Graduate Thesis Or Dissertation
 

Selective inhibition of ion absorption by uranyl

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  • The research presented in this thesis evaluated the effects of uranyl (UO₂⁺⁺) upon the absorption of Li, Na, K, Rb, and Cl. Due to the biological importance of Na and K, these two ions were studied in the greatest detail. The results of this research showed that, at UO₂⁺⁺ concentrations above 1 X 10⁻¹ milliequivalents per liter and pH's above 4.5, uranyl selectively inhibited K and Rb absorption but had essentially no effect upon Na and Li. Under these same conditions it was concluded that uranyl polymers such as (UO₂)3(OH)₄⁺⁺ were formed. It was suggested that these polymers produced the inhibition of K and Rb absorption. When the pH was below 4.0 and the UO₂⁺⁺ concentration below 1 X 10⁻² millequivalents per liter the simple UO₂⁺⁺ cation was the predominant form of uranyl. Under these conditions uranyl acted in a fashion similar to many of the other divalent cations in that it stimulated the absorption of K and Rb (and to some extent Na) from single-alkali cation solutions. When K and Na were both in a test solution at pH 5, the simple UO₂⁺⁺ cation stimulated K but slightly inhibited Na absorption. By pre-treating root samples for thirty minutes in a 1 milli-equivalent uranyl solution the absorption of K could be greatly reduced and the absorption of Na stimulated. These effects of the UO₂⁺⁺ could be completely reversed by subsequently treating the pretreated tissues with EDTA for one hour. The addition of UO₂⁺⁺ to root tissues resulted in a slight reduction in the rate of respiration and produced a marked inhibition of K absorption but had no effect upon Na absorption. The results of this study suggest that there are at least two carriers transporting Na and K. One of these carriers was inhibited by the higher uranyl concentrations at pH's above 4.5. This carrier shows a "preference" for K. The second carrier was unaffected by UO₂⁺⁺ and showed a "preference" for Na. When only one of this pair of ions was present it could travel via either of the carriers. Competition of K with Na was greatest during absorption via the "UO₂⁺⁺-sensitive" carrier. Na competition with K was greatest during transport via the "UO₂⁺⁺ resistant" carrier. It is suggested that UO₂⁺⁺ may bind to a phosphate containing organic compound which is either the K carrier or a compound closely related to this carrier.
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file details MasonBenjaminJ1967_Redacted.pdf 2017-08-07 Pubblico Scaricare