Stress-induced phenylpropanoid metabolism in plants involves the biosynthesis of a wide range of compounds, including phytoalexins, lignin, and suberin, which play critical roles in plant defense and stress responses. Phenylpropanoids are derived from cinnamic acid, which is synthesized from phenylalanine via the enzyme phenylalanine ammonia-lyase (PAL). The biosynthesis pathway includes several key enzymes, such as chalcone synthase (CHS), which catalyzes the formation of flavonoids, and isoflavone synthase (IFS), which produces isoflavonoids. These compounds are often induced in response to biotic and abiotic stresses, such as pathogen attack, UV irradiation, and cold or nutrient stress. Phenylpropanoids serve multiple functions in plant defense, including antimicrobial activity, protection against UV radiation, and the formation of physical barriers. For example, flavonoids and sinapate esters act as UV protectants, while lignin and suberin contribute to wound healing and pathogen resistance. The biosynthesis of these compounds is regulated by a complex network of transcriptional and post-transcriptional mechanisms, involving genes such as those encoding PAL, CHS, and other enzymes. Molecular and genetic approaches have been used to identify and characterize these genes, as well as to study their roles in stress responses. The spatial and subcellular organization of phenylpropanoid biosynthesis is also important, with many enzymes and metabolites localized in specific cell compartments, such as the vacuole or endoplasmic reticulum. The regulation of phenylpropanoid metabolism is influenced by various signaling pathways, including those involving salicylic acid, which is involved in systemic acquired resistance (SAR). Recent advances in molecular biology have provided new insights into the enzymology and regulation of phenylpropanoid biosynthesis, as well as the functions of these compounds in plant defense and stress responses.Stress-induced phenylpropanoid metabolism in plants involves the biosynthesis of a wide range of compounds, including phytoalexins, lignin, and suberin, which play critical roles in plant defense and stress responses. Phenylpropanoids are derived from cinnamic acid, which is synthesized from phenylalanine via the enzyme phenylalanine ammonia-lyase (PAL). The biosynthesis pathway includes several key enzymes, such as chalcone synthase (CHS), which catalyzes the formation of flavonoids, and isoflavone synthase (IFS), which produces isoflavonoids. These compounds are often induced in response to biotic and abiotic stresses, such as pathogen attack, UV irradiation, and cold or nutrient stress. Phenylpropanoids serve multiple functions in plant defense, including antimicrobial activity, protection against UV radiation, and the formation of physical barriers. For example, flavonoids and sinapate esters act as UV protectants, while lignin and suberin contribute to wound healing and pathogen resistance. The biosynthesis of these compounds is regulated by a complex network of transcriptional and post-transcriptional mechanisms, involving genes such as those encoding PAL, CHS, and other enzymes. Molecular and genetic approaches have been used to identify and characterize these genes, as well as to study their roles in stress responses. The spatial and subcellular organization of phenylpropanoid biosynthesis is also important, with many enzymes and metabolites localized in specific cell compartments, such as the vacuole or endoplasmic reticulum. The regulation of phenylpropanoid metabolism is influenced by various signaling pathways, including those involving salicylic acid, which is involved in systemic acquired resistance (SAR). Recent advances in molecular biology have provided new insights into the enzymology and regulation of phenylpropanoid biosynthesis, as well as the functions of these compounds in plant defense and stress responses.