INHIBITION OF OLEIC-ACID INCORPORATION INTO A NONLIPID FRACTION BY CHLOROACETAMIDE HERBICIDES

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremel y sensitive to the chloroacetamide herbicide, metazachlor (I-50 = ca 2 0 nM). Therefore, factors influencing the incorporation of radioactivi ty from oleic acid into this non-lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [C-14]-oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fr action monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethen amid and mefenacet (an oxyacetamide). In contrast, it could not be fou nd with diuron, oryzalin, nor could it be observed with a non-herbicid al metazachlor derivative or iodoacetamide. Incorporation of oleic aci d into that fraction required metabolically active cells and was stimu lated by light. Other fatty acids (16:0, 18:2, and 18:3) were also inc orporated into the non-lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contain s proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet a bout mechanism and chemistry of oleic acid incorporation but this find ing opens a new path for investigations towards the primary target of these herbicides.