Effect of cytokinins on the phospholipid phosphorylation of the suspension cultured Catharanthus roseus cells

Previous work has shown that the components (phosphorylated phosphatinositols) and enzyme activities (phosphatidylinositol kinase and diacylglycerol kinase) of the phosphatidylinositol (PI) cycle are present in suspension cultured Catharanthus roseus cells. The phospholipid kinase activities can be determined in situ by phosphorylation with labeled exogenous ATP. Incorporation of ³²P into phosphorylated PI and phosphatidic acid, the products of PI kinase and diacylglycerol kinase, is reduced in the presence of low cytokinin concentrations; the concentrations for 50% inhibition are in the range 1 μM. The molecular targets of this phytohormone action are discussed.