Abstract
Three species of Symplocarpus, S. foetidus, S. nipponicus and S. nabekuraensis, are distributed in Japan. Except for S. foetidus, however, detailed measurements of heat-production and genes that confer thermogenic metabolism have been poorly investigated. In the present study, we have compared the levels of heat-production and gene expressions of mitochondrial uncoupling proteins (UCPs) and alternative oxidase (AOX), both of which act as an important heat generator, in S. foetidus and S. nipponicus. Continuous records of the spadix temperatures revealed that S. foetidus maintains a body temperature of around 20oC even when the ambient temperature drops below freezing, while S. nipponicus does not show any significant increases in its body temperature. Interestingly, both S. foetidus and S. nipponicus accumulate high levels of UCPb and AOX transcripts in the spadix. These results suggest that expression of UCP and AOX genes does not fully explain the capacity of heat-production in the Symplocarpus family.