title: Importance of the alternative oxidase (AOX) pathway in regulating cellular redox and ROS homeostasis to optimize photosynthesis during restriction of the cytochrome oxidase pathway in Arabidopsis thaliana.
abstract: OBJECTIVE
  The importance of the alternative oxidase (AOX) pathway, particularly AOX1A, in optimizing photosynthesis during de-etiolation, under elevated CO2, low temperature, high light or combined light and drought stress is well documented. In the present study, the role of AOX1A in optimizing photosynthesis was investigated when electron transport through the cytochrome c oxidase (COX) pathway was restricted at complex III.
  
  
  METHODS
  Leaf discs of wild-type (WT) and aox1a knock-out mutants of Arabidopsis thaliana were treated with antimycin A (AA) under growth-light conditions. To identify the impact of AOX1A deficiency in optimizing photosynthesis, respiratory O2 uptake and photosynthesis-related parameters were measured along with changes in redox couples, reactive oxygen species (ROS), lipid peroxidation and expression levels of genes related to respiration, the malate valve and the antioxidative system.
  
  
  RESULTS
  In the absence of AA, aox1a knock-out mutants did not show any difference in physiological, biochemical or molecular parameters compared with WT. However, after AA treatment, aox1a plants showed a significant reduction in both respiratory O2 uptake and NaHCO3-dependent O2 evolution. Chlorophyll fluorescence and P700 studies revealed that in contrast to WT, aox1a knock-out plants were incapable of maintaining electron flow in the chloroplastic electron transport chain, and thereby inefficient heat dissipation (low non-photochemical quenching) was observed. Furthermore, aox1a mutants exhibited significant disturbances in cellular redox couples of NAD(P)H and ascorbate (Asc) and consequently accumulation of ROS and malondialdehyde (MDA) content. By contrast, WT plants showed a significant increase in transcript levels of CSD1, CAT1, sAPX, COX15 and AOX1A in contrast to aox1a mutants.
  
  
  CONCLUSIONS
  These results suggest that AOX1A plays a significant role in sustaining the chloroplastic redox state and energization to optimize photosynthesis by regulating cellular redox homeostasis and ROS generation when electron transport through the COX pathway is disturbed at complex III.
authors: Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India.
authors: Abhaypratap
authors: A
authors: Vishwakarma
authors: Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India.
authors: Sarada Devi
authors: SD
authors: Tetali
authors: Department of Plant Physiology, FB5, University of Osnabrück, 49069 Osnabrück, Germany and.
authors: Jennifer
authors: J
authors: Selinski
authors: Department of Plant Physiology, FB5, University of Osnabrück, 49069 Osnabrück, Germany and.
authors: Renate
authors: R
authors: Scheibe
authors: Department of Biotechnology and Bioinformatics, University of Hyderabad, Hyderabad 500 046, India kpssl@uohyd.ac.in.
authors: Kollipara
authors: K
authors: Padmasree
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D000975:Antioxidants / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D004579:Electron Transport; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D008293:Malates / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010788:Photosynthesis; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D000099188:Alternative Oxidase
chemical_list: D000968:Antimycin A; D000975:Antioxidants; D008293:Malates; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D000099188:Alternative Oxidase; C030298:malic acid
keywords: AOX; Alternative oxidase pathway; Arabidopsis thaliana; NPQ; ROS; antimycin A; antioxidants; non-photochemical quenching; photosynthesis; reactive oxygen species; redox; respiration