Chloroacetamide Mode of Action, I: Inhibition of Very Long Chain Fatty Acid Synthesis in Scenedesmus acutus
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چکیده
H erbicidal chloroacetam ides cause a very sensitive inhibition of fatty acid incorporation into an insoluble cell wall fraction of Scenedesm us acutus. The m olecular basis was investi gated in m ore detail. A fter incubation of the algae with [14C]oleic acid and saponification, the rem aining pellet was solubilized and fractionated consecutively with chloroform /m ethanol, phosphate buffer, amylase, pronase, and finally with dioxane/H Cl. By acid hydrolysis in dioxane a part of the cell wall residue was solubilized showing inhibition of exogenously applied oleic acid and o ther labelled precursors such as stearic acid, palm itic acid, and acetate. A fter extraction of this dioxane-soluble subfraction with hexane, H PLC could separate labelled m etabolites less polar than oleic acid. T heir form ation was com pletely inhibited by chloroacetam ides, e.g. 1 (.im metazachlor. This effect was also observed with the herbicidally active 5-enantiom er of m etolachlor while the inactive /?-enantiom er had no influence. These strongly inhibited m etabolites could be characterized by radio-H PLC /M S as very long chain fatty acids (VLCFAs) with a carbon chain betw een 20 and 26. Incubating a metazachlor-resistant cell line of 5. acutus (Mz-1) with [14C]oleic acid, VLCFAs could not be detected in the dioxane/ HCl-subfraction. Furtherm ore, com paring the presence of endogenous fatty acids in wildtype and m utant Mz-1 the VLCFA content of the m utant is very low, while the content of long chain fatty acids (C 1 6 -1 8 ) is increased, particularly oleic acid. Obviously, the phytotoxicity of chloroacetam ides in S. acutus is due to inhibition of VLCFA synthesis. The resistance of the m utant to m etazachlor has a bearing on the higher am ount of long chain fatty acids replacing the missing VLCFAs in essential m em branes or cell wall components.
منابع مشابه
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تاریخ انتشار 1999