In the heat of the night--alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum.
• Philodendron bipinnatifidum inflorescences heat up to 42 °C and thermoregulate. We investigated whether they generate heat via the cytochrome oxidase pathway uncoupled by uncoupling proteins (pUCPs), or the alternative oxidase (AOX). • Contribution of AOX and pUCPs to heating in fertile (FM) and sterile (SM) male florets was determined using a combination of oxygen isotope discrimination, protein and substrate analyses. • Both FM and SM florets thermoregulated independently for up to 30 h ex planta. In both floret types, AOX contributed > 90% of respiratory flux during peak heating. The AOX protein increased fivefold with the onset of thermogenesis in both floret types, whereas pUCP remained low throughout development. These data indicate that AOX is primarily responsible for heating, despite FM and SM florets potentially using different substrates, carbohydrates or lipids, respectively. Measurements of discrimination between O₂ isotopes in strongly respiring SM florets were affected by diffusion; however, this diffusional limitation was largely overcome using elevated O₂. • The first in vivo respiratory flux measurements in an arum show AOX contributes the bulk of heating in P. bipinnatifidum. Fine-scale regulation of AOX activity is post-translational. We also demonstrate that elevated O₂ can aid measurement of respiratory pathway fluxes in dense tissues.
Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia.|Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.|School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia.
Rebecca E
RE
Miller
Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia.|Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.
Nicole M
NM
Grant
Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St, Stanford, CA 94305, USA.
Larry
L
Giles
Departament de Biologia, Universitat de les Illes Balears, Unitat de Fisiologia Vegetal, Illes Balears, Spain.
Miquel
M
Ribas-Carbo
Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St, Stanford, CA 94305, USA.
Joseph A
JA
Berry
Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.
Jennifer R
JR
Watling
Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia.
Sharon A
SA
Robinson
D050260:Carbohydrate Metabolism; D019069:Cell Respiration; D003624:Darkness; D003720:Densitometry; D003576:Electron Transport Complex IV / Q000378:metabolism; D035264:Flowers / Q000502:physiology; D006358:Hot Temperature; D007473:Ion Channels / Q000378:metabolism; D050356:Lipid Metabolism; D008163:Luminescent Measurements; D024101:Mitochondrial Proteins / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D031062:Philodendron / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D051479:Plant Infertility; D010940:Plant Proteins; D013213:Starch / Q000378:metabolism; D013379:Substrate Specificity; D022722:Thermogenesis; D014280:Triglycerides / Q000378:metabolism; D000071256:Uncoupling Protein 1; D000099188:Alternative Oxidase
D003576:Electron Transport Complex IV; D007473:Ion Channels; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D013213:Starch; D014280:Triglycerides; D000071256:Uncoupling Protein 1; D000099188:Alternative Oxidase