Induced Defense in Japanese White Birch Seedlings against Insect Herbivores

概要

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Plants defend themselves against herbivores, pests and abiotic stresses. Although some defense traits in plants are constitutive, some are switched on, or increased, only when the plants have suffered from stresses (i.e. induced defense). Growth (i.e. lignin) and the synthesis of most defensive compounds in broad-leaved trees derive from phenylalanine. If, therefore, plants allocate photosynthates mainly to defense, these resources would not be available for growth (lignin synthesis). In this study, we examined the defense induced against grazing by the gypsy moth (Lymantria dispar) in seedlings of the white birch (Betula platyphylla var. japonica) grown under two nitrogen levels. We exposed white birch leaves to be grazed by gypsy moths, and we cut the leaves with scissors in early spring. The defenses of white birch seedlings, especially the amount of total phenolics and condensed tannin, were found to be induced by cutting, to extents that were influenced by the soil nitrogen condition. Induced defense of white birch seedlings may depend on the heterophyllous type of shoot development.