Influence of the Safener Benoxacor on the Metabolism of Metolachlor in Corn*

C. K. Cottingham and K. K. Hatzios Laboratory for Molecular Biology of Plant Stress, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, U.S.A., 24061-0330 Z. Naturforsch. 46c, 846-849 (1991); received March 26, 1991 Metolachlor, Glutathione-S-transferase, Glutathione, Benoxacor, Corn, Zeamays L. The herbicide safener benoxacor (CGA -154281) is effective in protecting corn from meto­ lachlor injury. Glutathione-S-transferase (GST) activity of corn seedlings was stimulated by low concentrations of benoxacor as was the formation of a polar metabolite identified as the glutathione (GSH) conjugate of metolachlor. A similar degree of enhancement of metolachlor metabolism was observed in both a metolachlor-tolerant (‘Cargill 7567’) and a metolachlorsusceptible (‘Northrup-King 9283’) corn line. The total GSH content of shoots of the metolachlor-susceptible corn hybrid was not affected by benoxacor treatment, but an increase was noted for shoots of the tolerant corn hybrid. The two corn hybrids with differential tolerance to metolachlor also differ in their dose response to benoxacor with higher safener concentra­ tions failing to induce or inhibit GST activity of the tolerant ‘Cargill 7567’ corn line. Stimula­ tion of GST activity and a corresponding enhanced rate of metolachlor metabolism can ac­ count for the safening effect of benoxacor. These mechanism of action of dichloroacetamide safeners.