Miho Kojima

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.

Effect of the lateral growth rate on wood properties in fast-growing hardwood species

We investigated the feasibility of using several fast-growing tropical or subtropical hardwood species for timber production by measuring key wood qualities in relationship to the high rates of lateral growth. The trees tested were sampled from even-aged plantations of Acacia mangium, A. auriculiformis, hybrid Acacia (A. mangium × A. auriculiformis), Eucalyptus grandis, E. globulus, and Paraserianthes falcataria (Solomon and Java origin) that had already reached commercial harvesting age. The released strain of the surface growth stress (RS), xylem density (XD), microfibril angle (MFA), and fiber length (FL) were measured at the outermost part of the xylem at breast height in each tree. Results were then compared to the lateral growth rate (radius/age) at breast height, which provides a relative indicator of the amount of tree growth per year. Our findings indicated that RS was constant, regardless of lateral growth rate in each species. Similar results were observed for XD, MFA, and FL, with a few exceptions, suggesting that high growth rates do not intrinsically affect the wood properties of fast-growing tropical or subtropical species that have reached harvesting age. However, special attention must be paid to patterns of xylem maturation when developing plantations of such species.

The interrelation between microfibril angle (MFA) and hygrothermal recovery (HTR) in compression wood and normal wood of Sugi and Agathis

Abstract Tree growth stress (GS) consists of an elastic component and a viscoelastic locked-in component. The elastic component is released instantaneously by cutting wood, whereas the locked-in component remains. The latter can be released by hot water treatment, which is known as hygrothermal recovery (HTR). In this paper the mechanism behind HTR is described and interpreted in terms of the microfibril angle (MFA) in the cell wall as follows: during cell-wall maturation, axial tensile stress is generated in the cellulose microfibrils (CMF), whereas isotropic compressive stress is generated in the matrix of lignin-hemicellulose (MT). Some amount of microscopic stresses remains following the removal of the wood from the living stem. Hygrothermal (HT) treatment induces recovery of remaining compressive stress in the MT, which causes its expansion. Axial tensile stress in the CMF are released by HT softening of the MT. This causes the CMF to contract along its length and to expand laterally. The combined effect of the expansions of the MT and contraction of the CMF causes the wood to deform anisotropically. This is the HTR of wood. The degree of anisotropy is determined by the MFA on the basis of reinforced-matrix theory.

ROOT GROWTH INHIBITING, a Rice Endo-1,4-β-d-Glucanase, Regulates Cell Wall Loosening and is Essential for Root Elongation

The molecular mechanism involved in cell wall dynamics has not been well clarified, although it is quite important for organ growth. We characterized a rice mutant, root growth inhibiting (rt), which is defective in root elongation. The rt mutant showed a severe defect in cell elongation at the root-elongating zone with additional collapse of epidermal and cortex cells at the root tip caused by the defect in the smooth exfoliation of root cap cells. Consistent with these phenotypes, expression of the RT gene, which encodes a member of the membrane-anchored endo-1,4-β-d-glucanase, was specifically localized in the root-elongating zone and at the junction between epidermal and root cap cells. The enzymatic analysis of root extracts from the wild-type and rt mutant indicated that RT hydrolyzes noncrystalline amorphous cellulose. The cellulose content was slightly increased but the crystallinity of cellulose was decreased in the rt root. In addition, the hemicellulose composition was different between wild-type and rt roots. The total extensibility was significantly lower in the rt root explants. Based on these results, we concluded that RT is involved in the disassembly of the cell wall for cell elongation in roots as well as for root cap exfoliation from the epidermal cell layer by hydrolyzing the noncrystalline amorphous cellulose fibers of cellulose microfibrils resulting in loosening of the hemicellulose and cellulose interaction.

Effects of the lateral growth rate on wood quality of Gmelina arborea from 3.5-, 7- and 12-year-old plantations

Abstract• Awareness of the shortage of fossil resources leads to an increasing demand for woody biomass. We investigated the feasibility of using fast-growing Gmelina arborea wood for material production. Gmelina arborea wood samples were collected from trees of varying cambium ages in Indonesia, from 3.5-, 7- and 12-year-old plantations.• The lateral growth rate and the cambium age did not significantly affect the longitudinal released strain of the growth stress, xylem density, or microfibril angle at the outermost surface of the secondary xylem at any sampling site. However, fiber length in the 3.5-year-old plantation tended to be shorter in smaller diameter trees, whereas in larger diameter trees it was almost the same as that in trees from the 7- and 12-year-old plantations. This suggests that smaller diameter trees in the 3.5-year-old plantation had not yet produced mature wood.• Xylem qualities had already reached values appropriate for harvesting, except in the smaller diameter trees from the 3.5-year-old plantation. This indicates that the larger diameter trees had already matured, regardless of their cambium age. These results suggest that the next step is to develop silvicultural treatments to increase the lateral growth rate during the early growing stage, in order to produce as much mature wood as possible, as quickly as possible.Résumé• La prise de conscience de la raréfaction des ressources fossiles conduit à une demande croissante de biomasse ligneuse. Dans ce contexte nous avons examiné la faisabilité d’utiliser une essence à croissance rapide Gmelina arborea pour la production de bois matériau.Nous avons collecté en Indonésie des échantillons de bois dans des arbres provenant de plantations de 3,5, 7 et 12 ans.• Pour tous les sites, le taux de croissance radiale et l’âge cambial n’affectent pas les déformations résiduelles longitudinales des contraintes de croissance, la densité du xylème ou l’angle des microfibrilles de la périphérie du xylème secondaire. Cependant pour les petits arbres de la plantation de 3,5 ans, les fibres sont plus courtes tandis que pour les gros arbres les fibres ont une longueur comparable à celle des arbres des plantations de 7 et 12 ans. Cela suggère que les petits arbres de la plantation de 3,5 ans ne produisent pas encore du bois mature.• Les qualités du xylème ont facilement atteint des valeurs justifiant l’exploitation exception faite des petits arbres de la plantation de 3,5 ans. Cela indique que les gros arbres sont déjà matures indépendamment de leur âge. Ces résultats suggèrent que l’étape suivante est le développement de traitements sylvicoles visant à augmenter le taux de croissance radiale durant le stade initial de croissance, dans le but de produire le plus rapidement possible le plus de bois adulte.

Determining factor of xylem maturation in Eucalyptus grandis planted in different latitudes and climatic divisions of South America: a view based on fiber length

The objective of this study was to determine the factor of xylem maturation in Eucalyptus grandis W. Hill ex Maid. planted in four different latitudes and climatic divisions of South America, based on the pattern of the radial distribution of fiber length. In the plantation closest to the equator, the extent of juvenile wood is determined by distance from the pith and is consistent from tree to tree, regardless of growth rate. In contrast, in the plantation farthest from the equator, xylem maturation is controlled by cambial age and varies from tree to tree, depending on growth rate. To produce as much mature wood as early as possible in E. grandis planted closer to the equator, lateral growth should be accelerated from the early growing stage, because the formation of mature wood starts after a certain trunk diameter is reached. Conversely, in plantations far from the equator, it is necessary to first arrest lateral growth at an early growth stage and then accelerate lateral growth after a certain cambiu...