Abstract
State 1-state 2 transitions in intact sugar maple leaves were monitored by following changes in energy storage (ES) of PSI (ESPSI) and PSII (ESPSII). ES of both photosystems (EST) was recorded under saturating background white light, while ESPSI was determined under saturating far-red light. The difference between EST and ESPSI represented ESPSII. Adaptation of the leaf to far-red light (light 1, λ > 715 nm) and red light (light 2, 650 nm) led to state 1 where light 2 was distributed mainly to PSII. Exposure of the leaf to state 2 conditions (light 2 alone) reversed the phenomenon. These state transitions needed about 20 min to occur. From our experiments on light to dark transitions, and vice-versa, we suggest that the dark state was state 2. We also studied the effect of NaF, a known inhibitor of state 2 to state 1 transition. Our results support the concept of phosphorylationand migration of light harvesting complexes, as responsible for the light energy distribution between both photosystems in vivo.