Display omitted
•Chemical heterogeneity is a common challenge in the application of biomaterials such as wood.•Chemical imaging methods unravel spatial heterogeneity in wood on different length ...scales.•These methods can quantify the chemical distribution in treated wood on macroscopic and cellular levels.•Combining imaging methods provides a holistic insight into structure–property relations of biomaterials.
An inhomogeneous chemical distribution can be problematic in many biomaterial applications, including wood impregnation. Since wood is a hierarchically structured material, the chemical distribution must be considered on different length scales. Here, a combination of imaging methods revealed the distribution of phenol–formaldehyde resin in impregnation-treated European beech wood within the scale of several millimeters or larger (macroscopic) and the micron scale (cellular level). The macroscopic resin distribution was quantified by hyperspectral near-infrared (NIR) image regression. A partial least square regression model accurately predicted the resin content in the range of 0–30 % with average prediction errors of ≤0.93 % for calibration and the test set. The cellular resin distribution was investigated by mapping the UV absorbance in selected regions of interest at high lateral resolution using UV microspectrophotometry (UMSP). The application of both imaging techniques to board sections revealed a process-dependent resin distribution. NIR image regression quantified the drying-induced migration of resin toward the board surfaces. UMSP measurements in selected regions revealed that this resin migration also affected the resin distribution across cell walls. Overall, the results demonstrate the potential of combining chemical imaging techniques to quantify process-dependent heterogeneity and to develop efficient treatments for wood and other biomaterials.
• Background and Aims The effect of heating and cooling on cambial activity and cell differentiation in part of the stem of Norway spruce (Picea abies) was investigated. • Methods A heating ...experiment (23–25 °C) was carried out in spring, before normal reactivation of the cambium, and cooling (9–11 °C) at the height of cambial activity in summer. The cambium, xylem and phloem were investigated by means of light- and transmission electron microscopy and UV-microspectrophotometry in tissues sampled from living trees. • Key Results Localized heating for 10 d initiated cambial divisions on the phloem side and after 20 d also on the xylem side. In a control tree, regular cambial activity started after 30 d. In the heat-treated sample, up to 15 earlywood cells undergoing differentiation were found to be present. The response of the cambium to stem cooling was less pronounced, and no anatomical differences were detected between the control and cool-treated samples after 10 or 20 d. After 30 d, latewood started to form in the sample exposed to cooling. In addition, almost no radially expanding tracheids were observed and the cambium consisted of only five layers of cells. Low temperatures reduced cambial activity, as indicated by the decreased proportion of latewood. On the phloem side, no alterations were observed among cool-treated and non-treated samples. • Conclusions Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.
The aim of this study was to visualize non-enzymatic oxidative degradation damages in the initial decay stage of the brown rot fungus Rhodonia placenta degradation in furfuryl alcohol (FA) modified ...wood cell walls and untreated wood cell walls of radiata pine (Pinus radiata) sapwood. A decay test with small wood blocks (1.5 × 1.5 × 5 mm³) of untreated and furfurylated radiata pine selected from two different furfurylation processes was performed until the first mass loss occurred. The samples were exposed to the brown rot fungus R. placenta, monitored by light microscopy and analyzed topochemically by cellular UV microspectrophotometry (UMSP). The results showed that the FA modification process directly influenced: i) the fungal colonization and hyphal growth, ii) the spectral UV behavior, and iii) degradation patterns of the entire cell wall layers. For the first time, UMSP area scans and selective line scans of individual cell wall regions provide topochemical insights into oxidative degradation at the initial decay stage of furfuryl alcohol-modified P. radiata visualizing oxidative degradation in situ. Knowledge of the initial decay stage of brown rot degradation in FA-modified wood compared to untreated wood extends our understanding of the brown rot decay processes of cell wall compounds.
•Initial brown rot decay in untreated and furfuryl alcohol modified radiata pine.•Light microscopy studies of hyphal colonization in modified and untreated wood.•Cellular UV microspectrophotometry (UMSP) monitoring over 18 days.•Topochemical insights into individual cell wall layers at the initial decay phase.•Visualization of non-enzymatic oxidative degradation pattern insitu.
Cedrelinga cateniformis (tornillo) is a timber species of the South American Amazon Basin. In its natural distribution area, the wood has various local uses, such as furniture, art work, door and ...window frames, and light construction. In order to promote this lesser known species for high valued applications on the international market, wood anatomical, topochemical and physical/mechanical studies were carried out to characterize the wood properties. The topochemical distribution of the lignin and phenolic extractives in the tissue were studied by means of cellular UV microspectrophotometry (UMSP). The results of the structural and topochemical analyses were compared with the interrelation of certain anatomical and subcellular structures as well as the chemical composition with regard to the physical and mechanical properties. The natural durability of the mature heartwood was analyzed according to the European Standards and is resulting in a durability class 1 against basidiomycetes. Based on the findings of the comprehensive investigations concerning physical and biological features, e.g. the dimensional stability and durability, Cedrelinga cateniformis is ideally suited as a substitute for overexploited tropical woods currently used in Europe for wooden window frames and other above ground outdoor applications and thus can contribute to increase the value-added production in Peruvian forests.
In addition to lignin, grass cell walls are characterized by the presence of hydroxycinnamic acids that play a significant role in cross-linking polymers into a cohesive network, and pretreatments ...are required to overcome the recalcitrance of lignocelluloses prior to enzymatic bioconversion of polysaccharides. The effects of dilute acid and ammonium hydroxide pretreatments were studied on the chemical composition and enzymatic saccharification of
Miscanthus
internodes fragments. The hydroxycinnamic acid content was reduced after both pretreatments, while lignin got enriched in condensed linked structures. In addition, dilute acid pretreatment was effective in decreasing xylan content of
Miscanthus
, while ammonia treatment induced a marked swelling effect on the cell walls of parenchyma, vascular sclerenchyma, and epidermal sclerenchyma. The phenol distribution at the cell level was estimated using UV transmission microspectrophotometry. Internode cell walls displayed different UV spectra according to the cell type. However, the secondary cell walls had similar UV spectra after pretreatment, whereas spectra recorded at the cell corner region displayed variations according to cell type and pretreatment. Acid pretreatment was more efficient than ammonia to improve the conversion of polysaccharides by a
Trichoderma
cellulolytic cocktail. Although pretreatments achieved moderate saccharification yields, the secondary cell walls were altered at some pit regions of the vascular sclerenchyma whereas parenchyma appeared recalcitrant. Variations in the UV spectra of enzyme-digested cell walls suggest pretreatment-dependent heterogeneity of the phenolic distribution in the more recalcitrant cell walls.
• Background and Aims The differentiation of terminal latewood tracheids of silver fir (Abies alba) trees grown in Slovenia was investigated in autumn/winter 2001/2002. • Methods The experimental ...trees were divided into three groups: one with narrow annual rings, width less than 1 mm; one with annual ring widths between 1 and 4 mm; and one group with broad rings larger than 4 mm. The differentiation of terminal latewood tracheids was investigated by light-, electron- and UV-microscopy in tissues sampled in October and November 2001 and March 2002. • Key Results In the middle of October, cambial divisions did not occur any more in any of the trees. In trees with narrow annual rings, cell wall deposition as well as lignification were completed in terminal latewood tracheids at this date, whereas in trees with annual ring widths of more than 1 mm these processes still continued. Electron microscopy as well as UV microscopy revealed an unlignified inner S2 layer and the absence of S3 and warty layers. With increasing distance from the cambium, wall formation and lignification gradually appeared to be completed. Samples of all trees taken in the middle of November only contained differentiated terminal latewood tracheids. At the structural and lignin topochemical level, November and March samples showed completed differentiation of walls of terminal latewood tracheids. • Conclusions In trees with broader annual rings, the final steps of differentiation of the youngest latewood tracheids near the cambium still continued during autumn, but were finished prior to winter. It was concluded from structural observations that duration of cambial activity is longer in trees with broad annual rings than in trees with narrow rings.
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.
PDF
