Poster: Photosynthesis
Abs #
381: Kinetic Analyses of State Transitions of the Phycobilisome-containing Synechococcus sp. PCC 7002 and Its Mutant Strains Impaired of Electron Transport.
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Presenter: |
Zhao, Jindong , jzhao@pku.edu.cn |
Authors | Zhao, Jindong (A) Huang, Chenghui (A) Yuan, Xiaolin (A) | | Affiliations: |
(A): State Key Lab of Protein & Plant Genetic Engrg., College of Life Sciences, Peking University
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State transitions regulate the distribution of absorbed light energy to photosystem I (PSI) and photosystem II (PSII) in all oxygenic organisms to achieve balanced electron transport activities between the two photosystems. The state transitions of the cyanobacterium Synechococcus sp. PCC 7002 and its three mutant strains, which were impaired in PsaE-dependent cyclic electron transport (psaE-), respiratory electron transport (ndhF-) and both activities (psaE-ndhF-), were analyzed. Dark incubation of the wild type and psaE- cells led to a transition to state 2 while the cells of the ndhF- strains remained in state 1 after dark incubation. The ndhF- cells adapted to state 2 when the cells were incubated under an anaerobic condition or in the presence of potassium cyanide. In the process of state 2 to state 1 transition of the wild type cells induced by light in the presence DCMU, there was still a significant reduction of the inter-photosystem electron carriers by both respiration and cyclic electron flow around PSI. Kinetic analysis of the state 2 to state 1 transitions shows that, in the absence of PSII activity, the relative contribution to the reduction of the inter-photosystem electron carriers by respiratory and cyclic electron transfer is 72% and 28%, respectively. The state 2 to state 1 transition was totally prevented by the cytochrome b6f DBMIB. On the other hand, the state 1 to state 2 transitions were induced by DBMIB with half times of approximately 8 seconds in all strains. The results of the state 1 to state 2 transitions induced by dark incubation showed that the ndhF- cells were inefficient in performing state 1 to state 2 transitions in the dark unless cytochrome oxidase activity was inhibited.
