Regulation of Electron Transport Composition in Cyanobacterial Photosynthetic System: Stoichiometry among Photosystem I and II Complexes and Their Light-Harvesting Antennae and Cytochrome b6/fComplex

This study was done to confirm our previous observation withthe pattern of changes in electron transport composition inducedby an imbalance of the electron transport state. Contents ofphotosystem (PS) I and II complexes and their antennae and Cytb₆/f complex were determined for systems of cyanobacterium SynechocystisPCC 6714 of different PS I/PS II ratios. The results indicatedthat (1) the observed changes in the PS I/PS II ratio are not-dueto regulation of the activities of the respective PS's but tochanges in their contents, (2) the molar ratio between PS IIand Cyt b₆/f complexes was fairly constant when marked changesoccurred in the PS I content, and (3) the PS II and Cyt b₆/fcontents per cell remained fairly constant while the PS I contentchanged markedly. These findings agree with our previous observationwith autotrophic cells of Anacystis nidulans Tx 20 and supportour argument that in cyanobacterial and red algal electron transportsystems, the content of the terminalcomponent(s), such as PSI complex, is regulated in order to maintain a balance betweenthe electron influx by PS II action to the system and the effluxby PS I action from it. (Received June 3, 1987; Accepted September 20, 1987)