Water-stress mitigation by selenium in Trifolium repens L.

This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)-induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG-induced water deficit alone or combined with 5 mu M Na2SeO4 for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se-treated plants had higher FW, RWC, and chlorophyll concentration than the PEG-treated plants. Smaller amounts of thiobarbituric acid-reactive substances (TBARS) and H2O2 accumulated in PEG+Se-treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water-deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG-treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG-induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.