Preferential uptake of potassium by excised cucumber cotyledons as influenced by benzyladenine

Excised cucumber cotyledons were grown in varying concentrations and ratios of KC1 and NaCl in absence and presence of Benzykdenine (BA) and the uptake of K⁺ and Na⁺ as influenced by BA was determined. BA stimulated the uptake of both K⁺ and Na⁺ but the magnitude of stimulation of K⁺ was much higher. When KCl concentration was kept constant and NaCl increased, uptake of K⁺ was reduced and the total uptake (K⁺+Na⁺) remained the same. On the other hand, when NaCl concentration was kept constant in the medium and KC1 concentration was increased, uptake of Na⁺ was not affected, suggesting the presence of specific site for Na⁺ uptake. Also the total ion uptake increased with increasing concentration range. When equimolar concentrations of NaCl and KC1 were in the medium, BA stimulated uptake of K⁺ was much more than Na⁺. The significance of this in altering the K/Na ratio in the tissue is discussed.