CHARACTERIZATION OF SPECIFIC INDUCTION, ACTIVITY, AND ISOZYME POLYMORPHISM OF EXTRACELLULAR CELLULASES FROM VENTURIA-INAEQUALIS DETECTED IN-VITRO AND ON THE HOST-PLANT

Specific induction of cellulases (EC 3.2.1.4 and EC 3.2.1.91) in cultu res of Venturia inaequalis was tested with various cellulosic substrat es and their derivatives. The low constitutive amount of extracellular enzymes produced in vitro was increased about 100-fold with cellulosi c sheets or with solvent-extracted leaves of apple in the medium. Enzy me induction required these materials to be intact. Grinding the subst rates did not stimulate cellulase production. Any mechanical disintegr ation of leaf substrate resulted in a complete loss of inductive capac ity. Presumably, topographic features of these substrates induce cellu lase production. The yield of enzyme was correlated with mycelial deve lopment and was not affected by the addition of further carbon sources . High-pressure liquid chromatography of cellulase degradation product s of cellodextrins and of cellulosic sheets indicated an endoglucanase type of cleavage with increasing activity toward substrates with high er degrees of polymerization. beta-Glucosidases (EC 3.2.1.21) were mai nly associated with fungal hyphae. Isoelectric focusing followed by a zymogram technique revealed a cellulase system of 12 isozymes with iso electric points in the range of 3.7-5.6. The molecular weights were ab out 60 kD for at least five enzymes and about 25 kD for the five more prominent isozymes. The cellulase pattern from 19 isolates of V. inaeq ualis were essentially identical, and their differences were restricte d mainly to quantitative variability, Cellulases produced in situ were isolated from leaf lesions of naturally infected apple trees. The cel lulase pattern derived from the host-parasite interaction was qualitat ively nearly identical to that of the enzymes produced in vitro.