SGER: Thermogenic Modeling

University Of Utah, Salt Lake City UT

Investigators

Abstract

CBET-0837987 Roemer The Australian endemic cycad plant Macrozamia lucida is derived from an ancient lineage of gymnosperms (non-flowering plants like pine trees) present on earth long before flowering plants. Its pollination system may be unique in terms of the interactions between the host plant and its specific insect pollinator. The heart of this system is a daily thermogenic event during which the cycad cones "spontaneously" heat up (maximum measured of 25F above ambient), an action that coincides with the midday flight activity of the pollinators between cones. Little is known about the mechanisms of this "unstable" heating process (it starts and stops in each cone on a daily basis for up to two weeks) including its functional significance in pollination. Through experiments inspired by prior observations and bio-thermal engineering modelling we have shown that these cyclic thermal events are likely driven by thermo-chemical instabilities that involve the Arrhenius equation based temperature dependence of the cone metabolism. Although sequences of such instabilities are well known in abiotic systems, this is the first reported biological instance of such an instability sequence. We will perform experiments on these cones and develop mathematical models that predict the cones' varying thermal behaviour (metabolism and temperature distribution in space and time) over the multiple weeklong series of events in order to analyze the bio-physical basis of these unique instabilities. The intellectual merit of this interdisciplinary, combined experimental and modelling research is that it will yield a basic biophysical understanding about the first known biological example of a thermo-chemically unstable system, and it will contribute to understanding the functional significance of thermogenesis in gymnosperms and angiosperms, topics of current biological interest. More broadly, the interdisciplinary work that we and several students will perform will contribute to the understanding of the nature and evolution of obligate pollination mutualisms, of which only a few flowering plant systems have been studied in depth including the yucca/yucca moth and fig/fig wasp systems. Our research on this pollination system will further complement that with angiosperm systems in being dioecious (separate male and female plants) and of an ancient non-flowering seed plant lineage, and in having a pollination system that is extremely temperature sensitive. Second, the strong role of ambient temperature in these plants' pollination process suggests that global warming may significantly impact this system, and those of other temperature dependent cycads, and cycads could be sensitive indicators of global warming. Because this lineage of plants precedes the flowering plants, studies of this cycad system may give insights into early pollination systems. Finally, our study has fundamental implications for the conservation of cycad/insect pollination systems worldwide, an important consideration since about half of all cycad species are endangered that are undergoing conservation management. In summary, the unique combination of biological and thermal engineering perspectives could provide a model for other interdisciplinary efforts. Integrating the engineering and biological research tools to develop an understanding of this unstable thermal-chemical biological system could provide unique insights into the nature of plant thermogenesis. Although much is understood about the biochemical pathways in basic thermogenic processes in plants, the work proposed here should lead to testable hypotheses on the mechanistic aspects of the correlated volatile production that is coincident with increased metabolism and thermogenesis.