Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission (ms-DLE) during the course of state transitions which were indicated by the chlorophyll fluores-cence at room temperature and 77 K. When dark-adapted leaves were induced to stateⅠ with far-red light, Fm/Fo, F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly. However, during the induction to stateⅡ with red light, both Fm/Fo and F685/F735 decreased immedi-ately and the former were quicker than the latter. In this interval, the intensity of fast phase of ms-DLE increased to a maximum and then decreased to a lower value during the transition to stateⅡ. Nigericin, an uncoupler which elimi-nates the proton gradient across thylakoid membrane, inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to stateⅡ. Another uncoupler, valino-mycin, which eliminates the membrane potential, did not affect the changes of the intensity of fast phase. These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to stateⅡ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.
SU Jihu & SHEN Yungang Shanghai Institute of Plant Physiology, Chinese Academy of Sciences, Shanghai 200032, China
