The use of soft rot fungi for determining the microfibrillar orientation in the S2 layer of pine tracheids

anglais. Soft rot cavities were induced in Scots pine (Pinus sylvestris) wood, and their orientation measured in relation to the longitudinal axis of tracheids in order to obtain information on the orientation of the cellulose microfibrilsin 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 tracheids 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 within the S2 layer, particularly in earlywood tracheids. Cavities in cell corners of earlywood tracheids were often oriented parallel to the longitudinal 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 different angles to the tracheid axis and sometimes even crossed one another. Observations suggest that there is a large variation in microfibril orientation even within one tracheid. The orientation of cavities was also used for measuring microfibril orientation in two cross-sections cut from different heights of a pine tree. The mean values for the microfibril angle of earlywood tracheids at both heights were smaller in the tangential than radial walls. The microfibril angle decreased from pith to the bark in both of the cross-sections.

allemand. Mit Hilfe von Moderfaeulepilzen wurden Aushoehlungen in Kieferntracheiden induziert. Die Ausrichtung zur Laengsachse der Tracheiden liefert Informationen ueber die Orientierung der Cellulosefibrillen in der Holzzellwand. Alle Beobachtungen unterstuetzen die Ansicht, dass diese Aushoehlungen an den Mikrofibrillen ausgerichtet sind. Zahlreiche mikroskopische Beobachtungen an Radialschnitten vom selben Jahrring zeigen, dass die meisten Aushoehlungen in etwa gleichen Winkeln zur Tracheiden-Laengsachse verlaufen. Bei hoeherer Vergroesserung zeigten sich jedoch betraechtliche Variationen innerhalb der S2, insbesondere im Fruehholz. In den Zellecken liegen die Aushoehlungen oft parallel zur Laengsachse. Die meisten Aushoehlungen in der S2 bilden eine Z-Helix, aber auch S-Helices kommen vor. In tuepfelfreien Bereichen waren die Aushoehlungen oefters in verschiedenen Richtungen orientiert, manchmal kreuzten sie sich sogar, d.h. dass innerhalb einer Tracheide die Fibrillenrichtung in grossem Ausmass variiert. Diese Messungen wurden an Proben von verschiedenen Stammhoehen durchgefuehrt. Im Mittel sind die Winkel der Mikrofibrillen in A geringer als in Radialwaenden des Fruehholzes. Vom Mark zur Rinde hin nehmen die Fibrillenwinkel in beiden Waendenab.