Functional role of wood fibersin water transpor in vessel-bearing hardwoods

人们普遍认为，在导管类阔叶林中，木材纤维在木质部的长期进化过程中具有专门的植物体内机械支撑作用。到目前为止，还不清楚木纤维在多大程度上有助于维管束被子植物木质部的水分运输。在这项研究中，我们进行了酸性品红的染料注射实验，以检查不同类型的木材纤维的水分传输。此外，用扫描电子显微镜观察了导管分子与各类型木材纤维之间的共同壁上的凹坑的分布和结构。因此，特殊的木材纤维，如柳状纤维和活纤维，在水分运输中没有发挥任何功能作用，而较不专门的木材纤维，如纤维管胞和维管中心管胞，对水分运输有相当大的贡献。维管分子和不太特化的木材纤维之间的共同壁上通常存在凹坑对。相反，导管分子和特化的木材纤维之间的共同壁上没有凹坑对。在一些具有特殊纤维的物种中，在公共壁中没有凹陷。在其他具有特殊纤维的物种中，在公共墙的两侧都发现了盲坑。综上所述，细胞壁修饰的这种差异是木材纤维在水分运输中功能差异的原因。在这项研究的过程中，作为副产品获得了有趣的发现。在一些物种中，位于生长轮特定层的导管在成熟后不久同时空化，没有严重的水分胁迫，尽管周围的木纤维在其管腔中保持水分。这给树木生理学、木材科学和功能植物解剖学等领域的研究人员提出了新的问题。

It is widely accepted that in vessel-bearing hardwoods wood fibers have specialized in mechanical support of plant body during long-term xylem evolution. To date, it is unclear to what extent wood fibers may contribute to water transport in xylem of vessel-bearing angiosperm species. In this study we conducted dye-injection experiments using acid fuchsin in order to examine the water transport of various types of wood fibers. In addition, distribution and structure of pits were examined by scanning electron microscopy in common walls between vessel elements and each type of wood fibers. As a result, specialized wood fibers such as libriform fibers and living fibers did not play any functional role in water transport, while less specialized wood fibers such as fiber-tracheids and vasicentric tracheids considerably contribute to water transport. Pit pairs were commonly present in common walls between vessel elements and the less specialized wood fibers. In contrast, pit pairs were absent from common walls between vessel elements and the specialized wood fibers. In some species with specialized fibers, no pits were found in the common walls. In others species with specialized fibers, blind pits were found on either side of the common walls. In conclusion, such differences in cell wall modifications are responsible for the differences in the function of the wood fibers in water transport. During the course of this study, interesting findings were obtained as by-products. In some species, vessels that were located in a particular layer of growth ring were simultaneously cavitated soon after maturation without severe water stress despite the fact that surrounding wood fibers retained water in their lumina. This put a new problem to researchers in some fields of tree physiology, wood science and functional plant anatomy.