Rencoret Jorge, Gutiérrez Ana, Nieto Lidia, Jiménez-Barbero J, Faulds Craig B, Kim Hoon, Ralph John, Martínez Angel T, Del Río José C
Instituto de Recursos Naturales y Agrobiología de Sevilla, Consejo Superior de Investigaciones Científicas, E-41080 Seville, Spain.
Plant Physiol. 2011 Feb;155(2):667-82. doi: 10.1104/pp.110.167254. Epub 2010 Nov 23.
Lignin changes during plant growth were investigated in a selected Eucalyptus globulus clone. The lignin composition and structure were studied in situ by a new procedure enabling the acquisition of two-dimensional nuclear magnetic resonance (2D-NMR) spectra on wood gels formed in the NMR tube as well as by analytical pyrolysis-gas chromatography-mass spectrometry. In addition, milled-wood lignins were isolated and analyzed by 2D-NMR, pyrolysis-gas chromatography-mass spectrometry, and thioacidolysis. The data indicated that p-hydroxyphenyl and guaiacyl units are deposited at the earlier stages, whereas the woods are enriched in syringyl (S) lignin during late lignification. Wood 2D-NMR showed that β-O-4' and resinol linkages were predominant in the eucalypt lignin, whereas other substructures were present in much lower amounts. Interestingly, open β-1' structures could be detected in the isolated lignins. Phenylcoumarans and cinnamyl end groups were depleted with age, spirodienone abundance increased, and the main substructures (β-O-4' and resinols) were scarcely modified. Thioacidolysis revealed a higher predominance of S units in the ether-linked lignin than in the total lignin and, in agreement with NMR, also indicated that resinols are the most important nonether linkages. Dimer analysis showed that most of the resinol-type structures comprised two S units (syringaresinol), the crossed guaiacyl-S resinol appearing as a minor substructure and pinoresinol being totally absent. Changes in hemicelluloses were also shown by the 2D-NMR spectra of the wood gels without polysaccharide isolation. These include decreases of methyl galacturonosyl, arabinosyl, and galactosyl (anomeric) signals, assigned to pectin and related neutral polysaccharides, and increases of xylosyl (which are approximately 50% acetylated) and 4-O-methylglucuronosyl signals.
在一个选定的蓝桉无性系中研究了植物生长过程中的木质素变化。通过一种新方法对木质素的组成和结构进行了原位研究，该方法能够在核磁共振管中形成的木材凝胶上采集二维核磁共振（2D-NMR）光谱，并结合分析热解-气相色谱-质谱联用技术。此外，分离出磨木木素，并通过二维核磁共振、热解-气相色谱-质谱联用和硫代酸解进行分析。数据表明，对羟基苯基和愈创木基单元在早期阶段沉积，而在木质化后期木材中紫丁香基（S）木质素含量增加。木材二维核磁共振显示，β-O-4'和树脂醇键在桉树木质素中占主导地位，而其他亚结构的含量则低得多。有趣的是，在分离出的木质素中可以检测到开放的β-1'结构。随着年龄的增长，苯基香豆素和肉桂基端基减少，螺二烯酮丰度增加，主要亚结构（β-O-4'和树脂醇）几乎没有变化。硫代酸解表明，醚键连接的木质素中S单元的优势高于总木质素，并且与核磁共振结果一致，也表明树脂醇是最重要的非醚键连接。二聚体分析表明，大多数树脂醇型结构由两个S单元（丁香树脂醇）组成，交叉的愈创木基-S树脂醇作为次要亚结构出现，而松脂醇完全不存在。未分离多糖的木材凝胶的二维核磁共振光谱也显示了半纤维素的变化。这些变化包括与果胶和相关中性多糖相关的甲基半乳糖醛酸基、阿拉伯糖基和半乳糖基（异头物）信号的减少，以及木糖基（约50%被乙酰化）和4-O-甲基葡萄糖醛酸基信号的增加。
