Specificity of phospholipids binding to indole acetic acid and other auxins.

In recent years, Hertel et al. 1 have studied the primary binding sites of auxins. They pointed out that the binding site in vitro should be specific “i. e., only growth-active transportable auxins, and competitive autiauxins or transport inhibitors but not inactive analogues should interact with the re­ ceptor.” They further suggested that “auxin inter­ acts with the plasma membrane at least during its transport and probably also during its action” . Since phospholipids are major constituents of the plasmalemma, a possible interaction between auxins and lecithin has been studied in recent years. Weigl2-4 showed a strong physical asso­ ciation of auxins with lecithin: 1 mol lecithin was found to bind up to 0.8 mol IAA. New evidence that auxins interact with lecithin has been presented re­ cently by Paleg et al. 5. With nuclear magnetic re­ sonance spectroscopy, they showed that there was a shift in the trimethylamino peak of lecithin after binding to IAA. Gibberellic acid exhibited a much weaker interaction.