Occurrence of xylan and mannan polysaccharides and their spatial relationship with other cell wall components in differentiating compression wood tracheids of Cryptomeria japonica

摘要

Compression wood (CW) tracheids have different cell wall components than normal wood (NW) tracheids. However, temporal and spatial information on cell wall components in CW tracheids is poorly understood. We investigated the distribution of arabino-4-O-methylglucuronoxylans (AGXs) and O-acetyl-galactoglucomannans (GGMs) in differentiating CW tracheids. AGX labeling began to be detected in the corner of the S_1 layer at the early S1 formation stage. Subsequently, the cell corner middle lamella (ccML) showed strong AGX labeling when intercellular spaces were not fully formed. AGX labeling was uniformly distributed in the S1 layer, but showed uneven distribution in the S_2 layer. AGX labeling was mainly detected in the inner S_2 layer after the beginning of the helical cavity formation. The outer S_2 layer showed almost no labeling of low substituted AGXs. Only a very small amount of high substituted AGXs was distributed in the outer S_2 layer. These patterns of AGX labeling in the S_2 layer opposed the lignin and β-1-4-galactan distribution in CW tracheids. GGM labeling patterns were almost identical to AGX labeling in the early stages of CW tracheids, and GGM labeling was detected in the entire S_2 layer from the early S_2 formation stage of CW tracheids with some spatial differences in labeling density depending on developmental stage. Compared with NW tracheids, CW tracheids showed significantly different AGX distributions in the secondary cell wall but similar GGM labeling patterns. No significant differences were observed in labeling after delignification of CW tracheids.