The Mechanism of Transmembrane Auxin Transport and Its Relation to the Chemiosmotic Hypothesis of the Polar Transport of Auxin

Abstract

The coordinated development of plants requires and reflects a controlled distribution of growth substances which, by interaction with receptors, bring about the biochemical and biophysical changes that culminate in morphogenesis. Transport is a central factor influencing cellular hormone concentration and hence the proportion of occupied receptors. Polar transport in a preferred morphologically defined direction has been most extensively studied and characterized for auxin although abscisic acid, gibberellins and perhaps cytokinins may behave similarly in some instances (1). The “chemiosmotic” hypothesis of polar auxin transport was proposed independently by Rubery and Sheldrake (2) and by Raven (3). It has recently been reviewed by Goldsmith (1). In this paper I shall discuss this new hypothesis together with the theoretical arguments and experimental data that led to its formulation. The key considerations are the mechanism and energetics of transmembrane auxin movement and the basis and maintenance of the cellular asymmetry underlying the polarity of the tissue as a whole.