Role of the Accompanying Anion in the Effect of Calcium Salts on Potassium Uptake by Excised Barley Roots

The effect of addition of Ca salts on accumulation of K from 5 mN KCl or K(2)SO(4) solutions was found to depend on whether Ca was added as Cl or SO(4) salt. Chloride as well as K uptake was increased when Ca and Cl concentrations in culture solutions were increased. Pre-treatment of roots with CaCl(2) stimulated subsequent K uptake from K(2)SO(4) solutions as compared to pre-treatment with distilled water but pre-treatment with CaSO(4) did not. The results indicate that addition of Ca salts to KCl or K(2)SO(4) solutions increased anion uptake and the effect of the addition of the Ca salts on K uptake was in part the result of increased anion uptake and not entirely a direct effect of Ca.In contrast, accumulation of Na and K from solutions containing these ions as SO(4) or Cl salts was changed from preferential uptake of Na to preferential uptake of K by addition of either CaCl(2) or CaSO(4). Thus, while Ca salts may influence K accumulation partly as a result of effects on anion uptake, the selectivity for K uptake depends on the presence of Ca and is influenced little by the accompanying anion.