The Interactions Between Monovalent Cations and Calcium During Their Adsorption on Isolated Cell Walls and Absorption by Intact Barley Roots

The adsorption of sodium, potassium, rubidium and calcium ionsat different concentrations was measured on cell walls frombarley roots (Hordeum vulgare L. cv. Union), prepared by detergenttreatment. It was found that sodium and calcium interacted verystrongly during their simultaneous adsorption, whereas potassiumdid not interfere with calcium. This has led us to concludethat calcium and sodium are adsorbed on identical sites in thecell wall, whereas potassium is adsorbed at another site. Rubidiumseems to be less specific for both sites and interferes onlymoderately with calcium. The adsorption on cell walls of thesecations was compared with their adsorption on intact roots at2 °C, where beside the cell wall, sites may be availableat the outer surface of the membrane, and further measurementswere made of absorption at 25 °C. The fact that sodium interactswith calcium and potassium alters the ratio of K to Na in thecell wall compared to their concentrations in the medium. Thepreferential shift towards potassium when calcium is presentcould be very important for the rates of initial uptake in lowsalt barley roots, since the membrane is in contact with a differentproportion of K to Na in the cell wall from the one suppliedin the medium. Hordeum vulgare L., barley, absorption of cations, adsorption, calcium, sodium, potassium rubidium