Research Planning Grant: Phloem Water Relations: Direct Measurements of Sieve-Tube Turgor Pressures

木质部和韧皮部的水分状态是紧密耦合的，但动力、组织结构和通常的运输方向是截然相反的。与大量关于木质部结构如何影响水分运输模式的研究相比，筛管的水分关系及其对同化物运输的影响很少受到关注。缺乏监测筛管膨胀压力的技术意味着一些关于韧皮部运输的最基本问题仍然没有答案。特别是，对膨胀梯度大小的估计以及筛管膨胀如何响应木质部水势的变化在很大程度上是未知的。该项目为长期研究韧皮部水分关系和韧皮部-木质部相互作用奠定了基础。Holbrook博士将通过结合蚜虫柱头和细胞压力探针开发筛管膨胀压力的原位监测技术，并将探索筛管膨胀压力随植物水分平衡变化的时空变化。有了这项研究计划资助，她将访问其他实验室学习组件技能，并将在自己的实验室进行初步实验。一种原位监测完整植物中筛管膨胀压力的方法的发展将大大提高对韧皮部水关系的理解。特别是，它将使研究人员能够检查木质部张力和韧皮部生理的相互作用，并通过实验探索通过木质部的水运输能力如何与通过韧皮部长距离运动产生足够的膨胀压力的要求相平衡。

The water status of the xylem and phloem are closely coupled, yet the driving force, tissue structure, and generally the direction of transport are diametrically opposed. In contrast to the numerous studies on how xylem structure influences patterns of water transport, the water relations of sieve tubes and their effect on assimilate transport have received little attention. Lack of a technique to monitor sieve-tube turgor pressures means that some of the most basic questions regarding phloem transport remain unanswered. In particular, estimates of the magnitude of turgor gradients and how sieve-tube turgor responds to changes in xylem water potential are largely unknown. This project lays the groundwork for a long-term effort in phloem water relations and phloem:xylem interactions. Dr. Holbrook will develop techniques for in-situ monitoring of sieve tube-turgor pressure through combining aphid stylets and cell-pressure probe, and will explore spatial and temporal variation in sieve-tube turgor pressure in response to changes in plant water balance. With this Research Planning Grant, she will visit other labs to learn component skills and will perform preliminary experiments in her own lab. Development of an in-situ method for monitoring sieve-tube turgor pressure in intact plants will greatly enhance understanding of phloem water relations. In particular, it would enable researchers to examine interactions of xylem tension and phloem physiology and to explore experimentally how the capacity for water transport through the xylem is balanced with the requirement of generating sufficient turgor pressures for long-distance movement through the phloem.