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BIOENERGETICS AND PHOTOSYNTHESIS

Contribution of the Alternative Pathway to Respiration during Thermogenesis in Flowers of the Sacred Lotus¹

School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia (J.R.W., R.S.S.); and Institute for Conservation Biology, Department of Biological Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia (S.A.R.)

We report results from in vivo measurements, using oxygen isotope discrimination techniques, of fluxes through the alternative and cytochrome respiratory pathways in thermogenic plant tissue, the floral receptacle of the sacred lotus (Nelumbo nucifera). Fluxes through both pathways were measured in thermoregulating flowers undergoing varying degrees of thermogenesis in response to ambient temperature. Significant increases in alternative pathway flux were found in lotus receptacles with temperatures 16°C to 20°C above ambient, but not in those with lesser amounts of heating. Alternative pathway flux in the hottest receptacles was 75% of the total respiratory flux. In contrast, fluxes through the cytochrome pathway did not change significantly during thermogenesis. These data support the hypothesis that increased flux through the alternative pathway is responsible for heating in the lotus and that it is unlikely that uncoupling proteins, which would have produced increased fluxes through the cytochrome pathway, contribute significantly to heating in this tissue. Comparisons of actual flux, with capacity determined using inhibitors, suggested that the alternative pathway was operating at close to maximum capacity in heating tissues of lotus. However, in nonheating tissues the inhibitor data significantly overestimated the alternative pathway flux. This confirms that isotopic measurements are necessary for accurate determination of fluxes through the two pathways.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jennifer R. Watling (jennifer.watling{at}adelaide.edu.au).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.075523.

^* Corresponding author; e-mail jennifer.watling{at}adelaide.edu.au; fax 61–8–83036222.

Received December 13, 2005; returned for revision January 19, 2006; accepted January 20, 2006.

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