Temperature Regulation of Endogenous Gibberellin Activity and Development of Tulipa gesneriana L.

The changes in the contents of free and bound gibberellin-like activity (GA) of Tulipa gesneriana L. cv. Ralph during development under 2 temperature conditions were studied. The results show that the content of free GA of bulbs grown at 18 degrees increased by 67% over the initial level during development. The bound GA showed a slight initial increase and was followed by a rapid decrease. In contrast, bulbs treated at 13 degrees showed a marked decline in free GA and a 2-fold increase in the content of bound GA. However, after the transfer of these bulbs from 13 degrees to 18 degrees the free GA increased to the initial level while the bound GA decreased to a low level.The rate of floral shoot and root development and time of flowering were accelerated at 18 degrees as compared to 13 degrees .From the data obtained, it was suggested that a temperature-sensitive interconversion mechanism between free and bound GA exists in tulip bulbs and that there is apparent synthesis or transformation of these phytohormones during development of the bulbs.