Plant diseases caused by fungal, bacterial, and viral pathogens represent a major constraint to global agricultural productivity. Plants rely on a complex and highly regulated defense system in which defense-related enzymes play central roles in restricting pathogen invasion and disease progression. This review provides a comprehensive overview of the enzymatic components of plant disease resistance, with a particular focus on key defense-related enzymes, including phenylalanine ammonia-lyase, peroxidases, chitinases, β-1,3-glucanases, and polyphenol oxidase. The biochemical functions of these enzymes in reinforcing cell walls, generating antimicrobial compounds, and regulating reactive oxygen species are discussed in relation to their contribution to plant immunity. Furthermore, the molecular regulation of defense-related enzymes is examined, emphasizing the roles of pathogen recognition, phytohormone-mediated signaling pathways, transcriptional control, and signal cross-talk. Recent advances in omics technologies are highlighted as powerful tools for elucidating regulatory networks underlying enzyme-mediated defense responses. In addition to molecular mechanisms, this review explores the agricultural and biotechnological applications of defense-related enzymes, including their use as biochemical markers in breeding programs, targets for genetic improvement, and key components of induced resistance strategies. Current challenges, such as growth–defense trade-offs and environmental influences on enzyme activity, are also addressed, along with future perspectives for integrating molecular insights into sustainable disease management and crop improvement. Overall, this review underscores the importance of defense-related enzymes as major contributors to plant disease resistance and their potential contribution to resilient and sustainable agricultural systems.
Fatma Gönül Sezgin (2026) studied this question.