Effects of Chloroacetanilide Herbicides on Membrane Fatty Acid Desaturation and Lipid Composition in Rice, Maize, and Sorghum

The effects of the chloroacetanilide herbicides pretilachlor and metolachlor on the composition of membrane fatty acids and lipids were studied in dark-grown rice (Oryza saliva L., cv. Lemont), maize (Zen mays L., cv. Cargill 7567), and grain sorghum (Sorghum bicolor (L.) Moench., cv. G522DR) seedlings. The main desaturated fatty acid found in control and herbicide-treated seedlings of rice, maize, and grain sorghum was 18:2. Applied at their respective GR(50) concentrations, pretilachlor (0.1 mu M) and metolachlor (10 and 5 mu M) did not inhibit the overall desaturation of 18:1 to 18:2 and 18:3 fatty acids in root and shoot tissues of rice, maize, or grain sorghum. However, seedlings of the three grass species treated with the two herbicides showed some decrease in 18:1 and a concomitant increase in 18:2 or 18:3 fatty acids, compared to control plants. The safeners fenclorim, benoxacor, and fluxofenim protected the three grass crops against injury caused by pretilachlor and metolachlor but did not change the composition of membrane fatty acids in any of the three plant species. The effects of metolachlor and pretilachlor on plant membranes were determined also by a detailed analysis of individual lipids extracted from the roots of the three grasses. Metolachlor and pretilachlor did not alter the composition of membrane lipids and the degree of desaturation of fatty acids in the individual lipids found in the roots of rice, maize, and grain sorghum. The obtained results do not seem to support recent suggestions correlating the herbicidal activity of chloroacetanilide herbicides with an inhibition of fatty acid desaturation in algal species. The mechanism of action of these herbicides may be related to an inhibition of the synthesis of very long chain fatty acids or of the incorporation of unsaturated fatty acids into nonlipids of plants. (C) 2000 Academic Press.