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Abstract
The compositional changes occurring in the cell wall of maturing and ripening pear fruits (Pyrus communis L. cv. Spadona) were examined in relation to the activity of pectolytic enzymes and cellulase. Fruit softening was accompanied by a rise in water and EDTA-soluble pectic fractions, and in free galacturonic acid. The latter reached peak levels after 15 weeks of cold storage and thereafter declined. Simultaneously with the degradation of pectin there was a 4 to 5 fold increase in polygalacturonase activity, but pectin-methyl-esterase activity declined as it did throughout the harvest and storage seasons. Cellulase activity which was present also in immature fruit increased 2 to 3 fold as the fruit softened, but in the last stages of softening it decreased. Treatment of the firm fruit with partially purified preparations of cellulase and polygalacturonase both caused a dissolution of insoluble pectin material.