title: The occurrence and control of nitric oxide generation by the plant mitochondrial electron transport chain.
abstract: The plant mitochondrial electron transport chain (ETC) is bifurcated such that electrons from ubiquinol are passed to oxygen via the usual cytochrome path or through alternative oxidase (AOX). We previously showed that knockdown of AOX in transgenic tobacco increased leaf concentrations of nitric oxide (NO), implying that an activity capable of generating NO had been effected. Here, we identify the potential source of this NO. Treatment of leaves with antimycin A (AA, Qi-site inhibitor of Complex III) increased NO amount more than treatment with myxothiazol (Myxo, Qo-site inhibitor) despite both being equally effective at inhibiting respiration. Comparison of nitrate-grown wild-type with AOX knockdown and overexpression plants showed a negative correlation between AOX amount and NO amount following AA. Further, Myxo fully negated the ability of AA to increase NO amount. With ammonium-grown plants, neither AA nor Myxo strongly increased NO amount in any plant line. When these leaves were supplied with nitrite alongside the AA or Myxo, then the inhibitor effects across lines mirrored that of nitrate-grown plants. Hence the ETC, likely the Q-cycle of Complex III generates NO from nitrite, and AOX reduces this activity by acting as a non-energy-conserving electron sink upstream of Complex III.
authors.affiliation: Department of Biological Sciences and Department of Cell and Systems Biology, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C1A4, Canada.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Alber
authors.affiliation: Department of Biological Sciences and Department of Cell and Systems Biology, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C1A4, Canada.
authors.forename: Hampavi
authors.initials: H
authors.lastname: Sivanesan
authors.affiliation: Department of Biological Sciences and Department of Cell and Systems Biology, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C1A4, Canada.
authors.forename: Greg C
authors.identifier: http://orcid.org/0000-0002-0685-4811
authors.initials: GC
authors.lastname: Vanlerberghe
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008689:Methacrylates / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D013844:Thiazoles / Q000494:pharmacology; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000099188:Alternative Oxidase
chemical_list: D000968:Antimycin A; D045222:Electron Transport Chain Complex Proteins; D008689:Methacrylates; D024101:Mitochondrial Proteins; D009569:Nitric Oxide; D010088:Oxidoreductases; D010940:Plant Proteins; D013844:Thiazoles; D000099188:Alternative Oxidase; C030517:myxothiazol
keywords: Complex III; Nicotiana tabacum; alternative oxidase; antimycin A; mitochondrial electron transport chain; myxothiazol; nitric oxide; nitrite; oligomycin; respiration