ALBERT

Description: The biotechnological application of the white rot fungusPhysisporinus vitreusnamed “bioincising” is currently being investigated for permeability improvement of Norway spruce (Picea abies(L.) Karst.) wood. During short-term (

Description: The white rot fungus Physisporinus vitreus is currently tested for several biotechnological applications such as permeability improvement of refractory wood species or the optimization of the acoustic properties of wood for violins. The enzymatic activity of P. vitreus results in the degradation of pit membranes and simultaneous alterations of the tracheid cell wall structure in wood of Norway spruce [Picea abies (L.) Karst]. By this means, selective delignification and simultaneous degradation occur in the latewood tracheids at short incubation times. To study the delignification of individual cell wall layers in latewood tracheids, cellular UV-microspectrophotometry was applied to wood of Norway spruce that had been incubated for between 3 and 9 weeks. By means of this technique, the progressing delignification was demonstrated in the latewood tracheid secondary walls. Moreover, local delignification in close proximity to hyphal tunneling, cavities, and notches was evident. Additionally, the mechanical changes were measured (a) at the macroscopic level by Brinell hardness test and (b) at the cellular level by nanoindentation. Brinell hardness was significantly reduced with increasing incubation time which was attributed to the partial delignification. Unlike Brinell tests, results from nanoindentation tests did not show a clear effect of fungal activity because of the material heterogeneity and the high spatial resolution of this technique. The present study provides methodological approaches for the investigation of wood-fungus interactions and contributes to a better understanding of the characteristics of wood decay at the subcellular level caused by the white rot fungus P. vitreus. Moreover, it establishes the basis for a subsequent chemical analysis, for which the results will be the topic of a second paper in this series.

Description: Furfurylation is one of the wood modification techniques via catalytic polymerization of the monomeric furfuryl alcohol (FA) in the impregnated cell wall. Little is known about the topochemistry of this process. Brown rot degradation begins with lignin modification and therefore, the reactions between FA and lignin was one focus of this research. Furfurylated radiata pine (Pinus radiata) with three different weight percent gains (WPGs of 57%, 60% and 70%) after FA uptake was observed by cellular ultraviolet microspectrophotometry (UMSP) to analyze chemical alterations of the individual cell wall layers. Moreover, light microscopy (LM) and scanning electron microscopy (SEM) analyses were performed. The ultraviolet (UV) absorbance of the modified samples increased significantly compared to the untreated controls, indicating a strong polymerization of the aromatic compounds. Highest UV absorbances were found in areas with the highest lignin concentration. The UMSP images of individual cell wall layers support the hypothesis concerning condensation reactions between lignin and FA.

Description: Chemically or physically modified wood materials have enhanced resistance to wood decay fungi. In contrast to treatments with traditional wood preservatives, where the resistance is caused mainly by the toxicity of the chemicals added, little is known about the mode of action of nontoxic wood modification methods. This study reviews established theories related to resistance in acetylated, furfurylated, dimethylol dihydroxyethyleneurea-treated, and thermally modified wood. The main conclusion is that only one theory provides a consistent explanation for the initial inhibition of brown rot degradation in modified wood, that is, moisture exclusion via the reduction of cell wall voids. Other proposed mechanisms, such as enzyme nonrecognition, micropore blocking, and reducing the number of free hydroxyl groups, may reduce the degradation rate when cell wall water uptake is no longer impeded.

Description: The aim of this study was to investigate Rhodonia placenta expression patterns of genes involved in the depolymerisation during the non-enzymatic phase in acetylated (WAc) and furfurylated wood (WFA). During the 98-day-long exposure, WAc [22.6% weight per cent gain (WPG) on average] and WFA (69% WPG on average) lost no more than 3% mass while the untreated wood (WUn) reached 41% mass loss (ML) in 55 days. Expression of six genes putatively involved in the non-enzymatic degradation process were investigated. In conclusion, expression levels of alcohol oxidase Ppl118723 (AlOx1) and laccase Ppl111314 (Lac) were significantly higher in the modified wood materials (WMod) than in WUn, which is in accordance with previous results and may be explained by the absence of the degradation products that have been proposed to down-regulate the non-enzymatic degradation process. However, copper radical oxidase Ppl156703 (CRO1) and a putative quinate transporter Ppl44553 (PQT) were expressed at significantly lower levels in WMod than in WUn while quinone reductase Ppl124517 (QRD) and glucose oxidase Ppl108489 (GOx) were expressed at similar levels as in WUn. These results suggest that gene regulation in WMod is more complex than a general up-regulation of genes involved in the non-enzymatic degradation phase.

Description: The thin-veneer strip technique was applied to investigate the modifying effects of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) on the tensile strength of wood. Pinewood veneers treated with solutions of DMDHEU alone and in combination with magnesium chloride (MgCl2) as a catalyst showed considerable strength losses of up to 50% in zero-span and up to 70% in finite-span testing modes. The higher strength losses in the latter case are due to hemicellulose degradation, which cannot be assessed in zero-span testing. Strength loss observed after treatment with DMDHEU and MgCl2 was approximately as high as the sum of the strength losses determined after individual treatments with MgCl2 or DMDHEU. Micrographs of veneers after finite-span testing revealed that catalysed DMDHEU treatment changed the predominant failure mode from interfibre fracture (in controls) to intrafibre fracture. The mechanism of strength loss resulting from treatment with DMDHEU is discussed.

Description: To understand the reasons for the high durability of tropical wood species, the chemistry of the extractives needs to be elucidated. As these extractives consist of a great variety of components differing in quantity and composition, the analysis is often time-consuming. To focus on the key bioactive substances, bioassay-guided fractionation is helpful, but the established bioassay methods cannot be readily adapted to basidiomycete fungi that are commonly used for the respective durability tests, because they do not sporulate easily in laboratory settings. The research therefore aims at developing a direct bioautography using homogenized hyphae from basidiomycetes, to overcome this restriction. Extracts from four tropical wood species were analyzed regarding their potential bioactivity on two selected basidiomycete fungi. To this end, the chemically complex mixtures and extract constituents were resolved by a two-dimensional planar chromatography and the metabolites were located by characteristic zones of fungal growth inhibition, which was accentuated by a color reaction. The bioactive fractions were analyzed by gas chromatography/mass spectrometry (GC/MS). Potentially responsible compounds could be identified, such as the alkaloid bicuculline from Mezilaurus itauba, which has not been described in this species yet. The presented bioassay method can be used as a rapid screening method for bioactive components from wood.