Ultrastructural analysis of the differentiation process of secondary xylem vessel element in Populus deltoides

Using electronic microscopy, ultrastructural changes were observed during differentiation in a secondary xylem vessel element (VE) in Populus deltoides. Results showed that morphological development of VE differentiation was successively divided into three stages. First was primary cell wall outspread (the initial stage), where the VE was highly vacuolated and the protoplasma distributed along the cell wall. Second was secondary cell wall construction (the pivotal stage), where substances accumulated before the tonoplast broke, and the VE organelle was distinct. Golgi bodies and vesicles, which were associated closely with synthesis and transportation of secondary cell wall substances, were also abundant. After the tonoplast broke, these substances accumulated faster. Simultaneously, the protoplasm was disaggregated and the agglomerated chromatin was distributed over the margin of the nucleus, showing the typical characteristics of programmed cell death (PCD). During secondary cell wall formation, no cell wall substances accumulated between the terminal cell walls of neighboring VEs. In addition, terminal cell wall substances were disaggregated in the post secondary cell wall formation. Later, when the remnant terminal cell wall was broken in the third stage, perforation occurred. Thus, for these successive stages of VE differentiation, the critical stage, when differentiation was not reversible, was at the start of secondary cell wall formation with succeeding VE differentiation similar to a typical PCD process.     

银合欢根瘤细胞的超微结构

银合欢是热带豆科固氮树种,已引起世界各国的普遍重视。我国大陆沿海亚热带地区已有60—70年的引种史。在过去引种栽培的基础上,80年代由国际固氮树种协会(NFTA)和麦威夷大学提供我们一批新银合欢种籽。厦门引种栽培的银合欢,与在其它热带地区有同样表现,速生快长、结果荚早、种籽成熟弹出,就地萌发丛生,压倒附近的其它植物。它的根系生长十分发达。幼苗期就结瘤很多,根瘤直径2.5—15mm,呈现不同形状的复式分叉瘤。测出固氮活性8.069—12.207βmC_2H_4·g~(-1)鲜瘤·时~(-1)。另外植株各部分蛋白质含量丰富,其中还含有一种特殊的氨基酸,与其固氮细胞累积转运有着密切关系。本文仅介绍银合欢根瘤细胞结构变化特征,和与其它豆科根瘤的比较进行了讨论。     

Micromechanics of wood subjected to axial tension

Summary The behaviour of a small group of wood fibers of Sitka spruce during tensile loading is investigated. The load-extension curves for both early and late wood fibers consist of three distinct segments. The first segment is almost a straight line, at some stage of loading a yield point is observed. Beyond this point the specimen becomes less stiff and undergoes a large, mainly irreversible deformation. As the load is increased further, the curve exhibits the third segment showed by a significant change in slope. These curves look different from those obtained on thick specimens. In this respect, the behaviour of a thin wood specimen subjected to cyclic type tensile loading along its longitudinal direction is also illustrated. Based on wood microstructure, a model is presented to interpret the evolution of the Young's modulus of a wood fiber during tensile loading. The model considers wood as an assembly of cylindrical fibers pasted together in a longitudinal direction. We have assumed the cell wall to comprise only an S₂ layer made of a composite material consisting of a lignin and hemicellulose matrix reinforced by helical microfibrils along the fiber. Furthermore, it is assumed that the microfibril angle a in the S₂ layer is not uniform along the fiber axis and matrix degradation occurs in the zones where the microfibril angles are bigger. The validity of this assumption is verified by using holographic interferometry to visualize the displacement field of the specimen's surface under tension.The work reported in this paper is supported by a grant from the Swiss National Science Foundation, and its support is gratefully acknowledged     

油樟油细胞和粘液细胞发育的超微结构

利用超薄切片法和透射电镜研究油樟油细胞和粘液细胞发育过程。依据油细胞3层细胞壁的发育将其分为4个阶段。阶段1：仅有初生纤维素壁层，又可分为原始细胞和细胞液泡化二时期。质体内具白色小泡和黑色嗜饿滴，细胞质中有黑色或灰色的嗜饿物质，以及嗜饿物质与液泡的融合。阶段2：栓质化壁层的形成。片层状的栓质叠加在初生纤维素壁内侧。阶段3：内纤维素壁层的形成。较厚而结构松散的内纤维素壁层逐步形成，并叠加在栓质化壁层的内侧，大液泡成为充满嗜饿油脂的油囊。阶段4：油细胞成熟及细胞质解体。杯形构造由内纤维素壁层向细胞腔内突起形成，油囊由液泡包被连接到杯形构造中。解体的细胞质变得电子不透明或呈杂乱状态。粘液细胞发育方式有两种：一种是由内纤维素形成以后的油细胞发育而来，其细胞质中不断产生以同心圆或螺旋线方式排列的多膜结构，并充满整个细胞腔，最后多膜结构解体而成为丝状或颗粒状的粘液；另一种是由已完全成熟的油细胞发育而来，其油囊中的油呈不均匀的状态，并产生局部降解点，逐步扩大，最后油完全降解成颗粒成或丝状的粘液。     

Etching of wood surfaces by glow discharge plasma

This research tests the hypothesis that plasma will cause differential etching of wood cell walls because of variation in the susceptibility of aromatic and aliphatic polymers to degradation by plasma. Wood was exposed to glow discharge plasma, and scanning electron microscopy and chromatic confocal profilometry were used to examine etching of cell walls. Plasma etched cell walls and made them thinner, but the middle lamella was more resistant to etching than the secondary wall. Plasma created small voids within the secondary wall, which were separated by thin lamellae connected to the middle lamella and tertiary wall layers. Larger voids were created in cell walls by the etching of bordered and half-bordered pits. Etching of the uppermost layer of cells at wood surfaces occurs first and when large voids are created in the walls of these cells then significant plasma etching of the underlying cells occurs. Etching of wood cell walls can be quantified using confocal profilometry, and using this technique a strong relationship between applied plasma energy and volume of cell wall etched by plasma was observed. It is concluded that all of wood’s polymers can be degraded by plasma even though cell wall layers that are rich in lignin are etched more slowly than other parts of the cell wall.     

New cell wall and cell lumen wood polymer composites

Summary Furfuryl alcohol-based (FA) cell wall and methyl methacrylate-based (MMA) combination formulations were used to make wood polymer composites (WPC). Swelling gradients developed during preparation. Properties (density, hardness, water extractables, antiswell efficiency) gradients were observed along samples in 5 of the 7 treating formulations. Two cell wall treatments based on furfuryl alcohol did not show the gradients. The results suggest treating solution separations occurred during impregnation and the resulting nonhomogenious chemical produced the properties gradients. WPC made using the combination formulations based on MMA had properties which fell between cell wall and cell lumen formulations.It is gratefully acknowledged that Mr. Michel Andrew, Student Assistant, carried out the experiment part of this study     

Cell wall fracture properties in relation to lignin distribution and cell dimensions among three genetic groups of radiata pine

Summary The position of fracture within the cell wall on split tangential longitudinal surfaces of air dry wood was quantified for three genetic groups of Pinus radiata D. Don. Differences in the position of fracture within the cell wall among these groups of trees were compared with lignin distribution and cell wall dimensions. In the control trees equivalent to typical New Zealand grown radiata pine, fracture occurred predominantly between the middle lamella and S1 layers as well as within the S1 layer, producing large numbers of fines on the fracture surface. In the open pollinated NZ850–55 group, fracture occurred predominantly between the S1 and S2 layers as well as within the S1 layer, producing fewer fines on the surface. In the NZ850–55 x Guadalupe group, fracture occurred in a similar fashion to the open pollinated group except for a greater number of transwall fractures exposing the cell lumen on the fracture surface. The differences in fracture behaviour between the control and genetically select groups are attributed to reduced lignification at the S1/S2 boundary in the genetically select trees. Observed differences in both the type of fracture and its location were unrelated to cell dimensions. These observations are discussed in relation to the observed differences in thermomechanical pulping properties exhibited by these groups of trees.     

Effect of moisture content on the longitudinal tensile creep behavior of wood

In our previous report, we investigated the effect of the microfibril angle (MFA) in the middle layer of the secondary wall (S₂) on the longitudinal creep behavior of a thin homogeneous earlywood specimen sugi. In the present study, we investigated the role of moisture on the tensile creep behavior of wood. We discuss the creep behavior of the wood cell wall from the viewpoint of the composite structure of the cell wall and the properties of the constituent materials. A microtomed thin specimen of earlywood of sugi (Cryptomeria japonica D.Don) was used for the longitudinal tensile creep test. Creep tests were conducted at three moisture stages (oven-dry, air-dry, fiber saturation point) over a broad range of MFA. Results showed that the longitudinal tensile creep behavior was highly dependent on both the moisture content and the MFA. With a small MFA, the variation in the creep function among the three moisture states was very small. For a large MFA, the variation in the creep function was larger. At low moisture contents, the magnitude of the creep function was very small, while at high moisture content, it was very large except for the case of specimens with very small MFA. Those results show that the longitudinal tensile creep behavior was directly affected by the fine composite structure and the internal properties of the cell wall constituents.     

Nanostructural assembly of cellulose,hemicellulose, and lignin in the middle layer of secondary wall of ginkgo tracheid

Physical, chemical, and biological properties of wood depend largely on the properties of cellulose, noncellulosic polysaccharides, and lignin, and their assembly mode in the cell wall. Information on the assembly mode in the main part of the ginkgo tracheid wall (middle layer of secondary wall, S2) was drawn from the combined results obtained by physical and chemical analyses of the mechanically isolated S2 and by observation under scanning electron microscopy. A schematic model was tentatively proposed as a basic assembly mode of cell wall polymers in the softwood tracheid as follows: a bundle of cellulose microfibrils (CMFs) consisting of about 430 cellulose chains is surrounded by bead-like tubular hemicellulose-lignin modules (HLM), which keep the CMF bundles equidistant from each other. The length of one tubular module along the CMF bundle is about 16 ± 2 nm, and the thickness at its side is about 3–4 nm. In S2, hemicelluloses are distributed in a longitudinal direction along the CMF bundle and in tangential and radial directions perpendicular to the CMF bundle so that they are aligned in the lamellae of tangential and radial directions with regard to the cell wall. One HLM contains about 7000 C₆-C₃ units of lignin, and 4000 hexose and 2000 pentose units of hemicellulose.     

A model of anisotropic swelling and shrinking process of wood

To elucidate the origin of the shrinking anisotropy of wood during the drying process, as well as to begin to gain an understanding of the interaction between the moisture and the cell wall components, the shrinking process of a single wood fiber regarding water desorption was simulated by using an analytical model which was developed in the previous report (Part 1). Resulting data were compared with the experimental ones in this paper. The following conclusions were obtained: (1) The matrix substance, as a skeleton in the secondary wall, tends to shrink isotropically. However, the cellulose microfibrils, as a rigid framework of the cell wall, almost did not shrink at all due to the water desorption. As result, wood shrinks anisotropically during a drying process. The microfibril angle in the S2 layer is one of the most important factors related to the degree of shrinking anisotropy of the wood while drying. (2) According to the simulation, the expansive strain caused in the matrix skeleton by the water sorption increases by 15% (= 150,000 micro-strains) from the oven-dried condition to the green condition. Based on this value, the moisture content at the fiber saturation point is calculated to be about 35%, which is close to the experimentally obtained one. These results give quantitative evidences that the hygroexpansion of the wood cell wall is controlled by the mechanism of the reinforced matrix hypothesis. Received: 28 July 1998     

The ultrastructure of cellulose from wood

Summary During the delignification of wood several processes overlap one another. One of these is the penetration of the wood samples by the delignifying solution. Penetration tests under different conditions show that there is almost no difference in the penetration depth of wood samples penetrated by diffusion only and of wood samples treated with pressure. In both cases the pits are closed during the flow of fluids. Vacuum treated samples show better penetration and most of the pits in these samples remain open. The distribution of fluids within the cell walls takes place in the intercellular spaces, in small openings in the compound middle lamella and in the secondary wall 1 as well as in very fine pores in the secondary wall 2. The penetration of a wood sample is greatly facilitated if the sample is mechanically injured. A slowly proceeding delignification with ethylene sulphite shows that the delignification obviously starts in the S 1 layer and proceeds from there towards the compound middle lamella and the S 2 layer. In the first stages of lignin removal the compound middle lamella is also attacked, the attack beginning at the border of the pit chambers.     

纳米压痕技术测量管胞次生壁S2层的纵向弹性模量和硬度

重点研究和详细介绍了利用纳米压痕技术测试管胞次生壁S2 层纵向弹性模量以及硬度的实验技术 ,并测试了人工林杉木早晚材管胞S2 层的纵向弹性模量和硬度。结果表明 :杉木晚材管胞S2 层的平均纵向硬度为0 390GPa ,弹性模量的平均值为 1 4 84 4GPa ;早材管胞S2 层的硬度和模量则小于晚材 ,平均值分别为 0 30 6GPa和9 82 3GPa。     

Eucalypt Wood Anatomical and Physical Properties and Their Effects on Plywood Veneer Quality

In order to better understand the reasons why eucalypt veneer checks easily and severely, wood samples of three eucalypt species were selected, and their anatomical and physical properties were examined according to conventional methods and the national standards. The effects of variances in cell wall thickness of wood fibre and vessel, and diameter of the cell lumen as well as the tissue ratio on the quality of plywood veneer were analysed. The results show that： 1） There is a great difference in fibre cell wall thickness and diameter of the cell lumen between early wood and late wood of Eucalyptus delegatensis. 2） E. obliqua has a high wood fibre tissue ratio and the thickest fibre cell wall, but the difference inthe fibre cell wall thickness between early wood and late wood is the smallest. 3） The wood fibre tissue ratio of E. regnans is smaller than that of E. obliqua, and its wood fibre cell wall isthe thinnest and there is only a very small difference in fibre cell wall thickness between early wood and late wood. The difference inthe diameter of wood fibre cell lumen among early wood, transition area and late wood is also small： 4） E. delegatensis has the highest tangential shrinkage rate and radial-tangential shrinkage rate, andE. obliqua has the lowest. It is the variability of wood anatomical properties of these species that cause the difference in the veneer shrinkagei and then affects plywood veneer quality.     

The intestinal microbiome: A separate organ inside the body with the metabolic potential to influence the bioactivity of botanicals

For many years, it was believed that the main function of the large intestine was the resorption of water and salt and the facilitated disposal of waste materials. However, this task definition was far from complete, as it did not consider the activity of the microbial content of the large intestine. Nowadays it is clear that the complex microbial ecosystem in our intestines should be considered as a separate organ within the body, with a metabolic capacity which exceeds the liver with a factor 100. The intestinal microbiome is therefore closely involved in the first-pass metabolism of dietary compounds. This is especially true for botanical supplements, which are now marketed for various health applications. Being of natural origin, their structural building blocks, such as polyphenols, are often highly recognized by the human and especially the intestinal microbial metabolism machinery. Intensive metabolism results in often low circulating levels of the original products, with the consequence that final health effects of botanicals are often related to specific active metabolites which are produced in the body rather than being related to the product's original composition. Understanding how such metabolic processes contribute to the in situ exposure is therefore crucial for the proper interpretation of biological responses. A multidisciplinary approach, characterizing the food and phytochemical intake as well as the metabolic potency of the gut microbiota, while measuring biomarkers of both exposure and response in target tissues, is therefore of critical importance. With polyphenol metabolism as example, this review describes how the incorporation of microbial metabolism as an important variable in the evaluation of the final bioactivity of botanicals strongly increases the relevance and predictive value of the outcome. Moreover, knowledge about intestinal processes may offer innovative strategies for targeted product development.     

A comparison of nanoindentation cell wall hardness and Brinell wood hardness in jack pine (Pinus banksiana Lamb.)

Nanoindentation is a powerful tool for hardness testing on a very small scale. Since the technique was first introduced for studying wood cell wall mechanics, it has been integrated as an important tool for measuring the modulus of elasticity and hardness of wood cell walls. In this study, hardness measured with nanoindentation (nanohardness) was compared with hardness measured by the standard Brinell test method (Brinell hardness) on jack pine (Pinus banksiana Lamb.) wood. Nanoindentation was performed on both the S2 layer of the secondary cell wall and the middle lamella (ML) of early- and latewood fibers. Four annual growth rings were studied. The influence of growth ring and initial spacing on both measurements was analyzed. The relationship between Brinell hardness, nanoindentation measurements, and average ring density was also studied. Results suggest that Brinell- and nanohardness are controlled by different mechanisms and factors. The location of nanohardness measurements (i.e., S2 layer or ML) also influenced hardness differently. It was concluded that nanomeasurements are not an exact representation of wood mechanical properties conducted at the macro level because of the hierarchical structure of wood. The effect of other factors such as moisture or wood extractive content may also need consideration.     

Berberine hydrochloride attenuates cyclooxygenase-2 expression in rat small intestinal mucosa during acute endotoxemia

The effect of berberine hydrochloride (BBR) on inducible cyclooxygenase-2 (COX-2) in small intestinal mucosa and related mechanisms was investigated in a rat model of acute endotoxemia. The results showed that lipopolysaccharide (LPS) increased COX-2 expression, whereas SB202190 and BBR curtailed it. LPS increased phosphorylation of mucosal p38 MAPK and ATF2 as well as production of ATF2, whereas BBR attenuated these effects. LPS upregulated mucosal peroxisome proliferator-activated receptor gamma (PPARγ), but BBR reduced this receptor. GW9662 aggravated LPS-induced and reversed BBR-attenuated COX-2 expression. The findings showed that BBR ameliorated COX-2 overexpression partially via modulation of p38 and PPARγ pathways during acute endotoxemia.     

The fluorescence characteristics of furfurylated wood studied by fluorescence spectroscopy and confocal laser scanning microscopy

The fluorescence of furfurylated wood was studied. Furfurylation of wood introduced fluorescent curing products into the cell walls. Fluorescent products were also found in the lumina if high loadings were used and/or if the wood contained cells with small radii. More intense fluorescence was obtained from lignin-rich parts of the compound cell wall (i.e., the middle lamella and the cell corners) than from the secondary cell wall if the wood was impregnated using furfuryl alcohol (FA), while impregnation using small poly(FA) oligomers showed no or only minor differences between different regions. The study also showed that when higher amounts of catalyst were added to the impregnation liquid, a red-shift in the fluorescence from the furfurylated wood was seen, corresponding to an increased conjugation length of conjugated poly(FA) formed within the wood cell wall. Longer conjugation length than within the cell wall was observed for the poly(FA) formed within the lumina. This indicates that the cell wall polymers restrict poly(FA) formation.     

Effects of chemical treatments on ultra-high-yield pulping 1. Fiber separation

Summary Specially designed wood blocks from Norway spruce were used to study the nature of the fracture surfaces developed in shear using a tensile tester. In the case of the control (water-soaked blocks), the fracture in the latewood takes place mainly in the S₁ layer while in the earlywood the fracture occurs across the double cell wall. After dilute alkali treatment, some earlywood cells also fracture in the S₁ layer. For sulfite-treated samples, on the other hand, both earlywood and latewood fracture in the middle lamella.Financial support from the Empire State Paper Research Associates (ESPRA) is greatly appreciated     

Comparative study of anatomy and lignin distribution in normal and tension wood of Salix gordejecii

Fibre morphology, anatomy and ultrastructure in cell wall of Salix gordejecii normal wood were examined by transmission electron microscopy (TEM). S. gordejecii tension wood can be recognized anatomically by the presence of gelatinous (G) fibres, which contain a conspicuously thickened inner cell wall layer. TEM images showed that cell wall of S. gordejecii normal wood was typically divided into three layers including the primary wall (P), the middle lamellar (ML) and the secondary wall (S₁, S₂ and S₃). Lignin distribution was determined by using confocal laser scanning microscopy (CLSM) and transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDXA). Confocal images (530 nm) of S. gordejecii normal wood showed strongly lignified CCML, and weakly lignified ML and S2 layer. Weakly lignified fibres (F) and strongly lignified vessels (V) were also detected by using CLSM. Results obtained from confocal microscopy were further confirmed by using TEM-EDXA, indicating that the ratio of lignin concentration in CCML, ML and S2 is 1.72 (1321):1.31 (1006):1 (768). Lignin distribution in tension wood is similar to that in normal wood, except for the non-lignified G layer.     

Development and structure of the terminal layer in bamboo culms

In bamboo, the inner lining of the culm wall towards the lacuna is designated as a terminal layer. It develops during culm elongation by separation of pith cells. Subsequently, these cells collapse thus forming a skin-like structure to be attached to a transition layer of the culm wall. The transition layer between the skin-like structure and the ground tissue consists of a few cell rows of mostly radially and axially shortened cells with often thickened walls. Both the skin-like structure and the transition layer exhibit structural differences between species. These characteristics of the inner culm wall have significance for culm seasoning and especially for the diffusion treatment with preservatives.