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 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.

Growth and gravireaction of maize roots treated with a phytotropin.

Effects of the phytotropin 1-(2'-carboxyphenyl)-3-phenylpropane-1,3-dione (CPD) on growth and gravireaction of intact roots and apical root segments of Zea mays L. cv LG-11 were analysed. It is concluded that the compound acts through sites of action in the extension zone and/or the root cap.

Phytotropins: III. NAPHTHYLPHTHALAMIC ACID BINDING SITES ON MAIZE COLEOPTILE MEMBRANES AS POSSIBLE RECEPTOR SITES FOR PHYTOTROPIN ACTION.

Certain members of the phytotropin class of auxin transport inhibitors are shown to bind with high affinity to the known naphthylphthalamic acid binding sites in maize (Zea mays) coleoptiles. The binding site is, thus, a phytotropin binding site. In general, the degree of binding correlates with the phytotropin structure activity rules and with physiological activities of model compounds.

Auxin Transport Inhibitors: IV. EVIDENCE OF A COMMON MODE OF ACTION FOR A PROPOSED CLASS OF AUXIN TRANSPORT INHIBITORS: THE PHYTOTROPINS.

The more active members of a proposed class of auxin transport inhibitors have been shown to have the ability to inhibit the active movement of auxin at concentrations where they have little effect on auxin action and no significant auxin activity. They have also been shown to give rise to characteristic biphasic dose-response curves on cress root growth. Based on these physiological similarities and other common physiological properties, it is concluded that they may achieve their effects by a common mode of action which differs from that of other known auxin transport inhibitors.

Auxin Transport Inhibitors: III. Chemical Requirements of a Class of Auxin Transport Inhibitors.

The structural requirements of a proposed class of auxin transport inhibitors have been shown to be very similar to those required to inhibit the cress (Lepidium sativum) root geotropic response. A 2-carboxyphenyl group separated by a conjugated system of atoms from a second aromatic ring appears to be necessary for a molecule to have high activity.