Silicon effects on photosynthesis and antioxidant parameters of soybean seedlings under drought and ultraviolet-B radiation.

Silicon (Si) may be involved in metabolic, physiological, and/or structural activity in higher plants exposed to abiotic and biotic stresses. This has not yet been determined due to the absence of direct evidence that it is part of the molecule of an essential plant constituent or metabolite. The aim of this study was to investigate the effect of silicon on soybean seedlings under drought and ultraviolet-B (UV-B) radiation stresses. The relative leaf water content (RWC), which was the main factor resulting in reduced growth in response to drought, increased 19.0% and 30.0% with Si application under drought and drought+UV-B stresses, respectively. Under UV-B radiation, the anthocyanin and phenol levels decreased 91.5% and 10.0% in the treatment of Si. Ultraviolet-B radiation and drought stress caused great membrane damage, as assessed by lipid peroxidation and osmolyte leakage, but Si application significantly reduced the membrane damage. Catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and hydrogen peroxide were observed under stress conditions. Proline increased primarily in drought-stressed seedlings and may be the drought-induced factor with a protective role in response to UV-B and silicon. Photosynthesis (P(N)) increased following Si application by 21.0%, 18.3% and 21.5% under UV-B radiation, drought and the combination, respectively. The physiological and biochemical parameters measured indicated that the UV-B light had more adverse effects on growth of soybean seedlings than drought, but the data also showed that Si could alleviate seedling damage under these stress conditions.