Rapid Induction of the Synthesis of Phenylalanine Ammonia‐Lyase and of Chalcone Synthase in Elicitor‐Treated Plant Cells

Abstract

Changes in the rate of synthesis of phenylalanine ammonia-lyase and chalcone synthase, two characteristic enzymes of phenylpropanoid biosynthesis, have been investigated by direct immunoprecipitation of in vivo [³⁵S]methionine-labelled enzyme subunits in elicitor-treated cells of dwarf French bean (Phaseolus vulgaris). Elicitor, heat-released from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes marked but transient increases in the rates of synthesis of both enzymes concomitant with the phase of rapid increase in enzyme activity at the onset of phaseollin accumulation during the phytoalexin defence response. Increased rates of synthesis of both enzymes can be observed 20 min after elicitor treatment and the pattern of induction of synthesis of phenylalanine ammonia-lyase and chalcone synthase are broadly similar with respect to elicitor concentration and time, maximum rates of synthesis being attained between 2.5 h and 3.0 h after elicitor treatment. Within this overall co-ordination small but distinct differences between the enzymes were observed in: (a) the elicitor concentrations giving maximum enzyme synthesis, and (b) the precise timing of maximum enzyme synthesis, with that for chalcone synthase occurring 20–30 min earlier than that for phenylalanine ammonia-lyase. However, for a given rate of enzyme synthesis, induction of the activities of phenyl-alanine ammonia-lyase and chalcone synthase is more efficient at high elicitor concentrations. This may reflect the operation under certain circumstances of post-translational control of the activity levels of these enzymes as implicated for phenylalanine ammonia-lyase by previous density-labelling experiments [Lawton et al. (1980) Biochim. Biophys. Acta, 633, 162–175]. The same pattern of induction of enzyme synthesis is observed with elicitor preparations from a variety of sources.