1
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Blatt MR. A charged existence: A century of transmembrane ion transport in plants. PLANT PHYSIOLOGY 2024; 195:79-110. [PMID: 38163639 PMCID: PMC11060664 DOI: 10.1093/plphys/kiad630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 11/01/2023] [Indexed: 01/03/2024]
Abstract
If the past century marked the birth of membrane transport as a focus for research in plants, the past 50 years has seen the field mature from arcane interest to a central pillar of plant physiology. Ion transport across plant membranes accounts for roughly 30% of the metabolic energy consumed by a plant cell, and it underpins virtually every aspect of plant biology, from mineral nutrition, cell expansion, and development to auxin polarity, fertilization, plant pathogen defense, and senescence. The means to quantify ion flux through individual transporters, even single channel proteins, became widely available as voltage clamp methods expanded from giant algal cells to the fungus Neurospora crassa in the 1970s and the cells of angiosperms in the 1980s. Here, I touch briefly on some key aspects of the development of modern electrophysiology with a focus on the guard cells of stomata, now without dispute the premier plant cell model for ion transport and its regulation. Guard cells have proven to be a crucible for many technical and conceptual developments that have since emerged into the mainstream of plant science. Their study continues to provide fundamental insights and carries much importance for the global challenges that face us today.
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Affiliation(s)
- Michael R Blatt
- Laboratory of Plant Physiology and Biophysics, University of Glasgow, Bower Building, Glasgow G12 8QQ, UK
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2
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Lu J, Dreyer I, Dickinson MS, Panzer S, Jaślan D, Navarro-Retamal C, Geiger D, Terpitz U, Becker D, Stroud RM, Marten I, Hedrich R. Vicia faba SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels. eLife 2023; 12:e86384. [PMID: 37991833 PMCID: PMC10665017 DOI: 10.7554/elife.86384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 10/12/2023] [Indexed: 11/23/2023] Open
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 Ca2+. In our search for species-dependent functional TPC1 channel variants with different luminal Ca2+ sensitivity, we found in total three acidic residues present in Ca2+ sensor sites 2 and 3 of the Ca2+-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 Ca2+. When AtTPC1 was mutated for these VfTPC1-homologous polymorphic residues, two neutral substitutions in Ca2+ sensor site 3 alone were already sufficient for the Arabidopsis At-VfTPC1 channel mutant to gain VfTPC1-like voltage and luminal Ca2+ 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.
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Affiliation(s)
- Jinping Lu
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
- School of Life Sciences, Zhengzhou UniversityZhengzhouChina
| | - Ingo Dreyer
- Universidad de Talca, Faculty of Engineering, Center of Bioinformatics, Simulation and ModelingTalcaChile
| | - Miles Sasha Dickinson
- University of California San Francisco, Department of Biochemistry and BiophysicsSan FranciscoUnited States
| | - Sabine Panzer
- Julius-Maximilians-Universität (JMU), Biocenter, Theodor-Boveri-Institute, Department of Biotechnology and BiophysicsWürzburgGermany
| | - Dawid Jaślan
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
- Ludwig Maximilians-Universität, Faculty of Medicine, Walther Straub Institute of Pharmacology and ToxicologyMunichGermany
| | - Carlos Navarro-Retamal
- Universidad de Talca, Faculty of Engineering, Center of Bioinformatics, Simulation and ModelingTalcaChile
- Department of Cell Biology and Molecular Genetics, University of MarylandCollege ParkUnited States
| | - Dietmar Geiger
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
| | - Ulrich Terpitz
- Julius-Maximilians-Universität (JMU), Biocenter, Theodor-Boveri-Institute, Department of Biotechnology and BiophysicsWürzburgGermany
| | - Dirk Becker
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
| | - Robert M Stroud
- University of California San Francisco, Department of Biochemistry and BiophysicsSan FranciscoUnited States
| | - Irene Marten
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
| | - Rainer Hedrich
- Julius-Maximilians-Universität (JMU), Biocenter, Department of Molecular Plant Physiology and BiophysicsWürzburgGermany
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3
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Dickinson MS, Lu J, Gupta M, Marten I, Hedrich R, Stroud RM. Molecular basis of multistep voltage activation in plant two-pore channel 1. Proc Natl Acad Sci U S A 2022; 119:e2110936119. [PMID: 35210362 PMCID: PMC8892357 DOI: 10.1073/pnas.2110936119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 11/29/2021] [Indexed: 12/26/2022] Open
Abstract
Voltage-gated ion channels confer excitability to biological membranes, initiating and propagating electrical signals across large distances on short timescales. Membrane excitation requires channels that respond to changes in electric field and couple the transmembrane voltage to gating of a central pore. To address the mechanism of this process in a voltage-gated ion channel, we determined structures of the plant two-pore channel 1 at different stages along its activation coordinate. These high-resolution structures of activation intermediates, when compared with the resting-state structure, portray a mechanism in which the voltage-sensing domain undergoes dilation and in-membrane plane rotation about the gating charge-bearing helix, followed by charge translocation across the charge transfer seal. These structures, in concert with patch-clamp electrophysiology, show that residues in the pore mouth sense inhibitory Ca2+ and are allosterically coupled to the voltage sensor. These conformational changes provide insight into the mechanism of voltage-sensor domain activation in which activation occurs vectorially over a series of elementary steps.
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Affiliation(s)
- Miles Sasha Dickinson
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
- Chemistry and Chemical Biology Graduate Program, University of California, San Francisco, CA 94143
| | - Jinping Lu
- Department of Molecular Plant Physiology and Biophysics, University of Würzburg, D-97082 Würzburg, Germany
| | - Meghna Gupta
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
| | - Irene Marten
- Department of Molecular Plant Physiology and Biophysics, University of Würzburg, D-97082 Würzburg, Germany
| | - Rainer Hedrich
- Department of Molecular Plant Physiology and Biophysics, University of Würzburg, D-97082 Würzburg, Germany
| | - Robert M Stroud
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143;
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4
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Amponsah J, Tegg RS, Thangavel T, Wilson CR. Subversion of Phytomyxae Cell Communication With Surrounding Environment to Control Soilborne Diseases; A Case Study of Cytosolic Ca 2+ Signal Disruption in Zoospores of Spongospora subterranea. Front Microbiol 2022; 13:754225. [PMID: 35300485 PMCID: PMC8921600 DOI: 10.3389/fmicb.2022.754225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 02/09/2022] [Indexed: 11/13/2022] Open
Abstract
Ca2+ signaling regulates physiological processes including chemotaxis in eukaryotes and prokaryotes. Its inhibition has formed the basis for control of human disease but remains largely unexplored for plant disease. This study investigated the role of Ca2+ signaling on motility and chemotaxis of Spongospora subterranea zoospores, responsible for root infections leading to potato root and tuber disease. Cytosolic Ca2+ flux inhibition with Ca2+ antagonists were found to alter zoospore swimming patterns and constrain zoospore chemotaxis, root attachment and zoosporangia infection. LaCl3 and GdCl3, both Ca2+ channel blockers, at concentrations ≥ 50 μM showed complete inhibition of zoospore chemotaxis, root attachment and zoosporangia root infection. The Ca2+ chelator EGTA, showed efficient chemotaxis inhibition but had relatively less effect on root attachment. Conversely the calmodulin antagonist trifluoperazine had lesser effect on zoospore chemotaxis but showed strong inhibition of zoospore root attachment. Amiloride hydrochloride had a significant inhibitory effect on chemotaxis, root attachment, and zoosporangia root infection with dose rates ≥ 150 μM. As expected, zoospore attachment was directly associated with root infection and zoosporangia development. These results highlight the fundamental role of Ca2+ signaling in zoospore chemotaxis and disease establishment. Their efficient interruption may provide durable and practical control of Phytomyxea soilborne diseases in the field.
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Affiliation(s)
- Jonathan Amponsah
- Tasmanian Institute of Agriculture, University of Tasmania, Hobart, TAS, Australia
- Biotechnology and Nuclear Agricultural Research Institute Centre, Ghana Atomic Energy Commission, Accra, Ghana
| | - Robert S. Tegg
- Tasmanian Institute of Agriculture, University of Tasmania, Hobart, TAS, Australia
| | | | - Calum R. Wilson
- Tasmanian Institute of Agriculture, University of Tasmania, Hobart, TAS, Australia
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5
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Hedrich R, Mueller TD, Becker D, Marten I. Structure and Function of TPC1 Vacuole SV Channel Gains Shape. MOLECULAR PLANT 2018; 11:764-775. [PMID: 29614320 DOI: 10.1016/j.molp.2018.03.017] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 03/12/2018] [Accepted: 03/22/2018] [Indexed: 05/20/2023]
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.
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Affiliation(s)
- Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany.
| | - Thomas D Mueller
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
| | - Dirk Becker
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
| | - Irene Marten
- Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, 97082 Würzburg, Germany
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6
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Pottosin I, Dobrovinskaya O. Two-pore cation (TPC) channel: not a shorthanded one. FUNCTIONAL PLANT BIOLOGY : FPB 2018; 45:83-92. [PMID: 32291023 DOI: 10.1071/fp16338] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Accepted: 11/05/2016] [Indexed: 06/11/2023]
Abstract
Two-pore cation (TPC) channels form functional dimers in membranes, delineating acidic intracellular compartments such as vacuoles in plants and lysosomes in animals. TPC1 is ubiquitously expressed in thousands of copies per vacuole in terrestrial plants, where it is known as slow vacuolar (SV) channel. An SV channel possesses high permeability for Na+, K+, Mg2+, and Ca2+, but requires high (tens of μM) cytosolic Ca2+ and non-physiological positive voltages for its full activation. Its voltage dependent activation is negatively modulated by physiological concentrations of vacuolar Ca2+, Mg2+and H+. Double control of the SV channel activity from cytosolic and vacuolar sides keeps its open probability at a minimum and precludes a potentially harmful global Ca2+ release. But this raises the question of what such' inactive' channel could be good for? One possibility is that it is involved in ultra-local Ca2+ signalling by generating 'hotspots' - microdomains of extremely high cytosolic Ca2+. Unexpectedly, recent studies have demonstrated the essential role of the TPC1 in the systemic Ca2+ signalling, and the crystal structure of plant TPC1, which became available this year, unravels molecular mechanisms underlying voltage and Ca2+ gating. This review emphasises the significance of these ice-breaking findings and sets a new perspective for the TPC1-based Ca2+ signalling.
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Affiliation(s)
- Igor Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián,Colima, Col. 28045, México
| | - Oxana Dobrovinskaya
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián,Colima, Col. 28045, México
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7
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Geilfus CM, Carpentier SC, Zavišić A, Polle A. Changes in the fine root proteome of Fagus sylvatica L. trees associated with P-deficiency and amelioration of P-deficiency. J Proteomics 2017. [PMID: 28625739 DOI: 10.1016/j.jprot.2017.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Phosphorus is often the least available macronutrient in soil. Lack in phosphorus has detrimental effect on growth and biomass production of European Fagus sylvatica L., a major trees species in temperate forests. In contrast to leaf tissues, few studies have examined changes in the root system and no study has ever investigated the proteomic changes affected in beech roots by a lack in available phosphate (P). Here, we studied roots of young Fagus sylvatica L. trees in their native soils from two forests sites with contrasting availability of P: one P rich and P poor soil. To understand also the response to P fertilization, the trees were fertilized with triple superphosphate and the proteome of fine roots of all conditions was compared. Gel-free mass-spectrometry-based shotgun proteomics revealed that the proteome was differentially affected by diverging P availabilities. The proteomic changes that took place as the result of P fertilization were dependent on the supply level of P before the fertilization. When P was supplied to the P-rich soil proteins related to cell biogenesis exhibited increased abundances. Addition of P to soil that was strongly limited in P resulted in increased abundance of proteins associated with amino acid metabolism and transport. BIOLOGICAL SIGNIFICANCE Beech (Fagus sylvatica L.) forests have a huge ecological and economic value across Europe. In recent years, however, these forest sites increasingly suffer under phosphorus (P) deficiency. As the consequence, growth and vitality of beech forests is impaired. For this reason, this study was conducted with the aim to identify and understand proteomic impairments and adjustments that evolve in the fine roots under both, a P deficiency and an amelioration thereof. For this, we analyzed (1) the fine root proteome of young beech trees grown (2) at two soil sites that contrast in their degree of availability P (low vs. high) in dependency (3) to a fertilization with P. This experiment revealed fundamental differences with respect to proteomic changes in dependency on the severity of P limitation and helped to identify processes that take place after amelioration of the deficiency. This information is useful to understand which physiological processes are impaired under P deficiency and, thus, impair growth. The fertilization experiment enabled to identify developmental processes that take place in fine roots when concentration of available P was increased. They are "cellular component organization and biogenesis" in the P rich soil and "synthesis of organonitrogen-containing compounds" in the P poor soil.
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Affiliation(s)
- Christoph-Martin Geilfus
- SYBIOMA, Proteomics Core Facility, KU Leuven, O&N II Herestraat 49 - Bus 901, B-3000 Leuven, Belgium; Division of Crop Product Quality, Institute of Crop Science, University of Hohenheim, Emil-Wolff-Straße 25, 70599 Stuttgart, Germany; Controlled Environment Horticulture, Faculty of Life Sciences, Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences, Humboldt-University of Berlin, Lentzeallee, 14195 Berlin, Germany.
| | - Sebastien Christian Carpentier
- SYBIOMA, Proteomics Core Facility, KU Leuven, O&N II Herestraat 49 - Bus 901, B-3000 Leuven, Belgium; Division of Crop Biotechnics, Department of Biosystems, KU Leuven, Willem de Croylaan 42, - Box 2455, B-3001 Leuven, Belgium
| | - Aljoša Zavišić
- Department of Forest Botany and Tree Physiology, Georg-August-Universität Göttingen, Büsgenweg 2, 37077 Göttingen, Germany
| | - Andrea Polle
- Department of Forest Botany and Tree Physiology, Georg-August-Universität Göttingen, Büsgenweg 2, 37077 Göttingen, Germany
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8
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Lüttge U. Physics and the molecular revolution in plant biology: union needed for managing the future. AIMS BIOPHYSICS 2016. [DOI: 10.3934/biophy.2016.4.501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
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9
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Affiliation(s)
- F. J. M. Maathuis
- Department of Plant Biology; University of Groningen; Ecotrans, P.O. Box 14 9750 A A Haren The Netherlands
| | - H. B. A. Prins
- Department of Plant Biology; University of Groningen; Ecotrans, P.O. Box 14 9750 A A Haren The Netherlands
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10
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Zhang X, Shen Z, Sun J, Yu Y, Deng S, Li Z, Sun C, Zhang J, Zhao R, Shen X, Chen S. NaCl-elicited, vacuolar Ca(2+) release facilitates prolonged cytosolic Ca(2+) signaling in the salt response of Populus euphratica cells. Cell Calcium 2015; 57:348-65. [PMID: 25840638 DOI: 10.1016/j.ceca.2015.03.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Revised: 02/24/2015] [Accepted: 03/09/2015] [Indexed: 10/23/2022]
Abstract
High environmental salt elicits an increase in cytosolic Ca(2+) ([Ca(2+)]cyt) in plants, which is generated by extracellular Ca(2+) influx and Ca(2+) release from intracellular stores, such as vacuole and endoplasmic reticulum. This study aimed to determine the physiological mechanisms underlying Ca(2+) release from vacuoles and its role in ionic homeostasis in Populus euphratica. In vivo Ca(2+) imaging showed that NaCl treatment induced a rapid elevation in [Ca(2+)]cyt, which was accompanied by a subsequent release of vacuolar Ca(2+). In cell cultures, NaCl-altered intracellular Ca(2+) mobilization was abolished by antagonists of inositol (1, 4, 5) trisphosphate (IP3) and cyclic adenosine diphosphate ribose (cADPR) signaling pathways, but not by slow vacuolar (SV) channel blockers. Furthermore, the NaCl-induced vacuolar Ca(2+) release was dependent on extracellular ATP, extracellular Ca(2+) influx, H2O2, and NO. In vitro Ca(2+) flux recordings confirmed that IP3, cADPR, and Ca(2+) induced substantial Ca(2+) efflux from intact vacuoles, but this vacuolar Ca(2+) flux did not directly respond to ATP, H2O2, or NO. Moreover, the IP3/cADPR-mediated vacuolar Ca(2+) release enhanced the expression of salt-responsive genes that regulated a wide range of cellular processes required for ion homeostasis, including cytosolic K(+) maintenance, Na(+) and Cl(-) exclusion across the plasma membrane, and Na(+)/H(+) and Cl(-)/H(+) exchanges across the vacuolar membrane.
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Affiliation(s)
- Xuan Zhang
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zedan Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Jian Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China.
| | - Yicheng Yu
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Shurong Deng
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Zongyun Li
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Cunhua Sun
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Jian Zhang
- Institute of Integrative Plant Biology, School of Life Science, Jiangsu Normal University, Xuzhou 221116, Jiangsu Province, People's Republic of China
| | - Rui Zhao
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Xin Shen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China
| | - Shaoliang Chen
- College of Biological Sciences and Technology, Beijing Forestry University (Box 162), Beijing 100083, People's Republic of China.
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11
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Pottosin I, Dobrovinskaya O. Non-selective cation channels in plasma and vacuolar membranes and their contribution to K+ transport. JOURNAL OF PLANT PHYSIOLOGY 2014; 171:732-42. [PMID: 24560436 DOI: 10.1016/j.jplph.2013.11.013] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 11/21/2013] [Accepted: 11/22/2013] [Indexed: 05/25/2023]
Abstract
Both in vacuolar and plasma membranes, in addition to truly K(+)-selective channels there is a variety of non-selective channels, which conduct K(+) and other ions with little preference. Many non-selective channels in the plasma membrane are active at depolarized potentials, thus, contributing to K(+) efflux rather than to K(+) uptake. They may play important roles in xylem loading or contribute to a K(+) leak, induced by salt or oxidative stress. Here, three currents, expressed in root cells, are considered: voltage-insensitive cation current, non-selective outwardly rectifying current, and low-selective conductance, activated by reactive oxygen species. The latter two do not only poorly discriminate between different cations (like K(+)vs Na(+)), but also conduct anions. Such solute channels may mediate massive electroneutral transport of salts and might be involved in osmotic adjustment or volume decrease, associated with cell death. In the tonoplast two major currents are mediated by SV (slow) and FV (fast) vacuolar channels, respectively, which are virtually impermeable for anions. SV channels conduct mono- and divalent cations indiscriminately and are activated by high cytosolic Ca(2+) and depolarized voltages. FV channels are inhibited by micromolar cytosolic Ca(2+), Mg(2+), and polyamines, and conduct a variety of monovalent cations, including K(+). Strikingly, both SV and FV channels sense the K(+) content of vacuoles, which modulates their voltage dependence, and in case of SV, also alleviates channel's inhibition by luminal Ca(2+). Therefore, SV and FV channels may operate as K(+)-sensing valves, controlling K(+) distribution between the vacuole and the cytosol.
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Affiliation(s)
- Igor Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián, 28045 Colima, Mexico.
| | - Oxana Dobrovinskaya
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Av. 25 de julio 965, Villa de San Sebastián, 28045 Colima, Mexico
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12
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Isayenkov SV. Plant vacuoles: Physiological roles and mechanisms of vacuolar sorting and vesicular trafficking. CYTOL GENET+ 2014. [DOI: 10.3103/s0095452714020042] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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13
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Pottosin I, Shabala S. Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling. FRONTIERS IN PLANT SCIENCE 2014; 5:154. [PMID: 24795739 PMCID: PMC4006063 DOI: 10.3389/fpls.2014.00154] [Citation(s) in RCA: 100] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 04/02/2014] [Indexed: 05/18/2023]
Abstract
Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm(4+) > Spd(3+) > Put(2+). On the contrary, effects of polyamines on the plasma membrane (PM) cation and K(+)-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H(+) pumps and Ca(2+) pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca(2+) influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment.
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Affiliation(s)
- Igor Pottosin
- Biomedical Centre, Centro Universitario de Investigaciones Biomédicas, University of ColimaColima, Mexico
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
| | - Sergey Shabala
- School of Land and Food, University of TasmaniaHobart, TAS, Australia
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14
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15
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Raschke K, Hedrich R, Reckmann U, Schroeder JI. Exploring Biophysical and Biochemical Components of the Osmotic Motor that Drives Stomatal Movement*. ACTA ACUST UNITED AC 2014. [DOI: 10.1111/j.1438-8677.1988.tb00046.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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16
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Dadacz-Narloch B, Kimura S, Kurusu T, Farmer EE, Becker D, Kuchitsu K, Hedrich R. On the cellular site of two-pore channel TPC1 action in the Poaceae. THE NEW PHYTOLOGIST 2013; 200:663-674. [PMID: 23845012 DOI: 10.1111/nph.12402] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 06/02/2013] [Indexed: 06/02/2023]
Abstract
The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.
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Affiliation(s)
- Beata Dadacz-Narloch
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, D-97082, Wuerzburg, Germany
| | - Sachie Kimura
- Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, 278-8510, Japan
| | - Takamitsu Kurusu
- Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, 278-8510, Japan
- School of Bioscience and Biotechnology, Tokyo University of Technology, Hachioji, Tokyo, 192-0982, Japan
| | - Edward E Farmer
- Department of Plant Molecular Biology, University of Lausanne, Biophore, 1015, Lausanne, Switzerland
| | - Dirk Becker
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, D-97082, Wuerzburg, Germany
| | - Kazuyuki Kuchitsu
- Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, 278-8510, Japan
| | - Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University of Wuerzburg, D-97082, Wuerzburg, Germany
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17
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Schönknecht G. Calcium Signals from the Vacuole. PLANTS (BASEL, SWITZERLAND) 2013; 2:589-614. [PMID: 27137394 PMCID: PMC4844392 DOI: 10.3390/plants2040589] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 09/21/2013] [Accepted: 09/26/2013] [Indexed: 01/13/2023]
Abstract
The vacuole is by far the largest intracellular Ca(2+) store in most plant cells. Here, the current knowledge about the molecular mechanisms of vacuolar Ca(2+) release and Ca(2+) uptake is summarized, and how different vacuolar Ca(2+) channels and Ca(2+) pumps may contribute to Ca(2+) signaling in plant cells is discussed. To provide a phylogenetic perspective, the distribution of potential vacuolar Ca(2+) transporters is compared for different clades of photosynthetic eukaryotes. There are several candidates for vacuolar Ca(2+) channels that could elicit cytosolic [Ca(2+)] transients. Typical second messengers, such as InsP₃ and cADPR, seem to trigger vacuolar Ca(2+) release, but the molecular mechanism of this Ca(2+) release still awaits elucidation. Some vacuolar Ca(2+) channels have been identified on a molecular level, the voltage-dependent SV/TPC1 channel, and recently two cyclic-nucleotide-gated cation channels. However, their function in Ca(2+) signaling still has to be demonstrated. Ca(2+) pumps in addition to establishing long-term Ca(2+) homeostasis can shape cytosolic [Ca(2+)] transients by limiting their amplitude and duration, and may thus affect Ca(2+) signaling.
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Affiliation(s)
- Gerald Schönknecht
- Department of Botany, Oklahoma State University, Stillwater, OK 74078, USA.
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18
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Bonales-Alatorre E, Shabala S, Chen ZH, Pottosin I. Reduced tonoplast fast-activating and slow-activating channel activity is essential for conferring salinity tolerance in a facultative halophyte, quinoa. PLANT PHYSIOLOGY 2013; 162:940-52. [PMID: 23624857 PMCID: PMC3668082 DOI: 10.1104/pp.113.216572] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 04/25/2013] [Indexed: 05/18/2023]
Abstract
Halophyte species implement a "salt-including" strategy, sequestering significant amounts of Na(+) to cell vacuoles. This requires a reduction of passive Na(+) leak from the vacuole. In this work, we used quinoa (Chenopodium quinoa) to investigate the ability of halophytes to regulate Na(+)-permeable slow-activating (SV) and fast-activating (FV) tonoplast channels, linking it with Na(+) accumulation in mesophyll cells and salt bladders as well as leaf photosynthetic efficiency under salt stress. Our data indicate that young leaves rely on Na(+) exclusion to salt bladders, whereas old ones, possessing far fewer salt bladders, depend almost exclusively on Na(+) sequestration to mesophyll vacuoles. Moreover, although old leaves accumulate more Na(+), this does not compromise their leaf photochemistry. FV and SV channels are slightly more permeable for K(+) than for Na(+), and vacuoles in young leaves express less FV current and with a density unchanged in plants subjected to high (400 mm NaCl) salinity. In old leaves, with an intrinsically lower density of the FV current, FV channel density decreases about 2-fold in plants grown under high salinity. In contrast, intrinsic activity of SV channels in vacuoles from young leaves is unchanged under salt stress. In vacuoles of old leaves, however, it is 2- and 7-fold lower in older compared with young leaves in control- and salt-grown plants, respectively. We conclude that the negative control of SV and FV tonoplast channel activity in old leaves reduces Na(+) leak, thus enabling efficient sequestration of Na(+) to their vacuoles. This enables optimal photosynthetic performance, conferring salinity tolerance in quinoa species.
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Affiliation(s)
- Edgar Bonales-Alatorre
- School of Agricultural Science, University of Tasmania, Hobart, Tas 7001, Australia (E.B.-A., S.S., I.P.)
- School of Science and Health, University of Western Sydney, Richmond, NSW 2753, Australia (Z.-H.C.); and
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28045 Colima, Mexico (I.P.)
| | | | - Zhong-Hua Chen
- School of Agricultural Science, University of Tasmania, Hobart, Tas 7001, Australia (E.B.-A., S.S., I.P.)
- School of Science and Health, University of Western Sydney, Richmond, NSW 2753, Australia (Z.-H.C.); and
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28045 Colima, Mexico (I.P.)
| | - Igor Pottosin
- School of Agricultural Science, University of Tasmania, Hobart, Tas 7001, Australia (E.B.-A., S.S., I.P.)
- School of Science and Health, University of Western Sydney, Richmond, NSW 2753, Australia (Z.-H.C.); and
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28045 Colima, Mexico (I.P.)
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19
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Abstract
Since the first recordings of single potassium channel activities in the plasma membrane of guard cells more than 25 years ago, patch-clamp studies discovered a variety of ion channels in all cell types and plant species under inspection. Their properties differed in a cell type- and cell membrane-dependent manner. Guard cells, for which the existence of plant potassium channels was initially documented, advanced to a versatile model system for studying plant ion channel structure, function, and physiology. Interestingly, one of the first identified potassium-channel genes encoding the Shaker-type channel KAT1 was shown to be highly expressed in guard cells. KAT1-type channels from Arabidopsis thaliana and its homologs from other species were found to encode the K+-selective inward rectifiers that had already been recorded in early patch-clamp studies with guard cells. Within the genome era, additional Arabidopsis Shaker-type channels appeared. All nine members of the Arabidopsis Shaker family are localized at the plasma membrane, where they either operate as inward rectifiers, outward rectifiers, weak voltage-dependent channels, or electrically silent, but modulatory subunits. The vacuole membrane, in contrast, harbors a set of two-pore K+ channels. Just very recently, two plant anion channel families of the SLAC/SLAH and ALMT/QUAC type were identified. SLAC1/SLAH3 and QUAC1 are expressed in guard cells and mediate Slow- and Rapid-type anion currents, respectively, that are involved in volume and turgor regulation. Anion channels in guard cells and other plant cells are key targets within often complex signaling networks. Here, the present knowledge is reviewed for the plant ion channel biology. Special emphasis is drawn to the molecular mechanisms of channel regulation, in the context of model systems and in the light of evolution.
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Affiliation(s)
- Rainer Hedrich
- University of Wuerzburg, Institute for Molecular Plant Physiology and Biophysics, Wuerzburg, Germany; and King Saud University, Riyadh, Saudi Arabia
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20
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Patch-clamp protocols to study cell ionic homeostasis under saline conditions. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2012; 913:3-18. [PMID: 22895749 DOI: 10.1007/978-1-61779-986-0_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Abstract
The patch-clamp technique was designed to measure any electrogenic transport across the whole cell and organelle (vacuolar) membranes and excised membrane patches. Here, we describe preparation of protoplasts and vacuoles, as well as patch-clamp assays, to detect the functional expression of K(+) and cation channels of plasma membrane and tonoplast, as well as plasma membrane anion channels and vacuolar and plasma membrane H(+) pumps. All of these contribute to the intracellular ionic homeostasis under saline conditions.
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21
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22
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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.
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Affiliation(s)
- Rainer Hedrich
- Institute for Molecular Plant Physiology and Biophysics, University Wuerzburg, Julius-von-Sachs Platz 2, D-97082 Wuerzburg, Germany
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23
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Peiter E. The plant vacuole: emitter and receiver of calcium signals. Cell Calcium 2011; 50:120-8. [PMID: 21376393 DOI: 10.1016/j.ceca.2011.02.002] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2011] [Revised: 02/04/2011] [Accepted: 02/05/2011] [Indexed: 12/20/2022]
Abstract
This review portrays the plant vacuole as both a source and a target of Ca(2+) signals. In plants, the vacuole represents a Ca(2+) store of enormous size and capacity. Total and free Ca(2+) concentrations in the vacuole vary with plant species, cell type, and environment, which is likely to have an impact on vacuolar function and the release of vacuolar Ca(2+). It is known that cytosolic Ca(2+) signals are often generated by release of the ion from internal stores, but in very few cases has a role of the vacuole been directly demonstrated. Biochemical and electrophysical studies have provided evidence for the operation of ligand- and voltage-gated Ca(2+)-permeable channels in the vacuolar membrane. The underlying molecular mechanisms are largely unknown with one exception: the slow vacuolar channel, encoded by TPC1, is the only vacuolar Ca(2+)-permeable channel cloned to date. However, due to its complex regulation and its low selectivity amongst cations, the role of this channel in Ca(2+) signalling is still debated. Many transport proteins at the vacuolar membrane are also targets of Ca(2+) signals, both by direct binding of Ca(2+) and by Ca(2+)-dependent phosphorylation. This enables the operation of feedback mechanisms and integrates vacuolar transport systems in the wider signalling network of the plant cell.
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Affiliation(s)
- Edgar Peiter
- Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences (IAEW), Faculty of Natural Sciences III, Martin-Luther-University of Halle-Wittenberg, 06099 Halle (Saale), Germany.
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24
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Rienmüller F, Beyhl D, Lautner S, Fromm J, Al-Rasheid KAS, Ache P, Farmer EE, Marten I, Hedrich R. Guard cell-specific calcium sensitivity of high density and activity SV/TPC1 channels. PLANT & CELL PHYSIOLOGY 2010; 51:1548-54. [PMID: 20630987 DOI: 10.1093/pcp/pcq102] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
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.
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Affiliation(s)
- Florian Rienmüller
- University of Wuerzburg, Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs Platz 2, D-97082 Wuerzburg, Germany
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25
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Vacuolar ion channels: Roles in plant nutrition and signalling. FEBS Lett 2010; 584:1982-8. [DOI: 10.1016/j.febslet.2010.02.050] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 02/17/2010] [Accepted: 02/18/2010] [Indexed: 11/19/2022]
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26
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Abstract
Ca(2+) signals are a core regulator of plant cell physiology and cellular responses to the environment. The channels, pumps, and carriers that underlie Ca(2+) homeostasis provide the mechanistic basis for generation of Ca(2+) signals by regulating movement of Ca(2+) ions between subcellular compartments and between the cell and its extracellular environment. The information encoded within the Ca(2+) transients is decoded and transmitted by a toolkit of Ca(2+)-binding proteins that regulate transcription via Ca(2+)-responsive promoter elements and that regulate protein phosphorylation. Ca(2+)-signaling networks have architectural structures comparable to scale-free networks and bow tie networks in computing, and these similarities help explain such properties of Ca(2+)-signaling networks as robustness, evolvability, and the ability to process multiple signals simultaneously.
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Affiliation(s)
- Antony N Dodd
- Department of Biology, University of York, York, United Kingdom.
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27
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Beyhl D, Hörtensteiner S, Martinoia E, Farmer EE, Fromm J, Marten I, Hedrich R. The fou2 mutation in the major vacuolar cation channel TPC1 confers tolerance to inhibitory luminal calcium. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2009; 58:715-23. [PMID: 19298454 DOI: 10.1111/j.1365-313x.2009.03820.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
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.
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Affiliation(s)
- Diana Beyhl
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute, University of Würzburg, Würzburg, Germany
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28
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Abstract
In numerous plant signal transduction pathways, Ca2+ is a versatile second messenger which controls the activation of many downstream actions in response to various stimuli. There is strong evidence to indicate that information encoded within these stimulus-induced Ca2+ oscillations can provide signalling specificity. Such Ca2+ signals, or 'Ca2+ signatures', are generated in the cytosol, and in noncytosolic locations including the nucleus and chloroplast, through the coordinated action of Ca2+ influx and efflux pathways. An increased understanding of the functions and regulation of these various Ca2+ transporters has improved our appreciation of the role these transporters play in specifically shaping the Ca2+ signatures. Here we review the evidence which indicates that Ca2+ channel, Ca2+-ATPase and Ca2+ exchanger isoforms can indeed modulate specific Ca2+ signatures in response to an individual signal.
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Affiliation(s)
- Martin R McAinsh
- Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK;Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Jon K Pittman
- Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK;Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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29
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Pérez V, Wherrett T, Shabala S, Muñiz J, Dobrovinskaya O, Pottosin I. Homeostatic control of slow vacuolar channels by luminal cations and evaluation of the channel-mediated tonoplast Ca2+ fluxes in situ. JOURNAL OF EXPERIMENTAL BOTANY 2008; 59:3845-55. [PMID: 18832189 PMCID: PMC2576637 DOI: 10.1093/jxb/ern225] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Revised: 08/05/2008] [Accepted: 08/06/2008] [Indexed: 05/09/2023]
Abstract
Ca(2+), Mg(2+), and K(+) activities in red beet (Beta vulgaris L.) vacuoles were evaluated using conventional ion-selective microelectrodes and, in the case of Ca(2+), by non-invasive ion flux measurements (MIFE) as well. The mean vacuolar Ca(2+) activity was approximately 0.2 mM. Modulation of the slow vacuolar (SV) channel voltage dependence by Ca(2+) in the absence and presence of other cations at their physiological concentrations was studied by patch-clamp in excised tonoplast patches. Lowering pH at the vacuolar side from 7.5 to 5.5 (at zero vacuolar Ca(2+)) did not affect the channel voltage dependence, but abolished sensitivity to luminal Ca(2+) within a physiological range of concentrations (0.1-1.0 mM). Aggregation of the physiological vacuolar Na(+) (60 mM) and Mg(2+) (8 mM) concentrations also results in the SV channel becoming almost insensitive to vacuolar Ca(2+) variation in a range from nanomoles to 0.1 mM. At physiological cation concentrations at the vacuolar side, cytosolic Ca(2+) activates the SV channel in a voltage-independent manner with K(d)=0.7-1.5 microM. Comparison of the vacuolar Ca(2+) fluxes measured by both the MIFE technique and from estimating the SV channel activity in attached patches, suggests that, at resting membrane potentials, even at elevated (20 microM) cytosolic Ca(2+), only 0.5% of SV channels are open. This mediates a Ca(2+) release of only a few pA per vacuole (approximately 0.1 pA per single SV channel). Overall, our data suggest that the release of Ca(2+) through SV channels makes little contribution to a global cytosolic Ca(2+) signal.
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Affiliation(s)
- V. Pérez
- Centro Universitario de Investigaciones Biomédicas. Universidad de Colima, 28045 Colima, Col., México
| | - T. Wherrett
- School of Agricultural Science, University of Tasmania, Tas7001, Australia
| | - S. Shabala
- School of Agricultural Science, University of Tasmania, Tas7001, Australia
| | - J. Muñiz
- Centro Universitario de Investigaciones Biomédicas. Universidad de Colima, 28045 Colima, Col., México
| | - O. Dobrovinskaya
- Centro Universitario de Investigaciones Biomédicas. Universidad de Colima, 28045 Colima, Col., México
| | - I. Pottosin
- Centro Universitario de Investigaciones Biomédicas. Universidad de Colima, 28045 Colima, Col., México
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30
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Schönknecht G, Trebacz K. Vacuolar ion channels in the liverwort Conocephalum conicum. PLANT SIGNALING & BEHAVIOR 2008; 3:404-5. [PMID: 19704580 PMCID: PMC2634316 DOI: 10.4161/psb.3.6.5430] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2007] [Accepted: 12/14/2007] [Indexed: 05/13/2023]
Abstract
As a liverwort Conocephalum conicum belongs to the oldest terrestrial plants1 and is phylogenetically located between green algae and higher plants. Recent patch-clamp recordings on Conocephalum vacuoles2,3 demonstrate ion channels very similar to higher plants and clearly different from vacuolar ion channels described in green algae. Here we summarize the features of a vacuolar cation channel and a vacuolar anion channel that both are common in terrestrial plants but are not detected in green algae, and we speculate about the molecular identity of these channels in the liverwort Conocephalum.
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Affiliation(s)
- Gerald Schönknecht
- Institute for Plant Biochemistry; Heinrich-Heine-University; Düsseldorf, Germany
| | - Kazimierz Trebacz
- Department of Biophysics; Institute of Biology; Maria Curie-Sklodowska University; Lublin, Poland
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31
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Trebacz K, Schönknecht G, Dziubinska H, Hanaka A. Characteristics of anion channels in the tonoplast of the liverwort Conocephalum conicum. PLANT & CELL PHYSIOLOGY 2007; 48:1747-57. [PMID: 17971334 DOI: 10.1093/pcp/pcm147] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Isolated vacuoles of the liverwort Conocephalum conicum thallus cells were investigated using the patch-clamp technique. At high cytosolic Ca(2+) activities, slowly activating currents were evoked by positive potentials. The currents were conducted by the SV (slow-vacuolar) channel. When isolation of vacuoles was carried out at high Mg(2+) and low Ca(2+) concentration and the same proportion of the cations was kept in the bath, currents were recorded at negative potentials. Once activated, these currents persisted even after replacing Mg(2+) with K(+) in the bath. Sr(2+) and Ba(2+) were also effective activators of the currents. With a Cl(-) gradient, 10 mM in the bath and 100 mM in the lumen, currents were significantly reduced and the current-voltage characteristics shifted towards the reversal potential of Cl(-), indicating Cl(-) selectivity. Currents almost vanished after substituting Cl(-) with gluconate. They were strongly reduced by anion channel inhibitors 4,4'-diisothicyanatostilbene-2,2'-disulfonic acid (DIDS; 1 mM), anthracene-9-carboxylic acid (A9C; 2 mM) and ethacrinic acid (0.5 mM). Single-channel recordings revealed a 32 pS channel activating at negative voltages. It is concluded that the currents at negative potentials are carried by anion channels suitable for conducting anions from the cytosol to the vacuole. The anion channels were weakly calcium dependent, remaining active at physiological calcium concentration. The channels were almost equally permeable to Cl(-), NO3(-) and SO4(2-), and much less permeable to malate(2-). Anion channels did not respond to ATP addition. cAMP (10 microM) had a weak effect on anion channels. Protein kinase A (0.4 U) added to the medium caused no significant effect on anion channels.
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Affiliation(s)
- Kazimierz Trebacz
- Department of Biophysics, Institute of Biology, Maria Curie-Sklodowska University, Akademicka 19, Lublin, Poland.
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32
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Latz A, Becker D, Hekman M, Müller T, Beyhl D, Marten I, Eing C, Fischer A, Dunkel M, Bertl A, Rapp UR, Hedrich R. 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 2007; 52:449-59. [PMID: 17764516 DOI: 10.1111/j.1365-313x.2007.03255.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
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.
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Affiliation(s)
- A Latz
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Biocenter, University of Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany
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33
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Gobert A, Isayenkov S, Voelker C, Czempinski K, Maathuis FJM. The two-pore channel TPK1 gene encodes the vacuolar K+ conductance and plays a role in K+ homeostasis. Proc Natl Acad Sci U S A 2007; 104:10726-31. [PMID: 17563365 PMCID: PMC1965580 DOI: 10.1073/pnas.0702595104] [Citation(s) in RCA: 177] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Arabidopsis thaliana genome contains five genes that encode two pore K+ (TPK) channels. The most abundantly expressed isoform of this family, TPK1, is expressed at the tonoplast where it mediates K+ -selective currents between cytoplasmic and vacuolar compartments. TPK1 open probability depends on both cytoplasmic Ca2+ and cytoplasmic pH but not on the tonoplast membrane voltage. The channel shows intrinsic rectification and can be blocked by Ba2+, tetraethylammonium, and quinine. TPK1 current was found in all shoot cell types and shows all of the hallmarks of the previously described vacuolar K (VK) tonoplast channel characterized in guard cells. Characterization of TPK1 loss-of-function mutants and TPK1-overexpressing plants shows that TPK1 has a role in intracellular K+ homeostasis affecting seedling growth at high and low ambient K+ levels. In stomata, TPK1 function is consistent with vacuolar K+ release, and removal of this channel leads to slower stomatal closure kinetics. During germination, TPK1 contributes to the radicle development through vacuolar K+ deposition to provide expansion growth or in the redistribution of essential minerals.
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Affiliation(s)
- Anthony Gobert
- *Department of Biology Area 9, University of York, York YO10 5DD, United Kingdom; and
| | - Stanislav Isayenkov
- *Department of Biology Area 9, University of York, York YO10 5DD, United Kingdom; and
| | - Camilla Voelker
- Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 20, D-14476 Golm, Germany
| | - Katrin Czempinski
- Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 20, D-14476 Golm, Germany
| | - Frans J. M. Maathuis
- *Department of Biology Area 9, University of York, York YO10 5DD, United Kingdom; and
- To whom correspondence should be addressed. E-mail:
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Scholz-Starke J, Naso A, Carpaneto A. A perspective on the slow vacuolar channel in vacuoles from higher plant cells. J Chem Inf Model 2006; 45:1502-6. [PMID: 16309246 DOI: 10.1021/ci050218a] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joachim Scholz-Starke
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Via De Marini 6, 16149 Genoa, Italy
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35
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Pottosin II, Martínez-Estévez M, Dobrovinskaya OR, Muñiz J. Regulation of the Slow Vacuolar Channel by Luminal Potassium: Role of Surface Charge. J Membr Biol 2005; 205:103-11. [PMID: 16283590 DOI: 10.1007/s00232-005-0766-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Revised: 08/16/2005] [Indexed: 11/26/2022]
Abstract
Voltage-dependent activation of slow vacuolar (SV) channels has been studied on isolated patches from red beet (Beta vulgaris L.) vacuoles. Isoosmotic variation of vacuolar K(+) from 10 to 400 mM in Ca(2+)-free solutions at the vacuolar side shifted the SV channel activation threshold to more positive voltages. The effect of K(+) could be mimicked by additions of choline or N-methyl D-glucamine and could be explained by unspecific screening of the negative surface charge. Fitting the dependence of voltage shift on K(+) concentration to the Gouy-Chapman model yields a surface charge density of 0.36 +/- 0.05 e(-)/nm(2). Negative surface potential also tended to increase the local concentration of permeable ions (K(+)), resulting in anomalously high single-channel conductance, approximately 200 pS in 10 mM KCl. An increase of ionic strength due to addition of impermeable cations greatly reduced the unitary conductance. Large positive shift of the SV channel voltage dependence, caused by physiological (0.5 mM) free vacuolar Ca(2+), was partly ameliorated by increasing luminal K(+). We interpreted these results as follows: K(+)induced a reduction of surface potential, hence i) causing a positive shift of the voltage dependence and ii) a dilution of Ca(2+) in the membrane vicinity, thus reducing the inhibitory effect of vacuolar Ca(2+) and causing a negative shift of the SV channel voltage dependence, with a sum of the two shifts being negative.
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Affiliation(s)
- I I Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima 28045, México.
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36
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Pottosin II, Martínez-Estévez M, Dobrovinskaya OR, Muñiz J, Schönknecht G. Mechanism of luminal Ca2+ and Mg2+ action on the vacuolar slowly activating channels. PLANTA 2004; 219:1057-70. [PMID: 15605179 DOI: 10.1007/s00425-004-1293-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2004] [Accepted: 04/17/2004] [Indexed: 05/12/2023]
Abstract
The non-selective slow vacuolar (SV) channel can dominate tonoplast conductance, making it necessary to tightly control its activity. Applying the patch-clamp technique to vacuoles from sugar beet (Beta vulgaris L.) taproots we studied the effect of divalent cations on the vacuolar side of the SV channel. Our results show that the SV channel has two independent binding sites for vacuolar divalent cations, (i) a less selective one, inside the channel pore, binding to which impedes channel conductance, and (ii) a Ca(2+)-selective one outside the membrane-spanning part of the channel protein, binding to which stabilizes the channel's closed conformations. Vacuolar Ca2+ and Mg2+ almost indiscriminately blocked ion fluxes through the open channel pore, decreasing measured single-channel current amplitudes. This low-affinity block displays marked voltage dependence, characteristic of a 'permeable blocker'. Vacuolar Ca(2+)-with a much higher affinity than Mg(2+)-slows down SV channel activation and shifts the voltage dependence to more (cytosol) positive potentials. A quantitative analysis results in a model that exactly describes the Ca(2+)-specific effects on the SV channel activation kinetics and voltage gating. According to this model, multiple (approximately three) divalent cations bind with a high affinity at the luminal interface of the membrane to the channel protein, favoring the occupancy of one of the SV channel's closed states (C2). Transition to another closed state (C1) diminishes the effective number of bound cations, probably due to mutual repulsion, and channel opening is accompanied by a decrease of binding affinity. Hence, the open state (O) is destabilized with respect to the two closed states, C1 and C2, in the presence of Ca2+ at the vacuolar side. The specificity for Ca2+ compared to Mg2+ is explained in terms of different binding affinities for these cations. In this study we demonstrate that vacuolar Ca2+ is a crucial regulator to restrict SV channel activity to a physiologically meaningful range, which is less than 0.1% of maximum SV channel activity.
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Affiliation(s)
- Igor I Pottosin
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28047 Colima, Col., México.
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37
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Schönknecht G, Spoormaker P, Steinmeyer R, Brüggeman L, Ache P, Dutta R, Reintanz B, Godde M, Hedrich R, Palme K. KCO1 is a component of the slow-vacuolar (SV) ion channel. FEBS Lett 2002; 511:28-32. [PMID: 11821043 DOI: 10.1016/s0014-5793(01)03273-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Arabidopsis double pore K+ channel KCO1 was fused to green fluorescent protein and expressed in tobacco protoplasts. Microscopic analysis revealed a bright green fluorescence at the vacuolar membrane. RT-PCR experiments showed that KCO1 is expressed in the mesophyll. Vacuoles from Arabidopsis wild-type and kco1 knockout plants were isolated for patch-clamp analyses. Currents mediated by slow-activating vacuolar (SV) channels of mesophyll cell vacuoles were significantly smaller in kco1 plants compared to the wild-type. This shows that KCO1 is involved in the formation of SV channels.
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Affiliation(s)
- Gerald Schönknecht
- Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pfanzenphysiologie und Biophysik, Universität Würzburg, 97082 Würzburg, Germany
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38
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Dietrich P, Sanders D, Hedrich R. The role of ion channels in light-dependent stomatal opening. JOURNAL OF EXPERIMENTAL BOTANY 2001; 52:1959-67. [PMID: 11559731 DOI: 10.1093/jexbot/52.363.1959] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Stomatal opening represents a major determinant of plant productivity and stress management. Because plants lose water essentially through open stomata, volume control of the pore-forming guard cells represents a key step in the regulation of plant water status. These sensory cells are able to integrate various signals such as light, auxin, abscisic acid, and CO(2). Following signal perception, changes in membrane potential and activity of ion transporters finally lead to the accumulation of potassium salts and turgor pressure formation. This review analyses recent progress in molecular aspects of ion channel regulation and suggests how these developments impact on our understanding of light- and auxin-dependent stomatal action.
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Affiliation(s)
- P Dietrich
- Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
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40
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van den Wijngaard PW, Bunney TD, Roobeek I, Schönknecht G, de Boer AH. Slow vacuolar channels from barley mesophyll cells are regulated by 14-3-3 proteins. FEBS Lett 2001; 488:100-4. [PMID: 11163804 DOI: 10.1016/s0014-5793(00)02394-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The conductance of the vacuolar membrane at elevated cytosolic Ca(2+) levels is dominated by the slow activating cation selective (SV) channel. At physiological, submicromolar Ca(2+) concentrations the SV currents are very small. Only recently has the role of 14-3-3 proteins in the regulation of voltage-gated and Ca(2+)-activated plasma membrane ion channels been investigated in Drosophila, Xenopus and plants. Here we report the first evidence that plant 14-3-3 proteins are involved in the down-regulation of ion channels in the vacuolar membrane as well. Using the patch-clamp technique we have demonstrated that 14-3-3 protein drastically reduces the current carried by SV channels. The current decline amounted to 80% and half-maximal reduction was reached within 5 s after 14-3-3-addition to the bath. The voltage sensitivity of the channel was not affected by 14-3-3. A coordinating role for 14-3-3 proteins in the regulation of plasma membrane and tonoplast ion transporters is discussed.
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Affiliation(s)
- P W van den Wijngaard
- BioCentrum Amsterdam, Department of Developmental Genetics, Faculty of Biology, Vrije Universiteit, Amsterdam, The Netherlands
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41
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Abstract
Calcium channels are involved principally in signal transduction. Their opening results in increased cytoplasmic Ca(2+) concentration, and the spatial and temporal variations in this are thought to elicit specific physiological responses to diverse biotic and abiotic stimuli. Calcium-permeable channels have been recorded in the plasma membrane, tonoplast, endoplasmic reticulum, chloroplast and nuclear membranes of plant cells. This article reviews their electrophysiological properties and discusses their physiological roles. Emphasis is placed on the voltage-dependent and elicitor-activated Ca(2+) channels of the plasma membrane and the depolarisation-activated (SV), hyperpolarisation-activated, IP(3)- and cADPR-dependent Ca(2+) channels of the tonoplast. The closing of stomatal guard cells in the presence of abscisic acid (ABA) is used to illustrate the co-ordination of Ca(2+) channel activities during a physiological response.
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Affiliation(s)
- P J White
- Department of Cell Physiology, Horticulture Research International, Wellesbourne, Warwick, UK.
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42
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Bewell MA, Maathuis FJ, Allen GJ, Sanders D. Calcium-induced calcium release mediated by a voltage-activated cation channel in vacuolar vesicles from red beet. FEBS Lett 1999; 458:41-4. [PMID: 10518930 DOI: 10.1016/s0014-5793(99)01109-6] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Little is known about the mechanisms underlying calcium-induced Ca2+ release (CICR) in plants. The slow-activating vacuolar (SV) channel is both permeable to, and activated by Ca2+, and is therefore a prime candidate for a role in CICR. Cytosol-side-out vacuolar membrane vesicles loaded with 45Ca2+ showed voltage- and Ca(2+)-dependent Ca2+ release, which was sensitive to the SV channel modulators DIDS, protein phosphatase 2B and calmodulin. Significantly, voltage-dependent Ca2+ release strongly depended on cytoplasmic Ca2+ concentrations. The results support the notion that CICR occurs in plant cells and that the process can be catalysed by the SV channel on the vacuolar membrane.
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Affiliation(s)
- M A Bewell
- Department of Biology, University of York, UK
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43
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Assmann S, Armstrong F. Hormonal regulation of ion transporters: the guard cell system. BIOCHEMISTRY AND MOLECULAR BIOLOGY OF PLANT HORMONES 1999. [DOI: 10.1016/s0167-7306(08)60495-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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44
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45
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46
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Affiliation(s)
- F J Maathuis
- Department of Biology, University of York, United Kingdom
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47
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Hedrich R, Becker D. Green circuits--the potential of plant specific ion channels. PLANT MOLECULAR BIOLOGY 1994; 26:1637-1650. [PMID: 7532027 DOI: 10.1007/bf00016494] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Affiliation(s)
- R Hedrich
- Institut für Biophysik, Hannover, Germany
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48
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Reifarth FW, Weiser T, Bentrup FW. Voltage- and Ca(2+)-dependence of the K+ channel in the vacuolar membrane of Chenopodium rubrum L. suspension cells. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1192:79-87. [PMID: 8204654 DOI: 10.1016/0005-2736(94)90145-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Voltage- and Ca(2+)-dependence of the slow-activating SV-K+ channel in the vacuolar membrane of Chenopodium rubrum suspension cells has been analyzed using the patch clamp technique in the vacuole-attached, outside-out and whole-vacuolar configuration. Patch-pipette perfusion was applied to measure Ca2+ dependence of single channels in the attached-configuration. Using the PCLAMP-software (Axon Instruments), an algorithm was developed to extract reliable individual channel data from multi-channel activity records, including open probability, mean open and closed times, as well as time constants for open and closed distributions. The channel conductance of the major open state was about 83 pS (seal resistance > 8 G omega) at 30 mV (transmembrane voltage Vm, vacuole negative), and symmetrical 100 mM KCl. the channel exhibited a strong voltage- and a weak Ca(2+)-activation: increasing Vm from 40 to 100 mV is equivalent to a Ca2+ concentration change from 10(-7) to 10(-4) M. Mean open probabilities at Vm = 30 mV were 0.03 with 1 microM and 0.09 with 100 microM Ca2+. Mean open times were approx. 7 ms, and almost independent of both, voltage and Ca2+. Mean closed times, however, varied in a strongly voltage- and Ca(2+)-dependent manner, e.g., at Vm = 30 mV dropped from 205 to 67 ms, if Ca2+ was raised from 10(-6) to 10(-4) M. Open and closed distributions of events within bursts could be fitted by the sum of two exponentials with time constants between 0.3 and 11 ms.
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Affiliation(s)
- F W Reifarth
- Institut für Tierphysiologie, Justus-Liebig-Universität, Giessen, Germany
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49
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Weiser T. Slowly-activating cation channels in the vacuolar membrane of plants. EXS 1993; 66:305-10. [PMID: 7505662 DOI: 10.1007/978-3-0348-7327-7_25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Among other ion channels and transport proteins, the membrane of plant vacuoles contains a voltage- and calcium-dependent cation channel with activation kinetics in the range of seconds. This SV(= slow vacuolar)-channel has a unit conductance of 60 to 80 pS (in symmetrical 100 mM cation solution) and is strictly inward rectifying. Investigations on the pharmacology of this protein revealed reasonable similarities to calcium-dependent potassium channels of large conductance.
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Affiliation(s)
- T Weiser
- Boehringer Ingelheim KG, ZNS-Pharmakologie, Ingelheim, FRG
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50
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Bertl A, Gradmann D, Slayman CL. Calcium- and voltage-dependent ion channels in Saccharomyces cerevisiae. Philos Trans R Soc Lond B Biol Sci 1992; 338:63-72. [PMID: 1280839 DOI: 10.1098/rstb.1992.0129] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Ion channels in both the tonoplast and the plasma membrane of Saccharomyces cerevisiae have been characterized at the single channel level by patch-clamp techniques. The predominant tonoplast channel is cation selective, has an open-channel conductance of 120 pS in 100 mM KCl, and conducts Na+ or K+ equally well, and Ca2+ to a lesser extent. Its open probability (Po) is voltage-dependent, peaking at about -80 mV (cytoplasm negative), and falling to near zero at +80 mV. Elevated cytoplasmic Ca2+, alkaline cytoplasmic pH, and reducing agents activate the channel. The predominant plasma membrane channel is highly selective for K+ over anions and other cations, and shows strong outward rectification of the time-averaged current-voltage curves in cell-attached experiments. In isolated inside-out patches with micromolar cytoplasmic Ca2+, this channel is activated by positive going membrane voltages: mean Po is zero at negative membrane voltages and near unity at 100 mV. At moderate positive membrane voltages (20-40 mV), elevating cytoplasmic Ca2+ activates the channel to open in bursts of several hundred milliseconds duration. At higher positive membrane voltages, however, elevating cytoplasmic Ca2+ blocks the channel in a voltage-dependent fashion for periods of 2-3 ms. The frequency of these blocking events depends on cytoplasmic Ca2+ and membrane voltage according to second-order kinetics. Alternative cations, such as Mg2+ or Na+, block the yeast plasma-membrane K+ channel in a similar but less pronounced manner.
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Affiliation(s)
- A Bertl
- Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut 06510
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