Second Most Abundant Organic Polymer on Planet: Lignin
Lignin is an aromatic heteropolymer of complex structure, synthesized by all plants and mainly deposited in the secondary cell walls. It is generated from the oxidative polymerization of monolignols, namely p-coumaryl, coniferyl, and sinapyl alcohols, and makes the wall rigid and hydrophobic, allowing transport of water and solutes through the vascular system. The relative proportion of each monomeric units varies within species, tissues such as leaf, root and stem, and maturity phase of crop plants. In addition to its structural role in the vascular tissues, lignin also protects plant against biotic stresses.