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 content (Qv), and the plasmamembrane 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 Qv for K+. Increasing 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 Qv increased as external Na+ was increased. In oat, however, no significant change was observed in Na+ flux across the tonoplast or in Qv 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.
ASJC Scopus subject areas
- Plant Science