Some Gibberellin Effects on Flowering of Plants

Abstract

The gibberellins probably play the most important role in flower formation of all plant growth substances thus far evaluated. Some flowering responses of higher plants subject to regulation by gibberellin are summarized in Table 1. The majority of rosette forming coldrequiring and long-day plants have been induced to flower with gibberellin. Facultative long-day plants also flower earlier when treated with gibberellin under both long and short photoperiods. Many obligate long-day plants have been induced to flower under strictly non-inductive conditions. Most biennials, which also have a long-day requirement, maintained in long days may be induced to flower without cold exposure, or the temperature requirement for flowering is greatly reduced. Usually, but not always, following gibberellin treatment of biennials or long-day plants, stem elongation occurs before flower primordia are formed. This is the reverse of the usual sequence in which flower primordia are first initiated and stem elongation follows. Thus far it has been noted that gibberellin replaces the cold but not the long day requirement for flowering in many biennials. The possibility remains, however, that both the low temperature and photoperiodic requirements for flowering of all biennials and long-day plants may be replaced by a suitable gibberellin and dosage regime. Flowering in two apparently facultative short day plants, Cosmos and Pharbitis maintained in long days has been accelerated by gibberellin treatment. Short day induction in Xanthium, Fragaria, and Perilla has been enhanced. Contrastingly, in Kalanchoe, Pisum, and Lycopersicon the effectiveness of a suitable photoperiod to enhance flowering is reduced with gibberellin. Flowering in Prunus, having no specific photoperiodic requirement for flowering, and in Weigela, where short day exposure promotes flower initiation, may be completely inhibited.