Abstract: Catalase and NR activity and soluble sugar content was analyzed in leaves of tobacco plants grown for 10 days in a nutrient solution containing heavy metal pollutants (Cd2+, Pb2+ and Cd2+ + Pb2+). Cadmium and lead induced changes in the ultra-structure of tobacco leaf cells, particularly in the structure of the chloroplast, mitochondrion and nucleus, were observed using electron microscopy. This showed that: 1) The activity of catalase was heavily inhibited by Cd, and first stimulated then inhibited with increasing concentrations of Pb; 2) The activity of NR was first stimulated and then inhibited with increasing concentration of Cd, but was inhibited by lead, with a small resistant peak at 1000mg·L-1; 3) Soluble sugar content was reduced by Cd, Ph and Cd + Pb; 4) Cadmium destroyed the cell membrane system. It is suggested that this may result from cadmium combining with, and denaturing, proteins. This would lead to change in structure and loss of function in the membrane and to disorder in the protoplasm; 5) Massive lead deposits were observed in the outer cell membrane, and lead deposits were found in the cytoplasm and chloroplast. The cell membrane was found to be a major barrier to lead migrating into the protoplasm. Lead also had a strong effect on the ultra-structure of chloroplasts, mitochondria and nuclei.

Key words: Tobacco, Physiological features, Ultra-structure, Cd2+, Pb2+, Pollution