Effect of mastoparan on phospholipase A2 activity in potato tubers treated with fungal elicitor

Participation of phospholipase (PL) Az in signal transduction has been reported to elicitate a resistance reaction in potato cells by inoculation of an incompatible race of Phytophthora infestans, the late blight fungus, or by treatment with fungal elicitor hyphal wall components (HWC). Mastoparan, a generic G protein activator, has been shown to activate PLA in a G protein-dependent manner in animal cells. We analyzed the effects of mastoparan and the inactive analog Mas-17 on PLA(2) activity in potato tubers. In healthy potato tubers, the activation of PLA2 by mastoparan was detected in the soluble fraction, but not microsomal fraction. However, in potato tubers treated with HWC, PLA, activity was stimulated by mastoparan in both soluble and microsomal fractions. Pretreatment of the microsomal fraction with neomycin, a PLC inhibitor, and staurosporine, a protein kinase inhibitor, inhibited the mastoparan-induced activation of PLA,. This suggested that the PLA, activation in potato tubers by mastoparan was mediated by the PLC pathway and protein phosphorylation, We also examined the accumulation of potato phytoalexin rishitin. Mastoparan stimulated rishitin accumulation induced by HWC, but did not induce the accumulation. This indicated that mastoparan might activate the signal transduction pathway in the resistance reactions induced in potato tubers.