Abstract: RESEARCH OF BIOLOGICAL ISOTOPE EFFECT OF DEUTERIUM IN ANABAENA AZOLLAEZhang Yongbo;Shi Dingji;Wang Wenqing;Luo Shanggeng1) (Department of Technical Physics，Beijing University，Beijing 100871)2)(Institute of Botany，The Chinese Academy of Sciences，Beijing 100044)3)(China Institute of Atomic Energy, P.O.Box 275(93)，Beijing102413) Abstract: Anabaena azollae is cultured in BG-11 medium whose mass fraction of heavy water is 0％，10％，30％，60％and 90％，respectively，During different time，activities of photosynthesis，respi ration and nitrogenase are measured．In addition，growth-curve，absorption spectrum and low temperature fluorescence spectrum are given. The change of cellular morphology is observed with scanning electron microscope，The results show that the addition of heavy water causes lagging of the exponential period of growth，and inhibits the activities of photosynthesis、respiration and ni trogenase markedly，Absorption spectrum shows that the ratio of phycobilin to carotenoid de creases with increasing percentage of heavy water. Low temperature fluorescence spectrum indi cates that the ratio of F733／F695 decreases and photo-energy is distributed to system Ⅱ more than to system Ⅰ．According to the maximum of net photosynthesis，the isotope effect is also dis cussed.Keywords: Anabaena azollae Photosynthesis Deuterium Isotope effect