Salt stress-induced chloride flux:: a study using transgenic Arabidopsis expressing a fluorescent anion probe

Salt stress leads to massive accumulation of toxic levels of Na+ and Cl- ions in plants. By using the recombinant fluorescent probe CLOMELEON, we demonstrate passive anion flux under salt stress. Chloride influx is restricted in the presence of divalent cations like Mg2+ and Ca2+, and completely blocked by La3+. The amount but not the rate of the reported chloride uptake is independent from the kind of corresponding permeable cation (K+ versus Na+), external pH and magnitude of osmotic stress. Cl- efflux however seems to involve stretch-activated transport. From the influence of Ca2+ on reported changes of cytosolic anion concentrations, we speculate that transport mechanisms of Cl- and Na+ might be thermodynamically coupled under saline conditions.