Free ABA concentration in fruit from water-stressed satsuma mandarin trees did not increase at night

摘要

To clarify the involvement of free ABA in the sugar accumulation induced by water stress, nighttime experiments were conducted in mid-September to determine the free ABA concentration in juice and peel for different water potentials (psi max). Simultaneously, the pH of the juice was also determined because it can regulate the ionization of ABA. As the water stress increased (psi max < -1.0 Mpa), the free ABA concentration in juice decreased, as did the juice pH (psi max < -0.8 Mpa), leading to a reduction in the ionization of ABA. In -1.0 Mpa < psi max < -1.5 Mpa, the free ABA concentration was almost stable, and the juice pH rose, leading to the induction of the ionization of ABA. The free ABA concentration in the peel showed almost no change, varying from 0.8 to 2.1 nmol per g fresh weight, regardless of the water potential. These results suggested that free ABA concentration in juice in September is kept at a lower level, even in water-stressed conditions, and that, therefore, endogenous freeABA is not involved in sugar accumulation induced by water stress, at least at night.