A Cytochemical Study of Extracellular Sheaths Associated with Rigidoporus lignosus during Wood Decay

Abstract

An ultrastructural and cytochemical investigation of the development of Rigidoporus lignosus, a white-rot fungus inoculated into wood blocks, was carried out to gain better insight into the structure and role of the extracellular sheaths produced by this fungus during wood degradation. Fungal sheaths had a dense or loose fibrillar appearance and were differentiated from the fungal cell wall early after wood inoculation. Close association between extracellular fibrils and wood cell walls was observed at both early and advanced stages of wood alteration. Fungal sheaths were often seen deep in host cell walls, sometimes enclosing residual wood fragments. Specific gold probes were used to investigate the chemical nature of R. lignosus sheaths. While labeling of chitin, pectin, 13-1,4and 13-1,3-glucans, 13-glucosides, galactosamine, mannose, sialic acid, RNA, fucose, and fimbrial proteins over fungal sheaths did not succeed, galactose residues and laccase (a fungal phenoloxidase) were found to be present. The positive reaction of sheaths with the PATAg test indicates that polysaccharides such as 13-1,6-glucans are important components. Our data suggest that extracellular sheaths produced by R. lignosus during host cell colonization play an important role in wood degradation. Transportation of lignin-degrading enzymes by extracellular fibrils indicates that alteration of plant polymers may occur within fungal sheaths. It is also proposed that R. lignosus sheaths may be involved in recognition mechanisms in fungal cell-wood surface interactions.

Immunocytochemical studies of the infection mechanisms of Botrytis fabae II. Host cell wall breakdown

“…However, we have, as yet, no evidence to support this. A similar phenomenon has been observed in wood-rotting fungi (Ruel & Joseleau, 1991 ;Nicole et al, 1993 ;Nicole, Ruel & Ouellette, 1994) and cassava bacterial blight caused by Xanthomonas campestris pv. manihotis (Boher et al, 1995).…”

Histological and Ultrastructural Changes in Leaves and Stems of Resistant and Susceptible Chickpea Cultivars to Ascochyta rabiei

“…Plants of resistant, but not susceptible, cultivars to A. rabiei were able to resist fungal penetration. ES contains polysaccharides and glycoproteins which are produced by various fungi (Nicole et al, 1993). TEM and cytochemical techniques have provided direct information on the roles ES may play in host-interactions.…”

Localizing an Ophiostoma piceae proteinase in sapwood of four tree species using polyclonal antibodies

“…This material may represent the melanin responsible for wood discolouration. Sheaths have been reported for other fungi (Gallagher & Evans, 1990;Daniel et al, 1992) and have been shown to contain wood-degrading enzymes (Ruel & Joseleau, 1991;Green HI et al, 1992;Nicole et al, 1993). As has been suggested for other fungi in wood, the sheaths might protect enzymes from inactivation and retain extracellular enzymes close to the micro-organism, offering a nutritional competitive advantage to the fungus in vivo (Wood, 1985;Kalisz, Wood & Moore, 1987;Green III et al, 1992).…”