In the heat of the night – alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum

Authors

  • Rebecca E. Miller,

    1. Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia
    2. Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
    3. School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia
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  • Nicole M. Grant,

    1. Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia
    2. Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
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  • Larry Giles,

    1. Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St, Stanford, CA 94305, USA
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  • Miquel Ribas-Carbo,

    1. Departament de Biologia, Universitat de les Illes Balears, Unitat de Fisiologia Vegetal, Illes Balears, Spain
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  • Joseph A. Berry,

    1. Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St, Stanford, CA 94305, USA
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  • Jennifer R. Watling,

    1. Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
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  • Sharon A. Robinson

    1. Institute for Conservation Biology and Environmental Management, The University of Wollongong, Wollongong, NSW 2522, Australia
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Author for correspondence:
Rebecca E. Miller
Tel: +61 3 99055217
Email: Rebecca.miller@monash.edu

Summary

  • 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.

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