The leaf as the site of gibberellin action in flower formation in Bryophyllum daigremontianum.

The long-short-day plant Bryophyllum daigremontianum can be induced to flower by transfer from long to short days (LD→SD), or by gibberellin (GA) application under SD. Application of GA to mature leaves of intact or partially defoliated plants induces flowering more effectively than when applications are made to the youngest leaf pair and the shoot tip.Mature leaves on de-budded plants in SD are induced to produce floral stimulus by GA application, as demonstrated by grafting LD receptor scions onto the debudded plants, or by grafting SD leaves treated with GA onto receptor stocks in LD. This shows that GA applied to Bryophyllum in SD exerts its flower-promoting effect in the leaves.The minimal number of SD necessary for flower formation in Bryophyllum is approximately 15, both in case of photoinduction by the shift LD→SD, and after GA treatment in SD. It is concluded that the LD part of photinduction establishes a high level of endogenous GAs in the leaves which is a prerequisite for production of floral stimulus under subsequent SD.