Collaborative Research: NSF-BSF: Under Pressure: The evolution of guard cell turgor and the rise of the angiosperms

气孔是叶子表面的气孔，光合作用所需的二氧化碳通过气孔进入。同时，气孔也是植物向大气中流失水分的主要途径。平衡叶片获得的二氧化碳和水分流失的比例对植物的生存至关重要，因为不受控制的水分流失会导致快速干燥和死亡。气孔通过增加成对的“保护”细胞的内部膨胀压力而打开，这导致细胞弯曲分开，形成一个孔或孔，并通过减少保护细胞的膨胀压力而关闭。尽管膨胀压力在气孔功能中起着关键作用，但由于缺乏测量光合作用叶片膨胀压力的方法，进展受到限制。该项目介绍了一种确定保护细胞膨胀压力的新方法，该方法使用激光触发细胞内气泡的形成，并记录气泡因膨胀压力而被推回溶液的大小和速度。该方法将用于量化维管植物保护细胞膨胀压力的范围，并阐明在干旱和热浪等环境胁迫下气孔打开和关闭的调节。该研究将促进对陆地生态系统（包括对美国生物经济和粮食安全至关重要的农业系统）生产力和弹性控制的理解，并为不同植物谱系的气孔调节演变提供见解。该项目包括与哈佛自然历史博物馆和普渡农业旅游展览的教育和推广活动，将吸引大量公众观众和K-12年级的学生。利用最先进的设备和技术进行现代科学研究的培训将包括博士后、研究生和本科生。学生还将在暑期项目中体验身临其境的实验室体验，并为不同年级的学生开发动手演示和教学模块。叶片维管系统效率的提高与气孔大小的减小和气孔数量的增加的协调进化被认为是白垩纪以来被子植物优势的重要组成部分之一。然而，控制更多较小尺寸的气孔可能会对实现更有效的水力所带来的潜在光合作用收益施加新的限制。利用一种新开发的方法，可以首次直接测量保护细胞和表皮细胞的膨胀，研究小组将确定被子植物是否保持较高的保护细胞膨胀，从而使它们的光合作用速率更高，并改变气孔动力学和控制。这些结果将与蕨类植物、石松植物和裸子植物进行比较，这些植物的气孔不与表皮细胞机械地相互作用，并用于建立保护细胞解剖、激素信号、相邻表皮细胞之间的相互作用和水力学之间的清晰和明确的联系，这些都是科学家几十年来由于缺乏直接的叶细胞膨胀测量而无法解决的问题。这些结果将揭示保护细胞控制的基本生物物理和物理化学原理，以确定最大光合作用的速率，以及对环境的敏感性，以响应干旱和保护叶片维管网络免受水力破坏。这将使我们能够更全面地了解气孔生物学和叶片生理学，无论是在进化过程中，还是在对快速变化的气候的反应中。对K-12和本科生的推广和教育工作将与哈佛自然历史博物馆和普渡农业旅游展览合作进行。利用最先进的设备和技术进行现代科学研究方面的培训，包括博士后和研究生在生理生态学方面的长期培训计划。该项目还涉及通过美以两国基金会建立的国际伙伴关系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Stomata are the pores on the surface of leaves through which the CO2 needed for photosynthesis enters. At the same time, stomata are also the main way that plants lose water to the atmosphere. Balancing the ratio of CO2 gained and water lost from leaves is essential for plant survival because unregulated water loss would lead to rapid desiccation and death. Stomata open by increasing the internal turgor pressure of paired “guard” cells, which causes the cells to bow apart creating a hole or pore, and close by reducing guard cell turgor pressure. Despite the key role of turgor pressure in stomatal functioning, progress has been limited by the lack of a method to measure turgor pressures in photosynthesizing leaves. This project introduces a new approach to determine guard cell turgor pressure in which a laser is used to trigger the formation of a gas bubble inside a cell, and the size and speed by which this bubble is pushed back into solution due to the turgor pressure is recorded. This method will be used to quantify the range of guard cell turgor pressure across vascular plants and to elucidate the regulation of stomatal opening and closing in response to environmental stresses such as drought and heatwaves. The research will advance understanding of controls on the productivity and resiliency of terrestrial ecosystems, including agricultural systems important to the U.S. bioeconomy and food security, and provide insights into the evolution of stomatal regulation across diverse plant lineages. The project includes educational and outreach activities with the Harvard Museum of Natural History and the Purdue Agriculture Traveling Exhibit that will reach large public audiences and students from K-12 levels. Training in modern scientific research using state of the art equipment and techniques will include postdoctoral fellows, graduate students, and undergraduate students. Immersive laboratory experiences in summer programs and the development of hands-on demonstrations and teaching modules for multiple grade levels will also be undertaken. The coordinated evolution of increased leaf vascular system efficiency with both a reduction in stomatal size and increase in stomatal number is believed to be one of the critical components of angiosperm dominance since the Cretaceous. Yet, controlling more stomata of smaller size likely imposed new constraints in realizing potential photosynthetic gains conferred by more efficient hydraulics. Using a newly developed method that enables for the first-time direct measurement of guard cell and epidermal cell turgor in situ, the research team will determine if angiosperms maintain higher guard cell turgor, enabling their higher rates of photosynthesis and altering stomatal dynamics and control. These results will be compared to ferns, lycophytes and gymnosperms that have stomata that do not interact mechanically with epidermal cells and used to establish clear and definitive links between guard cell anatomy, hormonal signaling, interaction between adjacent epidermal cells, and hydraulics, all of which have eluded scientists for decades because of a lack of direct leaf cell turgor measurements. The results will reveal fundamental biophysical and physiochemical principles of guard cell control in determining the rate of maximum photosynthesis, but also sensitivity to the environment in response to drought and the protection of the leaf vascular network from hydraulic failure. This will enable the development of a more comprehensive understanding of stomatal biology and leaf physiology, both over evolutionary time but also in response to a rapidly changing climate. Outreach and educational efforts for K-12 and undergraduate students will be conducted in collaboration with the Harvard Museum of Natural History and the Purdue Agriculture Traveling Exhibit. Training in modern scientific research using state of the art equipment and techniques will include postdoctoral fellows and graduate students in a long-running training program in physiological ecology. This project also involves international partnerships via the US-Israel Binational Foundation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.