Effects of cadmium on photosynthesis, antioxidant enzyme and nitrogen metabolism of cucumber seedlings

A solution culture experiment was conducted to study the effects of Cd on plant growth, photosynthesis, antioxidant enzyme activity and nitrogen metabolism of cucumber seedlings. The results indicate that cucumber seedling growth, chlorophyll (a and b) and carotenoid contents, net photosynthetic rate (Pn), and stomatal conductance(Gs) are decreased with the increase of Cd concentration, while intercellular CO2 (Ci) are significantly increased. The primary maximum photochemical efficiency of PSII (Fv/Fm) is significantly decreased by high concentrations of Cd. Under the Cd 10 and 100 mol/L treatments, activities of catalas (CAT), guaiacol peroxidase (G-POD), superoxide dismutase (SOD) and ascorbate peroxidase (APX), are increased, while under the Cd 200 mol/L treatment, their activities are dramatically inhibited. With the increase concentration of Cd, the activities of nitrate reductase (NR), glutanine synthetase (GS) and glutamate synthase (GOGAT) are significantly decreased.