The lignin distribution in poles of waterlogged archaeological
(L.) Karst, which was decayed by erosion bacteria (EB) under anoxic conditions for approximately 400 years, was topochemically ...identified by transmission electron microscopy (TEM) and high resolution UV-microspectrophotometry (UMSP). Lignin rich cell wall compartments such as cell corner (CC), compound middle lamella (CML), torus, initial pit border and mild compression wood (CW) appeared morphologically well preserved together with S1 and S3 layers and epithelial and ray parenchyma cells. Residual material (RM) from degraded S2 showed a varied lignin distribution as evidenced by the different local UV-absorbance intensities. However, evaluation of UV-absorbance line spectra of RM revealed no change in conjugation of the aromatic ring system. Presence of RM with both very low and very high lignin absorbances showed evidence for disassembly of lignin during degradation combined with aggregation of lignin fragments and physical movement of these fractions. In contrast to TEM analysis, locally decreasing lignin content was found by UMSP in CML regions.
Anatomical and histometrical investigations were carried out on bark tissues (non-collapsed and collapsed phloem, and periderm) of beech (Fagus sylvatica L.) trees growing at a forest site near ...Ljubljana, Slovenia (400 m a.s.l.). Secondary changes in bark, especially sclereid formation and lignification, were followed at cellular and sub-cellular levels by light microscopy (LM), UV microspectrophotometry (UMSP), and transmission electron microscopy (TEM). The average width of the whole bark was 5960 μm; non-collapsed phloem on average occupied 4%, collapsed phloem 89%, and periderm 7% of the bark. Secondary changes in mature phloem were characterized by a collapse of sieve tubes, inflation of axial parenchyma, and development of sclereids. The percentage of sclereid areas and the stage of their development elevated with increasing distance from the cambium. The most pronounced increment in the sclereid proportion was observed in the second- and third-fifth of the bark. Sclereid cell walls were thick and poly-lamellated and had similar spectral characteristics but distinctly higher UV absorbance values than xylem fibers. By means of a combination of LM, TEM and UMSP techniques, the structure and secondary changes in the bark could be precisely identified.
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.
Micropropagated hybrid aspen clones (
Michx.×
L.) and a plus-tree (superior phenotypes selected) aspen (
L.) were grown under similar conditions in the central part of Latvia. After cutting at the ...age of 12 years, 64 sample trees were examined. The dimensions of the vessels and the content of cellulose, lignin, extractives and ash were determined. The cell walls were characterised by UV microspectrophotometry (UMSP) in the UV range. The dimensions of fibres obtained by kraft pulping were determined such as length, width, and their shape factors. Coarseness measurements were performed, and strength properties of the handsheets were tested. One of the clones (no. 44) had a significantly higher stem volume of 208 dm
and stem diameter of 17 cm at a height of 1.3 m. This clone had otherwise no notable differences to the other clones concerning the chemical composition, except a slightly higher lignin content (20.0% as compared with the mean value of 19.3% for other clones). Kraft cooking of hybrid aspen chips gave pulp yields in the range of 48.6–52.4%. Slightly higher strength properties (10–15%) were found for the handsheets prepared from a common aspen pulp (reference) as compared with those from hybrid aspen fibres.
Information about fine structure following wounding in differentiating xylem tissue is still scarce. This study provides information on cell wall modifications with special emphasis on lignin ...distribution in xylem fibres of poplar differentiating at the time of wounding. Samples were collected from wounded Populus spp. trees after response periods of up to twenty-three months and processed for microscopic analyses. General studies on the wall structure of wound-adjacent xylem fibres were carried out with light and transmission electron microscopy, whereas lignin distribution patterns of these cells were examined by UV-microspectrophotometry. Xylem fibres close to the wound and within a transition zone between differentiated xylem laid down prior to and tissue laid down after wounding developed a distinctively thicker secondary wall than normal fibres. These modified walls also showed a slightly higher lignin content, than normal and a heterogeneous lignin distribution in the middle lamella and the secondary wall. Wounding in poplar induces a modified wall structure and lignin topochemistry in xylem fibres differentiating at the time of wounding. It is assumed that this wound response is part of the compartmentalization process and therefore contributes to an increased resistance.
Topochemical detection of lignin and phenolic compounds was carried out at subcellular level in tension wood fibres of maple (Acer spp.), beech (Fagus sylvatica) and oak (Quercus robur) by means of ...cellular UV-microspectrophotometry (UMSP) and confocal Raman microscopy. UMSP field scans at 278 nm revealed the presence of aromatic compounds in the gelatinous layer (G-layer) in tension wood of all three species. Characterisation of the detected substances by point measurements from 240 nm to 400 nm revealed a plausible relationship to by-products from the lignin biosynthesis pathway. Raman spectra, recorded from different regions within the G-layer, showed a high affinity to spectra of lignins. The degree of aromatic compounds in the G-layer of oak tension wood fibres was approximately three-fold higher than that in maple and beech. Moreover, the oak G-layer showed an accumulation of aromatic compounds towards the cell lumen up to 50% higher than that detected in the secondary cell wall. UMSP and Raman microscopy are considered valuable complementary methods for topochemical investigation on a subcellular level.
Wood anatomical characteristics, content of phenolic extractives, and topochemistry of two lesser known and underutilised hardwood species, Bombax ceiba and Bombax insigne were studied. Heartwood and ...sapwood material was obtained from logs originating from natural forests of Pyinmana District, Myanmar. The basic qualitative anatomical features agreed with descriptions reported for the species in other regions (e.g. India, Bangladesh, Southeast Asia). However, there were some light differences in the quantitative wood anatomical data among the regions due to the influence of environmental conditions. The amount of phenolic extractives obtained by gradual extraction with acetone-water was almost the same in heartwood and sapwood (about 1.2%) in B. insigne, while heartwood showed a higher amount (2.8%) than sapwood (2.5%) in B. ceiba. Topochemical distribution of lignin and phenolic deposits in heartwood tissues investigated by scanning UV microspectrophotometry (UMSP) revealed that B. insigne is more highly lignified than B. ceiba. For both species, a lower UV-absorbance by the fiber and ray cell wall as compared to that of the cell wall of vessels was observed. Also, phenolic compounds were mostly deposited in the lumina of parenchyma cells and vessels rather than in cell walls. The results further improve the knowledge on the wood anatomy and chemistry of the species and in this respect are useful in future research to broaden their utilisation potential.
Effects of drying temperature and artificial UV irradiation on the pH of veneer surfaces, water absorption, thickness swelling, as well as shear strength of plywood manufactured from untreated and ...treated veneer sheets were evaluated. Rotary cut veneer sheets from beech (Fagus orientalis Lipsky) log were selected. The veneer sheets were dried at either 100°C or 180°C after peeling. Then the surfaces were exposed to artificial UV irradiation in an UV chamber for 1, 2, and 3 days representing a natural sun irradiation of 2, 4, and 6 months, respectively. Tests by UV microspectrophotometry showed that after high temperature drying and UV irradiation treatment, lignin condensation occurs. Also with increasing drying temperature and UV irradiation duration phenolic extractives are mainly concentrated in parenchyma cells and vessel lumens. HPLC analysis of the treated tissue showed distinct signals of catechin and 2,6-dimethoxybenzoquinon, which are two chromophoric compounds in discolored red hearted beech wood. Increasing drying temperature up to 180°C improved water absorption, thickness swelling, and shear strength of plywood samples. Especially, when veneers were exposed to UV irradiation (6 months), increased water absorption and thickness swelling and decreased the shear strength of plywood samples were observed.
Decayed-wood samples were collected from a naturally-infected bridge made of Quercus robur. Fruiting bodies of the white-rot basidiomycetes Hymenochaete rubiginosa and Stereum hirsutum were sampled. ...The white-rot fungus Fuscoporia ferrea and the secondary saprobiont Mycena galericulata were identified from the rotten wood by means of rDNA-ITS sequencing. The topochemistry of lignin degradation within individual cell-wall layers was determined by cellular UV-microspectrophotometry (UMSP) at 278 nm wavelength. Increased delignification occurred in compound middle lamella regions (CML), secondary wall layers of fibres (S2), longitudinal and ray parenchyma cells as well in vessels. The highest lignin content at initial and medium decay was recorded in the CML, whereas in advanced decay secondary wall layers of the vessels exhibited the highest content of residual lignin. In all stages of degradation, the S2 layers of fibres had the lowest lignin amount.
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