Research On Cell Wall Ultrastructure And Topochemistry Of Wood

With rapid social development, the tremendous exhaustion of natural resources has resulted in a high demand for renewable materials. Wood is an important renewable resource, which has made a significant contribution to the survival and development of human society in various fields, such as construction industry, furniture production and pulping and papermaking industry. However, the application of wood is influenced by its species, chemical composition and cell wall ultrastructure. Thereby, in this study, the anatomy, cell wall ultrastructure and topochemistry of hardwood and softwood were systematically discussed. The wood samples were investigated by SEM, TEM, FM and CRM.The main conclusions of this study were summarized as follows:(1) As shown by TEM images, the cell wall ultrastructure of hardwood and softwood is of some similarity, which can be typically divided into three lays:middle lamellar (ML), primary wall (P) and secondary wall (S1, S2and S3). However, the difference between hardwood and softwood is that the latewood tracheid cell walls of softwood are thicker than the fiber cell walls of hardwood.(2) As revealed by TEM, FM and CRM microscopic imaging techniques, the distribution of cellulose and lignin in cell wall layers is not uniform both in hardwood and softwood. Lignin concentration in different morphological areas follows the decreasing order:CCML> CML> S2. In contrast, cellulose distribution shows the opposite pattern-low concentration in CCML and CML and high in S2regions. However, by comparison with higher microfibril angle (MFA) detected in S2layers of hardwood, higher MFA was observed in S1layers of softwood.(3) As determined by CRM microscopic imaging approach, the topochemistry of normal and compression wood is of some difference. By comparison with normal wood, highly lignified outer S2layer (S2(L)) with smaller MFA, thicker S1layer and conspicuously reduced lignification in the middle lamella (ML) were the characteristics of compression wood. In addition, the distribution of coniferyl alcohol and coniferyl aldehyde was contrast with the lignin distribution both in normal and compression wood, which was enriched in SI and S2regions.