Ultrastructural and Photosynthetic Response of Populus 107 Leaves to Cadmium Stress

As Populus 107 is an efficient phytoextraction plant, it was used in the present investigation in order to better understand the mechanisms of detoxification and tolerance of Cd. Cd-induced impacts on photosynthetic parameters (chlorophyll content, soluble protein, and chlorophyll fluorescence) and ultrastructural changes in leaves of Populus 107 exposed to 50 mu M, 100 mu M, and 500 mu M for 40 days were carried out. The results showed that in the Cd-treated cells, almost all the chloroplasts seemed to be affected. Cd induced several significant ultrastructural changes, including swollen chloroplast thylakoids, dissolved thylakoid grana, disintegrated chloroplasts, and numerous plastoglobuli in chloroplasts. Data from chlorophyll fluorescence showed that F-v/F-m, F-v/F-m', phi PSll, ETR, and qP decreased while qN increased in leaves of Populus 107 exposed to Cd when compared to control. The content of soluble protein increased with increasing Cd concentration and declined with prolonged duration of treatment. The soluble protein content in leaves treated with 50 mu M Cd reached the maximum, which was 14.29% more than that of control. The content in leaves exposed to 500 mu M Cd were only 61.76% of control. At the end of the experiment the contents of chlorophyll a, b, and a+b of Populus 107 treated with 500 mu M Cd decreased to the minimum, which were 47.69%, 37.10%, and 45.49% of control, and respectively, and significantly (P < 0.05) lower than control. The toxic mechanisms of Cd are briefly explained.