EXCHANGE OF SODIUM IONS IN ROOT OF ZEA MAYS

The apparent cation-exchange capacity of maize roots has been estimated in 100 mM NaCL and I mM NaCl by observing the efflux kinetics of isotopically labelled sodium from this tissue. This approach indicated that the apparent capacity was 70 m.equiv/kg of 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 was 5.8 in each case.Similar sodium efflux experiments were performed on isolated stelar tissue from these roots and such experiments gave an apparent exchange capacity of 86 m.equiv/kg of tissue (fresh weight) and 6 m.equiv/kg of tissue (fresh weight) in 100 mM and I mM NaCl respectively, both at pH 5.8.The dependence of the magnitude of the apparent exchange capacity upon the electrolyte concentration of the external medium is discussed. © 1969 Oxford University Press.