Phytotropin-binding sites and auxin transport inCucurbita pepo:evidence for two recognition sites

✍ Scribed by Wolfgang Michalke; Gerard F. Katekar; Art E. Geissler

• Book ID: 104661413
• Publisher: Springer-Verlag
• Year: 1992
• Tongue: English
• Weight: 749 KB
• Volume: 187
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00201948

✦ Synopsis

Two properties of phytotropins, their ability to bind to 1-N-naphthylphthalamic acid (NPA) receptors located on microsomal vesicles isolated from Cucurbita pepo L. hypocotyls, and to stimulate auxin (indol-3-yl acetic acid, IAA) accumulation into such vesicles by blocking its efflux from them, were assessed in double labelling experiments using [2,3,4,5-(3)H]1-N-naphthylphthalamic acid and 3-indolyl-[2-(14)C]acetic acid. Two sites of differing affinities and activities on IAA accumulation were found. 1-N-Naphthylphthalamic acid was found to have high affinity (KD at 10(-8)mol·l(-1)) for one site and low affinity (KD at 10(-6) mol·l(-1)) for the other, whereas 2-(1-pyrenoyl)benzoic acid displaced NPA with high efficiency (KD below 10(-8) mol·l(-1)) from both sites. Other phytotropins had intermediate affinities for either site. Occupation of the site with low affinity for NPA stimulated auxin accumulation, while occupation of the high-affinity site with a phytotropin did not interfere with auxin accumulation into vesicles.