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Close coupling between extrusion of H + and uptake of K + by barley roots

Rudolf Behl and Klaus Raschke
Planta
Vol. 172, No. 4 (1987), pp. 531-538
Published by: Springer
Stable URL: http://www.jstor.org/stable/23379081
Page Count: 8
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Close coupling between extrusion of H
          +
          and uptake of K
          +
          by barley roots
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Abstract

Extrusion of H+ by intact barley (Hordeum vulgare L.) roots was automatically titrated. Simultaneously, uptake of K+ into the roots, transport of K+ through the roots, and (as a residual term) accumulation of K+ within the root tissue were determined. When no monovalent cation was present in the medium the steady rate of H+ release was close to zero. Addition of K+ stimulated H+ extrusion within less than 1 min. The stimulation of H+ release was apparently limited only by the movement of K+ through the apoplast of the roots. The steady rate of H+ extrusion depended on the availability of external K+ and saturated at a K+ concentration of about 100 μmol·dm-3. Half-maximum rates of net K+ uptake and H+ extrusion were reached at a K+ concentration of about 10 μmol·dm-3. With (slowly absorbable) sulfate as the only union present, the stoichiometry between H+ release and net K+ uptake was one. In conclusion, the uptake of K+ across the plasmalemma of the cells of the root cortex is electrically coupled to H+ extrusion.

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