ABSTRACT
More knowledge about the chemical structure of lignin in plant cell walls and its formation mechanism can lead to a better understanding and developments in a wide area of science and technology related to woody plants as follows:
(1) From the viewpoint of plant science, lignin is one of the major cell wall polymers, which makes difference between trees (woody plants) and non-woody plants. The word “lignin” is derived from the Latin “Lignum” meaning wood. In the course of the evolution of plants, some species acquired a metabolic pathway to produce lignin, and their cell walls were endowed by lignification with characteristic physical, chemical and biological properties as follows: (a) lignification makes cell walls hydrophobic so that aqueous nutrients can be conducted through tissues, (b) lignification makes cell walls mechanically strong so that plants can grow higher and can extend branches to receive more sunlight, (c) lignification makes cell walls resistant to attacks by microorganisms and animals, and (d) lignification protects living cells from physico-chemical effects by sunlight. These unique properties of lignified cell walls enabled trees to grow and survive for hundreds of years, and the largest portion of organic substances (fixed carbon dioxide in stable form) on the earth including humic substances in the soil originate from lignified cell walls of woody plants.
