Supramolecular cation transporters alter root morphology in the Arabidopsis thaliana plant

Abstract

Bibracchial (two-armed) 4,13-diaza-18-crown-6 lariat ether and tris(macrocycle) hydraphile synthetic amphiphiles alter root morphology in Arabidopsis thaliana plants. The effect on root structure and growth depends both on the hydraphile spacer chain length and lariat ether side chain length as well as the concentration of compound in the growth medium. In some cases a correlation to ion transport activity was apparent, but such a correlation is not always manifested. Surprisingly, planar bilayer conductance (BLM) studies showed that lariat ethers and lariat ether amides both exhibited well controlled membrane activity. Pore formation in soybean asolectin membranes occurred readily and the pores were stable and sustained. Low concentrations of active hydraphiles and lariat ethers altered the primary:lateral root density ratio, generally increasing it. The transporter-mediated alterations in lateral root density were suggestive of the activity of plant auxins such as indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid, which are known to depend on cytosolic potassium ion concentrations. The hypothesis that the compounds interfere with the auxin pathway was tested and discounted by using auxin-resistant A. thaliana mutants. Rather than functioning directly as auxin mimics, ionophores affect the ion gradients producing an auxin-like effect on root development.