Flower abscission in Vitis vinifera L. triggered by gibberellic acid and shade discloses differences in the underlying metabolic pathways

Understanding abscission is both a biological and an agronomic challenge. Flowerabscission induced independently by shade and gibberellic acid (GAc) sprays wasmonitored in grapevine (Vitis vinifera L.) growing under a soilless greenhouse systemduring two seasonal growing conditions, in an early and late production cycle.Physiological and metabolic changes triggered by each of the two distinct stimuli weredetermined. Environmental conditions exerted a significant effect on fruit set as showedby the higher natural drop rate recorded in the late production cycle with respect tothe early cycle. Shade and GAc treatments increased the percentage of flower dropcompared to the control, and at a similar degree, during the late production cycle.The reduction of leaf gas exchanges under shade conditions was not observed inGAc treated vines. The metabolic profile assessed in samples collected during thelate cycle differently affected primary and secondary metabolisms and showed thatmost of the treatment-resulting variations occurred in opposite trends in inflorescencesunbalanced in either hormonal or energy deficit abscission-inducing signals. Particularlyconcerning carbohydrates metabolism, sucrose, glucose, tricarboxylic acid metabolitesand intermediates of the raffinose family oligosaccharides pathway were lower in shadedand higher in GAc samples. Altered oxidative stress remediation mechanisms andindolacetic acid (IAA) concentration were identified as abscission signatures commonto both stimuli. According to the global analysis performed, we report that grape flowerabscission mechanisms triggered by GAc application and C-starvation are not basedon the same metabolic pathways.