Inhibition of oleic acid incorporation into a non‐lipid fraction by chloroacetamide herbicides

Abstract

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I50= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non‐lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [14C]‐oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non‐herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta‐bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non‐lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains 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 about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these herbicides.

Towards the primary target of chloroacetamides -new findings pave the way

“…Furthermore, the fatty acid bound in this precipitate is not degraded since its 14 C‐label was found to the same extent in the NLF using either a C‐1 or C‐10 position. The striking finding was the strong inhibition of oleate incorporation by phytotoxic chloro‐ or oxyacetamides 32. A 50% inhibition was obtained with about 8 × 10 −8 M metazachlor32 or with 10 −7 M S ‐dimethenamid20 (Fig 1A).…”

“…A 50% inhibition was obtained with about 8 × 10 −8 M metazachlor32 or with 10 −7 M S ‐dimethenamid20 (Fig 1A). Mitosis or photosynthesis inhibitors were found to be inactive; iodoacetamide exhibited a poor I 50 value close to 10 −5 M 32…”