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首页> 外文学位 >Calcium transport and delivery to the xylem in onion (Allium cepa L.) roots.
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Calcium transport and delivery to the xylem in onion (Allium cepa L.) roots.

机译：钙在洋葱（Allium cepa L.）根中运输并传递到木质部。

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摘要

This study concerns the pathway of Ca2+ transport in onion (Allium cepa L.) roots. Ca2+ is an essential macronutrient, which must be present in ionic form in the soil solution to be absorbed by plant roots. To sustain their growth, plants require a continuous supply of Ca2+, as it is not redistributed from mature organs to the meristems. The pathway(s) and mechanism(s) of Ca2+ uptake and transport across the root have not been previously resolved. Because of low level of Ca2+ in the cell cytosol, the symplastic pathway may be insufficient to meet the Ca2+ requirements of the developing shoot. The apoplastic pathway, however, is obstructed by the deposition of hydrophobic materials (Casparian bands) in the walls of the endodermis and exodermis. It is commonly believed that Ca2+ follows an apoplastic pathway on its route to the xylem by entering the root tip, where the wall modifications in the endodermis and exodermis are not yet developed. In the present study, onion roots were used as a model system. These roots did not possess any measurable capacity for apoplastic transport, as determined by exclusion of 8-hydroxy-1-3-6-pyrenetrisuphonate (PTS) from the transpiration stream. Direct application of 45Ca2+ to discrete zones of the root revealed that Ca2+ applied to the root tip was not translocated to the shoot, ruling out the root tip as a point of entry for this ion. Further, an antimonate precipitation study ruled out the possibility that Ca2+ was delivered to the transpiration stream by maturation of tracheary elements. 45Ca2+ applied to more mature zones indicated that the ion moved radially through the mature endodermis and exodermis. The permeability of the exodermal Casparian bands to Ca 2+ was tested by means of compartmental elution, and the results indicated that these wall modifications hindered apoplastic Ca 2+ transport. Since Ca2+ was translocated from the oldest root zone, but could not pass through the exodermis apoplastically, its uptake into the symplast was investigated. Results of experiments with a number of inhibitors led to the hypothesis that lanthanum-sensitive Ca 2+ channels in the plasma membranes of the cells at the root margin mediate Ca2+ uptake while, at the other end of the radial path, P-type Ca2+-ATPases load Ca2+ into the xylem. A new model of radial Ca2+ transport is proposed, in which Ca2+ enters the cytoplasm of the cells at peripheral layer, is then extruded into the walls of the central cortex, where its transport occurs by cation exchange reaction, crosses the endodermis via the symplastic pathway, and is actively delivered to the apoplast of the xylem.
机译：这项研究涉及洋葱根（Caium L.）中Ca2 +的运输途径。 Ca2 +是必不可少的大量营养素，必须以离子形式存在于土壤溶液中才能被植物根吸收。为了维持其生长，植物需要持续供应Ca2 +，因为Ca2 +不会从成熟器官重新分配到分生组织。 Ca 2+吸收和跨根运输的途径和机制之前尚未得到解决。由于细胞溶质中Ca2 +含量较低，因此共生途径可能不足以满足发育中芽的Ca2 +需求。然而，外胚层途径被内胚层和外胚层壁中疏水性物质（里海带）的沉积所阻碍。通常认为，Ca 2+通过进入根尖而沿木质部外生途径发生，其中内胚层和外胚层的壁修饰尚未形成。在本研究中，洋葱根被用作模型系统。这些根不具有任何可测量的质外性转运能力，这是通过从蒸腾流中排除8-羟基-1-3-6-吡咯烷酮（Pyrenetrisuphonate）（PTS）来确定的。将45Ca2 +直接施加到根的离散区域显示，施加到根尖的Ca2 +不会转移到芽上，排除了根尖作为该离子的进入点。此外，锑酸盐沉淀研究排除了通过气管元素成熟将Ca2 +传递到蒸腾流的可能性。将45Ca2 +应用于更成熟的区域表示离子沿径向移动通过了成熟的内胚层和外皮。通过隔室洗脱测试表皮Casparian带对Ca 2+的渗透性，结果表明这些壁修饰阻碍了质外性Ca 2+的运输。由于Ca2 +从最老的根部区域转移而来，但不能通过外胚层外生，因此研究了Ca2 +对共质体的吸收。使用多种抑制剂的实验结果得出这样的假设：在根边缘的细胞质膜中，镧敏感性Ca 2+通道介导Ca2 +的吸收，而在radial径路径的另一端，P型Ca2 +- ATPase将Ca2 +加载到木质部中。提出了一种新的径向Ca2 +转运模型，其中Ca2 +进入外周层细胞的细胞质，然后被挤出到中央皮层的壁中，通过阳离子交换反应进行转运，通过共生途径穿过内皮。 ，并被积极地输送到木质部的质外体。

著录项

  • 作者

    Cholewa, Ewa M.;

  • 作者单位

    University of Waterloo (Canada).;

  • 授予单位 University of Waterloo (Canada).;
  • 学科 Plant biology.
  • 学位 Ph.D.
  • 年度 2000
  • 页码 158 p.
  • 总页数 158
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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