Finding the Target Site of Chioroacetamides: A Thorny Subject

Experimental approaches are described to find the primary mode of action of chloroacetamides using the microalga Scenedesmus as a model system. The data corroborate lipid metabolism as the target domain, particularly the processing of fatty acids. Incorporation of labeled oleic acid into a non-soluble cell-wall residue was found to be severely inhibited by chloro- and oxyacetamides with I50 values down to 10-8 molar. A quantitative rapid assay on acetamide activity based on this 14C-oleate incorporation was developed which correlated with phytotoxicity. Herbicidally active S-enantiomers exhibited activity in the new assay, not the R-forms.