Cell Wall Modifications during On-Tree Development and Maturation of 'Golden Reinders' Apples

The objective of this study was to examine possible relationships between softening, cell wall composition, and activities of pectate lyase (PL), polygalacturonase (PG) and endo-1,4-beta-glucanase (EGase) throughout on-tree maturation of 'Golden Reinders' apple fruit. Fruit were picked weekly during two months prior to and at commercial harvest. Non-covalently bound pectins, a main constituent of the middle lamella, were found to decrease concurrently with firmness, possibly in relation to higher PL and PG activities at the beginning of the experimental period and at commercial harvest, respectively. In contrast, softening was not related to the yield of the hemicellulose-containing fraction, in accordance with the absence of significant changes in EGase activity throughout the experimental period.