The activities of several cell wall-associated enzymes of the outer pericarp were assayed during softening of kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Hayward] treated with ethylene. The activity of polygalacturonase (EC 126.96.36.199) increased slightly during fruit softening, while β-galactosidase (EC 188.8.131.52) activity remained constant. Salt-extracted pectinesterase (EC 184.108.40.206) activity increased during ethylene treatment, then dropped rapidly to low levels as fruit softened. Residual pectinesterase activity, extracted after digestion of the cell wall pellet with a fungal enzyme mix, decreased on softening. The rapid softening of kiwifruit in response to ethylene treatment may be initiated by an induction of pectinesterase activity, causing increased de-esterification of cell wall pectins, followed by degradation of solubilized pectin.
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