Effects of copper on the growth, antioxidant enzymes and photosynthesis of spinach seedlings.

Examination of plants with strong Cu tolerance and an understanding of their Cu-tolerance mechanisms are of considerable significance for the remediation of Cu-contaminated soil. Although spinach may be a plant with strong Cu tolerance, the threshold of Cu tolerance in this plant and its physiological response mechanisms to Cu are still unclear. In this study, we examined that the effects of different Cu concentrations on the growth parameters, antioxidant enzyme activities, and photosynthesis of spinach seedlings. The results showed that when treated with a low Cu concentration (100 mg L-1 CuSO4), the biomass of spinach seedlings increased, whereas the MDA content, the activities of antioxidant enzymes, Pn, gs and Tr were not significantly different from those in the control (P > 0.05), and Y(II), qP reached their maximum values, indicating that a low Cu concentration (100 mg L-1 CuSO4) had minimal negative effects on the life activities of spinach seedlings. In contrast, when treated with high Cu concentrations (800-1000 mg L-1 CuSO4), the total biomass of spinach seedlings was markedly decreased, the MDA contents increased, antioxidant enzyme activities initially increased and then decreased to varying degrees, the contents of chlorophyll, Pn, Tr, Fv/Fm, qP, NPQ, and Y(II) were all decreased. However the growth of spinach did not terminate, implying that the lethal threshold concentration of Cu for spinach is greater than 1000 mg L-1 CuSO4 used in this study. In summary, spinach exhibits a high tolerance to Cu and can be considered as an alternative plant for the remediation of Cu-contaminated soils.