Effect of phytohormones on ATP-dependent accumulation of Ca2+ in plasma membrane vesicles from tubers of potato Solanum tuberosum L.

A membrane fraction enriched with plasmalemma vesicles was isolated from potato tubers using the polyethylene glycol 3550--dextran T-500 phase partitioning. As judged by the activities of enzyme markers of the inner plant cell membranes, the fraction consisted of plasmalemma vesicles with tonoplast vesicle contamination and contained no mitochondrial membranes, endoplasmic reticulum or Golgi apparatus. Under conditions of total inhibition of nitrate-sensitive ATPase of the tonoplast, the vesicles of the fraction obtained exhibited the ATP-dependent accumulation of Ca2+. It was inhibited to various extents by Na3VO4, dicyclohexyl carbodiimide (DCCD) and phytohormones--gibberellic acid (GA3), abscisic acid (ABA) and indoleacetic acid (IAA), whereas kinetin rendered a stimulating effect. The action of phytohormones on the accumulation of Ca2+ in the presence of DCCD or Na3VO4 suggests that GA3, ABA and kinetin affect the activity of Ca2+,Mg(2+)-ATPase, whereas IAA most probably stimulates the efflux of Ca2+ from the vesicles or the separation of membrane-bound Ca2+.