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 SeO42-. SeO42- inhibition was enhanced by supplementation of the rooting medium with CaCl2, MgCl2, SrCl2, 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 SeO42- 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 SeO42- 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.