BETA-GALACTOSIDASE, POLYGALACTURONASE AND PECTINESTERASE IN DIFFERENTIAL SOFTENING AND CELL-WALL MODIFICATION DURING PAPAYA FRUIT RIPENING

Papaya (Carica papaya L. cv. Eksotika) fruit softens differentially in relation to position of the tissue. The inner mesocarp tissue is soft er, and its firmness decreases more rapidly during ripening than that of the outer mesocarp tissue. As the fruit ripens, pectin solubility a nd depolymerisation increase. Hemicellulose, too, appears to be depoly merised but, unlike pectins, this apparent degradation of hemicellulos e is associated with an increase rather than a decrease in its level. Pectin and hemicellulose depolymerisation began in the inner mesocarp tissue at about the same time as beta-galactosidase (EC 3.2.1.23) acti vity started to increase and tissue firmness began to decrease more ra pidly In contrast, pectin solubilisation in both outer and inner mesoc arp tissues occurred steadily throughout ripening at a comparable rate and paralleled closely the increase of polygalacturonase (PG; EC 3.2. 1.67) and pectinesterase (EC 3.1.1.11). In general, irrespective of en zyme distribution, tissue softening during ripening was more closely r elated to changes in beta-galactosidase activity than to PG or pectine sterase activity. Papaya, beta-galactosidase appears to be an importan t wall degrading enzyme and may contribute significantly to differenti al softening, perhaps by complementing the action of polygalacturonase . Polygalacturonase activity increased with increasing depth of the me socarp tissue, as did softening of the fruit.