Effect of heavy metals on plasma membrane lipids and antioxidant enzymes of Zygophyl I urn species

Background: Heavy metals are major environmental pollutant when they present in high concentration in soil and have toxic effects on growth and development of plants. Industrial activities result in heavy metal pollution of large areas of land, which greatly affects natural vegetation. Understanding the mechanism of how plants combat heavy metals adverse effects is hence of great importance. Materials and Methods: Two different localities were chosen; one locality was in the vicinity of gypsum factory and the other one was 25 km away from the factory. Two Zygophyllum species (Z. album and Z. coccineum) were naturally grown in the studied areas. The effects of soil heavy metal stress on shoot heavy metal concentrations, lipid peroxidation, antioxidant enzyme activities and the root plasma membrane (PM) lipid composition were analyzed. Results: Heavy metal concentrations and Lipid peroxidation increased in the shoot of both species grown in the polluted area. The activities of ascorbate oxidase (ASO), guaiacal peroxidase (GPX), ascorbate peroxidase (APX) and superoxide dismutase (SOD) were increased whereas these of catalase (CAT) were decreased in both species under the polluted conditions. PM total lipids, phospholipids, glycolipids and sterols were decreased in Z. album and Z. coccineum as a result of the polluted soil. Heavy metal stress increased phosphatidylethanolamine (PE) and decreased phosphatidylinositol (PI) and phophatidylglycerol (PG), with no significant change in phosphatidylcholine (PC) in the root PM of both species. Phosphatidylserine (PS) decreased in the PM of Z. album whereas it increased in the PM of Z. coccineum under the pollution conditions. Heavy metal stress changed the composition and concentration of fatty acids of the root PM, resulting in increased sat/unsat ratio of both species. Conclusion: the results suggest that efficient antioxidant machinery and favorable PM lipid homeostasis are important to enable Zygophyllum species to withstand the prevailing heavy metal stress.