Ap. Singh et La. Donaldson, Ultrastructure of tracheid cell walls in radiate pine (Pinus radiata) mildcompression wood, CAN J BOTAN, 77(1), 1999, pp. 32-40
Citations number
38
Categorie Soggetti
Plant Sciences
Journal title
CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE
The structure of tracheid cell walls in mild compression wood of Pinus radi
ata D. Don was examined by confocal laser scanning fluorescence microscopy
(CLSM) and transmission electron microscopy (TEM). Fluorescence microscopy
using lignin autofluorescence revealed cell to cell variations in lignifica
tion of the cell corner middle lamella (CCML) and outer S2 (S2(L)) regions
supporting observations made at higher resolution with TEM. The mild compre
ssion wood sample examined lacked the characteristic intercellular spaces o
f most grades of compression wood and thus represents the least severe grad
e of compression wood. TEM observations revealed evidence for radial striat
ions in the 52 region probably representing regions of alternating high and
low lignin concentration, which may be the precursor to the helical caviti
es found in severe compression wood. These radial striations typically show
ed a sinuous and branched structure, extending partly into the S2(L) region
, where the orientation of lignin lamellae was predominantly tangential fol
lowing the arrangement of the cellulose microfibrils. At high magnification
lignin occurred in a patchy distribution overlaying the typical lamellate
arrangement associated with normal wood. Significant variability in the lig
nification of the CCML region was also observed sometimes giving a patchy o
r granular appearance. The lignification of the CCML and the S2(L) regions
was generally comparable, while S1 and S2 layers were less lignified. A res
idual S3 layer was sometimes present in the form of a very thin layer sligh
tly more lignified than the adjacent S2 layer.