Molecular and Physiological Mechanisms of Heavy Metal Tolerance in Atriplex halimus

A study was carried out to identify the mechanisms underlying stress caused by Cd and Pb accumulation in leaves of Atriplex halimus L. collected from habitats representing different kinds of pollution. Mean concentrations of Cd and Pb in aerial parts exceeded the critical levels in polluted plants as compared to reference plants. There were significant reduction in guiacol peroxidase, ascorbate peroxidase and glutathione content in most of polluted plants. The results showed increase in superoxide dismutase enzyme in all polluted plants. The significant increment in catalase enzyme, glutathione S-transeferase and ascorbic acid content were observed in most of polluted plants. Results of the nine differential expressed bands showed down regulation of NADH dehydrogenase and Sedoheptulose-bisphosphatase in polluted plants. In contrast, there were six regulated genes in highly polluted plants, representing transcription factors, membrane transporters and ROS detoxification. The transcription level of phytochelatin synthase showed a significant increase in all polluted plants, while heavy metal ATPase transporter expression significantly increased in some polluted plants. In conclusion, A. halimus may use two different strategies against Cd and Pb stress, in which the molecular and physiological features affords similar levels of Cd and Pb tolerance through binding, sequestration and the reduction of harmful effect of heavy metals.