Effects of kinetin on phosphorylation of leaf membrane proteins

Isolated Chinese cabbage leaf membranes were phosphorylated by membrane-associated protein kinase(s) in the presence or [gamma-32P]ATP. Membrane-associated 32P radioactivity appeared to be bound to membrane proteins. Both smooth cell membranes and chloroplast lamellae reacted with ATP. Phosphorylation of the membranes was inhibited by Ca2+ and partially inhibited by kinetin or 6-benzyladenine. The possibility that cytokinin effects on membrane phosphorylation might increase ion availability was investigated in vivo. It was found that Ca2+ could substitute for kinetin in the leaf disc expansion assay.