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Abstract：
Lignin engineering is a promising tool to reduce the energy input and the need of chemical pre-treatments for the efficient conversion of plant biomass into fermentable sugars for downstream applications. At the same time, lignin engineering can offer new insight into the structure-function relationships of plant cell walls by combined mechanical, structural and chemical analyses. Here, this comprehensive approach was applied to poplar trees (Populus tremula × Populus alba) downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD) in order to gain insight into the impact of lignin reduction on mechanical properties. The downregulation of CAD resulted in a significant decrease in both elastic modulus and yield stress. As wood density and cellulose microfibril angle (MFA) did not show any significant differences between the wild type and the transgenic lines, these structural features could be excluded as influencing factors. Fourier transform infrared spectroscopy (FTIR) and Raman imaging were performed to elucidate changes in the chemical composition directly on the mechanically tested tissue sections. Lignin content was identified as a mechanically relevant factor, as a correlation with a coefficient of determination (r²) of 0.65 between lignin absorbance (as an indicator of lignin content) and tensile stiffness was found. A comparison of the present results with those of previous investigations shows that the mechanical impact of lignin alteration under tensile stress depends on certain structural conditions, such as a high cellulose MFA, which emphasizes the complex relationship between the chemistry and mechanical properties in plant cell walls.
摘要：
木质素工程是一种有前途的工具，可以减少能量输入和化学预处理的需求，以将植物生物质有效转化为可发酵糖，用于下游应用。同时,木质素工程可以通过联合机械，为植物细胞壁的结构-功能关系提供新的见解，结构和化学分析。这里,这种综合方法被应用于杨树（Populustremula×Populusalba）下调了CINNAM醇脱氢酶（CAD），以深入了解木质素减少对机械性能的影响。CAD的下调导致弹性模量和屈服应力均显着降低。由于野生型和转基因系之间的木材密度和纤维素微纤丝角（MFA）没有显示出任何显着差异，这些结构特征可以排除为影响因素。进行傅里叶变换红外光谱(FTIR)和拉曼成像以直接在机械测试的组织切片上阐明化学组成的变化。木质素含量被确定为机械相关因素，发现木质素吸光度（作为木质素含量的指标）和拉伸刚度之间的决定系数（r²）为0.65。将当前结果与先前研究的结果进行比较表明，在拉伸应力下木质素改变的机械影响取决于某些结构条件，如高纤维素MFA，强调了植物细胞壁中化学和机械性能之间的复杂关系。
