CHARACTERIZATION OF A CA2-STIMULATED POLYPHOSPHOINOSITIDE-PHOSPHOLIPASE-C IN ISOLATED PLASMA-MEMBRANES FROM SPINACIA-OLERACEA AND CHENOPODIUM-RUBRUM LEAVES()

A polyphosphoinositide-phospholipase C has been identified in highly p urified plasma membranes from leaves of Spinacia oleracea and Chenopod ium rubrum. The enzyme hydrolysed phosphatidylinositol, 4-5 biphosphat e into a mixture of inositol biphosphate and inositol triphosphate. It was activated by micromolar Ca2+ concentration and its optimum pH was between 7 to 7.5. The enzyme activity was also activated by sodium de oxycholate. Preliminary experiments have shown that the enzyme activit y was different in plasma membrane isolated from dark-grown or light g rown spinach plants. This enzyme may participate in signal transductio n of light over plant plasma membrane. Possible implication in floweri ng process of the light regulation of this enzyme activity will be dis cussed.