CA-2+ AND NUCLEOTIDE DEPENDENT REGULATION OF VOLTAGE DEPENDENT ANION CHANNELS IN THE PLASMA-MEMBRANE OF GUARD-CELLS

Using the patch-clamp technique we discovered that the voltage dependent anion channels in the plasma membrane of guard cells are activated by a rise in cytoplasmic Ca2+ in the presence of nucleotides. Upon activation, these anion channels catalyse anion currents 10-20 times higher than in the inactivated state, thus shifting the plasma membrane from a K+ conducting state to an anion conducting state. Prolonged stimulation by depolarizing voltages results in the inactivation of the anion current (t( 1/2 ) = 10-12 s). We suggest that activation of the anion channel by Ca2+ and nucleotides is a key event in the regulation of salt efflux from guard cells during stomatal closure.