POSSIBLE INVOLVEMENT OF LIPID-PEROXIDATION IN SALICYLIC ACID-MEDIATEDINDUCTION OF PR-1 GENE-EXPRESSION

Salicylic acid (SA) is a natural signal molecule which plays an import ant role in plant defense responses against pathogen infection. Previo us work has demonstrated that catalase may be involved in the mechanis m of SA action. Recently, SA has been shown to inhibit catalase by ser ving as a one electron-donating substrate for its peroxidative reactio n. One of the likely by-products of this interaction is a SA free radi cal. Since free radicals are potent inducers of lipid peroxidation, SA and its analogues were tested for their ability to induce lipid perox idation in tobacco cell cultures. SA and its biologically active analo gues, which increase PR gene expression, enhance disease resistance an d also inhibit catalase, induced accumulation of lipid peroxidation pr oducts. Inactive analogues did not. Exogenous application of lipid per oxides induced PR-I gene expression. Furthermore, the induction of PR- I genes by SA was inhibited by diethyldithiocarbamic acid, a compound that converts lipid peroxides into their hydroxyl derivatives. We sugg est that the induction of lipid peroxidation by a SA radical may be in volved in the action of SA and that one or more of the lipid peroxidat ion products may mediate signal transduction leading to PR-I expressio n. (C) 1997 Elsevier Science Ltd. All rights reserved.