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• Reyer, A., Bazihizina, N., Jaślan, J., Scherzer, S., Schäfer, N., Jaślan, D., Becker, D., Müller, T.D., Pommerrenig, B., Neuhaus, H.E., Marten, I., und Hedrich, R. (2024) „Sugar beet PMT5a and STP13 carriers suitable for proton‐driven plasma membrane sucrose and glucose import in taproots“, The Plant Journal, verfügbar unter: https://doi.org/10.1111/tpj.16740.
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  @article{Reyer_2024, author = {Reyer, Antonella and Bazihizina, Nadia and Jaślan, Justyna and Scherzer, Sönke and Schäfer, Nadine and Jaślan, Dawid and Becker, Dirk and Müller, Thomas D. and Pommerrenig, Benjamin and Neuhaus, H. Ekkehard and Marten, Irene and Hedrich, Rainer}, journal = {The Plant Journal}, keywords = {imported}, month = {04}, publisher = {Wiley}, title = {Sugar beet <scp>PMT5a</scp> and <scp>STP13</scp> carriers suitable for proton‐driven plasma membrane sucrose and glucose import in taproots}, year = 2024 }

  %0 Journal Article %1 Reyer_2024 %A Reyer, Antonella %A Bazihizina, Nadia %A Jaślan, Justyna %A Scherzer, Sönke %A Schäfer, Nadine %A Jaślan, Dawid %A Becker, Dirk %A Müller, Thomas D. %A Pommerrenig, Benjamin %A Neuhaus, H. Ekkehard %A Marten, Irene %A Hedrich, Rainer %D 2024 %I Wiley %J The Plant Journal %R 10.1111/tpj.16740 %T Sugar beet <scp>PMT5a</scp> and <scp>STP13</scp> carriers suitable for proton‐driven plasma membrane sucrose and glucose import in taproots %U http://dx.doi.org/10.1111/tpj.16740

• Lu, J., Dreyer, I., Dickinson, M.S., Panzer, S., Jaślan, D., Navarro-Retamal, C., Geiger, D., Terpitz, U., Becker, D., Stroud, R.M., Marten, I., und Hedrich, R. (2023) „Vicia faba SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels“, eLife, 12, e86384-, verfügbar unter: https://doi.org/10.7554/eLife.86384.
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  To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca(2+). In our search for species-dependent functional TPC1 channel variants with different luminal Ca(2+) sensitivity, we found in total three acidic residues present in Ca(2+) sensor sites 2 and 3 of the Ca(2+)-sensitive AtTPC1 channel from Arabidopsis thaliana that were neutral in its Vicia faba ortholog and also in those of many other Fabaceae. When expressed in the Arabidopsis AtTPC1-loss-of-function background, wild-type VfTPC1 was hypersensitive to vacuole depolarization and only weakly sensitive to blocking luminal Ca(2+). When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca(2+) sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca(2+) sensitivity that together rendered vacuoles hyperexcitable. Thus, natural TPC1 channel variants exist in plant families which may fine-tune vacuole excitability and adapt it to environmental settings of the particular ecological niche.

  @article{lu2023vicia, abstract = {To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca(2+). In our search for species-dependent functional TPC1 channel variants with different luminal Ca(2+) sensitivity, we found in total three acidic residues present in Ca(2+) sensor sites 2 and 3 of the Ca(2+)-sensitive AtTPC1 channel from Arabidopsis thaliana that were neutral in its Vicia faba ortholog and also in those of many other Fabaceae. When expressed in the Arabidopsis AtTPC1-loss-of-function background, wild-type VfTPC1 was hypersensitive to vacuole depolarization and only weakly sensitive to blocking luminal Ca(2+). When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca(2+) sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca(2+) sensitivity that together rendered vacuoles hyperexcitable. Thus, natural TPC1 channel variants exist in plant families which may fine-tune vacuole excitability and adapt it to environmental settings of the particular ecological niche.}, address = {England}, author = {Lu, Jinping and Dreyer, Ingo and Dickinson, Miles Sasha and Panzer, Sabine and Jaślan, Dawid and Navarro-Retamal, Carlos and Geiger, Dietmar and Terpitz, Ulrich and Becker, Dirk and Stroud, Robert M and Marten, Irene and Hedrich, Rainer}, journal = {eLife}, keywords = {imported}, month = 11, pages = {e86384–}, title = {Vicia faba SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels}, volume = 12, year = 2023 }

  %0 Journal Article %1 lu2023vicia %A Lu, Jinping %A Dreyer, Ingo %A Dickinson, Miles Sasha %A Panzer, Sabine %A Jaślan, Dawid %A Navarro-Retamal, Carlos %A Geiger, Dietmar %A Terpitz, Ulrich %A Becker, Dirk %A Stroud, Robert M %A Marten, Irene %A Hedrich, Rainer %C England %D 2023 %J eLife %P e86384-- %R 10.7554/eLife.86384 %T Vicia faba SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels %U https://pubmed.ncbi.nlm.nih.gov/37991833 %V 12 %X To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca(2+). In our search for species-dependent functional TPC1 channel variants with different luminal Ca(2+) sensitivity, we found in total three acidic residues present in Ca(2+) sensor sites 2 and 3 of the Ca(2+)-sensitive AtTPC1 channel from Arabidopsis thaliana that were neutral in its Vicia faba ortholog and also in those of many other Fabaceae. When expressed in the Arabidopsis AtTPC1-loss-of-function background, wild-type VfTPC1 was hypersensitive to vacuole depolarization and only weakly sensitive to blocking luminal Ca(2+). When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca(2+) sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca(2+) sensitivity that together rendered vacuoles hyperexcitable. Thus, natural TPC1 channel variants exist in plant families which may fine-tune vacuole excitability and adapt it to environmental settings of the particular ecological niche.
• Jaślan, J., Marten, I., Jakobson, L., Arjus, T., Deeken, R., Sarmiento, C., De Angeli, A., Brosché, M., Kollist, H., und Hedrich, R. (2023) „ALMT-independent guard cell R-type anion currents“, The New phytologist, 239(6), 2225–2234, verfügbar unter: https://doi.org/10.1111/nph.19124.
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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, CO(2) -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{jaslan2023almtindependent, 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, CO(2) -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.}, address = {England}, author = {Jaślan, Justyna and Marten, Irene and Jakobson, Liina and Arjus, Triinu and Deeken, Rosalia and Sarmiento, Cecilia and De Angeli, Alexis and Brosché, Mikael and Kollist, Hannes and Hedrich, Rainer}, journal = {The New phytologist}, keywords = {imported}, month = {09}, number = 6, pages = {2225–2234}, title = {ALMT-independent guard cell R-type anion currents}, volume = 239, year = 2023 }

  %0 Journal Article %1 jaslan2023almtindependent %A Jaślan, Justyna %A Marten, Irene %A Jakobson, Liina %A Arjus, Triinu %A Deeken, Rosalia %A Sarmiento, Cecilia %A De Angeli, Alexis %A Brosché, Mikael %A Kollist, Hannes %A Hedrich, Rainer %C England %D 2023 %J The New phytologist %N 6 %P 2225--2234 %R 10.1111/nph.19124 %T ALMT-independent guard cell R-type anion currents %U https://pubmed.ncbi.nlm.nih.gov/37434346 %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, CO(2) -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.
• Hedrich, R., Müller, T.D., Marten, I., und Becker, D. (2023) „TPC1 vacuole SV channel gains further shape - voltage priming of calcium-dependent gating“, Trends in plant science, 28(6), 673–684, verfügbar unter: https://doi.org/10.1016/j.tplants.2023.01.001.
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  Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation. Two independent reports on the structure of a partially opened AtTPC1 channel protein have led to working models that offer promising insights into the molecular switches associated with the gating process. We review new structure-function models and also discuss the evolutionary impact of two-pore channels (TPCs) on K(+) homeostasis and vacuolar excitability.

  @article{hedrich2023vacuole, abstract = {Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation. Two independent reports on the structure of a partially opened AtTPC1 channel protein have led to working models that offer promising insights into the molecular switches associated with the gating process. We review new structure-function models and also discuss the evolutionary impact of two-pore channels (TPCs) on K(+) homeostasis and vacuolar excitability.}, address = {England}, author = {Hedrich, Rainer and Müller, Thomas D and Marten, Irene and Becker, Dirk}, journal = {Trends in plant science}, keywords = {imported}, month = {06}, number = 6, pages = {673–684}, title = {TPC1 vacuole SV channel gains further shape - voltage priming of calcium-dependent gating}, volume = 28, year = 2023 }

  %0 Journal Article %1 hedrich2023vacuole %A Hedrich, Rainer %A Müller, Thomas D %A Marten, Irene %A Becker, Dirk %C England %D 2023 %J Trends in plant science %N 6 %P 673--684 %R 10.1016/j.tplants.2023.01.001 %T TPC1 vacuole SV channel gains further shape - voltage priming of calcium-dependent gating %U https://pubmed.ncbi.nlm.nih.gov/36740491 %V 28 %X Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation. Two independent reports on the structure of a partially opened AtTPC1 channel protein have led to working models that offer promising insights into the molecular switches associated with the gating process. We review new structure-function models and also discuss the evolutionary impact of two-pore channels (TPCs) on K(+) homeostasis and vacuolar excitability.
• Graus, D., Li, K., Rathje, J.M., Ding, M., Krischke, M., Müller, M.J., Cuin, T.A., Al-Rasheid, K.A.S., Scherzer, S., Marten, I., Konrad, K.R., und Hedrich, R. (2023) „Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling“, The New phytologist, 237(1), 217–231, verfügbar unter: https://doi.org/10.1111/nph.18501.
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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 (Ca(2+) ) 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 Ca(2+) signaling.

  @article{graus2023tobacco, 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 (Ca(2+) ) 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 Ca(2+) signaling.}, address = {England}, author = {Graus, Dorothea and Li, Kunkun and Rathje, Jan M and Ding, Meiqi and Krischke, Markus and Müller, Martin J and Cuin, Tracey Ann and Al-Rasheid, Khaled A S and Scherzer, Sönke and Marten, Irene and Konrad, Kai R and Hedrich, Rainer}, journal = {The New phytologist}, keywords = {imported}, month = {01}, number = 1, pages = {217–231}, title = {Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling}, volume = 237, year = 2023 }

  %0 Journal Article %1 graus2023tobacco %A Graus, Dorothea %A Li, Kunkun %A Rathje, Jan M %A Ding, Meiqi %A Krischke, Markus %A Müller, Martin J %A Cuin, Tracey Ann %A Al-Rasheid, Khaled A S %A Scherzer, Sönke %A Marten, Irene %A Konrad, Kai R %A Hedrich, Rainer %C England %D 2023 %J The 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 https://pubmed.ncbi.nlm.nih.gov/36128659 %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 (Ca(2+) ) 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 Ca(2+) signaling.

• Dickinson, M.S., Lu, J., Gupta, M., Marten, I., Hedrich, R., und Stroud, R.M. (2022) „Molecular basis of multistep voltage activation in plant two-pore channel 1“, Proceedings of the National Academy of Sciences of the United States of America, 119(9), e2110936119-, verfügbar unter: https://doi.org/10.1073/pnas.2110936119.
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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 Ca(2+) 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{dickinson2022molecular, 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 Ca(2+) 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.}, address = {United States}, author = {Dickinson, Miles Sasha and Lu, Jinping and Gupta, Meghna and Marten, Irene and Hedrich, Rainer and Stroud, Robert M}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {imported}, month = {03}, number = 9, pages = {e2110936119–}, title = {Molecular basis of multistep voltage activation in plant two-pore channel 1}, volume = 119, year = 2022 }

  %0 Journal Article %1 dickinson2022molecular %A Dickinson, Miles Sasha %A Lu, Jinping %A Gupta, Meghna %A Marten, Irene %A Hedrich, Rainer %A Stroud, Robert M %C United States %D 2022 %J Proceedings of the National Academy of Sciences of the United States of America %N 9 %P e2110936119-- %R 10.1073/pnas.2110936119 %T Molecular basis of multistep voltage activation in plant two-pore channel 1 %U https://pubmed.ncbi.nlm.nih.gov/35210362 %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 Ca(2+) 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.

• Jaślan, D., Dreyer, I., Lu, J., O’Malley, R., Dindas, J., Marten, I., und Hedrich, R. (2019) „Voltage-dependent gating of SV channel TPC1 confers vacuole excitability“, Nature communications, 10(1), 2659–2659, verfügbar unter: https://doi.org/10.1038/s41467-019-10599-x.
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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 Ca(2+) levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca(2+), 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 Ca(2+)- and voltage-induced electrical excitability to the central organelle of plant cells.

  @article{jaslan2019voltagedependent, 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 Ca(2+) levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca(2+), 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 Ca(2+)- and voltage-induced electrical excitability to the central organelle of plant cells.}, address = {England}, author = {Jaślan, Dawid and Dreyer, Ingo and Lu, Jinping and O'Malley, Ronan and Dindas, Julian and Marten, Irene and Hedrich, Rainer}, journal = {Nature communications}, keywords = {imported}, month = {06}, number = 1, pages = {2659–2659}, title = {Voltage-dependent gating of SV channel TPC1 confers vacuole excitability}, volume = 10, year = 2019 }

  %0 Journal Article %1 jaslan2019voltagedependent %A Jaślan, Dawid %A Dreyer, Ingo %A Lu, Jinping %A O'Malley, Ronan %A Dindas, Julian %A Marten, Irene %A Hedrich, Rainer %C England %D 2019 %J Nature communications %N 1 %P 2659--2659 %R 10.1038/s41467-019-10599-x %T Voltage-dependent gating of SV channel TPC1 confers vacuole excitability %U https://pubmed.ncbi.nlm.nih.gov/31201323 %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 Ca(2+) levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca(2+), 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 Ca(2+)- and voltage-induced electrical excitability to the central organelle of plant cells.

• Graus, D., Konrad, K.R., Bemm, F., Patir Nebioglu, M.G., Lorey, C., Duscha, K., Güthoff, T., Herrmann, J., Ferjani, A., Cuin, T.A., Roelfsema, M.R.G., Schumacher, K., Neuhaus, H.E., Marten, I., und Hedrich, R. (2018) „High V-PPase activity is beneficial under high salt loads, but detrimental without salinity“, The New phytologist, 219(4), 1421–1432, verfügbar unter: https://doi.org/10.1111/nph.15280.
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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 PP(i) 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 3 d 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{graus2018vppase, 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 PP(i) 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 3 d 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.}, address = {England}, author = {Graus, Dorothea and Konrad, Kai R and Bemm, Felix and Patir Nebioglu, Meliha Görkem and Lorey, Christian and Duscha, Kerstin and Güthoff, Tilman and Herrmann, Johannes and Ferjani, Ali and Cuin, Tracey Ann and Roelfsema, M Rob G and Schumacher, Karin and Neuhaus, H Ekkehard and Marten, Irene and Hedrich, Rainer}, journal = {The New phytologist}, keywords = {imported}, month = {09}, number = 4, pages = {1421–1432}, title = {High V-PPase activity is beneficial under high salt loads, but detrimental without salinity}, volume = 219, year = 2018 }

  %0 Journal Article %1 graus2018vppase %A Graus, Dorothea %A Konrad, Kai R %A Bemm, Felix %A Patir Nebioglu, Meliha Görkem %A Lorey, Christian %A Duscha, Kerstin %A Güthoff, Tilman %A Herrmann, Johannes %A Ferjani, Ali %A Cuin, Tracey Ann %A Roelfsema, M Rob G %A Schumacher, Karin %A Neuhaus, H Ekkehard %A Marten, Irene %A Hedrich, Rainer %C England %D 2018 %J The 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 https://pubmed.ncbi.nlm.nih.gov/29938800 %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 PP(i) 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 3 d 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.
• Hedrich, R., Mueller, T.D., Becker, D., und Marten, I. (2018) „Structure and Function of TPC1 Vacuole SV Channel Gains Shape“, Molecular plant, 11(6), 764–775, verfügbar unter: https://doi.org/10.1016/j.molp.2018.03.017.
  • [ Abstract ]
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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{hedrich2018structure, 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.}, address = {England}, author = {Hedrich, Rainer and Mueller, Thomas D and Becker, Dirk and Marten, Irene}, journal = {Molecular plant}, keywords = {imported}, month = {06}, number = 6, pages = {764–775}, title = {Structure and Function of TPC1 Vacuole SV Channel Gains Shape}, volume = 11, year = 2018 }

  %0 Journal Article %1 hedrich2018structure %A Hedrich, Rainer %A Mueller, Thomas D %A Becker, Dirk %A Marten, Irene %C England %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 https://pubmed.ncbi.nlm.nih.gov/29614320 %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.

• Lenglet, A., Jaślan, D., Toyota, M., Mueller, M., Müller, T., Schönknecht, G., Marten, I., Gilroy, S., Hedrich, R., und Farmer, E.E. (2017) „Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity“, The New phytologist, 216(4), 1161–1169, verfügbar unter: https://doi.org/10.1111/nph.14754.
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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 (Ca(2+) ) imaging was used to study the effects fou2 on cytosolic Ca(2+) 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 Ca(2+) concentrations caused channel occlusion, selectively blocking K(+) fluxes towards the cytoplasm. Cytosolic Ca(2+) 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{lenglet2017control, 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 (Ca(2+) ) imaging was used to study the effects fou2 on cytosolic Ca(2+) 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 Ca(2+) concentrations caused channel occlusion, selectively blocking K(+) fluxes towards the cytoplasm. Cytosolic Ca(2+) 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.}, address = {England}, author = {Lenglet, Aurore and Jaślan, Dawid and Toyota, Masatsugu and Mueller, Matthias and Müller, Thomas and Schönknecht, Gerald and Marten, Irene and Gilroy, Simon and Hedrich, Rainer and Farmer, Edward E}, journal = {The New phytologist}, keywords = {imported}, month = 12, number = 4, pages = {1161–1169}, title = {Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity}, volume = 216, year = 2017 }

  %0 Journal Article %1 lenglet2017control %A Lenglet, Aurore %A Jaślan, Dawid %A Toyota, Masatsugu %A Mueller, Matthias %A Müller, Thomas %A Schönknecht, Gerald %A Marten, Irene %A Gilroy, Simon %A Hedrich, Rainer %A Farmer, Edward E %C England %D 2017 %J The 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 https://pubmed.ncbi.nlm.nih.gov/28885692 %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 (Ca(2+) ) imaging was used to study the effects fou2 on cytosolic Ca(2+) 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 Ca(2+) concentrations caused channel occlusion, selectively blocking K(+) fluxes towards the cytoplasm. Cytosolic Ca(2+) 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.
• 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., und Sauer, N. (2017) „Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet (Beta vulgaris L.) source leaves“, Plant biology (Stuttgart, Germany), 19(3), 315–326, verfügbar unter: https://doi.org/10.1111/plb.12546.
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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 β-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{nieberl2017functional, 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 β-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.}, address = {England}, 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 (Stuttgart, Germany)}, keywords = {imported}, month = {05}, number = 3, pages = {315–326}, title = {Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet (Beta vulgaris L.) source leaves}, volume = 19, year = 2017 }

  %0 Journal Article %1 nieberl2017functional %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 %C England %D 2017 %J Plant biology (Stuttgart, Germany) %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 (Beta vulgaris L.) source leaves %U https://pubmed.ncbi.nlm.nih.gov/28075052 %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 β-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.

• Jaślan, D., Mueller, T.D., Becker, D., Schultz, J., Cuin, T.A., Marten, I., Dreyer, I., Schönknecht, G., und Hedrich, R. (2016) „Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain“, Plant biology (Stuttgart, Germany), 18(5), 750–760, verfügbar unter: https://doi.org/10.1111/plb.12478.
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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{jaslan2016gating, 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.}, address = {England}, author = {Jaślan, 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 (Stuttgart, Germany)}, keywords = {imported}, month = {09}, 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}, volume = 18, year = 2016 }

  %0 Journal Article %1 jaslan2016gating %A Jaślan, 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 %C England %D 2016 %J Plant biology (Stuttgart, Germany) %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 https://pubmed.ncbi.nlm.nih.gov/27270880 %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.
• Cubero-Font, P., Maierhofer, T., Jaslan, J., Rosales, M.A., Espartero, J., Díaz-Rueda, P., Müller, H.M., Hürter, A.-L., Al-Rasheid, K.A.S., Marten, I., Hedrich, R., Colmenero-Flores, J.M., und Geiger, D. (2016) „Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation“, Current biology : CB, 26(16), 2213–2220, verfügbar unter: https://doi.org/10.1016/j.cub.2016.06.045.
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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{cuberofont2016silent, 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.}, address = {England}, author = {Cubero-Font, Paloma and Maierhofer, Tobias and Jaslan, Justyna and Rosales, Miguel A and Espartero, Joaquín and Díaz-Rueda, Pablo and Müller, Heike M and Hürter, Anna-Lena and Al-Rasheid, Khaled A S and Marten, Irene and Hedrich, Rainer and Colmenero-Flores, José M and Geiger, Dietmar}, journal = {Current biology : CB}, keywords = {imported}, month = {08}, number = 16, pages = {2213–2220}, title = {Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation}, volume = 26, year = 2016 }

  %0 Journal Article %1 cuberofont2016silent %A Cubero-Font, Paloma %A Maierhofer, Tobias %A Jaslan, Justyna %A Rosales, Miguel A %A Espartero, Joaquín %A Díaz-Rueda, Pablo %A Müller, Heike M %A Hürter, Anna-Lena %A Al-Rasheid, Khaled A S %A Marten, Irene %A Hedrich, Rainer %A Colmenero-Flores, José M %A Geiger, Dietmar %C England %D 2016 %J Current biology : CB %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 https://pubmed.ncbi.nlm.nih.gov/27397895 %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.

• 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., und Neuhaus, H.E. (2015) „Identification of the transporter responsible for sucrose accumulation in sugar beet taproots“, Nature plants, 1, 14001–14001, verfügbar unter: https://doi.org/10.1038/nplants.2014.1.
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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{jung2015identification, 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.}, address = {England}, author = {Jung, Benjamin and Ludewig, Frank and Schulz, Alexander and Meißner, Garvin and Wöstefeld, Nicole and Flügge, Ulf-Ingo and Pommerrenig, Benjamin and Wirsching, Petra and Sauer, Norbert and Koch, Wolfgang and Sommer, Frederik and Mühlhaus, Timo and Schroda, Michael and Cuin, Tracey Ann and Graus, Dorothea and Marten, Irene and Hedrich, Rainer and Neuhaus, H Ekkehard}, journal = {Nature plants}, keywords = {imported}, month = {01}, pages = {14001–14001}, title = {Identification of the transporter responsible for sucrose accumulation in sugar beet taproots}, volume = 1, year = 2015 }

  %0 Journal Article %1 jung2015identification %A Jung, Benjamin %A Ludewig, Frank %A Schulz, Alexander %A Meißner, Garvin %A Wöstefeld, Nicole %A Flügge, Ulf-Ingo %A Pommerrenig, Benjamin %A Wirsching, Petra %A Sauer, Norbert %A Koch, Wolfgang %A Sommer, Frederik %A Mühlhaus, Timo %A Schroda, Michael %A Cuin, Tracey Ann %A Graus, Dorothea %A Marten, Irene %A Hedrich, Rainer %A Neuhaus, H Ekkehard %C England %D 2015 %J Nature plants %P 14001--14001 %R 10.1038/nplants.2014.1 %T Identification of the transporter responsible for sucrose accumulation in sugar beet taproots %U https://pubmed.ncbi.nlm.nih.gov/27246048 %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.

• Klemens, P.A.W., Patzke, K., Trentmann, O., Poschet, G., Büttner, M., Schulz, A., Marten, I., Hedrich, R., und Neuhaus, H.E. (2014) „Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination“, The New phytologist, 202(1), 188–197, verfügbar unter: https://doi.org/10.1111/nph.12642.
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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{klemens2014overexpression, 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.}, address = {England}, author = {Klemens, Patrick A W and Patzke, Kathrin and Trentmann, Oliver and Poschet, Gernot and Büttner, Michael and Schulz, Alexander and Marten, Irene and Hedrich, Rainer and Neuhaus, H Ekkehard}, journal = {The New phytologist}, keywords = {imported}, month = {04}, number = 1, pages = {188–197}, title = {Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination}, volume = 202, year = 2014 }

  %0 Journal Article %1 klemens2014overexpression %A Klemens, Patrick A W %A Patzke, Kathrin %A Trentmann, Oliver %A Poschet, Gernot %A Büttner, Michael %A Schulz, Alexander %A Marten, Irene %A Hedrich, Rainer %A Neuhaus, H Ekkehard %C England %D 2014 %J The 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 https://pubmed.ncbi.nlm.nih.gov/24329902 %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.

• Mumm, P., Imes, D., Martinoia, E., Al-Rasheid, K.A.S., Geiger, D., Marten, I., und Hedrich, R. (2013) „C-terminus-mediated voltage gating of Arabidopsis guard cell anion channel QUAC1“, Molecular plant, 6(5), 1550–1563, verfügbar unter: https://doi.org/10.1093/mp/sst008.
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  Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel families—SLAC/SLAH and ALMT—are 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 activation–deactivation 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{mumm2013cterminusmediated, abstract = {Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel families—SLAC/SLAH and ALMT—are 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 activation–deactivation 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.}, address = {England}, author = {Mumm, Patrick and Imes, Dennis and Martinoia, Enrico and Al-Rasheid, Khaled A S and Geiger, Dietmar and Marten, Irene and Hedrich, Rainer}, journal = {Molecular plant}, keywords = {imported}, month = {09}, number = 5, pages = {1550–1563}, title = {C-terminus-mediated voltage gating of Arabidopsis guard cell anion channel QUAC1}, volume = 6, year = 2013 }

  %0 Journal Article %1 mumm2013cterminusmediated %A Mumm, Patrick %A Imes, Dennis %A Martinoia, Enrico %A Al-Rasheid, Khaled A S %A Geiger, Dietmar %A Marten, Irene %A Hedrich, Rainer %C England %D 2013 %J Molecular plant %N 5 %P 1550--1563 %R 10.1093/mp/sst008 %T C-terminus-mediated voltage gating of Arabidopsis guard cell anion channel QUAC1 %U https://pubmed.ncbi.nlm.nih.gov/23314055 %V 6 %X Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel families—SLAC/SLAH and ALMT—are 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 activation–deactivation 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.
• Imes, D., Mumm, P., Böhm, J., Al-Rasheid, K.A.S., Marten, I., Geiger, D., und Hedrich, R. (2013) „Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells“, The Plant journal : for cell and molecular biology, 74(3), 372–382, verfügbar unter: https://doi.org/10.1111/tpj.12133.
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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 S-type 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 abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.

  @article{imes2013stomata, 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 S-type 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 abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.}, address = {England}, author = {Imes, Dennis and Mumm, Patrick and Böhm, Jennifer and Al-Rasheid, Khaled A S and Marten, Irene and Geiger, Dietmar and Hedrich, Rainer}, journal = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = {05}, number = 3, pages = {372–382}, title = {Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells}, volume = 74, year = 2013 }

  %0 Journal Article %1 imes2013stomata %A Imes, Dennis %A Mumm, Patrick %A Böhm, Jennifer %A Al-Rasheid, Khaled A S %A Marten, Irene %A Geiger, Dietmar %A Hedrich, Rainer %C England %D 2013 %J The Plant journal : for cell and molecular biology %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 https://pubmed.ncbi.nlm.nih.gov/23452338 %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 S-type 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 abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.

• Seidel, T., Scholl, S., Krebs, M., Rienmüller, F., Marten, I., Hedrich, R., Hanitzsch, M., Janetzki, P., Dietz, K.-J., und Schumacher, K. (2012) „Regulation of the V-type ATPase by redox modulation“, The Biochemical journal, 448(2), 243–251, verfügbar unter: https://doi.org/10.1042/BJ20120976.
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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. In vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.

  @article{seidel2012regulation, 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. In vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.}, address = {England}, author = {Seidel, Thorsten and Scholl, Stefan and Krebs, Melanie and Rienmüller, Florian and Marten, Irene and Hedrich, Rainer and Hanitzsch, Miriam and Janetzki, Patricia and Dietz, Karl-Josef and Schumacher, Karin}, journal = {The Biochemical journal}, keywords = {imported}, month = 12, number = 2, pages = {243–251}, title = {Regulation of the V-type ATPase by redox modulation}, volume = 448, year = 2012 }

  %0 Journal Article %1 seidel2012regulation %A Seidel, Thorsten %A Scholl, Stefan %A Krebs, Melanie %A Rienmüller, Florian %A Marten, Irene %A Hedrich, Rainer %A Hanitzsch, Miriam %A Janetzki, Patricia %A Dietz, Karl-Josef %A Schumacher, Karin %C England %D 2012 %J The Biochemical journal %N 2 %P 243--251 %R 10.1042/BJ20120976 %T Regulation of the V-type ATPase by redox modulation %U https://pubmed.ncbi.nlm.nih.gov/22943363 %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. In vivo data suggest that oxidative inhibition might not represent a general regulatory mechanism in plants.
• Rienmüller, F., Dreyer, I., Schönknecht, G., Schulz, A., Schumacher, K., Nagy, R., Martinoia, E., Marten, I., und Hedrich, R. (2012) „Luminal and cytosolic pH feedback on proton pump activity and ATP affinity of V-type ATPase from Arabidopsis“, The Journal of biological chemistry, 287(12), 8986–8993, verfügbar unter: https://doi.org/10.1074/jbc.M111.310367.
  • [ Abstract ]
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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{rienmuller2012luminal, 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.}, address = {United States}, author = {Rienmüller, Florian and Dreyer, Ingo and Schönknecht, Gerald and Schulz, Alexander and Schumacher, Karin and Nagy, Réka and Martinoia, Enrico and Marten, Irene and Hedrich, Rainer}, journal = {The Journal of biological chemistry}, keywords = {imported}, month = {03}, number = 12, pages = {8986–8993}, title = {Luminal and cytosolic pH feedback on proton pump activity and ATP affinity of V-type ATPase from Arabidopsis}, volume = 287, year = 2012 }

  %0 Journal Article %1 rienmuller2012luminal %A Rienmüller, Florian %A Dreyer, Ingo %A Schönknecht, Gerald %A Schulz, Alexander %A Schumacher, Karin %A Nagy, Réka %A Martinoia, Enrico %A Marten, Irene %A Hedrich, Rainer %C United States %D 2012 %J The 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 Arabidopsis %U https://pubmed.ncbi.nlm.nih.gov/22215665 %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.

• Koers, S., Guzel-Deger, A., Marten, I., und Roelfsema, M.R.G. (2011) „Barley mildew and its elicitor chitosan promote closed stomata by stimulating guard-cell S-type anion channels“, The Plant journal : for cell and molecular biology, 68(4), 670–680, verfügbar unter: https://doi.org/10.1111/j.1365-313X.2011.04719.x.
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  Stomatal closure is known to be associated with early defence responses of plant cells triggered by microbe-associated molecular patterns (MAMPs). However, the molecular mechanisms underlying these guard-cell responses have not yet been elucidated. We therefore studied pathogen-induced changes in ion channel activity in Hordeum vulgare guard cells. Barley mildew (Blumeria graminis) hyphae growing on leaves inhibited light-induced stomatal opening, starting at 9 h after inoculation, when appressoria had developed. Alternatively, stomatal closure was induced by nano-infusion of chitosan via open stomata into the sub-stomatal cavity. Experiments using intracellular double-barreled micro-electrodes revealed that mildew stimulated S-type (slow) anion channels in guard cells. These channels enable the efflux of anions from guard cells and also promote K(+) extrusion by altering the plasma membrane potential. Stimulation of S-type anion channels was also provoked by nano-infusion of chitosan. These data suggest that MAMPs of mildew hyphae penetrating the cuticle provoke activation of S-type anion channels in guard cells. In response, guard cells extrude K(+) salts, resulting in stomatal closure. Plasma membrane anion channels probably represent general targets of MAMP signaling in plants, as these elicitors depolarize the plasma membrane of various cell types.

  @article{koers2011barley, abstract = {Stomatal closure is known to be associated with early defence responses of plant cells triggered by microbe-associated molecular patterns (MAMPs). However, the molecular mechanisms underlying these guard-cell responses have not yet been elucidated. We therefore studied pathogen-induced changes in ion channel activity in Hordeum vulgare guard cells. Barley mildew (Blumeria graminis) hyphae growing on leaves inhibited light-induced stomatal opening, starting at 9 h after inoculation, when appressoria had developed. Alternatively, stomatal closure was induced by nano-infusion of chitosan via open stomata into the sub-stomatal cavity. Experiments using intracellular double-barreled micro-electrodes revealed that mildew stimulated S-type (slow) anion channels in guard cells. These channels enable the efflux of anions from guard cells and also promote K(+) extrusion by altering the plasma membrane potential. Stimulation of S-type anion channels was also provoked by nano-infusion of chitosan. These data suggest that MAMPs of mildew hyphae penetrating the cuticle provoke activation of S-type anion channels in guard cells. In response, guard cells extrude K(+) salts, resulting in stomatal closure. Plasma membrane anion channels probably represent general targets of MAMP signaling in plants, as these elicitors depolarize the plasma membrane of various cell types.}, address = {England}, author = {Koers, Sandra and Guzel-Deger, Aysin and Marten, Irene and Roelfsema, M Rob G}, journal = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = 11, number = 4, pages = {670–680}, title = {Barley mildew and its elicitor chitosan promote closed stomata by stimulating guard-cell S-type anion channels}, volume = 68, year = 2011 }

  %0 Journal Article %1 koers2011barley %A Koers, Sandra %A Guzel-Deger, Aysin %A Marten, Irene %A Roelfsema, M Rob G %C England %D 2011 %J The Plant journal : for cell and molecular biology %N 4 %P 670--680 %R 10.1111/j.1365-313X.2011.04719.x %T Barley mildew and its elicitor chitosan promote closed stomata by stimulating guard-cell S-type anion channels %U https://pubmed.ncbi.nlm.nih.gov/21781196 %V 68 %X Stomatal closure is known to be associated with early defence responses of plant cells triggered by microbe-associated molecular patterns (MAMPs). However, the molecular mechanisms underlying these guard-cell responses have not yet been elucidated. We therefore studied pathogen-induced changes in ion channel activity in Hordeum vulgare guard cells. Barley mildew (Blumeria graminis) hyphae growing on leaves inhibited light-induced stomatal opening, starting at 9 h after inoculation, when appressoria had developed. Alternatively, stomatal closure was induced by nano-infusion of chitosan via open stomata into the sub-stomatal cavity. Experiments using intracellular double-barreled micro-electrodes revealed that mildew stimulated S-type (slow) anion channels in guard cells. These channels enable the efflux of anions from guard cells and also promote K(+) extrusion by altering the plasma membrane potential. Stimulation of S-type anion channels was also provoked by nano-infusion of chitosan. These data suggest that MAMPs of mildew hyphae penetrating the cuticle provoke activation of S-type anion channels in guard cells. In response, guard cells extrude K(+) salts, resulting in stomatal closure. Plasma membrane anion channels probably represent general targets of MAMP signaling in plants, as these elicitors depolarize the plasma membrane of various cell types.
• Schulz, A., Beyhl, D., Marten, I., Wormit, A., Neuhaus, E., Poschet, G., Büttner, M., Schneider, S., Sauer, N., und Hedrich, R. (2011) „Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2“, The Plant journal : for cell and molecular biology, 68(1), 129–136, verfügbar unter: https://doi.org/10.1111/j.1365-313X.2011.04672.x.
  • [ 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{schulz2011protondriven, 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.}, address = {England}, author = {Schulz, Alexander and Beyhl, Diana and Marten, Irene and Wormit, Alexandra and Neuhaus, Ekkehard and Poschet, Gernot and Büttner, Michael and Schneider, Sabine and Sauer, Norbert and Hedrich, Rainer}, journal = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = 10, number = 1, pages = {129–136}, title = {Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2}, volume = 68, year = 2011 }

  %0 Journal Article %1 schulz2011protondriven %A Schulz, Alexander %A Beyhl, Diana %A Marten, Irene %A Wormit, Alexandra %A Neuhaus, Ekkehard %A Poschet, Gernot %A Büttner, Michael %A Schneider, Sabine %A Sauer, Norbert %A Hedrich, Rainer %C England %D 2011 %J The Plant journal : for cell and molecular biology %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 https://pubmed.ncbi.nlm.nih.gov/21668536 %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.
• Mumm, P., Wolf, T., Fromm, J., Roelfsema, M.R.G., und Marten, I. (2011) „Cell type-specific regulation of ion channels within the maize stomatal complex“, Plant & cell physiology, 52(8), 1365–1375, verfügbar unter: https://doi.org/10.1093/pcp/pcr082.
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  The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear. In order to bridge this gap, we performed patch-clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca(2+) and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with BCECF [(2',7'-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined. Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening. Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.

  @article{mumm2011typespecific, abstract = {The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear. In order to bridge this gap, we performed patch-clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca(2+) and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with BCECF [(2',7'-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined. Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening. Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.}, address = {Japan}, author = {Mumm, Patrick and Wolf, Thomas and Fromm, Jörg and Roelfsema, M Rob G and Marten, Irene}, journal = {Plant & cell physiology}, keywords = {imported}, month = {08}, number = 8, pages = {1365–1375}, title = {Cell type-specific regulation of ion channels within the maize stomatal complex}, volume = 52, year = 2011 }

  %0 Journal Article %1 mumm2011typespecific %A Mumm, Patrick %A Wolf, Thomas %A Fromm, Jörg %A Roelfsema, M Rob G %A Marten, Irene %C Japan %D 2011 %J Plant & cell physiology %N 8 %P 1365--1375 %R 10.1093/pcp/pcr082 %T Cell type-specific regulation of ion channels within the maize stomatal complex %U https://pubmed.ncbi.nlm.nih.gov/21690176 %V 52 %X The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear. In order to bridge this gap, we performed patch-clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca(2+) and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with BCECF [(2',7'-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined. Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening. Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.
• Hedrich, R. und Marten, I. (2011) „TPC1-SV channels gain shape“, Molecular plant, 4(3), 428–441, verfügbar unter: https://doi.org/10.1093/mp/ssr017.
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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{hedrich2011tpc1sv, 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.}, address = {England}, author = {Hedrich, Rainer and Marten, Irene}, journal = {Molecular plant}, keywords = {imported}, month = {05}, number = 3, pages = {428–441}, title = {TPC1-SV channels gain shape}, volume = 4, year = 2011 }

  %0 Journal Article %1 hedrich2011tpc1sv %A Hedrich, Rainer %A Marten, Irene %C England %D 2011 %J Molecular plant %N 3 %P 428--441 %R 10.1093/mp/ssr017 %T TPC1-SV channels gain shape %U https://pubmed.ncbi.nlm.nih.gov/21459829 %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.
• 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., und Hedrich, R. (2011) „Stomatal closure by fast abscisic acid signaling is mediated by the guard cell anion channel SLAH3 and the receptor RCAR1“, Science signaling, 4(173), ra32-ra32, verfügbar unter: https://doi.org/10.1126/scisignal.2001346.
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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{geiger2011stomatal, 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.}, address = {United States}, author = {Geiger, Dietmar and Maierhofer, Tobias and Al-Rasheid, Khaled A S and Scherzer, Sönke and Mumm, Patrick and Liese, Anja and Ache, Peter and Wellmann, Christian and Marten, Irene and Grill, Erwin and Romeis, Tina and Hedrich, Rainer}, journal = {Science signaling}, keywords = {imported}, month = {05}, number = 173, pages = {ra32–ra32}, title = {Stomatal closure by fast abscisic acid signaling is mediated by the guard cell anion channel SLAH3 and the receptor RCAR1}, volume = 4, year = 2011 }

  %0 Journal Article %1 geiger2011stomatal %A Geiger, Dietmar %A Maierhofer, Tobias %A Al-Rasheid, Khaled A S %A Scherzer, Sönke %A Mumm, Patrick %A Liese, Anja %A Ache, Peter %A Wellmann, Christian %A Marten, Irene %A Grill, Erwin %A Romeis, Tina %A Hedrich, Rainer %C United States %D 2011 %J Science signaling %N 173 %P ra32--ra32 %R 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 https://pubmed.ncbi.nlm.nih.gov/21586729 %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.

• Krebs, M., Beyhl, D., Görlich, E., Al-Rasheid, K.A.S., Marten, I., Stierhof, Y.-D., Hedrich, R., und Schumacher, K. (2010) „Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation“, Proceedings of the National Academy of Sciences of the United States of America, 107(7), 3251–3256, verfügbar unter: https://doi.org/10.1073/pnas.0913035107.
  • [ Abstract ]
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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 Zn(2+)/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{krebs2010arabidopsis, 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 Zn(2+)/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.}, address = {United States}, author = {Krebs, Melanie and Beyhl, Diana and Görlich, Esther and Al-Rasheid, Khaled A S and Marten, Irene and Stierhof, York-Dieter and Hedrich, Rainer and Schumacher, Karin}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {imported}, month = {02}, number = 7, pages = {3251–3256}, title = {Arabidopsis V-ATPase activity at the tonoplast is required for efficient nutrient storage but not for sodium accumulation}, volume = 107, year = 2010 }

  %0 Journal Article %1 krebs2010arabidopsis %A Krebs, Melanie %A Beyhl, Diana %A Görlich, Esther %A Al-Rasheid, Khaled A S %A Marten, Irene %A Stierhof, York-Dieter %A Hedrich, Rainer %A Schumacher, Karin %C United States %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 https://pubmed.ncbi.nlm.nih.gov/20133698 %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 Zn(2+)/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.
• 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., und Hedrich, R. (2010) „Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca2+ affinities“, Proceedings of the National Academy of Sciences of the United States of America, 107(17), 8023–8028, verfügbar unter: https://doi.org/10.1073/pnas.0912030107.
  • [ Abstract ]
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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 Ca(2+)-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. Ca(2+)-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca(2+)-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{geiger2010guard, 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 Ca(2+)-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. Ca(2+)-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca(2+)-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.}, address = {United States}, 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 = {imported}, month = {04}, number = 17, pages = {8023–8028}, title = {Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca2+ affinities}, volume = 107, year = 2010 }

  %0 Journal Article %1 geiger2010guard %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 %C United States %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 Ca2+ affinities %U https://pubmed.ncbi.nlm.nih.gov/20385816 %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 Ca(2+)-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. Ca(2+)-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca(2+)-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.
• Rienmüller, F., Beyhl, D., Lautner, S., Fromm, J., Al-Rasheid, K.A.S., Ache, P., Farmer, E.E., Marten, I., und Hedrich, R. (2010) „Guard cell-specific calcium sensitivity of high density and activity SV/TPC1 channels“, Plant & cell physiology, 51(9), 1548–1554, verfügbar unter: https://doi.org/10.1093/pcp/pcq102.
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  The slow vacuolar (SV) channel, a Ca2+-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 Ca2+ 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{rienmuller2010guard, abstract = {The slow vacuolar (SV) channel, a Ca2+-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 Ca2+ 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.}, address = {Japan}, author = {Rienmüller, Florian and Beyhl, Diana and Lautner, Silke and Fromm, Jörg and Al-Rasheid, Khaled A S and Ache, Peter and Farmer, Edward E and Marten, Irene and Hedrich, Rainer}, journal = {Plant & cell physiology}, keywords = {imported}, month = {09}, number = 9, pages = {1548–1554}, title = {Guard cell-specific calcium sensitivity of high density and activity SV/TPC1 channels}, volume = 51, year = 2010 }

  %0 Journal Article %1 rienmuller2010guard %A Rienmüller, Florian %A Beyhl, Diana %A Lautner, Silke %A Fromm, Jörg %A Al-Rasheid, Khaled A S %A Ache, Peter %A Farmer, Edward E %A Marten, Irene %A Hedrich, Rainer %C Japan %D 2010 %J Plant & 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 https://pubmed.ncbi.nlm.nih.gov/20630987 %V 51 %X The slow vacuolar (SV) channel, a Ca2+-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 Ca2+ 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.
• Meyer, S., Mumm, P., Imes, D., Endler, A., Weder, B., Al-Rasheid, K.A.S., Geiger, D., Marten, I., Martinoia, E., und Hedrich, R. (2010) „AtALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells“, The Plant journal : for cell and molecular biology, 63(6), 1054–1062, verfügbar unter: https://doi.org/10.1111/j.1365-313X.2010.04302.x.
  • [ Abstract ]
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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{meyer2010atalmt12, 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.}, address = {England}, author = {Meyer, Stefan and Mumm, Patrick and Imes, Dennis and Endler, Anne and Weder, Barbara and Al-Rasheid, Khaled A S and Geiger, Dietmar and Marten, Irene and Martinoia, Enrico and Hedrich, Rainer}, journal = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = {09}, number = 6, pages = {1054–1062}, title = {AtALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells}, volume = 63, year = 2010 }

  %0 Journal Article %1 meyer2010atalmt12 %A Meyer, Stefan %A Mumm, Patrick %A Imes, Dennis %A Endler, Anne %A Weder, Barbara %A Al-Rasheid, Khaled A S %A Geiger, Dietmar %A Marten, Irene %A Martinoia, Enrico %A Hedrich, Rainer %C England %D 2010 %J The Plant journal : for cell and molecular biology %N 6 %P 1054--1062 %R 10.1111/j.1365-313X.2010.04302.x %T AtALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells %U https://pubmed.ncbi.nlm.nih.gov/20626656 %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.
• Marten, I., Deeken, R., Hedrich, R., und Roelfsema, M.R.G. (2010) „Light-induced modification of plant plasma membrane ion transport“, Plant biology (Stuttgart, Germany), 12 Suppl 1, 64–79, verfügbar unter: https://doi.org/10.1111/j.1438-8677.2010.00384.x.
  • [ Abstract ]
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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 Ca(2+)-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{marten2010lightinduced, 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 Ca(2+)-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.}, address = {England}, author = {Marten, I and Deeken, R and Hedrich, R and Roelfsema, M R G}, journal = {Plant biology (Stuttgart, Germany)}, keywords = {imported}, month = {09}, pages = {64–79}, title = {Light-induced modification of plant plasma membrane ion transport}, volume = {12 Suppl 1}, year = 2010 }

  %0 Journal Article %1 marten2010lightinduced %A Marten, I %A Deeken, R %A Hedrich, R %A Roelfsema, M R G %C England %D 2010 %J Plant biology (Stuttgart, Germany) %P 64--79 %R 10.1111/j.1438-8677.2010.00384.x %T Light-induced modification of plant plasma membrane ion transport %U https://pubmed.ncbi.nlm.nih.gov/20712622 %V 12 Suppl 1 %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 Ca(2+)-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.
• Wingenter, K., Schulz, A., Wormit, A., Wic, S., Trentmann, O., Hoermiller, I.I., Heyer, A.G., Marten, I., Hedrich, R., und Neuhaus, H.E. (2010) „Increased activity of the vacuolar monosaccharide transporter TMT1 alters cellular sugar partitioning, sugar signaling, and seed yield in Arabidopsis“, Plant physiology, 154(2), 665–677, verfügbar unter: https://doi.org/10.1104/pp.110.162040.
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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 CO(2) 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{wingenter2010increased, 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 CO(2) 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.}, address = {United States}, author = {Wingenter, Karina and Schulz, Alexander and Wormit, Alexandra and Wic, Stefan and Trentmann, Oliver and Hoermiller, Imke I and Heyer, Arnd G and Marten, Irene and Hedrich, Rainer and Neuhaus, H Ekkehard}, journal = {Plant physiology}, keywords = {imported}, month = 10, 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}, volume = 154, year = 2010 }

  %0 Journal Article %1 wingenter2010increased %A Wingenter, Karina %A Schulz, Alexander %A Wormit, Alexandra %A Wic, Stefan %A Trentmann, Oliver %A Hoermiller, Imke I %A Heyer, Arnd G %A Marten, Irene %A Hedrich, Rainer %A Neuhaus, H Ekkehard %C United States %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 https://pubmed.ncbi.nlm.nih.gov/20709831 %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 CO(2) 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.

• 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., und Hedrich, R. (2009) „Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair“, Proceedings of the National Academy of Sciences of the United States of America, 106(50), 21425–21430, verfügbar unter: https://doi.org/10.1073/pnas.0912021106.
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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{geiger2009activity, 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.}, address = {United States}, author = {Geiger, Dietmar and Scherzer, Sönke and Mumm, Patrick and Stange, Annette and Marten, Irene and Bauer, Hubert and Ache, Peter and Matschi, Susanne and Liese, Anja and Al-Rasheid, Khaled A S and Romeis, Tina and Hedrich, Rainer}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {imported}, month = 12, number = 50, pages = {21425–21430}, title = {Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair}, volume = 106, year = 2009 }

  %0 Journal Article %1 geiger2009activity %A Geiger, Dietmar %A Scherzer, Sönke %A Mumm, Patrick %A Stange, Annette %A Marten, Irene %A Bauer, Hubert %A Ache, Peter %A Matschi, Susanne %A Liese, Anja %A Al-Rasheid, Khaled A S %A Romeis, Tina %A Hedrich, Rainer %C United States %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 https://pubmed.ncbi.nlm.nih.gov/19955405 %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.
• Beyhl, D., Hörtensteiner, S., Martinoia, E., Farmer, E.E., Fromm, J., Marten, I., und Hedrich, R. (2009) „The fou2 mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium“, The Plant journal : for cell and molecular biology, 58(5), 715–723, verfügbar unter: https://doi.org/10.1111/j.1365-313X.2009.03820.x.
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  The SV channel encoded by the TPC1 gene represents a Ca(2+)- 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 Ca(2+)-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 fou2 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 Ca(2+) 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{beyhl2009mutation, abstract = {The SV channel encoded by the TPC1 gene represents a Ca(2+)- 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 Ca(2+)-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 fou2 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 Ca(2+) 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.}, address = {England}, author = {Beyhl, Diana and Hörtensteiner, Stefan and Martinoia, Enrico and Farmer, Edward E and Fromm, Jörg and Marten, Irene and Hedrich, Rainer}, journal = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = {06}, number = 5, pages = {715–723}, title = {The fou2 mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium}, volume = 58, year = 2009 }

  %0 Journal Article %1 beyhl2009mutation %A Beyhl, Diana %A Hörtensteiner, Stefan %A Martinoia, Enrico %A Farmer, Edward E %A Fromm, Jörg %A Marten, Irene %A Hedrich, Rainer %C England %D 2009 %J The Plant journal : for cell and molecular biology %N 5 %P 715--723 %R 10.1111/j.1365-313X.2009.03820.x %T The fou2 mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium %U https://pubmed.ncbi.nlm.nih.gov/19298454 %V 58 %X The SV channel encoded by the TPC1 gene represents a Ca(2+)- 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 Ca(2+)-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 fou2 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 Ca(2+) 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.

• Latz, A., Becker, D., Hekman, M., Müller, T., Beyhl, D., Marten, I., Eing, C., Fischer, A., Dunkel, M., Bertl, A., Rapp, U.R., und Hedrich, R. (2007) „TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins“, The Plant journal : for cell and molecular biology, 52(3), 449–459, verfügbar unter: https://doi.org/10.1111/j.1365-313X.2007.03255.x.
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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 Ca(2+)-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 Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.

  @article{latz2007ca2regulated, 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 Ca(2+)-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 Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.}, address = {England}, author = {Latz, A and Becker, D and Hekman, M and Müller, 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 = {The Plant journal : for cell and molecular biology}, keywords = {imported}, month = 11, number = 3, pages = {449–459}, title = {TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins}, volume = 52, year = 2007 }

  %0 Journal Article %1 latz2007ca2regulated %A Latz, A %A Becker, D %A Hekman, M %A Müller, 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 %C England %D 2007 %J The Plant journal : for cell and molecular biology %N 3 %P 449--459 %R 10.1111/j.1365-313X.2007.03255.x %T TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins %U https://pubmed.ncbi.nlm.nih.gov/17764516 %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 Ca(2+)-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 Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.

• Wolf, T., Heidelmann, T., und Marten, I. (2006) „ABA regulation of K(+)-permeable channels in maize subsidiary cells“, Plant & cell physiology, 47(10), 1372–1380, verfügbar unter: https://doi.org/10.1093/pcp/pcl007.
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  An antiparallel-directed potassium transport between subsidiary cells and guard cells which form the graminean stomatal complex has been proposed to drive stomatal movements in maize. To gain insights into the coordinated shuttling of K(+) ions between these cell types during stomatal closure, the effect of ABA on the time-dependent K(+) uptake and K(+) release channels as well as on the instantaneously activating non-selective cation channels (MgC) was examined in subsidiary cells. Patch-clamp studies revealed that ABA did not affect the MgC channels but differentially regulated the time-dependent K(+) channels. ABA caused a pronounced rise in time-dependent outward-rectifying K(+) currents (K(out)) at alkaline pH and decreased inward-rectifying K(+) currents (K(in)) in a Ca(2+)-dependent manner. Our results show that the ABA-induced changes in time-dependent K(in) and K(out) currents from subsidiary cells are very similar to those previously described for guard cells. Thus, the direction of K(+) transport in subsidiary cells and guard cells during ABA-induced closure does not seem to be grounded solely on the cell type-specific ABA regulation of K(+) channels.

  @article{wolf2006regulation, abstract = {An antiparallel-directed potassium transport between subsidiary cells and guard cells which form the graminean stomatal complex has been proposed to drive stomatal movements in maize. To gain insights into the coordinated shuttling of K(+) ions between these cell types during stomatal closure, the effect of ABA on the time-dependent K(+) uptake and K(+) release channels as well as on the instantaneously activating non-selective cation channels (MgC) was examined in subsidiary cells. Patch-clamp studies revealed that ABA did not affect the MgC channels but differentially regulated the time-dependent K(+) channels. ABA caused a pronounced rise in time-dependent outward-rectifying K(+) currents (K(out)) at alkaline pH and decreased inward-rectifying K(+) currents (K(in)) in a Ca(2+)-dependent manner. Our results show that the ABA-induced changes in time-dependent K(in) and K(out) currents from subsidiary cells are very similar to those previously described for guard cells. Thus, the direction of K(+) transport in subsidiary cells and guard cells during ABA-induced closure does not seem to be grounded solely on the cell type-specific ABA regulation of K(+) channels.}, address = {Japan}, author = {Wolf, Thomas and Heidelmann, Tobias and Marten, Irene}, journal = {Plant & cell physiology}, keywords = {imported}, month = 10, number = 10, pages = {1372–1380}, title = {ABA regulation of K(+)-permeable channels in maize subsidiary cells}, volume = 47, year = 2006 }

  %0 Journal Article %1 wolf2006regulation %A Wolf, Thomas %A Heidelmann, Tobias %A Marten, Irene %C Japan %D 2006 %J Plant & cell physiology %N 10 %P 1372--1380 %R 10.1093/pcp/pcl007 %T ABA regulation of K(+)-permeable channels in maize subsidiary cells %U https://pubmed.ncbi.nlm.nih.gov/16973684 %V 47 %X An antiparallel-directed potassium transport between subsidiary cells and guard cells which form the graminean stomatal complex has been proposed to drive stomatal movements in maize. To gain insights into the coordinated shuttling of K(+) ions between these cell types during stomatal closure, the effect of ABA on the time-dependent K(+) uptake and K(+) release channels as well as on the instantaneously activating non-selective cation channels (MgC) was examined in subsidiary cells. Patch-clamp studies revealed that ABA did not affect the MgC channels but differentially regulated the time-dependent K(+) channels. ABA caused a pronounced rise in time-dependent outward-rectifying K(+) currents (K(out)) at alkaline pH and decreased inward-rectifying K(+) currents (K(in)) in a Ca(2+)-dependent manner. Our results show that the ABA-induced changes in time-dependent K(in) and K(out) currents from subsidiary cells are very similar to those previously described for guard cells. Thus, the direction of K(+) transport in subsidiary cells and guard cells during ABA-induced closure does not seem to be grounded solely on the cell type-specific ABA regulation of K(+) channels.
• Hedrich, R. und Marten, I. (2006) „30-year progress of membrane transport in plants“, Planta, 224(4), 725–739, verfügbar unter: https://doi.org/10.1007/s00425-006-0341-x.
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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, Jülich, 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' [Lüttge 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{hedrich200630year, 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, Jülich, 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' [Lüttge 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?}, address = {Germany}, author = {Hedrich, Rainer and Marten, Irene}, journal = {Planta}, keywords = {imported}, month = {09}, number = 4, pages = {725–739}, title = {30-year progress of membrane transport in plants}, volume = 224, year = 2006 }

  %0 Journal Article %1 hedrich200630year %A Hedrich, Rainer %A Marten, Irene %C Germany %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 https://pubmed.ncbi.nlm.nih.gov/16835760 %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, Jülich, 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' [Lüttge 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?

• Büchsenschütz, K., Marten, I., Becker, D., Philippar, K., Ache, P., und Hedrich, R. (2005) „Differential expression of K+ channels between guard cells and subsidiary cells within the maize stomatal complex“, Planta, 222(6), 968–976, verfügbar unter: https://doi.org/10.1007/s00425-005-0038-6.
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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{buchsenschutz2005differential, 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.}, address = {Germany}, author = {Büchsenschütz, Kai and Marten, Irene and Becker, Dirk and Philippar, Katrin and Ache, Peter and Hedrich, Rainer}, journal = {Planta}, keywords = {imported}, month = 12, number = 6, pages = {968–976}, title = {Differential expression of K+ channels between guard cells and subsidiary cells within the maize stomatal complex}, volume = 222, year = 2005 }

  %0 Journal Article %1 buchsenschutz2005differential %A Büchsenschütz, Kai %A Marten, Irene %A Becker, Dirk %A Philippar, Katrin %A Ache, Peter %A Hedrich, Rainer %C Germany %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 https://pubmed.ncbi.nlm.nih.gov/16021501 %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.
• Wolf, T., Guinot, D.R., Hedrich, R., Dietrich, P., und Marten, I. (2005) „Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex“, Plant & cell physiology, 46(10), 1682–1689, verfügbar unter: https://doi.org/10.1093/pcp/pci184.
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  Voltage-dependent inward-rectifying (K(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 Mg(2+) dependencies of time-dependent K(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 Mg(2+) 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{wolf2005nucleotides, abstract = {Voltage-dependent inward-rectifying (K(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 Mg(2+) dependencies of time-dependent K(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 Mg(2+) 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.}, address = {Japan}, author = {Wolf, Thomas and Guinot, David Roger and Hedrich, Rainer and Dietrich, Petra and Marten, Irene}, journal = {Plant & cell physiology}, keywords = {imported}, month = 10, number = 10, pages = {1682–1689}, title = {Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex}, volume = 46, year = 2005 }

  %0 Journal Article %1 wolf2005nucleotides %A Wolf, Thomas %A Guinot, David Roger %A Hedrich, Rainer %A Dietrich, Petra %A Marten, Irene %C Japan %D 2005 %J Plant & cell physiology %N 10 %P 1682--1689 %R 10.1093/pcp/pci184 %T Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex %U https://pubmed.ncbi.nlm.nih.gov/16081526 %V 46 %X Voltage-dependent inward-rectifying (K(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 Mg(2+) dependencies of time-dependent K(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 Mg(2+) 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.
• Debarry, M., Marten, I., Ngezhayo, A., und Kolb, H.-A. (2005) „Differential defense responses in sweet potato suspension culture.“, PLant Science, 168, 1171–1179.
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  @article{debarry2005differential, author = {Debarry, M. and Marten, I. and Ngezhayo, A. and Kolb, H.-A.}, journal = {PLant Science}, keywords = {imported}, pages = {1171-1179}, title = {Differential defense responses in sweet potato suspension culture.}, volume = 168, year = 2005 }

  %0 Journal Article %1 debarry2005differential %A Debarry, M. %A Marten, I. %A Ngezhayo, A. %A Kolb, H.-A. %D 2005 %J PLant Science %P 1171-1179 %T Differential defense responses in sweet potato suspension culture. %V 168

• Majore, I., Wilhelm, B., und Marten, I. (2002) „Identification of K(+) channels in the plasma membrane of maize subsidiary cells“, Plant & cell physiology, 43(8), 844–852, verfügbar unter: https://doi.org/10.1093/pcp/pcf104.
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  The stomatal complex of Zea mays consists of two guard cells with the pore in between them and two flanking subsidiary cells. Both guard cells and subsidiary cells are important elements for stoma physiology because a well-coordinated transmembrane shuttle transport of potassium and chloride ions occurs between these cells during stomatal movement. To shed light upon the corresponding transport systems from subsidiary cells, subsidiary cell protoplasts were enzymatically isolated and in turn, analyzed with the patch-clamp technique. Thereby, two K(+)-selective channel types were identified in the plasma membrane of subsidiary cells. With regard to their voltage-dependent gating behavior, they may act as hyperpolarization-dependent K(+) uptake and depolarization-activated K(+) release channels during stomatal movement. Interestingly, the K(+) channels from subsidiary cells and guard cells similarly responded to membrane voltage as well as to changes in the K(+) gradient. Further, the inward- and outward-rectifying K(+) current amplitude decreased upon a rise in the intracellular free Ca(2+) level from 2 nM to the micro M-range. The results indicate that the plasma membrane of subsidiary cells and guard cells has to be inversely polarized in order to achieve the anti-parallel direction of K(+) fluxes between these cell types during stomatal movement.

  @article{majore2002identification, abstract = {The stomatal complex of Zea mays consists of two guard cells with the pore in between them and two flanking subsidiary cells. Both guard cells and subsidiary cells are important elements for stoma physiology because a well-coordinated transmembrane shuttle transport of potassium and chloride ions occurs between these cells during stomatal movement. To shed light upon the corresponding transport systems from subsidiary cells, subsidiary cell protoplasts were enzymatically isolated and in turn, analyzed with the patch-clamp technique. Thereby, two K(+)-selective channel types were identified in the plasma membrane of subsidiary cells. With regard to their voltage-dependent gating behavior, they may act as hyperpolarization-dependent K(+) uptake and depolarization-activated K(+) release channels during stomatal movement. Interestingly, the K(+) channels from subsidiary cells and guard cells similarly responded to membrane voltage as well as to changes in the K(+) gradient. Further, the inward- and outward-rectifying K(+) current amplitude decreased upon a rise in the intracellular free Ca(2+) level from 2 nM to the micro M-range. The results indicate that the plasma membrane of subsidiary cells and guard cells has to be inversely polarized in order to achieve the anti-parallel direction of K(+) fluxes between these cell types during stomatal movement.}, address = {Japan}, author = {Majore, Ingrida and Wilhelm, Bettina and Marten, Irene}, journal = {Plant & cell physiology}, keywords = {imported}, month = {08}, number = 8, pages = {844–852}, title = {Identification of K(+) channels in the plasma membrane of maize subsidiary cells}, volume = 43, year = 2002 }

  %0 Journal Article %1 majore2002identification %A Majore, Ingrida %A Wilhelm, Bettina %A Marten, Irene %C Japan %D 2002 %J Plant & cell physiology %N 8 %P 844--852 %R 10.1093/pcp/pcf104 %T Identification of K(+) channels in the plasma membrane of maize subsidiary cells %U https://pubmed.ncbi.nlm.nih.gov/12198186 %V 43 %X The stomatal complex of Zea mays consists of two guard cells with the pore in between them and two flanking subsidiary cells. Both guard cells and subsidiary cells are important elements for stoma physiology because a well-coordinated transmembrane shuttle transport of potassium and chloride ions occurs between these cells during stomatal movement. To shed light upon the corresponding transport systems from subsidiary cells, subsidiary cell protoplasts were enzymatically isolated and in turn, analyzed with the patch-clamp technique. Thereby, two K(+)-selective channel types were identified in the plasma membrane of subsidiary cells. With regard to their voltage-dependent gating behavior, they may act as hyperpolarization-dependent K(+) uptake and depolarization-activated K(+) release channels during stomatal movement. Interestingly, the K(+) channels from subsidiary cells and guard cells similarly responded to membrane voltage as well as to changes in the K(+) gradient. Further, the inward- and outward-rectifying K(+) current amplitude decreased upon a rise in the intracellular free Ca(2+) level from 2 nM to the micro M-range. The results indicate that the plasma membrane of subsidiary cells and guard cells has to be inversely polarized in order to achieve the anti-parallel direction of K(+) fluxes between these cell types during stomatal movement.

• Tang, X.D., Marten, I., Dietrich, P., Ivashikina, N., Hedrich, R., und Hoshi, T. (2000) „Histidine(118) in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in Xenopus oocytes“, Biophysical journal, 78(3), 1255–1269, verfügbar unter: https://doi.org/10.1016/S0006-3495(00)76682-3.
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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 on 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{tang2000histidine118, 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 on 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.}, address = {United States}, author = {Tang, X D and Marten, I and Dietrich, P and Ivashikina, N and Hedrich, R and Hoshi, T}, journal = {Biophysical journal}, keywords = {imported}, month = {03}, number = 3, pages = {1255–1269}, title = {Histidine(118) in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in Xenopus oocytes}, volume = 78, year = 2000 }

  %0 Journal Article %1 tang2000histidine118 %A Tang, X D %A Marten, I %A Dietrich, P %A Ivashikina, N %A Hedrich, R %A Hoshi, T %C United States %D 2000 %J Biophysical journal %N 3 %P 1255--1269 %R 10.1016/S0006-3495(00)76682-3 %T Histidine(118) in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in Xenopus oocytes %U https://pubmed.ncbi.nlm.nih.gov/10692314 %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 on 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.
• Jedamzik, B., Marten, I., Ngezahayo, A., Ernst, A., und Kolb, H.A. (2000) „Regulation of lens rCx46-formed hemichannels by activation of protein kinase C, external Ca(2+) and protons“, The Journal of membrane biology, 173(1), 39–46, verfügbar unter: https://doi.org/10.1007/s002320001005.
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  Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <--> C(2)(closed) <--> O(open) <--> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.

  @article{jedamzik2000regulation, abstract = {Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <–> C(2)(closed) <–> O(open) <–> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.}, address = {United States}, author = {Jedamzik, B and Marten, I and Ngezahayo, A and Ernst, A and Kolb, H A}, journal = {The Journal of membrane biology}, keywords = {imported}, month = {01}, number = 1, pages = {39–46}, title = {Regulation of lens rCx46-formed hemichannels by activation of protein kinase C, external Ca(2+) and protons}, volume = 173, year = 2000 }

  %0 Journal Article %1 jedamzik2000regulation %A Jedamzik, B %A Marten, I %A Ngezahayo, A %A Ernst, A %A Kolb, H A %C United States %D 2000 %J The Journal of membrane biology %N 1 %P 39--46 %R 10.1007/s002320001005 %T Regulation of lens rCx46-formed hemichannels by activation of protein kinase C, external Ca(2+) and protons %U https://pubmed.ncbi.nlm.nih.gov/10612690 %V 173 %X Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <--> C(2)(closed) <--> O(open) <--> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.

• Marten, I., Hoth, S., Deeken, R., Ache, P., Ketchum, K.A., Hoshi, T., und Hedrich, R. (1999) „AKT3, a phloem-localized K+ channel, is blocked by protons“, Proceedings of the National Academy of Sciences of the United States of America, 96(13), 7581–7586, verfügbar unter: https://doi.org/10.1073/pnas.96.13.7581.
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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, AKT3 was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell K+ 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 H+ and K+ fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.

  @article{marten1999phloemlocalized, 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, AKT3 was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell K+ 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 H+ and K+ fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.}, address = {United States}, 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 = {imported}, month = {06}, number = 13, pages = {7581–7586}, title = {AKT3, a phloem-localized K+ channel, is blocked by protons}, volume = 96, year = 1999 }

  %0 Journal Article %1 marten1999phloemlocalized %A Marten, I %A Hoth, S %A Deeken, R %A Ache, P %A Ketchum, K A %A Hoshi, T %A Hedrich, R %C United States %D 1999 %J Proceedings of the National Academy of Sciences of the United States of America %N 13 %P 7581--7586 %R 10.1073/pnas.96.13.7581 %T AKT3, a phloem-localized K+ channel, is blocked by protons %U https://pubmed.ncbi.nlm.nih.gov/10377458 %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, AKT3 was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell K+ 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 H+ and K+ fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.

• Ngezahayo, A., Zeilinger, C., Todt, I., Marten, I., und Kolb, H.A. (1998) „Inactivation of expressed and conducting rCx46 hemichannels by phosphorylation“, Pflugers Archiv : European journal of physiology, 436(4), 627–629, verfügbar unter: https://doi.org/10.1007/s004240050681.
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  Hemichannels of rat connexin 46 (rCx46) were expressed in Xenopus laevis oocytes and analysed by two-electrode voltage-clamp experiments. It is established that rCx46 hemichannels can be activated at low external Ca2+ and positive membrane potentials. Upon larger depolarizations, the hemichannels of oocytes activate in a time-dependent manner, occasionally followed by a spontaneous inactivation. We found that, in the absence of inactivation, treatment of oocytes with 1-oleoyl-2-acetyl-sn-glycerol (OAG), an activator of protein kinase C (PKC), reversibly reduced the amplitude of the rCx46-mediated current and, after an incubation time of about 30 min, induced inactivation of the voltage-dependent current. After wash-out of OAG the corresponding membrane conductance increased and the inactivation behaviour disappeared. The OAG-induced inactivation, as well as the spontaneous inactivation, could be removed by application of the specific PKC inhibitor calphostin C and also by phloretin. The data provide evidence that the activation and inhibition of PKC affect the rCx46-mediated membrane conductance as well as the voltage-dependent current inactivation in an inverse manner.

  @article{ngezahayo1998inactivation, abstract = {Hemichannels of rat connexin 46 (rCx46) were expressed in Xenopus laevis oocytes and analysed by two-electrode voltage-clamp experiments. It is established that rCx46 hemichannels can be activated at low external Ca2+ and positive membrane potentials. Upon larger depolarizations, the hemichannels of oocytes activate in a time-dependent manner, occasionally followed by a spontaneous inactivation. We found that, in the absence of inactivation, treatment of oocytes with 1-oleoyl-2-acetyl-sn-glycerol (OAG), an activator of protein kinase C (PKC), reversibly reduced the amplitude of the rCx46-mediated current and, after an incubation time of about 30 min, induced inactivation of the voltage-dependent current. After wash-out of OAG the corresponding membrane conductance increased and the inactivation behaviour disappeared. The OAG-induced inactivation, as well as the spontaneous inactivation, could be removed by application of the specific PKC inhibitor calphostin C and also by phloretin. The data provide evidence that the activation and inhibition of PKC affect the rCx46-mediated membrane conductance as well as the voltage-dependent current inactivation in an inverse manner.}, address = {Germany}, author = {Ngezahayo, A and Zeilinger, C and Todt, I and Marten, I and Kolb, H A}, journal = {Pflugers Archiv : European journal of physiology}, keywords = {imported}, month = {07}, number = 4, pages = {627–629}, title = {Inactivation of expressed and conducting rCx46 hemichannels by phosphorylation}, volume = 436, year = 1998 }

  %0 Journal Article %1 ngezahayo1998inactivation %A Ngezahayo, A %A Zeilinger, C %A Todt, I %A Marten, I %A Kolb, H A %C Germany %D 1998 %J Pflugers Archiv : European journal of physiology %N 4 %P 627--629 %R 10.1007/s004240050681 %T Inactivation of expressed and conducting rCx46 hemichannels by phosphorylation %U https://pubmed.ncbi.nlm.nih.gov/9683738 %V 436 %X Hemichannels of rat connexin 46 (rCx46) were expressed in Xenopus laevis oocytes and analysed by two-electrode voltage-clamp experiments. It is established that rCx46 hemichannels can be activated at low external Ca2+ and positive membrane potentials. Upon larger depolarizations, the hemichannels of oocytes activate in a time-dependent manner, occasionally followed by a spontaneous inactivation. We found that, in the absence of inactivation, treatment of oocytes with 1-oleoyl-2-acetyl-sn-glycerol (OAG), an activator of protein kinase C (PKC), reversibly reduced the amplitude of the rCx46-mediated current and, after an incubation time of about 30 min, induced inactivation of the voltage-dependent current. After wash-out of OAG the corresponding membrane conductance increased and the inactivation behaviour disappeared. The OAG-induced inactivation, as well as the spontaneous inactivation, could be removed by application of the specific PKC inhibitor calphostin C and also by phloretin. The data provide evidence that the activation and inhibition of PKC affect the rCx46-mediated membrane conductance as well as the voltage-dependent current inactivation in an inverse manner.
• Marten, I. und Hoshi, T. (1998) „The N-terminus of the K channel KAT1 controls its voltage-dependent gating by altering the membrane electric field“, Biophysical journal, 74(6), 2953–2962, verfügbar unter: https://doi.org/10.1016/S0006-3495(98)78002-6.
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  Functional roles of different domains (pore region, S4 segment, N-terminus) of the KAT1 potassium channel in its voltage-dependent gating were electrophysiologically studied in Xenopus oocytes. The KAT1 properties did not depend on the extracellular K+ concentration or on residue H267, equivalent to one of the residues known to be important in C-type inactivation in Shaker channels, indicating that the hyperpolarization-induced KAT1 inward currents are related to the channel activation rather than to recovery from inactivation. Neutralization of a positively charged amino acid in the S4 domain (R176S) reduced the gating charge movement, suggesting that it acts as a voltage-sensing residue in KAT1. N-terminal deletions alone (e.g., delta20-34) did not affect the gating charge movement. However, the deletions paradoxically increased the voltage sensitivity of the R176S mutant channel, but not that of the wild-type channel. We propose a simple model in which the N-terminus determines the KAT1 voltage sensitivity by contributing to the electric field sensed by the voltage sensor.

  @article{marten1998nterminus, abstract = {Functional roles of different domains (pore region, S4 segment, N-terminus) of the KAT1 potassium channel in its voltage-dependent gating were electrophysiologically studied in Xenopus oocytes. The KAT1 properties did not depend on the extracellular K+ concentration or on residue H267, equivalent to one of the residues known to be important in C-type inactivation in Shaker channels, indicating that the hyperpolarization-induced KAT1 inward currents are related to the channel activation rather than to recovery from inactivation. Neutralization of a positively charged amino acid in the S4 domain (R176S) reduced the gating charge movement, suggesting that it acts as a voltage-sensing residue in KAT1. N-terminal deletions alone (e.g., delta20-34) did not affect the gating charge movement. However, the deletions paradoxically increased the voltage sensitivity of the R176S mutant channel, but not that of the wild-type channel. We propose a simple model in which the N-terminus determines the KAT1 voltage sensitivity by contributing to the electric field sensed by the voltage sensor.}, address = {United States}, author = {Marten, I and Hoshi, T}, journal = {Biophysical journal}, keywords = {imported}, month = {06}, number = 6, pages = {2953–2962}, title = {The N-terminus of the K channel KAT1 controls its voltage-dependent gating by altering the membrane electric field}, volume = 74, year = 1998 }

  %0 Journal Article %1 marten1998nterminus %A Marten, I %A Hoshi, T %C United States %D 1998 %J Biophysical journal %N 6 %P 2953--2962 %R 10.1016/S0006-3495(98)78002-6 %T The N-terminus of the K channel KAT1 controls its voltage-dependent gating by altering the membrane electric field %U https://pubmed.ncbi.nlm.nih.gov/9635749 %V 74 %X Functional roles of different domains (pore region, S4 segment, N-terminus) of the KAT1 potassium channel in its voltage-dependent gating were electrophysiologically studied in Xenopus oocytes. The KAT1 properties did not depend on the extracellular K+ concentration or on residue H267, equivalent to one of the residues known to be important in C-type inactivation in Shaker channels, indicating that the hyperpolarization-induced KAT1 inward currents are related to the channel activation rather than to recovery from inactivation. Neutralization of a positively charged amino acid in the S4 domain (R176S) reduced the gating charge movement, suggesting that it acts as a voltage-sensing residue in KAT1. N-terminal deletions alone (e.g., delta20-34) did not affect the gating charge movement. However, the deletions paradoxically increased the voltage sensitivity of the R176S mutant channel, but not that of the wild-type channel. We propose a simple model in which the N-terminus determines the KAT1 voltage sensitivity by contributing to the electric field sensed by the voltage sensor.

• Marten, I. und Hoshi, T. (1997) „Voltage-dependent gating characteristics of the K+ channel KAT1 depend on the N and C termini“, Proceedings of the National Academy of Sciences of the United States of America, 94(7), 3448–3453, verfügbar unter: https://doi.org/10.1073/pnas.94.7.3448.
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  We studied how the C and N termini of the plant K+ channel KAT1 influence the voltage-dependent gating behavior by generating C- and N-terminal deletion mutants. Functional expression was observed only when C-terminal deletions were downstream of the putative cyclic nucleotide binding site. Treatments of oocytes expressing KAT1 channels with anticytoskeletal agents indicated that intact microtubules are important for functional expression. C-terminal deletions altered the voltage sensitivity of the KAT1 channel with greater deletions resulting in smaller equivalent charge movements. In contrast, a deletion in the N terminus (delta20-34) shifted the half-activation voltage by approximately -65 mV without markedly affecting the number of equivalent charges. The results reveal novel roles of the N and C termini in regulation of the voltage-dependent gating of KAT1.

  @article{marten1997voltagedependent, abstract = {We studied how the C and N termini of the plant K+ channel KAT1 influence the voltage-dependent gating behavior by generating C- and N-terminal deletion mutants. Functional expression was observed only when C-terminal deletions were downstream of the putative cyclic nucleotide binding site. Treatments of oocytes expressing KAT1 channels with anticytoskeletal agents indicated that intact microtubules are important for functional expression. C-terminal deletions altered the voltage sensitivity of the KAT1 channel with greater deletions resulting in smaller equivalent charge movements. In contrast, a deletion in the N terminus (delta20-34) shifted the half-activation voltage by approximately -65 mV without markedly affecting the number of equivalent charges. The results reveal novel roles of the N and C termini in regulation of the voltage-dependent gating of KAT1.}, address = {United States}, author = {Marten, I and Hoshi, T}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {imported}, month = {04}, number = 7, pages = {3448–3453}, title = {Voltage-dependent gating characteristics of the K+ channel KAT1 depend on the N and C termini}, volume = 94, year = 1997 }

  %0 Journal Article %1 marten1997voltagedependent %A Marten, I %A Hoshi, T %C United States %D 1997 %J Proceedings of the National Academy of Sciences of the United States of America %N 7 %P 3448--3453 %R 10.1073/pnas.94.7.3448 %T Voltage-dependent gating characteristics of the K+ channel KAT1 depend on the N and C termini %U https://pubmed.ncbi.nlm.nih.gov/9096414 %V 94 %X We studied how the C and N termini of the plant K+ channel KAT1 influence the voltage-dependent gating behavior by generating C- and N-terminal deletion mutants. Functional expression was observed only when C-terminal deletions were downstream of the putative cyclic nucleotide binding site. Treatments of oocytes expressing KAT1 channels with anticytoskeletal agents indicated that intact microtubules are important for functional expression. C-terminal deletions altered the voltage sensitivity of the KAT1 channel with greater deletions resulting in smaller equivalent charge movements. In contrast, a deletion in the N terminus (delta20-34) shifted the half-activation voltage by approximately -65 mV without markedly affecting the number of equivalent charges. The results reveal novel roles of the N and C termini in regulation of the voltage-dependent gating of KAT1.

• Marten, I., Gaymard, F., Lemaillet, G., Thibaud, J.B., Sentenac, H., und Hedrich, R. (1996) „Functional expression of the plant K+ channel KAT1 in insect cells“, FEBS letters, 380(3), 229–232, verfügbar unter: https://doi.org/10.1016/0014-5793(96)00042-7.
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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 focussed on the expression and characterization of the Arabidopsis 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 -80mV 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-traditional modification and assembly of a green inward rectifier.

  @article{marten1996functional, 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 focussed on the expression and characterization of the Arabidopsis 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 -80mV 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-traditional modification and assembly of a green inward rectifier.}, address = {England}, author = {Marten, I and Gaymard, F and Lemaillet, G and Thibaud, J B and Sentenac, H and Hedrich, R}, journal = {FEBS letters}, keywords = {imported}, month = {02}, number = 3, pages = {229–232}, title = {Functional expression of the plant K+ channel KAT1 in insect cells}, volume = 380, year = 1996 }

  %0 Journal Article %1 marten1996functional %A Marten, I %A Gaymard, F %A Lemaillet, G %A Thibaud, J B %A Sentenac, H %A Hedrich, R %C England %D 1996 %J FEBS letters %N 3 %P 229--232 %R 10.1016/0014-5793(96)00042-7 %T Functional expression of the plant K+ channel KAT1 in insect cells %U https://pubmed.ncbi.nlm.nih.gov/8601430 %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 focussed on the expression and characterization of the Arabidopsis 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 -80mV 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-traditional modification and assembly of a green inward rectifier.

• Schulz-Lessdorf, B., Dietrich, P., Marten, I., Lohse, G., Busch, H., und Hedrich, R. (1994) „Coordination of plasma membrane and vacuolar membrane ion channels during stomatal movement“, Symposia of the Society for Experimental Biology, 48, 99–112, verfügbar unter: https://pubmed.ncbi.nlm.nih.gov/7541165.
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  Transduction of extracellular signals in guard cells requires coupling of ion fluxes across the vacuolar and plasma membrane. Changes in cytoplasmic proton and Ca2+ concentrations are important messages during stomatal movement. Here we summarize the different biophysical properties of voltage- and ligand-dependent ion channels in both the vacuolar and plasma membranes of guard cells, focusing on how cytoplasmic Ca2+ and proton concentrations direct ion fluxes towards stomatal opening or closure. Particular attention is given to the patch clamp analysis of plasma membrane cation channels (GCKCin, GCKCout and Ca2+ channels), the anion channel (GCAC1) and the vacuolar SV-type channels. A working model is presented of how the ion channels of both membrane systems could communicate to synchronize potassium salt release during stomatal closure.

  @article{schulzlessdorf1994coordination, abstract = {Transduction of extracellular signals in guard cells requires coupling of ion fluxes across the vacuolar and plasma membrane. Changes in cytoplasmic proton and Ca2+ concentrations are important messages during stomatal movement. Here we summarize the different biophysical properties of voltage- and ligand-dependent ion channels in both the vacuolar and plasma membranes of guard cells, focusing on how cytoplasmic Ca2+ and proton concentrations direct ion fluxes towards stomatal opening or closure. Particular attention is given to the patch clamp analysis of plasma membrane cation channels (GCKCin, GCKCout and Ca2+ channels), the anion channel (GCAC1) and the vacuolar SV-type channels. A working model is presented of how the ion channels of both membrane systems could communicate to synchronize potassium salt release during stomatal closure.}, address = {England}, author = {Schulz-Lessdorf, B and Dietrich, P and Marten, I and Lohse, G and Busch, H and Hedrich, R}, journal = {Symposia of the Society for Experimental Biology}, keywords = {imported}, pages = {99–112}, title = {Coordination of plasma membrane and vacuolar membrane ion channels during stomatal movement}, volume = 48, year = 1994 }

  %0 Journal Article %1 schulzlessdorf1994coordination %A Schulz-Lessdorf, B %A Dietrich, P %A Marten, I %A Lohse, G %A Busch, H %A Hedrich, R %C England %D 1994 %J Symposia of the Society for Experimental Biology %P 99--112 %T Coordination of plasma membrane and vacuolar membrane ion channels during stomatal movement %U https://pubmed.ncbi.nlm.nih.gov/7541165 %V 48 %X Transduction of extracellular signals in guard cells requires coupling of ion fluxes across the vacuolar and plasma membrane. Changes in cytoplasmic proton and Ca2+ concentrations are important messages during stomatal movement. Here we summarize the different biophysical properties of voltage- and ligand-dependent ion channels in both the vacuolar and plasma membranes of guard cells, focusing on how cytoplasmic Ca2+ and proton concentrations direct ion fluxes towards stomatal opening or closure. Particular attention is given to the patch clamp analysis of plasma membrane cation channels (GCKCin, GCKCout and Ca2+ channels), the anion channel (GCAC1) and the vacuolar SV-type channels. A working model is presented of how the ion channels of both membrane systems could communicate to synchronize potassium salt release during stomatal closure.
• Hedrich, R., Marten, I., Dietrich, P., Lohse, G., Winter, H., Lohaus, G., und Heldt, H. (1994) „Malate-sensitive anion channels enable guard cells to sense changes in the ambient CO2 concentration.“, Plant Journal, 6, 741–748.
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  @article{hedrich1994malatesensitive, author = {Hedrich, R. and Marten, I. and Dietrich, P. and Lohse, G. and Winter, H. and Lohaus, G. and Heldt, H.W.}, journal = {Plant Journal}, keywords = {myown}, pages = {741-748}, title = {Malate-sensitive anion channels enable guard cells to sense changes in the ambient CO2 concentration.}, volume = 6, year = 1994 }

  %0 Journal Article %1 hedrich1994malatesensitive %A Hedrich, R. %A Marten, I. %A Dietrich, P. %A Lohse, G. %A Winter, H. %A Lohaus, G. %A Heldt, H.W. %D 1994 %J Plant Journal %P 741-748 %T Malate-sensitive anion channels enable guard cells to sense changes in the ambient CO2 concentration. %V 6

• Hedrich, R. und Marten, I. (1993) „Malate-induced feedback regulation of plasma membrane anion channels could provide a CO2 sensor to guard cells“, The EMBO journal, 12(3), 897–901, verfügbar unter: https://doi.org/10.1002/j.1460-2075.1993.tb05730.x.
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  Plants have developed strategies to circumvent limitations in water supply through the adjustment of stomatal aperture in relation to the photosynthetic capacity (water-use efficiency). The CO2 sensor of guard cells, reporting on the metabolic status of the photosynthetic tissue, is, however, as yet unknown. We elucidated whether extracellular malate has the capability to serve as a signal metabolite in regulating the membrane properties of guard cells. Patch-clamp studies showed that slight variations in the external malate concentration induced major alterations in the voltage-dependent activity of the guard cell anion channel (GCAC1). Superfusion of guard cell protoplasts with malate solutions in the physiological range caused the voltage-gate to shift towards hyperpolarized potentials (Km(mal) = 0.4 mM elicits a 38 mV shift). The selectivity sequence of the anion channel NO3- (4.2) > or = I- (3.9) > Br- (1.9) > Cl- (1) >> mal (0.1) indicates that malate is able to permeate GCAC1. The binding site for shifting the gate is, however, located on the extracellular face of the channel since cytoplasmic malate proved ineffective. Single-channel analysis indicates that extracellular malate affects the voltage-dependent mean open time rather than the unitary conductance of GCAC1. In contrast to malate the rise in the extracellular Cl- concentration increases the unit conductance of the anion efflux channel. We suggest that stomata sense changes in the intercellular CO2 concentration and thus the photosynthetic activity of the mesophyll via feedback regulation of anion efflux from guard cells through malate-sensitive GCAC1.

  @article{hedrich1993malateinduced, abstract = {Plants have developed strategies to circumvent limitations in water supply through the adjustment of stomatal aperture in relation to the photosynthetic capacity (water-use efficiency). The CO2 sensor of guard cells, reporting on the metabolic status of the photosynthetic tissue, is, however, as yet unknown. We elucidated whether extracellular malate has the capability to serve as a signal metabolite in regulating the membrane properties of guard cells. Patch-clamp studies showed that slight variations in the external malate concentration induced major alterations in the voltage-dependent activity of the guard cell anion channel (GCAC1). Superfusion of guard cell protoplasts with malate solutions in the physiological range caused the voltage-gate to shift towards hyperpolarized potentials (Km(mal) = 0.4 mM elicits a 38 mV shift). The selectivity sequence of the anion channel NO3- (4.2) > or = I- (3.9) > Br- (1.9) > Cl- (1) >> mal (0.1) indicates that malate is able to permeate GCAC1. The binding site for shifting the gate is, however, located on the extracellular face of the channel since cytoplasmic malate proved ineffective. Single-channel analysis indicates that extracellular malate affects the voltage-dependent mean open time rather than the unitary conductance of GCAC1. In contrast to malate the rise in the extracellular Cl- concentration increases the unit conductance of the anion efflux channel. We suggest that stomata sense changes in the intercellular CO2 concentration and thus the photosynthetic activity of the mesophyll via feedback regulation of anion efflux from guard cells through malate-sensitive GCAC1.}, address = {England}, author = {Hedrich, R and Marten, I}, journal = {The EMBO journal}, keywords = {imported}, month = {03}, number = 3, pages = {897–901}, title = {Malate-induced feedback regulation of plasma membrane anion channels could provide a CO2 sensor to guard cells}, volume = 12, year = 1993 }

  %0 Journal Article %1 hedrich1993malateinduced %A Hedrich, R %A Marten, I %C England %D 1993 %J The EMBO journal %N 3 %P 897--901 %R 10.1002/j.1460-2075.1993.tb05730.x %T Malate-induced feedback regulation of plasma membrane anion channels could provide a CO2 sensor to guard cells %U https://pubmed.ncbi.nlm.nih.gov/7681395 %V 12 %X Plants have developed strategies to circumvent limitations in water supply through the adjustment of stomatal aperture in relation to the photosynthetic capacity (water-use efficiency). The CO2 sensor of guard cells, reporting on the metabolic status of the photosynthetic tissue, is, however, as yet unknown. We elucidated whether extracellular malate has the capability to serve as a signal metabolite in regulating the membrane properties of guard cells. Patch-clamp studies showed that slight variations in the external malate concentration induced major alterations in the voltage-dependent activity of the guard cell anion channel (GCAC1). Superfusion of guard cell protoplasts with malate solutions in the physiological range caused the voltage-gate to shift towards hyperpolarized potentials (Km(mal) = 0.4 mM elicits a 38 mV shift). The selectivity sequence of the anion channel NO3- (4.2) > or = I- (3.9) > Br- (1.9) > Cl- (1) >> mal (0.1) indicates that malate is able to permeate GCAC1. The binding site for shifting the gate is, however, located on the extracellular face of the channel since cytoplasmic malate proved ineffective. Single-channel analysis indicates that extracellular malate affects the voltage-dependent mean open time rather than the unitary conductance of GCAC1. In contrast to malate the rise in the extracellular Cl- concentration increases the unit conductance of the anion efflux channel. We suggest that stomata sense changes in the intercellular CO2 concentration and thus the photosynthetic activity of the mesophyll via feedback regulation of anion efflux from guard cells through malate-sensitive GCAC1.
• Marten, I., Busch, H., Raschke, K., und Hedrich, R. (1993) „Modulation and block of the plasma membrane anion channel of guard cells by stilbene derivatives“, European Biophysics Journal, 21, 403–408.
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  @article{noauthororeditor, author = {Marten, I. and Busch, H. and Raschke, K. and Hedrich, R.}, journal = {European Biophysics Journal}, keywords = {myown}, pages = {403-408}, title = {Modulation and block of the plasma membrane anion channel of guard cells by stilbene derivatives}, volume = 21, year = 1993 }

  %0 Journal Article %1 noauthororeditor %A Marten, I. %A Busch, H. %A Raschke, K. %A Hedrich, R. %D 1993 %J European Biophysics Journal %P 403-408 %T Modulation and block of the plasma membrane anion channel of guard cells by stilbene derivatives %V 21

• Marten, I., Zeilinger, C., Redhead, C., Landry, D.W., al Awqati, Q., und Hedrich, R. (1992) „Identification and modulation of a voltage-dependent anion channel in the plasma membrane of guard cells by high-affinity ligands“, The EMBO journal, 11(10), 3569–3575, verfügbar unter: https://doi.org/10.1002/j.1460-2075.1992.tb05440.x.
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  Guard cell anion channels (GCAC1) catalyze the release of anions across the plasma membrane during regulated volume decrease and also seem to be involved in the targeting of the plant growth hormones auxins. We have analyzed the modulation and inhibition of these voltage-dependent anion channels by different anion channel blockers. Ethacrynic acid, a structural correlate of an auxin, caused a shift in activation potential and simultaneously a transient increase in the peak current amplitude, whereas other blockers shifted and blocked the voltage-dependent activity of the channel. Comparison of dose-response curves for shift and block imposed by the inhibitor, indicate two different sites within the channel which interact with the ligand. The capability to inhibit GCAC1 increases in a dose-dependent manner in the sequence: probenecid less than A-9-C less than ethacrynic acid less than niflumic acid less than IAA-94 less than NPPB. 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, indicating an interaction with the open mouth of the channel. IAA-23, a structural analog of IAA-94, was used to enrich ligand-binding polypeptides from the plasma membrane of guard cells by IAA-23 affinity chromatography. From this protein fraction a 60 kDa polypeptide crossreacted specifically with polyclonal antibodies raised against anion channels isolated from kidney membranes. In contrast to guard cells, mesophyll plasma membranes were deficient in voltage-dependent anion channels and lacked crossreactivity with the antibody.

  @article{marten1992identification, abstract = {Guard cell anion channels (GCAC1) catalyze the release of anions across the plasma membrane during regulated volume decrease and also seem to be involved in the targeting of the plant growth hormones auxins. We have analyzed the modulation and inhibition of these voltage-dependent anion channels by different anion channel blockers. Ethacrynic acid, a structural correlate of an auxin, caused a shift in activation potential and simultaneously a transient increase in the peak current amplitude, whereas other blockers shifted and blocked the voltage-dependent activity of the channel. Comparison of dose-response curves for shift and block imposed by the inhibitor, indicate two different sites within the channel which interact with the ligand. The capability to inhibit GCAC1 increases in a dose-dependent manner in the sequence: probenecid less than A-9-C less than ethacrynic acid less than niflumic acid less than IAA-94 less than NPPB. 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, indicating an interaction with the open mouth of the channel. IAA-23, a structural analog of IAA-94, was used to enrich ligand-binding polypeptides from the plasma membrane of guard cells by IAA-23 affinity chromatography. From this protein fraction a 60 kDa polypeptide crossreacted specifically with polyclonal antibodies raised against anion channels isolated from kidney membranes. In contrast to guard cells, mesophyll plasma membranes were deficient in voltage-dependent anion channels and lacked crossreactivity with the antibody.}, address = {England}, author = {Marten, I and Zeilinger, C and Redhead, C and Landry, D W and al Awqati, Q and Hedrich, R}, journal = {The EMBO journal}, keywords = {imported}, month = 10, number = 10, pages = {3569–3575}, title = {Identification and modulation of a voltage-dependent anion channel in the plasma membrane of guard cells by high-affinity ligands}, volume = 11, year = 1992 }

  %0 Journal Article %1 marten1992identification %A Marten, I %A Zeilinger, C %A Redhead, C %A Landry, D W %A al Awqati, Q %A Hedrich, R %C England %D 1992 %J The EMBO journal %N 10 %P 3569--3575 %R 10.1002/j.1460-2075.1992.tb05440.x %T Identification and modulation of a voltage-dependent anion channel in the plasma membrane of guard cells by high-affinity ligands %U https://pubmed.ncbi.nlm.nih.gov/1382976 %V 11 %X Guard cell anion channels (GCAC1) catalyze the release of anions across the plasma membrane during regulated volume decrease and also seem to be involved in the targeting of the plant growth hormones auxins. We have analyzed the modulation and inhibition of these voltage-dependent anion channels by different anion channel blockers. Ethacrynic acid, a structural correlate of an auxin, caused a shift in activation potential and simultaneously a transient increase in the peak current amplitude, whereas other blockers shifted and blocked the voltage-dependent activity of the channel. Comparison of dose-response curves for shift and block imposed by the inhibitor, indicate two different sites within the channel which interact with the ligand. The capability to inhibit GCAC1 increases in a dose-dependent manner in the sequence: probenecid less than A-9-C less than ethacrynic acid less than niflumic acid less than IAA-94 less than NPPB. 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, indicating an interaction with the open mouth of the channel. IAA-23, a structural analog of IAA-94, was used to enrich ligand-binding polypeptides from the plasma membrane of guard cells by IAA-23 affinity chromatography. From this protein fraction a 60 kDa polypeptide crossreacted specifically with polyclonal antibodies raised against anion channels isolated from kidney membranes. In contrast to guard cells, mesophyll plasma membranes were deficient in voltage-dependent anion channels and lacked crossreactivity with the antibody.

• Marten, I., Lohse, G., und Hedrich, R. (1991) „Plant growth hormones control voltage-dependent activity of anion channels in the plasma membrane of guard cells“, Nature, 353, 759–762.
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  @article{imartenglohse1991plant, author = {Marten, I. and Lohse, G. and Hedrich, R.}, journal = {Nature}, keywords = {myown}, pages = {759-762}, title = {Plant growth hormones control voltage-dependent activity of anion channels in the plasma membrane of guard cells}, volume = 353, year = 1991 }

  %0 Journal Article %1 imartenglohse1991plant %A Marten, I. %A Lohse, G. %A Hedrich, R. %D 1991 %J Nature %P 759-762 %T Plant growth hormones control voltage-dependent activity of anion channels in the plasma membrane of guard cells %V 353