INVOLVEMENT OF CALCIUM IN THE IN-VITRO SENSITIVITY CHANGE OF THE PLASMA-MEMBRANE H-ATPASE TO INDOLE-3-ACETIC-ACID()

The proton pumping activity of phase-partitioning purified plasma memb rane fraction from spinach leaves was tested in vitro in the presence of exogenous indole-3-acetic acid. The sensitivity of the H+ pumping a ctivity to the auxin was changed after flowering induction. We investi gated the effect of whole spinach leaf treatments with substances affe cting the phosphatidylinositol diphosphate transduction pathway on the in vitro sensitivity modification by photoperiodic induction. A role of calcium ions was supported by studies on leaves treated with a spec ific Ca2+ chelator (EGTA), a synthetic Ca2+ ionophore (A23187) or with calcium channel blokers (verapamil, lanthan chloride). An experiment using the transduction pathway inhibitor, lithium chloride, indicated that the intracellular concentration of Ca2+ was increased by inositol triphosphate.