Uptake of Iodide by Excised Bean Roots

Mesophyll cells of leaf slices of bean (Phaseolus vulgaris L.) absorb six to ten times more K⁺ than Rb⁺ from 0.1 mM single chlorides of these cations. Absorption of ⁴²K⁺ from 0.1 mM⁴²KCl is much more inhibited by low concentrations of Rb₂SO₄ than by K₂SO₄. The isotherm for K⁺ absorption is biphasic in the range 0.1–1.1 mM, and K⁺ is more effective than Rb⁺ in causing transition from phase 1 to phase 2.