POTENTIAL ROLE OF LIPOXYGENASES IN DEFENSE AGAINST INSECT HERBIVORY

The potential role of the plant enzyme lipoxygenase in host resistance against the corn earworm Helicoverpa zea was examined. Lipoxygenase i s present in most of the common host plants of H. zea, with highest ac tivity in the leguminous hosts such as soybean and redbean. Treatment of dietary proteins with linoleic acid and lipoxygenase significantly reduced the nutritive quality of soybean protein and soy foliar protei n. Larval growth was reduced from 24 to 63% depending upon treatment. Feeding by H. zea on soybean plants caused damage-induced increases in foliar lipoxygenase and lipid peroxidation products. Larvae feeding o n previously wounded plant tissue demonstrated decreased growth rates compared to larvae feeding on unwounded tissue. Midgut epithelium from larvae feeding on wounded tissues showed evidence of oxidative damage as indicated by significant increases in lipid peroxidation products and losses in free primary amines. The potential role of oxidative and nutritional stress as a plant defensive response to herbivory is disc ussed.