A chemoreceptive bilayer lipid membrane based on an auxin-receptor ATPase electrogenic pump

Auxin-binding proteins have been extracted from coleoptiles and primary leaves of maize and diffusion--reconstituted in phosphatidyl choline/partially-oxidized cholesterol membranes. Measurement of membrane ion flux at 25 mV external potential with buffered KCl electrolyte was performed for the receptor support matrix and various combinations of ATP, receptor and naphthalene-1-acetic acid. Addition of the three components in any order results in a substantial increase in current with a limit-of-detection for auxin of about 10(-7)M. The pH-dependence of the response is consistent with previous suggestions that an ATPase pump acts to translocate protons in the presence of K+ and Mg2+ and that the pump can be activated by auxin. This work provides the first direct link between the binding of a plant hormone to a putative receptor and the evocation of a biochemical response.