Selenium affects physiological parameters and phytochelatins accumulation in cucumber (Cucumis sativus L.) plants grown under cadmium exposure

• Phytotoxicity of Cd for cucumber may be partially ameliorated by Se supplementation.
• The presence of Se reduces the accumulation of Cd in roots and vice versa.
• Se decreases PCs accumulation in the roots of Cd-exposed plants.
• Se improves the cell membrane stability in the Cd-exposed plants.
• Effects of Se on the Cd-exposed plants depend on the proportion of these ions in the medium.

The aim of the present study was to examine the effects of exogenous selenium (Se) on the tolerance of cucumber plants to cadmium (Cd) stress. The cucumber plants grown in a nutrient solution were supplied with Cd (0, 25 or 50 μM) and Se (0, 5 or 10 μM), individually or simultaneously. Under Cd-stress, there were no significant differences in the shoot biomass of the Se-supplied plants as compared to the Cd-exposed plants. However, the fresh weight (FW) of roots increased significantly after supplementation of a 50 μM Cd-polluted nutrient solution with 10 μM Se. The accumulation of phytochelatins (PCs) was detected in the plants treated with 25 or 50 μM Cd, individually or simultaneously with Se, with a higher level noted in the roots. When the individual PCs isoforms were considered, the predominance of PC4 in the Cd-exposed roots and of PC2 in the Cd-exposed leaves was evident. An enrichment of Cd-treated plants with Se caused a reduction of PCs accumulation in roots, but did not change its concentration in leaves. The addition of Se to the Cd-containing growth media did not affect GSH accumulation in roots and leaves, as compared to Cd-alone treatment. Moreover, the supplementation of Cd-exposed plants with Se provoked a significant decrease in the level of lipid peroxides as well as a reduction of Cd content in the root tissues. Our results imply that the degree of disturbances provoked by Cd could be partially ameliorated by Se supplementation, probably due to the inhibition of Cd accumulation and a reduced lipid peroxidation in the root tissues as well as the improvement of cell membranes stability in the leaf tissues. However, the effect of Se on the Cd-stressed plants greatly depended on the proportion of these two elements in the nutrient solution.