Institute for Building Materials (IfB), ETH Zurich, 8093, Zurich, Switzerland.
Institute for Biophysics, University of Natural Resources and Life Sciences Vienna, 1190, Vienna, Austria.
Planta. 2018 Apr;247(4):887-897. doi: 10.1007/s00425-017-2828-z. Epub 2017 Dec 21.
CAD-deficient poplars enabled studying the influence of altered lignin composition on mechanical properties. Severe alterations in lignin composition did not influence the mechanical properties. Wood represents a hierarchical fiber-composite material with excellent mechanical properties. Despite its wide use and versatility, its mechanical behavior has not been entirely understood. It has especially been challenging to unravel the mechanical function of the cell wall matrix. Lignin engineering has been a useful tool to increase the knowledge on the mechanical function of lignin as it allows for modifications of lignin content and composition and the subsequent studying of the mechanical properties of these transgenics. Hereby, in most cases, both lignin composition and content are altered and the specific influence of lignin composition has hardly been revealed. Here, we have performed a comprehensive micromechanical, structural, and spectroscopic analysis on xylem strips of transgenic poplar plants, which are downregulated for cinnamyl alcohol dehydrogenase (CAD) by a hairpin-RNA-mediated silencing approach. All parameters were evaluated on the same samples. Raman microscopy revealed that the lignin of the hpCAD poplars was significantly enriched in aldehydes and reduced in the (relative) amount of G-units. FTIR spectra indicated pronounced changes in lignin composition, whereas lignin content was not significantly changed between WT and the hpCAD poplars. Microfibril angles were in the range of 18°-24° and were not significantly different between WT and transgenics. No significant changes were observed in mechanical properties, such as tensile stiffness, ultimate stress, and yield stress. The specific findings on hpCAD poplar allowed studying the specific influence of lignin composition on mechanics. It can be concluded that the changes in lignin composition in hpCAD poplars did not affect the micromechanical tensile properties.
缺乏 CAD 的杨树使研究改变木质素组成对机械性能的影响成为可能。木质素组成的严重改变并不影响机械性能。木材是一种具有优异机械性能的层次纤维复合材料。尽管它用途广泛，但它的机械行为尚未完全被理解。尤其是细胞壁基质的机械功能一直难以解开。木质素工程一直是增加对木质素机械功能的认识的有用工具，因为它允许改变木质素的含量和组成，并随后研究这些转基因的机械性能。在这里，在大多数情况下，木质素的组成和含量都发生了改变，并且木质素组成的特定影响几乎没有被揭示出来。在这里，我们对通过发夹 RNA 介导的沉默方法下调肉桂醇脱氢酶 (CAD) 的转基因杨树木质部条进行了全面的微观力学、结构和光谱分析。所有参数都在相同的样品上进行了评估。拉曼显微镜显示，hpCAD 杨树的木质素醛基含量显著增加，G 单元的含量相对减少。FTIR 光谱表明木质素组成发生了明显变化，而 WT 和 hpCAD 杨树之间的木质素含量没有显著变化。微纤维角在 18°-24°之间，WT 和转基因之间没有显著差异。在拉伸刚度、极限应力和屈服应力等机械性能方面没有观察到显著变化。在 hpCAD 杨树中发现的特定结果允许研究木质素组成对力学的特定影响。可以得出结论，hpCAD 杨树中木质素组成的变化不会影响微力学拉伸性能。
