Treatment of grape berries, a nonclimacteric fruit with a synthetic auxin, retards ripening and alters the expression of developmentally regulated genes

Treatment of grape (Vitis vinifera L.) berries with the synthetic auxin-like compound benzothiazole-2-oxyacetic acid (BTOA) caused a delay in the onset of ripening of approximately 2 weeks. This was manifested as a retardation of the increases in berry weight, color, deformability, and hexose concentration. BTOA treatment also delayed by 2 weeks the increase in abscisic acid level that normally accompanies ripening and altered the expression of a number of developmentally regulated genes. A putative vacuolar invertase, which is normally expressed from berry set until ripening and turned off after ripening commences, remained expressed throughout development in BTOA-treated grape berries. This elevated expression resulted in increased levels of invertase activity. In contrast, the up-regulation of four other genes normally switched on at the time of ripening was delayed in BTOA-treated fruit. These included chalcone synthase and UDP-glucose-flavonoid 3-O-glucosyl transferase, both of which are involved in anthocyanin synthesis, a chitinase, and a ripening-related gene of an unknown function. These observations support the view that auxins (perhaps in conjunction with abscisic acid) may have a role in the control of grape berry ripening by affecting the expression of genes involved in the ripening process.