Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
Ann Bot. 2011 May;107(6):953-64. doi: 10.1093/aob/mcr042. Epub 2011 Mar 8.
Imperforate tracheary elements (ITEs) in wood of vessel-bearing angiosperms may or may not transport water. Despite the significance of hydraulic transport for defining ITE types, the combination of cell structure with water transport visualization in planta has received little attention. This study provides a quantitative analysis of structural features associated with the conductive vs. non-conductive nature of ITEs.
Visualization of water transport was studied in 15 angiosperm species by dye injection and cryo-scanning electron microscopy. Structural features of ITEs were examined using light and electron microscopy.
ITEs connected to each other by pit pairs with complete pit membranes contributed to water transport, while cells showing pit membranes with perforations up to 2 µm were hydraulically not functional. A close relationship was found between pit diameter and pit density, with both characters significantly higher in conductive than in non-conductive cells. In species with both conductive and non-conductive ITEs, a larger diameter was characteristic of the conductive cells. Water transport showed no apparent relationship with the length of ITEs and vessel grouping.
The structure and density of pits between ITEs represent the main anatomical characters determining water transport. The pit membrane structure of ITEs provides a reliable, but practically challenging, criterion to determine their conductive status. It is suggested that the term tracheids should strictly be used for conductive ITEs, while fibre-tracheids and libriform fibres are non-conductive.
在具导管的被子植物木材中，不具穿孔的导管分子（ITE）可能具有或不具有输水功能。尽管水力传输对于定义 ITE 类型具有重要意义，但细胞结构与在植物体内的水分传输可视化的结合受到的关注较少。本研究对与 ITE 的导水性质相关的结构特征进行了定量分析。
通过染料注射和冷冻扫描电子显微镜对 15 种被子植物物种中的水分传输可视化进行了研究。使用光镜和电子显微镜检查了 ITE 的结构特征。
由具有完整穿孔膜的纹孔对连接的 ITE 有助于水分传输，而显示穿孔直径达 2 µm 的穿孔膜的细胞在水力上不起作用。发现纹孔直径和纹孔密度之间存在密切关系，这两个特征在导水细胞中明显高于非导水细胞。在具有导水和非导水 ITE 的物种中，导水细胞的直径较大。水分传输与 ITE 长度和导管群集之间没有明显的关系。
ITE 之间的纹孔结构和密度是决定水分传输的主要解剖学特征。ITE 纹孔膜结构提供了一个可靠的，但实际上具有挑战性的标准，用于确定它们的导水状态。建议将术语“导管分子”严格用于导水的 ITE，而将“纤维-导管分子”和“韧型纤维”用于非导水的 ITE。
