Sodium and potassium absorption by bean stem tissue

The effect of various periods of pretreatment in CaSO₄ solutions (aging) on the absorption of Na and K by bean stem slices was investigated. Freshly sliced tissue absorbed Na over the entire range of concentrations studied (0.02-50 mm). Potassium absorption by fresh tissue was nil at concentrations below 0.5 mm but at higher concentrations was similar to that of Na. When tissue was aged by aerating slices for 20 hr in 0.5 mm CaSO₄, K absorption was substantial over the entire range (0.01-50 mm), with evidence of a dual mechanism of absorption, whereas Na absorption was nil at concentrations below 0.2 mm. The formation of K-absorbing capacity with aging, and the loss of Na-absorbing capacity at low concentrations, were temperature-dependent and did not result from significant changes in rates of efflux of either ion. The absorption of Na by fresh tissue and K by aged tissue was sensitive to antimetabolites, with K uptake the more sensitive. Benzyladenine, an analog of kinetin, suppressed the formation of K-absorbing capability in aged tissue but did not prevent the loss of Naabsorbing capacity. Possible mechanisms for this alteration in ion-specificity of transport mechanisms are discussed.