Partially N-Deacetylated Chitin Oligomers (Pentamer to Heptamer) are Potential Elicitors for (+)-Pisatin Induction in Pea Epicotyls

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Abstract
Oligomers (dimer to heptamer) of chitosan and their partially/completely N-acetylated derivatives were examined for (+)-pisatin-inducing activities in pea epicotyl elicitor assay at concentrations ranging from 6.25 to 100 μg/ml. The structures of the oligomers were analyzed by 1H NMR and MALDI TOF MS spectrometers. The chitosan oligomers from dimer to tetramer were inactive, while the pentamer exhibited a moderate activity at 100 μg/ml. The hexamer showed a pronounced activity at 100 μg/ml, whereas the oligomer had no activity at the higher concentrations. Although the chitosan heptamer induced a moderate amount of (+)-pisatin (ca. 60 μg/g fr. wt.) at 50 μg/ml, the oligomer did not elicit pisatin formation at 100 μg/ml. The dimer to tetramer of both partially N-deacetylated chitin (DAC) and chitin were totally inactive. The DAC pentamers (d.a. 31%, 52%), DAC hexamers (d.a. 26%, 41%), and DAC heptamers (d.a. 26%, 36%) exhibited significant elicitor activities at lower concentrations (6.25-25 μg/ml) than the native chitosan oligomers. The chitin pentamer to heptamer had weak or no activity. Both glucosamine and N-acetylglucosamine were inactive in the assay. These facts suggest that the DAC pentamer to heptamer may act as elicitors for pisatin induction in pea-fungus interactions.

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