POSSIBLE APPROACHES FOR STUDYING THREE DIMENSIONAL STRUCTURE OF LIGNIN

摘要

Information on three dimensional structure of lignin in the cell walls is essential for better understanding of chemical and biological properties of wood. An advanced structural model should provide following information on structural heterogeneities and macromolecular properties of lignin in the cell walls, (1) distribution and frequencies of different kinds of C_9 units, inter-unit bonds including stereochemistry, functional groups, lignin-polysaccharide bonds within a lignin macromolecule and within the cell walls; (2) higher order structure and size of lignin macromolecule; and (3) assembly of lignin and polysaccharides in different morphological regions of cell walls and in different kinds of cells. An effective approach is nondestructive observation of growing process of lignin macromolecule during formation of cell wall from an early stage to a last stage. Nondestructive observation of lignin formation process and its structural analysis were carried out by radio-and stable isotope tracer techniques combined with light microscopy and nuclear magnetic resonance spectroscopy. Combination of mild degradation analyses with nondestructive analysis is also effective approach. A 3D model can be proposed tentatively based on the information on (1～3) obtained by the nondestructive analyses and the information obtained by electron microscopy and other various destructive analyses. For further revision of the model, more improvements of the approaches to obtain more reliable information on (1～3) are required.