Interactions in the Absorption of Monovalent Cations by Excised Radish Roots

Preferential absorption of potassium over sodium has been observed with excised radish roots using a wide range of concentrations in the bathing medium. This result is contrary to the situation observed in most other plants which have been investigated, where it is found that at high external concentrations (>1·0 mM) the uptake of potassium is less specific and the rate of sodium absorption exceeds that of potassium. In radish roots calcium does not interact with the monovalent cation absorption in the higher range of concentration and the sodium absorption is not sensitive to chloride-sulphate substitution. These results are discussed in relation to salinity-tolerance and potassium:sodium interactions.