The Exchange of sodium Ions in the Root of Zea mays

The apparent cation-exchange capacity of maize roots has beenestimated in 100 mM NaCL and I mM NaCl by observing the effluxkinetics of isotopically labelled sodium from this tissue. Thisapproach indicated that the apparent capacity was 70 m.equiv/kgof tissue (fresh weight) and 2 m.equiv/kg of tissue (fresh weight)in 100 mM and I mM NaCl respectively; the pH of the medium was5.8 in each case.Similar sodium efflux experiments were performedon isolated stelar tissue from these roots and such experimentsgave an apparent exchange capacity of 86 m.equiv/kg of tissue(fresh weight) and 6 m.equiv/kg of tissue (fresh weight) in100 mM and I mM NaCl respectively, both at pH 5.8.The dependenceof the magnitude of the apparent exchange capacity upon theelectrolyte concentration of the external medium is discussed.