Mechanism of photoinactivation in photosynthetic systems IV. Light-induced changes in the fluorescence transient

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1. Light-induced changes in the fluorescence transient (685 nm) of spinach chloroplast fragments at room temperature were investigated in an attempt to correlate these changes with photoinactivation in photosystem II. 2. Parallel decreases in the steady-state level of fluorescence and in the variable fraction, observed under aerobic light-treatment, were not related processes but separate reactions as indicated by an anaerobic-interruption experiment where the decrease in the steady-state level occurred only after the disappearance of induction. 3. Anaerobic light-treatment caused an increase in the initial level of fluorescence parallel to photoinactivation in photosystem II, and a more rapid partial decrease in the steady-state level of fluorescence. 4. The steady-state level of fluorescence showed pronounced pH dependency, and had an optimum at about pH 6.5, while the initial level was practically independent of environmental pH within a neutral range. Aerobic or anaerobic light-treatment completely eliminated pH dependency. 5. Effects of electron acceptors, dichlorophenyl-dimethylurea, dithionite, and of electron donors for photosystem II on the fluorescence transient of photoinactivated chloroplast fragments were investigated. Based on the data presented here, it seems reasonable to assume that photoinactivation in photosystem II is closely related to the state or reaction centers in the photosystem.
日本植物生理学会の論文