Complex formation between indole-3-acetic acid and phospholipid membrane components in aqueous media. 1. Parameters of the system

Changes in proton nuclear magnetic resonance (NMR) chemical shifts have been used to investigate the interaction between the plant hormone indole-3-acetic acid (IAA) and soybean phosphatidylcholine (PC). The interaction is pH dependent and is significantly stronger with un-ionized IAA than with ionized IAA. Na super(+) and K super(+) ions did not produce differential effects on the IAA-induced upfield proton chemical shift changes in PC, and different concentrations of K super(+) ion did not affect the interaction. IAA also effects cation movement through phospholipid bilayers as monitored with NMR by the effects of Pr super(3+) and Mn super(2+) ions on the inside and outside trimethylammonium groups of the PC vesicles.