RUI: Regulation of Water Uptake in Tank Bromeliads

水箱菠萝是生长在新热带地区森林树冠上的树木上的植物，从树叶底部形成的水箱中收集的水和养分中获取营养。除了由于池塘水中和池塘水维持的丰富群落而具有生态重要性外，它们还是研究环境变量(如光照)在控制叶片水分吸收中的作用的极佳案例。许多菠萝科植物可以出现在树冠的几个位置，因此即使是一棵寄主树也可以提供不同光照下的一系列植物。叶片的水分输送能力，或叶片的水力传导性，可以决定植物在其环境中取得成功的能力，而光可以通过对叶片解剖和形态的长期影响和对叶片生理的短期影响来决定这种能力。由于盆栽菠萝实际上缺乏吸收根和茎，它们也提供了研究叶片水力传导性的外部和内部调节的极好模型。叶片的相对简单的带状形状以及它们平行的脉序便于测量和模拟菠萝的叶片水力传导性，它们使用水箱作为水库，允许操纵供水以调查环境和内部调节器的影响。具体地说，众所周知，光和pH至少部分是通过对水通道蛋白的影响来影响叶片的水力传导性的，水通道蛋白是一种调节跨膜水分运动的蛋白质。这项研究真正是综合性的，因为将在田间和实验室使用光、水槽水pH和水通道蛋白抑制剂的实验操作，在林冠内植物对光变化的反应水平上评估叶片水力传导性的调节。水通道蛋白基因在不同光照下的叶片和不同叶片区域的表达也将被测量和比较。对于田间和实验室中的植物，将研究解剖和形态特征，并将其纳入叶片水力传导性模型，该模型将通过对示踪剂和诊断染色指示的途径的显微镜检查进一步了解和测试。由于坦克凤梨的叶子既是供需器官，了解它们的叶片水力传导性是了解它们的生态功能以及它们如何应对热带森林中迅速发生的变化的基础。随着原始森林变得更加分散，被次生林取代，热带树冠树枝上生长的水箱凤梨和其他植物的作用预计将变得更加重要。这项研究将完全由首席研究员和本科生进行，他们既在哥斯达黎加的La Selva生物站进行实地研究，也在西方学院的实验室进行。这项拟议中的研究的一个关键组成部分是使用哥斯达黎加的一个实地考察站，部分原因是西方学院位于洛杉矶的位置吸引了许多与拉丁美洲有个人和智力联系的学生。拟议研究的一个主要目标是加强这些联系，并为本科生开发一种国际经验，展示科学在理解人类和其他生物如何通过全球过程(如用水和森林结构变化)联系在一起方面的作用。

Tank bromeliads are plants that grow on trees in the forest canopy in the Neotropics, deriving sustenance from the water and nutrients collected in the tanks formed at the base of their leaves. In addition to the ecological importance of tank bromeliads due to the rich communities sustained in and by the tank water, they are excellent case studies for investigating the role of environmental variables such as light in governing leaf water uptake. Many bromeliad species can occur at several positions in the canopy, thus even a single host tree can provide a range of plants from different light exposures. The capacity of leaves to transport water, or leaf hydraulic conductance, can determine a plant's ability to succeed in its environment, and light can determine that capacity due to long-term effects on leaf anatomy and morphology and short-term effects on leaf physiology. Because tank bromeliads virtually lack absorptive roots and stems, they also provide excellent models in which to investigate external and internal regulators of leaf hydraulic conductance. The relatively simple strap-shape of the leaves as well as their parallel venation facilitate measurement and modeling of leaf hydraulic conductance for bromeliads, and their use of tanks as reservoirs allows manipulation of the water supply to investigate the effects of environmental and internal regulators. Specifically, light and pH are known to affect leaf hydraulic conductance at least in part via their effects on aquaporins, proteins that regulate water movement across membranes. This research is truly integrative in that the regulation of leaf hydraulic conductance will be assessed in the field at the level of plant responses to light variation within the forest canopy as well as in the laboratory, using experimental manipulations of light, tank-water pH, and aquaporin inhibitors. Aquaporin gene expression in leaves from different light exposures and in different leaf regions will also be measured and compared. For plants in both field and laboratory, anatomical and morphological traits will be investigated and incorporated into a model of leaf hydraulic conductance that will be further informed and tested by microscopic examination of the pathways indicated by tracer and diagnostic staining. Because the leaves of tank bromeliads are the organs of both supply and demand, understanding how their leaf hydraulic conductance is regulated is fundamental to understanding their ecological function and how they might respond to changes that are rapidly occurring in tropical forests. The role of tank bromeliads and other plants that grow in the branches of the tropical tree canopy is predicted to become even more important as primary forest becomes more fragmented and is replaced by secondary forest.The research will be carried out entirely by the principal investigator and undergraduate students, both in the field at La Selva Biological Station in Costa Rica and in the laboratory at Occidental College. A key component of the proposed research is its use of a field station in Costa Rica, in part because Occidental College's location in Los Angeles attracts many students with personal and intellectual ties to Latin America. One major goal of the proposed research is to strengthen those ties and to develop an international experience for undergraduates that will demonstrate the role of science in understanding how people and other organisms are linked by global processes such as water use and changes in forest structure.