Sodium and potassium fluxes and compartmentation in roots of Atriplex and oat

K⁺ and Na⁺ fluxes and ion content have been studied in roots of Atriplex nummularia Indl. and Aiena sativa L. cv Goodlield grown in 3 millimolar K⁺ with or without 3 or 50 millimolar NaCI. Compartmental analysis was carried out with entire root systems under steady-state conditions. Increasing ambient Na+ concentrations from 0 to 50 millimolar altered K⁺, in Atripkx, as follows: slightly decreased the cytoplasmic content (Qc), the vacuolar c_ontent (Qv), and the plasm_amembrane influx and efflux. Xylem transport for K⁺ decreased by 63% in Atripkx. For oat roots, similar increases in Na⁺ altered K⁺ parameters as follows: plasma membrane influx and efflux decreased by about 80%. Qc decreased by₆5%, and xylem transport decreased by 91%. No change, however, was observed in Q_v for K⁺. Incre_asing ambient Na⁺ resulted in higher (3 to 5-fold) Na⁺ fluxes across the plasma membrane and in Qc of both species_. In Atripkx, Na⁺ fluxes across the tonoplast and Q_v increased as external Na⁺ was increased. In oat, however, no significant change was observed in Na⁺ flux across the tonoplast or in Q_v as external Na⁺ was increased. In oat roots, Na⁺ reduced K⁺ uptake markedly; in Atriplex, this was not as pronounced. However, even at high Na⁺ levels, the influx transport system at the plasma membrane of both species preferred K⁺ over Na⁺ Based upon the Ussing-Teorell equation, it was concluded that active inward transport of K⁺ occurred across the plasma membrane, and passive movement of K⁺ occurred across the tonoplast in both species. Na⁺, in oat roots, was actively pumped out of the cytoplasm to the exterior, whereas, in Atripex, Na⁺ was passively distributed between the free space, cytoplasm, and vacuole.