ENDOGENOUS GIBBERELLIN LEVEL IN ORNITHOGALUM ARABICUM AND ITS RELATIONSHIP TO STORAGE TEMPERATURES OF BULBS AND TO FLOWER DEVELOPMENT
In the first series of experiments bulbs were stored in a sequence of temperatures to promote earliest flowering: 33°C (preparation and retarding temperature) followed by 20°C to promote flower initiation and 11°C to enhance stem elongation. Gibberellin level declined markedly when bulbs were transferred to 20°C and this level remained low during flower development at this temperature. The activity increased sharply upon transferring of the bulbs to 11°C. Later at 11°C the level declined and rose again after emergence of the flower stem in the field.
The changes in GA-level were further followed in bulbs held at a constant temperature of 20°C following a period of 2 months at 34°C. A relatively high gibberellin activity was detected in the buds and scales of completely vegetative bulbs at the end of the storage period at 34°C. The activity declined sharply after the transfer to 20°C, when the buds were at the transitional stage. When 1–2 bracts were initiated and the bud reached the prefloral stage, a rise in the activity was found in the bud accompanied by a further decline in the scales. When more bracts were formed, a decline was observed in the bud and an increase in the activity in the scales. Later a slow increase in both bud and scales was detected, while flowers were initiated.
The changes in the gibberellin level are therefore related both to the storage temperature and to the developmental stage of the bud.