Abstract
Abstract Important role of auxin polar transport inhibitors such as TIBA (2,3,5- triiodobenzoic acid), NPA (N-(1-naphthyl)phthalamic acid) and morphactin (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) in stem growth of tulips was intensively studied. After the application of morphactin above the 3rd node of decapitated tulips, the stimulated growth of the 4th internode was clearly observed. On the other hand, NPA and TIBA were slightly effective in stimulating the 4th internode growth of tulips. Endogenous levels of IAA in the 4th internode after the treatment of auxin polar transport inhibitors were determined using gas-liquid chromatography-mass spectrometry (GC-MS) and gas-liquid chromatography-mass spectrometry selected ion monitoring system (GC-SIM) with deuterium labelled IAA (Indole-2,4,5,6,7-d5-3- acetic acid, d5-IAA) as an internal standard, resulted in significant accumulation of IAA in the 4th internode of tulips after the treatment of morphactin. In the treatment of NPA and TIBA, there was almost no such an accumulation of IAA. These results strongly suggest that stimulated growth of the 4th internode of tulips induced by the application of morphactin is the consequence of accumulated endogenous levels of IAA after the treatment. The possible mode of action of auxin polar transport inhibitors in tulip stem growth is also discussed.
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