A contribution to the ultrastructure of tension wood fibers
TL;DR: After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils.
Abstract: Pronounced tension wood from four North-American hardwood species has been examined by light and electron microscopy. Delignified fibers were also studied. The gelatinous layer was in all cases loosely attached to S2 but varied considerably in thickness within each species and was in one case terminated towards the lumen by a layer resembling S3. A terminal lamella was not observed. After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils. In the absence of hemicelluloses and lignin, the microfibrils are probably bound together less firmly than they are in other cell wall layers. The gelatinous layer is more readily separated from the remainder of the cell wall by mechanical forces than by chemical reagents.
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TL;DR: The variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood are considered.
Abstract: The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.
437 citations
TL;DR: Scanning Raman microscopy was shown to be a powerful, nondestructive tool for imaging changes in molecular cell wall organization with high spatial resolution.
Abstract: Confocal Raman microscopy was used to illustrate changes of molecular composition in secondary plant cell wall tissues of poplar (Populus nigra × Populus deltoids) wood. Two-dimensional spectral maps were acquired and chemical images calculated by integrating the intensity of characteristic spectral bands. This enabled direct visualization of the spatial variation of the lignin content without any chemical treatment or staining of the cell wall. A small (0.5 μm) lignified border toward the lumen was observed in the gelatinous layer of poplar tension wood. The variable orientation of the cellulose was also characterized, leading to visualization of the S1 layer with dimensions smaller than 0.5 μm. Scanning Raman microscopy was thus shown to be a powerful, nondestructive tool for imaging changes in molecular cell wall organization with high spatial resolution.
368 citations
TL;DR: This work investigates the structural and compositional basis of a sophisticated plant movement mechanism--the hydration-dependent unfolding of ice plant seed capsules--the reversible origami-like folding pattern proceeds via a cooperative flexing-and-packing mechanism actuated by a swellable cellulose layer filling specialized plant cells.
Abstract: Hydro-responsive plant movements have provided inspiration for the design of adaptive materials. Harrington et al. investigate the hydration-dependent unfolding of ice plant seed capsules and find an origami-like folding pattern, which could aid the development of biomimetic folding structures.
237 citations
TL;DR: This review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers.
Abstract: Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.
197 citations
TL;DR: Measurements show that mesoporosity is high in tension wood with a typical thick G-layer while it is much less with a thinner G- layer, sometimes no more than normal wood.
Abstract: The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called G-layer, in the fibre wall. The structure of G-layer has been recently described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2 to 50 nm). This led us to revisit the concept of G-layer that was until now only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with typical thick G-layer while it is much less with thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without G-layer is as low as in normal wood. Not depending on the amount of pores, the pore sizes distribution are always centred around 6-12 nm. These results suggest that, among species producing fibres with G-layer, large structural differences of G-layer exist between species
196 citations
Cites background from "A contribution to the ultrastructur..."
...This layer is composed of cellulosic microfibrils that are nearly parallel to the fibre axis (Dadswell and Wardrop, 1955; Wardrop, 1964; Côté et al., 1969) embedded in a highly hydrated polysaccharide matrix (Nishikubo et al....
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...This layer is composed of cellulosic microfibrils that are nearly parallel to the fibre axis (Dadswell and Wardrop, 1955; Wardrop, 1964; Côté et al., 1969) embedded in a highly hydrated polysaccharide matrix (Nishikubo et al., 2007; Bowling and Vaughn, 2008; Mellerowicz et al., 2008)....
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References
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Journal Article•
307 citations
TL;DR: In this article, different organic solvents were passed through green cylindric samples of sapwood of Abies alba Miller and Picea abies Karst, at a pressure equal to 5 cm water column.
Abstract: On the Longi tudinal Permeabi l i ty of Green Sapwood of Abies alba Miller and Piceaabies Karst. to Organic Solvents Summary Different organic solvents were passed through green cylindric samples of sapwood of Abies alba Miller and Picea abies Karst, at a pressure equal to 5 cm water column. By this means the factors influencing the rate of flow could be determined. 1. The rate of flow of an organic solvent is essentially dependent on its viscosity. 2. Although viscosity of the solvent influences the rate of flow especially at the onset of filtration, a high surface tension of the solvent can cause a continuous decrease of the rate of flow with the progress of the experiment. On the contrary a low surface tension effects only a small decrease in the rate of flow. 3. Hydrophobie solvents cannot be filtrated through untreated green sapwood even under application of a higher pressure. 4. For the solvents used here, no influence of the molecular size on the rate of flow is detectable.
156 citations
TL;DR: Microscopic examination of collapsed samples of tension wood has led to the conclusion that the appearance of collapse in specimens containing tendon wood can often be attributed in part to excessive shrinkage associated with the development of fissures between cells, although true collapse does also occur.
Abstract: The cell wall organization, the cell wall texture, and the degree of lignification of tension wood fibres have been investigated in a wide variety of temperate and tropical species. Following earlier work describing the cell wall structure of tension wood fibres, two additional types of cell wall organization have been observed. In one of these, the inner thick "gelatinous" layer which is typical of tension wood fibres exists in addition to the normal three-layered structure of the secondary wall; in the other only the outer layer of the secondary wall and the thick gelatinous layer are present. In all the tension wood examined the micellar orientation in the inner gelatinous layer has been shown to be nearly axial and the cellulose of this layer found to be in a highly crystalline state. A general argument is presented as to the meaning of differences in the degree, of crystallinity of cellulose. The high degree of crystallinity of cellulose in tension wood as compared with normal wood is attributed to a greater degree of lateral order in the crystalline regions of tension wood, whereas the paracrystalline phase is similar in both cases. The degree of lignification in tension wood fibres has been shown to be extremely variable. However, where the degree of tension wood development is marked as revealed by the thickness of the gelatinous layer the lack of lignification is also most marked. Severity of tension wood formation and lack of lignification have also been correlated with the incidence of irreversible collapse in tension wood. Such collapse can occur even when no whole fibres are present, e.g. in thin cross sections. Microscopic examination of collapsed samples of tension wood has led to the conclusion that the appearance of collapse in specimens containing tendon wood can often be attributed in part to excessive shrinkage associated with the development of fissures between cells, although true collapse does also occur. Possible explanations of the irreversible shrinkage and collapse of tension wood fibres are advanced.
91 citations