METABOLISM OF CELL-WALL POLYSACCHARIDES FROM PERSIMMON FRUIT - PECTINSOLUBILIZATION DURING FRUIT RIPENING OCCURS IN APPARENT ABSENCE OF POLYGALACTURONASE ACTIVITY

Pectins from persimmon (Diospyros kaki L.) fruit pericarp were sequent ially extracted with 0.05 M trans-1,2-diaminocyclohexane-N,N,N',N'-tet raacetic acid (CDTA), 0.05 M Na2CO3 (1-degrees-C) and Na2CO3 (20-degre es-C) and the carbohydrate composition and metabolism during developme nt determined. Young persimmon fruits contained a large proportion of pectins, 46% by dry weight, that decreased to 20% with ripening. This decrease occurred in the CDTA and Na2CO3 (1-degrees-C) fractions, main ly composed of uronic acids, and represents a net loss of uronic acids , arabinose and galactose. The amount of non-cellulosic neutral sugars was especially high in the Na2CO, (20-degrees-C) fraction. The loss o f pectins was also accompanied by a depolymerisation of the polysaccha rides extracted in the three pectic fractions. However, none of these changes can be attributed to the action of polygalacturonase activity. Proteins were extracted from the pericarp tissue, but endopolygalactu ronase (EC 3.2.1.15) activity, determined as a decrease in viscosity o f polygalacturonic acid, was not observed in the extract. Determinatio n of exopolygalacturonase (EC 3.2.1.67) activity by measuring the rele ase of reducing groups from polygalacturonic acid was also negative. T he results presented indicate that polygalacturonase is not responsibl e for the metabolism of pectins during persimmon fruit ripening.