Characterization of Specific Induction, Activity, and Isozyme Polymorphism of Extracellular Cellulases from Venturia inaequalis Detected in Vitro and on the Host Plant. Andreas Kollar. Biologische Bundesanstalt, Institut fur Pflanzenschutz im Obstbau, P.O. Box 1264, D-69216 Dossenheim, Federal Republic of Germany. MPMI 7:603-611. Accepted 25 May 1994. Copyright 1994 The American Phytopathological Society.

Specific induction of cellulases (EC 3.2.1.4 and EC 3.2.1.91) in cultures of Venturia inaequalis was tested with various cellulosic substrates and their derivatives. The low constitutive amount of extracellular enzymes produced in vitro was increased about 100-fold with cellulosic sheets or with solvent-extracted leaves of apple in the medium. Enzyme induction required these materials to be intact. Grinding the substrates did not stimulate cellulas production. Any mechanical disintegration of leaf substrate resulted in a complete loss of inductive capacity. Presumably, topographic features of these substrates induce cel-lulase production. The yield of enzyme was correlated with mycelial development and was not affected by the addition of further carbon sources. High-pressure liquid chromatography of cellulase degradation products of cel-lodextrins and of cellulosic sheets indicated an endoglucanase type of cleavage with increasing activity toward substrates with higher degrees of polymerization. ß-Glu-cosidases (EC 3.2.1.21) were mainly associated with fungal hyphac. Isoelectric focusing followed by a zymogram technique revealed a cellulase system of 12 isozymes with isoelectric points in the range of 3.7-5.6. The molecular weights were about 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. inaequalis were essentially identical, and their differences were restricted mainly to quantitative variability. Cellulases produced in situ were isolated from leaf lesions of naturally infecled apple trees. The cellulase pattern derived from the host-parasite interaction was qualitatively nearly identical to that of the enzymes produced in vitro