Chloroacetamide inhibition of fatty acid synthesis

The influence of alachlor and metazachlor on fatty acid synthesis of the green alga Scenedesmus acutus has been investigated. Autotrophic growth for 40 hr in the presence of 5 μ M alachlor or metazachlor led to a strong decrease in linolenic acid (18:3) content, while an increase in the palmitic (16:0) and oleic acid (18:1) content was observed. Furthermore, short-term incorporation studies (3 hr) with [2- 14C]acetate as the precursor of fatty acids showed a substantial inhibition of acetate incorporation into the fatty acid extract. Using TLC and HPLC techniques this extract exhibited one 14C-labeled fraction. As analyzed by gas chromatography linolenic acid is the main component in this fraction (more than 30%). A 5-μ M and 10-μ M sethoxydim application had no effect on acetate uptake with Scenedesmus. A combination of either metazachlor or alachlor with sethoxydim markedly improved the inhibitory activity of the chloroacetamides on acetate uptake. Our data suggest an inhibition of fatty acid biosynthesis between the C-elongation step of palmitic acid and the desaturation of oleic acid yielding linolenic acid.