Intrinsic factors controlling growth under sink limited conditions

植物的生长要么受源活动(固碳)的限制，要么受汇利用或储存碳的能力的限制。我们仍然不知道到底是什么限制了主要水槽的增长，比如储存器官。在春季短命植物中，贮藏器官的生长主要由细胞大小决定，而不是由细胞数量决定，当植物在较低的温度下生长时，这些器官会变得更大。我们想要测试内复制在决定这些器官的细胞大小中所起的作用。内复制水平可以通过用流式细胞仪定量细胞DNA含量来监测。我们将确定内复制何时发生，以及不同春季短暂植物和一些温带储藏作物(如甜菜和土豆)的生长温度如何影响内复制。然后，我们将尝试通过应用已知的影响细胞周期的代谢物和植物激素来调节内复制周期的数量。 源汇活动被持续地调节以避免不平衡。例如，在库限制下，光合作用被下调，甚至可能导致叶片衰老。然而，到目前为止，从库到源的信号通路还没有得到确凿的证实。我们最近发现了一些代谢产物，它们可能参与了在库容量有限的条件下诱导美洲棘豆叶片衰老的过程。我们现在将使用不同的方法来确认它们作为信号分子的作用。首先，我们将通过使用植物激素延缓叶片衰老来延长库房的生长。这种方法应该允许我们从叶片衰老的库限信号中分离出来，并利用代谢组学识别每个过程的特定代谢物。其次，我们将比较同一物种的源和库限制植物在叶片衰老开始时的叶和鳞茎代谢物的分布。我们将使用不同年龄的野生大葱，因为我们最近发现，幼苗的生长是受来源限制的，随着植物年龄的增长，逐渐变得有限。第三，我们将比较来自不同分类家族的春季短暂物种的代谢物谱，以确定这些汇限制信号分子的分布范围有多广。 这项研究将帮助我们理解为什么植物在库容量有限的条件下进化到衰老它们的叶片，尽管这会降低植物的总生长能力。识别相关的信号分子是回答这个问题的重要一步，如果我们试图延缓叶片衰老和改善库容量有限物种的生长，也是重要的一步。这项研究还将表征内复制在决定许多温带物种贮藏器官最终细胞大小中所起的作用，这将有助于我们更好地理解限制库房生长从而提高产量的因素。两个博士学位，一个硕士学位和五个理学学士学位。在该项目的5年中，学生将获得全植物源-汇研究和功能代谢组学方面的专业知识。

Growth in plants is either limited by source activity (carbon fixation) or by the capacity of the sinks to use or store carbon. We still do not know exactly what limits growth in major sinks such as storage organs. In spring ephemerals, storage organ growth is mostly determined by cell size rather than by cell number, and these organs get larger when plants are grown at lower temperatures. We want to test the role plays by endoreduplication in determining cell size in these organs. The level of endoreduplication can be monitored by quantifying cell DNA content using flow cytometry. We will determine when endoreduplication takes place and how it is influenced by growth temperatures in different spring ephemerals and a few temperate storage crops such as beet and potato. We will then try to modulate the number of endoreduplication cycles by applying metabolites and phytohormones known to influence the cell cycle. Source and sink activities are continuously modulated to avoid disequilibrium. For example, under sink limitation, photosynthesis is downregulated, which can even lead to leaf senescence. However, so far no signaling pathway from sink to source has been conclusively confirmed. We have recently identified metabolites that could be involved in inducing leaf senescence under sink limited conditions in Erythronium americanum. We will now confirm their role as signaling molecules, using different approaches. First, we will prolong sink growth by delaying leaf senescence using phytohormones. This approach should allow us to separate the sink limitation signal from that of leaf senescence and identify metabolites specific to each process, using metabolomics. Second, we will compare leaf and bulb metabolite profiles at the onset of leaf senescence in both source and sink limited plants of the same species. We will use wild leek of different ages, as we have recently found that growth is source limited in seedlings, and gradually becomes sink limited as plant ages. Third, we will compare metabolite profiles of spring ephemeral species from different taxonomic families to determine how widespread these sink limited signaling molecules are. This study will help us understand why plants have evolved to senesce their leaves under sink limited conditions, even though this reduces total plant growth capacity. Identifying the signaling molecules involved is an important step toward answering this question, but also if we attempt to delay leaf senescence and improve growth in sink limited species. This study will also characterize the role played by endoreduplication in determining final cell size in storage organs of many temperate species which will improve our comprehension of the factors that limit sink growth and thus yield. Two Ph.D., one master's, and 5 B.Sc. students will gain expertise in whole-plant source-sink studies and in functional metabolomics during the 5 years of the project.