Information AboutLignin |
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BIOLOGICAL FUNCTION Lignin fills the spaces in the Cell Wall between Cellulose , Hemicellulose and Pectin components. It confers mechanical strength to the Cell Wall and therefore the entire plant. It is particularly abundant in Compression Wood , but curiously scarce in Tension Wood . Lignin plays a crucial part in conducting water in Plant stems. The Polysaccharide components of plant Cell Wall s are highly Hydrophilic and thus permeable to water. Lignin makes it possible to form vessels which conduct water efficiently. Lignin is difficult to degrade and is therefore an efficient physical barrier against Pathogen s which would invade plant tissues. For example an infection by a Fungus causes the plant to deposit more lignin near the infection site. ECONOMIC SIGNIFICANCE Highly lignified Wood is durable and therefore a good raw material for many applications. It is also an excellent fuel, since lignin yields more energy when burned than Cellulose . However, lignin is detrimental to Paper manufacture and must be removed from Pulp before paper can be manufactured. This is costly both in terms of energy and environment. In the Sulfite and Sulfate (also called kraft) Chemical Pulping processes, lignin is removed from wood pulp as Sulphate s. These materials have several uses:
The first investigations into commercial use of lignin were done by Marathon Corporation in Rothschild , Wisconsin ( USA ), starting in 1927 . The first class of products which showed promise were Leather Tanning agents. The lignin chemical business of Marathon is now known as LignoTech USA, Inc., and is owned by the Norwegian company, Borregaard . STRUCTURE AND BIOSYNTHESIS to lignin. The reaction has two alternative routes Catalysed by two different oxidative enzymes, Peroxidase s or Oxidase s.]] Lignin is a large Macromolecule with Molecular Mass in excess of 10,000 Amu . It is Hydrophobic and Aromatic in nature. The Molecule consists of various types of substructures which repeat in random manner. Lignin , Sinapyl Alcohol and Paracoumaryl Alcohol . Different Plants use different monolignols. For example, Norway Spruce lignin is almost entirely Coniferyl Alcohol while paracoumaryl alcohol is found almost exclusively in Grass es. Monolignols are synthetised in the Cytosol as Glucoside s. The Glucose is added to the monolignol to make them water soluble and to reduce their toxicity. The Glucoside s are transported through the Cell Membrane to the Apoplas t. The Glucose is then removed and the monolignols are polymerised into lignin. The Polymerisation step is Catalysed by Oxidative Enzyme s. Both Peroxidase and Laccase Enzyme s are present in the Plant Cell Walls , and it is not known whether one or both of these groups participates in the Polymerisation . The oxidative enzyme Catalyses the formation of monolignol Radicals . These radicals then undergo chemical coupling to form the lignin Polymer . The details of this final step are being debated, since it is not known how the abundance of various possible Bond types between monolignols in controlled. Some theories favour pure chemical coupling, while other state that Dirigent Protein s control this step. EXTERNAL LINKS |
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