Physiological and molecular analyses of selenium induced chromium tolerance in rapeseed seedlings

Industrial activities have increased chromium (Cr) contamination in environment. Increasing content of Cr in soil can be absorbed and accumulated in plants, caused toxicity, directly or indirectly damaging human health via food chain. Therefore, it is necessary to find approaches to reduce Cr uptake by plant growing in Cr polluted soils and thus decrease health risks from Cr threats. As a beneficial element to plants, selenium (Se) plays positive roles in plants under various biotic and abiotic stresses. The beneficial effects of Se have been established in improving plant growth and reducing Cr accumulation in plant under Cr stress. However, little information can be used to reveal the protective mechanism of Se in improving Cr stress tolerance of colza plants. In the present study, the role of Se in inducing tolerance to Cr stress in colza (Brassica napus L.) seedlings was revealed by a gel based proteomic approach combined with physiological and biochemical analysis. Seven-day-old rapeseed seedlings grown hydroponically were exposed to 10 μM Cr stress and 5 μM Se treatments for 14 days. Results showed that Cr stress decreased growth and caused Cr accumulation and lipid peroxidation in colza seedlings. Exogenously applied Se enhanced plant growth, but reduced lipid peroxidation and Cr accumulation in Cr-stressed colza seedlings. Additionally, Se treatment elevated depressed catalase and ascorbate peroxidase activities in leaves and caused further increase in Cr-induced increase in leaf superoxide dismutase and guaiacol peroxidase activities. In proteomic analysis, a total of 60 proteins were significantly influenced by Se in leaves under Cr stress, and 54 proteins were identified by mass spectrometry. The three largest functional categories included proteins involved in photosyhntesis (48.1%), defense response (27.8%), and protein metabolism (11.1%). Exogenous Se regulated most identified proteins involved in photosyhntesis, implying a modulation in CO2 fixation. Proteins involved in defense response and protein metabolism were differently regulated by Se, which indicated the roles of Se in stress resistance and proteome rearrangement. Selenium could increase the Cr tolerance by promoting photosynthesis efficiency, ROT scavenging ability, protein biosynthesis and processing, and other adaptive responses.