Effect of exogenous selenium on mineral nutrition and antioxidative capacity in cucumber (Cucumis sativus L.) seedlings under cadmium stress

The ameliorative effects and its mitigation mechanisms of selenium (Se) on cadmium (Cd) toxicity in cucumber seedlings were studied through hydroponic experiments. Cd and other mineral nutrient concentrations, antioxidant enzyme activities, and antioxidant contents in cucumber were studied. The results revealed that exogenous Se significantly decreased the Cd concentrations in all tissues, especially in the leaves. Moreover, exogenous Se (Cd + Se) could increase Zn, Na, leaf Cu, stem/root Fe, stem/root Ca, and stem/root Mg concentrations; and reduce leaf Mg concentration, compared with Cd alone treatment. Additionally, the application of Se ameliorated the toxicity of Cd by harmonising the activities of antioxidase, such as Cd + Se treatment reduced Cd-induced increase of superoxide dismutase, glutathione peroxidase, leaf/stem ascorbate peroxidase (APX) activities, which resulted in the significant decrease of the content of hydrogen peroxide, and malondialdialdehyde; increased root APX, and glutathione reductase activities. In addition, the content of nonenzymatic antioxidants such as root-reduced glutathione and oxidised glutathione was significantly increased by adding Se under Cd stress. Also, exogenous Se enhanced the total antioxidant capacity in terms of cupric-reducing antioxidant capacity and decreased total phenols, flavonoids, and leaf/root proline contents under Cd stress. In general, 3 μmol/L Se was conducive to plant growth and improved the cucumber’s ability to alleviate Cd stress.