EFFECTS OF EXOGENOUS GIBBERELLINS AND PACLOBUTRAZOL ON FLORAL STALK GROWTH OF TULIP SPROUTS ISOLATED FROM COOLED AND NON-COOLED TULIP BULBS

The involvement of gibberellins (GAs) in the regulation of floral stal k elongation and flower development has been studied in tulip. The bio logical activity of GA(4) and GA(9), both endogenous in tulip bulb spr outs, and GA(1), was tested in vitro on sprouts of cooled and non-cool ed tulip bulbs (Tulipa gesneriana L,. cv. Apeldoorn), in the presence or absence of the GA biosynthesis inhibitor paclobutrazol. At early st arting dates of incubation, floral stalks from both cooled and non-coo led bulbs hardly showed any elongation in the absence of exogenous GA. Paclobutrazol had no effect on floral stalk elongation, and the respo nse to GAs of sprouts from cooled bulbs was greater than that of sprou ts from non-cooled bulbs. At later starts of incubation, considerable floral stalk elongation occurred without GA application. Paclobutrazol inhibited this floral stalk elongation, and the growth of sprouts fro m both cooled and non-cooled bulbs was stimulated by GA application. T he effect of paclobutrazol was reversed by simultaneous application of GA(4) or GA(9). Application of GA with and without paclobutrazol resu lted in the same elongation of the floral stalk, indicating the absenc e of substantial side effects of the inhibitor. The isolated sprouts d id not develop a full-grown flower without the addition of GA. GA(4) w as more effective than GA(9) in stimulating this flower development. T he results demonstrate that both sprouts from cooled and non-cooled bu lbs are responsive to exogenous GAs in vitro, and may be a site of GA biosynthesis.