CELL-WALL METABOLISM IN GROWING AND RIPENING STONE FRUITS

The time-course changes of the composition of the cold water soluble, the hot water soluble, the ammonium oxalate soluble, the 4% KOH soluble, the 24% KOH soluble and the 24% KOH insoluble cell wall fractions, as well as of the activities of beta-D-xylosidase, alpha-D-mannosidase, beta-D-galactosidase and beta-D-glucosidase, were monitored during growth and ripening of the fleshy pericarp of wild plums, peaches and apricots. All fractions increased up to a peak, which occurred before the onset of ripening. During ripening the pectic fractions were extensively decreased, the hemicellulosic fractions were restrictively decreased, while the crude cellulosic fraction was not affected, being always present in greater amounts in comparison to the previous mentioned fractions during all phases of fruit development. The relative changes of the two pectic fractions and the two hemicellulosic ones indicate conversion of the more soluble fractions to the less soluble ones during growth and the reverse conversion during ripening. The cold water soluble fraction appeared only during ripening and its changes were closely related to the extensive breakdown of pectic fractions during ripening. The enzymic activities were not found during growth. They appeared at the begining of ripening (apricots) or a little earlier and followed a concrete pattern of changes.