Polyphenol oxidase (PPO) is one of the most widely distributed metalloproteinases in the nature. It is ubiquitous in plants, fungi, and insects. The activity of polyphenol oxidase can be detected even on the decaying plant residues of the soil. PPO catalyzes the formation of lignin and quinone compounds, which can prevent cells from being harmed by pathogens, and can also play a direct role in disease resistance by forming quinone substances. Therefore, through the research on the activity of PPO, it can more directly reflect the disease resistance of plant organism in the process of growth.
