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

在长时间的木质部演化过程中，木管硬木的木质纤维专门为植物体提供机械支撑。到目前为止，还不清楚木材纤维在多大程度上参与了血管被子植物木质部的水分运输。在这项研究中，我们进行了染料注射实验，使用酸性品红来研究不同类型的木材纤维的水分运输。此外，通过扫描电子显微镜检查了容器元件和每种木纤维之间的共同壁的凹坑分布和结构。因此，libriform纤维和活纤维等特化木纤维在水分运输中没有发挥任何功能作用，而纤维管胞和vasicentric管胞等非特化木纤维对水分运输有很大贡献。坑对通常存在于容器元件和不太专门化的木纤维之间的共同壁上。相比之下，在容器元件和专门的木纤维之间的普通壁上没有坑对。在一些具有特殊纤维的物种中，在共同壁上没有发现凹坑。在其他具有特殊纤维的物种中，在共同壁的两侧发现了盲坑。总之，这种细胞壁修饰的差异导致了木纤维在水运输中的功能差异。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，位于生长环特定层的血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腔内保留了水分。这给树木生理学、木材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.