Chitosan derivatives classed into three groups according to their molecular size were examined for the relationships between degree of N -acetylation and phytoalexin (+)-pisatin-inducing activity in pea epicotyl assay. Partially N-deacetylated chitin with degree of N-acetylation 56% (DAC 56%) was the most potent inducer of (+)-pisatin among sparingly water-soluble polysaccharides including chitosan (degree of N -acetylation 0%), DAC 32%, and chitin. Among the intermediate-sized molecules obtained from degradation of the chitosan and the DACs by NaNO2, the chitosan fragment was the most powerful elicitor for (+)-pisatin induction. The NaNO2-degraded DAC 56% exhibited a com parable activity to the NaNO2 -degrad-ed chitosan at low concentrations. The NaNO2-degraded fragments as well as the native polymer induced a relatively high amount of (+)-pisatin, while the acetone precipitate of chitosan oligomers from the HCl-catalyzed hydrolysate and their partially N-acetylated derivatives exhibited a moderate (+)-pisatin-inducing activity. These findings suggest the possibility that partially N-deacetylated chitin fragments could be one of the most promising elicitors in the pea system.
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