Browsing by Author "Igamberdiev, Abir U"

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Alternative oxidase is an important player in the regulation of nitric oxide levels under normoxic and hypoxic conditions in plants
(Oxford University Press, 2019) Kumari, Aprajita; Pathak, Pradeep Kumar; Bulle, Mallesham; Igamberdiev, Abir U; Gupta, Kapuganti Jagadis
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 suggested 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 of 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.
Interaction of nitric oxide with the components of plant mitochondrial electron transport chain
(Oxford University Press, 2018) Gupta, Kapuganti Jagadis; Kumari, Aprajita; Florez-Sarasa, Igor; Fernie, Alisdair R; Igamberdiev, Abir U
Mitochondria are not only major sites for energy production but also participate in several alternative functions, among these generation of nitric oxide (NO) and its different impacts on this organelle is increasing attention. The inner mitochondrial membrane contains the chain of protein complexes, and electron transfer via oxidation of various organic acids and reducing equivalents leads to generation of proton gradient that results in energy production. Recent evidence suggests that these complexes are sources and targets for NO. Complex I and rotenone-insensitive NAD(P)H dehydrogenases regulate hypoxic NO production, while complex I also participates in the formation of supercomplex with complex III under hypoxia. Complex II is a target for NO which by inhibiting Fe-S centres regulates ROS generation, and complex III is one of the major sites for NO production and the produced NO participates in the phytoglobin-NO cycle that leads to the maintenance of redox level and limited energy production under hypoxia. Expression of the alternative oxidase (AOX) is induced by NO under various stress conditions, and evidence exists that AOX can regulate mitochondrial NO production. Complex IV is another major site for NO production which can also be linked to ATP generation via the phytoglobin-NO cycle. Inhibition of complex IV by NO can prevent oxygen depletion at the frontier of anoxia. The NO production and action on various complexes play a major role in NO signalling and energy metabolism.