Lignins and Abiotic Stress: An Overview

Abstract

Lignin is a major carbon sink in the biosphere accounting for about 30 % of total carbon sequestered in terrestrial plants. Being the second most abundant polymer on earth, it is a complex 3-dimensional polymer which is the principal structural component of plant cell wall. The phenylpropanoid pathway is responsible for biosynthesis of a variety of products that include lignin flavonoids and hydroxycinnamic acid conjugates. The phenylpropanoid metabolism has attracted significant research attention as lignin is a limiting factor in a number of agroindustrial processes like chemical pulping, forage digestibility and the processing of lignocellulosic plant biomass to bioethanol. Further, many functions of lignins and related products make the phenylpropanoid pathway essential to the health and survival of plants by providing resistance from abiotic and biotic stresses. These polymers play crucial role in plethora of ecological and biological functions which include shaping of wood characteristics, mechanical support in plants and most importantly stress management (biotic and abiotic stresses). Since lignins act synergistically in a number of agricultural processes, viz. crop production, vigour and disease resistance, thus insights into both the biosynthetic pathway and biodegradation of lignins are of prime significance. Due to the urgent requirement of upregulation and downregulation of lignin genes, focus has been drawn on the genetic engineering of its biosynthetic pathway. This proposed book chapter lays intensive focus on abiotic stress management through lignins by drawing a comparison between the process of lignification of plants under normal conditions as opposed to plants subjected to a variety of abiotic stresses such as drought, flooding, UV rays, heat, chilling and freezing and heavy metal stress.