Changes in Fatty Acid Composition of Neutral Lipid in Mung Bean Cotyledons by Oxyfluorfen-Induced Peroxidation

Abstract To investigate the mechanism by which short-chain hydrocarbons such as ethane are formed under the influence of peroxidizing herbicides, we examined oxyfluorfen-induced lipid hydroperoxide content and changes of fatty acids constituting the neutral lipid in mung bean cotyledons. Lipid hydroperoxides, detected by a chemiluminescence-HPLC system, were separated into neutral lipid, free fatty acid, and phospholipid fractions using BUND ELUT NH 2 . Lipid hydroperoxide is present primarily in the neutral lipid fraction. This indicates that lipid peroxidation caused by oxyfluorfen may occur in the neutral lipid including glycolipid. Next, we analyzed the change of fatty acid composition in the neutral lipid in which the most lipid hydroperoxide was observed. Polyunsaturated fatty acids (PUFAs: C18:2, C18:3) markedly decreased after a 1-h treatment with oxyfluorfen under the light, but increased during the next 5 h. However, the PUFA content decreased from 6 to 13 h after oxyfluorfen treatment. It is suggested that peroxidation occurs during the early stages after herbicide application, and antioxidants together with fatty acid synthesis are instrumental in recovering PUFAs decreased by peroxidation in plant cells. However, the defense system of a plant is overtaxed by the continuous oxidative stress, eventually leading to destruction of cell membranes. Whereas the amount of PUFAs decreased, monounsaturated (C16:1, C18:1) fatty acid content tended to increase by oxyfluorfen treatment. It is suggested that the regulatory network for the biosynthesis of different fatty acid species may be disturbed by the oxidative stress imposed.