Poster: Environmental physiology

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Abs # P01008: Alternative pathway flux in thermogenic flowers of the sacred lotus, Nelumbo nucifera.

Presenter:	Watling, Jennifer R       Contact Presenter
Authors	Watling, Jennifer R (A)   Robinson, Sharon A (B)   Seymour, Roger S (A)
Affiliations:	(A): Earth and Environmental Sciences, University Of Adelaide (B): School of Biological Sciences, University of Wollongong

We report the first 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 16-20 ^oC 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 to heating in this tissue. Alternative pathway capacity in lotus receptacles, determined from inhibitor titrations, was 72% of total respiratory flux in the heating tissues, which was similar to the alternative pathway capacity determined from the isotope discrimination data. In contrast, using inhibitors to determine alternative pathway capacity in non-heating tissues resulted in an overestimation of alternative pathway flux, confirming that while this technique is suitable for assessing alternative pathway capacity, it is not appropriate for quantifying fluxes through the two respiratory pathways in vivo.