Changes of free and conjugated ABA in the fruit of 'Satohnishiki' sweet cherry and the ABA metabolism after application of (s)-(+)-ABA

The fruit from the sweet cherry cv. Satohnishiki (Prunus avium L.) was analysed to investigate changes of free and conjugated ABA in the pulp and seed, and the ABA metabolism after application of (s)-(+) ABA solution. Fruit firmness dramatically decreased 38 d after full bloom (DAFB). In the pulp, the level of cia-trans ABA (s-ABA) was highest between 29-38 DAFB after which they gradually decreased, while the levels of conjugated s-ABA were highest on 33-38 DAFB and then gradually decreased until harvest. It was observed that before the decrease of fruit firmess, the s-ABA level in the pulp reached a maximum, it is therefore assumed that ABA is related to fruit softening. In the seed, the s-ABA content substantially increased from 19-24 DAFB and then remained at an almost constant level, in contrast, the conjugated s-ABA was highest during the earlier stages of growth (19-24 DAFB) and then dramatically decreased towards harvest. Both trans-trans ABA (t-ABA) and conjugated t-ABA in the seed maintained lower levels compared to s-ABA and conjugated s-ABA. The levels of endogenous s-ABA, t-ABA, conjugated s-ABA and conjugated t-ABA in the fruit applied with (s)-(+)-ABA solution were higher than the untreated control on day 7 after application but after day 13 the levels decreased and became the same as the untreated control. These results suggest that within 7 d after application, a portion of applied s-ABA changed t-ABA, conjugated s-ABA, conjugated t-ABA or another metabolite of ABA, and then within 13 d applied s-ABA almost all had metabolized into further metabolites of ABA.