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 (Q A ) to the secondary quinone acceptor (Q B ) was retarded, as indicated by chlorophyll (Chl) a fluorescence induction, S-state distribution, and Q A Ϫ 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 NO X -rich flue gases and proved to be a promising industrial strategy for flue gas NO X bioremediation (W. Chen et al., Environ Sci Technol 50:1620 -1627, 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 Q A Ϫ and Q B is 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.

Ammonium Nitrogen Tolerant Chlorella Strain Screening and Its Damaging Effects on Photosynthesis

“…Mo is the initial slope of the OJIP curve, which represents the Q A reduction rate; whereas the Ψo value reflects the probability that captured excitons will transfer electrons to QA−, the downstream electron acceptor in the electron transport chain (Zhang et al, 2016). Therefore, changes in Mo and Ψo reflect changes in electron transport from QA− to Q B .…”

“…Quantum Yield (QY), chlorophyll fluorescence induction kinetics (OJIP), and Non-Photochemical Quenching (NPQ) were measured using an AquaPen-C AP-C 100 fluorometer. Red light was used as the measuring light, the measuring flash pulse was set to 0.009 μmol m −2 s −1 , the saturating pulse was 2,100 μmol m −2 s −1 , and the actinic light (A-pulse) level was 400 μmol m −2 s −1 (Zhang et al, 2016). Chlorophyll fluorescence parameters Fv/Fm, Y(II), and Y(NO) and JIP-test parameters Qp and Mo, Ψo, φEo, and Wk were used in this study, which were calculated according to the following equations: eqnarrayright center leftFv/Fm=false(Fm-Fofalse)/Fm eqnarrayright center leftYfalse(IIfalse)=false(Fm-Ffalse)/Fm eqnarrayright center leftYfalse(NOfalse)=F/Fm eqnarrayright center leftQp=false(Fm-Ffalse)/false(Fm-Fofalse) eqnarrayright center leftφEo=false(1-false(FO/FMfalse)false)*Ψo eqnarrayright center leftWk=false(Ft-Fofalse)…”

“…SDS-PAGE and immunoblot analysis of cellular proteins were performed according to Zhang et al (2016).…”

Stem Photosynthesis—A Key Element of Grass Pea (Lathyrus sativus L.) Acclimatisation to Salinity

“…The disruptions of LET also imply disorders in the formation of a proton gradient between stroma and lumen, leading to a reduction of ATP synthesis, finally reducing the rate of photosynthesis [ 74 ]. Such disturbances were observed in plants that were growing under Ni and Cd stress [ 107 ], as well as in the presence of excess NO 2 – [ 108 ] or NaCl [ 109 , 110 ]. Non-heme Fe is involved in the electron transport between Q A and Q B .…”

Selective nitration of PsbO1, PsbO2, and PsbP1 decreases PSII oxygen evolution and photochemical efficiency in intact leaves of Arabidopsis

“…strain PCC 6803, high levels of NO 2 ¡ (70.4 mM) primarily impair electron flow in PSII, and NO 2 ¡ stress is highly damaging to PSII, in which the acceptor side is the initial target. 22 However, this inhibitory effect of NO 2 ¡ does not seem to contribute to the observed decreases in oxygen evolution and maximal photochemical efficiency of PSII (Table 1) because the concentration of NO 2 remaining in exposed leaves was zero in Arabidopsis (Takahashi et al, unpublished results) and spinach leaves. 23 O 2 evolution and Fv/Fm in psbo1, psbo2, and psbp1 mutants Insertion mutants such as psbo1, psbo2, and psbp1 that lack PsbO1, PsbO2, and PsbP1, respectively, have been reported previously.…”