Origin of unusual behaviors of the tension wood cell wall and its biomechanical functions

在本研究中，研究了与凝胶层（g层）形成有关的张力木纤维异常行为和生物力学功能的机制。首先，用数学方法描述了分离TW纤维在一定生物力学状态变化下的变形过程。同时，对一株70年树龄槭（Acer sieboldianum Miq）的张力木（TW）特性进行了研究。采用g纤维模型进行分析。在g纤维模型模拟的基础上，讨论了g层对TW木质部(1)高拉伸生长应力、(2)大纵向杨氏模量和(3)高纵向干燥收缩率的影响。接下来，研究了含有凝胶层（g层）的张力木材的异常湿力学性能的机制，包括29年树龄的Keyaki （Zelkova serrata）的斜直立枝和75年树龄和40年树龄的Kunugi oak （Quercus acutissima）的倾斜茎。结果表明，在绿色状态下，g层中的多糖基质表现为水膨胀凝胶；然而，在水分解吸过程中，它被强烈的表面张力转化为冷凝和硬包装结构，这是一种干湿凝胶的形式。然而，在l层中，疏水性木质素通过机械强化基质，阻止了多糖基质的缩合和随后的干湿凝胶化。

In the present study, the mechanism responsible for unusual behaviors and biomechanical functions of tension wood fiber was investigated in relation to the formation of the gelatinous layer (G-layer) .First, the deformation process of an isolated TW fiber caused by a certain biomechanical state change was formulated mathematically. And, the tension wood (TW) properties from a 70-year-old-specimen of Acer sieboldianum Miq. were analyzed by using the G-fiber model. The roles of the G-layer on the origins of (1) a high tensile growth stress, (2) a large longitudinal Young's modulus, and (3) a high longitudinal drying shrinkage in the TW xylem were discussed on the basis of the simulations using the G-fiber model.Next, the mechanism responsible for unusual hygro-mechanical properties of tension wood containing the gelatinous layer (G-layer) was investigated for the oblique upright branch of a 29-year-old Keyaki (Zelkova serrata) and the leaning stems of a 75 and a 40-year-old Kunugi oak (Quercus acutissima) trees. The result suggests that in the green state, the polysaccharide matrix in the G-layer behaves as a water-swollen gel ; however, it is transformed into a condensed and hard-packed structure by strong surface tension during moisture desorption, which is a form of xero-gelation. However, in the L-layer, condensation and subsequent xero-gelation of the polysaccharide matrix was prevented by the hydrophobic lignin that mechanically reinforces the matrix.