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. 2020 Mar 18;133(3):343–371. doi: 10.1007/s10265-020-01176-1

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© The Author(s) 2020

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — Production and elimination of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in mitochondria and cytosol. H₂O₂, NO, O^·−₂, and ONOO⁻ produced under hypoxic stress conditions are detoxified by the mitochondrial electron transport chain (mETC) and ascorbate/glutathione cycle in the mitochondrial matrix to maintain a redox balance in the cells. The alternative oxidase (AOX) and type II NAD(P)H dehydrogenases (NDs), ND_ex, and ND_in (NDs located at the outer and inner surfaces of the mitochondrial inner membrane, respectively), can consume the accumulated reducing equivalents for maintaining the mitochondrial homeostasis. AOX has lower affinity to O₂ than cytochrome c oxidase (COX, complex IV); NDs, especially Ca²⁺ dependent ND_in, have lower affinity to NAD(P)H than complex I and nitrate reductase (NR). In NO scavenging under hypoxic stress condition, ascorbate can contribute to the reduction of NO to N₂O in the mitochondrial matrix. Ascorbate is converted to monodehydroascorbate by ascorbate peroxidase (APX), which also involves the scavenging of ONOO⁻ and converting it into NO, The NO generated is resupplied to mETC. Ascorbate can also participate in Class 1 hemoglobin (Class 1 Hb) regeneration from methemoglobin (metHb) in the cytosol. Abbreviations are as follows: Cyt c, cytochrome c; DHAR, dehydroascorbate reductase; GR, glutathione reductase; IM, inner membrane; IMS, inter-membrane space; MDHAR, monodehydroascorbate reductase; NO, nitric oxide; NR, nitrate reductase; OM, outer membrane; SOD, superoxide dismutase; TCA, tricarboxylic acid; UQH₂, ubiquinol