Physiological and Biochemical Aspects of Tolerance in Lepidium Sativum (cress) to Lead Toxicity

The present study was undertaken to assess the toxicity of Pb²⁺ on photosynthetic pigments, total soluble protein and malondialdehyde (MDA) contents as well as the activities of superoxide dismutase SOD (EC 1.15.1.1), catalase CAT (EC 1.11.1.6) and peroxidase POD (EC 1.11.1.7) in Lepidium sativum L. leaves after 10-days of supplying Lead (0-600 ppm) in the nutrient solution. The results indicated that Lead treatment adversely affected plant growth and disturbed the cell metabolism seriously. The development of toxic symptoms, corresponded to a high accumulation of Pb²⁺, was due to the increase in H₂O₂ and MDA contents decrease in protein content and to the much elevated SOD and POD activities in leaves. In addition, the results demonstrated that the high concentration of lead (Pb²⁺ > 400 ppm) could result in a disintegration of the antioxidant system in Lepidium seedlings. Also,the significant decrease in the contents of photosynthetic pigments was related to high-level of metal stress. High concentrations of Pb²⁺, especially 400 and 600 ppm, resulted in a great variation in protein pattern distribution. It can be concluded that Lepidium sativum can tolerate low levels of lead in contaminated soil.