THE ROLE OF GIBBERELLINS IN THE COLD REQUIREMENT OF TULIP
At first, an inventory was made of GAs including the conjugated forms, in sprouts of cooled and uncooled bulbs (Tulipa gesneriana L. cv. Apeldoorn). By combined gas chromatography-mass spectrometry (GC-MS) and GC-selected ion monitoring (SIM), GA4, GA9, GA24, GA34 and four GA-related compounds were detected. Most detected GAs and GA-related compounds were found in the free as well as in the conjugated form and occurred in sprouts of both cold and non-cold treated bulbs.
The biological activity of GA4 and GA9, and the not detected but in many plants active GA1, was tested by applying them in vitro to sprouts of uncooled and cooled bulbs, in the presence or absence of the GA-biosynthesis inhibitor paclobutrazol. Stem elongation and flower quality in this in vitro system were poor, even after an optimum cold treatment of the bulbs. The sensitivity to applied GAs increased during cold treatment and the three GAs were equally effective in stimulating stem elongation. Paclobutrazol had no effect on stem length, but flower quality had increased in paclobutrazol treated compared to untreated sprouts.