P-700 photooxidation in state 1 and state 2 in cyanobacteria upon flash illumination with phycobilin- and chlorophyll-absorbed light

Abstract

We have measured the flash yield of P-700 photooxidation in cells of the cyanobacteria Synechococcus 6301 and Nostoc MAC adapted to light-states 1 and 2. Using excitation at 337 nm, the flash yield of P-700 photooxidation at limiting flash intensity was larger in state 2 in both species, indicating an increased absorption cross-section of PS I in state 2 for light absorbed by both chlorophyll and phycobilin pigments. Using excitation at 532 nm, the flash yield of P-700 photooxidation at limiting intensity was also larger in state 2 in both species, indicating an increased absorption cross-section of PS I for light absorbed specifically by phycocyanin or phycoerythrin. Differences in P-700 re-reduction kinetics between states 1 and 2 were consistently observed following flash excitation at either wavelength. Our results are consistent with a model for redistribution of excitation energy in state 2 that involves decoupling of the phycobilisome from PS II and its functional reassociation with PS I. Photosynthesis; Light harvesting; Photosystem I; State transition; Phycobilisome; Excitation energy distribution; Cyanobacteria; ( Nostoc MAC; Synechococcus 6301)