A proposed mode of action for green island induction by the eremophilane phytotoxins produced by Drechslera gigantea

Abstract

Drechslera gigantea , a phytopathogen of several graminaceous species, produces numerous phytotoxins belonging to the eremophilane family. When applied to detached leaves of Avena sativa cv. Park, several of these eremophilanes cause green islands, localized areas of chlorophyll retention. In experiments using a wheat germ in vitro protein translation assay system, gigantenone and petasol, two of these eremophilanes, inhibited protein synthesis at 1 m m concentrations. The same eremophilanes also inhibited incorporation of [ 14 C]-leucine into proteins during in vivo studies using detached oat leaves. Proteolytic enzyme activity levels were found to be lower in leaf tissue treated with gigantenone and petasol. 11,12-Epoxypetasol, an eremophilane which does not induce green islands, showed little inhibition of protein synthesis in either the in vitro or the in vivo studies. 11,12-Epoxypetasol-treated leaves had higher proteolytic enzyme activity levels than leaves treated with gigantenone and petasol. We conclude that green island formation by these eremophilanes proceeds through the inhibition of protein synthesis.