Differential responses of bean (Phaseolus vulgaris L.) to elicitor fractions from Colletotrichum lindemuthianum

Abstract

Polysaccharide elicitor preparations from culture filtrate and cell walls of Colletotrichum lindemuthianum had broadly similar monosaccharide compositions. Treatment with culture filtrate or cell wall elicitors had no effect on the electrolyte leakage from bean leaf slices or mesophyll cells and resulted in similarly reduced viability of suspension cultured bean cells. Both elicitor preparations had similar effects on the induction of extractable activities, synthesis and mRRA activities of phenylalanine ammonia-lyase, chalcone synthase and chalcone isomerase, on the induction of synthesis and mRRA activities of chalcone synthase multiple subunit isoforms in bean cell suspension cultures and on the patterns of active phenylalanine ammonia-lyase and chalcone synthase multiple forms separated by chromatofocussing. Both qualitative and quantitative differences were observed in the effects of the two elicitor preparations on the accumulation of 5-deoxy and 5-hydroxy isoflavonoids, deposition of wall-bound phenolics and on the levels of free and esterified hydroxycinnamic acids. The two elicitor preparations induced prolyl hydroxylase activity although only the cell wall elicitor induced accumulation of hydroxyproline in the cell walls of suspension cultured bean cells. In addition, although the overall patterns of polysomal mRRA activities in bean cell cultures following treatment with cell wall or culture filtrate elicitors were broadly similar, distinct differences were observed in the effects of the two elicitor preparations on the induction/reduction of the activities of mRNAs encoding a number of polypeptides as shown by two-dimensonal gel electrophoresis.An unaltered monosaccharide composition and ability to induce phenylpropanoid biosynthetic pathway enzymes were associated with all fractions obtained after chromatography of culture filtrate elicitor on the basis of size and charge. Fractions obtained after affinity chromatography on Concanavalin A-Sepharose had different monosaccharide compositions but exhibited similar effects on the viability of cultured cells and on the induction of synthesis of phenylalanine ammonia-lyase, chalcone synthase and chalcone isomerase as did the crude culture filtrate elicitor. However, although the three Concanavalin A-Sepharose-purified fractions induced chalcone synthase activity to higher levels than the crude culture filtrate elicitor preparation, little or no induction of phenylalanine ammonia-lyase and chalcone isomerase activities was observed following treatment with the Concanavalin A-unbound and a-methyl mannoside-eluted fractions. In addition, the Concanavalin A-Sepharose-purified fractions induced the activities of mRNAs encoding phenylalanine ammonia-lyase and the most basic chalcone synthase subunit isoform to higher levels than the culture filtrate elicitor. The three Concanavalin A-Sepharose-purified fractions had broadly similar effects on the overall patterns of protein synthesis in vitro although their effects were clearly different from those obtained with crude elicitor preparations. Possible physiological importance of putative multielicitar components with non-identical biological activities and their value in elucidating biochemical control mechanisms underlying regulation and co-ordination of host gene expression are discussed.