title: Mitochondrial alternative oxidase pathway protects plants against photoinhibition by alleviating inhibition of the repair of photodamaged PSII through preventing formation of reactive oxygen species in Rumex K-1 leaves.
abstract: The purpose of this study was to explore how the mitochondrial AOX (alternative oxidase) pathway alleviates photoinhibition in Rumex K-1 leaves. Inhibition of the AOX pathway decreased the initial activity of NADP-malate dehydrogenase (EC 1.1.1.82, NADP-MDH) and the pool size of photosynthetic end electron acceptors, resulting in an over-reduction of the photosystem I (PSI) acceptor side. The over-reduction of the PSI acceptor side further inhibited electron transport from the photosystem II (PSII) reaction centers to the PSII acceptor side as indicated by an increase in V(J)  (the relative variable fluorescence at J-step), causing an imbalance between photosynthetic light absorption and energy utilization per active reaction center (RC) under high light, which led to the over-excitation of the PSII reaction centers. The over-reduction of the PSI acceptor side and the over-excitation of the PSII reaction centers enhanced the accumulation of reactive oxygen species (ROS), which inhibited the repair of the photodamaged PSII. However, the inhibition of the AOX pathway did not change the level of photoinhibition under high light in the presence of the chloroplast D1 protein synthesis inhibitor chloramphenicol, indicating that the inhibition of the AOX pathway did not accelerate the photodamage to PSII directly. All these results suggest that the AOX pathway plays an important role in the protection of plants against photoinhibition by minimizing the inhibition of the repair of the photodamaged PSII through preventing the over-production of ROS.
authors: State Key Laboratory of Crop Biology, Shandong Key Laboratory of Crop Biology, Shandong Agricultural University, Tai'an 271018, Shandong, China.
authors: Li-Tao
authors: LT
authors: Zhang
authors: Zi-Shan
authors: ZS
authors: Zhang
authors: Hui-Yuan
authors: HY
authors: Gao
authors: Zhong-Cai
authors: ZC
authors: Xue
authors: Cheng
authors: C
authors: Yang
authors: Xiang-Long
authors: XL
authors: Meng
authors: Qing-Wei
authors: QW
authors: Meng
mesh_terms: D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000378:metabolism; D004579:Electron Transport; D050538:Malate Dehydrogenase (NADP+) / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D024101:Mitochondrial Proteins / Q000378:metabolism*; D018384:Oxidative Stress; D010088:Oxidoreductases / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism* / Q000528:radiation effects; D018515:Plant Leaves / Q000201:enzymology / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D031804:Rumex / Q000201:enzymology* / Q000528:radiation effects; D000099188:Alternative Oxidase
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A; D050538:Malate Dehydrogenase (NADP+); D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D000099188:Alternative Oxidase