Steady State of Photosynthetic Electron Transport in Cells of the Cyanophyte Synechocystis PCC 6714 Having Different Stoichiometry between PS I and PS II: Analysis of Flash-Induced Oxidation-Reduction of Cytochrome f and P700 under Steady State of Photosy

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The steady state of photosynthetic electron transport driven by two photosystems was studied with cells of the cyanophyie Synechocystis PCC 67 14 by analyzing the flash-induced oxidation-reduction of Cyt f and P700 under continuous background illumination. We first analyzed the spectra and the kinetics of flash-induced absorption changes in the 400 to 440 nm wavelength region and defined the absorption changes due to oxidation-reduction of Cyt f and P700. Results indicated that the flash-induced absorption changes at 420 and 435 nm are due to the oxidation-reduction of Cyt f and P700, respectively. Determination of the steady state of Cyt f(420 nm) and P700 (435 nm) was made for the cells grown under a weak orange light exciting mainly PS II (PS II light) and having a high ratio of PS I to PS II (PS I/PS II), and those grown under a weak red light exciting preferentially PS I (PS I light) and having a low PS I/PS II. The steady state of electron transport in cells of the two types were compared under PS I and PS II lights. The results indicated that: (1) under the light conditions used for growth (both red and orange light), the intermediate electron pool between the two photosystems remained in a redox state so as to keep both photosystems in the open state. (2) When shifted to PS I light, the intermediate pool and PS I in cells of high PS I/PS II became extremely electron-poor, and so most of the PS I reaction centers were closed. (3) The intermediate pool in cells of low PS I/PS II became extremely electron-rich when shifted to PS II light, and most of the PS II reaction centers were closed. The electron transport state is released from such biased states by regulation of PS I/PS II. Results supported our previously proposed hypothesis that the stoichiometry between PS I and PS II is regulated so as to keep the two photosystems in the open state. The relationship between the steady state of electron transport and the regulation of PS I/PS II is discussed.
日本植物生理学会の論文

Steady State of Photosynthetic Electron Transport in Cells of the Cyanophyte Synechocystis PCC 6714 Having Different Stoichiometry between PS I and PS II: Analysis of Flash-Induced Oxidation-Reduction of Cytochrome f and P700 under Steady State of Photosy

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