Analysis of anaerobic fluorescence decay in Scenedesmus obliquus

With reduction of System II acceptors during dark anaerobic adaptation in Scenedesmus obliquus fluorescence yield rises to a maximum value in two distinct transitions. Subsequent illumination results in a decay of fluorescence yield with the following characteristics: 1. In low intensity light it is independent of temperature and is an expression of light reaction I. 2. In high intestity light it reflects the dark limiting step in the reoxidation mechanism of System II primary acceptors. 3. There is strong inhibition by agents known to block electron transport between the two systems. 4. At light limiting conditions decay kinetics include an initial delay phase and thereafter close to second order behaviour. 5. Following a single brief saturating flash a maximum of 80% quenching is restored and a second flash yields approx. 95% restoration. Comparison with the fluorescence rise in the presence of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea suggests that the decay reflects transfer of one positive charge from System I to the primary System II acceptor with the intermediary carrier pool remaining reduced.