title: Net light-induced oxygen evolution in photosystem I deletion mutants of the cyanobacterium Synechocystis sp. PCC 6803.
abstract: Oxygenic photosynthesis in cyanobacteria, algae, and plants requires photosystem II (PSII) to extract electrons from H(2)O 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 (ΔPSI) are capable of net light-induced O(2) evolution in vivo. The net light-induced O(2) 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 O(2) 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 b(6)f complex. Moreover, both O(2) evolution and chlorophyll a fluorescence kinetics of the ΔPSI mutants are highly sensitive to KCN, indicating the involvement of a KCN-sensitive enzyme(s). Experiments using (14)C-labeled bicarbonate show that the ΔPSI mutants assimilate more CO(2) in the light compared to the dark. However, the rate of the light-minus-dark CO(2) assimilation accounts for just over half of the net light-induced O(2) evolution rate, indicating the involvement of unidentified terminal electron acceptors. Based on these results we suggest that O(2) evolution in ΔPSI cells can be sustained by an alternative electron transport pathway that results in CO(2) assimilation and that includes PSII, the platoquinone pool, and a KCN-sensitive enzyme.
authors.affiliation: Center for Biophysics & Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. qingjun.wang@uky.edu
authors.forename: Qing Jun
authors.initials: QJ
authors.lastname: Wang
authors.forename: Abhay
authors.initials: A
authors.lastname: Singh
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: Ladislav
authors.initials: L
authors.lastname: Nedbal
authors.forename: Louis A
authors.initials: LA
authors.lastname: Sherman
authors.lastname: Govindjee
authors.forename: John
authors.initials: J
authors.lastname: Whitmarsh
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration / Q000187:drug effects / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D045346:Cytochrome b6f Complex / Q000378:metabolism; D003624:Darkness; D003991:Dibromothymoquinone / Q000494:pharmacology; D004237:Diuron / Q000494:pharmacology; D005453:Fluorescence; D017353:Gene Deletion; D005947:Glucose / Q000494:pharmacology; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010971:Plastoquinone / Q000378:metabolism; D011190:Potassium Cyanide / Q000494:pharmacology; D017693:Sodium Bicarbonate / Q000494:pharmacology; D013057:Spectrum Analysis; D046939:Synechocystis / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D003991:Dibromothymoquinone; D017693:Sodium Bicarbonate; D045346:Cytochrome b6f Complex; D004237:Diuron; D005947:Glucose; D011190:Potassium Cyanide; D010971:Plastoquinone; D010100:Oxygen; D000077194:Chlorophyll A