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

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...

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Bibliographic Details
Published in:Planta 1992-05, Vol.187 (2), p.254-260
Main Authors: Michalke, Wolfgang, Katekar, Gerard F., Geissler, Art E.
Format: Article
Language:English
Subjects:
Auxins
binding
Binding sites
Biological and medical sciences
Cell membranes
characterization
Coleoptiles
Corn
Cucurbita pepo
endoplasmic reticulum
Fundamental and applied biological sciences. Psychology
Growth regulators
Hypocotyls
Insulin antibodies
mediation
Metabolism
Pepos
phytotropin
Plant physiology and development
Receptors
sites
transport
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Summary: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 [2,3,4,5-3H]1-N-naphthylphthalamic acid and 3-indolyl-[2-14C]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.
ISSN:0032-0935
1432-2048
DOI:10.1007/BF00201948