The controlling influence of cell‐surface electrical potential on the uptake and toxicity of 
selenate (SeO₄²–)

Root elongation in wheat seedlings ( Triticum aestivum L. cv. Atlas 66) was inhibited by micromolar activities of SeO 4 2– . SeO 4 2– inhibition was enhanced by supplementation of the rooting medium with CaCl 2 , MgCl 2 , SrCl 2 , or the reduction of pH. These solute treatments, as well as the addition of tris (ethylenediamine)cobalt 3+ , enhanced the uptake of Se by the roots. The results are interpreted to reflect an elevated PM‐surface activity of SeO 4 2– caused by solute‐induced reductions of plasma membrane (PM) surface negativity. (PM‐surface electrical potential is sometimes measured electrophoretically as the zeta potential.) This study complements an extensive literature documenting the suitability of an electrostatic model (Gouy‐Chapman‐Stern), based almost entirely upon experiments with cations rather than anions. The close correspondence among uptake, intoxication, and model‐computed SeO 4 2– activity at the PM surface adds credibility to the model and its evaluated parameters. The model may be useful for the interpretation of other plant‐anion interactions, and phosphate and sulphate nutrition in acidic soils are considered as examples.