title: O2-dependent large electron flow functioned as an electron sink, replacing the steady-state electron flux in photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, but not in the cyanobacterium Synechococcus sp. PCC 7942.
abstract: To determine whether alternative electron flow (AEF) can replace the photosynthetic electron flow in cyanobacteria, we used an open O2-electrode system to monitor O2-exchange over a long period. In air-grown Synechocystis sp. PCC 6803 (S. 6803(WT)), the quantum yield of PSII, Y(II), held even after photosynthesis was suppressed by CO2 shortage. The S. 6803 mutant, deficient in flavodiiron (FLV) proteins 1 and 3, showed the same phenotype as S. 6803(WT). In contrast, Y(II) decreased in Synechococcus sp. PCC 7942 (S. 7942). These results suggest that AEF functioned as the Y(II) in S. 6803 and replaced the photosynthetic electron flux. In contrast, the activity of AEF in S. 7942 was lower. The affinity of AEF for O2 in S. 6803 did not correspond to those of FLVs in bacteria or terminal oxidases in respiration. AEF might be driven by photorespiration.
authors.affiliation: a Department of Biological and Environmental Sciences, Faculty of Agriculture , Graduate School of Agricultural Science, Kobe University , Kobe , Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Hayashi
authors.forename: Ginga
authors.initials: G
authors.lastname: Shimakawa
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Shaku
authors.forename: Satoko
authors.initials: S
authors.lastname: Shimizu
authors.forename: Seiji
authors.initials: S
authors.lastname: Akimoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Katsumi
authors.initials: K
authors.lastname: Amako
authors.forename: Toshio
authors.initials: T
authors.lastname: Sugimoto
authors.forename: Masahiro
authors.initials: M
authors.lastname: Tamoi
authors.forename: Amane
authors.initials: A
authors.lastname: Makino
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
mesh_terms: D019069:Cell Respiration; D002734:Chlorophyll / Q000378:metabolism / Q000502:physiology; D004579:Electron Transport / Q000235:genetics / Q000502:physiology*; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D046940:Synechococcus / Q000235:genetics / Q000502:physiology*; D046939:Synechocystis / Q000235:genetics / Q000502:physiology*
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010100:Oxygen
keywords: alternative electron flow; cyanobacteria; oxygen; photorespiration; photosynthesis