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Mitochondrial AOX Supports Redox Balance of Photosynthetic Electron Transport, Primary Metabolite Balance, and Growth in Arabidopsis thaliana under High Light

1
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Graduate School of Science and Engineering, Saitama University, 225 Shimo-Okubo, Sakura-ku, Saitama-city, Saitama 338-8570, Japan
3
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Int. J. Mol. Sci. 2019, 20(12), 3067; https://doi.org/10.3390/ijms20123067
Received: 29 March 2019 / Revised: 3 June 2019 / Accepted: 20 June 2019 / Published: 23 June 2019
(This article belongs to the Special Issue Oxidative Stress and Redox Regulation in Plants)
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Abstract

When leaves receive excess light energy, excess reductants accumulate in chloroplasts. It is suggested that some of the reductants are oxidized by the mitochondrial respiratory chain. Alternative oxidase (AOX), a non-energy conserving terminal oxidase, was upregulated in the photosynthetic mutant of Arabidopsis thaliana, pgr5, which accumulated reductants in chloroplast stroma. AOX is suggested to have an important role in dissipating reductants under high light (HL) conditions, but its physiological importance and underlying mechanisms are not yet known. Here, we compared wild-type (WT), pgr5, and a double mutant of AOX1a-knockout plant (aox1a) and pgr5 (aox1a/pgr5) grown under high- and low-light conditions, and conducted physiological analyses. The net assimilation rate (NAR) was lower in aox1a/pgr5 than that in the other genotypes at the early growth stage, while the leaf area ratio was higher in aox1a/pgr5. We assessed detailed mechanisms in relation to NAR. In aox1a/pgr5, photosystem II parameters decreased under HL, whereas respiratory O2 uptake rates increased. Some intermediates in the tricarboxylic acid (TCA) cycle and Calvin cycle decreased in aox1a/pgr5, whereas γ-aminobutyric acid (GABA) and N-rich amino acids increased in aox1a/pgr5. Under HL, AOX may have an important role in dissipating excess reductants to prevent the reduction of photosynthetic electron transport and imbalance in primary metabolite levels. View Full-Text
Keywords: alternative oxidase; metabolic interaction; mitochondrial respiratory chain; photosynthesis; redox balance alternative oxidase; metabolic interaction; mitochondrial respiratory chain; photosynthesis; redox balance
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Jiang, Z.; Watanabe, C.K.A.; Miyagi, A.; Kawai-Yamada, M.; Terashima, I.; Noguchi, K. Mitochondrial AOX Supports Redox Balance of Photosynthetic Electron Transport, Primary Metabolite Balance, and Growth in Arabidopsis thaliana under High Light. Int. J. Mol. Sci. 2019, 20, 3067.

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