Transport of organic anions in root cells and its role in cell signaling in higher plants

Abstract

The organic anion balance is critical for metabolic, bioenergetic, and electrochemical processes in plant cells, controlling the quality and quantity of yield and plant stress resistance. Nevertheless, the redistribution and membrane transport of these substances in plant tissues have not been investigated in detail. The mechanism of passive anion efflux from a plant cell through the ion channels has not been established so far. Here, using the patch-clamp technique, we have characterized the ion channel-mediated conductances of ascorbate, malate, gluconate, citrate, fumarate, and pronionate in the root cells of Arabidopsis thaliana, Triticum aestivum, and Helianthus annuus. These conductances showed high permeability to ascorbate, malate, and citrate, as well as low permeability to fumarate, propionate, and gluconate. Anion channel conductances of root cells showed rapid activation kinetics and low potential dependence. They were also inhibited by 9-anthracenecarboxylic acid, suggesting that they belong to the ALMT family of anion channels found only in higher plants. Aequorin chemilu minometry was used to test the effect of organic anions on the Ca2+ signaling in root cells. Among four organic anions tested, only ascorbate induced a significant increase in the cytosolic Ca2+ activity at physiological levels (1 and 10 mM). This effect may underlie the previously unknown functions of exogenous ascorbate related to short- and long-distance signaling in higher plants.