Cell wall polysaccharide metabolism during fruit development in sweet cherry 'Satohnishiki' as affected by gibberellic acid

Abstract

Cell wall polysaccharide metabolism during fruit development in 'Satohnishiki' sweet cherries (Prunus avium L.) and the effect of gibberellic acid (GA) treatment on the fruit were investigated. Fruit firmness decreased dramatically, and sugar concentration increased rapidly from 30 to 36 days after full bloom (DAFB), accompanied by increases in abscisic acid (ABA) and water-soluble pectic substances (WSP) fraction and decreases in sodium hexametaphosphate-soluble pectic substances (HMP) fraction, HC1-soluble pectic substances (HP) fraction, and cell wall bound neutral sugars. Therefore, the period from 30 to 36 DAFB is considered the onset of fruit ripening. Pectinesterase (PE) activity decreased from 30 to 42 DAFB; endo-polygalacturonase (PG) activity was not detectable. Contrarily, cell wall bound neutral sugars decreased greatly as fruit ripened which demonstrates that the softening of sweet cherries may cause, not a dissolution of homogalacturonan, but a decrease of cell wall bound neutral sugars, leading to lower molecular weight by the cleavage of the neutral sugar region. An application of 0.289 mM (100 ppm) GA3 solution to whole branches at 23 DAFB inhibited the solubilization of polysaccharides until 56 DAFB and the accumulation of anthocyanins in the skin. The effect of GA3 treatment on endogenous ABA concentration which plays an important role in the cherry fruit ripening was also examined. Although ABA concentration in GA3-treated fruit was lower than that in untreated control fruit 36 DAFB, its concentration was, contrarily, higher at 56 DAFB. These results suggest that GA3 treatment delayed fruit ripening by blocking ABA activity.