Evidence for the contribution of the S-state transitions of oxygen evolution to the initial phase of fluorescence induction.

Fluorescence induction of isolated spinach chloroplasts was measured by using weak continuous light. It is found that the kinetics of the initial phase of fluorescence induction as well as the initial fluorescence level Fj are influenced by the number of preilluminating flashes, and shows damped period 4 oscillation. Evidence is given to show that it is correlated with the S-state transitions of oxygen evolution. Based on the previous observations that the S states can modulate the fluorescence yield of Photosystem II, a simulating calculation suggests that, in addition to the Photosystem II centers inactive in the plastoquinone reduction, the S-state transitions can also make a contribution to the intial phase of fluorescence induction.