Protective role of selenium in plant subjected to severe UV irradiation stress

Abstract

Recently selenium (Se) has been found to increase the antioxidative capacity and stress-defending ability of plants and even to enhance the growth of plants subjected to short-term UV episodes. Based on these findings, this study was undertaken to investigate if these effects can be obtained also under severe irradiation stress. Lettuce (Lactuca sativa L.), grown without Se or at two Se addition levels (0.01 and 0.05 mg kg -1 soil) and without UV or subjected to prolonged UV episodes (UV-B and a small amount of UV-C), was monitored for 8 weeks at 1-week intervals using growth and physiological parameters. Electron micrographs revealed that young plants grown without UV used Se to build up energy reserves, which was reflected as increased shoot yields. UV stress caused structural changes and disorders in cells and it also diminished shoot yields. At a low stress level, the thickening of cell walls mechanically protected the cells, which was reflected as diminished lipid peroxidation. Under severe UV stress, lipid peroxidation markedly increased, and the protecting role of Se via enhanced antioxidative capacity became apparent. Selenium was able to promote the growth of the UV-stressed plants, presumably through protection of chloroplast enzymes. It also postponed the death of plants subjected to severe irradiation stress. At the higher addition level Se exerted a toxic effect, but it was alleviated by the UV irradiation episodes, which promoted plant growth.