Elicitor-mediated induction of chalcone isomerase inPhaseolus vulgariscell suspension cultures

摘要

Approximately fourfold increases in the extractable activity of the enzyme chalcone isomerase (CHI, EC 5.5.1.6) were observed within 24 h of treatment of cell suspension cultures ofPhaseolus vulgariswith a crude elicitor preparation heatreleased from the cell walls of the bean pathogenColletotrichum lindemuthianum. The induction of CHI activity was highly dependent upon elicitor concentration, with maximum induction occurring in two discrete concentration ranges. A basal half-life for CHI>32 h in control cultures was determined by labelling with2H from2H2O followed by analysis of the equilibrium distribution of enzyme activity in CsCl density gradients. Comparative density labelling indicated that at both the lower and higher effective elicitor concentrations, the induced appearance of CHI activity was the result of an apparent initial activation of pre-existing enzyme followed by an increase in the rate of de-novo synthesis of the enzyme as compared with non-elicited controls. The increased appearance of the enzyme over the first 8 h in elicitor-treated cultures was inhibited by cycloheximide, cordycepin and actinomycin D. The results are discussed in relation to the mechanisms of co-ordinate enzyme induction operating in French-bean cell cultures exposed to fungal elicitors.