Cell wall metabolism in gibberellin-treated persimmon fruits

The application of gibberellin [GA₃] to persimmon fruits as an orchard spray, at least 2 weeks prior to harvest, has been shown to delay ripening of the fruit on the tree and its rate of softening after harvest. This effect persisted during and after cold storage. The delay in softening has been attributed to the effect of the phytohormone on cell wall metabolism. To examine this hypothesis, cell walls of GA₃-treated fruit were compared to those of non-treated fruit. Comparison between fruit was from harvest till the termination of post-storage softening. The study included TEM examinations, assay of certain hydrolase activities and determination of compositional changes occurring in the various cell-wall carbohydrate polymers. Our findings indicate that GA₃ either delays or inhibits all of the cell wall changes that were found to accompany fruit softening, including dissolution of the middle lamella, separation of the plasmalemma from the cell-wall, mitigation of the structural coherence and density of the primary cell wall, increases solubilization of pectic polymers, loss of neutral sugars, predominantly arabinose and galactose, and increased activities of exo-polygalacturonase [PG] and endo-1,4--glucanase [EGase]. The principal discernible compositional difference between GA₃-treated fruit and control fruit at harvest was a higher total carbohydrate content in the cell wall material extracted from GA₃-treated fruit, which was due chiefly to an increased amount of cellulose.