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Malate transport by the vacuolar AtALMT6 channel in guard cells is subject to multiple regulation
Author(s) -
Meyer Stefan,
ScholzStarke Joachim,
De Angeli Alexis,
Kovermann Peter,
Burla Bo,
Gambale Franco,
Martinoia Enrico
Publication year - 2011
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2011.04587.x
Subject(s) - guard cell , vacuole , microbiology and biotechnology , cytosol , arabidopsis , biology , arabidopsis thaliana , biophysics , biochemistry , cytoplasm , gene , enzyme , mutant
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.