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Effect of Diethylstilbestrol on Ion Fluxes in Oat Roots ¹

^a Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

Effects of diethylstilbestrol (DES) on ion fluxes in oat roots (Avena sativa L.) were investigated by measuring K⁺ and Cl^– absorption and K⁺ efflux. DES rapidly decreased the absorption of K⁺ (⁸⁶Rb) and ³⁶Cl^– by excised roots; 10^–4 molar DES inhibited Cl^– absorption in 1 minute and K⁺ absorption in 1 to 2 minutes. With a 10-minute incubation period, K⁺ and Cl^– absorption were inhibited 50% by 1.1x10^–5 molar and 8.4x10^–6 molar DES, respectively. Treatment for 3 minutes with 10^–4 molar DES caused irreversible inhibition of K⁺ absorption. Increasing concentrations of KCl in the absorption media decreased the DES inhibition. Experiments with the DES analogs, DES dipropionate, dienestrol and hexestrol, showed that the steric configuration and the hydroxyl group of the DES molecule are important in determining the inhibitory capacity of the compound.

DES increased the efflux of ⁸⁶Rb from excised roots only after a 10-minute lag period. In 10^–4 molar DES, roots lost 82% of their radionuclide content in 1 hour. Comparison of efflux curves for roots loaded for 20 hours and those loaded for 15 minutes suggested that DES increased the permeability of the plasma membrane after about 10 minutes and the permeability of the tonoplast after 10 to 20 minutes. Oligomycin and dinitrophenol also increased the loss of ⁸⁶Rb, but the lag period was about 4 hours.

The rapid effect of DES on ion absorption and the slower effect on ion efflux suggest that DES initially inhibits ion uptake by affecting the transport mechanism at the plasma membrane in some manner other than alteration of membrane permeability.

¹ This research was supported by National Science Foundation Grant 31052X. Journal Paper No. 7151 of the Purdue University Agriculture Experiment Station.