SOFTENING OF KIWIFRUIT DISCS - EFFECT OF INHIBITION OF GALACTOSE LOSS FROM CELL-WALLS

Ripening-related cell wall changes that are characteristic of intact kiwifruit (Actinidia deliciosa var. deliciosa) were examined in excised outer pericarp discs, in the presence and absence of metabolic inhibitors. Cell wall materials (CWMs) were prepared from discs at time 0 and 24, 48 and 72 hr after excision. Control discs softened rapidly over 72 hr, showing a decrease in cell wall-associated galactose and an increase in pectin solubilization. When discs were treated with 50 mM galactose there was complete inhibition of galactose loss from the CWMs 24 hr after excision and a retardation of galactose loss after 72 hr, but no effect on either the rate of disc softening or pectin solubilization. Discs treated with aminooxyacetic acid, an inhibitor of ethylene biosynthesis, did not soften or show any sign of pectin solubilization after 72 hr but did show a loss of galactose from the CWM. The results suggest that the loss of cell wall-associated galactose and pectin solubilization in ripening kiwifruit are separate processes and that galactose loss, in part, may be independent of ethylene.