LOCALIZED WOUNDING BY HEAT INITIATES THE ACCUMULATION OF PROTEINASE-INHIBITOR-II IN ABSCISIC ACID-DEFICIENT PLANTS BY TRIGGERING JASMONIC ACID BIOSYNTHESIS

To test whether the response to electrical current and heat treatment is due to the same signaling pathway that mediates mechanical wounding , we analyzed the effect of electric-current application and localized burning on proteinase inhibitor II (Pin2) gene expression in both wil d-type and abscisic acid (ABA)-deficient tomato (Lycopersicon esculent um Mill.) and potato (Solanum phureja) plants. Electric-current applic ation and localized burning led to the accumulation of Pin2 mRNA in po tato and tomato wildtype plants. Among the treatments tested, only loc alized burning of the leaves led to an accumulation of Pin2 mRNA in th e ABA-deficient plants. Electric-current application, like mechanical injury, was able to initiate ABA and jasmonic acid (JA) accumulation i n wild-type but not in ABA-deficient plants. In contrast, heat treatme nt led to an accumulation of JA in both wild-type and ABA-deficient pl ants. Inhibition of JA biosynthesis by aspirin blocked the heat-induce d Pin2 gene expression in tomato wild-type leaves. These results sugge st that electric current, similar to mechanical wounding, requires the presence of ABA to induce Pin2 gene expression. Conversely, burning o f the leaves activates Pin2 gene expression by directly triggering the biosynthesis of JA by an alternative pathway that is independent of e ndogenous ABA levels.