Poster: Respiratory Pathways

Abs # 265: Computer simulation of mitochondrial respiratory activity that controls the homeothermic heat-production in the spadix of skunk cabbage, Symplocarpus foetidus

Presenter:	Ito, Takanori , taka1@iwate-u.ac.jp
Authors	Ito, Takanori  (A)   Ito, Kikukatsu  (A)
Affiliations:	(A): Cryobiosystem Research Center, Iwate University

Flowers of certain primitive plants produce enough heat to raise their temperatures up to 30 ^oC above the external air and regulate it at a nearly constant level. Skunk cabbage, Symplocarpus foetidus, is a well investigated plant that shows a distinct behavior similar to that of warm-blooded mammals. Although it has been assumed that such a thermoregulation involves successive alteration of mitochondrial activities, the mechanism that governs homeothermic heat-production has been poorly investigated. To elucidate the biological system that is required for the thermoregulation in skunk cabbage, a theoretical analysis with a series of computer simulations was performed using a set of temperature data obtained either from a field or from an artificial environmental condition. First, our analysis revealed that the temperature of the thermogenic spadix displayed a typical chaotic character, and the embedding index of the chaotic system was found to be two. These observations suggest that the mitochondrial respiratory activity, which is the major pathway in heat-production in skunk cabbage, can be simply implicated by efflux and influx models using two pools of respiratory intermediates. Interestingly, our detailed computer simulation further indicated the requirement of two energy efflux systems, both alternative oxidase (AOX) and uncoupling protein (UCP), for successive homeothermic heat-production. Our proposed thermogenic model also indicates the existence of mitochondrial factor(s) which respond to the external temperature. Thus, our computer simulation analysis suggests that the mitochondrial respiration activity, which is involved in AOX and UCP functions, is responsible for both heat-production and temperature sensing.