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

9 pages, 4 figures, 1 table, 38 references.

Wood decay experiments have been carried out aiming at the selective removal of lipophilic compounds with selected basidiomycetes isolated from E. globulus plantations in Uruguay: Dendrophora albobadia, Lentinus tigrinus, Peniophora cinerea, Peniophora lycii and Phanerochaete crassa. Localization and composition of lipophilic compounds and lignin of Eucalyptus globulus were determined by gas chromatography-mass spectrometry (GC-MS), fluorescence microscopy (FM) using filipin stain, confocal laser scanning microscopy (CLSM) and low temperature scanning electron microscopy (LTSEM). 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 of E. globulus wood were determined. P. lycii showed 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 by P. lycii. Eucalypt lignin located in vessel walls and fiber cell corners was more resistant to fungal attack as was revealed by CLSM. The initial decay stage of L. tigrinus was restricted to vessels and tyloses where the sterol compounds were removed.

This work has been supported by the European contract QLK5-99-1357, the Spanish project 1FD97-742 and BIO2003-00621. M. Speranza thanks a fellowship from the Spanish Agency for International Cooperation.

Peer reviewed