LIGNIN: A DEFENSIVE SHIELD HALTING THE ENVIRONMENTAL STRESSES – A REVIEW

Abstract

Plants are exposed to various environmental stresses, like mineral deficiency, heavy metals, high and low temperature, and drought, causing adverse effects on plant growth and productivity. Currently, various strategies are employed to generate plants that can withstand these environmental stresses. To this end, the induction of phenylpropanoid pathways are triggered by the signaling network of extracellular ATP (eATP) and dinucleotide polyphosphates (NpnN’s) yielding several metabolites including lignin. Depending upon the stress, lignin plays protective, sustaining or disruptive roles in addition to its involvement in plant growth, development and defense responses. Aside from its involvement in plant development, lignin is also active in the response to numerous abiotic and biotic stress, and hence plays a significant role in plant adaptation to their environment. To differentiate it from developmental lignin, the lignin polymer generated in response to stress is referred to as ‘stress lignin’ or ‘defense lignin.’ In this review, we analyzed the role of lignin as a defensive shield under environmental stress. The physiological and molecular aspects of lignin biosynthesis were also summarized. The analysis and information presented in this review article will help in understanding and the future investigation of lignin in plants with respects to its defensive role under environmental stressed conditions.