Abstract
The basipetal transport of the auxin, indoleacetic acid, in sunflower stem sections is markedly suppressed by washing the tissue in ethylenediaminetetraacetate, and transport is restored by subsequent application of calcium solutions. The ethylenediaminetetraacetate treatment is shown to result in the removal of substantial amounts of calcium from the tissue, and the restoration of transport is distinctive for calcium solutions, lesser effects being observed for magnesium and lanthanum, and little effect for monovalent cations. The calcium effects are interpreted as indicating that the auxin transport system depends upon structural or functional features of cellular membranes which involve calcium in a manner analogous to the transport of inorganic ions.