Hydroxycinnamate Amides: Intriguing Conjugates of Plant Protective Metabolites.

The syntheses of aromatic monoamines and aliphatic polyamines (PAs) are responsive to environmental stresses, with some modulating aspects of plant defense. Conjugation of amines to hydroxycinnamic acids (HCAs) generates HCA amides (HCAAs), with the conjugates possessing properties from both compounds. Conjugation may reduce the polarity of the resulting metabolite and assist in translocation, stability, and compartmentalization. Recent metabolomic insights identified HCAAs as biomarkers during plant-pathogen interactions, supporting a functional role in defense. The conjugates may contribute to regulation of the dynamic metabolic pool of hydroxycinnamates. This review highlights the occurrence of aromatic amines (AAs) and PAs in stress metabolism, conjugation to HCAs, and the roles of HCAAs during host defense, adding emphasis on their involvement in hydrogen peroxide (H2O2) production and cell-wall strengthening.