Comparative Effects of Quizalofop and Its Esters on Acetyl-CoA Carboxylase and Fatty Acid Biosynthesis in Corn Leaf Chloroplasts

Abstract

We studied relative inhibitory activities of R(+)-quizalofop (R(+)-2-[4-(6-chloro-2quinoxalinyloxy) 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 x 10-5 M) and free acid (Iso 7.0 x 10-$ M) 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 x 1C-9 M) than the ethyl ester (Iso 4.1 x 10-7 M). In further studies on the ACC from corn chloroplasts free acid also showed more potent inhibitory activity (I50i 1.6 x 10-8 M) than ethyl ester (I50 1.1 x 10-s M) and oxime glycol ester (I50 1.0 x 1G-7 M). 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.

Membrane Response to Diclofop Acid Is pH Dependent and Is Regulated by the Protonated Form of the Herbicide in Roots of Pea and Resistant and Susceptible Rigid Ryegrass

“…The target site of the aryloxyphenoxypropionate and cyclohexanedione herbicides in sensitive grasses is ACCase, a plastid-localized enzyme that catalyzes the ATP-dependent carboxylation of acetyl-COA to form malonyl-COA (Kobek et al, 1988;Burton et al, 1989;Secor et al, 1989;Nakahira et al, 1990;Rendina et al, 1990). This reaction is the first committed step in the de novo synthesis of fatty acids (Harwood, 1988).…”

Differential enantioselectivity of quizalofop ethyl and its acidic metabolite: Direct enantiomeric separation and assessment of multiple toxicological endpoints

“…The other is the inhibition of ACCase, highly representing herbicidal activity with the involvement of chirality [13]. The inactivation of ACCase by the herbicides which rapidly hydrolyzes to the free acids can cause subsequent rapid disruption of membrane structure [38]. Disruption and permeation of membranes which are the primary physiological barrier and essentially the first cell constituent encountered by xenobiotic, are recognized initiators of cytotoxicity [39].…”

Enzyme Inhibitors to Increase Poly-3-hydroxybutyrate Production by Transgenic Tobacco

“…18) The actions of these herbicides are arise from the plastidial ACCase of Gramineae, 19) such as rice and wheat.…”