The Initial Uptake of Ions by Barley Roots: III. THE UPTAKE OF CATIONS

Abstract

Experiments have been carried out to determine the extent to which rubidium and strontium, recently absorbed by excised barley roots, can be divided into discrete fractions, namely, ions which are extractable with water, those which are exchangeable, and those remaining in the tissue at the end of the experiment. The object of this study was to determine whether the behaviour of cations could be validly interpreted in terms of the electrical double-layer theory as had been previously demonstrated for anions. To facilitate the interpretation of the results obtained, comparable experiments were carried out on a cation-exchange resin and on gelatin. The behaviour of strontium accorded qualitatively with the theory providing allowance was made for effects due to the hydrolysis of negative sites and for the presence of positive charges in the roots. For rubidium, on the other hand, the situation was much more complex. Not only was there evidence even at 0-2° C for sites which retained a high specificity for this ion, but also movement of the ion due to physical diffusion was masked by concurrent metabolic activity. It was concluded that a meaningful separation of the over-all uptake of rubidium into successive steps of exchange absorption and metabolic accumula tion cannot be made.