Sterols and lignin in Eucalyptus globulus Labill. wood: Spatial distribution and fungal removal as revealed by microscopy and chemical analyses

Abstract

AbstractWood decay experiments were carried out aiming at the selective removal of lipophilic compounds with selected basidiomycetes isolated fromEucalyptus globulusplantations in Uruguay:Dendrophora albobadia,Lentinus tigrinus,Peniophora cinerea,Peniophora lycii, andPhanerochaete crassa. Localization and composition of lipophilic compounds and lignin ofE. globuluswere determined by gas chromatography-mass spectrometry, fluorescence microscopy using filipin staining, confocal laser scanning microscopy (CLSM), and low temperature scanning electron microscopy. Free and esterified sterols, mainly sitosterol, were the predominant lipophilic compounds in the control wood. Sterols were present in ray parenchyma cells, together with polyphenols, and in vessels. This confirms earlier observations indicating that these cell types are the principal source of lipophilic extractives involved in pitch problems during pulping and bleaching. Sterols are also present in the vestures of fiber and vessel pits. Different fungal degradation patterns ofE. globuluswood were determined.P. lyciishowed the highest specificity for lignin degradation during short incubation time together with considerable sterol removal capacity. Ray parenchyma cells and their lumen deposits were strongly degraded byP. lycii. Eucalypt lignin located in vessel walls and fiber cell corners was more resistant to fungal attack, as revealed by CLSM. The initial decay stage ofL. tigrinuswas restricted to vessels and tyloses where the sterol compounds were removed.