Laser-induced optoacoustic calorimetry of cyanobacteria. The efficiency of primary photosynthetic processes in state 1 and state 2

The heat released by all primary processes of photosynthesis within 2 μs of a laser flash was measured by optoacoustic spectroscopy of the cyanobacteria Synechococcus sp. PCC 6301 adapted to state 1 and state 2. Heat production was compared between intact cells with open and closed reaction centres allowing direct determination of the efficiency of photosynthetic energy storage. The fraction of absorbed energy released as heat was the same for cells in state 1 and state 2 for excitation of either phycocyanin or chlorophyll a. We conclude that the efficiency of excitation energy transfer and primary photochemical energy storage was not affected by the state transition. These results contradict proposed models for the state transition in cyanobacteria, which involve the uncoupling of phycobilin pigments from energy transfer to chlorophyll a.