Cell wall degrading enzymes

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Cell wall degrading enzymes play a key role in the development on plant diseases caused by plant pathogens.

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By: framsis2nd (142 month(s) ago)

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Cell wall degrading enzymes : 

Cell wall degrading enzymes These are macerating factors. These includes; 1. Cellulases 2. Pectinases 3. Hemicelluloses 4. Proteases 5. Cutinases 6. Lignases Chile

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Cuticular enzymes : 

Cuticular enzymes The major chemical substances in cuticle is a cutin framework with waxes embedded in it and extruded from its surface to give a water proof surface (the Cuticular wax). Cutin is a polyester of hydroxylated monocarboxylic acids ( with 16 to 18 carbons and 2 to 3 hydroxyl groups.) Wax contains complex mixture of long chains paraffin, alcohols, ketones, esters and acids. Chile

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Role of enzymes in the dissolution of cuticle is not very well understood. Various enzymes have been suggested in dissolution of cuticle; Cutinesterases Cutinases Lipases A mixture of enzymes includes protease. Cellulases and Pectinases etc.( Germinating spores of Colletotrichum gloeosprioides on orange leaves, Spaerothece pannosa on Rose leaves, Venturia inaequalis on Apple, and Helminthosporium victoriae. Chile

Cellulose : 

Cellulose Cellulose is probably the single most abundant organic molecule in the biosphere. It is the major structural material of which plants are made. Wood is largely cellulose while cotton and paper are almost pure cellulose. Chile

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Because of the orientation of the glycosidic bonds linking the glucose residues, the rings of glucose are arranged in a flip-flop manner. This produces a long, straight, rigid molecule. There are no side chains in cellulose as there are in starch. The absence of side chains allows these linear molecules to lie close together. Chile

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Because of the many -OH groups, as well as the oxygen atom in the ring, there are many opportunities for hydrogen bonds to form between adjacent chains. The result is a series of stiff, elongated fibrils — the perfect material for building the cell walls of plants. Chile

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This electron micrograph shows the cellulose fibrils in the cell wall of a green alga. These long, rigid fibrils are a clear reflection of the nature of the cellulose molecules of which they are composed. Chile

Cellulolytic enzymes : 

Cellulolytic enzymes Comparatively little is known about the role of Cellulases in the tissue degradation during pathogenesis. Not all the pathogenic fungi are Cellulolytic although they do cause tissue disintegration. A team of C1 enzyme, Cx enzymes and ß-glycosidase is suggested to be involved during pathogenesis. Chile

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Pectic enzymes : 

Pectic enzymes Pectic substances or pectin are major component of middle lamella which binds the cells together. Pathogens like fungi, bacteria and nematodes are known to produce Pectic or Pectinolytic enzymes. Pectic substances are polymers a 1?4 linked galacturonic acid units. Chile

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Carboxylic group at 6 th position is intact in Polygalacturonic acid which in state can be referred to as Pectic acid. Carboxylic group are esterified with methyl groups gives rise to Pectinic acid. Pectin are Pectinic acids of high methoxy content or more of methylated carboxyl groups. Chile

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Pectic substances are degraded by Polygalacturonases (PG), Exo and Endo. Pectinmethylgalacturonases (PMG), Exo and Endo. Pectinesterases or Pectinmethylesterases (PME) Polygalacturonase Transeliminases (PGT) Chile

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Polygalacturonases (PG), Exo and Endo. Exo PG and Endo PG hydrolytically break the Pectic acid respectively acting on the terminals and mid part of the polymer. Pectinmethylgalacturonases (PMG), Exo and Endo. Exo and Endo PMG also act in a similar manner. Chile

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Pectinesterases or Pectinmethylesterases (PME) PME hydrolyses and breaks the ester linkage, thus coverts Pectinic acid to Pectic acid the later is ultimately degraded by PG enzyme. PME Chile

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Polygalacturonase Transeliminases (PGT) PGT breaks the polymer by a nonhydrolytic method thus releasing unsaturated sugars. Unsaturated Sugars released after Lyase activity Chile

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These enzymes are primarily produced by soft rot pathogens such as Erwinia dissolvens, E. carotovara, Pseudomonas spp., Botrytis cinerea, Sclerotinia sclerotiorum, Sclerotium rolfsi, Rhizoctonia solani, species of Pythium, Phytophthora and Rhizopus. Specialized pathogen like Puccinia graminis tritici also produces Pectic enzymes during spore germination. Chile

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Role of Hemicellulases, Lignolytic enzymes, Amylase, Proteases and Lipases :- Not very significant. Wood rotters are known to produce Lignolytic and Cellulolytic enzymes during brown rot and white rot pathogenesis. Some filamentous fungi are also known to break down lignin. Chile

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