Showing papers by "Masato Yoshida published in 2013"

Crystallization of cellulose microfibrils in wood cell wall by repeated dry-and-wet treatment, using X-ray diffraction technique

Abstract: The purpose of this study is to investigate the effect of repeated moisture change on the crystallinity and crystal size of cellulose microfibrils (CMF) in sugi (Cryptomeria japonica D.Don) and karamatsu (Larix kaempferi Gord.) wood cell wall. Based on obtained results, we discussed the qualitative change in the fine structure of CMF caused by repeated dry-and-wet (RDW) treatments. Green quarter-sawn specimens (5 × 16 × 15 mm in thickness × length × width) and microcrystalline cellulose powder (Avicel) were prepared, and these specimens were subjected to 7 times at most of heated or unheated RDW treatments. After giving RDW treatments, specimens were seasoned to the fiber saturated point and absolutely dried. Wide angle X-ray diffraction measurements were adopted to determine the crystallinity and the crystal size in each condition. Results indicate that crystallinity and crystal size in wood specimens gradually increased with the progress of heated or unheated RDW treatments, while no such increases were observed in Avicel powder. Those results suggest that RDW treatments promote the crystallization of CMF in wood cell wall, regardless of heating. We presume that noncrystalline cellulose forms hydrogen bonding with the cellulose at the surface of crystalline region with the progress of RDW treatments, thus enlarging the crystal size. Avicel powder did not show features that were observed in wood specimens by RDW treatments, because it contained few noncrystalline cellulose.

Micromechanical detection of growth stress in wood cell wall by wide-angle X-ray diffraction (WAX)

Abstract: Abstract The present study is aimed at the detection of mechanical stresses generated in the cellulose microfibril (CMF) crystals situated in the secondary wall (S2) of living cells. Green wood specimens were boiled in water to release the internal stress in the CMF by the hygrothermal softening of the lignin-hemicellulose matrix (MT). Thereafter, the changes in d200 and d004 lattice spacings of crystalline cellulose were observed in boiled and nonboiled samples by wide-angle X-ray diffraction. The d200 lattice spacing increased, whereas d004 lattice spacing decreased. The results show that a mechanical stress still remained in the CMF and the MT region in the green cell wall, even after releasing the macroscopic surface growth stresses by removal of the wood block from the living stem. The interpretation is that CMF generates tensile stress in the longitudinal direction, and surrounding MT substances generate compressive stress in the living cell wall, which compresses the CMF in the lateral direction. The results confirm the “unified hypothesis” for explaining the mechanism of growth stress generation.

RICE SALT SENSITIVE3 binding to bHLH and JAZ factors mediates control of cell wall plasticity in the root apex.

Abstract: Plasticity of root growth in response to environmental cues and stresses is a fundamental characteristic of plants, in accordance with their sessile lifestyle. This is linked to the balance between plasticity and rigidity of cells in the root apex, and thus is coordinated with the control of cell wall properties. However, mechanisms underlying such harmonization are not well understood, in particular under stressful conditions. We have recently demonstrated that RICE SALT SENSITIVE3 (RSS3), a nuclear factor that mediates restrictive expression of jasmonate-induced genes, plays an important role in root elongation under saline conditions. In this study, we report that loss-of-function of RSS3 results in changes in cell wall properties such as lignin deposition and sensitivity to a cellulose synthase inhibitor, concomitant with altered expression of genes involved in cell wall metabolism. Based on these and previous phenotypic observations of the rss3 mutant, we propose that RSS3 plays a role in the coordin...

On the mechanical interaction between cellulose microfibrils and matrix substances in wood cell walls: effects of chemical pretreatment and subsequent repeated dry-and-wet treatment

Abstract: We investigated the influences of chemical pretreatments and subsequent repeated dry-and-wet (RDW) treatments on the mechanical linkage between cellulose microfibrils (CMFs) and matrix substances (MT) in wood cell wall. Sugi (Cryptomeria japonica D. Don) quarter-sawn specimens were subjected to various types of chemical pretreatments, including ethanol and benzene extraction, delignification, alkali extraction, and hygrothermal treatment, to give substantial damages to principal constituents of wood cell wall, followed by 5 times of RDW treatment. After giving chemical pretreatment, the d-spacing of (200) lattice plane of cellulose Iβ (d 200), the crystallinity of wood cell wall, and the crystal size of the cellulose were measured at the fiber saturated point, using X-ray diffraction techniques. Thereafter, these were measured again at the absolutely dried condition in the process of subsequent RDW treatments. The d 200 in specimens, which were given to light pretreatments, largely expanded by drying at the early stages of RDW treatments, then it decreased and became constant after 5 times of RDW treatments. On the other hand, d 200 in specimens, which were given to intensive pretreatments, remained constant at a relatively small level throughout the whole process of RDW treatments. After 5 times of RDW treatments, d 200 became similar values between the above two groups. This suggests that RDW treatments have similar effects as intensive pretreatments, which induce substantial damages to the microscopic region in the wood cell wall such as interfacial separation between CMF, MT, and so forth. These defects would weaken mechanical interaction between CMF and MT in the wood cell wall during drying.

In situ measurement of tensile elastic moduli of individual component polymers with a 3D assembly mode in wood cell walls

Abstract: We attempted to measure in situ the tensile elastic moduli of individual component polymers with a three-dimensional (3D) assembly mode in the cell walls of Sugi (Cryptomeria japonica D. Don) without isolating the polymers. To prepare wood tangential slices [50 × 6 × 0.2 mm (L × T × R)] consisting of lignin with a 3D assembly mode in the cell walls, cellulose and hemicellulose were removed using the method of Terashima and Yoshida (2006) to obtain methylated periodate lignin slices. To prepare wood slices consisting of polysaccharide with a 3D assembly mode in the cell walls, lignin was removed using the method of Maekawa and Koshijima (1983) to obtain holocellulose slices. Static tensile test was applied to determine the elastic moduli of 3D lignin and 3D polysaccharide slices. The followings were revealed. The elastic modulus of the 3D lignin slices was 2.8 GPa, regardless of the microfibril angle (MFA) in the slices. The elastic moduli of the 3D polysaccharide slices with MFAs of 14°, 23°, 34°, and 42° were 18, 12, 9, and 4 GPa, respectively. The former shows that the lignin with a 3D assembly mode behaves as an isotropic substance in the cell walls, while the latter suggests that the 3D polysaccharide slice shows marked anisotropic structure in the cell wall. Despite the fact that cellulose content increased after lignin removal, values of substantial elastic modulus of the cell wall slightly decreased regardless of MFA. Following two possible reasons were pointed out for explaining this phenomenon. First, lignin removal caused an artifactual deterioration in the polysaccharide slices at the level of macromolecular aggregate. Second, rigid and fusiform-shaped cellulose crystallites are dispersed in the soft matrix of amorphous polysaccharide, and those are loosely connected to each other by the intermediary of matrix polysaccharide. Those suggest that the rigid cellulose crystallite can optimize its strong mechanical performance in the polysaccharide framework of the wood cell wall in combination with the ligninification.

Changes in xylem tissue and laccase transcript abundance associated with posture recovery in Chamaecyparis obtusa saplings growing on an incline

Abstract: Lignin is a major component of plant cell walls and is synthesised through oxidative polymerisation of monolignols. The transcription level of laccase, an enzyme implicated in monolignol polymerisation, is higher in the tissue forming compression wood than in normal wood. Compression wood, which is a special xylem tissue that develops to reorient inclined stems, also has a higher lignin content than normal wood. In the present study, Chamaecyparis obtusa Endl. saplings were grown on an incline and the following variables were tracked for 10 weeks: posture recovery of the saplings; development of xylem tissue on the lower side of inclined stems; and the transcription level of laccase. The posture of saplings approached vertical after 8 weeks, the development of compression wood reached a peak around 6 weeks and laccase transcription was the highest after 4 weeks. These results suggest a sequence of righting mechanisms. Inclination stimulates an increase in the abundance of laccase transcript and this increase encourages the formation of compression wood. The accumulation of compression wood then causes the stem to bend upward.

Effects of Repeated Wet-and-dry Treatments on Water and Gas Adsorption Performance of Wood

Abstract: We evaluated the water and gas adsorption performances of sugi (Cryptomeria japonica D. Don) crosscut and quarter-sawn specimens, which were given three or six repetitions of dry-and-wet treatments under the room temperature or high temperature conditions. Equilibrium moisture content of all specimens decreased with the progress of repeated wet-and-dry treatments, regardless of the effect of heating. On the other hand, amounts of nitrogen gas adsorption increased with the progress of repeated wet-and-dry treatments, especially in the quarter-sawn specimen. These phenomena, observed in both water and nitrogen gas adsorption, suggest that repeated drying and re-swelling decreased the amount of hydrophilic regions such as noncrystalline cellulose at the microscopic level. It is also considered that cracks and pores would arise on the surface of wood cell walls at the submicroscopic level.