Immunolocalization and structural variations of xylan in differentiating earlywood tracheid cell walls of Cryptomeria japonica

Abstract

We investigated the spatial and temporal distribution of xylans in the cell walls of differentiating earlywood tracheids of Cryptomeria japonica using two different types of monoclonal antibodies (LM10 and LM11) combined with immunomicroscopy. Xylans were first deposited in the corner of the S(1) layer in the early stages of S(1) formation in tracheids. Cell corner middle lamella also showed strong xylan labeling from the early stage of cell wall formation. During secondary cell wall formation, the innermost layer and the boundary between the S(1) and S(2) layers (S(1)/S(2) region) showed weaker labeling than other parts of the cell wall. However, mature tracheids had an almost uniform distribution of xylans throughout the entire cell wall. Xylan localization labeled with LM10 antibody was stronger in the outer S(2) layer than in the inner layer, whereas xylans labeled with LM11 antibody were almost uniformly distributed in the S(2) layer. In addition, the LM10 antibody showed almost no xylan labeling in the S(1)/S(2) region, whereas the LM11 antibody revealed strong xylan labeling in the S(1)/S(2) region. These findings suggest that structurally different types of xylans may be deposited in the tracheid cell wall depending on the developmental stage of, or location in, the cell wall. Our study also indicates that deposition of xylans in the early stages of tracheid cell wall formation may be spatially consistent with the early stage of lignin deposition in the tracheid cell wall.

Localization of Cell Wall Polysaccharides in Normal and Compression Wood of Radiata Pine: Relationships with Lignification and Microfibril Orientation

“…The idea that polysaccharides, especially galactan, are in some way involved in controlling lignification has recently been extended to include mannans and xylans (Kim et al, 2010b(Kim et al, , 2010c(Kim et al, , 2011. These polysaccharides are known to form chemical bonds with lignin to form lignin-carbohydrate complexes (Tenkanen et al, 1999;Lawoko et al, 2005;Barakat et al, 2007), and since hemicelluloses are deposited prior to or concurrently with lignin (Kim et al, 2010a(Kim et al, , 2010b(Kim et al, , 2010c(Kim et al, , 2011, the possibility that they influence lignin deposition seems reasonable.…”

“…These polysaccharides are known to form chemical bonds with lignin to form lignin-carbohydrate complexes (Tenkanen et al, 1999;Lawoko et al, 2005;Barakat et al, 2007), and since hemicelluloses are deposited prior to or concurrently with lignin (Kim et al, 2010a(Kim et al, , 2010b(Kim et al, , 2010c(Kim et al, , 2011, the possibility that they influence lignin deposition seems reasonable. This study extends these earlier results by definitively colocalizing lignin and polysaccharides on the same field of view and measuring their association by image analysis.…”

“…Based on the developmental studies of Kim et al (2010aKim et al ( , 2010bKim et al ( , 2010cKim et al ( , 2011, deposition of mannan and xylan in the S1 region precedes the initial lignification of compression wood. These polysaccharides may thus act jointly as a barrier to infiltration of monolignols into the middle lamella region, resulting in the reduced lignification of the outer wall, typical of both mild and severe forms of compression wood.…”

“…In the inner S2 region, a subsequent increase in mannan/ xylan, and reduction in galactan, is associated with decreased lignification. Further studies are needed to quantify porosity changes during cell wall development to study lignin/polysaccharide/enzyme (peroxidase/ laccase) localization during this process and to differentiate infiltrative and surface deposition of polysaccharides (Maeda et al, 2000;Hosoo et al, 2006;Kim et al, 2010bKim et al, , 2010c.…”

“…Glucuronoxylans are the main constituents of hardwood hemicellulose but are less abundant components of softwood cell walls (Timell, 1967;Nanayakkara et al, 2009;Kim et al, 2010c). Altaner et al (2010) have examined the distribution of heteroxylans in radiata pine (Pinus radiata) by immunoelectron microscopy showing unsubstituted xylans (LM10) in the S1 and S3 layers and more highly substituted xylans (LM11) across all areas of the cell wall except the primary wall.…”