Effects of selenium application on cadmium uptake, antioxidant activity, and ultrastructure of winter wheat seedlings under cadmium stress

Objectives Selenium (Se) plays an important role in improving plant stress resistance. We studied the direct and indirect mechanisms of selenium alleviating the toxicity of heavy metal–cadmium in plants, which needs further study.

Methods The test method was hydroponic experiment, and the test crop was wheat (Triticum aestivum L.). The treatments included Hoagland basal nutrient solution (CK), Cd 5 μmol/L (Cd5Se0), Cd 5 μmol/L and Se 5 μmol/L (Cd5Se5), Cd 20 μmol/L (Cd20Se0), and Cd 20 μmol/L and Se 5 μmol/L (Cd20Se5). The total Cd content, kinetics of Cd absorption, and the activity of antioxidant enzymes of wheat seedlings were determined, and the ultrastructure of leaf and root cells was observed.

Results Under Cd stress, Se application reduced the Cd content in the aboveground part of wheat by 18.20%−38.16%, and significantly reduced Cd accumulation by 40.79%−43.05%. The dynamics of wheat root Cd absorption in 0−24 h conformed with the quadratic equation. Under Cd5 and Cd20 condition, Se application decreased Cd absorption within 24 h by 48.96% and 11.47%, respectively. Compared with CK, Cd20 markedly increased the \rmO_\small 2^\overline \,\cdot\, production rate, H₂O₂ and malondialdehyde (MDA) content in wheat roots and leaves, increased the activities of superoxide dismutase (SOD), peroxidase (POD) and the content of ascorbic acid, and decreased the activity of ascorbic acid peroxidase (APX) significantly. While Se application significantly reduced the content of H₂O₂ in roots by 34.21%−50.32%, MDA content in leaves by 10.34%−24.91%, it increased the activity of APX in leaves by 29.09%−30.46% and restored the activities of SOD and POD to the control level. The organelles in wheat under Cd stress were damaged at varying degrees, and were alleviated under Se application.

Conclusions Under Cd stress, Se application reduced the content and accumulation of Cd in aboveground part and root of winter wheat, reduced the maximum absorption and accumulation of Cd, enhanced the antioxidant capacity of wheat seedlings, thus alleviated the damage of ultrastructure of wheat root and leaf cells due to Cd stress, and alleviated the toxicity of Cd in wheat seedlings.