Microscopic evaluation of the cell wall in sugar maple chips after hot water treatment and fungal decay

Decay weight loss tests were performed with Acer saccharum wood chips to determine effects of hot water treatment and/or decay on fungal resistance. Light microscopy and scanning electron microscopy were used to observe changes in anatomical features of the cell wall of hard maple wood chips after extraction and/or fungal exposure, and immuno-gold labeling with transmission electron microscopy (IEM) was used to investigate the distribution of xylan and syringyl-lignin in the cell wall and the change of ultrastructural features in the wood cell wall after hot water extraction and/or fungal exposure.;Hot water treatments (140°, 160°, and 170°) had a positive effect on decay resistance, as indicated by lower weight loss, from exposure to Trametes versicolor and Ceriporiopsis subvermispora . However, an opposite effect, higher weight loss, was observed in hot water extracted-wood from exposure to Gloeophyllum trabeum and P. dimorphospora. Changes to wood chips after hot water treatment alone included color change from yellow to dark brown, and damage (erosion, voids) to the cell wall. Droplets were observed on cell lumens and through pits, on extracted wood chips, but not on unextracted controls. Xylan and syringyl-lignin were not detected on the droplets using IEM against low- or un-substituted xylan (LM10) and syringyl lignin antibodies.;In extracted, un-decayed chips, at higher treatment temperatures (160° and 170°C), the amount of labeling of the cell wall xylan (LM10) and syringyl-lignin was less than the controls (unextracted), while wood chips treated at 140°C exhibited greater labeling of xylan (LM10) than in unextracted controls. Labeled xylan (LM10) was not observed in cell corners (CC) or middle lamellae (ML). Gold labeled syringyl-lignin was found in the secondary cell walls of vessels, fibers, and rays as well as in CC and ML. In the wood chips treated at 160°C and subsequently degraded by P. dimorphospora, xylan was strongly detected in the cell wall of fibers, and syringyl-lignin was detected in fungal hyphae (by imaging internalized gold beads) indicating that the fungus was likely consuming syringyl lignin.