We investigated concentrations of soluble proteins, changes of photosynthetic (chlorophyll content, chlorophyll fluorescence), and ultrastructural characteristics in leaves of Populus 2025 (Populus×euramericana) grown in Hoagland nutrient solution spiked with different concentrations of Cd (0, 50, 100 and 500 μM) for 40 days. Concentration of chlorophylls decreased in the groups treated with Cd when compared with control, and declined with prolonged duration of treatment in the most cases. The soluble protein content decreased at the 40th day of Cd treatments. The photosynthetic parameters Fv/Fm, Fv′/Fm′, ΦPSII, ETR, qP decreased and qN increased. Analysis of the chloroplast ultrastructure showed that Cd induced senescence like symptoms, such as loosening and disorientation of the grana, dilation and degradation of the thylakoids and disruption of the outer membrane of the chloroplasts envelope. These ultrastructural changes observed in Cd-treated chloroplasts suggest that Cd probably induced premature senescence.

Key words: Chloroplast ultrastructure, Chlorophylls, Chlorophyll fluorescence parameters, Soluble proteins, Populus.