Increased respiratory restriction during phosphate-limited growth in transgenic tobacco cells lacking alternative oxidase.
We found that mitochondrial alternative oxidase (AOX) protein and the capacity for CN-resistant respiration are dramatically increased in wild-type tobacco (Nicotiana tabacum) suspension-cultured cells in response to growth under P limitation, and antisense (AS8) tobacco cells unable to induce AOX under these conditions have altered growth and metabolism. Specifically, we found that the respiration of AS8 cells was restricted during P-limited growth, when the potential for severe adenylate control of respiration (at the level of C supply to the mitochondrion and/or at the level of oxidative phosphorylation) is high due to the low cellular levels of ADP and/or inorganic P. As a result of this respiratory restriction, AS8 cells had altered growth, morphology, cellular composition, and patterns of respiratory C flow to amino acid synthesis compared with wild-type cells with abundant AOX protein. Also, AS8 cells under P limitation displayed high in vivo rates of generation of active oxygen species compared with wild-type cells. This difference could be abolished by an uncoupler of mitochondrial oxidative phosphorylation. Our results suggest that induction of non-phosphorylating AOX respiration (like induction of adenylate and inorganic P-independent pathways in glycolysis) is an important plant metabolic adaptation to P limitation. By preventing severe respiratory restriction, AOX acts to prevent both redirections in C metabolism and the excessive generation of harmful active oxygen species in the mitochondrion.
Parsons
H L
HL
Division of Life Science and Department of Botany, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, Ontario, Canada M1C 1A4.
Yip
J Y
JY
Vanlerberghe
G C
GC
D000596:Amino Acids / Q000378:metabolism; D002478:Cells, Cultured; D003486:Cyanides / Q000494:pharmacology; D016373:DNA, Antisense; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism*; D010947:Plants, Toxic; D014026:Nicotiana / Q000378:metabolism*; D000099188:Alternative Oxidase
D000596:Amino Acids; D003486:Cyanides; D016373:DNA, Antisense; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase