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

夏普首席研究员实验室的研究表明，在水分限制条件下，玉米主根伸长的维持需要激素脱落酸（ABA）的积累。最近的证据表明，ABA在这方面的一个作用是调节脯氨酸积累的渗透调节。提出的研究旨在确定这种关系背后的细胞机制。基于最近的数据和对植物、动物和细菌系统的已发表工作的回顾，提出了一种假设，即在低水势下，ABA在根生长区的积累调节了膜离子运输和细胞内离子水平，这反过来又诱导了包括脯氨酸积累在内的生长维持机制。虽然ABA在气孔保护细胞中调节离子运输的作用已经确立，但关于ABA在生长调节中的作用还缺乏相关信息。主要目的是利用电生理学方法验证这一假设，强调低水势和内源ABA水平操纵引起的根生长区膜电位和离子浓度和通量的变化。重点将放在K+和H+的测量上。在之前的研究中，内源ABA将被控制在低水势下生长的根中有生理意义的水平，使用抑制剂氟烷酮和玉米vp5突变体来抑制类胡萝卜素（和ABA）的生物合成。在所有的实验中，将强调高度的空间分辨率，以解决根系生长区域内对ABA的差异响应。常规和离子选择性微电极将用于测量在高水势和低水势下生长的根之间以及在低水势下内源ABA水平改变的根中的膜电位、细胞质离子水平和离子运输的变化。为此，研究人员开发了一种土壤溶液培养系统，初步实验表明，随着水势和外源ABA的改变，根生长区的膜电位发生了变化。离子水平的电生理测量值将与x射线微分析（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。在离子调控研究的同时，还将研究低水势和ABA对根生长期脯氨酸积累的生化影响。增加合成，减少分解代谢，增加摄取和减少并入蛋白质的贡献将被评估。提出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。在水分限制条件下的ABA生理和根系生长调控方面的研究进展缓慢。＊＊＊

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. ***