Extrusion of Sodium Ions by Barley Roots

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Abstract
An active sodium effux hasbeen demonstrated in excised barley roots. Isolated cortical and stelar tissues from the same material do not show any evidence of such an efflux mechanism. When intact barley plantswere allowed to absorb 22Na active sodium extrusion was not observed, although the percentage of 22Na transported to the shoot was stimulated 20 to 40 percent by ouabain at 5 × 10−4 M. Absorption and long-distance transport of phosphate was unaffected by ouabain at this concentration. Interpretation of these data lead to the conclusion.that the sodium-efflux pump in barley roots is located at or near the endodermis external to the Casparian band. This pump thus provides a mechanism whereby sodium can be partially excluded from the shoots of barley plants.

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