Changes in Photosystem Stoichiometry in Response to Environmental Conditions for Cell Growth Observed with the Cyanophyte Synechocystis PCC 6714 |
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Authors: | Murakami, Akio Kim, Sung-Jun Fujita, Yoshihiko |
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Affiliation: | Department of Cell Biology, National Institute for Basic Biology Okazaki, Aichi, 444 Japan |
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Abstract: | Changes in photosystem stoichiometry in response to shift ofenvironments for cell growth other than light regime were studiedwith the cyanophyte Synechocystis PCC 6714 in relation to thechange induced by light-quality shift. Following two environment-shiftswere examined: the shift of molecular form of inorganic carbonsource for photosynthesis from CO2 to HCO3 (CO2 stress)and the increase in salinity of the medium with NaCl (0.5 M)(Na+ stress). Both CO2 and Na+ stresses induced the increasein PSI abundance resulting in a higher PSI/PSII stoichiometry.CO2 stress was found to elevate simultaneously Cyt c oxidaseactivity (Vmax). The feature was the same as that caused bylight-quality shift from preferential excitation of PSI to PSII(light stress) though the enhancement by either stress was smallerthan that by light stress. Under our experimental conditions,PSI/PSII stoichiometry appeared to increase at a fairly constantrate to the basal level even when the basal level had been differentlydetermined by the light-quality. Enhancing rates for PSI/PSIIstoichiometry and for Cyt c oxidase activity were also similarto each other. Since the two stresses affect the thylakoid electrontransport similarly to the shift of light-quality, we interpretedour results as follows: three environmental stresses, CO2, Na+,and light stresses, cause changes in electron turnover capacityof PSI and Cyt c oxidase under a similar, probably a common,mechanism for monitoring redox state of thylakoid electron transportsystem. 1On leave from Department of Biology, College of Natural Science,Kyngpook National University, Taegu 702-701, Korea.2Present address: Department of Marine Bioscience, Fukui Pre-fecturalUniversity, Obama, Fukui, 917 Japan. |
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