Altered fatty acid profile of polar lipids in maize seedlings in response to excess copper

A wide range of cellular responses occur when plants are exposed to heavy metal stress, including changes in the membrane fatty acid composition. In this study, we examined the effect of excess copper (100 mu M) on the degree of unsaturation [double bond index (DBI) of 18-C fatty acids] and the polar lipid profiles in maize (Zea mays L.). The level of unsaturation of total fatty acids decreased from 1.42 to 1.28 in maize roots. However, copper-induced compositional changes of polar fatty acid composition show a general trend of increasing DBI. These responses suggest that individual 18-C fatty acid classes may have specific roles in maintaining optimal membrane function, enabling plant growth under copper stress. The results also reveal key changes including marked decrease in total root phospholipid levels and consistent increase in the steryl lipid/phospholipid (SL/PL) ratio, as well as a decrease in monogalactosyldiacylglycerol/digalactosyldiacylglycerol (MGDG/DGDG) ratio, reflecting alteration of membrane permeability and fluidity. In shoots, the DBI obtained from phosphatidylcholine (PC), sulphoquinovosyldiacylglycerol (SQDG) and monogalactosyldiacylglycerol (MGDG) was increased. In contrast, these indices were decreased in phosphatidylinositol (PI) and phosphatidylglycerol (PG). However, the PI, PC, PG, MGDG and DGDG contents in shoots were significantly decreased, suggesting alterations in the photosynthetic membranes.