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 with [gamma-P-32]ATP) was Ca2+-dependent and was inhibited by protein kinase inhibitors, but it was not affected by the phosphatase inhibitor okodaic acid. Results indicate that a signal transport system in cucumber 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.