Lignin barrier

Circumventing the lignin barrier to enzymatic digestion of the polysaccharides occurs when wood is finely ground. Below a certain wood particle size, the polysaccharides (celluloses and hemicellu-... 

Peroxidase enzymes exhibit low enthalpies of activation AHf2 for the formation of Compound I (k12 step), 12, 9.6, and 22 kJ mol 1 for horseradish (86), turnip (75), and lignin (77) peroxidases, respectively. Similarly low activation barriers have been found for Fem-TAML activators (Table III). The ks pathway for 11 is characterized by Aof 24kJmol 1, which is only... 

Lignin is a phenolic polymer. It is the second most abundant bio-polymer on Earth (after cellulose), and plays an important role in providing structural support to plants. Its hydrophobicity also facilitates water transport through the vascular tissue. Finally, the chemical complexity and apparent lack of regularity in its structure make lignin extremely suitable as a physical barrier against insects and fungi. 

Cell walls are biochemically rather inert with reduced digestibility to many organisms because of their complex cellulose, pectin, and lignin molecules. Callose and lignin are often accumulated at the site of infection or wounding (6,7) and form a penetration barrier. Synthesis of inhibitory proteins (e.g., lectins, protease inhibitors) or enzymes (e.g., chitinase, lysozyme, hydrolases, nucleases) that could degrade microbial cell walls or other microbial constituents would be protective, as well as synthesis of peroxidase and phe-nolase, which could help inactivate phytotoxins produced by many bacteria and fungi. These proteins are either stored in the vacuole... 

Do, G.T., Pollet, B., Thevenin, ]., Sibout, R., Denoue, D., Barriere, Y., Lapierre, C. and Jouanin, L. (2007) Both caffeoyl coenzyme A 3-O-methyltransferase 1 and caffeic acid O-methyltransferase 1 are involved in redundant functions for lignin, flavonoids and sinapoyl malate biosynthesis in Arabidopsis. Planta, 226,1117-29. 

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