SGER: Thermogenic Modeling

澳大利亚特有的苏铁植物Macrozamia lucida起源于一个古老的裸子植物谱系（裸子植物是一种不开花的植物，如松树），早在开花植物出现之前就存在了。其传粉系统在寄主植物与其特定昆虫传粉者之间的相互作用方面可能是独特的。这个系统的核心是苏铁球果“自发”升温的每日产热活动（最高测量值高于环境温度25华氏度），这一行动与传粉者在球果之间的中午飞行活动相吻合。人们对这种“不稳定”加热过程（每天在每个球果中开始和停止，持续长达两周）的机制知之甚少，包括它在授粉中的功能意义。通过先前观察和生物热工模型启发的实验，我们已经表明，这些循环热事件可能是由热化学不稳定性驱动的，涉及基于阿伦尼乌斯方程的锥细胞代谢的温度依赖性。虽然这种不稳定序列在非生物系统中是众所周知的，但这是第一次报道这种不稳定序列的生物学实例。我们将对这些锥体进行实验，并建立数学模型，预测锥体在多个星期的一系列事件中不同的热行为（空间和时间的代谢和温度分布），以分析这些独特的不稳定性的生物物理基础。这项跨学科、结合实验和建模研究的智力价值在于，它将对已知的第一个热化学不稳定系统的生物例子产生基本的生物物理学理解，并有助于理解裸子植物和被子植物中产热的功能意义，这是当前生物学感兴趣的话题。更广泛地说，我们和几位学生将进行的跨学科工作将有助于理解专性授粉相互作用的本质和进化，其中只有少数开花植物系统得到了深入的研究，包括丝兰/丝兰蛾和无花果/无花果黄蜂系统。我们对这种传粉系统的研究将进一步补充被子植物系统的雌雄异株（雌雄分开的植物）和古老的非开花种子植物谱系，并具有对温度极其敏感的传粉系统。其次，环境温度在这些植物授粉过程中的重要作用表明，全球变暖可能会显著影响这一系统，以及其他温度依赖性苏铁的授粉过程，苏铁可能是全球变暖的敏感指标。由于这种植物谱系早于开花植物，对这种苏铁系统的研究可能有助于了解早期授粉系统。最后，我们的研究对世界范围内苏铁/昆虫授粉系统的保护具有重要意义，因为大约一半的苏铁物种是濒临灭绝的，正在进行保护管理。总之，生物和热工程视角的独特结合可以为其他跨学科的努力提供一个模型。整合工程和生物学研究工具来发展对这种不稳定的热化学生物系统的理解，可以为植物产热的本质提供独特的见解。尽管对植物基本产热过程的生化途径了解甚多，但本文提出的工作应导致对与代谢和产热增加相一致的相关挥发物产生的机制方面的可测试假设。

CBET-0837987RoemerThe 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.