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Open AccessArticle

Oxidation of P700 Induces Alternative Electron Flow in Photosystem I in Wheat Leaves

1
Department of Biological and Environmental Sciences, Faculty of Agriculture, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
2
Graduate School of Agricultural Science, Tohoku University, Aramaki-Aoba 468-1, Aoba-ku, Sendai 980-8572, Japan
3
Faculty of Agriculture, Iwate University, 3-18-8 Ueda, Morioka, Iwate 020-8550, Japan
*
Author to whom correspondence should be addressed.
Plants 2019, 8(6), 152; https://doi.org/10.3390/plants8060152
Received: 12 March 2019 / Revised: 4 June 2019 / Accepted: 4 June 2019 / Published: 5 June 2019
(This article belongs to the Special Issue ROS Responses in Plants)
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Abstract

Oxygen (O2)-evolving photosynthetic organisms oxidize the reaction center chlorophyll, P700, in photosystem I (PSI) to suppress the production of reactive oxygen species. The oxidation of P700 is accompanied by alternative electron flow in PSI (AEF-I), which is not required for photosynthetic linear electron flow (LEF). To characterize AEF-I, we compared the redox reactions of P700 and ferredoxin (Fd) during the induction of carbon dioxide (CO2) assimilation in wheat leaves, using dark-interval relaxation kinetics analysis. Switching on an actinic light (1000 μmol photons m−2 s−1) at ambient CO2 partial pressure of 40 Pa and ambient O2 partial pressure of 21 kPa gradually oxidized P700 (P700+) and enhanced the reduction rate of P700+ (vP700) and oxidation rate of reduced Fd (vFd). The vFd showed a positive linear relationship with an apparent photosynthetic quantum yield of PSII (Y[II]) originating at point zero; the redox turnover of Fd is regulated by LEF via CO2 assimilation and photorespiration. The vP700 also showed a positive linear relationship with Y(II), but the intercept was positive, not zero. That is, the electron flux in PSI included the electron flux in AEF-I in addition to that in LEF. This indicates that the oxidation of P700 induces AEF-I. We propose a possible mechanism underlying AEF-I and its physiological role in the mitigation of oxidative damage. View Full-Text
Keywords: charge recombination; cyclic electron flow; ferredoxin; photosystem I; P700; reactive oxygen species charge recombination; cyclic electron flow; ferredoxin; photosystem I; P700; reactive oxygen species
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Kadota, K.; Furutani, R.; Makino, A.; Suzuki, Y.; Wada, S.; Miyake, C. Oxidation of P700 Induces Alternative Electron Flow in Photosystem I in Wheat Leaves. Plants 2019, 8, 152.

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