Induction of chalcone isomerase in elicitor-treated bean cells. Comparison of rates of synthesis and appearance of immunodetectable enzyme

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Abstract
Chalcone isomerase, an enzyme involved in the formation of flavonoid-derived compounds in plants, was purified nearly 600-fold from cell suspension cultures of dwarf French bean (Phaseolus vulgaris L.). Chromatofocusing yielded a single form of the enzyme of apparent pI [isoelectric point] 5.0. This preparation was used to raise rabbit anti-(chalcone isomerase) serum. Changes in the rate of synthesis of chalcone isomerase were investigated by indirect immunoprecipitation of enzyme labeled in vivo with [35S]methionine in elicitor-treated cultures of P. vulgaris. Elicitor, heat-released from cell walls of the phytopathogenic fungus Colletotrichium lindemuthianum, the causal agent of anthracnose disease of bean, causes increased synthesis of the isomerase, with maximum synthetic rate occurring 11-12 h after exposure to elicitor. Immune blotting studies indicate that the elicitor-mediated increase in extractable activity of the isomerase is associated with increased appearance of immunodetectable isomerase protein of MW 27,000. However, the maximum level of immunodetectable isomerase was attained .apprx. 6 h earlier than maximum extractable activity. Furthermore, a 2.8-fold increase in enzyme activity above basal levels at 12 h after elicitor-treatment was associated with a corresponding 5.8-fold increase in immunodetectable enzyme. Elicitor probably induces the synthesis of both active and inactive chalcone isomerase of MW 27,000, and some activation of inactive enzyme occurs during the elicitor-mediated increase in isomerase activity. The presence of a pool of inactive chalcone isomerase in bean cell cultures was recently suggested on the basis of density labeling experiments using 2H from 2H2O.

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