Malate transport by the vacuolar AtALMT6 channel in guard cells is subject to multiple regulation

• Published in: The Plant journal : for cell and molecular biology Vol. 67; no. 2; pp. 247 - 257
• Main Authors: Meyer, Stefan, Scholz‐Starke, Joachim, De Angeli, Alexis, Kovermann, Peter, Burla, Bo, Gambale, Franco, Martinoia, Enrico
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.07.2011; Blackwell
• Subjects: Aluminum; anion exchange; Anions; Arabidopsis; Arabidopsis - cytology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; AtALMT6; Biochemistry; Biological and medical sciences; Biological Transport; calcium; Calcium - metabolism; calcium‐activation; Cellular biology; cytology; flowers; Flowers & plants; Fundamental and applied biological sciences. Psychology; Gas exchange; Gene expression; Gene Knockout Techniques; genetics; guard cells; Hydrogen-Ion Concentration; ion transport; knockout mutants; malate transport; malates; Malates - metabolism; membrane potential; Membrane Potentials; metabolism; Mutagenesis, Insertional; nutrient transport; Organic Anion Transporters; Organic Anion Transporters - genetics; Organic Anion Transporters - metabolism; Patch-Clamp Techniques; Plant biology; Plant physiology and development; Plant Stomata; Plant Stomata - metabolism; potassium; Respiration; stem cells; stomatal movement; tonoplast; transporters; turgor; vacuoles; Vacuoles - metabolism; Tonoplast; Multiple; guard cells; Calcium; Activation; Guard cell; AtALMT6; Arabidopsis thaliana; calcium-activation; Regulation(control); Cruciferae; Dicotyledones; Angiospermae; Spermatophyta; malate transport
• ISSN: 0960-7412; 1365-313X; 1365-313X
• DOI: 10.1111/j.1365-313X.2011.04587.x

Summary Gas exchange in plants is controlled by guard cells, specialized cells acting as turgor pressure‐driven valves. Malate is one of the major anions accumulated inside the vacuole during stomatal opening counteracting the positive charge of potassium. AtALMT6, a member of the aluminum‐activated malate transporter family, is expressed in guard cells of leaves and stems as well as in flower organs of Arabidopsis thaliana. An AtALMT6‐GFP fusion protein was targeted to the vacuolar membrane both in transient and stable expression systems. Patch‐clamp experiments on vacuoles isolated from AtALMT6‐GFP over‐expressing Arabidopsis plants revealed large inward‐rectifying malate currents only in the presence of micromolar cytosolic calcium concentrations. Further analyses showed that vacuolar pH and cytosolic malate regulate the threshold of activation of AtALMT6‐mediated currents. The interplay of these two factors determines the AtALMT6 function as a malate influx or efflux channel depending on the tonoplast potential. Guard cell vacuoles isolated from Atalmt6 knock‐out plants displayed reduced malate currents compared with wild‐type vacuoles. This reduction, however, was not accompanied by phenotypic differences in the stomatal movements in knock‐out plants, probably because of functional redundancy of malate transporters in guard cell vacuoles.