THE POSSIBLE ROLE OF MEMBRANE ELECTROPHORESIS IN THE POLAR TRANSPORT OF IAA AND OTHER SOLUTES IN PLANT TISSUES

Abstract

SummaryPolar transport of IAA in young higher plant shoot tissue requires an asymmetric distribution of membrane‐transport sites in the plasmalemma of the cells. The ‘chemiosmotic’ hypothesis of IAA transport requires that IAA‐ uniporters be largely on the basal side of the cells. It is suggested that the longitudinal gradient of electrical potential difference (PD, base positive to apex) which may result from activation of plasmalemma H+ efflux in the basal cells by transported IAA, may serve to maintain and reinforce this asymmetric distribution of carriers by the process of membrane electrophoresis of the carriers. The origin of this asymmetric distribution (and hence of polar IAA transport) may lie in electrical potential differences in maternal tissue around the developing embryo. Maintenance of polarity through seed dormancy may be related to gradients in cell‐wall fixed charges (and hence of electrical potential difference) along the shoot axis related to the uronate content of cell walls at different stages of cell development. The possibility of testing this hypothesis, and its relevance to other polar transport phenomena in plants, are briefly discussed.