title: The Acceptor Side of Photosystem II Is the Initial Target of Nitrite Stress in Synechocystis sp. Strain PCC 6803.
abstract: Nitrite, a common form of inorganic nitrogen (N), can be used as a nitrogen source through N assimilation. However, high levels of nitrite depress photosynthesis in various organisms. In this study, we investigated which components of the photosynthetic electron transfer chain are targeted by nitrite stress in Synechocystis sp. strain PCC 6803 cells. Measurements of whole-chain and photosystem II (PSII)-mediated electron transport activities revealed that high levels of nitrite primarily impair electron flow in PSII. Changes in PSII activity in response to nitrite stress occurred in two distinct phases. During the first phase, which occurred in the first 3 h of nitrite treatment, electron transfer from the primary quinone acceptor (QA) to the secondary quinone acceptor (QB) was retarded, as indicated by chlorophyll (Chl) a fluorescence induction, S-state distribution, and QA-reoxidation tests. In the second phase, which occurred after 6 h of nitrite exposure, the reaction center was inactivated and the donor side of photosystem II was inhibited, as revealed by changes in Chl fluorescence parameters and thermoluminescence and by immunoblot analysis. Our data suggest that nitrite stress is highly damaging to PSII and disrupts PSII activity by a stepwise mechanism in which the acceptor side is the initial target. IMPORTANCE In our previous studies, an alga-based technology was proposed to fix the large amounts of nitrite that are released from NOX-rich flue gases and proved to be a promising industrial strategy for flue gas NOXbioremediation (W. Chen et al., Environ Sci Technol 50:1620-1627, 2016, https://doi.org/10.1021/acs.est.5b04696; X. Zhang et al., Environ Sci Technol 48:10497-10504, 2014, https://doi.org/10.1021/es5013824). However, the toxic effects of high concentrations of nitrite on algal cells remain obscure. The analysis of growth rates, photochemistry, and protein profiles in our study provides important evidence that the inhibition by nitrite occurs in two phases: in the first phase, electron transfer between QA-and QBis retarded, whereas in the second, the donor side of PSII is affected. This is an excellent example of investigating the "early" inhibitory effects (i.e., within the first 6 h) on the PSII electron transfer chain in vivo This paper provides novel insights into the mechanisms of nitrite inhibition of photosynthesis in an oxygenic phototrophic cyanobacterium.
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Ma
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Zhu
authors.affiliation: SINOPEC Research Institute of Petroleum Processing, Beijing, China.
authors.forename: Junying
authors.initials: J
authors.lastname: Zhu
authors.affiliation: SINOPEC Research Institute of Petroleum Processing, Beijing, China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Rong
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.
authors.forename: Jiao
authors.initials: J
authors.lastname: Zhan
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China.
authors.forename: Chenliu
authors.initials: C
authors.lastname: He
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, China wangqiang@ihb.ac.cn.
authors.forename: Qiang
authors.identifier: http://orcid.org/0000-0002-7388-4703
authors.initials: Q
authors.lastname: Wang
mesh_terms: D004579:Electron Transport; D009573:Nitrites / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013312:Stress, Physiological; D046939:Synechocystis / Q000235:genetics / Q000502:physiology*
chemical_list: D009573:Nitrites; D045332:Photosystem II Protein Complex
keywords: PSII; Synechocystis sp. strain PCC 6803; nitrite stress