Abstract:The fluorescence emission and excitation spectra at 77 K showed that Cd2+ treatment reduced the ratio of F686/F736, F696/F736 and F480/F436 in spinach chloroplasts. It is suggested that Cd2+ impeded the excitation energy transfer from light harvesting chlorophyll to PSⅡ trap. The chlorophyll protein complexes of spinach chloroplasts were resolved by SDS-PAGE. It showed that the total amount of LHCⅡ decreased after Cd2+ treatment. A decrease of 27 kD polypeptide in LHCⅡ was also found by the treatment of Cd2+. Since LHCⅡ play an important role in the absorption and transfer of light energy and the distribution of excitation energy between PSⅡ and PSⅠ, a decrease of LHCⅡ certainly may cause a decrease of excitation energy transfer from LHCⅡ to PSⅡ reaction center.