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In order to chemically identify the putative indole-3-acetic acid (IAA) and to confirm the native source of auxins account for rapid elongation of the floral stalk of tulip, we examined diffusible IAA from various parts of tulip plant during rapid elongation of the flower stalk. IAA was identified in the diffusates collected from the leaves, internodes, and floral organs with gas chromatography (GC)-mass spectrometry. The amount of diffusible IAA from different plant organs followed the order of that the internodes [ flower organs [ leaves during the period of rapid elongation of the floral stalk. The diffusible IAA from internodes reached its peak amount at different time than did diffusible IAA from the flower. The results obtained indicated that the top internode is probably the major source of auxins account for rapid elongation of the flower stalk.

Endogenous free IAA was examined with an immunohistochemical method for its involvement in the reduction of bud deterioration after GA 3 was injected into the bulbs. We found that tulip bulbs stored at 20°C constantly developed severe bud deterioration, whereas the symptoms of deterioration was lighter in the bulbs with GA 3 injection and not observed in the bulbs with 4°C treatment. 73% success in overcoming bud deterioration was achieved in 20°C with GA 3 treatment after 8 weeks of bulb storage, and the success rate was 7% after 12 weeks of storage. IAA was detected in the parenchyma cells in the internodes of the shoot after the bulbs were stored at 4°C or at 20°C with GA 3 injection for 4 weeks, but little was detected in the bulbs stored at 20°C constantly. Moreover, a weak IAA signal was present in between the cells of the internodes irrespective of bulb treatment. After planting, the bulbs that had been treated differently exhibited different flowering ability. The bulbs stored at 4°C for 4, 8 and 12 weeks attained high flowering percentage, which was lower in the 20°C with GA 3 treatment and lowest in the 20°C treatment. It may be concluded that GA 3 injection decreases bud deterioration of tulip bulbs during dry storage at 20°C by promoting the endogenous IAA in the internodes.