The effect of day length on diurnal differences in the innermost surface of the S2 layer in differentiating tracheids

This article describes the effect of day length during the photoperiodic cycle on the diurnal differences in the innermost surface of developing secondary walls. Saplings of Cryptomeria japonica D. Don. were grown in growth chambers at constant temperature and relative humidity, but with different photoperiods. Samples of differentiating xylem were collected during the light and dark periods. The innermost surface of developing secondary walls in differentiating tracheids were observed using field emission scanning electron microscopy, and observations made during the light and dark periods were compared. In the saplings grown under long-day or short-day conditions, diurnal differences in aspects of the innermost surface of developing secondary walls were observed. Cellulose microfibrils were observed on the innermost surface of developing secondary walls during the light period when the volumes of differentiating cells were low, and amorphous material was observed during the dark period, when differentiating tracheids were turgid. The amorphous material was labeled with antiglucomannan antiserum. These results suggest that the range of day-length conditions set in this study does not affect the diurnal periodicity in the supply of cell wall components to the innermost surface of developing secondary walls.     

Arrangement of cortical microtubules in compression wood tracheids of Taxus cuspidata visualized by confocal laser microscopy

Cortical microtubules (MTs) in differentiating compression wood tracheids of Taxus cuspidata stems were visualized by confocal laser microscopy. They were oriented obliquely at an angle of about 45° to the tracheid axis during formation of the secondary wall. Artificial inclination altered the pattern of alignment of MTs. Banding MTs were helically oriented late during the formation of the secondary walls. These results indicate that MTs might control the orientation and localized deposition of cellulose microfibrils in the secondary walls of compression wood tracheids.Part of this report was presented at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy

Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnated with a low-viscous epoxy resin using a vacuum process. The epoxy was cured in situ and the specimens sectioned. Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The investigation concentrated on tracing the transverse movements of a viscous liquid in the wood, and special attention was therefore given to the cross-field area between ray cells and longitudinal tracheids. A damage hypothesis is proposed based on the results obtained in the present investigation in combination with those from earlier studies on linseed oil-impregnated pine: In addition to the morphology of the bordered pits, viscous liquid flow in wood is dependent on damage that occurs during the impregnation procedure. For pine sapwood, liquid flow is enabled through disrupted window pit membranes, which divide the longitudinal tracheids and the ray parenchyma cells. A mechanism accounting for the reduced permeability of pine heartwood is believed to be deposits of higher-molecular-weight substances (extractives) in the ray parenchyma cells and on the cell walls. In spruce the thicker ray cells in combination with the smaller pits, which are connected to the longitudinal tracheids, reduce permeability considerably.     

Ultrastructure of the S2 layer in relation to lignin distribution inPinus radiata tracheids

The ultrastructure of the S₂ layer in relation to its lignin distribution was examined using transmission electron microscopy in the tracheids ofPinus radiata. The S₂ layer had a striated appearance at low magnification. Observations at higher magnifications showed lignin to be distributed inhomogeneously in this layer, appearing as a mosaic of electron-dense and electron-lucent regions. These regions are scattered, showing a pattern of often interconnecting sinuous features in a predominantly radial profile. The significance of these features of the S₂ layer is discussed, particularly in relation to the available information from recent ultrastructural observations on the appearance of cellulose microfibrils and the pattern of their distribution in the S₂ layer using rapid freeze-deep etching in conjunction with transmission electron microscopy. Predictions are made as to the likely distribution and arrangement of cellulose microfibrils in the S₂ layer based on the pattern of lignin distribution observed in this layer.     

Microfracture in wood monitored by confocal laser scanning microscopy

The paper deals with the experimental characterisation of damage evolution within the radial (R)–tangential (T) growth plane of softwood loaded in tension perpendicular to the grain. The reported investigations comprise in-situ monitoring of crack propagation by means of Confocal Laser Scanning Microscopy (CLSM) and evaluations of crack patterns of broken specimens. Three types of notched specimens, representing different crack propagation systems, were tested; for all configurations, both, loading and crack propagation direction were located within the RT plane of wood. The CLSM pictures of broken specimens show distinct differences among the regarded configurations with respect to crack paths. Two different damage mechanisms were identified being rupture of earlywood cell walls in the case of crack propagation in tangential direction and debonding of wood fibers, i.e. rupture of the interface zone between adjacent tracheids, in case of crack progression in radial direction. In the case of an intermediate crack system with an angle of 45° between initial notch direction and radial direction the crack evolution was monitored in-situ during the tension test, whereby the combined action of both basic fracture mechanisms was observed.     

Analysis of acetylated wood by electron microscopy

The properties of acetylated solid wood were investigated earlier, in particular the anti-shrink efficiency and the resistance against decay. This study focuses on the possible changes and damage to the wood structure due to an acetylation process leading to weight per cent gains of up to 20%. Electron microscopy (SEM and TEM) was used to investigate the fine structure of acetylated beech, pine and spruce. Cell wall swelling was observed, but no evidence of damage could be seen as a result of the acetylation procedure. The fine structure of the wood tissue such as the pits and the thin parenchyma walls appeared untouched.     

Three-dimensional imaging of a sawn surface: a comparison of confocal microscopy,scanning electron microscopy,and light microscopy combined with serial sectioning

The three-dimensional structure of a transverse sawn wood surface was investigated using several methods, to compare techniques, and to study the types of deformation in tracheids at the saw cut. A sample of spruce sapwood was cut with a fret saw across the grain. The transverse sawn surface was imaged by confocal microscopy, field emission scanning electron microscopy (FESEM), and by light microscopy combined with serial sectioning and three-dimensional (3D) reconstruction. Both confocal microscopy and FESEM were restricted to visualising the cut surface of the wood. However, serial sectioning was able to reveal the internal structure below the cut surface providing more information on the types of cell deformation present. The wood structure was deformed to depths of more than 600 μm below the surface with twisting, crushing and tearing deformations. Near the outer surface, gaps were formed between groups of tracheids where the cell walls had been torn away to form saw dust. The deformation tended to form groups of tracheids that were twisted relative to each other. Latewood was less distorted, forming a dense solid surface compared to the highly fibrous earlywood.     

Measurement of urea-formaldehyde resin distribution as a function of MDF fiber size by laser scanning microscopy

A technique has been developed to show the extent of the distribution of the adhesive on the fiber surface. This involves treatment of the resinated fibers with the dye Toluidine blue O, to quench the autofluorescence of the wood materials, to show only the fluorescence of the UF resin in the presence of the dye. The results indicate that this method is a simple and practical way to understand UF resin coverage on wood fibers. With image analysis, the adhesive has been shown to cover a small percentage (3.5%) of the fiber surface, although the percent by weight (based on wood fiber) of resin is much more (13%). The fiber size strongly affects the resin coverage ratio and the chance to collect resin droplets, but it is not significant in the resin-droplets size distribution. Decreasing the proportion of shorter fibers is beneficial in improving resin coverage uniformity. A model for calculating the resin-coverage ratio was developed. The resin coverage is about 4.8% for the resin content of 13% by the model.     

A study of lignification in loblolly pine tracheids by the SEM-EDXA technique

Summary The lignification process in different morphological regions of loblolly pine tracheids was studied by the SEM-EDXA technique. Prior to S₂ layer formation, lignification was initiated in the cell corner middle lamella and compound middle lamella regions. Subsequently a rapid lignin deposition was observed in both regions, whereas secondary wall lignification was a more gradual process and initiated when the middle lamella lignin concentration was approximately 50% of maximum. Within the secondary wall, the S₁ layer is lignified first. Then, lagging just behind cell wall formation, lignification of the S₂ layer is initiated adjacent to the S₁ layer and extends toward the lumen. Finally, the S₃ layer lignified. Upon completion of lignification, the cell walls had a higher concentration of lignin in both the S₁ and S₃ layers than in the S₂ layer.This Paper is an excerpt from the Ph.D. dissertation of Shiro Saka     

Size, shape and surface morphology of starch granules from Norway spruce needles revealed by transmission electron microscopy and atomic force microscopy: effects of elevated CO(2) concentration

We compared the effects of ambient (350 ppm) and elevated CO(2) concentration (700 ppm) on the size and shape of starch granules in Norway spruce (Picea abies (L.) Karst.) needles during one growing season. Starch granules were isolated from needles by alkaline digestion and analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Measurements made with a particle size analyzer indicated that starch granules ranged between 0.5 and 10 microm. Granule size and shape varied according to needle developmental stage and CO(2) concentration. Generally, elevated CO(2) concentration increased the size of the starch granules. Fine surface structures (< 10 nm in size) studied by AFM were characterized by the presence of protrusions, furrows and pores.     

Microdistribution of metal elements in wood impregnated with a copper-chrome-arsenic preservative as determined by analytical electron microscopy

Summary The distribution of Cu, Cr and As in the walls of tracheids of Scots pine impregnated with Tanalith C at a retention of 2.5 lb/ft³ has been examined at the submicroscopic level in the electron microscope microanalyser, EMMA-4, using the absolute method, as well as in the conventional electron microscope. All three elements are present in all regions examined (probe area 0.2 m diameter). The concentration of Cu ranges from 0.4–0.9% (w/w), that of Cr is about 0.8%, while As ranges from 2%–2.6%. The morphology of this fine deposit is clearly dictated by the run of the cellulose microfibrils. There is in the wall an occasional coarse deposit, almost entirely copper, and the inner face of the tracheid wall is covered by a thin layer 20–30 m thick which contains all these elements at high concentration.     

薄层扫描法测定几种植物中熊果酸的含量

采用薄层扫描法对车前草、夏枯草、山茱萸中熊果酸的含量进行了测定,其TLC测定条件为:展开剂:环己烷-氯仿-乙酸乙酯(20∶5∶8),显色剂:10%H2SO4乙酸溶液。结果表明:在几种植物中,夏枯草的熊果酸含量最高,达0·812%,车前草的熊果酸含量最低,为0·516%,二者相差1·59倍。该方法简便、快速、准确、经济、数据可靠。     

Evaluation of preservative distribution in thermally modified European aspen and birch boards using computed tomography and scanning electron microscopy

The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Träskydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.     

Locating the initial in the vascular cambium of Pinus strobus L. by electron microscopy

Summary The results of this investigation by electron microscopy on the vascular cambium in Pinus strobus L. confirm the results of earlier investigations by light microscopy. First, they showed that differences in the thickness of tangential walls of cambial cells exist and that these differences permit grouping of cells according to the sequence of the previous divisions of the initial. This, in turn, permits the site of the initial cell in the cambial zone to be deducted. The thicker distal tangential wall of the initial in the successive series of tissue production allows for precluding the direction in which the initial function proceeds, toward the xylem or toward the phloem. Second, it was demonstrated that immature xylem cells exist in groups of four, that immature phloem cells exist in pairs, and that at all times more cells are produced toward the xylem than toward the phloem. Third, it was shown that the extra-thick tangential wall in immature xylem serves as a landmark to signal the changeover in the initial function from phloem to xylem production.     

The supply of matrix containing glucomannans to the innermost surface of S2 layers is associated with changes in turgor pressure of differentiating tracheids in Cryptomeria japonica

We investigated the relationship between turgor pressure and diurnal differences in secondary wall formation of differentiating tracheids. Saplings of Cryptomeria japonica were grown in a growth chamber with 12-h light:12-h dark cycles, and the tangential strain on the inner bark surface was measured as an indicator of the volumetric changes of differentiating cells. The innermost surface of developing secondary walls was then observed using field emission scanning electron microscopy at 1-h intervals after both light and dark periods. Dramatic changes in the aspects of the innermost surface of developing secondary walls occurred 3h after the light was switched on and 4h after the light was switched off. The amorphous material containing glucomannans became evident when the differentiating cells became fully turgid during the dark period. Conversely, cellulose microfibrils became clearly visible when the cell volume was low during the light period. These results suggest that the diurnal periodicity in the supply of hemicellulose-containing matrix to developing secondary walls is associated with the changes in turgor pressure of differentiating tracheids that result from the change in light conditions during the photoperiodic cycle.     

Helical orientation of the microfibrils in tracheids,fibres and vessels

The helical winding direction of microfibrils in the S2 wall layer in the tracheids, fibres and vessel members of over 250 woody species, both indigenous and exotic, growing in New Zealand has been determined. A Z helix was observed in all the tracheids, fibres and narrower vessel members. The orientation in the wider vessel members could not always be determined with any certainty.     

Slow viscous flow and the organization of the cell wall in conifer tracheids

Summary In view of the known orientation of microfibrils about pits in conifer tracheids a model is presented which is consistent with the assumption that this pattern derives from the slow viscous flow of a fluid about a cylindrical obstacle.At present at the Botany Department, La Trobe University, Bundoora, 3083, Victoria, AustraliaThe authors wish to thank Dr. W. B. Thompson and Professor A. B. Wardrop for their constructive criticism.