Abstract: The toxic effects of Cr⁶⁺(0,1,10,30,50 mg·L^-1) on chlorophyll, chlorophyll fluorescence parameters, antioxidant systems, soluble protein, lipid peroxidation, soluble sugar, active oxygen generation and ultrastructure changes in leaf of Potamogeton crispus were studied. The results showed that with increasing concentration of Cr⁶⁺,the contents of chlorophyll, chlorophyll a, chlorophyll b and chlorophyll a/b decreased gradually, and F_o enhanced progressively up to 10 mg·L^-1 Cr⁶⁺ and followed by a decline at higher dose. F_v/F_m, F_m and F_v/F_o decreased gradually. Soluble protein content and ascorbic acid(AsA) content enhanced and followed by a decline, glutathione(GSH) content decreased gradually.The activity of superoxide dismutase(SOD) decreased gradually, and activities of peroxidase(POD), catalase(CAT), ascorbate peroxidase(APX), glutathione reductase(GR) increased first and then decreased. While O₂^—·, MDA and soluble sugar content enhanced and followed by a decline. Transmission electron microscope observation indicated that Cr⁶⁺ also imposed injury action on ultrastructure of leaf cells, swelling of chloroplast and breakage of chloroplast envelope, decreasing of cristae quantity and vacuolization of mitochondria were observed. The conclusion could be reached that the plant death was resulted from destruction under structure foundation of physiological function, disorder of physiological metabolism.

Key words: Potamogeton crispus, chlorophyll fluorescence, Cr⁶⁺ Stress, antioxidant System, ultrastructure