1990 Volume 15 Issue 2 Pages 189-197
We studied relative inhibitory activities of R(+)-quizalofop {R(+)-2-[4-(6-chloro-2-quinoxalinyloxy) phenoxy] propionic acid}, its ethyl ester (quizalofop-ethyl) and oxime glycol ester (propaquizafop) on the 14C-acetate incorporation into fatty acids in excised corn leaf segments and isolated corn chloroplasts, and on acetyl-CoA carboxylase (ACC) from corn chloroplasts. Both ethyl ester (I50, 4.3×10-8M) and free acid (I50, 7.0×10-8M) showed equally high inhibitory activity on fatty acid biosynthesis in the leaf segments. On the fatty acid biosynthesis in the corn chloroplasts, however, the free acid showed a stronger inhibitory efect (I50, 3.6×10-9M) than the ethyl ester (I50, 4.1×10-7M). In further studies on the ACC from corn chloroplasts, free acid also showed more potent inhibitory activity (I50, 1.6×10-8M) than ethyl ester (I50, 1.1×10-6M) and oxime glycol ester (I50, 1.0×10-7M). In an ACC assay medium, the oxime glycol ester was hydrolyzed about 10% during 5-min incubation, while the ethyl ester was hydrolyzed about 3% during 10-min incubation. The results indicate that a hydrolyzed product in free acid form is an actual active ingredient. In addition, our previous reports and present results suggest that ACC is the primary target site of quizalofop.
