Transport of Sodium in Plant Tissue.

Two mechanisms are implicated in the absorption of alkali cations by barley roots. Mechanism 1 has a high affinity for potassium, but its affinity for sodium is so low that, in the presence of even a low concentration of potassium (1 mM), sodium absorption by this mechanism is all but abolished. Mechanism 2 has a much lower affinity for alkali cations and is not highly selective; it transports sodium as well as potassium.