Geibberllin and temperature influence carbohydrate content and flowering in Phalaenopsis

When Phalaenopsis amabilis is grown under high temperature (30/25°C, day/night), flowering is blocked, and this can be reversed by gibberellin A₃ (GA₃) treatment. Associated with GA₃ treatment under high temperature are increases in sucrose, glucose and fructose as compared with warm‐treated plants. Spraying with sucrose solution alone caused leaf epinasty in plants grown under high temperature. Epinasty was released by about 9 days of GA₃ treatment. In GA₃‐treated plants under high temperatures, sucrose application to the source leaves led to an increase in sugar content in both leaves and inflorescence. In contrast, although in warm‐treated plants sucrose application to the source leaves increased sugar content in the leaves, it did not increase sucrose content in the inflorescence. These results corroborate our hypothesis that in Phalaenopsis GA₃ stimulates sink activity in the apical meristem and promotes the translocation of sucrose from source leaves to the apex of the inflorescence, where it accumulates. GA₃ treatment led to an increase in sucrose synthase activity and had no effect on invertase activity.