Accumulation of potassium and sodium by barley roots in a k-na replacement series

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated for 24 hr in solutions containing constant total concentrations of KCl and NaCl but in which the mole fractions of K and Na were varied in replacement series. In solutions containing 1, 10, or 50 mm concentrations of K(+) plus Na(+), total cation accumulation was dependent upon the total salt concentration but was relatively independent of the mole fractions of K(+) and Na(+). These results imply that accumulation of K(+) and Na(+) was limited by a common factor. In solutions containing 0.01 mm K(+) plus Na(+) there was a strong preference for K(+) over Na(+) and the sum of K(+) and Na(+) accumulation increased with increasing K(+) concentration.In the replacement series utilizing 0.1 mm K(+) plus Na(+), K(+) accumulation reached a peak at solution concentrations of 0.04 mm K(+) and 0.06 mm Na(+). Potassium accumulation then decreased as Na(+) was further replaced by K(+) to concentrations of 0.06 mm K(+) and 0.04 mm Na(+). Potassium accumulation again increased with additional replacement of Na(+) by K(+).