Visualization of higher structures of lignin by TOF-SIMS

点击翻译按钮获取中文摘要

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.