Antimicrobial Functions of the Plant Hydrolases, Chitinase and ß-1,3-Glucanase

Many plant species accumulate chitinases and s-1,3-glucanases in response to infection by plant pathogens and to treatments with the plant stress hormone, ethylene. The substrates of these two enzymes, chitin and s-1,3-glucan, are the main components of the cell walls of most higher fungi. Taken individually, purified chitinases and s-1,3-glucanases inhibit some fungi but do not affect most of them. However, combinations of the two enzymes inhibit many saprophytic and pathogenic fungi on agar plates or in liquid medium. Microscopic studies indicate that the enzymes attack primarily the hyphal tip. Growing hyphae are highly sensitive when suddenly brought into contact with the antifungal hydrolases. However, they have a potential to adapt and become resistant when exposed continually to the enzymes. This suggests that antifungal hydrolases may be more effective in defense when suddenly brought into contact with invading fungi, e.g. by release from an intracellular compartment, than when present constitutively in the extracellular space.