PHOSPHORYLATION OF PROTEINS IN CUCUMBER EXUDATES AND EVIDENCE FOR PROTEIN-KINASE ACTIVITY

Proteins and their phosphorylation were examined in cucumber exudates collected From transversely cut internodes. In vitro phosphorylation w ith [gamma-P-32]ATP) was Ca2+-dependent and was inhibited by protein k inase inhibitors, but it was not affected by the phosphatase inhibitor okodaic acid. Results indicate that a signal transport system in cucu mber phloem may involve protein phosphorylation. There is evidence for the presence in cucumber exudates of both serine/threonine kinase and soluble phosphatase, bur the phosphatase is not type 1 or 2a.