RESUMEN
The toxic effects of cadmium (2 mug/ml) on membrane lipids and growth of Euglena gracilis were studied using autotrophic (AUTO), heterotrophic (DARK) and mixotrophic (LIGHT) cells. Cadmium caused inhibition of cellular proliferation (IC50 1.2 mug/ml) and morphological alterations which were most pronounced in chloroplasts. The chlorophyll content of LIGHT cadmium-treated cells was reduced 42.5 per cent. Cadmium also caused an increase in protein and total lipid content per cell in all three cell types. Among the membrane lipids, cholesterol content was lower in cadmium-treated cells cultivated under illumination (AUTO: 0.40 ñ 0.02 vs 0.64 ñ 0.08 and LIGHT: 0.40 ñ 0.09 vs 0.53 ñ 0.01 mug/l0(5) cells). There were no changes in total phospholipid content, although cardiolipin content was altered in all three cell types, and in mixotrophic cells there was an increase in phosphatidylglycerol, a phospholipid typically found in chloroplasts. These results suggest that cadmium has an overall toxic effect on Euglena gracilis and that part of the effect can be ascribed to defects in the structure of chloroplasts and mitochondrial membranes.