Abstract
Jasmonic acid or its methyl ester induce de novo synthesis of a number of proteins of mostly unknown function in barley (Hordeum vulgare L.). In a topical spray application, 30 [mu]g of jasmonic acid per plant effectively protected barley against subsequent infection by Erysiphe graminis f.sp. hordei. Examination of jasmonic acid-induced barley proteins revealed the presence of several acid-soluble (pH 2.8) proteins. Two prominent groups of 25 kD and 10 to 12 kD apparent molecular mass were present in the intercellular washing fluid. The set of extracellular, induced proteins showed no similarity to barley pathogenesis-related proteins. An in vivo test against E. graminis revealed no antifungal activity of the extracellular jasmonic acid-induced proteins. Experiments with the transcription inhibitor cordycepin showed no correlation between accumulation of jasmonic acid-induced proteins and protection. The application of jasmonic acid and E. graminis simultaneously resulted in independent extracellular accumulation of both jasmonic acid-induced proteins and of pathogenesis-related proteins. The data suggest that jasmonic acid directly inhibits appressoria differentiation of the fungus, and that it is not involved in the signal transduction mechanism leading to induction of pathogenesis-related proteins.