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 auxi n-like compound benzothiazole-2-oxyacetic acid (BTOA) caused a delay i n the onset of ripening of approximately 2 weeks. This was manifested as a retardation of the increases in berry weight, color, deformabilit y, and hexose concentration. BTOA treatment also delayed by 2 weeks th e increase in abscisic acid level that normally accompanies ripening a nd altered the expression of a number of developmentally regulated gen es. A putative vacuolar invertase, which is normally expressed from be rry set until ripening and turned off after ripening commences, remain ed expressed throughout development in BTOA-treated grape berries. Thi s elevated expression resulted in increased levels of invertase activi ty. In contrast, the up-regulation of four other genes normally switch ed on at the time of ripening was delayed in BTOA-treated fruit. These included chalcone synthase and UDP-glucose-flavonoid 3-O-glucosyl tra nsferase, both of which are involved in anthocyanin synthesis, a chiti nase, and a ripening-related gene of an unknown function. These observ ations support the view that auxins (perhaps in conjunction with absci sic acid) may have a role in the control of grape berry ripening by af fecting the expression of genes involved in the ripening process.