Abstract

Little is known about the decay pattern of bamboo by wood decay fungi, and the information available on fungal degradation of wood from other plant taxa cannot form the basis for understanding wood decay in bamboo because of differences in lignin composition and distribution. The present work was undertaken to elucidate the degradation pattern of bamboo by a lignin-degrading white rot fungus Lentinus edodes using various microscopic techniques, with a particular focus on the relation of bamboo lignin composition to the decay patterns produced by this fungus. Small blocks of bamboo, Phyllostachys pubescens, were examined after 16 weeks of incubation with the white rot fungus L. edodes. The compound middle lamellae (CML), including the cell corner regions, were preferentially degraded at an early stage of decay, whereas the fiber secondary walls remained largely intact at this point. Bamboo fiber walls were also eroded from the cell lumen side but the extent of degradation was limited. The FT-IR bands assigned to lignin exhibited a significant decrease. Cellular ultraviolet microspectrophotometric investigation showed that CML and vessel walls were composed of not only guaiacyl and syringyl unit (GS lignin) but also grass lignin. In contrast, the secondary wall of fibers consisted mainly of the GS lignin. Even though the CML and vessel walls exhibited higher lignin concentration, these cell walls were nevertheless degraded. The preferential degradation of the CML over the fiber secondary walls strongly suggested the involvement of not only enzyme systems of the white rot fungus but also a relationship to physicochemical properties of bamboo cell walls, particularly the influence of lignin composition and distribution.