion Channel. Dietrich, P.; Hedrich, R. In Planta, 195(2), pp. 301–304. 1994.
  • [ Abstract ]
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  For guard-cell protoplasts of Vicia faba L. we elucidated whether the slow (S-type) and rapid (R-type) activating anion channels represent different gating modes of GCAC1, the Guard Cell Anion Channel. in the whole-cell configuration of the patch-clamp technique, GCAC1 was activated in a Ca2+- and nucleotide-dependent manner. Cell-free outside-out membrane patches were isolated to determine the relative contribution of different gating modes or channel types to the overall anion current in this cell type. Within 2-15 min after the loss of cytoplasmic control through patch excision, depolarization-activated 38-pS channels characterized by flickering openings in the millisecond range convert into a channel of similar conductance but prolonged open times (hundreds of milliseconds) and lack of pronounced voltage-dependence. The rapid (R-type) and slow (S-type) gating modes exhibited similar ion selectivity but different susceptibility towards block by the stilbene derivative DNDS (4,4'-dinitrostilbene-2,2'-disulfonic acid). On R-type channels DNDS caused a flickering block and a shift in the threshold potential of activation whereas S-type channels remained unaffected. Because of the striking similarities of both channels with respect to single-channel conductance and relative permeability sequence on the one hand, but time-dependent conversion of R- into S-type gating after patch-excision on the other, we conclude that the mode of action of GCAC1 is under the control of cytoplasmic factors.

  @article{RN1266, abstract = {For guard-cell protoplasts of Vicia faba L. we elucidated whether the slow (S-type) and rapid (R-type) activating anion channels represent different gating modes of GCAC1, the Guard Cell Anion Channel. in the whole-cell configuration of the patch-clamp technique, GCAC1 was activated in a Ca2+- and nucleotide-dependent manner. Cell-free outside-out membrane patches were isolated to determine the relative contribution of different gating modes or channel types to the overall anion current in this cell type. Within 2-15 min after the loss of cytoplasmic control through patch excision, depolarization-activated 38-pS channels characterized by flickering openings in the millisecond range convert into a channel of similar conductance but prolonged open times (hundreds of milliseconds) and lack of pronounced voltage-dependence. The rapid (R-type) and slow (S-type) gating modes exhibited similar ion selectivity but different susceptibility towards block by the stilbene derivative DNDS (4,4'-dinitrostilbene-2,2'-disulfonic acid). On R-type channels DNDS caused a flickering block and a shift in the threshold potential of activation whereas S-type channels remained unaffected. Because of the striking similarities of both channels with respect to single-channel conductance and relative permeability sequence on the one hand, but time-dependent conversion of R- into S-type gating after patch-excision on the other, we conclude that the mode of action of GCAC1 is under the control of cytoplasmic factors.}, author = {Dietrich, P. and Hedrich, R.}, journal = {Planta}, keywords = {channels}, note = {Py377 Times Cited:36 Cited References Count:16}, number = 2, pages = {301-304}, title = {Interconversion of Fast and Slow Gating Modes of Gcac1, a Guard-Cell Anion Channel}, type = {Journal Article}, volume = 195, year = 1994 }

  %0 Journal Article %1 RN1266 %A Dietrich, P. %A Hedrich, R. %D 1994 %J Planta %N 2 %P 301-304 %T Interconversion of Fast and Slow Gating Modes of Gcac1, a Guard-Cell Anion Channel %U /brokenurl#<Go to ISI>://WOS:A1994PY37700017 %V 195 %X For guard-cell protoplasts of Vicia faba L. we elucidated whether the slow (S-type) and rapid (R-type) activating anion channels represent different gating modes of GCAC1, the Guard Cell Anion Channel. in the whole-cell configuration of the patch-clamp technique, GCAC1 was activated in a Ca2+- and nucleotide-dependent manner. Cell-free outside-out membrane patches were isolated to determine the relative contribution of different gating modes or channel types to the overall anion current in this cell type. Within 2-15 min after the loss of cytoplasmic control through patch excision, depolarization-activated 38-pS channels characterized by flickering openings in the millisecond range convert into a channel of similar conductance but prolonged open times (hundreds of milliseconds) and lack of pronounced voltage-dependence. The rapid (R-type) and slow (S-type) gating modes exhibited similar ion selectivity but different susceptibility towards block by the stilbene derivative DNDS (4,4'-dinitrostilbene-2,2'-disulfonic acid). On R-type channels DNDS caused a flickering block and a shift in the threshold potential of activation whereas S-type channels remained unaffected. Because of the striking similarities of both channels with respect to single-channel conductance and relative permeability sequence on the one hand, but time-dependent conversion of R- into S-type gating after patch-excision on the other, we conclude that the mode of action of GCAC1 is under the control of cytoplasmic factors.
• Green Circuits - the Potential of Plant Specific Ion Channels. Hedrich, R.; Becker, D. In Plant Molecular Biology, 26(5), pp. 1637–1650. 1994.
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  @article{RN1267, author = {Hedrich, R. and Becker, D.}, journal = {Plant Molecular Biology}, keywords = {protoplasts}, note = {Qh874 Times Cited:60 Cited References Count:108}, number = 5, pages = {1637-1650}, title = {Green Circuits - the Potential of Plant Specific Ion Channels}, type = {Journal Article}, volume = 26, year = 1994 }

  %0 Journal Article %1 RN1267 %A Hedrich, R. %A Becker, D. %D 1994 %J Plant Molecular Biology %N 5 %P 1637-1650 %R Doi 10.1007/Bf00016494 %T Green Circuits - the Potential of Plant Specific Ion Channels %U /brokenurl#<Go to ISI>://WOS:A1994QH87400023 %V 26
• Malate-Sensitive Anion Channels Enable Guard-Cells to Sense Changes in the Ambient Co2 Concentration. Hedrich, R.; Marten, I.; Lohse, G.; Dietrich, P.; Winter, H.; Lohaus, G.; Heldt, H. W. In Plant Journal, 6(5), pp. 741–748. 1994.
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  Malate is a characteristic metabolite in the photosynthesis of C4 and CAM plants. Furthermore, changes in the intracellular concentration of this organic acid provide part of the osmotic motor for guard cells. Since alterations in the malate concentration influence the photosynthetic capacity on one side and stomatal action on the other, it was studied whether the extracellular malate level represents an indicator of changes in the ambient CO2 concentration and a key regulator of ion transport in guard cells. Here it is demonstrated that alterations in the ambient CO2 level modify the extracellular malate concentration of Vicia faba leaves. Elevated external malate caused stomatal closure in a concentration-dependent manner (K-m(mal) = 0.3 mM). Slight variations in the external malate concentration strongly regulate the voltage-dependent properties of GCAC1, an anion-release channel in the plasma membrane of guard cells. Superfusion of guard cell protoplasts with malate levels in the physiological range (K-m(mal) = 0.4 mM) caused the voltage gate to shift towards the resting potential of the cell-activating GCAC1. Single-channel conductance was dependent on the extracellular chloride concentration (K-m(Cl) = 3 mM). In the absence of extracellular chloride the plasma membrane lacked anion conductance until the addition of malate induced channel opening. Isophthalate was a powerful agonist in both malate-induced processes, channel regulation and stomatal closure, indicating that modulation of GCAC1 is a key step in stomatal action. It was thus concluded that feedback regulation of volume and turgor with respect to the ambient CO2 concentration via malate-sensitive anion channels may provide a CO2 sensor to guard cells.

  @article{RN1283, abstract = {Malate is a characteristic metabolite in the photosynthesis of C4 and CAM plants. Furthermore, changes in the intracellular concentration of this organic acid provide part of the osmotic motor for guard cells. Since alterations in the malate concentration influence the photosynthetic capacity on one side and stomatal action on the other, it was studied whether the extracellular malate level represents an indicator of changes in the ambient CO2 concentration and a key regulator of ion transport in guard cells. Here it is demonstrated that alterations in the ambient CO2 level modify the extracellular malate concentration of Vicia faba leaves. Elevated external malate caused stomatal closure in a concentration-dependent manner (K-m(mal) = 0.3 mM). Slight variations in the external malate concentration strongly regulate the voltage-dependent properties of GCAC1, an anion-release channel in the plasma membrane of guard cells. Superfusion of guard cell protoplasts with malate levels in the physiological range (K-m(mal) = 0.4 mM) caused the voltage gate to shift towards the resting potential of the cell-activating GCAC1. Single-channel conductance was dependent on the extracellular chloride concentration (K-m(Cl) = 3 mM). In the absence of extracellular chloride the plasma membrane lacked anion conductance until the addition of malate induced channel opening. Isophthalate was a powerful agonist in both malate-induced processes, channel regulation and stomatal closure, indicating that modulation of GCAC1 is a key step in stomatal action. It was thus concluded that feedback regulation of volume and turgor with respect to the ambient CO2 concentration via malate-sensitive anion channels may provide a CO2 sensor to guard cells.}, author = {Hedrich, R. and Marten, I. and Lohse, G. and Dietrich, P. and Winter, H. and Lohaus, G. and Heldt, H. W.}, journal = {Plant Journal}, keywords = {myOwn}, note = {Pq144 Times Cited:126 Cited References Count:31}, number = 5, pages = {741-748}, title = {Malate-Sensitive Anion Channels Enable Guard-Cells to Sense Changes in the Ambient Co2 Concentration}, type = {Journal Article}, volume = 6, year = 1994 }

  %0 Journal Article %1 RN1283 %A Hedrich, R. %A Marten, I. %A Lohse, G. %A Dietrich, P. %A Winter, H. %A Lohaus, G. %A Heldt, H. W. %D 1994 %J Plant Journal %N 5 %P 741-748 %R DOI 10.1046/j.1365-313X.1994.6050741.x %T Malate-Sensitive Anion Channels Enable Guard-Cells to Sense Changes in the Ambient Co2 Concentration %U /brokenurl#<Go to ISI>://WOS:A1994PQ14400011 %V 6 %X Malate is a characteristic metabolite in the photosynthesis of C4 and CAM plants. Furthermore, changes in the intracellular concentration of this organic acid provide part of the osmotic motor for guard cells. Since alterations in the malate concentration influence the photosynthetic capacity on one side and stomatal action on the other, it was studied whether the extracellular malate level represents an indicator of changes in the ambient CO2 concentration and a key regulator of ion transport in guard cells. Here it is demonstrated that alterations in the ambient CO2 level modify the extracellular malate concentration of Vicia faba leaves. Elevated external malate caused stomatal closure in a concentration-dependent manner (K-m(mal) = 0.3 mM). Slight variations in the external malate concentration strongly regulate the voltage-dependent properties of GCAC1, an anion-release channel in the plasma membrane of guard cells. Superfusion of guard cell protoplasts with malate levels in the physiological range (K-m(mal) = 0.4 mM) caused the voltage gate to shift towards the resting potential of the cell-activating GCAC1. Single-channel conductance was dependent on the extracellular chloride concentration (K-m(Cl) = 3 mM). In the absence of extracellular chloride the plasma membrane lacked anion conductance until the addition of malate induced channel opening. Isophthalate was a powerful agonist in both malate-induced processes, channel regulation and stomatal closure, indicating that modulation of GCAC1 is a key step in stomatal action. It was thus concluded that feedback regulation of volume and turgor with respect to the ambient CO2 concentration via malate-sensitive anion channels may provide a CO2 sensor to guard cells.

• Identification and Biochemical-Characterization of the Plasma-Membrane H+-Atpase in Guard-Cells of Vicia-Faba L. Becker, D.; Zeilinger, C.; Lohse, G.; Depta, H.; Hedrich, R. In Planta, 190(1), pp. 44–50. 1993.
  • [ Abstract ]
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  The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysiological studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+-ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+ -pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.

  @article{RN1285, abstract = {The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysiological studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+-ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+ -pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.}, author = {Becker, D. and Zeilinger, C. and Lohse, G. and Depta, H. and Hedrich, R.}, journal = {Planta}, keywords = {cell}, note = {Ky173 Times Cited:47 Cited References Count:39}, number = 1, pages = {44-50}, title = {Identification and Biochemical-Characterization of the Plasma-Membrane H+-Atpase in Guard-Cells of Vicia-Faba L}, type = {Journal Article}, volume = 190, year = 1993 }

  %0 Journal Article %1 RN1285 %A Becker, D. %A Zeilinger, C. %A Lohse, G. %A Depta, H. %A Hedrich, R. %D 1993 %J Planta %N 1 %P 44-50 %T Identification and Biochemical-Characterization of the Plasma-Membrane H+-Atpase in Guard-Cells of Vicia-Faba L %U /brokenurl#<Go to ISI>://WOS:A1993KY17300006 %V 190 %X The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysiological studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+-ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+ -pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.
• Modulation and Block of the Plasma-Membrane Anion Channel of Guard-Cells by Stilbene Derivatives. Marten, I.; Busch, H.; Raschke, K.; Hedrich, R. In European Biophysics Journal with Biophysics Letters, 21(6), pp. 403–408. 1993.
  • [ Abstract ]
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  An anion channel in the plasma membrane of guard cells (GCAC1) provides a regulatory element for the voltage-dependent release of anions during stomatal closure (Keller et al. 1989) as well as excitability (Hedrich et al. 1990). Recognition sites for plant growth hormones on the extracellular surface of GCAC1 further indicate that this channel may also serve as a transduction element in hormone signaling (Marten et al. 1991 a). Stilbene derivatives were used to study the inhibitor-structure channel-function relationship of GCAC1. We have analyzed the activity, voltage-gate and kinetics of this channel as affected by stilbenes. The stilbene derivatives SITS and DNDS caused a shift in activation potential and a decrease in the peak current amplitude. Channel block through the action of DIDS, on the other hand, was not accompanied by a shift in voltage-dependence. Differences in the dose-dependence of the two effects give clues to the presence of channel sites responsible for gate-shifting and block. The ability to inhibit anion currents (K(d)) increased in the sequence: SITS (4 muM) < DNDS (0.5 muM) < DIDS (0.2 muM). All inhibitors reversibly blocked the anion channel from the extracellular side. Channel block on the level of single anion-channels is characterized by a reduction of long open-transitions into flickering bursts and a decrease in channel amplitude.

  @article{RN1286, abstract = {An anion channel in the plasma membrane of guard cells (GCAC1) provides a regulatory element for the voltage-dependent release of anions during stomatal closure (Keller et al. 1989) as well as excitability (Hedrich et al. 1990). Recognition sites for plant growth hormones on the extracellular surface of GCAC1 further indicate that this channel may also serve as a transduction element in hormone signaling (Marten et al. 1991 a). Stilbene derivatives were used to study the inhibitor-structure channel-function relationship of GCAC1. We have analyzed the activity, voltage-gate and kinetics of this channel as affected by stilbenes. The stilbene derivatives SITS and DNDS caused a shift in activation potential and a decrease in the peak current amplitude. Channel block through the action of DIDS, on the other hand, was not accompanied by a shift in voltage-dependence. Differences in the dose-dependence of the two effects give clues to the presence of channel sites responsible for gate-shifting and block. The ability to inhibit anion currents (K(d)) increased in the sequence: SITS (4 muM) < DNDS (0.5 muM) < DIDS (0.2 muM). All inhibitors reversibly blocked the anion channel from the extracellular side. Channel block on the level of single anion-channels is characterized by a reduction of long open-transitions into flickering bursts and a decrease in channel amplitude.}, author = {Marten, I. and Busch, H. and Raschke, K. and Hedrich, R.}, journal = {European Biophysics Journal with Biophysics Letters}, keywords = {channel}, note = {Km494 Times Cited:41 Cited References Count:24}, number = 6, pages = {403-408}, title = {Modulation and Block of the Plasma-Membrane Anion Channel of Guard-Cells by Stilbene Derivatives}, type = {Journal Article}, volume = 21, year = 1993 }

  %0 Journal Article %1 RN1286 %A Marten, I. %A Busch, H. %A Raschke, K. %A Hedrich, R. %D 1993 %J European Biophysics Journal with Biophysics Letters %N 6 %P 403-408 %T Modulation and Block of the Plasma-Membrane Anion Channel of Guard-Cells by Stilbene Derivatives %U /brokenurl#<Go to ISI>://WOS:A1993KM49400004 %V 21 %X An anion channel in the plasma membrane of guard cells (GCAC1) provides a regulatory element for the voltage-dependent release of anions during stomatal closure (Keller et al. 1989) as well as excitability (Hedrich et al. 1990). Recognition sites for plant growth hormones on the extracellular surface of GCAC1 further indicate that this channel may also serve as a transduction element in hormone signaling (Marten et al. 1991 a). Stilbene derivatives were used to study the inhibitor-structure channel-function relationship of GCAC1. We have analyzed the activity, voltage-gate and kinetics of this channel as affected by stilbenes. The stilbene derivatives SITS and DNDS caused a shift in activation potential and a decrease in the peak current amplitude. Channel block through the action of DIDS, on the other hand, was not accompanied by a shift in voltage-dependence. Differences in the dose-dependence of the two effects give clues to the presence of channel sites responsible for gate-shifting and block. The ability to inhibit anion currents (K(d)) increased in the sequence: SITS (4 muM) < DNDS (0.5 muM) < DIDS (0.2 muM). All inhibitors reversibly blocked the anion channel from the extracellular side. Channel block on the level of single anion-channels is characterized by a reduction of long open-transitions into flickering bursts and a decrease in channel amplitude.
• Osmocytosis and Vacuolar Fragmentation in Guard-Cell Protoplasts - Their Relevance to Osmotically-Induced Volume Changes in Guard-Cells. Diekmann, W.; Hedrich, R.; Raschke, K.; Robinson, D. G. In Journal of Experimental Botany, 44(267), pp. 1569–1577. 1993.
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  Guard cell protoplasts were prepared from young leaves of pea plants. Under hypertonic conditions they shrink and large numbers of endocytotic ('osmocytotic') vacuoles are formed by invagination of the plasma membrane. In thin section these are indistinguishable from other small vacuoles ('mini-vacuoles') which are formed by fragmentation of the large central vacuole. However, the two types of vacuole can be individually recognized by labelling the central vacuole with neutral red and by performing the osmotic shrinkage with fluorochromes such as Lucifer Yellow-CH or Cascade Blue present in the extracellular medium. Osmocytotic vacuoles do not fuse with the plasma membrane nor with the mini-vacuoles during a subsequent swelling phase. After several hours, osmocytosed Lucifer Yellow gradually leaks out of the endocytotic vacuoles when protoplasts are returned to hypotonic conditions. This leakage is not prevented by probenecid at concentrations (20-50 mmol m-3) which do not give rise to pathological changes in protoplast ultrastructure. In order to determine the relevance of these observations to the situation in planta, intact guard cells in epidermal strips were first allowed to accumulate neutral red in their vacuoles and then subjected to osmotic shrinkage in the presence of external Lucifer Yellow. Osmocytotic vacuoles were not formed, although the production of mini-vacuoles was frequently observed.

  @article{RN1284, abstract = {Guard cell protoplasts were prepared from young leaves of pea plants. Under hypertonic conditions they shrink and large numbers of endocytotic ('osmocytotic') vacuoles are formed by invagination of the plasma membrane. In thin section these are indistinguishable from other small vacuoles ('mini-vacuoles') which are formed by fragmentation of the large central vacuole. However, the two types of vacuole can be individually recognized by labelling the central vacuole with neutral red and by performing the osmotic shrinkage with fluorochromes such as Lucifer Yellow-CH or Cascade Blue present in the extracellular medium. Osmocytotic vacuoles do not fuse with the plasma membrane nor with the mini-vacuoles during a subsequent swelling phase. After several hours, osmocytosed Lucifer Yellow gradually leaks out of the endocytotic vacuoles when protoplasts are returned to hypotonic conditions. This leakage is not prevented by probenecid at concentrations (20-50 mmol m-3) which do not give rise to pathological changes in protoplast ultrastructure. In order to determine the relevance of these observations to the situation in planta, intact guard cells in epidermal strips were first allowed to accumulate neutral red in their vacuoles and then subjected to osmotic shrinkage in the presence of external Lucifer Yellow. Osmocytotic vacuoles were not formed, although the production of mini-vacuoles was frequently observed.}, author = {Diekmann, W. and Hedrich, R. and Raschke, K. and Robinson, D. G.}, journal = {Journal of Experimental Botany}, keywords = {cell}, note = {Mf242 Times Cited:31 Cited References Count:27}, number = 267, pages = {1569-1577}, title = {Osmocytosis and Vacuolar Fragmentation in Guard-Cell Protoplasts - Their Relevance to Osmotically-Induced Volume Changes in Guard-Cells}, type = {Journal Article}, volume = 44, year = 1993 }

  %0 Journal Article %1 RN1284 %A Diekmann, W. %A Hedrich, R. %A Raschke, K. %A Robinson, D. G. %D 1993 %J Journal of Experimental Botany %N 267 %P 1569-1577 %R DOI 10.1093/jxb/44.10.1569 %T Osmocytosis and Vacuolar Fragmentation in Guard-Cell Protoplasts - Their Relevance to Osmotically-Induced Volume Changes in Guard-Cells %U /brokenurl#<Go to ISI>://WOS:A1993MF24200006 %V 44 %X Guard cell protoplasts were prepared from young leaves of pea plants. Under hypertonic conditions they shrink and large numbers of endocytotic ('osmocytotic') vacuoles are formed by invagination of the plasma membrane. In thin section these are indistinguishable from other small vacuoles ('mini-vacuoles') which are formed by fragmentation of the large central vacuole. However, the two types of vacuole can be individually recognized by labelling the central vacuole with neutral red and by performing the osmotic shrinkage with fluorochromes such as Lucifer Yellow-CH or Cascade Blue present in the extracellular medium. Osmocytotic vacuoles do not fuse with the plasma membrane nor with the mini-vacuoles during a subsequent swelling phase. After several hours, osmocytosed Lucifer Yellow gradually leaks out of the endocytotic vacuoles when protoplasts are returned to hypotonic conditions. This leakage is not prevented by probenecid at concentrations (20-50 mmol m-3) which do not give rise to pathological changes in protoplast ultrastructure. In order to determine the relevance of these observations to the situation in planta, intact guard cells in epidermal strips were first allowed to accumulate neutral red in their vacuoles and then subjected to osmotic shrinkage in the presence of external Lucifer Yellow. Osmocytotic vacuoles were not formed, although the production of mini-vacuoles was frequently observed.

• Patch Clamp Techniques to Study Ion Channels from Organelles. Keller, B. U.; Hedrich, R. In Methods in Enzymology, 207, pp. 673–681. 1992.
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  @article{RN1288, author = {Keller, B. U. and Hedrich, R.}, journal = {Methods in Enzymology}, keywords = {channel}, note = {Jm500 Times Cited:7 Cited References Count:18}, pages = {673-681}, title = {Patch Clamp Techniques to Study Ion Channels from Organelles}, type = {Journal Article}, volume = 207, year = 1992 }

  %0 Journal Article %1 RN1288 %A Keller, B. U. %A Hedrich, R. %D 1992 %J Methods in Enzymology %P 673-681 %T Patch Clamp Techniques to Study Ion Channels from Organelles %U /brokenurl#<Go to ISI>://WOS:A1992JM50000046 %V 207
• Characterization of the Plasma-Membrane H+-Atpase from Vicia-Faba Guard-Cells - Modulation by Extracellular Factors and Seasonal-Changes. Lohse, G.; Hedrich, R. In Planta, 188(2), pp. 206–214. 1992.
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  Stomatal movement is controlled by external and internal signals such as light, phytohormones or cytoplasmic Ca2+. Using Vicia faba L., we have studied the dose-dependent effect of auxins on the modulation of stomatal opening, mediated through the activity of the plasma-membrane H+-ATPase. The patch-clamp technique was used to elucidate the electrical properties of the H+-ATPase as effected by growth regulators and seasonal changes. The solute composition of cytoplasmic and extracellular media was selected to record pump currents directly with high resolution. Proton currents through the ATPase were characterized by a voltage-dependent increase in amplitude, positive to the resting potential, reaching a plateau at more depolarized values. Upon changes in extracellular pH, the resting potential of the cell shifted with a non-Nernst potential response (+/- 21 mV), indicating the contribution of a depolarizing ionic conductance other than protons to the permeability of the plasma membrane. The use of selective inhibitors enabled us to identify the currents superimposing the H+-pump as carried by Ca2+. Auxin-stimulation of this electroenzyme resulted in a rise in the outwardly directed H+ current and membrane hyperpolarization, indicating that modulation of the ATPase by the hormone may precede salt accumulation as well as volume and turgor increase. Annual cycles in pump activity (1.5-3.8-mu-A . cm-2) were expressed by a minimum in pump current during January and February. Resting potentials of up to - 260 mV and plasma-membrane surface area, on the other hand, did not exhibit seasonal changes. The pump activity per unit surface area was approximately 2- to 3-fold higher in guard cells than in mesophyll cells and thus correlates with their physiological demands.

  @article{RN1287, abstract = {Stomatal movement is controlled by external and internal signals such as light, phytohormones or cytoplasmic Ca2+. Using Vicia faba L., we have studied the dose-dependent effect of auxins on the modulation of stomatal opening, mediated through the activity of the plasma-membrane H+-ATPase. The patch-clamp technique was used to elucidate the electrical properties of the H+-ATPase as effected by growth regulators and seasonal changes. The solute composition of cytoplasmic and extracellular media was selected to record pump currents directly with high resolution. Proton currents through the ATPase were characterized by a voltage-dependent increase in amplitude, positive to the resting potential, reaching a plateau at more depolarized values. Upon changes in extracellular pH, the resting potential of the cell shifted with a non-Nernst potential response (+/- 21 mV), indicating the contribution of a depolarizing ionic conductance other than protons to the permeability of the plasma membrane. The use of selective inhibitors enabled us to identify the currents superimposing the H+-pump as carried by Ca2+. Auxin-stimulation of this electroenzyme resulted in a rise in the outwardly directed H+ current and membrane hyperpolarization, indicating that modulation of the ATPase by the hormone may precede salt accumulation as well as volume and turgor increase. Annual cycles in pump activity (1.5-3.8-mu-A . cm-2) were expressed by a minimum in pump current during January and February. Resting potentials of up to - 260 mV and plasma-membrane surface area, on the other hand, did not exhibit seasonal changes. The pump activity per unit surface area was approximately 2- to 3-fold higher in guard cells than in mesophyll cells and thus correlates with their physiological demands.}, author = {Lohse, G. and Hedrich, R.}, journal = {Planta}, keywords = {auxin}, note = {Jl122 Times Cited:148 Cited References Count:34}, number = 2, pages = {206-214}, title = {Characterization of the Plasma-Membrane H+-Atpase from Vicia-Faba Guard-Cells - Modulation by Extracellular Factors and Seasonal-Changes}, type = {Journal Article}, volume = 188, year = 1992 }

  %0 Journal Article %1 RN1287 %A Lohse, G. %A Hedrich, R. %D 1992 %J Planta %N 2 %P 206-214 %R Doi 10.1007/Bf00216815 %T Characterization of the Plasma-Membrane H+-Atpase from Vicia-Faba Guard-Cells - Modulation by Extracellular Factors and Seasonal-Changes %U /brokenurl#<Go to ISI>://WOS:A1992JL12200008 %V 188 %X Stomatal movement is controlled by external and internal signals such as light, phytohormones or cytoplasmic Ca2+. Using Vicia faba L., we have studied the dose-dependent effect of auxins on the modulation of stomatal opening, mediated through the activity of the plasma-membrane H+-ATPase. The patch-clamp technique was used to elucidate the electrical properties of the H+-ATPase as effected by growth regulators and seasonal changes. The solute composition of cytoplasmic and extracellular media was selected to record pump currents directly with high resolution. Proton currents through the ATPase were characterized by a voltage-dependent increase in amplitude, positive to the resting potential, reaching a plateau at more depolarized values. Upon changes in extracellular pH, the resting potential of the cell shifted with a non-Nernst potential response (+/- 21 mV), indicating the contribution of a depolarizing ionic conductance other than protons to the permeability of the plasma membrane. The use of selective inhibitors enabled us to identify the currents superimposing the H+-pump as carried by Ca2+. Auxin-stimulation of this electroenzyme resulted in a rise in the outwardly directed H+ current and membrane hyperpolarization, indicating that modulation of the ATPase by the hormone may precede salt accumulation as well as volume and turgor increase. Annual cycles in pump activity (1.5-3.8-mu-A . cm-2) were expressed by a minimum in pump current during January and February. Resting potentials of up to - 260 mV and plasma-membrane surface area, on the other hand, did not exhibit seasonal changes. The pump activity per unit surface area was approximately 2- to 3-fold higher in guard cells than in mesophyll cells and thus correlates with their physiological demands.

• Stretch-Activated Chloride, Potassium, and Calcium Channels Coexisting in Plasma-Membranes of Guard-Cells of Vicia-Faba L. Cosgrove, D. J.; Hedrich, R. In Planta, 186(1), pp. 143–153. 1991.
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  Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl-, K+ and Ca2+ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.

  @article{RN1291, abstract = {Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl-, K+ and Ca2+ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.}, author = {Cosgrove, D. J. and Hedrich, R.}, journal = {Planta}, keywords = {cell}, note = {Gv367 Times Cited:273 Cited References Count:34}, number = 1, pages = {143-153}, title = {Stretch-Activated Chloride, Potassium, and Calcium Channels Coexisting in Plasma-Membranes of Guard-Cells of Vicia-Faba L}, type = {Journal Article}, volume = 186, year = 1991 }

  %0 Journal Article %1 RN1291 %A Cosgrove, D. J. %A Hedrich, R. %D 1991 %J Planta %N 1 %P 143-153 %T Stretch-Activated Chloride, Potassium, and Calcium Channels Coexisting in Plasma-Membranes of Guard-Cells of Vicia-Faba L %U /brokenurl#<Go to ISI>://WOS:A1991GV36700020 %V 186 %X Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl-, K+ and Ca2+ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.
• Vacuolar Lucifer Yellow Uptake in Plants - Endocytosis or Anion Transport - a Critical Opinion. Robinson, D. G.; Hedrich, R. In Botanica Acta, 104(4), pp. 257–264. 1991.
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  Because of its membrane-impermeant-properties Lucifer Yellow-CH (LY) is regarded by animal cell biologists as an ideal tracer for fluid-phase endocytosis. When presented to plant cells or protoplasts this fluoroprobe accumulates in the vacuole. On the other hand there are many cases where LY does not enter the vacuole when loaded into the plant cytosol. These, superficially divergent, results have previously been explained in terms of endocytosis whereby access to the vacuole is considered to occur through vesicle transport. This interpretation has now been challenged in three recent papers where the benzoic acid derivative, probenecid, has been shown to prevent vacuolar LY accumulation in plants. Since probenecid is a well-known inhibitor of organic anion transport in animal cells it has been argued that anion carriers capable of transporting LY might also exist at the plasma membrane and tonoplast of plant cells. Unfortunately probenecid has rarely, if ever, been used in plant transport studies. The fact that it is a weak acid, whose inhibitory effects are observed at concentrations of around 1 mM suggests that caution should prevail when interpreting results obtained with probenecid. The purpose of this article is therefore to highlight the current controversy surrounding LY uptake by plants and to critically evaluate the recent probenecid data.

  @article{RN1290, abstract = {Because of its membrane-impermeant-properties Lucifer Yellow-CH (LY) is regarded by animal cell biologists as an ideal tracer for fluid-phase endocytosis. When presented to plant cells or protoplasts this fluoroprobe accumulates in the vacuole. On the other hand there are many cases where LY does not enter the vacuole when loaded into the plant cytosol. These, superficially divergent, results have previously been explained in terms of endocytosis whereby access to the vacuole is considered to occur through vesicle transport. This interpretation has now been challenged in three recent papers where the benzoic acid derivative, probenecid, has been shown to prevent vacuolar LY accumulation in plants. Since probenecid is a well-known inhibitor of organic anion transport in animal cells it has been argued that anion carriers capable of transporting LY might also exist at the plasma membrane and tonoplast of plant cells. Unfortunately probenecid has rarely, if ever, been used in plant transport studies. The fact that it is a weak acid, whose inhibitory effects are observed at concentrations of around 1 mM suggests that caution should prevail when interpreting results obtained with probenecid. The purpose of this article is therefore to highlight the current controversy surrounding LY uptake by plants and to critically evaluate the recent probenecid data.}, author = {Robinson, D. G. and Hedrich, R.}, journal = {Botanica Acta}, keywords = {carriers}, note = {Gj305 Times Cited:13 Cited References Count:81}, number = 4, pages = {257-264}, title = {Vacuolar Lucifer Yellow Uptake in Plants - Endocytosis or Anion Transport - a Critical Opinion}, type = {Journal Article}, volume = 104, year = 1991 }

  %0 Journal Article %1 RN1290 %A Robinson, D. G. %A Hedrich, R. %D 1991 %J Botanica Acta %N 4 %P 257-264 %R DOI 10.1111/j.1438-8677.1991.tb00227.x %T Vacuolar Lucifer Yellow Uptake in Plants - Endocytosis or Anion Transport - a Critical Opinion %U /brokenurl#<Go to ISI>://WOS:A1991GJ30500001 %V 104 %X Because of its membrane-impermeant-properties Lucifer Yellow-CH (LY) is regarded by animal cell biologists as an ideal tracer for fluid-phase endocytosis. When presented to plant cells or protoplasts this fluoroprobe accumulates in the vacuole. On the other hand there are many cases where LY does not enter the vacuole when loaded into the plant cytosol. These, superficially divergent, results have previously been explained in terms of endocytosis whereby access to the vacuole is considered to occur through vesicle transport. This interpretation has now been challenged in three recent papers where the benzoic acid derivative, probenecid, has been shown to prevent vacuolar LY accumulation in plants. Since probenecid is a well-known inhibitor of organic anion transport in animal cells it has been argued that anion carriers capable of transporting LY might also exist at the plasma membrane and tonoplast of plant cells. Unfortunately probenecid has rarely, if ever, been used in plant transport studies. The fact that it is a weak acid, whose inhibitory effects are observed at concentrations of around 1 mM suggests that caution should prevail when interpreting results obtained with probenecid. The purpose of this article is therefore to highlight the current controversy surrounding LY uptake by plants and to critically evaluate the recent probenecid data.
• Plant-Growth Hormones Control Voltage-Dependent Activity of Anion Channels in Plasma-Membrane of Guard-Cells. Marten, I.; Lohse, G.; Hedrich, R. In Nature, 353(6346), pp. 758–762. 1991.
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  THE opening of stomatal pores in the epidermis of plant leaves is caused by an increase in turgor pressure of the guard cells as a result of the accumulation of potassium salts 1,2. Although growth hormones have been shown to affect stomatal opening 3, the transduction pathways by which growth regulators exert their effects on stomatal action are largely unknown. Here we report that auxins can elicit stomatal opening. These phytohormones modulate anion channels 4,5 in the plasma membrane in what may be an initial step in regulated volume increase in guard cells. Our patch-clamp experiments demonstrate that auxins can directly interact with the extracellular face of the channel. As a result, its activation potential is shifted towards the resting potential of the cell to favour transient channel opening.

  @article{RN1289, abstract = {THE opening of stomatal pores in the epidermis of plant leaves is caused by an increase in turgor pressure of the guard cells as a result of the accumulation of potassium salts 1,2. Although growth hormones have been shown to affect stomatal opening 3, the transduction pathways by which growth regulators exert their effects on stomatal action are largely unknown. Here we report that auxins can elicit stomatal opening. These phytohormones modulate anion channels 4,5 in the plasma membrane in what may be an initial step in regulated volume increase in guard cells. Our patch-clamp experiments demonstrate that auxins can directly interact with the extracellular face of the channel. As a result, its activation potential is shifted towards the resting potential of the cell to favour transient channel opening.}, author = {Marten, I. and Lohse, G. and Hedrich, R.}, journal = {Nature}, keywords = {protoplasts}, note = {Gl696 Times Cited:140 Cited References Count:17}, number = 6346, pages = {758-762}, title = {Plant-Growth Hormones Control Voltage-Dependent Activity of Anion Channels in Plasma-Membrane of Guard-Cells}, type = {Journal Article}, volume = 353, year = 1991 }

  %0 Journal Article %1 RN1289 %A Marten, I. %A Lohse, G. %A Hedrich, R. %D 1991 %J Nature %N 6346 %P 758-762 %R DOI 10.1038/353758a0 %T Plant-Growth Hormones Control Voltage-Dependent Activity of Anion Channels in Plasma-Membrane of Guard-Cells %U /brokenurl#<Go to ISI>://WOS:A1991GL69600070 %V 353 %X THE opening of stomatal pores in the epidermis of plant leaves is caused by an increase in turgor pressure of the guard cells as a result of the accumulation of potassium salts 1,2. Although growth hormones have been shown to affect stomatal opening 3, the transduction pathways by which growth regulators exert their effects on stomatal action are largely unknown. Here we report that auxins can elicit stomatal opening. These phytohormones modulate anion channels 4,5 in the plasma membrane in what may be an initial step in regulated volume increase in guard cells. Our patch-clamp experiments demonstrate that auxins can directly interact with the extracellular face of the channel. As a result, its activation potential is shifted towards the resting potential of the cell to favour transient channel opening.

• Ca-2+ and Nucleotide Dependent Regulation of Voltage Dependent Anion Channels in the Plasma-Membrane of Guard-Cells. Hedrich, R.; Busch, H.; Raschke, K. In Embo Journal, 9(12), pp. 3889–3892. 1990.
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  @article{RN1292, author = {Hedrich, R. and Busch, H. and Raschke, K.}, journal = {Embo Journal}, keywords = {myOwn}, note = {Ek538 Times Cited:287 Cited References Count:19}, number = 12, pages = {3889-3892}, title = {Ca-2+ and Nucleotide Dependent Regulation of Voltage Dependent Anion Channels in the Plasma-Membrane of Guard-Cells}, type = {Journal Article}, volume = 9, year = 1990 }

  %0 Journal Article %1 RN1292 %A Hedrich, R. %A Busch, H. %A Raschke, K. %D 1990 %J Embo Journal %N 12 %P 3889-3892 %R DOI 10.1002/j.1460-2075.1990.tb07608.x %T Ca-2+ and Nucleotide Dependent Regulation of Voltage Dependent Anion Channels in the Plasma-Membrane of Guard-Cells %U /brokenurl#<Go to ISI>://WOS:A1990EK53800011 %V 9