Determination of the distribution and reaction of polysaccharides in wood cell walls by the isotope tracer technique VIII: Selective radiolabeling of xylan in mature cell walls of magnolia (Magnolia kobus DC.) and visualization of its distribution by microautoradiography

To radiolabel xylan in mature cell walls selectively, magnolia (Magnolia kobus DC.) was administered withmyo-inositol-[2-³H] and allowed to metabolize for 1 month. The radiolabeled xylem tissue was then submitted to sulfuric acid hydrolysis and nitrobenzene oxidation. A large amount of radioactivity was found mainly in xylose, although slight activities were detected in glucose and in vanillin and syringaldehyde. The labeled tissue was submitted to a preparation of holocellulose followed by treatment with 24% potassium hydroxide (KOH). Radioactivity was distributed mainly in the KOH-soluble part of the holocellulose. These results indicate that most radioactivity was incorporated into xylan in the cell walls. The distribution of the incorporated radioactivity in the xylem tissue was visualized by microautoradiography. Radioactivities were distributed in the xylem more than 400 m from the cambium; and an inner layer of a secondary wall had formed at the labeled xylem. Consequently, selective radio-labeling of xylan was visualized in mature cell walls.Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kouchi, April 1997     

Biosynthesis of (+)-syringaresinol inLiriodendron tulipifera I: feeding experiments withl-[U-14C]phenylalanine and [8-14C]sinapyl alcohol

To clarify the biosynthesis of syringyl lignans and lignan formation by stereoselective coupling of monolignols, formation of (+)-syringaresinol and (+)-pinoresinol inLiriodendron tulipifera were investigated by means of feeding experiments. Following individual administration ofl-[U-¹⁴C]phenylalanine and [8-¹⁴C]sinapyl alcohol to excised shoots ofL. tulipifera and their subsequent metabolism for 3h, free [¹⁴C] lignans and [¹⁴C] lignan glucosides were extracted from both of the stems and leaves with methanol and divided into an ether fraction and an aqueous one, respectively. The glucosides were hydrolyzed by a combination of cellulase and-glucosidase to liberate [¹⁴C]lignans as aglycones.l-[U-¹⁴C]Phenylalanine was incorporated into free (+)-[¹⁴C]syringaresinol and its glucosides; the (+)-[¹⁴C]syringaresinols in the stems and leaves had 52% enantiomeric excess (% e.e.) and 42% e.e., respectively; and the (+)-[¹⁴C]syringaresinol aglycones from the glucosides in the stems and leaves had 20% e.e. and 22% e.e., respectively. Furthermore, [8-¹⁴C]sinapyl alcohol was incorporated into (+)-[¹⁴C]syringaresinol and its glucosides in the stems. These results suggest that the (+)-enantiomer of syringaresinol was enantioselectively formed from two molecules of sinapyl alcohol inL. tulipifera followed by transformation into the (+)-syringaresinol glucosides, accompanying the formation of racemic syringaresinol by nonselective coupling and the subsequent transformation of the racemate into their glucosides.l-[U-¹⁴C]Phenylalanine was incorporated also into free (+)-[¹⁴C]pinoresinol and its glucosides with 12%–42% e.e.Part of this paper was presented at the 47th Annual Meeting of the Japan Wood Research Society, Kochi, April 1997     

Mineralization of the methoxyl carbon of isolated lignin by brown-rot fungi under solid substrate conditions

Summary The objectives of this work were to begin developing an experimental system for studying the demethylation of lignin by brown-rot fungi and to examine the influence of selected culture parameters. As substrate for demethylation, we used partially 3-O-demethylated lignin that had been isolated earlier from brown-rotted spruce wood; we remethylated with¹⁴CH₃I, giving a lignin with both [3-¹⁴C]methoxyl and [4-¹⁴C]methoxyl groups. This lignin was added to pine wood flakes, which were incubated with selected brown-rot fungi, and the evolved¹⁴CO₂ was trapped and measured. Of eight fungi examined,Gloeophyllum trabeum andWolfiporia cocos gave the highest rates of mineralization of the¹⁴C-methoxyl carbons. With the former but not the latter fungus, methoxyl mineralization was over twice as fast in an atmosphere of O₂ than in air. Amending the cultures with ammonium tartrate suppressed mineralization to some extent. Further studies withG. trabeum showed that glutamate lowered the rate of mineralization and that glucose and glycerol sharply suppressed it. Addition of Fe²⁺ and Mn²⁺ slightly increased the rate of mineralization. Our results suggest that in unsupplemented cultures the rate-limiting step in methoxyl mineralization is the initial demethylation. Thus the two likely initial C₁ products, methanol and formaldehyde (as¹⁴C compounds), were mineralized much more rapidly than the methoxyl carbon of the lignin (as was formic acid), and no low molecular weight labeled intermediates from the [¹⁴C]-methoxyl lignin accumulated in the cultures. Our results also provide evidence that the spruce lignin was partially polymerized byG. trabeum. Mineralization of the methoxyl carbon of a synthetic [3-¹⁴C]-methoxyl lignin was slower than that of the spruce lignin, suggesting either that the synthetic lignin was more recalcitrant or that the [4-¹⁴C]methoxyl group in the [3,4-¹⁴C]-methoxyl spruce lignin was attacked more readily.We thank Karen L. Martinson and Michael D. Mozuch for excellent technical help, and Tor P. Schultz for valuable suggestions. This research was supported in part by the U.S. Department of Agriculture, Wood Utilization Research Program, Project No. 350-0612, to Mississippi State University.The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright in the United States.     

Structure of xylan from culms of bamboo grass (Sasa senanensis Rehd.)

Xylan prepared from culms of kumaizasa (Sasa senanensis Rehd.), a representative species of bamboo grass, was hydrolyzed with-xylanase ofStreptomyces olivaceoviridis E-86. Four arabinoxylo-oligosaccharides and two glucuronoxylo-oligosaccharides were isolated from the enzymatic hydrolysate of the xylan by chromatography on a charcoal column, a Dowex 1-x8 column, a Toyo-pearl HW-40S column, and a LiChrospher 100 NH₂ column and on preparative paper chromatography. The results of the structural analyses of the saccharides showed that the isolated oligosaccharides had the structures of 3²--l-arabinofuranosyl-xylobiose, 3²--l-arabinofuranosyl-xylotriose, 3²--[-d-xylopyranosyl-(1 2)-l-arabinofuranosyl]-xylobiose, 3³--[-d-xylopyranosyl-(1 2)-l-arabinofuranosyl]-xylotriose, 2³--4-O-methyl-d-glucuronosyl-xylotriose, and 2³--d-glucuronosyl-xylotriose. From the structural analysis of the oligosaccharides derived from the xylan, kumaizasa xylan was concluded to be a kind of arabinoglucuronoxylan having not only stubs of singlel-arabinose and singled-glucuronic acid but also stubs of disaccharide units such as-d-xylopyranosyl-(1 2)-l-arabinofuranose.     

Stereochemistry and biosynthesis of (+)-lyoniresinol,a syringyl tetrahydronaphthalene lignan in <Emphasis Type="Italic">Lyonia ovalifolia</Emphasis> var. <Emphasis Type="Italic">elliptica</Emphasis> II: feeding experiments with <Superscript>14</Superscript>C labeled precursors

To clarify the biosynthetic pathway for syringyl lignans, especially syringyl tetrahydronaphthalene lignans and formation of the C2–C7′ linkage, production of (+)-lyoniresinol (LYR) and its predicted intermediates [syringaresinol (SYR), 5,5′-dimethoxylariciresinol (DMLR), and 5,5′-dimethoxysecoisolariciresinol (DMSLR)] in Lyonia ovalifolia var. elliptica was investigated by means of feeding experiments with radiolabeled precursors. Following individual administration of l-[U-¹⁴C]phenylalanine (Phe), [8-¹⁴C]sinapyl alcohol (SA), and [8,8′-¹⁴C]SYR to excised young shoots of L. ovalifolia and their subsequent metabolism, free [¹⁴C]lignans and [¹⁴C]lignan glycosides were extracted with methanol from stems and leaves and were divided into ethyl acetate-soluble fractions (lignans) and aqueous fractions (lignan glycosides), respectively. Using a combination of xylanase, cellulase, and β-glucosidase, the glycosides were hydrolyzed to liberate [¹⁴C]lignans as aglycones. l-[U-¹⁴C]Phe was incorporated into (+)-[¹⁴C]SYR [stem 0.38%, 8% enantiomeric excess (e.e.)], (−)-[¹⁴C]SYR (leaves 2.75%, 72% e.e.), (+)-[¹⁴C]DMLR (stem 0.07%, 18% e.e. and leaves 0.009%, 58% e.e.), (−)-[¹⁴C]DMSLR (stem 0.03%, 46% e.e. and leaves 0.05%, 20% e.e.), (+)-[¹⁴C]LYR (leaves 0.013%, 22% e.e.) and glycosides of (+)-[¹⁴C]LYR (stem 0.036%, 50% e.e.) in 24h. Based on the percent incorporation and enantiomeric composition of the lignans, the biosynthetic pathway of (8R,8′R)-(+)-LYR was proposed as follows: a nonselective dehydrogenative dimerization of sinapyl alcohol yields (±)-SYR, which is reduced with low specificity to give (8R,8′R)-(+)-DMLR. This is cyclized to directly give (+)-LYR as well as reduced again to (8R,8′R)-(−)-DMSLR. Although further transformation of (−)-DMSLR also leads to the formation of (+)-LYR, cyclization could be a main pathway for (+)-LYR biosynthesis. This report was presented at the IAWPS 2005 International Symposium on Wood Science and Technology, Yokohama, November 2005     

Biosynthesis of a syringyl 8-O-4′ neolignan in Eucommia ulmoides: formation of syringylglycerol-8-O-4′-(sinapyl alcohol) ether from sinapyl alcohol

To investigate the biosynthesis and stereochemistry of syringylglycerol-8-O-4′-(sinapyl alcohol) ether (SGSE), a syringyl 8-O-4′ neolignan, feeding experiments and enzyme assays using Eucommia ulmoides were carried out. Diastereoselective formation of erythro-SGSE was found. When [8-¹⁴C]sinapyl alcohol was administered to excised shoots of E. ulmoides, ¹⁴C was incorporated into free SGSE and SGSE glucosides. In stems, incorporation into (+)-erythro-[¹⁴C]SGSE (0.037%) with 9.1% enantiomeric excess (% e.e.) was found; incorporation into the threo isomer was not detectable. Erythro-[¹⁴C]SGSE glucosides (0.047%) dominated over threo forms (0.007%) with 74.0% diastereomeric excess (% d.e.); both diastereomers were levorotatory with 32.0% e.e. and 18.3% e.e., respectively. In leaves, higher incorporation into (−)-erythro-[¹⁴C]SGSE (0.500%, 15.9% e.e.) than into the threo isomer (0.206%, 7.4% e.e.) was observed (41.6% d.e.). (−)-Erythro-[¹⁴C]SGSE glucosides (1.692%, 25.0% e.e.) were produced at higher rates than threo isomers (0.177%, 16.4% e.e.) with 81.0% d.e. In incubations of a mixture of [8-¹⁴C]sinapyl and [8-¹⁴C]coniferyl alcohols with an insoluble enzyme preparation from stems of E. ulmoides, erythro-SGSE was preferentially produced. The highest % d.e. (82.8) was observed at 60 min with the (+)-erythro isomer (21.4% e.e.) and the (−)-threo form (4.3% e.e.).Part of this report was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002, and the 47th Lignin Symposium, Fukuoka, October 2002     

Screening for condensed tannin-degrading fungi with a synthetic <Superscript>14</Superscript>C-labeled compound

To find fungi that are potent for degradation of condensed tannin, a two-step screening was used. This involved measurement of fungal growth rate on Japanese cedar (Cryptomeria japonica) bark, followed by determination of [¹⁴C]-labeled CO₂ generated from fungal degradation of synthetic [¹⁴C]-labeled condensed tannin model. In the first screening, 75 strains of wood rot fungi were tested, and 19 strains effectively decreased bark weight and/or the weight of the methanol-soluble fraction. For the second screening, [¹⁴C]-labeled condensed tannin model compound was synthesized in 11.8% yield based on radioactivity measurements. Over the incubation period, Coriolus hirsutus K-2671, Lentinus edodes Is, and Lampteromyces japonicus Nn showed higher cumulative [¹⁴C]-labeled CO₂ emissions than the other strains and mineralized the [¹⁴C]-labeled condensed tannin model compound by 3.7%, 3.0%, and 3.0%, respectively. Fractionation of the methanol extracts from the medium by gel permeation chromatography after fungal treatment suggested that fungi that can induce the emission of significant levels of [¹⁴C]-labeled CO₂ can extensively depolymerize condensed tannins.     

Infrared spectral characteristics and surface inactivation of wood at high temperatures

Summary Spectra resulting from chemical changes in white spruce [Picea glauca (Moench) Voss] microsections heated in air or nitrogen at high temperatures (100 to 240°C) were continuously recorded on an infrared spectrophotometer.A significant change occurred in the intensity of the 1730 cm^-1 band which indicates a carbonyl absorption of carboxyl and ester groups of wood. This intensity initially decreased and the increased at a greater rate. The time periods to reach the minimum inflection point, termed the times to initiate a significant oxidative carboxylation or oxidation, showed a good curvilinear relationship with heating temperatures.Quantification of this time-temperature relationship required to reach a significant level of oxidation was achieved, using wood microsections that had extractives removed to varying degrees. It was concluded that the extractives served only as catalysts for oxidation. When drying wood at temperatures over 180°C, in addition to oxidation, pyrolytic degradation occurred.Chemical evidence was further confirmed by tests of plywood panels bonded with phenolformaldehyde glue. Three separate types of veneers were investigated—non-extracted, acetone extracted, and veneer with the surface chemically stabilized by treatment with sodium borohydride. The results suggest that the time period to reach a significant level of oxidative carboxylation is also the time period to initiate a wood surface inactivated to polymer adhesion.The author wishes to thank Miss D. Bouchard and Mr. H. N. Mukai for their assistance in the experiments. Appreciation also is due to Mr. H. MacLean for a critical review of this paper.     

Assignment of the 1H and 13C NMR spectra of 2-aminobenzamide-labeled galacto- and arabinooligosaccharides

1,4-Linked β-d-galactooligosaccharides with a degree of polymerization (DP) between 1 and 7 and 1,5-linked α-l-arabinooligosaccharides with a DP between 1 and 8 were labeled at their reducing ends with 2-aminobenzamide (2AB) in the presence of sodium cyanoborohydride. The 2AB-labeled oligosaccharides were shown to be homogeneous using high-performance anion-exchange chromatography (HPAEC) and by electrospray ionization mass spectrometry (ESI-MS). The signals in the ¹H and ¹³C nuclear magnetic resonance (NMR) spectra of the 2AB-labeled oligosaccharides were then assigned using one- and two-dimensional NMR spectroscopy. These NMR data will be useful for the structural analysis of enzymatically synthesized galactan and arabinan side chains derived from rhamnogalacturonan I.     

Stereochemistry and biosynthesis of 8-O-4′ neolignans in Eucommia ulmoides: diastereoselective formation of guaiacylglycerol-8-O-4′-(sinapyl alcohol) ether

Stereochemistry and biosynthesis of guaiacylglycerol-8-O-4′-(sinapyl alcohol) ether (GGSE), an 8-O-4′ neolignan, which consists of coniferyl and sinapyl alcohol moieties, in Eucommia ulmoides were investigated. Four 8-O-4′ neolignans, GGSE, syringylglycerol-8-O-4′-(coniferyl alcohol) ether (SGCE), guaiacylglycerol-8-O-4′-(coniferyl alcohol) ether (GGCE), and syringylglycerol-8-O-4′-(sinapyl alcohol) ether (SGSE), were synthesized. Their erythro and threo diastereomers were separated through acetonide derivatives, intermediates of the synthesis, and identified by means of nuclear magnetic resonance (NMR) spectroscopy. All of the erythro-acetonide derivatives have larger coupling constants (ca 9 Hz) for the C₇-H resonances than those of the threo ones (1.5–2 Hz). In the case of the four 8-O-4′ neolignans, the C₇-H coupling constants of the threo-isomers are not smaller than those of the erythro ones. GGSE isolated previously from this plant was identified as the erythro isomer by comparison of the ¹³C-NMR data with synthetic erythro-GGSE and threo-GGSE and the other 8-O-4′ neolignans mentioned as above. Administration of a mixture of [8-¹⁴C]coniferyl alcohol and [8-¹⁴C]sinapyl alcohol to excised shoots of E. ulmoides was carried out and the incorporation of ¹⁴C into erythro-[¹⁴C]GGSE was found to be higher than that in threo-[¹⁴C]GGSE. The occurrence of diastereoselective formation of erythro-GGSE by cross coupling of coniferyl and sinapyl alcohols is suggested.Part of this paper was presented at the 47th Lignin Symposium, Fukuoka, October 2002 and the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, April 2003     

Synthesis of isoacteoside, a dihydroxyphenylethyl glycoside

The total chemical synthesis of isoacteoside (1), 2-(3,4-dihydroxyphenyl)ethyl 6-O-caffeoyl-3-O-(-l-rhamnopyranosyl)--d-glucopyranoside, is described. An acteoside acetate with benzyl groups at the catechols (3: 2-(3,4-dibenzyloxyphenyl)ethyl 2,6-di-O-acetyl-4-O-[3,4-bis(O-benzyl)caffeoyl]-3-O-(-l-rhamnopyranosyl)--d-glucopyranoside) was treated with a solution of methy-lamine in methanol (MeNH₂ in MeOH) to perform both deacetylation and caffeoyl migration, affording an isoacteoside derivative with benzyl groups at the catechols4b: 2-(3,4-dibenzyloxyphenyl)ethyl 6-O-[3,4-bis(O-benzyl) caffeoyl] -3-O-(-l-rhamnopyranosyl)--d-glucopyranoside —in 34% yield. Debenzylation of4b was successfully accomplished by catalytic transfer hydrogenation using 1,4-cyclohexadiene to give the target compound isoacteoside (1) in 54% yield.¹H and¹³C nuclear magnetic resonance spectral data of the synthesized isoacteoside (1) were identical with those of the natural isoacteoside isolated fromPaulownia tomentosa (Thumb.) Steud.Part of this research was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001     

Investigation on hydrogen abstraction from methyl glucoside by active oxygen species under oxygen delignification conditions III: effects of the origin of active oxygen species

Carbohydrate model compounds methyl β-d-glucopyranoside (MGPβ), methyl α-d-glucopyranoside (MGPα), and methyl β-d-mannopyranoside (MMPβ) and the deuterium compounds of MGPβ labeled at the anomeric or C-2 positions (MGPβ-1D, MGPβ-2D) were reacted with active oxygen species (AOS) generated in situ by reactions between O₂ and a co-treated phenolic lignin model compound, 4-hydroxy-3-methoxybenzyl alcohol (VAlc), under conditions simulating oxygen delignification (0.5 mol/l NaOH, 0.36 mmol/l Fe³⁺, 1.1 MPa O₂, 95°C). MGPβ was degraded more than MGPα but less than MMPβ when the pairs MGPβ/MGPα and MGPβ/MMPβ, respectively, were treated, which indicates that the configurational differences at the anomeric and C-2 positions influence the reactivity of AOS toward these compounds. When the pairs MGPβ/MGPβ-1D and MGPβ/MGPβ-2D were treated, no clear kinetic isotope effects were observed in either case. These results contrasted with those obtained when another phenolic compound, 2,4,6-trimethylphenol (TMPh), was used as the AOS generator instead of VAlc under exactly the same conditions. Clear kinetic isotope effects were observed when using TMPh. Because it is not easily accepted that the anomeric and C-2 hydrogen abstractions are minor reaction modes only for AOS generated in the VAlc system, it is suspected that the AOS do not show any clear kinetic isotope effect even though the AOS abstract an objective hydrogen.     

Sulfated glycofuranans as inhibitors of melanoma lung metastasis

Chemically synthesized (1 5)--d-glucofuranan, (1 5)--d-galactofuranan, (1 5)--d-xylofuranan, (1 5)--L-arabinofuranan, natural xylan, and curdlan were sulfated to investigate their inhibitory activities on B16-BL6 lung metastasis and anticoagulant activities. (1 5)--d-Glucofuranan sulfate, (1 5)--d-galactofuranan sulfate, xylan sulfate, and curdlan sulfate had binding abilities with B16-BL6 melanoma lysate. The inhibitory activities of sulfated polysaccharides on B16-BL6 lung metastasis selected by heparin binding assay were in the order (1 5)--d-galactofuranan sulfate > (1 5)---d-glucofuranan sulfate > xylan sulfate curdlan sulfate. Furthermore, (1 5)--d-galactofuranan sulfate, (1 5)--d-glucofuranan sulfate, and xylan sulfate had not only high inhibitory activity on B16-BL6 lung metastasis but also low anticoagulant activity. The correlation between chemical structure and biological activity is discussed.Part of this paper was presented at the 10th International Synposium on Wood and Pulping Chemistry, Yokohama, Japan, June 1999     

Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer

Abstract

This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [¹H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.     

Cyclisation of farnesyl pyrophosphate into sesquiterpenoids in ginger rhizomes (Zingiber officinale)

The atomic ratios (¹⁴C/³H) obtained in ar-curcumene, α-zingiberene, β-bisabolene obtained from the essential oil of rhizomes of Zingiber officinale which were fed with [2-¹⁴C, 2-³H₂], [2-¹⁴C, 4R-³H₁] and [2-¹⁴C, 5-³H₂]mevalonic acid and [1-³H₂]farnesylpyrophosphate (FPP) revealed that (a) (2E,6E)-isomer of FPP is isomerised to (2Z,6E)-isomer without loss of epimeric hydrogen that means without a redox process; (b) (2Z,6E)-FPP is cyclised to bisabolyl cation which is the penultimate precursor of α-zingiberene, ar-curcumene and β-bisabolene; and (c) two 1,2-hydrogen shifts take place during the formation of α-zingiberene whereas one 1,2 shift has been observed during the formation of ar-curcumene.     

Lignin as a cross-linker of acrylic acid-grafted carboxymethyl lignocellulose

Cunninghamia lanceolata wood meal samples with different lignin contents after delignification with an acidic NaClO₂ system were carboxymethylated, and the degree of substitution (DS) and the distribution of the carboxymethyl (CM) groups were investigated by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Cellulose samples prepared from bleached kraft softwood pulp, food-grade konjac mannan, and commercial oat xylan (containing 10% arabinosyl and 15% glucosyl residues) were also investigated. The chemical shift of methylene protons in ¹H NMR spectra of CM groups of carboxymethyl konjac mannan and commercial oat xylan appeared in the same region as those of carboxymethylcellulose. The DS of carboxymethyl lignocellulose (CMLC) increased slightly from 1.36 to 1.48 with decreasing lignin content, but the water solubility of CMLC clearly increased with decreasing lignin content. It was suggested that the covalent linkages between lignin and cell-wall polysaccharides play the role of cross-linker in CMLC. Water absorbents were synthesized by graft-copolymerization of acrylic acid onto CMLC samples with different lignin contents. The highest level of water absorbency was obtained from CMLC containing 14% of lignin, suggesting the importance of lignin as the cross-linker.     

Reactions between Cr(VI) and wood and its model compounds

Wood, macromolecular and simple model compounds, were reacted with CrO₃ or K₂CrO₄ aqueous solutions. Extracted lignin, guaiacol, vanillin, vanillyl alcohol and homovanillyl alcohol were chosen as model compounds for lignin, whilst cellulose, gum Ghatti, xylan, extracted hemicellulose from pine, methyl-β-D-glucopyranoside and methyl-β-cellobioside were used as models for wood polysaccharides. The kinetics of the reduction reactions of Cr(VI) were monitored using UV-Vis spectroscopy and the results obtained for several temperatures are discussed. In general terms, wood, lignin and lignin model compounds reduced Cr(VI) faster and to a greater extent than polysaccharides or simple sugar molecules. Moreover, lignin model compounds were reduced even faster than lignin. Simple sugars showed a reduction pattern similar to that of cellulose. Extracted hemicellulose revealed to be a poorer reductant while gum Ghatti was the strongest among the polysaccharides. As expected, CrO₃ aq. behaved as a more powerfull oxidant than K₂CrO₄ aq. for these substances. Even at 100 °C, sugars or polysaccharides did not seem to be oxidised by K₂CrO₄ aq. 0.01 M. These results suggest that, because of the differences in reactivity, lignin reacts preferentially when wood is treated with Cr(VI)-containing formulations, like those which are applied in wood preservation treatments.     

Stiffness and wood variation of 3-year old<Emphasis Type="Italic"> Pinus radiata</Emphasis> clones

The objective of this study was to explore wood variation, especially modulus of elasticity ( moe), density, and microfibril angle ( mfa), in a three-year old Pinus radiata tree clone trial. Moreover, the study examined the potential for genetic selection of radiata pine clones with high moe using current acoustic technology. The clone selection criteria were based on growth traits, basic density, and sound velocity indices to mirror the range in wood density and moe amongst c. 1000 clones. The selected 22 clones, represented by two trees each, were measured for moe, spiral grain, wood density, compression wood percentage, and mfa. Good agreement was found between static moe and dynamic moe. Both static and dynamic moe measurements were found to be primarily dependent on mfa (clonal range 28–39 degrees). Although wood density (clonal range 300–400 kg/m³) did not have a significant influence on moe alone, it was significant in combination with mfa. Compression wood tended to reduce moe and inflate wood density. The opportunities for genetic selection of radiata clones with high stiffness seem promising as the 22 selected clones exhibited a two-fold range of static moe (2.2–4.7 GPa) and the clonal heritabilities ( ) for moe, density and mfa were high.     

In vitro decay of Aextoxicon punctatum and Fagus sylvatica woods by white and brown-rot fungi

Summary The in vitro decay of Aextoxicon punctatum and Fagus sylvatica wood by the fungi Trametes versicolor, Ganoderma australe, Phlebia chrysocrea and Lentinus cyathiformis was studied by the agar-block method, and then the decayed woods were analyzed by chemical and spectroscopic techniques. The results demonstrated the strong resistance of the A. punctatum wood to the brown-rot fungus L. cyathiformis; the resistance might be related to the low S/G lignin ratio in this Austral hardwood. Wood decay by the Austral white-rot fungi G. australe and P. chrysocrea was rather limited, and preferential degradation of lignin was not produced although all the fungi studied increased wood digestibility. The most characteristic white and brown-rot decay patterns were observed during the in vitro decay with T. versicolor and L. cyathiformis, respectively. Trametes versicolor caused high weight losses and reduced the lignin content of the wood, whereas L. cyathiformis produced a preferential removal of xylan. No important changes in the solid-state ¹³C NMR spectra were observed after wood degradation by T. versicolor, but this technique evidenced an increase in aromatic carbon by L. cyathiformis. This increase was higher than that found in the Klason lignin content, suggesting the presence of altered lignin fractions in the brown-rotted wood.The authors are indebted to Prof. H. D. Lüdemann for the facilities at the Institut für Biophysik und physikalische Biochemie (Regensburg), to A. Navarrete (INIA, Madrid) for her collaboration, and to C. F. Warren (ICE, Alcalá de Henares) for her linguistic assistance. The computer program for spectra treatment was developed by G. Almendros (Centro de Ciencias Medioambientales, CSIC, Madrid). This investigation has been funded by the Spanish Biotechnology Program (Grant BIO88-0185)     

3-(4-Hydroxyphenyl)propionic acid is involved in the biosynthesis of myricanol in Myrica rubra

There is little evidence concerning the biosynthetic pathways for cyclic diarylheptanoids. We previously demonstrated that the cyclic diarylheptanoids myricanol and myricanone were biologically synthesized from two molecules of 4-coumaric acid by the feeding of 4-[8,9-¹³C₂]coumaric acid to young shoots of Myrica rubra. In the present study, using a ¹³C-labeled compound, we revealed that two molecules of 3-(4-hydroxyphenyl)propionic acid could also be a biosynthetic precursor of myricanol in M. rubra. These results indicated that both 4-coumaric acid and its dihydro-derivative were incorporated into myricanol. Competitive feeding experiments with 4-[8,9-¹³C₂]coumaric acid and 3-(4-hydroxyphenyl)-[1-¹³C]propionic acid were performed in M. rubra to determine the preferential incorporation of these two precursors. ¹³C-NMR studies indicated that 3-(4-hydroxyphenyl)-[1-¹³C]propionic acid was preferentially incorporated into myricanol. The data provided evidence for a biosynthetic sequence originating from 4-coumaric acid and leading to myricanol, through 3-(4-hydroxyphenyl)propionic acid, in M. rubra.