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

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2011
Author Meyer S, Scholz-Starke J, De Angeli A, Kovermann P, Burla B, Gambale F, Martinoia E,
Project ABC transporters involved in signalling events
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Original article (peer-reviewed)

Journal PLANT JOURNAL
Volume (Issue) 67(2)
Page(s) 247 - 257
Title of proceedings PLANT JOURNAL
DOI DOI: 10.1111/j.1365-313X.2011.04587.x

Abstract

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.
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