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Abstract
Plants interact with insects and pathogens leading to complex defense approaches against their feeding strategies and disease reactions. Among these defenses, the polyphenol oxidases (PPOs) are the most commonly associated enzymes in both higher plants and fungi.They are significant for entrapment and anti-nutritive defensive mechanisms against these herbivores and micro-organisms. There is increase in the synthesis of polyphenols aided by PPO enzymes under abiotic and biotic stress conditions, which helps the plants to overcome with these environmental or exogenous constraints. PPOs and theirphenolic substrates (mainly quinone compounds) are localized separately within the plants, in plastids and in the vacuoles, respectively, and they get into direct contact only after cellular wounding by external entities like insects and pathogens.In this review, the possible and reported roles or functions of PPOsare discussed in the light of the available literatures. In addition, since PPOs are versatile enzymes, they are expected to have other, newly reported oryet to be discovered functions in plant systems.