Root absorption and transport behavior of technetium in soybean

The absorption characteristics and mechanisms of pertechnetate (TcO₄⁻) uptake by hydroponically grown soybean seedlings (Glycine max cv Williams) were determined. Absorption from 10 micromolar solutions was linear for at least 6 hours, with 30% of the absorbed TcO₄⁻ being transferred to the shoot. Evaluation of concentration-dependent absorption rates from solutions containing 0.02 to 10 micromolar TcO₄⁻ shows the presence of multiphasic absorption isotherms with calculated K_s values of 0.09, 8.9, and 54 micromolar for intact seedlings. The uptake of TcO₄⁻ was inhibited by a 4-fold concentration excess of sulfate, phosphate, selenate, molybdate, and permanganate; no reduction was noted with borate, nitrate, tungstate, perrhenate, iodate, or vanadate. Analyses of the kinetics of interaction between TcO₄⁻ and inhibiting anions show permanganate to be a noncompetitive inhibitor, while sulfate, phosphate, and selenate, and molybdate exhibit characteristics of competitive inhibitors of TcO₄⁻ transport suggesting involvement of a common transport process.