Selenium Modifies the Effect of Short-Term Chilling Stress on Cucumber Plants

The objective of this study was to investigate the effect of selenium (Se) supply (0, control; 2.5, 5, 10, or 20 mu M) on cucumber (Cucumis sativus L.) cv. Polan F1 plants grown under short-term low temperature stress. About 14-16 day-old seedlings, grown at an optimal temperature (25/20 degrees C; day/night), were exposed to short-term chilling stress with a day/night temperature of 10 degrees C/5 degrees C for 24 h, for a further 24 h at 20 degrees C/15 degrees C, and then transferred to 25/20 degrees C (re-warming) for 7 days. Se did not affect the fresh weight (FW) of plants at a concentration of 2.5-10 mu M, but in the presence of 20 mu M Se, the biomass of shoots significantly decreased. The contents of chlorophylls and carotenoids witnessed no significant change after Se supplementation. Compared with the control, the Se-treated plants showed an increase of proline content in leaves, once after chilling and again after 7 days of re-warming. However, proline levels were much higher immediately after chilling than after re-warming. The malondialdehyde (MDA) content in the root of plants treated with 2.5-10 mu M Se decreased directly after stress. This was in comparison with the plants grown without Sc, whereas it increased in roots and leaves of plants exposed to 20 mu M Se. Seven days later, the MDA level in the root of plants grown in the presence of Se was still lower than those of plants not treated with Se and generally witnessed no significant change in leaves. Although Sc at concentrations of 2.5-10 mu M modified the physiological response of cucumber to short-term chilling stress, causing an increase in proline content in leaves and diminishing lipid peroxidation in roots, the resistance of plants to low temperature was not clearly enhanced, as concluded on the basis of FW and photosynthetic pigments accumulation.