Inhibition of Acetolactate Synthase Activity by Chlorsulfuron, Triasulfuron and Their Metabolites in vitro

The metabolism of two sulfonylurea herbicides chlorsulfuron and triasulfuron was investigated by using wheat cytochrome P450 cDNA(CYP71C6v1) which expressed in yeast.The results showed that chlorsulfuron and triasulfuron were hydroxylated at 5-position on the phenyl ring.The difference in IC50 of parent compound and 5-hydroxy metabolites to acetolactate synthase(ALS) was small.However,their metabolites injured neither wheat nor bean,when applied as post-emergence treatment.The IC50 of chlorsulfuron and its metabolites to wheat ALS were 7.1×10-9 and 7.9×10-9 mol/L,respectively,and to bean ALS were 3.6×10-9 and 4.1×10-9mol/L,respectively.The IC50of triasulfuron and its metabolites to wheat ALS were 4.6×10-9 and 5.3×10-9 mol/L,respectively,and to bean ALS were 4.7×10-9 and 4.9×10-9 mol/L,respectively.These results suggested that proper groups at 5-position on phenyl ring of sulfonylurea molecule might possess high herbicidal activity.