Role of Abscisic Acid in the Regulation of Root Growth at Low Water Potentials

主要研究者实验室的Sharp研究表明，激素脱落酸（阿坝）的积累是在水分有限的条件下维持玉米主根伸长所必需的。 最近的证据表明，阿坝在这方面的作用之一是调节脯氨酸积累的渗透调节。 拟议的研究旨在确定这种关系背后的细胞机制。 基于最近的数据和植物以及动物和细菌系统中发表的工作的回顾，一个假设是，阿坝积累在根生长区在低水势调节膜离子运输和细胞内离子水平，这反过来又诱导生长维持机制，包括脯氨酸的积累。 虽然阿坝在调节气孔保卫细胞离子运输中的作用是公认的，但关于阿坝在生长调节中的作用的信息很少。 主要目的是测试这一假设，使用电生理方法，强调在膜电位和离子浓度和通量的变化引起的低水势和内源阿坝水平的操纵根生长区。 重点将放在测量K+和H+。 如在以前的工作中，内源性阿坝将被操纵在生理上有意义的水平在低水势下生长的根中使用抑制剂氟啶酮和玉米的VP5突变体来抑制类胡萝卜素（和阿坝）的生物合成。 在所有的实验中，高度的空间分辨率将被强调，以解决差异响应阿坝根生长区内。 常规和离子选择性微电极将用于测量膜电位、细胞质离子水平和在高和低水势下生长的根之间的离子运输的变化，以及在其中内源阿坝水平改变的低水势下的根中的变化。 为这项工作已经开发了一个溶液培养系统，初步的实验表明，在根生长区的膜电位的变化响应于改变的水势和外源阿坝。 将离子水平的电生理测量值与X射线微量分析（EDX）获得的值进行比较。 已经建立了适当的合作，以促进电生理和EDX测量。 平行的离子调节的研究，脯氨酸积累的生物化学在根生长区在低水势和阿坝的影响将被检查。 将评估合成增加、催化剂减少、摄取增加和蛋白质掺入减少的贡献。 拟议的研究是朝着确定可用于作物种质改良计划的特定植物过程或性状的长期目标迈出的一步。 这些研究将为阿坝生理学和水分限制条件下根系生长调控领域提供急需的信息，这些领域的特点是进展缓慢。 ***

9306935 Sharp Studies in the Principal Investigator's laboratory have shown that accumulation of the hormone abscisic acid (ABA) is required for the maintenance of primary root elongation in maize under water-limited conditions. Recent evidence indicates that one role of ABA in this regard is the regulation of proline accumulation for osmotic adjustment. The proposed research aims to determine the cellular mechanisms underlying this relationship. Building upon recent data and a review of the published work in plant as well as animal and bacterial systems, a hypothesis is developed that ABA accumulation in the root growth zone at low water potentials regulates membrane ion transport and intracellular ion levels, which in turn induces mechanisms for growth maintenance including the accumulation of proline. While the role of ABA in regulating ion transport in stomatal guard cells is well-established, such information is scant with regard to the action of ABA in growth regulation. The primary objective is to test this hypothesis using electrophysiological approaches, emphasizing changes in membrane potential and ion concentrations and fluxes in the root growth zone caused by low water potentials and manipulation of endogenous ABA levels. Emphasis will be placed on measurements of K+ and H+. As in previous work, endogenous ABA will be manipulated within physiologically meaningful levels in roots growing at low water potentials using both the inhibitor fluridone and the vp5 mutant of maize to inhibit carotenoid (and ABA) biosynthesis. In all experiments a high degree of spatial resolution will be emphasized to address differential responsiveness to ABA within the root growth zone. Conventional and ion- selective microelectrodes will be used to measure changes in membrane potential, cytoplasmic ion levels and ion transport between roots grown at high and low water potential, and in roots at low water potentials in which endogenous ABA levels are altered. A sol ution culture system has been developed for this work, and preliminary experiments have shown changes in membrane potentials in the root growth zone in response to altered water potentials and to exogenous ABA. The electrophysiological measurements of ion levels will be compared with values obtained by x-ray microanalysis (EDX). Appropriate collaborations have been established to facilitate the electrophysiological and EDX measurements. Parallel to the studies of ionic regulation, the biochemistry of proline accumulation in the root growth zone at low water potentials and as affected by ABA will be examined. The contributions of increased synthesis, decreased catabolism, increased uptake, and decreased incorporation into protein will be assessed. The proposed research is a step toward the long-range goal of identifying specific plant processes or traits which could be used in crop germplasm improvement programs. The studies should provide much needed information in the fields of ABA physiology and root growth regulation under water- limited conditions, which have been characterized by slow progress. ***