Distribution of excitation energy between photosystem I and photosystem II in red algae. II. Kinetics of the transition between state 1 and state 2.

The kinetics of chlorophyll fluorescence were measured during the state 1-state 2 and the state 2-state 1 transition in some members of the Florideae (Halymenia latifolia, Phycodrys rubens and Delesseria sanguinea) and in Porphyra umbilicalis as a member of the Bangiales. With the members of the Florideae it was possible to induce 70-80% of the maximum transition in direction to state 1 (obtained by us in longtime experiments) by an illumination of only a few (2-5) seconds with medium intensities of light 1. A complete transition back could be induced by a similar short illumination with light 2. The transition process itself is slow with values of tau1/2 in the range of 10 to 20 s and occurs in the dark with nearly the same speed as in continuous light 1 or light 2. The state 1-state 2 transient of chlorophyll fluorescence is kinetically clearly different from the dark-light transient phenomenon. In dark times longer than 1 min Halymenia (starting from state 1) slowly approaches state 2. This decay of state 1 is slower by a factor of about five in Halymenia than in Porphyra. This may explain, why in Halymenia, but not in Porphyra, the whole transition process can be resolved experimentally into a fast light reaction and a slow dark reaction. The results are discussed on the basis of a model which assumes the rearrangement of charges in the plane of the thylakoid membrane as a primary inducing event in the state 1-state 2 transition. This may lead to a redistribution of excitation energy among Photosystems I and II by a slow dark process, which may include a conformation change of some protein(s).