Yuzo Furuta

Suppression and acceleration of cell elongation by integration of xyloglucans in pea stem segments.

Xyloglucan is a key polymer in the walls of growing plant cells. Using split pea stem segments and stem segments from which the epidermis had been peeled off, we demonstrate that the integration of xyloglucan mediated by the action of wall-bound xyloglucan endotransglycosylase suppressed cell elongation, whereas that of its fragment oligosaccharide accelerated it. Whole xyloglucan was incorporated into the cell wall and induced the rearrangement of cortical microtubules from transverse to longitudinal; in contrast, the oligosaccharide solubilized xyloglucan from the cell wall and maintained the microtubules in a transverse orientation. This paper proposes that xyloglucan metabolism controls the elongation of plant cells.

Enhancement of growth and cellulose accumulation by overexpression of xyloglucanase in poplar

Because the loosening of xyloglucan in the cell wall promotes plant growth (Takeda et al. (2002) Proc. Natl. Acad. Sci. USA 99, 9055–9060; Park et al. (2003) Plant J. 33, 1099–1106), we expressed Aspergillus xyloglucanase constitutively in Populus alba. The expression increased the length of stem even in the presence of sucrose. Increased stem growth was accompanied by a decrease in Youngs elastic modulus in the growth zone but an increased elasticity in mature tissue. The increased internode length corresponded to an increase in cellulose content as well as specific gravity, showing that the removal of xyloglucan might cause an increase in cellulose density in the secondary xylem.

Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate

Abstract Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when GPA was introducted into the wood cell wall. At room temperature the dynamic Youngs modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the softening of wood components plasticized with GPA.

The creep of wood destabilized by change in moisture content. Part 2: The creep behaviors of wood during and immediately after adsorption

Abstract To better understand mechano-sorptive creep, creep behaviors were compared in wood samples during the drying process, immediately after drying, and after a long conditioning under constant humidity and temperature. Creep was greater in the sample tested immediately after drying than in the sample conditioned for a long time under relative humidity equal to that after drying, despite the fact that these samples had almost the same moisture content (MC). While the wood that has been moisture-conditioned for a long time is in a stable state, the wood tested immediately after the drying is presumed to be in an unstable state. Moreover, creep of the sample tested during the drying process was greater than that of the sample tested immediately after the drying. It has also been found that the instability decreased with time, indicating that stabilization and destabilization occur simultaneously during the drying process. In recent studies, a decrease in the elastic modulus and an increase in the fluidity of wood immediately after a change in MC or temperature have been reported. These findings are attributed to the instability caused by changes in MC or temperature. Based on the results of the present study and recent studies, we consider the increase in the fluidity of wood as the MC changes to be attributable to instability.

Thermal-softening properties of water-swollen wood: The relaxation process due to water soluble polysaccharides

To clarify the thermal-softening properties of water-swollen wood, the viscoelastic properties of wood specimens conditioned to various moisture contents and of water solutions of amorphous cellulose, hemicellulose and milled wood lignin, have been studied in the temperature range from −150 to 0°C at frequencies ranging between 0.5 and 10 Hz. A relaxation process around −40°C was observed in wood specimen with high moisture content. It was observed in wood specimens with lower moisture content at higher temperature. The value of apparent activation energy for the relaxation process was 50 kJ/mol. On the other hand, a similar relaxation process was observed in water solutions of amorphous cellulose and hemicellulose around −40°C, but it was not observed in water or water solution of milled wood lignin. The values of apparent activation energy for the relaxation process were 230–545 kJ/mol. Therefore, we considered that the relaxation process was due to the water-swollen polysaccharides and affected by the situations of water molecules.

Changes in micropores in dry wood with elapsed time in the environment

To investigate the changes in microstructures of wood with elapsed time in the environment, CO2 adsorption onto dry wood was measured at ice-water temperature (273 K) for samples aged from 0.1 years to over 1000 years. The micropore size distribution was obtained using the Horvath-Kawazoe method. Micropores smaller than 0.6 nm in wood decreased in number with elapsed time in the environment, and a negative correlation was found between cumulative pore volume for pores smaller than 0.6 nm and elapsed time in the environment. Cumulative pore volume in the 1000-year sample was almost half of that in the 0.1- year sample. Micropores smaller than 0.6 nm in wood with a few decades or more of elapsed time increased in number after rewetting and drying. Consequently, microstructures of wood with longer time elapsed in the environment were considered to be more stable, because of longer-term thermal motion and possibly more repeated moisture adsorption and desorption and/or temperature variation in the environment.

The creep of wood destabilized by change in moisture content. Part 3: The influence of changing moisture history on creep behavior

Abstract The creep of wood increases remarkably during moisture changes, a phenomenon called mechano-sorptive creep. The microstructure in cell walls of wood is destabilized by changes in temperature and/or moisture content. The mechanical properties of destabilized wood change over long periods of time. In the present study, the influence of moisture conditioning history on bending creep was examined. During changes in moisture, greater creep occurred in wood subjected to the first moisture change after long-term moisture conditioning than immediately after desorption or adsorption. This result indicates a kind of memory effect immediately after moisture change. During desorption processes, greater creep occurred immediately after slow adsorption than immediately after rapid adsorption. In the course of adsorption, the reverse was observed: the creep was greater immediately after rapid desorption than immediately after slow desorption. Accordingly, greater instability immediately after a change in moisture does not always cause greater creep during the next moisture change. The size of the moisture change and the load level affect the recovery of creep during adsorption processes.

Influence of heating and drying history on micropores in dry wood

To investigate the influence of heating and drying history on the microstructure of dry wood, in addition to the dynamic viscoelastic properties, CO2 adsorption onto dry wood at ice.water temperature (273 K) was measured, and the micropore size distribution was obtained using the Horvath-Kawazoe (HK) method. Micropores smaller than 0.6 nm exist in the microstructures of dry wood, and they decreased with elevating out-gassing temperature and increased again after rewetting and drying. Dry wood subjected to higher temperatures showed larger dynamic elastic modulus (E′) and smaller loss modulus (E″). This is interpreted as the result of the modification at higher temperature of the instability caused by drying. Drying history influenced the number of micropores smaller than 0.6 nm in dry wood not subjected to high temperature, although the difference in the number of micropores resulting from the drying history decreased with increasing out-gassing temperature. A larger number of micropores smaller than 0.6 nm exist in the microstructure of dry wood in more unstable states, corresponding to smaller E′ and larger E″ than in the stable state. Consequently, unstable states are considered to result from the existence of temporary micropores in the microstructures of dry wood, probably in lignin.

Micropore structure of wood: Change in micropore structure accompanied by delignification

In our preceding study, we clarified that liquids having similar molecular sizes to ethanol were mainly adsorbed onto lignin among the major constituents of wood. This suggests that most micropores or adsorption sites loosely hydrogen-bonded to each other, which are accessible to these liquids, exist in lignin. In the present study, to examine micropores in wood and lignin, micropore distribution was measured by CO2 gas adsorption at ice-water temperature (273 K). Dry samples prepared by gradual delignification from wood meal were used as adsorbents. The pore-size distributions were determined by analyzing adsorption isotherms using the Horvath-Kawazoe method. It was found that the number of micropores decreased with the decrease in residual lignin, and micropores were hardly found in cellulose and hemicellulose. It is considered that most micropores smaller than 0.6 nm in wood exist in lignin.

Influence of variation in modulus of elasticity on creep of wood during changing process of moisture

Abstract This study considered the influence of variations in the modulus of elasticity (MOE) on the mechano-sorptive (MS) creep of wood. MOE in the radial direction (ER) was investigated as a function of changes in moisture content (MC). ER values were lower during both adsorption and desorption processes than under constant MC, despite the same MC values. However, the effects observed were small and are thus not of great practical importance.