Distribution of Antioxidatases in Cell of Diatom Nitzschia Closterium and Response to Different Environmental Silicon Concentrations

The outbreak mechanism of red tide and the rapid reproducing mechanism of red-tide species are not very clear so far. Diatom is one of the main red tide microalgae species. It can utilize the environmental silicon to biosynthesize its nano-silicon cell wall, so its growth and reproduction are closely related to the absorption and bioaccumulation of environmental silicon. Therefore, study on the response of diatom to the environmental silicon will have important significance in the exploration of the outbreak mechanism of red tide caused by diatom. Antioxidatases have been reported to have close relationship with the accumulation of silicon. Therefore, the present paper studied the distribution of the four antioxidatases--polyphenoloxidase (PPO), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the diatom Nitzschia closterium, and their response to environmental soluble silicon. The results showed that PPO, SOD and POD were found in the diatom Nitzschia closterium. PPO distributed only in the plasma membrane, POD distributed only in the cytosol, and SOD distributed in both the plasma membrane and the cytosol. But SOD activity in the plasma membrane was much higher than that in the cytosol. After the diatom were cultivated in the low Si culture (10 mg/L), high silicon culture (100 mg/L) and normal silicon culture (30 mg/L, control ) for 12 days respectively, the plasma membranes of the diatom were extracted and purified by two-phase method, and the activities of SOD and PPO were analyzed. The results showed that the two antioxidatases in the low Si culture were not remarkably different from those in the control, but they were significantly inhibited in the high Si culture (p<0.05).