Changes in fatty acid composition of neutral lipid in mung bean cotyledonsby oxyfluorfen-induced peroxidation

To investigate the mechanism by which short-chain hydrocarbons such as etha ne are formed under the influence of peroxidizing herbicides, we examined o xyfluorfen-induced lipid hydroperoxide content and changes of fatty acids c onstituting 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 NH2. Lip id hydroperoxide is present primarily in the neutral lipid fraction. This i ndicates that lipid peroxidation caused by oxyfluorfen may occur in the neu tral 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 decre ased 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 aft er oxyfluorfen treatment. It is suggested that peroxidation occurs during t he early stages after herbicide application, and antioxidants together with fatty acid synthesis are instrumental in recovering PUFAs decreased by per oxidation in plant cells. However. the defense system of a plant is overtax ed by the continuous oxidative stress, eventually leading to destruction of cell membranes. Whereas the amount of PUFAs decreased. monounsaturated (C1 6:1, C18:1) fatty acid content tended to increase by oxyfluorfen treatment. It is suggested that the regulatory network for the biosynthesis of differ ent fatty acid species may be disturbed by the oxidative stress imposed. (C ) 2001 Academic Press.