Biochimica et Biophysica Acta, 460 (1977) 220-229 ~) Elsevier/North-Holland Biomedical Press BBA 47281 TEMPERATURE DEPENDENCE OF THE DELAYED FLUORESCENCE OF CHLOROPI-IYLL a IN BLUE-GREEN ALGAE TAKA-AKI ONO and NORIO MIfRATA * Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Hongo, Tokyo (Japan) (Received October 4th, 1976) SUMMARY 1. The delayed fluorescence of chlorophyll a was measured with a phos- phoroscope by changing the temperature in a range of room temperatures in intact cells of blue-green algae, Anacystis nidulans, two strains of Anabaena variabilis and Plectonema boryanum, and other kinds of algae, Cyanidium caldarium and Chlorella pyrenoidosa. The induction of delayed fluorescence remarkably depended on the temperature of measurement. Nevertheless, the induction pattern was characterized by three levels of intensity; the initial rise level at the onset of excitation light, the maximum level after a period of excitation and the steady-state level after 10 min of excitation. 2. In A. nidulans and a strain of A. variabilis grown at various temperatures, a close relationship was found between the phase transition of membrane lipids and the initial rise and the steady-state levels of delayed fluorescence. The initial rise level showed the maximum at the temperature of phase transition between the liquid crystalline and the mixed solid-liquid crystalline states. The steady-state level showed a remarkable change from a high in the liquid crystalline state to a low level in the mixed solid-liquid crystalline state. 3. The millisecond decay kinetics of the delayed fluorescence measured at the steady-state level in A. nidulans grown at 38 °C consisted of two components with different decay rates. The half-decay time of the fast component was about 0.17 ms and was constant throughout the temperature range of measurement. The half decay time of slow component ranged from 0.6 to 1.5 ms, depending on the temperature of measurement. INTRODUCTION In recent years, the role of the physical phase of lipids in the biological mem- branes has been recognized in some of the characteristic temperature dependencies of * To whom correspondence should be addressed.