Indole-3-acetic acid-mediated transport of Mn2+ and other ions across phosphatidylinositol vesicular membranes as determined by 31P-NMR.

The indolic plant hormone, indole-3-acetic acid (IAA), mediated the transport of Mn2+ and other ions into small unilamellar vesicles prepared from soybean phosphatidylinositol (PI) and this process has been studied using 31P nuclear magnetic resonance spectroscopy (NMR). The rate of Mn2+ movement into PI vesicles is dependent on IAA concentration and temperature with an IAA stoichiometry of 4.1 and an activation energy of 16.8 kcal mol-1 derived for the rate-determining process. These values are altered by low concentrations of endogenous ions (which can be removed by treatment with EDTA) present in the PI. With non-EDTA-treated PI, values of 2.3 and 23.0 kcal mol-1 were obtained for the stoichiometry and activation energy, respectively. These values indicate that (a) IAA interacts with PI membranes; (b) IAA-induced changes in membrane permeability can be substantially modulated by ions and (c) IAA very significantly influences the rate of movement of some (but possibly not all) cations across PI membranes. Such effects are also modified by the oxidation state of the PI.