Responses of Antioxidative Systems to Oxyfluorfen and Their Role in Herbicidal Tolerance of Plnts.

To further investigate the role of antioxidative systems in plant tolerance to diphenylether (DPE) herbicides, the relationship between the antioxidative enzyme activities, antioxidant content and the level of oxidative damage by oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-trifluoromethyl benzene] were investigated in rice, corn, radish and buckwheat. Rice showed the highest tolerance to oxyfluorfen, while buckwheat showed the lowest. However, both plants accumulated a larger amount of protoporphyrin IX (Proto IX) than corn or radish which showed intermediate tolerance to the herbicide. The measurement of antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR), and antioxidant contents of carotenoids and reduced glutathione (GSH) in four plants showed that SOD and CAT activities and GSH content were much higher in rice than in the other plants. Furthermore, activities of all the enzymes in rice were increased until Proto IX accumulation reached maximum (4hr after light irradiation). The antioxidative ability of buckwheat was lowest and was not increased by the herbicide treatment at all. The results strongly suggested that antioxidative ability is one of the critical factors determining the tolerance to oxyflourfen in some plant species.

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