Plant and Cell Physiology Advance Access originally published online on October 20, 2006
Plant and Cell Physiology 2006 47(12):1612-1621; doi:10.1093/pcp/pcl024
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Acclimation to the Growth Temperature and Thermosensitivity of Photosystem II in a Mesophilic Cyanobacterium, Synechocystis sp. PCC6803
Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Garden City,Hyogo, 678-1297 Japan
* Corresponding author: E-mail, rl04i001{at}stkt.u-hyogo.ac.jp Fax, +81-791-58-0185.
| Abstract |
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Differences in the temperature dependence and thermosensitivities of PSII activities in Synechocystis sp. PCC6803 grown at 25 and 35°C were studied. Hill reactions in cells, thylakoid membranes and purified PSII core complexes were measured at high temperatures or at their growth temperatures after high-temperature treatments. In the presence of 2,5-dichloro-p-benzoquinone as an electron acceptor, which can accept electrons directly from QA, the temperature dependence of the oxygen-evolving activity was almost the same in thylakoid membranes and in the purified PSII complexes from cells grown at 25 or 35°C. When duroquinone, which accepts electrons only through QB plastoquinone, was used as an electron acceptor, the temperature dependence was the same for purified PSII core complexes but was different between thylakoids isolated from the cells grown at 25 and 35°C. No remarkable difference was observed in protein compositions between thylakoids and between purified PSII complexes from cells grown at 25 or 35°C. However, the fluidity of thylakoids, measured by electron flow to P700, was affected by the growth temperature. These results suggest that one of the major factors which cause the changes in the thermosensitivity of PSII is the change in the fluidity of thylakoid membranes. As for the acclimation of PSII in thylakoids to high temperatures, one of the main causes is the decrease in the high-temperature-induced formation of non-QB PSII due to the decreased fluidity in the cells grown at 35°C.
Keywords: Fluidity of thylakoid membranes - Heat stress - Oxygen-evolving activity - PSII - QB site - Synechocystis sp. PCC6803
Abbreviations: BQ, p-benzoquinone; DBMIB, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone; 2,5-DCBQ, 2,5-dichloro-p-benzoquinone; DDM, n-dodecyl-ß-D-maltoside; DQ, tetramethyl-p-benzoquinone (duroquinone); Fv, variable part of Chl fluorescence; HSP, heat shock protein; MGDG, monogalactosyldiacylglycerol; P700, reaction center Chl of PSI; PQ, plastoquinone; QA and QB, primary and secondary plastoquinone electron acceptors of PSII; TQ, 2-methyl-p-benzoquinone (toluquinone).
(Received September 5, 2006; Accepted October 16, 2006)
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