Comparative study of cadmium effects on membrane lipid composition of Brassica juncea and Brassica napus leaves

The term phytoremediation is used to describe the clean-up of heavy metals from contaminated soils by plants. In this study, we examined cadmium (Cd) accumulation by Brassica napus in comparison with the known Cd-hyperaccumulator Brassica juncea, in a hydroponic medium. Cd treatment was applied as a concentration series between 0 and 50 μM for 15 days. Most of the Cd taken up was retained in roots in both species, however, B. juncea accumulated more Cd in the shoots compared to B. napus. Excess metal supply resulted in an increase in the lipid content of B. juncea leaves grown under cadmium treatment, but did not affect fatty acids composition. In contrast, an alteration in the lipid composition of B. napus leaves was observed together with a decrease in the lipid contents. The amounts of chloroplastic lipids: monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfolipids (SL) and phosphatidylglycerol (PG) decreased drastically under the effect of metallic treatments. Whereas, amounts of extrachloroplastic lipids: phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were significantly increased. The latter finding suggested that PC and PE synthesis was enhanced by metal application. Moreover, the levels of polyunsaturated fatty acids mainly linolenic acid (C18:3) and hexadecatrienoïc acid (C16:3) and that of trans palmitoleic acid (C16:1t) from PG declined. So, cadmium seems to affect preferentially chloroplastic lipids containing higher levels of polyunsaturated fatty acids. Lipid changes in B. juncea, the well known Cd-hyperaccumulator specie, revealed a more stability of its cellular membranes to cadmium-stress as compared to Cd-sensitive specie, B. napus.