Effect of gibberellic acid (GA_3) at a concentration of 200mgl^1 on shoot growth and flowering in nonprecooled derooted tulip bulbs cvs. Gudosthnik and Apeldoom was investigated. In control nonprecooled derooted bulbs flower bud blasting occurred and no growth of stem was observed. GA_3 greatly induced shoot growth and flowering. The stimulatory effect of gibberellin on shoot growth and flowering in nonprecooled derooted bulbs was much stronger than in case of nonprecooled rooted bulbs (previously published results). GA_1 stimulated also stem growth after excision of flower bud with upper part of leaves and scales. It is probable that excision of all roots in nonprecooled bulbs decreases the level of abscisic acid and exogenous gibberellic acid is more effective in comparison to nonprccoolcd rooted bulbs. Or it is also possible that better penetration and uptake of gibberellin take place after removal of roots. It seems that gibberellin can substitute for cold requirement and that interaction of exogenous gibberellin with endogenous auxin controls stem growth.
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