Ultrastructural Localization of Hemicellulose in Birch Wood (Betula papyrifera) Decayed by Brown and White Rot Fungi

Hemicellulose within cells of birch wood (Betula papyrifera) was determined using periodic acid — thio-carbohydrazide-silver proteinate (PATAg) coupled with energy dispersive X-ray microanalyses — Scanning Transmission Electron Microscopy (EDXA-STEM). Counts of Ag-L electrons, indicating sites of hemicellulose, were obtained from all cell wall layers of sound wood. Increased concentrations of hemicellulose were found in middle lamellae and inner regions of the secondary walls. Wood decayed by white rot fungi had two patterns of hemicellulose degradation. Coriolus versicolor degraded hemicellulose in the wall from the lumen toward the middle lamella, whereas Phlebia tremellosus and Phellinus pini caused extensive loss of hemicellulose throughout the entire cell wall. The brown rot fungus, Fomitopsis pinicola also degraded extensive amounts of hemicellulose throughout cells and greater losses were observed in the middle lamellae than in secondary walls. Electron density observed in micrographs was found not to be a reliable method of detecting hemicellulose due to other reactions that caused cell walls to darken. The PATAg method coupled with EDXA-STEM, however, provided a precise determination of hemicellulose distribution in sound and decayed wood.