INHIBITION BY PHOSPHATE OF LIGHT-STATE TRANSITIONS IN CYANOBACTERIAL CELLS

Light-state transitions in cyanobacteria are a rapid physiological adaptation mechanism which changes the distribution of excitation energy absorbed by the light-harvesting complexes between Photosystem II and Photosystem I. State transitions in two cyanobacterial species are shown to be inhibited by buffers containing 0.2-0.4 M phosphate. Both the state 1 and the state 2 transition are inhibited, so that cells may be locked in the state to which they were adapted before the addition of phosphate. The inhibition of the state 1 transition is due to inhibition of photosynthetic electron transport. However, the inhibition of the state 2 transition is probably due to a direct effect on the biochemical signal transduction pathway. The implications for the biochemical mechanism of state transitions are discussed.