Bioactive gibberellins show differential abundance at key phenological stages for berry growth in table grapes

Berry size, a key trait in table grape production, results from complex physiological and biochemical events occurring from anthesis to ripening. Gibberellins (GAs) play a crucial role in the regulation of this process as widely demonstrated by exogenous applications of gibberellin acid (GA3), but the endogenous evolution in concentration and its relation with berry size is poorly understood. Using berries from a crossing of ‘Ruby Seedless’ × ‘Sultanina’ (RxS) with contrasting phenotypes for berry and seed size, we analyzed GA metabolites at four key phenological stages for berry size: 50% flowering (FL50), 2–4 mm (CU24), 2–4 mm plus one week (CU24+1) and 6–8 mm. Our results show that both bioactive metabolites GA1 and GA4 are produced, demonstrating that both the 13-hydroxylation and the non-13-hydroxylation GA biosynthetic routes are functional in grape berries. The variable abundance of both bioactive GAs along berry growth suggests a complex regulation of this pathway. GA1 is prevalent over GA4 during the developmental stages that go from 50% flowering up to the stage of berry size around 2–4 mm plus one week, whereas GA4 raises later, at berry setting stage, exhibiting a roughly constant presence up to the 6–8 mm stage. Higher accumulation of GA1, with a three-fold concentration at CU24+1 than GA4 was observed. In addition, our results suggest that GAs synthesis occurs in smaller seedless berries, but accumulating GA4 slightly later than in bigger berries with full seeds.