DEVELOPMENTAL AND RIPENING-RELATED EFFECTS ON THE CELL-WALL OF PEPINO(SOLANUM-MURICATUM) FRUIT

Several cell wall components in ripening pepino fruit have been quanti tatively and qualitatively characterised, with the aim of identifying their contributions to the loss of tissue firmness. Pepinos were grade d into nine groups based on progressive, characteristic skin colour ch anges, previously shown to correspond with decreasing fruit firmness. While fruit softening began when the pepinos were still green but with newly acquired purple stripes, the first significant quantitative sig ns of cell wall modification (total pectin and hemicellulose content d eclining and CDTA-soluble pectin content increasing, on a fresh weight basis) were detectable later in ripening, when the fruit began to acq uire yellow skin pigmentation. Gel fractionation studies demonstrated that there were increased levels of low-molecular-weight pectin and xy loglucan during pepino ripening. The change in molecular weight distri bution of CDTA-soluble pectin occurred as fruit started to acquire yel low pigmentation, while xyloglucan polymers were modified at an earlie r stage that coincided with the initial loss of firmness.