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.

Gibberellic acid application on biomass, oxidative stress response, and photosynthesis in spinach (Spinacia oleracea L.) seedlings under copper stress.

The mechanism of Cu tolerance in plants and its control measures are of considerable significance for the remediation of Cu-contaminated soils. Gibberellic acid (GA3) is involved in plant growth and development and in the response to heavy metal stress. In the present study, changes in the biomass, oxidative stress response responses, and photosynthesis of spinach seedlings were examined under Cu stress with exogenous GA3 applied at concentrations of 0, 3, 5, 10, 20, 40, 60, or 80 mg L-1. Under Cu stress, the plant Cu concentration and oxidative damage were greater, photosynthetic parameters and biomass declined, and antioxidant enzyme activities and the proline concentration increased. However, spinach growth did not terminate, indicating that spinach seedlings had strong Cu tolerance. When low concentrations of GA3 (3-5 mg L-1) were added to Cu-stressed spinach seedlings, the damage caused by Cu stress to spinach seedlings was reduced, and the Cu tolerance of spinach seedlings was enhanced, which mainly manifested as reduced oxidation damage, an increased proline concentration, elevated antioxidant enzyme activities, decreased Cu concentration in leaves, and increased Cu concentration in roots, increased photosynthetic parameters, and an increased in the total biomass. In contrast, additions of GA3 at concentrations higher than 40 mg L-1 intensified oxidative damage and decreased the activities of antioxidant enzymes, photosynthetic parameters, and biomass. Additionally, the Cu concentration increased in leaves and decreased Cu concentration in roots, indicating that high concentrations of GA3 aggravated stress damage and severely influenced physiological functions in spinach seedlings. In summary, the application of 3-5 mg L-1 GA3 to spinach seedlings in Cu-contaminated soil can be used to reduce Cu toxicity to plants and increase Cu tolerance.

Exogenous of Indole-3-Acetic Acid Application Alleviates Copper Toxicity in Spinach Seedlings by Enhancing Antioxidant Systems and Nitrogen Metabolism.

Indole-3-acetic acid (IAA) is a potential mediator in the protection of plants from copper (Cu) toxicity and the enhancement of Cu tolerance. In this paper, spinach (Spinacia oleracea L.) seedlings were cultivated in soil containing 700 mg kg-1 Cu and the leaves of seedlings were sprayed with different concentrations of IAA. Exogenous IAA treatment reduced the malondialdehyde (MDA) concentrations in Cu-stressed seedlings and increased biomass, proline content, and the activities of antioxidant enzymes. Exogenous IAA treatment also increased the levels of nitrogen (N) assimilation compounds and the activities of N-metabolizing enzymes, but reduced NH4+ content. Notably, lower concentrations of IAA (10-40 mg L-1) increased the Cu concentrations in roots and reduced the Cu concentrations in leaves, while higher concentrations of IAA (50 mg L-1) reduced the Cu concentrations in both roots and leaves to the lowest levels. The findings indicated that the application of IAA reduced Cu accumulation, alleviated Cu toxicity, and enhanced Cu tolerance in spinach seedlings. IAA application could be used as an alternative strategy for reducing Cu accumulation in vegetable crops and for remediating Cu-contaminated soil, in turn reducing the hazardous effects of heavy metal contamination on human health and the environment.