Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox

The respiration rate of the thermogenic inflorescences of Japanese skunk cabbage Symplocarpus renifolius can reach 300 nmol s−1 g−1, which is sufficient to raise spadix temperature (Ts) up to 15 °C above ambient air temperature (Ta). Respiration rate is inversely related to Ta, such that the Ts achieves a degree of independence from Ta, an effect known as temperature regulation. Here, we measure oxygen consumption rate (Ṁo2) in air (21% O2 in mainly N2) and in heliox (21% O2 in He) to investigate the diffusive conductance of the network of gas-filled spaces and the thermoregulatory response. When Ts was clamped at 15 °C, the temperature that produces maximal Ṁo2 in this species, exposure to high diffusivity heliox increased mean Ṁo2 significantly from 137 ± 17 to 202 ± 43 nmol s−1 g−1 FW, indicating that respiration in air is normally limited by diffusion in the gas phase and some mitochondria are unsaturated. When Ta was clamped at 15 °C and Ts was allowed to vary, exposure to heliox reduced Ts 1 °C and increased Ṁo2 significantly from 116 ± 10 to 137 ± 19 nmol s−1 g−1, indicating that enhanced heat loss by conduction and convection can elicit the thermoregulatory response.