Elicitor Actions of<i>N</i>-Acetylchitooligosaccharides and Laminarioligosaccharides for Chitinase and<scp>l</scp>-Phenylalanine Ammonia-lyase Induction in Rice Suspension Culture

Abstract

When a series of chitin oligosaccharides was added into a rice suspension culture, N-acetylchito- hexaose, N-acetylchitopentaose, and N-acetylchitotetraose caused an increase in extracellular chitinase activity, mainly due to induction of a class III chitinase. In the case of N-acetylchitohexaose, a substantial increase in the chitinase activity was observed at a concentration higher than 0.01 μg/ml, and a maximum effect was reached at 1 μg/ml. In contrast, N-acetylchitotriose, N-acetylchitobiose, N-acetyl-d-glucosamine, and chitohexaose (a chitosan oligosaccharide) were not very effective. Chitinase induction was also observed with laminarihexaose (a β-1,3-glucan oligosaccharide), but about a 10-fold higher concentration, compared with N-acetylchitohexaose, was needed to get the maximum effect. β-1,3-Glucanase activity was found in cells (but not in medium), and the activity was increased by neither N-acetylchitohexaose nor laminarihexaose. When cells were incubated with N-acetylchitohexaose, l-phenylalanine ammonia-lyase (PAL) activity increased promptly. A biphasic profile was obtained when a dose-dependent effect of the elicitor on the PAL induction was examined; the first phase was observed in a range from 0.01 to 1 μg/ml and the second phase from 3 to 300 μg/ml. Laminarihexaose also acted as an elicitor for PAL induction.