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At least 1,513 records · Page 84Linked to original sources
PubMed2003

A candidate-gene approach to clone the sorghum Brown midrib gene encoding caffeic acid O-methyltransferase.

The brown midrib (bmr) mutants of sorghum have brown vascular tissue in the leaves and stem as a result of changes in lignin composition. The bmr mutants were generated via chemical mutagenesis with diethyl sulfate (DES) and resemble the brown midrib (bm) mutants of maize. The maize and sorghum brown midrib mutants are of particular value for the comparison of lignin biosynthesis across different, yet evolutionarily related, species. Although the sorghum brown midrib mutants were first described in 1978, none of the Brown midrib genes have been cloned. We have used a candidate-gene approach to clone the first Brown midrib gene from sorghum. Based on chemical analyses of the allelic mutants bmr12, bmr18 and bmr26, we hypothesized that these mutants had reduced activity of the lignin biosynthetic enzyme caffeic acid O-methyltransferase (COMT). After a northern analysis revealed strongly reduced expression of the COMT gene, the gene was cloned from the mutants and the corresponding wild types using PCR. In all three mutants, point mutations resulting in premature stop codons were identified: bmr12, bmr18 and bmr26 are therefore mutant alleles of the gene encoding COMT. RT-PCR indicated that all three mutants express the mutant allele, but at much lower levels relative to the wild-type controls. Molecular markers were developed for each of the three mutant alleles to facilitate the use of these mutant alleles in genetic studies and breeding programs.

Alleles↗
PubMed2002

O-4-Linked coniferyl and sinapyl aldehydes in lignifying cell walls are the main targets of the Wiesner (phloroglucinol-HCl) reaction.

The nature and specificity of the Wiesner test (phloroglucinol-HCl reagent) for the aromatic aldehyde fraction contained in lignins is studied. Phloroglucinol reacted in ethanol-hydrochloric acid with coniferyl aldehyde, sinapyl aldehyde, vanillin, and syringaldehyde to yield either pink pigments (in the case of hydroxycinnamyl aldehydes) or red-brown pigments (in the case of hydroxybenzaldehydes). However, coniferyl alcohol, sinapyl alcohol, and highly condensed dehydrogenation polymers derived from these cinnamyl alcohols and aldehydes did not react with phloroglucinol in ethanol-hydrochloric acid. The differences in the reactivity of phloroglucinol with hydroxycinnamyl aldehydes and their dehydrogenation polymers may be explained by the fact that, in the latter, the unsubstituted (alpha,beta-unsaturated) cinnamaldehyde functional group, which is responsible for the dye reaction, is lost due to lateral chain cross-linking reactions involving the beta carbon. Fourier transform infrared spectroscopy and thioacidolysis analyses of phloroglucinol-positive lignifying plant cell walls belonging to the plant species Zinnia elegans L., Capsicum annuumvar. annuum, Populus albaL., and Pinus halepensisL. demonstrated the presence of 4- O-linked hydroxycinnamyl aldehyde end groups and 4- O-linked 4-hydroxy-3-methoxy-benzaldehyde (vanillin) end groups in lignins. However, given the relatively low abundance of 4- O-linked vanillin in lignifying cell walls and the low extinction coefficient of its red-brown phloroglucinol adduct, it is unlikely that vanillin contributes to a great extent to the phloroglucinol-positive stain reaction. These results suggest that the phloroglucinol-HCl pink stain of lignifying xylem cell walls actually reveals the 4- O-linked hydroxycinnamyl aldehyde structures contained in lignins. Histochemical studies showed that these aldehyde structures are assembled, as in the case of coniferyl aldehyde, during the early stages of xylem cell wall lignification.

Arachidonic Acids↗
PubMed2003

Production of laccase and manganese peroxidase by Fomes sclerodermeus grown on wheat bran.

The aim of this work was to study the growth and production of ligninolytic enzymes by Fomes sclerodermeus using a natural medium based on wheat bran as the principal substrate in a solid-state fermentation. Growth was monitored by measuring the chitin content in the substrate. The maximum rate of growth was observed between days 7 and 18. A 38% total dry-weight loss of the substrate was measured after 28 days of cultivation. Differential hydrolysis of the substrate revealed that cellulose was more extensively degraded than lignin. In the 28-day incubation period, the losses of cellulose and lignin were 38 and 15%, respectively. No lignin peroxidase activity was found in any of the media tested. The maximum manganese-dependent peroxidase activity recorded was 6.3 U g(-1) at 14 days, while the maximum laccase activity was 270 U g(-1) at 28 days post-inoculation. Addition of commonly used inducers such as copper or manganese did not produce a further increase in the enzyme activities, nor did addition of glucose, asparagine, or malt extract.

Cellulose↗
PubMed2006

Protoplast fusion between Geotrichum candidium and Phanerochaete chrysosporium to produce fusants for corn stover fermentation.

Lignin impedes the digestion of corn stover when used as an animal feed. Phanerochaete chrysosporium is an efficient lignindegrader. Geotrichum candidum can be used to produce single-cell protein. In this study, protoplasts of the two fungi were prepared and fused. After screening, one of the fusants, Fusant R1, was selected for corn stover fermentation. It decreased lignin from 109 to 54 g/kg and increased protein from 48 to 67 g/kg in corn stover. Comparison with their parental strains indicated that the fusant obtained the lignin-degrading ability from P. chrysosporium and the protein-accumulating ability from G. candidium.

Biomass↗
PubMed2006

L-DOPA increases lignification associated with Glycine max root growth-inhibition.

L-3,4-dihydroxyphenylalanine (L: -DOPA), an allelochemical exuded from the roots of velvet bean [Mucuna pruriens (L.) DC. var. utilis], presents a highly inhibitory action to plant growth. The effects of L-DOPA on phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.7) activities, and phenolic compound and lignin content in soybean [Glycine max (L.) Merr.] roots were investigated to determine the possible phytotoxic mechanism. Three-day-old seedlings were cultivated in half-strength Hoagland nutrient solution (pH 6.0), without or with 0.1 to 1.0 mM L-DOPA in a growth chamber (25 degrees C, 12-hr light to 12-hr darkness photoperiod, irradiance of 280 micromol m-2 s-1) for 24 hr. In general, the length, fresh weight, and dry weight of the roots decreased, whereas PAL and POD activities and phenolic compound and lignin content increased after L-DOPA treatments. Results showed the susceptibility of soybean to L-DOPA and reinforce the role of this nonprotein amino acid as a strong allelochemical. The present findings also suggest that L-DOPA-induced inhibition in soybean roots may be because of a cell wall stiffening process related to the formation of cross-linking between cell wall polymers linked to lignin production.

Levodopa↗
PubMed1987

Dietary fibre--definition, chemistry and analytical determination.

Dietary fibre includes non-starch polysaccharides and lignin that are not digested or absorbed in the human small intestine. It contains a mixture of chemically complex polysaccharides. Lignin is a highly cross-linked complex polymer of phenylpropane units. The plant cell wall is the main source of dietary fibre and its structure is reviewed briefly. The structure of the main dietary fibre polysaccharides is then summarized. The demarcation between starch--the main digestible polysaccharide--and dietary fibre presents some problems due to more or less enzyme resistant starch fractions that occur naturally or are formed with processing. "Resistant starch" formed during baking passes through the small intestine in the rat and, probably, in man and is fermented in the colon. It should therefore also be regarded as dietary fibre. Methods for dietary fibre determination fall into two categories: gravimetric methods, weighing the dietary fibre after removal of other components; component analysis methods, determining monomeric composition of fibre polysaccharides (preferably by gas-liquid chromatography) supplemented with a gravimetric lignin determination and separate assay of uronic acid components (pectin). Recently developed enzymatic gravimetric methods are most convenient for the assay of total dietary fibre or water soluble and insoluble fibre separately, whereas component analysis is required for determining the dietary fibre composition.

Chemical Phenomena↗
PubMed1994

Seedling growth and development on space shuttle.

Young pine seedlings, and mung bean and oat seeds were flown on shuttle flights, STS-3 and STS-51F, in March, 1982 and July/August, 1985, respectively. The plant growth units built to support the two experiments functioned mechanically as anticipated and provided the necessary support data. Pine seedlings exposed to the microgravity environment of the space shuttle for 8 days continued to grow at a rate similar to ground controls. Pine stems in flight seedlings, however, averaged 10 to 12% less lignin than controls. Flight mung beans grew slower than control beans and their stems contained about 25% less lignin than control seedlings. Reduced mung bean growth in microgravity was partly due to slower germination rate. Lignin also was reduced in flight oats as compared to controls. Oats and mung beans exhibited upward growing roots which were not observed in control seedlings. Chlorophyll A/B ratios were lower in flight tissues than controls. The sealed PGCs exhibited large variations in atmospheric gas composition but the changes were similar between flight and ground controls. Ethylene was present in low concentrations in all chambers.

Avena↗
PubMed1988

Ligninase-mediated phenoxy radical formation and polymerization unaffected by cellobiose:quinone oxidoreductase.

Phanerochete chrysosporium ligninase (+ H2O2) oxidized the lignin substructure-related compound acetosyringone to a phenoxy radical which was identified by ESR spectroscopy. Cellobiose:quinone oxidoreductase (CBQase) + cellobiose, previously suggested to be a phenoxy radical reducing system, was without effect on the radical. Ligninase polymerized guaiacol and it increased the molecular size of a synthetic lignin. These polymerizations, reflecting phenoxy radical coupling reactions, were also unaffected by the CBQase system. We conclude that ligninase catalyzes phenol polymerization via phenoxy radicals, which CBQase does not affect. The CBQase system also did not produce H2O2, and its physiological role remains obscure. Glucose oxidase + glucose did produce H2O2 as expected, but, like CBQase, it did not reduce the phenoxy radical of acetosyringone. Because intact cultures of P. chrysosporium depolymerize lignins, it is likely that phenol polymerization by ligninase is prevented or reversed in vivo by an as yet undescribed system.

Basidiomycota↗
PubMed2004

Wet oxidation pretreatment for the increase in anaerobic biodegradability of newspaper waste.

Wet oxidation was investigated for its process performance on methane fermentation of newspaper waste. The mechanisms of solubilization of newspaper waste were investigated using the following criteria: destruction of total COD (TCOD), production of soluble COD (SCOD), production of volatile fatty acids, production of soluble carbohydrates, production of soluble lignin derivatives (SLD), production of furan (F) and destruction of lignin and cellulose. Wet oxidation was carried out at 170, 190, and 210 degrees C, with a retention time of 1 h. The highest removal efficiencies of TCOD and cellulose were achieved at 210 degrees C, approximately 40% and 69% were destroyed, respectively. On the other hand, highest lignin removal efficiency was achieved at 190 degrees C in which approximately 65% was removed. Batch methane fermentation tests were performed in 2-l glass bottles filled with the wet oxidized newspaper samples. Methane fermentation of newspaper pretreated at 190 degrees C gave the highest CH(4) conversion efficiency (59% of the initial TCOD was recovered as CH(4) gas). Anaerobic cellulose removals varied from 74% to 88%.

Biodegradation, Environmental↗
PubMed2004

Fractionation of wheat straw by atmospheric acetic acid process.

Fractionation of wheat straw was investigated using an atmospheric acetic acid process. Under the typical conditions of 90% (v/v) aqueous AcOH, 4% H(2)SO(4) (w/w, on straw), ratio of liquor to straw (L/S) 10 (v/w), pulping temperature 105 degrees C, and pulping time 3h, wheat straw was fractionated to pulp (cellulose), lignin and monosaccharides mainly from hemicellulose with yields of approximately 50%, 15% and 35%, respectively. Acetic acid pulp from the straw had an acceptable strength for paper and could be bleached to a high brightness over 85% with a short bleaching sequence. Acetic acid pulp was also a potential feedstock for fuels and chemicals. The acetic acid process separated pentose and hexose in wheat straw to a large extent. Most of the pentose (xylan) was dissolved, whereas the hexose (glucan) remained in the pulp. Approximately 30% of carbohydrates in wheat straw were hydrolyzed to monosaccharides during acetic acid pulping, of which xylose accounted for 70% and glucose for 12%. The acetic acid lignin from wheat straw showed relatively lower molecular weight and fusibility, which made the lignin a promising raw material for many products, such as adhesive and molded products.

Acetic Acid↗
PubMed2006

Deconvolution of fluorescence spectra: contribution to the structural analysis of complex molecules.

Fluorescence spectroscopy is a sensitive analytical tool in the studies of both simple and complex molecular structures. In complex molecules, however, determining the number and position of components may give a specific insight into the structure, complementary to the other analytical techniques. We applied log-normal model to analyze fluorescence of simple monofluorophore molecule. In order to analyze spectra where both fluorophores and Raman emission bands were present, we developed a method obtained by combination of the symmetric, Gaussian, for Raman and asymmetric, log-normal model, for fluorescence, applicable to the molecules of different complexity. Technically, for each sample we varied excitation wavelength with 5 nm step and recorded the corresponding emission spectra. They were subsequently used for component analysis. Position of each component was plotted against the excitation wavelength. Applying this approach we could identify minimal number of components having stable positions, while their approximate probability density (APD) in a spectral series was correlated with the probable number of fluorophores in the molecule. The method was tested on molecules containing different number of fluorophores: monomers involved in the synthesis of plant polymer lignin-coniferyl alcohol (one fluorophore), ferulic acid (two fluorophores) and on lignin model compound produced from these monomers (many fluorophores). All investigated species belong to benzene-substituted class of compounds, and it is reasonable to assume that they have similar fluorescence band contour. We also report the results of environmental scanning electron microscopy (ESEM) studies showing multilayered dehydrogenative polymer (DHP) structure, in order to show complexity of the polymer. Our results present complementarity of these two approaches in the structural studies of the lignin model compound.

Biopolymers↗
PubMed2006

Plant genetic engineering to improve biomass characteristics for biofuels.

Currently, most ethanol produced in the United States is derived from maize kernel, at levels in excess of four billion gallons per year. Plant lignocellulosic biomass is renewable, cheap and globally available at 10-50 billion tons per year. At present, plant biomass is converted to fermentable sugars for the production of biofuels using pretreatment processes that disrupt the lignocellulose and remove the lignin, thus allowing the access of microbial enzymes for cellulose deconstruction. Both the pretreatments and the production of enzymes in microbial tanks are expensive. Recent advances in plant genetic engineering could reduce biomass conversion costs by developing crop varieties with less lignin, crops that self-produce cellulase enzymes for cellulose degradation and ligninase enzymes for lignin degradation, or plants that have increased cellulose or an overall biomass yield.

Biomass↗
PubMed2005

Methane fermentation of Japanese cedar wood pretreated with a white rot fungus, Ceriporiopsis subvermispora.

Methane fermentation of Japanese cedar wood was carried out after pretreatment with four strains of white rot fungi, Ceriporiopsis subvermispora ATCC 90467, CZ-3, CBS 347.63 and Pleurocybella porrigens K-2855. These fungi were cultivated on wood chip media with and without wheat bran for 4-8 weeks. The pretreated wood chip was fermented anaerobically with sludge from a sewage treatment plant. Pretreatments with C. subvermispora ATCC 90467, CZ-3 and CBS 347.63 in the presence of wheat bran for 8 weeks decreased 74-76% of beta-O-4 aryl ether linkages in the lignin to accelerate production of methane. After fungal treatments with C. subvermispora ATCC 90467 and subsequent 30-days methane fermentation, the methane yield reached 35 and 25% of the theoretical yield based on the holocellulose contents of the decayed and original wood, respectively. In contrast, treatment with the three strains of C. subvermispora without wheat bran cleaved 15-26% of the linkage and produced 6-9% of methane. There were no significant accelerating effects in wood chips treated with P. porrigens which has a lower ability to decompose the lignin. Thus, it was found that C. subvermispora, with a high ability to decompose aryl ether bonds of lignin, promoted methane fermentation of softwood in the presence of wheat bran.

Basidiomycota↗
PubMed2004

Use of analytical microscopy to analyze the speciation of copper and chromium ions onto a low-cost biomaterial.

In this paper, we present our study of the speciation of copper and hexavalent chromium sorbed onto a lignocellulosic substrate, using analytical microscopy. The lignocellulosic substrate constitutes a low-cost biomaterial that can be used in wastewater treatment. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) was used to determine the speciation of the two metal ions on the constitutive moieties of the lignocellulosic substrate. The use of a staining agent sensitive to carbon unsaturation allowed us to differentiate between the microstructures rich in lignin entities and those rich in cellulose entities. The EDX analysis showed that metal ions are preferentially sorbed onto microstructures rich in lignin moieties. The energy electron loss spectroscopy (EELS) was used to determine the oxidation states of chromium in association with lignocellulosic moieties. We showed that the sorption process of hexavalent chromium requires the reduction of Cr(VI) into Cr(III) and the probable oxidation of lignin moieties.

Cellulose↗
PubMed2005

Application of the NICA-Donnan approach to calculate equilibrium between proton and metal ions with lignocellulosic materials.

The NICA (nonideal competitive adsorption)-Donnan model is employed to describe the interactions between Cu2+, Pb2+, Cd2+, Mn2+, and Fe3+ ions and the lignins extracted from wheat bran (lignocellulosic substrate, LS) and from kraft pulp (residual kraft lignin, RKL), and between Cu2+, Mn2+, and Fe3+ ions and wood fibers from kraft pulps. The charge of the LS and the fiber charge need to be obtained from potentiometric titration data for the LS, and by use of Donnan equilibrium, mass balance, and electroneutrality equations for the kraft fiber. The proton binding parameters for the LS and the kraft fiber, the total site densities (Qmax,1 and Qmax,2), the median protonation constants (K1 and K2), and nonideality-generic heterogeneity parameters (m1 and m2) (subscripts 1 and 2 refer to the carboxyl and phenolic functional groups) are obtained by fitting these charge data. With the above proton parameters, the interactions between metal ions and the lignins (LS and RKL)/kraft fibers are calculated, and the metal binding parameters are obtained. These parameters are the binding constants of metal i (K(i,1) and K(i,2)), ion-specific nonideality parameters (n(i,1) and n(i,2)), and intrinsic heterogeneity parameters (p1 and p2). p1 and p2 are the same for all metal ions binding to a specific sorbent. Here, p1 and p2 values obtained by fitting the binding data of a specific metal ion are used directly in binding calculations for other metal ions, and do not need to be fitted. By use of the above parameters for single metal ion binding, the binding relationship between a mixed metal ion and lignocellulosic substrate/kraft fiber can be predicted.

Adsorption↗
PubMed2006

Forest products decomposition in municipal solid waste landfills.

Cellulose and hemicellulose are present in paper and wood products and are the dominant biodegradable polymers in municipal waste. While their conversion to methane in landfills is well documented, there is little information on the rate and extent of decomposition of individual waste components, particularly under field conditions. Such information is important for the landfill carbon balance as methane is a greenhouse gas that may be recovered and converted to a CO(2)-neutral source of energy, while non-degraded cellulose and hemicellulose are sequestered. This paper presents a critical review of research on the decomposition of cellulosic wastes in landfills and identifies additional work that is needed to quantify the ultimate extent of decomposition of individual waste components. Cellulose to lignin ratios as low as 0.01-0.02 have been measured for well decomposed refuse, with corresponding lignin concentrations of over 80% due to the depletion of cellulose and resulting enrichment of lignin. Only a few studies have even tried to address the decomposition of specific waste components at field-scale. Long-term controlled field experiments with supporting laboratory work will be required to measure the ultimate extent of decomposition of individual waste components.

Biodegradation, Environmental↗
PubMed2001

The biosynthesis of monolignols: a "metabolic grid", or independent pathways to guaiacyl and syringyl units?

Lignin is a complex polymer formed by the oxidative polymerization of hydroxycinnamyl alcohol derivatives termed monolignols. The major monolignols in dicotyledonous angiosperm lignin are monomethylated guaiacyl (G) units derived from coniferyl alcohol, and dimethylated syringyl (S) units derived from sinapyl alcohol. The biochemical pathways leading to the formation of monolignols feature successive hydroxylation and O-methylation of the aromatic ring and conversion of the side chain carboxyl to an alcohol function. The current view of the monolignol biosynthetic pathway envisages a metabolic grid leading to G and S units, through which the successive hydroxylation and O-methylation reactions may occur at different levels of side chain oxidation. The present article assesses biochemical and genetic evidence for and against such a model, including recent data on the methylation reactions of monolignol biosynthesis in alfalfa. We draw attention to portions of the currently accepted monolignol pathway that may require revision, and suggest an alternative model in which metabolic channeling allows for independent pathways to G and S lignin.

Fabaceae↗
PubMed2001

Dirigent proteins and dirigent sites in lignifying tissues.

Tissue-specific dirigent protein gene expression and associated dirigent (site) localization were examined in various organs of Forsythia intermedia using tissue printing, in situ mRNA hybridization and immunolabeling techniques, respectively. Dirigent protein gene expression was primarily noted in the undifferentiated cambial regions of stem sections, whereas dirigent protein sites were detected mainly in the vascular cambium and ray parenchyma cell initials. Immunolocalization also revealed cross-reactivity with particular regions of the lignified cell walls, these being coincident with the known sites of initiation of lignin deposition. These latter regions are considered to harbor contiguous arrays of dirigent (monomer binding) sites for initiation of lignin biopolymer assembly. Dirigent protein mRNA expression was also localized in the vascular regions of roots and petioles, whereas in leaves the dirigent sites were primarily associated with the palisade layers and the vascular bundle. That is, dirigent protein mediated lignan biosynthesis was initiated primarily in the cambium and ray cell initial regions of stems as well as in the leaf palisade layers, this being in accordance with the occurrence of the lignans for defense purposes. Within lignified secondary xylem cell walls, however, dirigent sites were primarily localized in the S(1) sublayer and compound middle lamella, these being coincident with previously established sites for initiation of macromolecular lignin biosynthesis. Once initiation occurs, lignification is proposed to continue through template polymerization.

Asteraceae↗