Phenylpropanoids are a class of secondary metabolites in plants that are derived from aromatic amino acids like tyrosine and phenylalanine. It mainly includes stilbenes, monolignols, coumarins, flavonoids, and phenolic acids. These are considered to play a crucial role in protecting the plants against both abiotic and biotic stress by quenching the generation of reactive oxygen species (ROS) through a wide range of mechanisms. Phenylpropanoids are found widely in the plant kingdom and serve an essential role in the development of plant by acting as an important cell wall component, floral pigments to mediate the interactions of plant–pollinator, antibiotics (phytoalexins) against pathogens and herbivores, and protectants against UV radiation and high light. Several phenylpropanoids are helpful for the plant to fight against microbial diseases and thereby show broad-spectrum antimicrobial activity. The biosynthetic pathway of phenylpropanoid is mostly activated under abiotic stress conditions including salinity, heavy metal, ultraviolet radiations, high/low temperature, and drought and results in the accumulation of different phenolic compounds that are helpful in scavenging the deleterious effect of ROS. A series of enzymes involved in the activation of the biosynthetic pathway are reductases, transferases, lyases, oxygenases, and ligases. Among these, many are encoded by superfamilies of genes, like NADPH-dependent reductase gene family, the 2-oxoglutarate dependent dioxygenase (2-ODD) gene family, the cytochrome P450 membrane-bound monooxygenase (P450) gene family, and the type III polyketide synthase (PKS III) gene family. Thus, keeping in view the importance of phenylpropanoids in plant defense, the present book chapter is focused on unraveling the role of these essential compounds in ameliorating the stressful conditions in plants.
Keywords: Antimicrobial, Biosynthetic pathway, Phenylpropanoids, Plant, ROS