S. Khalili et al., The use of soft rot fungi for determining the microfibrillar orientation in the S2 layer of pine tracheids, HOLZ ROH WE, 58(6), 2001, pp. 439-447
Soft rot cavities were induced in Scots pine (Pinus sylvestris) wood, and t
heir orientation measured in relation to the longitudinal axis of tracheids
in order to obtain information on the orientation of the cellulose microfi
brils in wood cell walls. All observations supported the view that cavities
are aligned along the microfibrils. Observations at low magnification of a
large number of tracheids in radial section or on a large number of trache
ids from the same annual ring suggested that most cavities were oriented at
a similar angle to the tracheid axis. More detailed observations at higher
magnification revealed, however, that there was a considerable variation w
ithin the S2 layer, particularly in earlywood tracheids. Cavities in cell c
orners of earlywood tracheids were often oriented parallel to the longitudi
nal axis of the tracheids. The majority of the cavities in the S2 spiralled
in a Z-helical arrangement, but S-helices were also occasionally observed.
Cavities observed in pit free areas of tracheids were often oriented at di
fferent angles to the tracheid axis and sometimes even crossed one another.
Observations suggest that there is a large variation in microfibril orient
ation even within one tracheid. The orientation of cavities was also used f
or measuring microfibril orientation in two cross-sections cut from differe
nt heights of a pine tree. The mean values for the microfibril angle of ear
lywood tracheids at both heights were smaller in the tangential than radial
walls. The microfibril angle decreased from pith to the bark in both of th
e cross-sections.