The effect of growth regulators on the growth and pigmentation of “Baccara” rose flowers

“Baccara” rose buds were treated with various growth regulators during late stages of bud development. The effect of these substances on growth and pigmentation were determined. Growth regulators were applied by spray or injection or as a lanolin paste, also in the nutrient media on which petals were cultured in vitro. Injection of GA into the base of the receptacle caused elongation of the bud whereas IAA, K, ABA, AMO-1618, CCC, and SADH had little or no effect. CCC and MeCl-F did not reduce the elongation caused by GA. GA treatments also enhanced flower weight and petal pigmentation and MeCl-F decreased the gibberellin effect on pigmentation. GA treatments of intact flowers and excised petals cultured in vitro, were only effective at low temperatures. Gibberellin treatments increased the size of petals, the receptacle and the pedicel only if applied directly to the receptacle. Treatments at lower positions on the flowering shoot either had no effect at all, or caused elongation of only the receptacle. Endogenous gibberellin levels are higher in the receptacle than in petals or in the pedicel. Injection of GA into the receptacle significantly increased gibberellin activity in all flower parts whereas injection into the flowering-shoot base increased gibberellin activity only in the receptacle. The possibility is discussed that GA, which is exogenously supplied directly to the receptacle, enhances flower dimensions and pigmentation by drawing photosynthates to the flower as a consequence of intensification of the sink.