Incorporation of Oleic Acid into Sporopollenin and Its Inhibition by the Chloroacetamide Herbicide Metazachlor

Abstract

Incorporation of exogenous [14C]oleic acid (18:1) into a nonlipid fraction of the green algaScenedesmus acutuswas strongly inhibited by chloroacetamide herbicides. This fraction was solubilized by 12 consecutive steps. Radioactivity from oleic acid was mostly recovered in proteins (soluble and insoluble), in starch, and in a dioxane-soluble subfraction. Incorporation of oleic acid into the protein and starch subfractions was not inhibited but it was strongly reduced in the dioxane subfraction. The nonlipid fraction could not be completely solubilized and a significant proportion of the original radioactivity was recovered in an insoluble subfraction. Inhibition of oleic acid incorporation into that subfraction was more potent than in the total nonlipid fraction. An inhibition of 50% was achieved with 50 nMherbicide. After the nonlipid fraction was solubilized by acetolysis, a residue was obtained in which the incorporation of oleic acid was also completely inhibited by 10 μMmetazachlor. The infrared spectra of the insoluble subfraction and the acetolysis residue were similar to that of sporopollenin isolated with comparable methods. Oleic acid as a precursor of sporopollenin is discussed together with the interference of chloroacetamides with oleic acid metabolism, especially its incorporation into sporopollenin. UsingScenedesmus,the inhibition of oleic acid incorporation into sporopollenin is a sensitive marker of chloroacetamide activity.