Abstract

Although there is considerable information on the chemistry of gelatinous (G) layers in tension wood (TW) fibers consisting of S-1+S-2+G cell wall structure (poplar), little is known on the chemistry of G-layers in TW fibers organized with S-1+G structure. This study investigated the distribution of lignin and noncellulosic polysaccharides in ash TW fibers (S-1+G) using histochemistry and immunolocalization methods. TW fibers studied were fully developed (mature fibers) and obtained from two (TW-1, TW-2) mature European ash trees (Fraxinus excelsior L.). Based on differences in microfibril angle (MFA) and TW trees used, TW fibers were mainly classified into three types; 1) Type-1 fibers with MFA almost parallel to the fiber axis that were found in TW-1, 2) Type-2 fibers with 12 degrees MFA that were abundant at the end of growth rings of TW-1 and 3) Type-3 fibers with 10 degrees MFA that were found in TW-2. The S-3 layer was absent in all TW fibers. In this study, the secondary cell wall structure of Type-1 and Type-2/Type-3 fibers were defined as G and GL (gelatinous-like) layers, respec-tively. Lignin with syringyl (S) units was detected in G/GL-layers, in which intensity and patterns of lignin staining likely related to the difference in MFA between G- and GL-layers. With hemicelluloses, heteroxylan and heteromannan epitopes were detected in G/GL-layers but these were much less abundant than those in S-2 layers of normal wood (NW) fibers. Like lignin, distribution patterns of heteromannan epitopes in G/GL-layers likely related to differences in MFA between fiber types. Sparse xyloglucan epitopes were also detected in G/GL-layers. Homogalacturonan epitopes were absent in G/GL-layers. All fiber types showed abundant a-1,5-arabinan epitopes in G/GL-layers. Overall results indicate that the chemistry of ash TW fibers studied differs significantly from that of other species reported previously, specifically TW fibers composed of S-1+S-2+G structure.

Keywords

Arabinan; gelatinous (G) layer; heteromannan; heteroxylan; lignin; microfibril angle (MFA); tension wood (TW)

Published in

IAWA Journal
2019, Volume: 40, number: 4, pages: 741-764

SLU Authors

• Daniel, Geoffrey

  • Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Wood Science
Forest Science
Botany


Publication identifier

DOI: https://doi.org/10.1163/22941932-40190252

Permanent link to this page (URI)

https://res.slu.se/id/publ/101071