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Lignin
Terms modified by Lignin Selected AbstractsLignin turnover in an agricultural field: from plant residues to soil-protected fractionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006D. P. Rasse Summary Lignin has long been suspected to be a major source of stable carbon in soils, notably because of the recalcitrant nature of its polyphenolic structure relative to other families of plant molecules. However, lignin turnover studies have produced conflicting results, most of them suggesting that large proportions of plant-residue lignin decompose within a year of incorporation into soils. Here, we propose a two-reservoir model where lignin in undecomposed plant residue (Lp) can either reach soil fractions where it is somewhat protected from further decomposition (Ls) or is transformed to non-lignin products. Model calibration data were obtained through compound-specific 13C isotopic analyses conducted in a zero- to 9-year chronosequence of maize monoculture after wheat in a temperate loam soil of the Paris basin. Lignin was quantified by CuO oxidation as VSC-lignin, i.e. the sum of vanillil- (V), syringyl- (S) and coumaryl-type (C) phenols. Model calibrations indicate that Lp has a turnover rate faster than 1 year and that 92% is mineralized as CO2 or transformed into other non-lignin products, while only 8% reaches the Ls fraction. Estimated turnover rate of the Ls fraction was 0.05 years,1. The model also suggested that about half of Lp was not measured because it had been excluded from the samples in the process of sieving at 5 mm. In conclusion, the model indicates that chemical recalcitrance alone is not sufficient to explain VSC-lignin turnover in soils, and that, functionally, the most relevant mechanism appears to be the transfer of VSC-lignin molecules and fragments from decomposing plant tissues to soil-protected fractions. [source] The Aerobic Oxidative Cleavage of Lignin to Produce Hydroxyaromatic Benzaldehydes and Carboxylic Acids via Metal/Bromide Catalysts in Acetic Acid/Water MixturesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Walt Partenheimer Abstract Roughly 30% of all woody plants is composed of lignin. Five different lignin samples, from wood and bagasse, were oxidized in air with a cobalt/manganese/zirconium/bromide (Co/Mn/Zr/Br) catalyst in acetic acid as a function of time, temperature, pressure, and lignin and catalyst concentrations. 18 products were identified via gas chromatography-mass spectrometry (GC/MS). The most valuable products from lignin were 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy-3-methoxybenzoic acid (vanillic acid), 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde) and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid). 10.9,wt% of the lignin was converted to the aromatic products. By the use of model compounds we demonstrate that 1) the presence of the phenolic functionality on an aromatic ring does inhibit the rate of reaction but that the alkyl group on the ring still does oxidize to the carboxylic acid, 2) that the masking of phenol by acetylation occurs at a reasonable rate in acetic acid, 3) that the alkyl group of the masked phenol does very readily oxidize, 4) that an acetic anhydride/acetic acid mixture is a good oxidation solvent and 5) that a two-step acetylation/oxidation to the carboxylic acid is feasible. [source] Studies on feed digestibilities in captive Asian elephants (Elephas maximus)JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 3-4 2003M. Clauss Summary In order to test the suitability of the horse as a nutritional model for elephants, digestibility studies were performed with six captive Asian elephants on six different dietary regimes, using the double marker method with acid detergent lignin as an internal and chromium oxide as an external digestibility marker. Elephants resembled horses in the way dietary supplements and dietary crude fibre content influenced digestibility, in calcium absorption parameters and in faecal volatile fatty acid composition. However, the absolute digestibility coefficients achieved for all nutrients are distinctively lower in elephants. This is because of much faster ingesta passage rates reported for elephants. No answer is given to why elephants do not make use of their high digestive potential theoretically provided by their immense body weight. Differences in volatile fatty acid concentrations between these captive elephants and those reported from elephants from the wild are in accord with a reported high dependence of free-ranging elephants on browse forage. Zusammenfassung Untersuchungen zur Verdaulichkeit von Futtermitteln bei Asiatischen Elefanten (Elephas maximus) Um zu überprüfen, ob das Pferd als ernährungsphysiolgisches Modelltier für Elefanten herangezogen werden kann, wurden Verdaulichkeitsstudien an sechs im Zoo gehaltenen Indischen Elefanten mit sechs verschiedenen Futterrationen durchgeführt. Dabei wurde die Doppelindikatormethode mit Lignin als internem und Chromoxid als externem Marker verwendet. Elefanten ähnelten Pferden hinsichtlich der Art und Weise, wie sich Ergänzungsfuttermittel und der Rohfasergehalt der Ration auf die Verdaulichkeit auswirkten, hinsichtlich der Kalziumabsorption, und hinsichtlich der Zusammensetzung der flüchtigen Fettsäuren im Kot. Die von Elefanten erzielten absoluten Verdaulich-keitswerte sind jedoch für alle Nährstoffe deutlich niedriger als bei Pferden, was auf die schnellere Passage der Ingesta durch den Verdauungstrakt der Elefanten zurückzuführen ist. Die Frage, warum Elefanten ihr großes Potential zu hohen Verdauungleistungen nicht ausnutzen, das ihnen theoretisch aufgrund ihrer immensen Körpermasse gegeben ist, ist noch nicht beantwortet. Unterschiede in den Konzentrationen von flüchtigen Fettsäuren im Kot zwischen diesen Zoo-Elefanten und Elefanten aus freier Wildbahn spiegeln den hohen Laubanteil in der Nahrung freilebender Tiere wieder. [source] Lignin in jute fabric,polypropylene compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009B. A. Acha Abstract In this work, the feasibility of using lignin as a compatibilizer for composites made from jute fiber fabric and polypropylene (PP) was studied. Since lignin contains polar (hydroxyl) groups and nonpolar hydrocarbon, it was expected to be able to improve the compatibility between the two components of the composite. It was found that lignin acted as , nucleation, fire retardant, and toughening agent for PP matrix. Jute composites exhibit higher stiffness, tensile strength, and impact behavior in respect to those of neat PP. Although scanning electron micrographic observations indicate that PP-jute adhesion was slightly improved by lignin addition, additional benefits were only obtained from impact behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Lignin-based polycondensation resins for wood adhesivesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007N.-E. El Mansouri Abstract Lignin-based wood adhesives are obtained that satisfy the requirements of relevant international standards for the manufacture of exterior-grade wood particleboard. Formulations based on low molecular mass lignin and presenting an increase in the relative proportion of reactive points yield better results than the higher molecular mass lignin used in the past. These lignins allow a higher proportion of hydroxymethylation during preparation of methylolated lignins. These lignin-based adhesives also yield acceptable results at particleboard pressing times that are sufficiently low to be of industrial significance. Lignin-based wood adhesives, in which a nonvolatile nontoxic aldehyde (glyoxal) is substituted for formaldehyde in their preparation, are prepared and tested for application to wood panels such as particleboard. The adhesives yield good internal bond strength results for the panels, which are good enough to comfortably pass relevant international standard specifications for exterior-grade panels. The adhesives also show sufficient reactivity to yield panels in press times comparable to that of formaldehyde-based commercial adhesives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1690,1699, 2007 [source] Changes in Cell Wall-bound Phenolic Compounds and Lignin in Roots of Date Palm Cultivars Differing in Susceptibility to Fusarium oxysporum f. sp. albedinisJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2000C. El Modafar The roots of date palm contain four cell wall-bound phenolic acids identified as p -hydroxybenzoic, p -coumaric, ferulic and sinapic acids. The ferulic acid represents the major phenolic compound since it constitutes 48.2,55.8% of cell wall-bound phenolic acids. All these phenolic acids were present in the resistant cultivar (BSTN) and the susceptible cultivar (JHL). However, the pre-infection contents of p -coumaric, ferulic and sinapic acids were greater in the resistant cultivar than in the susceptible one. For the contents of p -hydroxybenzoic acid, there was no significant difference between the resistant cultivar and the susceptible cultivar. Similarly, the pre-infection contents of lignin were approximately equal for both cultivars. Inoculation of the date palm roots by Fusarium oxysporum f. sp. albedinis induced important modifications to the contents of the cell wall-bound phenolic compounds and lignin, which made it possible to distinguish between resistant and susceptible cultivars. The post-infection contents of cell wall-bound phenolic compounds underwent a rapid and intense increase with a maximum accumulation on the tenth day for p -hydroxybenzoic acid (1.54 ,mol/g), p -coumaric acid (2.77 ,mol/g) and ferulic acid (2.64 ,mol/g) and on the fifteenth day for sinapic acid (1.85 ,mol/g). The maximum contents accumulated in the resistant cultivar were greater than those in the susceptible cultivar, namely, 11 times for p -hydroxybenzoic acid, 2.6 times for p -coumaric acid, 1.8 times for ferulic acid and 12.3 times for sinapic acid. In the susceptible cultivar, p -coumaric acid and ferulic acid contents also increased after inoculation although they did not reach the pre-infection contents of the resistant cultivar. The contents of p -hydroxybenzoic acid in the susceptible cultivar roots did not present post-infection modification and those of sinapic acid decreased instead. The lignin contents increased in both cultivars with a maximum accumulation on the fifteenth day. However, the maximum contents accumulated in the resistant cultivar roots were 1.5 times greater than those of the susceptible cultivar. These results showed clear differences between the resistant BSTN and the susceptible JHL cultivars. The implication of cell wall-bound phenolic compounds and lignin in the resistance of date palm to F. oxysporum f. sp. albedinis appears to be dependent on the speed and intensity of their accumulation with greater contents in the first stage of infection. Zusammenfassung Die Wurzeln der Dattelpalme enthalten vier zellwandgebundene Phenolsäuren, die als p -Hydroxybenzoesäure, p- Cumarsäure, Ferulasäure und Sinapinsäure identifiziert wurden. Ferulasäure ist die wichtigste phenolische Verbindung, denn sie stellt 48,2 bi 55,8% der zellwandgebundenen Phenolsäuren. Alle vier Phenolsäuren waren in der resistenten Sorte BSTN und in der anfälligen Sorte JHL vorhanden. Die Gehalte an p -Cumarsäure, Ferulasäure und Sinapinsäure waren vor der Infektion bei der resistenten Sorte jedoch höher als bei der anfälligen Sorte. Hinsichtlich des Gehalts an p -Hydroxybenzoesäure unterschieden sich die resistente und die anfällige Sorte nicht signifikant voneinander. Auch die Ligningehalte vor der Infektion waren bei beiden Sorten ungefähr gleich. Die Inokulation von Dattelpalmenwurzeln mit Fusarium oxysporum f. sp. albedinis induziert wichtige Änderungen der Gehalte an zellwandgebundenen phenolischen Verbindungen und Lignin, was eine Unterscheidung resistenter von anfälligen Sorten ermöglicht. Nach der Infektion nehmen die Gehalte an zellwandgebundenen phenolischen Verbindungen rasch und erheblich zu, mit maximaler Akkumulation am 10. Tag bei p -Hydroxybenzoesäure (1,54 ,mol/g), p -Cumarsäure (2,77 ,mol/g) und Ferulasäure (2,64 ,mol/g) sowie am 15. Tag bei Sinapinsäure (1,85 ,mol/g). Die in der resistenten Sorte akkumulierten maximalen Gehalte waren höher als die maximalen Gehalte der anfälligen Sorte , um das Elffache bei p -Hydroxybenzoesäure, das 2,6-fache bei p -Cumarsäure, das 1,8-fache bei Ferulasäure und das 2,3-fache bei Sinapinsäure. Bei der anfälligen Sorte steigen die Gehalte an p -Cumarsäure und Ferulasäure nach der Inokulation ebenfalls an, bleiben aber niedriger als die Werte der resistenten Sorte vor der Infektion. Der p -Hydroxybenzoesäuregehalt in den Wurzeln der anfälligen Sorte ist nach der Infektion nicht verändert, und der Sinapinsäuregehalt nimmt ab. Der Ligningehalt steigt bei beiden Sorten, mit maximaler Akkumulation am 15. Tag. Der maximale Gehalt in den Wurzeln der resistenten Sorte war jedoch 1,5-mal höher als bei der anfälligen Sorte. Diese Ergebnisse zeigen deutliche Unterschiede zwischen der resistenten Sorte (BSTN) und der anfälligen Sorte (JHL). Die Bedeutung der zellwandgebundenen phenolischen Verbindungen und des Lignins für die Resistenz der Dattelpalme gegen F. oxysporum f. sp. albedinis scheint von der Geschwindigkeit und der Intensität der Akkumulation abzuhängen, wobei die Gehalte im ersten Stadium der Infektion höher sind. [source] Compound-specific stable-isotope (,13C) analysis in soil scienceJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2005Bruno Glaser Abstract This review provides current state of the art of compound-specific stable-isotope-ratio mass spectrometry (,13C) and gives an overview on innovative applications in soil science. After a short introduction on the background of stable C isotopes and their ecological significance, different techniques for compound-specific stable-isotope analysis are compared. Analogous to the ,13C analysis in bulk samples, by means of elemental analyzer,isotope-ratio mass spectrometry, physical fractions such as particle-size fractions, soil microbial biomass, and water-soluble organic C can be analyzed. The main focus of this review is, however, to discuss the isotope composition of chemical fractions (so-called molecular markers) indicating plant- (pentoses, long-chain n-alkanes, lignin phenols) and microbial-derived residues (phospholipid fatty acids, hexoses, amino sugars, and short-chain n-alkanes) as well as other interesting soil constituents such as "black carbon" and polycyclic aromatic hydrocarbons. For this purpose, innovative techniques such as pyrolysis,gas chromatography,combustion,isotope-ratio mass spectrometry, gas chromatography,combustion,isotope-ratio mass spectrometry, or liquid chromatography,combustion,isotope-ratio mass spectrometry were compared. These techniques can be used in general for two purposes, (1) to quantify sequestration and turnover of specific organic compounds in the environment and (2) to trace the origin of organic substances. Turnover times of physical (sand < silt < clay) and chemical fractions (lignin < phospholipid fatty acids < amino sugars , sugars) are generally shorter compared to bulk soil and increase in the order given in brackets. Tracing the origin of organic compounds such as polycyclic aromatic hydrocarbons is difficult when more than two sources are involved and isotope difference of different sources is small. Therefore, this application is preferentially used when natural (e.g., C3-to-C4 plant conversion) or artificial (positive or negative) 13C labeling is used. Substanzspezifische Stabilisotopenanalyse (,13C) in der Bodenforschung Dieser Artikel fasst den Stand der Forschung bezüglich der substanzspezifischen Stabilisotopenanalyse (,13C) zusammen. Innovative Anwendungen und ein Ausblick für künftige Forschungsaktivitäten werden anhand von Fallbeispielen gegeben. Zunächst wird die ökologische Bedeutung von stabilen C-Isotopen kurz erläutert. Daran schließt sich ein methodischer Teil an, in welchem die verschiedenen Techniken gegenüber gestellt werden. Analog zu ,13C-Messungen der Feinerde mittels Elementaranalysator-Isotopenverhältnis-Massenspektrometrie können physikalisch isolierte Fraktionen (z.,B. Korngrößenfraktionen, mikrobielle Biomasse, DOC) analysiert werden. Der Schwerpunkt dieses Übersichtsartikels liegt jedoch in der Diskussion der C-Isotopensignatur chemischer Fraktionen (sog. Biomarker), welche Rückschlüsse auf Herkunft und Dynamik pflanzlicher (Pentosen, langkettige n-Alkane, Ligninphenole) und mikrobieller Rückstände (Phospholipidfettsäuren, Hexosen, Aminozucker und kurzkettige n-Alkane) sowie anderer interessanter Substanzen im Boden erlaubt wie z.,B. ,Black Carbon" und polyzyklische aromatische Kohlenwasserstoffe. Zu diesem Zweck kommen innovative Techniken zum Einsatz wie z.,B. Pyrolyse-Gaschromatographie-Isotopenverhältnismassenspektrometrie, Gaschromatographie-Verbrennungs-Isotopenverhältnismassenspektrometrie und Flüssigkeitschromatographie-Oxidations-Isotopenverhältnismassenspektrometrie. Innovative ökologische Anwendungen werden erläutert, welche sich prinzipiell in zwei Kategorien einteilen lassen: (1) Quantifizierung der Sequestrierung und des Umsatzes dieser Verbindungen in der Umwelt; (2) Untersuchung der Herkunft spezifischer organischer Substanzen. Umsatzzeiten physikalischer (Sand < Schluff < Ton) und chemischer Fraktionen (Lignin < Phospholipidfettsäuren < Aminozucker , Zucker) sind generall kleiner als jene der gesamten organischen Substanz in der Feinerde und nehmen in der in Klammern angegebenen Reihenfolge zu. Die Untersuchung der Herkunft organischer Substanzen (z.,B. polyzyklischer aromatischer Kohlenwasserstoffe) ist problematisch, weil die Unterschiede der Isotopensignatur verschiedener Quellen gering sind und meist mehr als zwei Quellen zur Isotopensignatur des untersuchten Biomarkers beitragen. Deswegen sollte die Untersuchung der Herkunft organischer Substanzen auf Tracer-Experimente beschränkt werden, wie z.,B. nach natürlicher (C3-C4-Pflanzenwechsel) bzw. künstlicher (13C-An- oder -Abreicherung) Markierung. [source] Application of Electrospray Ionization Mass Spectrometry to the Elucidation of the Primary Structure of LigninMACROMOLECULAR BIOSCIENCE, Issue 7 2003Dmitry V. Evtuguin Abstract Electrospray ionization mass spectrometry (ESI-MS) was successfully applied to the structural analysis of lignin. The structure of oligomers fractionated from Eucalyptus globulus dioxane lignin was elucidated using tandem mass spectrometry, and the information on fragmentation patterns was provided by experiments on dimeric model compounds. Data obtained revealed a significant abundance in the lignin macromolecules of linear fragments that were composed of 8- O -4,-linked syringyl/guaiacyl units and syringaresinol. The proposed linear fragment of the E. globulus lignin molecule. [source] Effect of Lignin on the Heat and Light Resistance of Lignocellulosic FibersMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2007Narendra Reddy Abstract The existence of lignin in lignocellulosic fibers increases the loss in breaking tenacity and elongation of fibers when they are exposed to heat and light. Delignification by sulfonation helps to remove some of the lignin from the fibers without affecting the breaking tenacity. The delignified fibers have higher resistance to heat and light exposure compared to the raw fibers. The effect of lignin on the heat and light resistance of kenaf and cornhusk fibers with three different lignin contents was studied in comparison to cotton at various periods of heat and light exposure. The changes in the breaking tenacity, breaking elongation and yellowness of the samples were studied. [source] Fiberboards Based on Sugarcane Bagasse Lignin and FibersMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2006William Hoareau Abstract Summary: Fiberboards were prepared using phenolic type resins (phenol-formaldehyde) and sugarcane bagasse fibers. Lignin extracted through an organosolv process from sugarcane bagasse was used as substitute of phenol in phenolic resins from 40 (lignin-phenol-formaldehyde) to 100 wt.-% (lignin-formaldehyde) substitution. Some of the fibers were chemically modified by oxidation with chlorine dioxide and treatment with furfuryl alcohol (FA), leading to fibers coated with polyfurfuryl alcohol. Thermal analysis (DSC and TGA) of the prepolymers allowed setting up an efficient curing to prepare fiberboards. Impact strength and water absorption were measured showing the importance of the curing pressure to obtain good performance. When chemically modified fibers were used to prepare board samples, enhanced durability against white root fungi is observed, and to a less degree against brown root fungi. Sugarcane bagasse fiberboards were prepared from prepolymers where lignin substituted phenol up to 100%. This replaces these materials in advantageous position, relating to those prepared from phenol-formaldehyde resins, due to their high content of renewable raw materials. The results obtained are promising for the utilization of sugarcane bagasse as raw materials for preparing fiberboards to be used in tropical areas. Stabilization of sugarcane bagasse fiberboards made with unmodified and modified (ClO2,+,furfuryl alcohol) fibers and phenolic resin after 8 weeks exposure against fungi. [source] Role of Star-Like Hydroxylpropyl Lignin in Soy-Protein PlasticsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2006Ming Wei Abstract Summary: Star-like hydroxypropyl lignin (HL) was compounded into soy protein isolated (SPI) to develop a potential biodegradable plastic with better mechanical performance than pure sheet-SPI. The structure and properties of the composite materials were characterized by WAXD, DSC, SEM, TEM and tensile tests. The addition of just 2 wt.-% HL resulted in tensile strength (,b) of 16.8 MPa, 2.3 times that of pure sheet-SPI, with no accompanying decrease in elongation at break as a result of strong interaction and with good miscibility among components. As the HL content increased, the HL molecules could self-aggregate as oblate supramolecular domains, while the stronger interactions between HL and glycerol resulted in the detaching of glycerol from the SPI matrix. It can be concluded that the insertion of HL as single molecules into the SPI matrix would provide materials with optimum mechanical properties. Compared with other lignin/SPI composites, the stretching chains on HL play a key role in the improvement of mechanical properties because of a stronger adhesion of HL onto the SPI matrix as well as the interpenetration of SPI into supramolecular HL domains. Schematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate. [source] Identifying residues in natural organic matter through spectral prediction and pattern matching of 2D NMR datasetsMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2004Andre J. Simpson Abstract This paper describes procedures for the generation of 2D NMR databases containing spectra predicted from chemical structures. These databases allow flexible searching via chemical structure, substructure or similarity of structure as well as spectral features. In this paper we use the biopolymer lignin as an example. Lignin is an important and relatively recalcitrant structural biopolymer present in the majority of plant biomass. We demonstrate how an accurate 2D NMR database of ,600 2D spectra of lignin fragments can be easily constructed, in ,2 days, and then subsequently show how some of these fragments can be identified in soil extracts through the use of various search tools and pattern recognition techniques. We demonstrate that once identified in one sample, similar residues are easily determined in other soil extracts. In theory, such an approach can be used for the analysis of any organic mixtures. Copyright © 2003 John Wiley & Sons, Ltd. [source] Low density polyethylene and grafted lignin polyblends using epoxy-functionalized compatibilizer: mechanical and thermal propertiesPOLYMER INTERNATIONAL, Issue 12 2005RRN Sailaja Abstract Lignin was graft copolymerized with methyl methacrylate using manganic pyrophosphate as initiator. This modified lignin was then blended (up to 50 wt%) with low density polyethylene (LDPE) using a small quantity of poly[ethylene- co -(glycidyl methacrylate)] (PEGMA) compatibilizer. The mechanical properties of the blend were substantially improved by using modified lignin in contrast to untreated lignin. Differential scanning calorimetry studies showed loss of crystallinity of the LDPE phase owing to the interaction between the blend components. Thermogravimetric analysis showed higher thermal stability of modified lignin in the domain of blend processing. This suggested that there is scope for useful utilization of lignin, which could also lead to the development of eco-friendly products. Copyright © 2005 Society of Chemical Industry [source] Effect of Technological Factors on Electrochemical Hydrogenation of LigninTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2002Jianan Zhang Abstract Lignin properties were improved by electrochemical hydrogenation. Various technological factors, such as cathode materials, temperature and concentrations of water, solvent, substrate, on the electrochemical hydrogenation of lignin in divided electrolytic cell were studied. The results showed that the hydrogen content (H %) and ratio of hydrogen to carbon (H/C) of hydrogenated lignin (HL) increased by 1.7 % and 0.04, respectively, and the softening point (SP) decreased by 24°C in comparison with lignin raw material. It was feasible for lignin to be electrochemically hydrogenated. Les propriétés de la lignine ont été améliorées par hydrogénation électrochimique. Divers facteurs technologiques, tels que le matériau des cathodes, la température et les concentrations de l'eau, du solvant, du substrat, sur l'hydrogénation électrochimique de la lignine dans une cellule électrolytique divisée, sont étudiés. Les résultats montrent que la teneur en hydrogène (H %) et le rapport entre l'hydrogène et le carbone (H/C) de la lignine hydrogénée (HL) augmente de 1,7% et 0,04, respectivement, et que le point d'adoucissement (SP) diminue de 24°C comparativement au matériau brut de la lignine. La lignine a pu être hydrogénée électrochimiquement. [source] Variety diversity effect on the chemical composition and dry matter degradation characteristics of residue and by-products of oil palm fruitsANIMAL SCIENCE JOURNAL, Issue 3 2009Musibau Adungbe BAMIKOLE ABSTRACT The materials palm press fibre (PPF), palm calyx (PCL) and palm oil sludge (POS) obtained from three varieties of oil palm: dura, oleifera and tenera were investigated for the effect of variety on their nutritive value. Analysis of proximate composition, cell wall fractions, some mineral concentration as well as in-situ dry matter degradation in the rumen of steers were carried out. Significant effects of materials (i.e. PPF, PCL and POS) as well as variety (i.e. dura, oleifera and tenera) were noticed in all the parameters studied except sodium (Na) and organic matter (OM) components. Crude protein (CP) values in all the varieties were lowest in PCL (3.15,5.48%) and highest in POS (9.02,10.02%), while crude fibre (CF) values were highest in PCL (33.00,46.19%) and lowest in POS (3.15,5.48%). The upper and lower values respectively for CP and CF in the materials were in most cases for the tenera variety. The cell wall fractions (NDF, ADF, Lignin, cellulose and hemicellulose) were all higher in PCL and lowest in POS. In the three varieties, POS had highest concentration of Mg (0.117,0.231 g/100 g), K (1.21,2.33 g/100 g) and Cu (75.07,87.34 mg/kg) but lowest content of Ca (0.016,0.089 g/100 g) while PPF had lowest concentration of Mg (0.031,0.039 g/100 g) and Cu (20.96,22.28 mg/kg). Iron (Fe, mg/kg) values were generally high, but highest in PCL (2015.41,4042.16). Dry matter degradability and effective degradability values were best in POS irrespective of the variety and least in PCL. Among the three varieties, dry matter degradation characteristics of tenera were the best and oleifera the least. Generally the residue and by-products irrespective of the variety of oil palm they are obtained from can be ranked for their nutritive value as POS > PPF > PCL, while nutritive ranking based on variety is tenera > dura > oleifera. Conclusively, POS and PPF from any variety of oil palm could be adopted directly as feed resources for ruminant livestock, while PCL will require hydrolytic nutritive value enhancement treatment. Ruminant livestock will however be at an advantage if materials from tenera variety are fed. [source] The integration of green chemistry into future biorefineriesBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 1 2009James H. Clark Abstract The use of biorefineries for the production of chemicals as well as materials and energy products is key to ensuring a sustainable future for the chemical and allied industries. Through the integration of green chemistry into biorefineries, and the use of low environmental impact technologies, we can establish future supply chains for genuinely green and sustainable chemical products. The first step in these future biorefineries should be the benign extraction of surface chemicals; here the use of greener solvents, such as supercritical carbon dioxide and bioethanol, should be considered. The residues will often be rich in lignocellulosics and the effective separation of the cellulose is a major challenge which may, in the future, be assisted by greener solvents, such as ionic liquids. Lignin is nature's major source of aromatics; we need new ways to produce small aromatic building blocks from lignin in order to satisfy the enormous and diverse industrial demand for aromatics. Fermentation can be used to convert biomass into a wide range of bioplatform chemicals in addition to ethanol. Their green chemical conversion to higher value chemicals is as important as their efficient production; here clean technologies such as catalysis , notably biocatalysis and heterogeneous catalysis , the use of benign solvents, and energy efficient reactors are essential. Thermochemical processes for the conversion of biomass, such as the production of pyrolysis oil, will also play an important role in future biorefineries and here again green chemistry methods should be used to go to higher value downstream chemicals. Published in 2008 by John Wiley & Sons, Ltd [source] Decomposition of a Lignin Model Compound under Hydrothermal ConditionsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2007Wahyudiono Abstract Lignin, which is the second most abundant polymeric aromatic organic substance in wood biomass after cellulose, and contains many oxygen-based functional groups, has been proposed as an alternative source of chemical compounds. Guaiacol, a model compound for lignin, was reacted in supercritical water using a batch-type reactor at temperatures of 653,673,K and various pressures under an argon atmosphere. The effects of temperature and reaction time at the same pressure were combined into a single severity parameter that was used to monitor the decomposition of guaiacol to its derived compounds. The main products in aqueous solution were catechol, phenol, and o -cresol. The amounts present approached 40.73,wt,%, 14.18,wt,%, and 4.45,wt,%, respectively. With an increase in the reaction time at the same conditions, the amount of guaiacol decreased and the quantity of derived compounds of guaiacol increased. Based on the experimental results, a reaction mechanism for the decomposition of guaiacol was proposed. The process investigated in this study may form the basis for an efficient method of wood biomass decomposition. [source] Oxypropylation of Lignins and Preparation of Rigid Polyurethane Foams from the Ensuing PolyolsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Hamid Nadji Abstract Summary: Different lignins were converted into polyols by a chain extension reaction with propylene oxide (PO). Thus, soda lignin from Alfa (Stipa tenacissima) (SL), organosolv lignin from hardwoods (OL), kraft lignin (KL) from softwood and oxidized organosolv lignin (OOL) were oxypropylated in a batch reactor at 180,°C in the presence of KOH as catalyst. The ensuing polyols were characterized by FTIR and 1H NMR spectroscopy, which showed that they had incorporated poly(propylene oxide) grafts into their structure. Their viscosity varied from 5 mPa,·,s to infinity, depending on the Lignin/PO ratio and their hydroxy index was in the range of 100,200, which made them suitable for rigid polyurethane foam (RPU) formulations. The RPUs thus obtained had a Tg of ca. 60,°C and a thermal conductivity of ,20 mW/m,·,K before ageing and ,25 mW/m,·,K after accelerated ageing for 10 d at 70,°C. The analyses of the gases inside the cells showed that these were mostly closed, since the partial pressure did not decrease significantly with ageing. Photograph of polyurethane foam made from OLOP. [source] Physics, Chemistry and Applications of the AC Diaphragm Discharge and Related Discharges in Electrolyte SolutionsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2007A. I. Maximov Abstract Three types of the underwater discharges produced by means of AC voltage sources (500-2000 V, 0.05-1 A) were investigated. Dynamic volt-ampere characteristics and radiation intensity of these discharges were measured. It was observed the optical afterglow time up to 0.1-0.2 s. The information about their chemical action was got by stimulation of the oxidation of the organic and inorganic substances. It was found that the treatment of the cellulose and the flax by means of the underwater discharges results in the change of their molecular mass, lignin contain and surface concentration of the oxygen containing functional groups. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Indigestibility of plant cell wall by the Australian plague locust, Chortoicetes terminiferaENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2004F.J. Clissold Abstract The plant cell wall may play an important role in defence against herbivores since it can be both a barrier to, and nutrient diluter of, the easily digested cell contents. The aim of this study was to investigate the digestibility of the cell wall of three grasses, Triticum aestivum L., Dactyloctenium radulans (R. Br.) Beauv., and Astrebla lappacea (Lindl.) Domin, by the Australian plague locust, Chortoicetes terminifera Walker (Orthoptera: Acrididae, Acridinae) as determined by the Van Soest method [Van Soest PJ, Robertson JB & Lewis BA (1991) Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3583,3597]. Determination of plant cell wall digestion by locusts required a precise methodological procedure to determine both the exact intake and the concentration of cell wall in the diet and the faeces. Plant cell wall determination is affected by the particle size distribution of the dried plant material. All three grasses differed in the percentage of cell wall per gram dry matter and the proportions of hemicellulose, cellulose, and acid-detergent sulphuric lignin within the cell wall. The locust was unable to digest the cell wall of any of the grasses. Thus, plant cell walls are a mechanical barrier hindering locusts assimilating nutrients. That is, access, rather than nutrient concentration per se, may be limiting nutrient factor. [source] Effect of residual vanadyl ions on the spectroscopic analysis of humic acids: a multivariate approachEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2008E. H. Novotny Summary In a study of the vanadyl (VO2+)-humic acids system, the residual vanadyl ion suppressed fluorescence and specific electron paramagnetic resonance (EPR) and NMR signals. In the case of NMR, the proton rotating frame relaxation times (T1,H) indicate that this suppression is due to an inefficient H-C cross polarization, which is a consequence of a shortening of T1,H. Principal components analysis (PCA) facilitated the isolation of the effect of the VO2+ ion and indicated that the organic free radical signal was due to at least two paramagnetic centres and that the VO2+ ion preferentially suppressed the species whose electronic density is delocalized over O atoms (greater g -factor). Additionally, the newly obtained variables (principal components , PC) indicated that, as the result of the more intense tillage a relative increase occurred in the accumulation of: (i) recalcitrant structures; (ii) lignin and long-chain alkyl structures; and (iii) organic free radicals with smaller g -factors. [source] The molecular composition of soil organic matter as determined by 13C NMR and elemental analyses and correlation with pesticide sorptionEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2006R. Ahmad Summary Although the chemical composition of soil organic matter (SOM) is known to significantly influence sorption of pesticides and other pollutants, it has been difficult to determine the molecular nature of SOM in situ. Here, using 13C nuclear magnetic resonance (NMR) data and elemental composition in a molecular mixing model, we estimated the molecular components of SOM in 24 soils from various agro-ecological regions. Substantial variations were revealed in the molecular nature of SOM. As a proportion of soil carbon the proportion of the carbonyl component ranged from 0.006 to 0.05, charcoal from 0 to 0.15, protein from 0.09 to 0.29, aliphatic from 0.14 to 0.30, carbohydrate from 0.21 to 0.31, and lignin from 0.05 to 0.42. The relationships between Koc (sorption per unit mass of organic carbon) of carbaryl (1-naphthyl methylcarbamate) and phosalone (S- 6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O -diethyl phosphorodithioate) and the molecular nature of organic matter in the soils were significant. Of the molecular components estimated, lignin and charcoal contents correlated best with sorption of carbaryl and phosalone. Aliphatic, carbohydrate and protein contents were found to be negatively correlated with the Koc of both pesticides. The study highlights the importance of the molecular nature of SOM in determining sorption affinities of non-ionic pesticides and presents an indirect method for sorption estimation of pesticides. [source] Lignin turnover in an agricultural field: from plant residues to soil-protected fractionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006D. P. Rasse Summary Lignin has long been suspected to be a major source of stable carbon in soils, notably because of the recalcitrant nature of its polyphenolic structure relative to other families of plant molecules. However, lignin turnover studies have produced conflicting results, most of them suggesting that large proportions of plant-residue lignin decompose within a year of incorporation into soils. Here, we propose a two-reservoir model where lignin in undecomposed plant residue (Lp) can either reach soil fractions where it is somewhat protected from further decomposition (Ls) or is transformed to non-lignin products. Model calibration data were obtained through compound-specific 13C isotopic analyses conducted in a zero- to 9-year chronosequence of maize monoculture after wheat in a temperate loam soil of the Paris basin. Lignin was quantified by CuO oxidation as VSC-lignin, i.e. the sum of vanillil- (V), syringyl- (S) and coumaryl-type (C) phenols. Model calibrations indicate that Lp has a turnover rate faster than 1 year and that 92% is mineralized as CO2 or transformed into other non-lignin products, while only 8% reaches the Ls fraction. Estimated turnover rate of the Ls fraction was 0.05 years,1. The model also suggested that about half of Lp was not measured because it had been excluded from the samples in the process of sieving at 5 mm. In conclusion, the model indicates that chemical recalcitrance alone is not sufficient to explain VSC-lignin turnover in soils, and that, functionally, the most relevant mechanism appears to be the transfer of VSC-lignin molecules and fragments from decomposing plant tissues to soil-protected fractions. [source] Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006T. Alekseeva Summary We investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse-textured smectite-free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite,kaolinite,chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (,-FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non-linear. The mean amounts of adsorbed AT for starting concentrations of 3,30 mg litre,1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non-decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono- and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure. [source] Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlandsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2005J. B. Yavitt Summary Rates of organic carbon mineralization (to CO2 and CH4) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid-boreal Alberta, Canada, two were in low-boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH4 production varied significantly as a function of peat type, transplant site, and the type,site interaction. All four peat soils had very small rates of CH4 production (< 20 nmol g,1 day,1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH4 production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH4 production (4000 nmol g,1 day,1) correlated with large holocellulose content, a large concentration of p -hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO2 production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO2 production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH4 and CO2 in Sphagnum -derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future. [source] Humus forms in two secondary semi-evergreen tropical forestsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2003G. Loranger Summary The dynamics and function of humus forms in tropical forests are still poorly understood. Humus profiles in two secondary semi-evergreen woodlands in Guadeloupe (French West Indies) were analysed micromorphologically. The humus forms are described under the canopy of five dominant tree species at two sites: under Pisonia subcordata and Bursera simaruba in a secondary forest on a Leptosol (Rendzina), and under Swietenia macrophylla, Tabebuia heterophylla and B. simaruba in a plantation on a calcareous Vertisol. In the secondary forest, two distinct humus forms were observed. A calcareous Amphimull, characterized by an OH horizon comprising the faecal pellets of millipedes, is formed under the canopy of P. subcordata, which produces a litter that is rich in nitrogen. A Dysmull with a thick root mat (OFRh horizon) develops under the canopy of B. simaruba, which produces a litter rich in lignin and phenol that is consumed slowly by the soil fauna. In the plantation on the Vertisol, the activity of the endoanecic earthworm Polypheretima elongata has led to the rapid disappearance of litter and the mixing of organic and mineral material. The humus form is a Eumull and is similar under all three tree species present. [source] Characterization of cinnamyl alcohol dehydrogenase of Helicobacter pyloriFEBS JOURNAL, Issue 5 2005An aldehyde dismutating enzyme Cinnamyl alcohol dehydrogenases (CAD; 1.1.1.195) catalyse the reversible conversion of p -hydroxycinnamaldehydes to their corresponding alcohols, leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helicobacter pylori (HpCAD) was cloned in Escherichia coli and the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium. It is specific for NADP(H) as cofactor and has a broad substrate specificity for alcohol and aldehyde substrates. Its substrate specificity is similar to the well-characterized plant enzymes. High substrate inhibition was observed and a mechanism of competitive inhibition proposed. The enzyme was found to be capable of catalysing the dismutation of benzaldehyde to benzyl alcohol and benzoic acid. This dismutation reaction has not been shown previously for this class of alcohol dehydrogenase and provides the bacterium with a means of reducing aldehyde concentration within the cell. [source] Oxidation of phenols by laccase and laccase-mediator systemsFEBS JOURNAL, Issue 21 2002Solubility, steric issues To investigate how solubility and steric issues affect the laccase-catalysed oxidation of phenols, a series of oligomeric polyphenol compounds, having increasing size and decreasing solubility in water, was incubated with laccase. The extent of substrate conversion, and the nature of the products formed in buffered aqueous solutions, were compared to those obtained in the presence of an organic cosolvent, and also in the presence of two mediating species, i.e. N -hydroxyphthalimide (HPI) and 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO). This approach showed not only an obvious role of solubility, but also a significant role of the dimension of the substrate upon the enzymatic reactivity. In fact, reactivity decreases as substrate size increases even when solubility is enhanced by a cosolvent. This effect may be ascribed to limited accessibility of encumbered substrates to the enzyme active site, and can be compensated through the use of the appropriate mediator. While TEMPO was highly efficient at enhancing the reactivity of large, less soluble substrates, HPI proved less effective. In addition, whereas the laccase/HPI system afforded the same products as laccase alone, the use of TEMPO provided a different product with high specificity. These results offer the first evidence of the role of ,oxidation shuttles' that the mediators of laccase may have, but also suggest two promising routes towards an environmentally friendly process for kraft pulp bleaching: (a) the identification of mediators which, once oxidized by laccase, are able to target strategic functional groups present in lignin, and (b) the introduction of those strategic functional groups in an appropriate pretreatment. [source] Metabolic fingerprinting allows discrimination between Ulmus pumila and U. minor, and between U. minor clones of different susceptibility to Dutch elm diseaseFOREST PATHOLOGY, Issue 4 2008J. A. Martin Summary Experiments were conducted to test whether Fourier transform-infrared (FT-IR) spectroscopy, coupled with chemometric methods, can distinguish healthy xylem tissues collected from elms known to differ significantly in their susceptibility to Ophiostoma novo-ulmi Brasier. Twig samples from resistant Ulmus pumila L., susceptible U. minor Mill. and resistant U. minor clones were harvested on 1 May, 15 May, 1 June, 1 July and 1 September 2004, and subjected to FT-IR analysis. The application of principal component analysis to the spectral data, followed by discriminant function analysis, discriminated between the three groups of samples in all harvesting dates. The examination of the DF-loading plots allowed the identification of key regions within the spectra for the separation between clusters. The chemical assignments of these key regions allowed the following interpretations to be made: (i) U. pumila tissues contained enhanced levels of starch, cellulose and lignin with respect to U. minor tissues and (ii) resistant U. minor tissues contained enhanced levels of starch, cellulose and pectic polysaccharides with respect to susceptible U. minor tissues. The possible roles of the compositional differences in disease resistance, as well as the potential use of FT-IR spectroscopy and chemometrics as a tool for screening resistant elms are discussed. [source] ,Defence lignin' and hydroxycinnamyl alcohol dehydrogenase activities in wounded Eucalyptus gunniiFOREST PATHOLOGY, Issue 2 2003S. Hawkins Summary To learn more about lignin formation in response to wounding in trees, we adopted two complementary approaches: (1) microscopic and histochemical studies of the wound response in 3.5-month-old Eucalyptus gunnii plantlets and (2) biochemical investigations of hydroxycinnamyl alcohol dehydrogenase activities in wounded 6-year-old, field-grown E. gunnii trees. The first approach revealed that a barrier zone was formed in response to wounding in both ground tissues (cortex barrier and pith reaction zone) and vascular tissues. The barrier zone was barely detectable after 24 h but well-developed 7 days after wounding. Microscopic analyses indicated that the barrier zone was formed by the reinforcement of cell walls with ,lignin-like material' in both ground tissues and vascular tissue, and that, in addition, the lumen of certain xylem cells (vessels and fibres) were blocked by the deposition of polymeric phenolic material. Histochemical characterization revealed that the lignin-like material (,defence lignin') deposited in ground tissue cell walls and xylem cell blockages was poor in syringyl (S-type) lignin units and therefore differed from the usual mixed guaiacyl,syringyl (G,S) lignin unit composition of E. gunnii developmental lignin. In contrast, S-type lignin appeared to be deposited in the cell walls of immature developing secondary xylem cells at a stage when the cell walls of comparable cells from unwounded control stems contained lignin poor in syringyl units. The second approach indicated that two different types of cinnamyl alcohol dehydrogenase activity are induced, and apparently regulated differentially, in response to wounding in E. gunnii trees. Coniferyl alcohol dehydrogenase activity was induced immediately and continued to increase throughout the first 15 days of the 17-day experimental period, while sinapyl alcohol dehydrogenase activity was first detected at 8 days after wounding and continued to increase throughout the experimental period. The biological roles of the two alcohol dehydrogenase activities are discussed in relation to the formation of defence lignin versus developmental lignin in trees. Résumé Afin d'approfondir nos connaissances concernant la formation de lignine en réponse aux blessures chez les arbres, nous avons utilisé deux approches complémentaires: (1) des études microscopiques et histochimiques de la réponse à la blessure chez les plantules d'Eucalyptus gunniiâgées de 3 mois et demi, et (2) des analyses biochimiques des activités alcools hydroxycinnamyliques déshydrogénases chez les arbres âgés de 6 ans blessés au champ. L'utilization de la première approche a révélé qu'une barrière physique se forme en réponse à la blessure aux niveaux des tissus vasculaires, de la moelle, et des tissus externes au phloème. A 24 h après la blessure, cette barrière est peu développée mais elle est bien formée après 7 jours. Les analyses microscopiques et histochimiques ont indiqué que les parois cellulaires au niveau de la barrière sont renforcées par un composé semblable à la lignine (,lignin-like material'). De plus, les lumens de plusieurs cellules xylémiennes (vaisseaux et fibres) sont bouchées par le dépôt d'un composé polymérique de nature phénolique. Les caractérizations histochimiques ont indiqué que le ,lignin-like material' (lignine de défense) déposé dans les parois cellulaires de la moelle et des tissus externes au phloème, et dans les lumens des cellules xylemiennes, contient peu d'unités syringyles (type-S). En conséquence, cette ,lignine de défense' se distingue de la ,lignine de développement' typique d'E. gunnii, qui est composée d'unités guaiacyles (type-G) et d'unités syringyles (type-S). En revanche chez les plantules blessées, des unités syringyles sont déposées dans les parois des cellules immatures du xylème à un stade où les cellules comparables des plantules témoins ne contiennent que très peu d'unités syringyles. La deuxième approche a indiqué que deux activités alcools cinnamyliques déshydrogénases différentes sont induites, et régulées d'une façon différencielle, en réponse à la blessure chez les arbres d'E. gunnii. L'activité alcool coniférylique déshydrogénase est induite rapidement et continue d'augmenter pendant les 15 premiers jours de la période expérimentale de 17 jours, tandis que l'activité alcool sinapylique déshydrogénase est seulement détectée à 8 jours après la blessure et continue d'augmenter le long de la période expérimentale. Les rôles biologiques potentiels de ces deux activités alcools déshydrogénases sont discutés en relation avec la formation de la lignine de défense et avec la lignine de développement chez les arbres. Zusammenfassung Zur Untersuchung der Ligninbildung nach Verletzungen bei Bäumen wurden zwei sich ergänzende Forschungsansätze gewählt: 1. Mikroskopische und histochemische Untersuchungen der Wundreaktion an Jungpflanzen (3,5 Monate alt) von Eucalyptus gunnii und 2. Biochemische Untersuchungen der Hydroxycinnamylalkohol-Dehydrogenase-Aktivität bei verletzten, sechs Jahre alten E. gunnii -Bäumen im Freiland. Der erste Ansatz zeigte, dass eine Barrierezone als Antwort auf die Verletzung sowohl in beiden Grundgeweben (Cortex-Barriere und Reaktionszone im Mark) als auch in den Leitgeweben gebildet wird. Die Barrierezone war 24 Stunden nach der Verletzung gerade erkennbar, nach sieben Tagen war sie gut entwickelt. Die mikroskopische Untersuchung zeigte, dass die Barrierezone durch Verstärkung der Zellwände mit ,,ligninartigem Material,, im Grund- und Leitgewebe gebildet wurde, und dass zusätzlich das Lumen gewisser Xylemzellen (Gefässe und Fasern) durch Ablagerung von polymerem phenolischem Material verschlossen wurde. Die histochemische Analyse ergab, dass das ligninartige Material (,,Abwehrlignin,,), das in den Zellwänden des Grundgewebes und in den Lumina der Xylemzellen abgelagert wurde, geringe Mengen an Syringyl-(S-Typ)-Lignineinheiten enthielt und sich somit von der normalen Guaiacyl-Syringyl(G-S)-Komposition des Lignins von E. gunnii unterschied. Das S-Typ-Lignin wurde offenbar in den Zellwänden sich entwickelnder sekundärer Xylemzellen abgelagert. Diese Einlagerung erfolgte in einem Stadium, in dem die Zellwände der vergleichbaren Zellen in unverletzten Kontrollstämmen Lignin mit geringem Syringylgehalt enthielten. Der zweite Versuchsansatz zeigte, dass als Reaktion auf die Verletzung zwei verschiedene Arten von Cinnamylalkohol-Dehydrogenase-Aktivitäten induziert und offensichtlich unterschiedlich reguliert werden. Die Aktivität der Coniferyl-Alkohol-Dehydrogenase wurde sofort induziert und sie nahm während 15 Tagen der 17tägigen Versuchsperiode stetig zu, während die Aktivität der Sinapyl-Dehydrogenase erstmals 8 Tage nach der Verletzung nachweisbar war und dann während der gesamten Versuchsperiode anstieg. Die biologische Bedeutung der beiden Alkoholdehydrogenase-Aktivitäten werden in Bezug auf die Bildung von Abwehr-Lignin im Vergleich zur normalen Ligninbildung in Bäumen diskutiert. [source] | |||||||||||||||||||||||||||||||||||||||||||