Cell Wall Metabolism of Two Varieties of Ber (Ziziphus mauritiana Lam.) Fruit During Ripening

Two ber varieties differing in their shelf lives (Umran, 8 to 9 and Illaichi, 4 to 5 days) were analyzed for cell wall components, cell wall degrading enzymes and their isoenzyme profile at immature green, mature green, turning colour, ripe and overripe stages of ripening. Cellulose and pectin contents decreased during ripening in both varieties. This decrease was accompanied by a corresponding increase in pectin methylesterase, polygalacturonase and cellulase. The increase in the activity of pectin methylesterase was about 20- and 10-fold, that of polygalacturonase about 8.4- and 5.7-fold, and of cellulase 5.5- and 4.4-fold in Umran and Illaichi, respectively. The basal level of activities of all these enzymes was higher at all the stages of ripening in Illaichi variety, having short shelf life, as compared to Umran, with long shelf life. This was further confirmed by the intensity of isoenzyme bands of these enzymes. The isoenzyme profile also revealed that two isoenzymes of each, pectin methylesterase and polygalacturonase, and one of cellulase could be considered as isoenzymes responsible for the softening of cell wall during ripening and could be potential targets for manipulation to delay softening during ripening.