Signal Transduction in Gravitropism-猫眼课题宝

DOI：

10.1002/9780470388297.ch2

发表时间：

2008-04

期刊：

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

B. Harrison;M. Morita;P. Masson;M. Tasaka

正如第一章所讨论的，大多数植物器官利用重力作为生长指南。然而，不同的器官将以不同的方式解释这些信息。芽向上生长，朝向光，地上环境，以优化光合作用，交换气体，并执行其生殖功能。另一方面，大多数根向下生长，进入土壤，在那里它们锚住植物并吸收植物生长、发育和繁殖所必需的水分和养分。为了了解这些器官如何以不同的方式解释重力提供的信息，我们首先需要了解控制重力感应细胞（称为平衡细胞）中重力信号转导的分子机制。在介绍植物重力信号转导机制的研究现状之前，我们必须了解高等植物的重力反应器官在组织结构和发育起源上是多样化的。禾本科植物幼苗的重力反应胚芽鞘是一个中空的圆柱形鞘，而成年植株的叶枕则位于每个节间的基部。双子叶植物幼苗的下胚轴和上胚轴以及成年植株的叶柄和茎都具有重力反应。同样地，单子叶植物和双子叶植物的主根和侧根都有重力反应，尽管根重力弯曲部位不含明显分化的平衡细胞。因此，不同植物器官的形态学和细胞学可能会影响调节其向重力反应的机制。尽管如此多样，所有的重力反应器官都有两个共同的特征：它们含有具有可沉积淀粉体的重力感受细胞（Sack 1997），并且它们在其上部和下部之间的生长素浓度中发展不对称性。（低浓度）和低浓度（较高浓度）在妊娠刺激后的侧腹（Philippar等人，1999; Muday和DeLong，2001; Friml等人，2002; Long等人，2002）。因此，在这些器官内，通过分化的平衡细胞内造淀粉体的重新定位而感知到的重力信号被转化为生化信号，并被传递到相邻的细胞，导致在伸长区形成生长素的横向梯度，这是向重力弯曲的原因（参见第3章）。虽然在全球范围内看似相似，但地上器官和根中伴随向地性的生理和生化事件在细节上有很大差异。例如，重力感知和信号传导的部位（内胚层细胞）与枝条中弯曲反应的部位重叠，这被认为是沿着器官同时均匀发生的（Firn和迪格比1980）。另一方面，根在重力感知和信号传导的主要部位（根冠柱）和弯曲反应的部位（根颈柱）之间显示出物理分离。

As discussed in Chapter 1, most plant organs use gravity as a growth guide. However, different organs will interpret that information in different ways. Shoots grow upward toward light, aboveground environments in order to optimize photosynthesis, exchange gases, and perform their reproductive functions. Most roots, on the other hand, grow downward, into the soil, where they anchor the plant and take up water and nutrients necessary for plant growth, development, and reproduction. To understand how these organs interpret differently the information provided by gravity, we first need to understand the molecular mechanisms that govern gravity signal transduction in gravity-sensing cells, termed statocytes. Before we describe the current state of our knowledge on the mechanisms that govern gravity signal transduction in plants, it is important to understand that the gravityresponding organs of higher plants are diversified in their tissue structure and developmental origin. In cereal grasses, the graviresponsive coleoptile of seedlings is a hollow cylindrical sheath, whereas the pulvini of adult plants are swellings at the base of each internode. In dicots, hypocotyls, and epicotyls of young seedlings and leaf petioles and stems of adult plants are all graviresponsive. Similarly, both primary and lateral roots are graviresponsive in monocots and dicots, even though the site of root gravicurvature does not contain obviously differentiated statocytes. Hence, the morphology and cytology of different plant organs may affect the machinery that modulates their gravitropic responses. In spite of such diversity, all graviresponsive organs share two common features: they contain graviperceptive cells with sedimentable amyloplasts (Sack 1997), and they develop asymmetry in auxin concentration between their upper (lower concentration) and lower (higher concentration) flanks upon gravistimulation (Philippar et al. 1999; Muday and DeLong 2001; Friml et al. 2002; Long et al. 2002). Thus, within these organs, a gravitational signal perceived through the relocalization of amyloplasts within differentiated statocytes is converted into biochemical signal (s) that is (are) transmitted to adjacent cells, leading to the formation of a lateral gradient of auxin at the elongation zone, responsible for the gravitropic curvature (see also Chapter 3). Although seemingly similar in global terms, the physiological and biochemical events that accompany gravitropism in aboveground organs and roots differ substantially in the details. For instance, the site of gravity perception and signal transduction (endodermal cells) overlaps with the site of curvature response in shoots, which has been proposed to occur simultaneously and uniformly along the organs (Firn and Digby 1980). Roots, on the other hand, show a physical separation between the primary site of gravity perception and signal transduction (the root cap columella) and the site of curvature response (the

Signal Transduction in Gravitropism

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