Effect of Darkness and Indoleacetic Acid Following Exposure to Short Day on the Floral Response of Xanthium, a Short-Day Plant

Abstract

It is reported that, when a second dark period immediately follows the inductive dark period responsible for flowering in Xanthium, the flowering response is reduced or completely inhibited. The effectiveness of the second dark period is proportional to its length, up to approximately 6 hours duration. Even when the inductive dark period is long enough to give maximum flowering, the effectiveness of the second dark period is still pronounced. A large variation in the effectiveness of the second dark period is also reported. but, when the plants are treated with indoleacetic acid (50 mg/l) at the beginning of the second dark period, the effectiveness of this dark period is greatly enhanced, and the variability in response is reduced. It is suggested that the second dark period and the IAA act either to destroy the flowering stimulus or to prevent intermediate reactions in the production of the stimulus.