GIBBERELLIN LEVELS AND COLD-INDUCED FLORAL STALK ELONGATION IN TULIP

To investigate the role of gibberellins (GAs) in the cold requirement of tulip (Tulipa gesneriana L. cv. Apeldoorn), bulbs were dry-stored a t 5 degrees C or at 17 degrees C for 12 weeks prior to planting at 20 degrees C. Only precooled bulbs showed rapid sprout growth and develop ed a full-grown flower. Endogenous GA levels were measured in sprouts and basal plates at the time of planting and in the second week after planting, by combined gas chromatography-mass spectrometry using deute rated internal standards. GA(4) was the major gibberellin, while GA(1) , GA(9) and GA(34) were present in lower amounts. At the time of plant ing, sprouts from non-cooled bulbs contained significantly more GA(4) and GA(1) per sprout than those from precooled bulbs. Hence, there is no direct correlation between rapid sprout growth after planting and h igh GA levels at planting. In the second week after planting, floral s talks of precooled bulbs contained 2 to 3 times more GA(4) and its met abolite GA(34) per floral stalk and per g fresh weight than those of n on-cooled bulbs. The results are discussed with regard to the role of gibberellins in the cold-induced floral stalk elongation of tulip.