ELICITOR INDUCTION OF MESSENGER-RNA ACTIVITY - RAPID EFFECTS OF ELICITOR ON PHENYLALANINE AMMONIA-LYASE AND CHALCONE SYNTHASE MESSENGER-RNA ACTIVITIES IN BEAN CELLS

Abstract

Changes in the activity levels of mRNA encoding phenylalanine ammonia-lyase and chalcone synthase, 2 characteristic enzymes of phenylpropanoid biosynthesis, in elicitor-treated cells of dwarf French bean (P. vulgaris L.) were investigated by immunoprecipitation of [35S]methionine-labeled enzyme subunits synthesized in vitro in an mRNA-dependent rabbit reticulocyte lysate translation system. Elicitor heat-released from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes marked rapid increases in the polysomal activities of the mRNA encoding the 2 enzymes concomitant with the phase of rapid increase in enzyme activity at the onset of phaseollin accumulation during the phytoalexin defense response. Increased polysomal mRNA activities encoding the 2 enzymes can be observed 30 min after elicitor treatment. The patterns of induction of the mRNA activities are broadly similar with respect to time and elicitor concentration, although small but distinct differences between the enzymes were observed in the elicitor concentration giving maximum induction. There is a close correlation between the induction of polysomal mRNA activity and the induction of enzyme synthesis in vivo by elicitor treatment with respect to both the kinetics of induction and the dependence on elicitor concentration. Apparently, elicitor stimulation of phenylalanine ammonia-lyase and chalcone synthase synthesis in vivo is largely a result of increased polysomal activity of the mRNA encoding these enzymes. Similar patterns of induction of polysomal mRNA activity are observed with elicitor preparations from a variety of sources. The marked increases in polysomal mRNA activities encoding phenylalanine ammonia-lyase and chalcone synthase are increases as a proportion of total cellular mRNA activity, indicating that elicitor does not increase these polysomal mRNA activities by stimulation of selective recruitment from the total pool of cellular mRNA.