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

气孔是叶片表面的气孔，光合作用所需的CO2通过气孔进入。同时，气孔也是植物向大气流失水分的主要途径。平衡从叶片获得的CO2和损失的水分的比例对于植物的生存至关重要，因为不受控制的水分损失会导致快速干燥和死亡。气孔通过增加成对的“保卫”细胞的内部膨压而打开，这导致细胞弓开，从而产生洞或孔，并且通过降低保卫细胞膨压而关闭。尽管膨压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压的方法，进展受到限制。该项目介绍了一种新的方法来确定保卫细胞膨压，其中使用激光来触发细胞内气泡的形成，并记录由于膨压而将气泡推回溶液中的大小和速度。这种方法将被用来量化整个维管植物的保卫细胞膨压的范围，并阐明气孔开放和关闭响应于环境胁迫，如干旱和热浪的调节。该研究将促进对陆地生态系统生产力和弹性控制的理解，包括对美国生物经济和粮食安全至关重要的农业系统，并为不同植物谱系的气孔调节进化提供见解。该项目包括与哈佛自然历史博物馆和普渡农业巡回展览的教育和推广活动，这些活动将接触到大量公众观众和K-12级的学生。使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员，研究生和本科生。还将在暑期课程中进行沉浸式实验室体验，并为多个年级水平开发动手演示和教学模块。叶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自白垩纪以来被子植物优势的关键组成部分之一。然而，控制更多的气孔较小的尺寸可能会施加新的限制，实现潜在的光合作用的收益所赋予的更有效的水力。使用一种新开发的方法，首次直接测量保卫细胞和表皮细胞的膨压，研究小组将确定被子植物是否保持较高的保卫细胞膨压，使其具有更高的光合作用速率并改变气孔动态和控制。这些结果将与蕨类植物，石松和裸子植物进行比较，这些植物具有不与表皮细胞机械相互作用的气孔，并用于在保卫细胞解剖学，激素信号传导，相邻表皮细胞之间的相互作用和水力学之间建立明确和明确的联系，所有这些都因为缺乏直接的叶细胞膨压测量而困扰了科学家几十年。结果将揭示基本的生物物理和物理化学原理的保卫细胞控制在确定最大光合速率，但也对环境的敏感性，在响应干旱和保护叶维管网络从液压故障。这将使气孔生物学和叶生理学的发展更全面的了解，无论是在进化的时间，而且在应对迅速变化的气候。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巡回展览合作进行。使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员和研究生，他们将参加生理生态学的长期培训计划。该项目还涉及通过美国-以色列两国基金会的国际合作伙伴关系。该奖项反映了NSF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.