Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox

Abstract

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.