CELLULASE ACTIVITY IN DEVELOPING APPLE FRUITS

Changes in cellulase, polygalacturonase and total protein were measured during the growth and ripening of three apple cultivars (Malus sylvestris Mill 'Stark Lodi', 'Paulared' and 'Golden Delicious') with the view of establishing the role of these cell wall-degrading enzymes in fruit development. In agreement with earlier work, no endo-polygalacturonase activity was evident at any stage of apple development. Cellulase was present in young expanding fruit and decreased in activity as the fruit reached full size and ripened. Separation of cellulase on MonoQ columns indicated the presence of three isoforms, two of which had molecular weights of 67 kDa. Electrophoresis of proteins from developing fruit indicated that proteins with molecular weights of 24, 26 and 67 kDa increased during ripening. Unlike other climacteric fruit, ripening in apples was not associated with an increase in extractable cellulase or polygalacturonase. The sodium dodecylsulfate-polyacrylamide gel electrophoresis studies suggest that a 67 kDa protein increased during ripening. The decrease in enzyme activity may be due to the inability of available extraction techniques to release this enzyme from apple cell walls.