Distribution of thermogenic activity in floral tissues of Nelumbo nucifera

Thermogenesis in Nelumbo nucifera (Gaertn.) has been known to scientists for many years; however, the extent of heating by different floral parts remains unclear. We present evidence that the receptacle, stamens and petals produce heat independently, and that the source of heating in these tissues is most likely the alternative oxidase (AOX). The temperatures of the receptacle, petals and stamens were significantly higher than non-thermogenic leaf tissue. After removal from the pedicel, the receptacle retained the most heat (8.1 ± 1.9°C above non-thermogenic tissue temperature) and the petals the least (2.8 ± 4.2°C), with the stamens intermediate. High AOX protein levels and flux through the AOX pathway (in all tissues) during the thermogenic period are consistent with AOX being the mechanism used for thermogenesis. Lipids and carbohydrates were investigated as possible substrates for thermogenesis. There was little change in total lipids during floral development; however, soluble carbohydrate levels decreased by 70% with the onset of thermogenesis. These sugars may fuel thermogenesis in the stamens. The localisation of AOX protein in the various floral parts and the evolutionary significance of its heating role are discussed.