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 (T_s ) up to 15 °C above ambient air temperature (T_a ). Respiration rate is inversely related to T_a , such that the T_s achieves a degree of independence from T_a , 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 T_s 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 T_a was clamped at 15 °C and T_s was allowed to vary, exposure to heliox reduced T_s 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.

Keywords: diffusion; flower; gas conductance; heliox; inflorescence; oxygen consumption; respiration; thermogenesis.