Function of polyphenol oxidase in higher plants

Abstract

Recent evidence has supported the folllowing views: 1. Polyphenol oxidase (PPO) is a plastidic enzyme that is unclear‐coded, but is inactive until incorporated into the plastid. 2. In healthy green tissues PPO exists in a latent form on the thylakoid membrane and is not involved in synthesis of phenolic compounds. In leucoplasts, proplastids, or amyloplasts PPO is often present in a latent form in rudimentary thylakoids. 3. PPO normally functions as a phenol oxidase in vivo only in sencent or damaged cells. 4. In the functional chloroplast, PPO may be involved in some aspect of oxygen chemistry – pherhaps mediation of pseudocyclic photophosphorylation.