The Effect of Calcium on the Uptake and Distribution of Sodium in Excised Barley Roots

The total uptake and relative distribution of Na⁺ along the root was investigated in excised barley roots (Hordeum vulgare L. cv. Union) of 6-day-old plants cultured on 0.25 mM CaSO₄. One technique involved cutting the roots at harvest time after different uptake periods into different segments each 2 cm long. These segments were ashed and sodium was measured by flame photometry. For each experiment two treatments were done, one containing calcium in the uptake solution and one without calcium. A second technique involved the measurement of sodium transport, using labelled ²²Na⁺ solution. Although no significant differences could be found between the calcium containing and the calciumless treatments at 24 h, there were clearcut differences for the first 6 to 8 h. The effect of calcium on the first stages of the sodium uptake was a large accumulation of sodium in the part close to the apex with a translocation close to nil; whereas the sodium taken up in the absence of calcium did not accumulate in such large amounts in the apex region but was immediately transported basipetally.     

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