Key Laboratory of Plant-Soil Interactions, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China.
Ann Bot. 2011 Apr;107(5):843-53. doi: 10.1093/aob/mcr005. Epub 2011 Feb 2.
The capacity of a plant to absorb and transport water and nutrients depends on anatomical structures within the roots and their co-ordination. However, most descriptions of root anatomical structure are limited to 2-D cross-sections, providing little information on 3-D spatial relationships and hardly anything on their temporal evolution. Three-dimensional reconstruction and visualization of root anatomical structures can illustrate spatial co-ordination among cells and tissues and provide new insights and understanding of the interrelation between structure and function.
Classical paraffin serial-section methods, image processing, computer-aided 3-D reconstruction and 3-D visualization techniques were combined to analyse spatial relationships among metaxylem vessels, passage cells and lateral roots in nodal roots of winter wheat (Triticum aestivum).
3-D reconstruction demonstrated that metaxylem vessels were neither parallel, nor did they run directly along the root axis from the root base to the root tip; rather they underwent substitution and transition. Most vessels were connected to pre-existent or newly formed vessels by pits on their lateral walls. The spatial distributions of both passage cells and lateral roots exhibited similar position-dependent patterns. In the transverse plane, the passage cells occurred opposite the poles of the protoxylem and the lateral roots opposite those of the protophloem. Along the axis of a young root segment, the passage cells were arranged in short and discontinuous longitudinal files, thus as the tissues mature, the sequence in which the passage cells lose their transport function is not basipetal. In older segments, passage cells decreased drastically in number and coexisted with lateral roots. The spatial distribution of lateral roots was similar to that of the passage cells, mirroring their similar functions as lateral pathways for water and nutrient transport to the stele.
With the 3-D reconstruction and visualization techniques developed here, the spatial relationships between vessels, passage cells and lateral roots and the temporal evolution of these relationships can be described. The technique helps to illustrate synchronization and spatial co-ordination among the root's radial and axial pathways for water and nutrient transport and the interdependence of structure and function in the root.
植物的吸水和养分运输能力取决于根部的解剖结构及其协调性。然而，大多数对根部解剖结构的描述仅限于 2-D 横切面，几乎没有提供关于 3-D 空间关系的信息，更不用说关于它们的时间演变的信息了。通过对根部解剖结构进行三维重建和可视化，可以说明细胞和组织之间的空间协调性，并为结构与功能之间的关系提供新的见解和理解。
本研究采用经典石蜡连续切片方法、图像处理、计算机辅助 3-D 重建和 3-D 可视化技术相结合，分析了冬小麦节点根中木质部导管、通道细胞和侧根之间的空间关系。
3-D 重建表明，木质部导管既不是平行的，也不是从根底部直接沿根轴延伸到根尖；而是发生了替代和转变。大多数导管通过侧壁上的纹孔与先前存在的或新形成的导管相连。通道细胞和侧根的空间分布都表现出相似的位置依赖性模式。在横切面上，通道细胞出现在原木质部的极点对面，而侧根出现在原韧皮部的极点对面。在一个年轻的根段轴上，通道细胞排列成短而不连续的纵向条纹，因此随着组织的成熟，通道细胞失去运输功能的顺序不是向基的。在较老的片段中，通道细胞数量急剧减少，并与侧根共存。侧根的空间分布与通道细胞相似，反映了它们作为侧向途径的相似功能，用于向中柱运输水和养分。
本研究采用的 3-D 重建和可视化技术可以描述导管、通道细胞和侧根之间的空间关系以及这些关系的时间演变。该技术有助于说明根的径向和轴向途径中水分和养分运输的同步性和空间协调性，以及根的结构和功能的相互依赖性。
