This protein functions as a defense against chitin containing fungal pathogens. Random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Intercellular space of infected plants. Expression of the acidic chitinase gene was not detected in normal, untreated plants nor in plants treated with ethylene or salicylic acid. Belongs to the glycosyl hydrolase 18 family. Chitinase class III subfamily.