Exogenous selenium improves the physiological resistance of cucumber to cadmium stress

To evaluate the effects of exogenous selenium on cadmium tolerance and accumulation in two varieties of cucumber, pot experiments with cadmium at 10 mg/kg soil were conducted. Plant biomass, cadmium bioaccumulation, cadmium speciation, and antioxidative enzyme activity, including superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase were determined. Exogenous selenium (1 mg/L for S1 and 2 mg/L for S2) was sprayed on the leaves on cucumbers, which significantly increased the biomasses of the roots, stems, leaves, and fruits in both cucumber varieties. The cadmium bioaccumulation in the cucumbers decreased with the increase of selenium. The contents of pectate/protein-bound cadmium increased and the cadmium - organic acid complexes and inorganic cadmium tended to decrease with the selenium addition. Supplementation with selenium improved the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in the two cucumber varieties.