INCORPORATION OF OLEIC-ACID INTO SPOROPOLLENIN AND ITS INHIBITION BY THE CHLOROACETAMIDE HERBICIDE METAZACHLOR

Incorporation of exogenous [C-14]oleic acid (18:1) into a nonlipid fra ction of the green alga Scenedesmus acutus was strongly inhibited by c hloroacetamide herbicides. This fraction was solubilized by 12 consecu tive steps. Radioactivity from oleic acid was mostly recovered in prot eins (soluble and insoluble), in starch, and in a dioxane-soluble subf raction. Incorporation of oleic acid into the protein and starch subfr actions was not inhibited but it was strongly reduced in the dioxane s ubfraction. The nonlipid fraction could not be completely solubilized and a significant proportion of the original radioactivity was recover ed in an insoluble subfraction. Inhibition of oleic acid incorporation into that subfraction was more potent than in the total nonlipid frac tion. An inhibition of 50% was achieved with 50 mM herbicide. After th e nonlipid fraction was solubilized by acetolysis, a residue was obtai ned in which the incorporation of oleic acid was also completely inhib ited by 10 mu M metazachlor. The infrared spectra of the insoluble sub fraction and the acetolysis residue were similar to that of sporopolle nin isolated with comparable methods. Oleic acid as a precursor of spo ropollenin is discussed together with the interference of chloroacetam ides with oleic acid metabolism, especially its incorporation into spo ropollenin. Using Scenedesmus, the inhibition of oleic acid incorporat ion into sporopollenin is a sensitive marker of chloroacetamide activi ty. (C) 1996 Academic Press