T. Awano et al., Deposition of glucuronoxylans on the secondary cell wall of Japanese beechas observed by immune-scanning electron microscopy, PROTOPLASMA, 212(1-2), 2000, pp. 72-79
Glucuronoxylans (GXs), the main hemicellulosic component of hardwoods, are
localized exclusively in the secondary wall of Japanese beech and gradually
increase during the course of fiber differentiation. To reveal where GXs d
eposit within secondary wall and how they affect cell wall ultrastructure,
immune-scanning electron microscopy using anti-GXs antiserum was applied in
this study. In fibers forming the outer layer of the secondary wall (S-1),
cellulose fibrils were small in diameter and deposited sparsely on the inn
er surface of the cell wall. Fine fibrils with approximately 5 nm width agg
regated and formed thick fibrils with 12 nm width. Some of these thick fibr
ils further aggregated to form bundles which labelled positively for GXs. I
n fibers forming the middle layer of the secondary wall (S-2), fibrils were
thicker than those found in S-1 forming fibers and were densely deposited.
The S-2 layer labelled intensely for GXs with no preferential distribution
recognized. Compared with newly formed secondary walls, previously formed
secondary walls were composed of thick and highly packed microfibrils. Labe
ls against GXs were much more prevalent on mature secondary walls than on n
ewly deposited secondary walls. This result implies that the deposition of
GXs into the cell wall may occur continuously after cellulose microfibril d
eposition and may be responsible for the increase in diameter of the microf
ibrils.