Visualization of higher structures of lignin by TOF-SIMS

木质素在植物细胞壁中的分布在浓度和结构上都是不均匀的，甚至在同一植物中也是如此，这取决于细胞类型和细胞壁的定位。因此，需要在形态和分子水平上对木质素进行进一步的研究。利用显微研究观察了细胞壁中完整木质素的化学结构。例如，结合木质部细胞溴化的扫描电子显微镜或透射电子显微镜的EDXA，选择性标记木质素2-5特定结构的显微放射自显影，以及UV/VTS显微光谱已被用于这一目的。这些技术提供了高分辨率的形态信息，但详细的化学信息有限。最近，各种免疫标记木质素的定位被报道，为在现场超微结构水平上的这些结构的化学分析提供了新的方向。飞行时间二次离子质谱仪(TOF-SIMS)是一种方便的提供固体样品表面化学信息的技术。利用质谱图和二次离子图可以确定样品表面成分的组成和分布。在本研究中，TOF-SIMS应用于木材细胞壁的非降解分析。用飞行时间质谱仪(TOF-SIMS)研究了树木木质部木质素的结构。在TOF-SIMS分析中，松木和山毛榉磨木素(MWL)产生了一些含有愈创木基核或丁香基核的二次离子。用苯丙氨酸-d7处理木兰木质部，在木质部表面产生了一幅显示重离子标记的图像。这些结果表明，TOF-SIMS分析方法适用于无定形生物聚合物木质素，因此可用于木材和纸浆质量的方便评估。该方法可进一步应用于木质素等生物聚合物的生物合成研究。

Lignin in plant cell walls is distributed heterogeneously, both in concentration and structure, even in the same plant, depending upon the cell type and cell wall localization. Further studies of lignin both at the morphological and molecular levels are therefore required. Microscopic studies have been utilized to observe the chemical structure of intact lignin in cell walls. For example, SEM- or TEM-EDXA, with the combination of bromination of xylem cells, microautoradiography with selective radiolabeling of specific structures of lignin2-5) and UV/VTS microspectroscopies have been used for this purpose. These techniques provide high-resolution morphological information ; however detailed chemical information is limited. Recently, the localization of various immunolabeled lignins was reported, showing a new direction for the chemical analysis of these structures at the ultrastructural level in situ.TOF-SIMS (time-of-flight secondary ion mass spectrometry) is a convenient technique providing chemical information on solid sample surfaces. The mass spectrum and secondary ion images can be used to determine the composition and distribution of the sample surface constituents.In this study, TOF-SIMS is applied to the non-degradative analysis of wood cell walls. The structure of tree xylem ligfiin was investigated by TOF-SIMS. On TOF-SIMS analysis, pine and beech milled wood lignins (MWLs) produced some secondary ions containing guaiacyl or syringyl nuclei. Magnolia xylem, fed with phenylalanine-d7, produced an image showing the localization of thedeuterium-label on the xylem surface.These results indicate that TOF-SIMS analysis is applicable to the amorphous biopolymer lignin, and is therefore useful for convenient estimations of wood and pulp quality. This method can be further applied to the study of the biosynthesis of biopolymers such as lignin.