PLANT DEFENSE RESPONSE TO FUNGAL PATHOGENS - ACTIVATION OF HOST-PLASMA MEMBRANE H+-ATPASE BY ELICITOR-INDUCED ENZYME DEPHOSPHORYLATION

Elicitor preparations containing the avr5 gene products from race 4 of Cladosporium fulvum and tomato (Lycopersicon esculentum L.) cells near isogenic;for the resistance gene Cf5 were used to investigate events following the treatment of host plasma membranes with elicitor. A 4-fold increase in H+-ATPase activity, coincident with the acidification of the extracellular medium, was detected immediately after elicitor treatment. The elicitor-induced stimulation of the plasma membrane H+-ATPase was inhibited by okadaic acid but not by staurosporine, suggesting that protein dephosphorylation was required for increased H+-ATPase activity. This observation was confirmed by gamma-(32)p labeling and immunodetection of the plasma membrane H+-ATPase. Effects of guanidine nucleotide analogs and mastoparan on the ATPase activity suggested the role of GTP-binding proteins in mediating the putative elicitor-receptor binding, resulting in activation of a phosphatase(s), which in turn stimulates the plasma membrane H+-ATPase by dephosphorylation.