Alternative oxidase is an important player in the regulation of nitric oxide levels under normoxic and hypoxic conditions in plants

Abstract

Plant mitochondria possess two different pathways for electron transport from ubiquinol: the cytochrome pathway and the alternative oxidase (AOX) pathway. The AOX pathway plays an important role in stress tolerance and is induced by various metabolites and signals. Previously, several lines of evidence indicated that the AOX pathway prevents overproduction of superoxide and other reactive oxygen species. More recent evidence suggests that AOX also plays a role in regulation of nitric oxide (NO) production and signalling. The AOX pathway is induced under low phosphate, hypoxia, pathogen infections, and elicitor treatments. The induction of AOX under aerobic conditions in response to various stresses can reduce electron transfer through complexes III and IV and thus prevents the leakage of electrons to nitrite and the subsequent accumulation of NO. Excess NO under various stresses can inhibit complex IV; thus, the AOX pathway minimizes nitrite-dependent NO synthesis that would arise from enhanced electron leakage in the cytochrome pathway. By preventing NO generation, AOX can reduce peroxynitrite formation and tyrosine nitration. In contrast to its function under normoxia, AOX has a specific role under hypoxia, where AOX can facilitate nitrite-dependent NO production. This reaction drives the phytoglobin–NO cycle to increase energy efficiency under hypoxia.

Nitrogen Depletion Blocks Growth Stimulation Driven by the Expression of Nitric Oxide Synthase in Tobacco

“…According to this, under low N condition, OtNOS transgenic plants display ∼40% inhibition of mitochondrial respiration respect to EV plants. In other reports, it has been shown that NO could inhibit aconitase, induce alternative oxidase (Kumari et al, 2019) and shift the metabolism toward amino acid and protein synthesis (Cvetkovska and Vanlerberghe, 2012;Gupta et al, 2012). We showed that transgenic tobacco lines have no different respiration rates under sufficient N availability.…”

The hypoxia–reoxygenation stress in plants

“…3 , mitochondria seem to act as organelles involved in NO generation under hypoxia but also as a target of NO regulatory actions ( Igamberdiev et al , 2014 ). Nitrite-dependent NO production in mitochondria is facilitated by the function of the alternative oxidase (AOX) complex in hypoxia but, in turn, minimizes NO synthesis, ROS, peroxynitrite formation, and tyrosine nitration under normoxia ( Kumari et al , 2019 ). Therefore, AOX might function as a key switch in the hypoxia–reoxygenation transition by regulating oxidative- and nitrosative-triggered protein modifications during re-aeration of plants ( Fig.…”

Effects of Salicylic Acid on the Metabolism of Mitochondrial Reactive Oxygen Species in Plants

“…•be generated by mitochondrial ETC. Complex II and IV, as well as alternative oxidase (AOX) were also described as part of reductive pathways for nitric oxide (NO) synthesis, especially under low oxygen concentration [28,29]. NO can modulate protein structure or activity through S-nitrosylation of specific cysteine residues, through nitration of specific tyrosines or through binding to metal cofactors of the enzymes such as in the case of MnSOD [30].…”

“…The role of AOX (together with UCP) is crucial when cyt c is released from mitochondria during the initiation of plant PCD because respiratory electron transport can continue under this circumstance [117][118][119][120]. In addition, AOX activity can help to decrease ROS production in mitochondria [121,122] and contribute to the NO production [28,29].…”