Lignin in plants

The ubiquity of lignin in plant tissue presents an obstacle to the removal and purification of xylan. Lignin retards or prevents the complete solution of xylan either because of mechanical obstruction or perhaps by reason of attachment through as yet unidentified covalent bonds. Furthermore, lignin is partially soluble in the various aqueous alkaline solutions used for dissolving xylan and, consequently, poses a purification problem in various subsequent steps designed to isolate the pure polysaccharide. 

THE BIOSYNTHESIS AND BIOGENESIS OF LIGNIN IN PLANT CELL WALLS... 

In this chapter, the results obtained from the combined use of specific radiolabeling of lignin in plant tissue and microautoradiography are discussed. 

In the oxidative polymerization of phenols catalyzed by Cu complexes, the substrate coordinates to the Cu(II) complex and is then activated. The activated phenol couples in the next step. The Cu complex acts effectively as a catalyst at concentrations of 0.2-2 mol% compared to the substrate. The oxidation proceeds rapidly at room temperature under an air atmosphere to give poly(phenylene ether) in a quantitative yield. The polymerization follows Michaelis-Menten-type kinetics [55]. Enzymatic oxidation of phenols is an important pathway in the biosynthesis of lignin in plants [56] catalyzed by a metalloenzyme. 

An example of cometabolism of pollutants is provided by the white rot fungus Phanerochaete chrysosporium, which degrades a number of kinds of organochlorine compounds, including DDT, PCBs, and chlorodioxins, under the appropriate conditions. The enzyme system responsible for this degradation is one that the fungus uses to break down lignin in plant material under normal conditions. 

H paratively simple method for the detection of lignin in plant materials as well as... 

In general, commonly used oxidants destroy phenolic rings or give complex products (25, 26). Some of the oxidants such as nitrobenzene produce reaction byproducts that may interfere with the analysis of the oxidation products (23, 27, 28). To obtain lignin oxidation products from coals, we resorted to the alkaline cupric oxide oxidation method which has been applied successfully to analysis of lignins in plants (23), fulvic and humic acids (24, 27), and land-derived marine sediments (23). 

R.T., Hanna, W.W. and Barton, F.B., II (1993) Mid-infrared microspectroscopy to assess lignin in plant tissues related to digestibility. Agron. J., 85,171-5. 

Nature is composed of minerals, air, water, and living matter. The latter contains polymers. The most abundant natural polymer is cellulose. It, together with lignin and hemicelluloses, are the principal components of plants. The principal function of lignin in plants is to assist in the movement of water the lignin forms a barrier for evaporation and, thus, helps to channel water to critical areas of the plant. 

The determination of lignin content using IR techniqnes has also been conducted in plants other than wood. For example, the determination of kenaf lignin in plant materials nsing DRIFT has been described [118]. A linear relationship existed between the peak area at 1506 cm i and lignin content. The lignin content of four kenaf varieties (by weight of plant material) was 10.4-10.8% in the bark, 20.5-20.6% in the wood, and 14.9-15.3% in the pith. 

Robinson (1990) traces the evolutionary history of lignin. There was no lignin in plants in the Ordovician. Ligninlike compounds were found in some of the first vascular plants in the Silurian. She estimates that the content of lignin in these small plants was comparable to that of herbs today (1()-1.S%). Subsequently, lignification rose to 40% in the Late Devonian, dropped to 30-35% at the end of the Mesozoic, and has subsequently declined to an average of about 20%. 

Chalcones are intermediates in the biosynthesis of lignins in plants oligomers were produced by the HRP-mediated polymerisation of aminochalcones in a mixture of 1,4-dioxane and phosphate buffer (Scheme 12.19) [197]. 

Fineran, B. A. Cyto- and histochemical demonstration of lignins in plant cell walls an evaluation of the chlorine water/ethanolamine-silver nitrate method of Coppick and Fowler. Protoplasma 1997,198, 186—201. 

The presence of lignin in plant cell walls interferes with the fermentation to produce biofuels, and enzymes are the single largest processing cost component for bioconversion of biomass after the biomass itself. The transgenic switchgrass requires lower temperature preprocessing and only one-quarter to one-third the level of enzymes... 

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