title: Mitochondrial alternative oxidase maintains respiration and preserves photosynthetic capacity during moderate drought in Nicotiana tabacum.
abstract: The mitochondrial electron transport chain includes an alternative oxidase (AOX) that is hypothesized to aid photosynthetic metabolism, perhaps by acting as an additional electron sink for photogenerated reductant or by dampening the generation of reactive oxygen species. Gas exchange, chlorophyll fluorescence, photosystem I (PSI) absorbance, and biochemical and protein analyses were used to compare respiration and photosynthesis of Nicotiana tabacum 'Petit Havana SR1' wild-type plants with that of transgenic AOX knockdown (RNA interference) and overexpression lines, under both well-watered and moderate drought-stressed conditions. During drought, AOX knockdown lines displayed a lower rate of respiration in the light than the wild type, as confirmed by two independent methods. Furthermore, CO2 and light response curves indicated a nonstomatal limitation of photosynthesis in the knockdowns during drought, relative to the wild type. Also relative to the wild type, the knockdowns under drought maintained PSI and PSII in a more reduced redox state, showed greater regulated nonphotochemical energy quenching by PSII, and displayed a higher relative rate of cyclic electron transport around PSI. The origin of these differences may lie in the chloroplast ATP synthase amount, which declined dramatically in the knockdowns in response to drought. None of these effects were seen in plants overexpressing AOX. The results show that AOX is necessary to maintain mitochondrial respiration during moderate drought. In its absence, respiration rate slows and the lack of this electron sink feeds back on the photosynthetic apparatus, resulting in a loss of chloroplast ATP synthase that then limits photosynthetic capacity.
authors.affiliation: Departments of Biological Sciences and Cell and Systems Biology, University of Toronto, Scarborough, Toronto, Ontario, Canada M1C1A4.
authors.forename: Keshav
authors.initials: K
authors.lastname: Dahal
authors.affiliation: Departments of Biological Sciences and Cell and Systems Biology, University of Toronto, Scarborough, Toronto, Ontario, Canada M1C1A4.
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.affiliation: Departments of Biological Sciences and Cell and Systems Biology, University of Toronto, Scarborough, Toronto, Ontario, Canada M1C1A4.
authors.forename: Greg D
authors.initials: GD
authors.lastname: Martyn
authors.affiliation: Departments of Biological Sciences and Cell and Systems Biology, University of Toronto, Scarborough, Toronto, Ontario, Canada M1C1A4.
authors.forename: Farkhunda
authors.initials: F
authors.lastname: Rahimy
authors.affiliation: Departments of Biological Sciences and Cell and Systems Biology, University of Toronto, Scarborough, Toronto, Ontario, Canada M1C1A4 gregv@utsc.utoronto.ca.
authors.forename: Greg C
authors.initials: GC
authors.lastname: Vanlerberghe
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D055864:Droughts; D004579:Electron Transport; D055785:Gene Knockdown Techniques; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D014026:Nicotiana / Q000502:physiology*; D000099188:Alternative Oxidase
chemical_list: D002245:Carbon Dioxide; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D000099188:Alternative Oxidase