Relationship between Free and Conjugated ABA Levels in Seeded and Gibberellin-treated Seedless, Maturing `Pione' Grape Berries

Abstract

Free and conjugated abscisic acid (ABA), anthocyanin and sugar concentrations were investigated in the skin of seedless `Pione' grapes (Vitis spp) treated with gibberellic acid (GA) and seeded `Pione' grapes. Seeded fruit were firmer than seedless fruit, until 53 days after full bloom (DAFB). The firmness of seeded fruit decreased dramatically between 43 and 53 DAFB. Anthocyanin concentrations increased in both types of fruit after 53 DAFB, but the concentration in seeded fruit was higher than in seedless fruit. Sugar concentration in the skin was higher in seedless than in seeded fruit prior to 53 DAFB, but at 80 DAFB sugar concentration was higher in the seeded fruit. ABA (free and conjugated forms) concentration in the skin showed a general increase towards harvest (80 DAFB). Skin ABA was higher in seeded than seedless fruit. After cis, trans-ABA (s-ABA) in the skin reached a maximum on 62 or 71 DAFB, its level decreased in both seeded and seedless fruit. The levels of trans, trans-ABA (t-ABA) and conjugated forms in both types of fruit failed to increase or increased only marginally after 62 or 71 DAFB. Free and conjugated ABA in the seed increased with DAFB until harvest. These results suggest that although maturation was promoted initially in the GA-treated seedless fruit, after 53 DAFB it was slowed relative to the seeded fruit. Enhanced maturation during the later stages of development of seeded fruit could be attributed to an increase in ABA concentration in the skin and the seed. These results also demonstrate that s-ABA is not metabolized in the skin to t-ABA and conjugated forms.