Effects of pesticide adjuvants on membrane lipid composition and fluidity in Lemna minor

Abstract

Lemna minor L. plants were exposed to 40 μM of the pesticide adjuvants Triton® X-15, X-35, X-100, and X-114 for a period of 2 weeks under laboratory conditions. Investigation on the individual principal phospholipids in Lemna membranes (phosphatidyl-choline, -ethanolamine, -glycerol, and -inositol) showed an increase in phosphatidyl-choline and -ethanolamine and a decrease in phosphatidyl-glycerol and -inositol. An analysis of the percentages of fatty acids of the phospholipids indicated a differential Triton® effect on phosphatidyl-ethanolamine; the hydrophobic adjuvants (Triton® X-15 and X-35) induced a greater unsaturation than the hydrophilic adjuvants (Triton® X-114 and X-100). Membrane lipid order was also perturbed as the membrane lipid fluidity of chloroplast membranes as determined by fluorescence polarization increased following adjuvant treatment. Radiolabeled investigations with two Triton® isotopes (14C ring labelled X-35 and X-100) showed membrane lipid to adjuvant ratios in chloroplasts at 100:4 for X-35 and 100:2 for X-100. This investigation further substantiates the fact that some adjuvants in pesticide formulations are not inert and can be phytotoxic. Key words: adjuvants, Lemna minor, membranes, lipids, fluidity.