Sulfate is both a substrate and an activator of the voltage-dependent anion channel of Arabidopsis hypocotyl cells

On the basis of the anion content of in vitro-cultured Arabidopsis plantlet s, we explored the selectivity of the voltage-dependent anion channel of th e plasma membrane of hypocotyl cells. In the whole-cell configuration, subs titution of cytosolic Cl- by different anions led to the following sequence of relative permeabilities: NO3- (2.6) greater than or equal to SO42- (2.0 ) > Cl- (1.0) > HCO3- (0.8) much greater than malate(2-)(0.03). Large whole -cell currents were measured for NO3- and SO42-, about five to six times hi gher than the equivalent Cl- currents. Since SO42- is usually considered to be a weakly permeant or non-permeant ion, the components of the large whol e-cell current were explored in more detail. Aside from its permeation thro ugh the channel with a unitary conductance, about two-thirds that of Cl-, S O42- had a regulatory effect on channel activity by preventing the run-down of the anion current both in the whole-cell and the outside-out configurat ion, increasing markedly the whole-cell current. The fact that the voltage- dependent plasma membrane anion channel of hypocotyl cells can mediate larg e NO3- and SO42- currents and is regulated by nucleotides favors the idea t hat this anion channel can contribute to the cellular homeostasis of import ant metabolized anions.