Antioxidative mechanisms on selenium accumulation in Pteris vittata L., a potential selenium phytoremediation plant

Selenium (Se) contamination due to industrial activities has received increasing concerns. Phytoremediation has been suggested to be an efficient and feasible way to remove Se from Se-contaminated environment. Recently, an arsenic (As) hyperaccumulator Pteris vittata L. (Chinese Brake fern) was found to be a Se accumulator. This study was carried out to investigate Se accumulation mechanisms concentrating on antioxidant responses of this plant to six levels of selenite (0, 1, 2, 5, 10, and 20 mg/L). The results showed that Chinese Brake fern can accumulate a large amount of Se without any visible toxic symptoms and significant decreases in its biomass. However, the root took up more Se than the fronds. The highest concentration of Se in the roots and fronds was 1.536 mg/kg and 242 mg/kg, respectively, demonstrating a typical accumulation character to Se. Addition of 2 mg/L Se decreased, but > 5 mg/L Se enhanced the production of malondialdehyde (MDA), suggesting an antioxidant role of low dosages of Se. The enzymes of catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) contributed their anti-oxidative functions only under low dosages of Se, as shown by their increased activities at Se levels 5 mg/L and lowered activities at Se levels > 5 mg/L. The concentration of glutathione (GSH) and enzyme activity of glutathione reductase (GR) were stimulated by > 5 mg/L Se. Superoxide dismutase (SOD) activity was also enhanced by 20 mg/L Se. Our results suggest that SOD, GSH and GR were likely responsible for, but enzymes of POD, APX, and CAT have limited roles in Se accumulation in Chinese Brake fern.