Comparison of Micropore Distribution in Cell Walls of Softwood and Hardwood Xylem

First author: Lloyd A. Donaldson; Affiliations: Scion (皇家研究院林业研究所): Rotorua, New Zealand

Corresponding author: Lloyd A. Donaldson

The porosity (多孔性) of wood cell walls is of interest for both understanding xylem functionality and from a wood materials perspective. The movement of water in xylem generally occurs through the macroporous networks (大孔网络) formed in softwood (软木) by bordered pits (具缘纹孔) and in hardwood (硬木) by the intervessel pits and open conduits (管道) created by vessels (导管) and perforation plates (穿孔板). In some situations, such as cavitated xylem (空腔木质部), water can only move through the micropores (微孔) that occur in lignified tracheid (木质化管胞) and fiber cell walls (纤维细胞壁); however, these micropore networks are poorly understood. Here, we used molecular microscopy (分子显微分析) analysis of radiata pine (Pinus radiataD. Don; 辐射松) and red beech (Nothofagus fuscaHook.f.; 红山毛榉) to determine the distribution of micropores in the secondary walls and middle lamellae of tracheids (管胞间层) and fibres in relation to cell wall composition. Using two different types of probe, we identified a greater porosity of secondary cell walls and a reduced porosity of the middle lamella. Areas of reduced porosity were observed in the outer regions of the secondary cell wall of both tracheids and fibres that appear unrelated to lignification or the distribution of cellulose, mannan (甘露聚糖), and xylan (木聚糖). Hardwood fibre cell walls were less lignified than those of softwood tracheids and showed greater accessibility to porosity probes. Vessel cell walls were comparable to those of fibres in terms of both porosity and lignification. Lignification is probably the primary determinant of cell wall porosity in xylem. The highly lignified middle lamella, and lumen surface (腔面), act as a barrier to probe movement and therefore water movement in both softwood and hardwood.

木材细胞壁的多孔性是理解木质部功能及木材材性的重要特征。水分在木质部的运输通常是在软木的具缘纹孔、硬木导管间隙及由导管和穿孔板形成的开放管道组成的大孔网络。在一些情况下，比如空腔木质部中，水分只能通过木质化管胞和纤维细胞壁上形成的微孔来运输，然而对于这些微孔网络的认知还很浅显。本文通过对辐射松和红山毛榉的分子显微分析研究微孔在次生细胞壁、管胞间层及与细胞壁组成相关纤维中的分布。利用两种不同类型的探针，作者鉴定到了在次生细胞壁中多孔性较强，而管胞间层多孔性较弱。在管胞和纤维外层与木质化或纤维素、甘露聚糖和木聚糖不相关的次生细胞壁多孔性较弱。相比于软木的管胞，硬木纤维细胞壁木质化程度更低，因此更加利于多孔性探针的通过。导管细胞壁在多孔性和木质化程度上与这些纤维相当。木质化可能是木质部中细胞壁多孔性的主要决定因素。高度木质化的管胞间层和空腔表面是探针移动的屏障，因此也是软木和硬木中水分流动的屏障。

通讯：Lloyd A. Donaldson（https://www.scionresearch.com/about-us/about-scion/our-people/people/m-and-b/lloyd-donaldson）

个人简介：1980年，奥克兰大学，植物学学士；1986年，坎特伯雷大学，植物学硕士；2002年，坎特伯雷大学，木材科学博士。

研究方向：松针与叶面疾病间的相关解析；不同针叶树种球果和芽发育与基因表达的关系；细胞壁孔隙度相关的木材荧光光谱；转化组织/植物的显微表型评估；生物材料显微术；光镜与电镜；数字图像处理与分析；木材鉴定。

doi: https://doi.org/10.1104/pp.18.00883

Journal: Plant Physiology

First Published: 14 September, 2018

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