Net light-induced oxygen evolution in photosystem I deletion mutants of the cyanobacterium Synechocystis sp. PCC 6803

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• 作者：Qing Jun Wang^a ; ^{qingjun.wang@uky.edu} ; Abhay Singh^b ; ¹ ; Hong Li^b ; ² ; Ladislav Nedbal^c ; ^d ; Louis A. Sherman^b ; Govindjee^a ; ^e ; ^f ; ^{gov@illinois.edu} ; John Whitmarsh^a ; ^e ; ^g
• 关键词：Chl ; chlorophyll ; PSII ; photosystem II ; Cyt bf ; cytochrome b6f ; Cyt c6 ; cytochrome c6 ; PSI ; photosystem I ; Fd ; ferredoxin ; FNR ; ferredoxin-NADP+-oxidoreductase ; Pheo ; pheophytin ; FQR ; ferredoxin-plastoquinone-oxidoreductase ; PQ ; plastoquinone ; PQH2 ; plast
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2012
• 期刊代码：13_00052728
• 类别：bio
• 出版时间：May, 2012
• 卷：1817
• 期：5
• 页码：792-801
• 文件大小：886 K

摘要

Oxygenic photosynthesis in cyanobacteria, algae, and plants requires photosystem II (PSII) to extract electrons from H₂O and depends on photosystem I (PSI) to reduce NADP⁺. Here we demonstrate that mixotrophically-grown mutants of the cyanobacterium Synechocystis sp. PCC 6803 that lack PSI (螖PSI) are capable of net light-induced O₂ evolution in vivo. The net light-induced O₂ evolution requires glucose and can be sustained for more than 30 min. Utilizing electron transport inhibitors and chlorophyll a fluorescence measurements, we show that in these mutants PSII is the source of the light-induced O₂ evolution, and that the plastoquinone pool is reduced by PSII and subsequently oxidized by an unidentified electron acceptor that does not involve the plastoquinol oxidase site of the cytochrome b₆f complex. Moreover, both O₂ evolution and chlorophyll a fluorescence kinetics of the 螖PSI mutants are highly sensitive to KCN, indicating the involvement of a KCN-sensitive enzyme(s). Experiments using ¹⁴C-labeled bicarbonate show that the 螖PSI mutants assimilate more CO₂ in the light compared to the dark. However, the rate of the light-minus-dark CO₂ assimilation accounts for just over half of the net light-induced O₂ evolution rate, indicating the involvement of unidentified terminal electron acceptors. Based on these results we suggest that O₂ evolution in 螖PSI cells can be sustained by an alternative electron transport pathway that results in CO₂ assimilation and that includes PSII, the platoquinone pool, and a KCN-sensitive enzyme.