Studies on the delayed light emission in spinach chloroplasts. II. Participation of primary electron donor and acceptor of photoreaction II in producing the delayed light emission

Abstract

1. The fluorescence of chlorophyll a and the delayed light emitted at 0.1–1.2 msec after repeated flash light (duration, 0.5 msec) were simultaneously measured in isolated spinach chloroplasts. An extensive study was made of the initial rapid-rise component of delayed light emission which is closely related to the primary photoact in photosynthesis. 2. Electron donors of System II (ascorbate, hydroquinone, p-phenylenediamine and MnCl 2) decreased the magnitude of the initial rapid-rise component of delayed light without producing any significant change in the time course of fluorescence. 3. Treatment of chloroplasts with a high concentration of Tris buffer, known to block the electron transport somewhere between Photoreaction II and water, enhanced the initial rapid-rise component but suppressed the second slow-increase component of delayed light. Addition of the electron donors to the Tris-washed chloroplasts suppressed the enhanced initial rapid-rise component of delayed light emission. 4. These results indicate that the production of delayed light requires the oxidized form of the primary electron donor in addition to the reduced form of the primary electron acceptor of Photoreaction II.