Changes in Endogenous Gibberellins during Internode Elongation of Tulip Flower Stalk as Affected by Light Conditions

Changes in endogenous gibberellins in the first and upper internodes of tulip were investigated under light and dark growing conditions. In darkness, the elongation of the first internode was increased. The level of polar, free gibberellin also increased, while the level of the bound form decreased. Under natural light, a rapid increase in the length of the last internode was parallelled by an increase in non-polar free gibberellin. It is suggested that two different gibberellins are involved in controlling the elongation of the lower and upper internodes of tulip flower stalk. An interconversion system between free and bound forms of polar and non-polar gibberellins, which act in the first and the upper internodes respectively, and the dependence of these upon light conditions were also suggested.