Potassium Fluxes in Excised Barley Roots

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Abstract
The method of the modified compartmental analysis for excised roots has been adopted for measuring K+-fluxes and compartmentation in barley (Hordeum distichon) roots. Efflux of 42K and 86Rb indicated that more than two intracellular compartments were involved in the tracer exchange; the 42K data clearly showed the components. On the basis of the efflux behaviour of the apical and more basal tissues of the roots, the three components of efflux were attributed to the cytoplasm of differentiated (fast) and meristematic tissues (intermediate) and to the vacuoles (slow exchange) of the roots. A model is proposed on the basis of which, the fluxes corresponding to the meristematic and differentiated tissues of the root can be estimated. Additionally, fluxes of the differentiated root tissues were determined by using efflux data obtained with root segments without apical tissues. The data obtained in both ways compare reasonably well and agree to independent chemical measurements. Comparison of the 42K and 86Rb efflux data show strong discrimination of K− in favour of Rb+ and indicate that 86Rb is not suitable as a tracer for K+ in efflux measurements, at least with barley roots.
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