Physiological Effects of Soybean Seed Lipoxygenases on Insects

Abstract

Defense against insect attack was investigated for the lipid oxidation products made by soybean seed lipoxygenases, to study the physiological role of the enzymes in seeds. The repellent effect against bean bugs (Riptortm clavatus Thunberg), a major soybean pest, was observed in products of linoleic acid oxidation by lipoxygenases such as linoleic acid monohydroperoxides and hexanal. Bean bugs preferred lipoxygenase isozyme (L-1, L-2, and L-3)-null seeds, especially L-2 null seeds, more than normal soybean seeds, although no significant difference was observed in feeding preference at the repening period. The lipid peroxidation products of lipoxygenases, such as linoleic acid hydroperoxide and hexanal, also repelled two species of leaf beetles that do not usually feed on soybean seeds, and the threshold value for the oligophagous strawberry leaf beetles (Galerucella vittaticollis Baly) was lower than that for the polyphagous false melon beetles (Atrachy a menetriesi Falderman). These results suggested that the lipid oxidation products repelled the tested insects and that the soybean seed lipoxygenases could act defensively, although the effects of the products on the soybean pest insects was not great.