Effect of Diethylstilbestrol on Ion Fluxes in Oat Roots

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Abstract
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 M DES inhibited Cl- absorption in 1 min and K+ absorption in 1-2 min. With a 10 min incubation period, K+ and Cl- absorption were inhibited 50% by 1.1 .times. 10-5 M and 8.4 .times. 10-6 M DES, respectively. Treatment for 3 min with 10-4 M 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 groups 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 min lag period. In 10-4 M DES, roots lost 82% of their radionuclide content in 1 h. Comparison of efflux curves for roots loaded for 60 h and those loaded for 15 min suggested that DES increased the permeability of the plasma membrane after about 10 min and the permeability of the tonoplast after 10-20 min. Oligomycin and dinitrophenol also increased the loss of 86Rb, but the lag period was about 4 h. 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.