Induction of nicotine in tobacco by herbivory and its relation to glucose oxidase activity in the labial gland of three noctuid caterpillars

Abstract

TobaccoNicotiana tabacum L. is a host plant ofHelicoverpa armigera (Hubner),Helicoverpa assulta Guenee andSpodoptera litura (Fabricius) (Lepidoptera, Noctuidae). The difference in leaf nicotine response to the feeding by these three larvae and the mechanical simulation of their feeding was examined by HPLC. Results indicated that nicotine induction was suppressed byH. armigera andH. assulta larvae feeding or by simulated damage treated with their labial glands extracts. The production of nicotine was also suppressed by the glucose oxidase fromAspergillus niger when it was treated on mechanically wounded leaf area. On the contrary, the nicotine production was stimulated byS. litura larva feeding or by simulated damage treated with its labial gland extract. Heat denature can not counteract the stimulation effect of theS. litura labial gland extracts to tobacco nicotine production. The glucose oxidase activity was detected in labial gland extracts of bothH. armigera andH. assulta, but the activity inH. armigera was significantly higher than that inH. assulta. No glucose oxidase activity was detected in labial gland extracts ofS. litura. It is shown that the glucose oxidase activity in labial glands of caterpillars plays an important role in the nicotine response to herbivory. The glucose oxidase was mainly contained in the labial gland ofH. armigera larva, and had the highest activity at pH 7.0. D-Glucose was the optimal substrate of the glucose oxidase. Labial gland glucose oxidase activities varied daily during larval development with high activities found when larvae were actively feeding.