P. Gaillardon

Effect of the cytochrome P-450 inactivator 1-aminobenzotriazole on the metabolism of chlortoluron andisoproturon in wheat☆

Abstract Roots of young wheat plants ( Triticum aestivum cv Clement) were treated with [ 14 C]chlortoluron or [ 14 C]isoproturon alone or mixed with 1-aminobenzotriazole (ABT), a mechanism-based inactivator of cytochrome P -450 monooxygenases. Radioactivity extracted from shoots slightly decreased during periods of metabolism, this decrease being reduced by ABT in the case of isoproturon. ABT strongly inhibited the metabolism of both herbicides. Accumulation of metabolites was generally depressed in the presence of ABT; however, levels of the free N -monodemethylated derivatives were little or not affected. It is concluded that ABT is a synergist of chlortoluron and isoproturon in wheat because it inhibits the enzymes responsible for the ring-alkyl hydroxylation of chlortoluron and putatively of isoproturon, as well as the second N -demethylation of isoproturon. The possibility that those enzymes belong to the class of cytochrome P -450 monooxygenases is discussed.

Phytotoxicity and metabolism of chlortoluron in two wheat varieties

Abstract Varietal susceptibility of winter wheat to chlortoluron, 1-(3-chloro-4-methylphenyl)-3,3 dimethylurea, has been studied in two varieties, Corin (susceptible) and Clement (tolerant). After a 24-hr root absorption of the herbicide, phytotoxicity was estimated from growth measurements. When administered at 12 to 96 μM concentrations, the herbicide reduced the growth of both varieties. A significant selective effect was found at 96 μM. Measurements of chlorophyll fluorescence-induction kinetics allowed to discriminate between the two varieties treated with 12 to 48 μM chlortoluron. The metabolism of chlortoluron was studied following absorption of 24 μM solutions. Both varieties produced the same pattern of metabolites but the tolerant variety degraded the herbicide and the phytotoxic mono-N-demethylated metabolite at a slightly higher rate. An unexpected result was that the more susceptible variety possessed a very significant ability to metabolize chlortoluron. In conclusion, it appears that further studies are necessary before deciding whether the differences in susceptibility of the two varieties can be explained by the only metabolic factor.