In vitro production of superoxide radical from paraquat and its interactions with monuron and diuron [Herbicides]

The abilities of herbicides to either produce superoxide radical or react with this radical were examined. The effect of the herbicides on the superoxide-induced reduction of p-nitro blue tetrazolium chloride was used as an index. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) enhanced and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibited the reduction of p-nitro blue tetrazolium chloride. Paraquat was reduced photochemically (riboflavin/methionine) or enzymatically (xanthine/xanthine oxidase) and produced superoxide radical upon reoxidation. Diuron and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] interacted with photochemically produced superoxide radical, but not with enzymatically produced superoxide radical. The product of the monuron/superoxide interaction was a demethylated, dechlorinated, water-soluble compound containing phenolic hydroxyl group(s), and was not toxic to oats (Avena sativa L.). The enzyme superoxide dismutase prevented the formation of this product.