Effects of cadmium stress on photosynthesis and antioxidant systems in Mirabilis jalapa under different light intensities
不同光强下镉胁迫对紫茉莉光合作用和抗氧化系统的影响

The effects of excessive cadmium (30 mg·kg-1 in soils) on plant growth, photosynthesis, lipid peroxidation, the activities of antioxidant enzymes, the contents of photosynthetic pigments, Cd, Mg, Fe, K, ascorbic acid (AsA) and glutathione (GSH) in Mirabilis jalapa plants were investigated and compared under high light (HL, fully exposed to ambient sunlight), intermediate light (ML, about 50% of full ambient sunlight) and low light (LL, about 10% of full ambient sunlight) conditions. The net photosynthetic rate (Pn) in the presence of excessive Cd in soils decreased more under HL treatment than under ML and LL treatments. Excessive Cd significantly reduced the maximal photochemical efficiency (Fv/Fm) under HL and LL treatments, but did not affect Fv/Fm under ML treatment. Excessive Cd remarkably increased the dark respiration rate (Rd), especially under ML treatment. The growth of plants was significantly inhibited in the presence of excessive Cd, especially under HL treatment. Excessive Cd greatly increased the Cd content, and reduced the contents of chlorophyll, carotinoid, Mg, Fe and K in the leaves, particularly under HL treatment. Under HL treatment, excessive Cd greatly increased the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD), the contents of hydrogen peroxide (H2O2), superoxide (O-·2) and malondialdehyde (MDA), and electrolyte leakage, whereas it decreased the activities of catalase (CAT) and ascorbate peroxidase (APX), and the contents of GSH and AsA. The results indicate that excessive Cd enhanced oxidative stress and growth inhibition to Mirabilis jalapa plants, especially under HL treatment.