THE EFFECTS OF Zn^2＋ STRESS ON THE GROWTH, PHYSIOLOGICAL CHARACTERISTICS AND CELL STRUCTURE OF CHLOROCOCCUM SP

ulture medium was served as the control. The results showed that Zn2+ affected markedly on the growth, physiological characteristics and cell structure of Chlorococcum sp. under certain concentration. When the concentration of Zn2+ was 0.1-1mg/L, the growth of Chlorococcum sp. showed no obvious difference compared with the control. When the concentration of Zn2+ was 10-50mg/L, Chlorococcum sp. could maintain certain growth rate yet. When the concentration of Zn2+ was higher than 100mg/L, the growth of Chlorococcum sp. was inhibited markedly. The contents of Chl a ＋ Chl b and Chl a decreased gradually with the increase of the concentrations of Zn2+ in the medium. When the concentration of Zn2+ was less than 10rag/L, the photosynthesis and respiration of Chlorococcum sp. increased gradually with the increase of Zn2+ concentrations; and when the concentration of Zn2+ was higher than 10mg/L, they decreased gradually with the increase of Zn2+ concentrations. The content of malondiadehyde and activity of peroxidase increased gradually with the increase of Zn2+ concentrations, and the activities of catalase and superox-ide dismutase increased at first and later decreased with the increase of Zn2+ concentrations. Compared with the cell cultured in BG11, the cell cultured in low concentrations (≤10mg/L) showed few changes in pigment and thickness of cell wall. The cell wall of cell cultured in high concentrations of Zn2+ became thicker, and the pigment decreased and the pyrenoid disappeared. When the concentration of Zn2+ was≤10mg/L, the removal rate of Chlorococcum sp. on Zn2+ reached the maximum and was 100%, and it was above 80% under the concentrations that Chlorococcum sp. could maintain the growth. The results demonstrated that the Chlorococcum sp. could be applied to the treatment of wastewater containing Zn2+, because the Chlorococcum sp. could endure the stress of Zn2+ and was of high removal rate on Zn2+.