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Mariken Rebers, Evert Vermeer, Erik Knegt, and Linus H.W. van der Plas

To find a suitable indicator for properly cold-treated tulip bulbs (Tulipa gesneriana L. cv. Apeldoorn), the content of the endogenous free gibberellins (GAs) GA1, GA4, GA9, GA24, and GA34 was investigated. GA levels were measured in the shoots and basal plates at the start and at the end of a complete cold treatment of 12 weeks at 5 °C by combined gas chromatography–mass spectrometry using deuterated internal standards. Bulbs stored at 17 °C for 12 weeks served as controls and the experiment was repeated three times. Before the cold treatment, GA1 and GA4 were the major occurring GAs in the shoots. After 12 weeks, GA4 was the main GA component and the levels of GA1 were low in precooled and nonprecooled bulb shoots. The levels of GA4, GA9, GA24, and GA34 in precooled and nonprecooled bulb shoots and basal plates were similar. Hence, no direct correlation between cold-stimulated growth and a change in the endogenous GA status in shoots or basal plates was determined during the cold treatment. The free GA content in shoots or basal plates at the end of bulb storage cannot be used as a marker in a test for properly cold-treated `Apeldoorn' tulip bulbs.