IDENTIFICATION OF 14KDA AUXIN-BINDING PROTEINS IN A TOBACCO PLASMA-MEMBRANE SUBFRACTION RESPONSIVE TO AUXIN

Auxin binding by tobacco plasma membrane proteins was investigated. Af ter photolabeling with [H-3]IAA, 350 polypeptides were resolved on 2D gels and analyzed. Thirteen polypeptides were selected according to ph ysico-chemical criteria. The labeling of three of them was further sho wn to increase, after treatment of cells with auxin, specifically in t hat plasma membrane subfraction where the sensitivity to the hormone o f the H+-ATPase is enhanced by the treatment of cells. These polypepti des were those that exhibited the more specific labeling features acco rding to physico-chemical criteria. They had similar apparent molecula r weight (ca 14 kDa) that distinguished them from other auxin-binding proteins described up to now, and exhibited similar amino acid composi tions. These 14 kDa polypeptides are proposed to constitute a group of new auxin-binding proteins, potentially involved, within specialized plasma membrane domains, in the stimulation of the proton pump by the hormone.