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EAGER: A novel mechanism regulating leaf water transport: Reversible collapse of xylem conduits

EAGER：调节叶水运输的新机制：木质部导管的可逆塌陷

基本信息

批准号：
1659918
负责人：
Noel Holbrook
金额：
$ 30万
依托单位：
Harvard University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-01-15 至 2019-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1659918&HistoricalAwards=false
关键词：
EAGER novel mechanism regulating leaf

项目摘要

This project investigates how plants protect their vascular system from damage due to excessive evaporative loads. The significance of the work arises from the fact that photosynthesis is dependent upon a plant's capacity to transport water from the soil. Thus, understanding how plants protect their water transport system will illuminate constraints on the productivity of agricultural and natural ecosystems. A new finding shows that the terminal water transporting vessels, which are located in leaves and consist of non-living cells, function like a mechanical valve: closing off as the stresses in the system increase and re-opening as the system relaxes. The principle goal of this research is to determine if the valve-like behavior of terminal conduits prevents the stresses in the system from reaching levels that could cause lasting damage to upstream conduits. A second objective is to explore linkages between the rapid stress-induced closure of terminal conduits and the slower closure of stomatal pores in the leaf epidermis. The findings of this research will contribute to the development of crop varieties that are resilient to drought. The project will enhance research mentoring and training of students, as well as provide fundamental insights in plant biology that will be incorporated into teaching and disseminated to the general public.A fundamental issue in plant ecophysiology is how plants protect themselves from cavitation. Challenges to the plant vascular system associated with soil drying occur slowly, such that stomatal closure, root shrinkage, and leaf shedding are effective means of regulating xylem potentials. In contrast, excursions in transpiration rate have the potential to be fast relative to the ability of stomata to close, and thus to expose leaves to potentially damaging water potentials. This is especially the case for angiosperms in which stomatal aperture does not passively track leaf water potential and increases in transpiration lead initially to opening, rather than closing. A recent discovery shows that in the smallest leaf veins, which are the ones in closest contact to the sites of evaporation and thus experience the most negative pressures, the conduits deform (collapse) rather than cavitate and the change in shape is completely (and rapidly) reversible. The goals of this project are to investigate (1) whether the reduction in hydraulic conductivity due to terminal conduit collapse protects upstream xylem from experiencing water potentials that cause cavitation and (2) how collapse contributes to stomatal regulation of transpiration. The study provides a new perspective on the coordination of liquid and vapor phase transport, with implications for both plant productivity and drought response. Greater understanding of the role of xylem mechanical properties may provide new targets for phenotyping crop varieties and understanding plant diversity.

本计画探讨植物如何保护其维管系统免受过度蒸发负荷所造成的伤害。这项工作的意义在于光合作用依赖于植物从土壤中运输水分的能力。因此，了解植物如何保护其水运输系统将阐明农业和自然生态系统生产力的制约因素。一项新的发现表明，位于叶片中并由非活细胞组成的终端水运输容器的功能就像一个机械阀门：随着系统中压力的增加而关闭，随着系统的放松而重新打开。本研究的主要目标是确定终端管道的阀状行为是否可以防止系统中的应力达到可能对上游管道造成持久损坏的水平。第二个目标是探索快速的压力诱导的终端管道关闭和叶表皮气孔关闭较慢之间的联系。这项研究的结果将有助于开发耐旱的作物品种。该项目将加强对学生的研究指导和培训，并提供植物生物学的基本见解，这些见解将纳入教学并向公众传播。植物生态生理学的一个基本问题是植物如何保护自己免受空化。与土壤干燥相关的植物维管系统的挑战缓慢发生，使得气孔关闭、根收缩和叶脱落是调节木质部潜力的有效手段。与此相反，蒸腾速率的波动有可能是快速相对于气孔关闭的能力，从而使叶片暴露于潜在的破坏性水势。这是特别是被子植物的情况下，气孔开度并不被动跟踪叶水势和增加蒸腾导致最初打开，而不是关闭。最近的一项发现表明，在最小的叶脉中，这些叶脉与蒸发部位接触最紧密，因此经历了最大的负压，导管变形（塌陷）而不是空化，形状的变化是完全（快速）可逆的。本项目的目标是调查（1）是否减少水力传导性，由于终端管道崩溃保护上游木质部经历水势，造成空化和（2）如何崩溃有助于气孔调节蒸腾。这项研究提供了一个新的视角，协调的液体和蒸汽相运输，与植物生产力和干旱反应的影响。对木质部力学性质作用的进一步了解可能为作物品种的表型分析和了解植物多样性提供新的目标。