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Although there is considerable information on the chemistry of gelatinous (G) layers in tension wood (TW) fibers consisting of S1 + S2 + G cell wall structure (poplar), little is known on the chemistry of G-layers in TW fibers organized with S1+ G structure. This study investigated the distribution of lignin and non-cellulosic polysaccharides in ash TW fibers (S1+ G) using histochemistry and immunolocalization methods. TW fibers studied were fully developed (mature fibers) and obtained from two (TW-1, TW-2) mature European ash trees (Fraxinus excelsior L.). Based on differences in microfibril angle (MFA) and TW trees used, TW fibers were mainly classified into three types; 1) Type-1 fibers with MFA almost parallel to the fiber axis that were found in TW-1, 2) Type-2 fibers with 12° MFA that were abundant at the end of growth rings of TW-1 and 3) Type-3 fibers with 10° MFA that were found in TW-2. The S3 layer was absent in all TW fibers. In this study, the secondary cell wall structure of Type-1 and Type-2/Type-3 fibers were defined as G and GL (gelatinous-like) layers, respectively. Lignin with syringyl (S) units was detected in G/GL-layers, in which intensity and patterns of lignin staining likely related to the difference in MFA between G- and GL-layers. With hemicelluloses, heteroxylan and heteromannan epitopes were detected in G/GL-layers but these were much less abundant than those in S2 layers of normal wood (NW) fibers. Like lignin, distribution patterns of heteromannan epitopes in G/GL-layers likely related to differences in MFA between fiber types. Sparse xyloglucan epitopes were also detected in G/GL-layers. Homogalacturonan epitopes were absent in G/GL-layers. All fiber types showed abundant a-1, 5-arabinan epitopes in G/GL-layers. Overall results indicate that the chemistry of ash TW fibers studied differs significantly from that of other species reported previously, specifically TW fibers composed of S1 + S2 + G structure.

Although there is considerable information on anatomy and gross chemistry of oak wood, little is known on the ultrastructure and chemistry at the individual cell wall level. In particular, differences in ultrastructure and chemistry within the same cell type between earlywood (EW) and latewood (LW) are poorly understood. This study investigated the ultrastructure and chemistry of (vasicentric) tracheids, vessels, (libriform) fibers and axial/ray parenchyma cells of English oak xylem (Quercus robur L.) using light-, fluorescence- and transmission electron microscopy combined with histo/cytochemistry and immunohisto/ cytochemistry. EW tracheids showed several differences from LW tracheids including thinner cell walls, wider middle lamella cell corner (MLcc) regions and lesser amounts of mannan epitopes. Fibers showed thicker cell walls and higher amounts of mannan epitopes than tracheids. EW vessels were rich in guaiacyl (G) lignin with a characteristic non-layered cell wall organization (absence of S1–3 layers), whereas LW vessels were rich in syringyl (S) lignin with a three layered cell wall structure (S1–3 layers). Formation of a highly lignified and wide protective layer (PL) inside axial/ray parenchyma cells was detected only in EW. Distribution of mannan epitopes varied greatly between cell types and between EW and LW, whereas distribution of xylan epitopes was almost identical in all cell types within a growth ring. Together, this study demonstrates that there are great variations in ultrastructure and chemistry of cell walls within a single growth ring of English oak xylem.

Although there is considerable information on the chemistry of bordered intervessel pit membranes, little is known on the pit membrane chemistry of other pit types in hardwoods. This study investigated distribution of phenolic compounds, pectins and hemicelluloses in different mature pit membranes of English oak xylem using transmission electron microscopy coupled with cytochemistry and immunocytochemistry. Mature bordered intertracheid (vasicentric)- and tracheid-vessel pits showed presence of xyloglucan and heteromannan (hemicelluloses) epitopes across the pit membrane (except for the annulus regions) with differences in amounts of epitopes between earlywood (EW) and latewood (LW). In contrast, pectin epitopes were detected only in the annulus regions of pit membranes. Unlike bordered pits, half-bordered (tracheary-parenchyma pits) and simple (parenchyma pits) pit membranes were rich in pectin epitopes but lacked heteromannan epitopes, indicating difference in pit membrane chemistry between pit types. Distribution of phenolic compounds also differed between pit types and between EW and LW. LW also showed great variations in distribution of phenolic compounds between vessels. Together, this study demonstrates that there are great variations in pit membrane chemistry between pit types and between EW and LW in English oak xylem.

Microdistribution of non-cellulosic polysaccharides in pit membranes of bordered pits (intertracheid pits between adjacent tracheids), cross-field pits (half bordered pits between tracheids and ray parenchyma cells) and ray pits (simple pits in nodular end walls of ray parenchyma cells) was investigated in mature earlywood of juvenile Scots pine and Norway spruce seedlings using immunocytochemistry combined with monoclonal antibodies specific to (1→4)-β-galactan (LM5), (1→5)-α-arabinan (LM6), homogalacturonan (HG, LM19, LM20), xyloglucan (LM15), xylan (LM10, LM11) and mannan (LM21, LM22) epitopes. Using phloroglucinol-HCl and KMnO4 staining, lignin distribution in pit membranes was also examined. Apart from cross-field pit membranes in Scots pine, all pit membranes observed showed a positive reaction for lignin with differences in staining intensity. Ray pit membranes showed strongest reaction with lignin staining in both species. Intensity of lignin staining in bordered pit membranes was stronger in Norway spruce than in Scots pine. With localization of non-cellulosic polysaccharide epitopes, Scots pine showed differences in cross-field pit membranes (rhamnogalacturonan-I (RG-I), HG and xyloglucan epitopes) from bordered and ray pit membranes (RG-I and HG epitopes). In contrast, Norway spruce showed significant differences in ray pit membranes (RG-I, HG, xyloglucan, xylan and mannan epitopes) from bordered and cross-field pit membranes (HG and no/trace amount of RG-I epitopes). Distributional differences in HG epitopes depending on antibody type/ membrane regions were also observed in cross-field pit membranes between the two species. Together, the results suggest that distribution patterns of lignin and non-cellulosic polysaccharides in pit membranes differ significantly between pit types and between Scots pine and Norway spruce. Compared with the same types of pit membranes in hardwoods, the results for Scots pine and Norway spruce (softwoods) differed significantly.

Axial resin canals in wood are distinguished into two types based on the morphology of epithelial cells; resin canals with narrow canals and thick-walled epithelial cells (Type I), and resin canals with wide canals and thin-walled epithelial cells (Type II). Following studies on Norway spruce (Type I), the distribution of non-cellulosic polysaccharides in axial resin canals of Scots pine (Type II) is reported here using cytochemical and immunocytochemical methods. The distribution of (1→4)-β-galactan (LM5), (1→5)-α-arabinan (LM6), homogalacturonan (LM19, LM20), xyloglucan (LM15), xylan (LM10, LM11) and mannan (LM21, LM22) epitopes were examined. Axial resin canal complexes in the xylem were composed of canal, epithelium and subsidiary cells (parenchyma and strand tracheids). Strand tracheids were absent in axial resin canals in the phloem. Strand tracheids showed a completely different ultrastructure and chemistry from normal mature tracheids and other types of axial resin canal cells. Immunolocalization of non-cellulosic polysaccharides in axial resin canals showed an overall similar cell wall composition in epithelial cells and subsidiary parenchyma between the xylem and phloem. All types of axial resin canal cells in both xylem and phloem contained homogalacturonan (HG), rhamnogalacturonan-I (RG-I) and xyloglucan with a high variation in amount and chemical structure depending on cell wall region and between cell types. In particular, epithelial cell walls facing the canal showed significant differences in HG distribution from other epithelial cell wall regions. No xylan and mannan epitopes were detected in any of axial resin canal cells. Together, our results suggest that the chemistry of axial resin canal cells in Scots pine may be highly compartmentalized depending on functional differences between both cell types and cell wall regions.

The microdistribution of non-cellulosic polysaccharides in epithelial cells of axial resin canals was investigated in Norway spruce xylem using immunolocalization methods combined with monoclonal antibodies specific for (1→4)-β-galactan (LM5), (1→5)-α-arabinan (LM6), homogalacturonan (LM 19, LM20), xyloglucan (LM15), xylan (LM10, LM11) and mannan (LM21, LM22). The ultrastructure and lignin distribution of epithelial cell walls was also examined after cytochemical staining for lignin. Compared with tracheids, epithelial cells showed several different ultrastructural characteristics, such as the thickness of three layers forming the cell wall, the boundary structure between layers and the lamellate structure of cell walls, with slightly stronger reaction with chemical staining for lignin than tracheids. After staining with potassium permanganate, the layer of the epithelial cell wall adjacent to the canal showed typical characteristics of middle lamella (C-ML). However, C-ML regions showed completely different chemical characteristics from E-ML (middle lamella between epithelial cells) regions of epithelial cells and compound middle lamella (CML) regions of tracheids. Unlike tracheids, epitopes of pectic polysaccharides were detected in the epithelial cell wall with variations in amounts between cell wall layers. Epitopes of hemicelluloses were also detected in the epithelial cells with differences in distribution patterns from tracheids, particularly xyloglucan (LM15) and low substituted xylan (LM10) epitopes. Together, our results suggest that the ultrastructure and chemistry of epithelial cells including C-ML regions significantly differ from tracheids.

Localization of homogalacturonan (HG) and xyloglucan epitopes in developing and mature pit membranes from different pit types in xylem of Populus tremula L. × P. tremuloides Michx. (hybrid aspen) and Populus tremula L. (European aspen) was investigated using immunogold labeling. Pit types not mediated by ray parenchyma (intervessel- and fiber pits) showed significant developmental changes in HG epitope localization. Both low- and high methyl-esterified HG epitopes (recognized by LM19 and LM20, respectively) were detected in developing pit membranes of intervessel- and fiber pits until late stages of xylem formation, whereas no HG- and high methyl-esterified HG epitopes were detected in mature intervessel (except for annulus regions of pit membranes)- and mature fiber pit membranes, respectively. In contrast, no notable developmental changes in HG epitope localization were detected in pit types mediated by ray parenchyma (vessel-ray-, ray- and fiber-ray pits) during pit maturation. Vesselray- and fiber-ray pits showed abundant low- and high methyl-esterified HG epitopes in pit membranes, while ray pits showed presence of primarily low methyl-esterified HG epitope during all stages of pit development including at maturity. With xyloglucan (recognized by LM15), specific developmental changes in epitope localization were detected in vessel-ray pits. Xyloglucan epitope was detected in developing vessel-ray pit membranes, but was almost absent in mature pit membranes. Instead, xyloglucan was detected in the protective layers of vessel-ray pits showing completely different localization pattern than homogalacturonan, which was only detected in pit membranes. Together, our results suggest that the chemistry of pit membranes varies depending on both the developmental stage and pit type.

Three lesser known wood species from Mozambique were studied to generate information for identification purposes and facilitate the introduction of these species into the wood working industry by assigning or widening the potential uses of these species. Selected anatomical features were used to predict some important wood properties, subsequently confirmed by measurements of both density and impregnability. Comparative wood anatomy showed that all three wood species have anatomical features typical for their genus after comparisons with their closest relatives. Both ntholo (Pseudolachnostylis maprounaefolia Pax) and muanga (Pericopsis angolensis Meeuwen) are diffuse-porous (with 14–24 and 16–20 vessels/mm2 respectively), have extractives in the heartwood vessels and thick-walled fibres, features consistent with good natural durability and strength respectively. Metil (Sterculia appendiculata K. Schum.) is also diffuse-porous with very wide vessels at much lower frequency (2), it lacks extractives in the heartwood vessels, and thin-walled axial and ray parenchyma constitutes the bulk of the ground tissue. This set of characteristics makes the wood light and satisfactory for construction purposes but highly vulnerable to biodegradation.

The purpose of the present study was to investigate the ultrastructure of the outer layer of the secondary cell wall (S1) of Norway spruce (Picea abies (L.) Karst.) tracheids with emphasis on microfibril orientation. Several methods were used to obtain complementary results. Macerated tracheids and wood blocks were exposed to degradation by soft rot fungi, different chemicals and mechanical forces. Observations were made using scanning and transmission electron microscopy and light microscopy. It was concluded that the S1 layer is rather homogeneous with respect to microfibril orientation. The major part of the S1 is composed of microfibrils oriented approximately perpendicular to the tracheid axis. Evidence for a crossed fibrillar structure with microfibrils in alternate S- and Z-helices was not obtained. The transition of microfibril orientation from the S1 to the S2 layer appeared abrupt. The transitional/intermediate lamella, where a gradual change in microfibril orientation occurs, should be considered to belong to the outer part of S2.

Electron microscopic examination of vessels and fibre-tracheids of Alstonia scholaris exposed to tunneIIing bacteria (TB) in liquid cuItures showed degradation of aU areas of the secondary waU incIuding the highly lignified middle lameUa in advanced stages of attack. However, vestured pit membranes and vestures appeared to be resistant to degradation by TB even when aU other waU areas in A. scholaris wood ceIIs were severely degraded. The size comparison indicated vestures to be considerably smaIIer than TB, and we suspect that this may be the primary reason why vestures in A. scholaris wood were resistant to degradation.