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This article in AJ

  1. Vol. 64 No. 4, p. 413-417
    Received: Jan 18, 1971

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Use of Rubidium as a Chemical Tracer for Potassium in Long-term Experiments in Cotton and Barley1

  1. A. Hafez and
  2. D. W. Rains2



Considerable controversy surrounds the technique of using Rb to chemically or isotopically label K. A series of experiments were conducted to determine the usefulness of this technique when other, potentially interactive, ions are present in the media and the plants are exposed to these solutions for extended periods.

Cotton (Gossypium hirsutum var. ‘Acala, SJ-1’) and barley (Hordeum vulgare var ‘Arivat’) were grown in the greenhouse for 45 days in culture solutions containing various ratios of Rb/K. Na and NH4 were added to determine the extent of the interaction of these cations with Rb and K.

The distribution of Rb and K in different plant parts was determined chemically at the end of the growth period. Quantitative tagging of Rb for K depends upon factors of ionic concentration of both ions, the ratio of Rb/K in the substrate, plant species, and the presence of other monovalent cations, such as NH4 or Na ions.

Roots of both cotton and barley plants retain Rb preferentially over K. Ammonium ions compete more with K than with Rb uptake. Cotton blades reflect the Rb/K ratios of the culture solution, with a maximum deviation of 20% over the fiftyfold range of K concentration examined.

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