Mechanism of Embolism Reversal in Vascular Plants: Studies at the Level of Individual Vessels

植物必须不断地为叶子提供水分，这些水分被根部吸收并通过茎输送到叶子。 其驱动力来自叶片表面的水分蒸发，这对水柱施加了“拉力”。 这使得植物可以通过中空的木质部细胞从土壤中吸取水分，木质部细胞形成了通过茎运输水分的管道--基本上是把茎当作稻草。 由于水处于张力下，空气偶尔被吸入木质部，导致栓塞，阻止水流。 众所周知，空气栓塞发生在植物中，有时达到向叶子的水分输送显著受损的程度。 本研究的目的是了解植物修复充气管道的机制，使其能够在水运输中重复使用。 只是在过去的十年中，研究人员才意识到植物可以逆转栓塞，并且有证据表明，即使在木质部中的水处于相当大的张力下的白天，这种修复也可能发生。 然而，栓塞修复的机制仍然知之甚少。 该提案概述了了解这一关键生理过程的研究，以及探索限制不同物种修复能力的因素。 拟议的工作的一个主要目标是使用磁共振成像监测栓塞和栓塞逆转在完整的植物的动力学。 迄今为止，在理解栓塞修复方面的主要限制是缺乏任何方法来检查体内的这一过程。 此外，PI将使用一套新的方法，允许确定单个输水管道的水力特性。 水的可利用性是限制农业生产的主要因素，在决定农业和自然系统的生态相互作用方面起着重要作用。 这项研究将增加我们对植物如何在低水可用性时期生存的理解，并提高我们预测植物对干旱和极端温度等环境因素的反应的能力。

Plants must continually supply their leaves with water that is absorbed by the roots and transported to the leaves through the stem. The driving force for this comes from the evaporation of water from leaf surfaces, which exerts a "pull" on the water column. This allows the plant to draw water from the soil through hollow xylem cells which form conduits for water transport through the stem -- essentially using the stem as a straw. Because the water is under tension, air is sucked into the xylem occasionally, causing an embolism that blocks water flow. It is well known that air embolism occurs in plants, sometimes to the extent that water delivery to leaves is significantly impaired. The goal of this study is to understand the mechanisms by which plants may be able to repair air-filled conduits such that they are able to reuse them in water transport. It is only in the past decade that researchers have realized that plants can reverse embolism, and there is some evidence that this repair may occur even during the day when the water in the xylem is under substantial tension. The mechanisms by which embolisms are repaired, however, remain poorly understood. This proposal outlines studies to understand this key physiological process as well as to explore factors limiting the capacity for repair in different species. A major objective of the proposed work is to use magnetic resonance imaging to monitor the dynamics of embolism and embolism reversal in intact plants. The major limitation to date in understanding embolism repair has been the lack of any method to examine this process in vivo. In addition, the PIs will use a suite of new approaches that allow the determination of hydraulic properties of individual water transport conduits. Water availability is a major factor limiting agricultural production and plays an important role in determining ecological interactions in both agricultural and natural systems. This study will increase our understanding of how plants survive periods of low water availability and improve our ability to predict plant responses to environmental factors such as drought and temperature extremes.