DIFFERENCES IN GENE-EXPRESSION BETWEEN NATURAL AND ARTIFICIALLY INDUCED LEAF SENESCENCE

Gene expression during artificially induced senescence of barley (Hordeum vulgare L.) leaves was examined by in-vitro translation and mRNA hybridization with several copy-DNA (cDNA) clones for newly induced transcripts. When detached barley leaves were incubated in darkness, senescence symptoms as indicated by chlorophyll loss were rapidly induced. By in-vitro translation, concomitant changes in translatable mRNA levels were shown to occur with some translation products decreasing and others increasing in abundance. For closer analysis, cDNA clones for newly induced transcripts were isolated by differential screening. Six cDNA clones, derived from three different transcripts were identified and classified according to the expression of the respective mRNAs. Two of the three transcripts showed very similar expression patterns: in detached leaves they were induced by abscisic acid and inhibited by kinetin. They were also induced by wounding and osmotic stress, but could not be detected in naturally senescing leaves. The third mRNA, represented by only one of the six cDNA clones, behaved differently. There was no significant effect of hormone application, wounding or drought conditions, but the transcript accumulated during natural senescence of barley flag leaves. We conclude that only a minor part of the mRNA changes observed during dark incubation of detached leaves is connected with leaf senescence, whereas stress-related transcripts appear to predominate quantitatively.