The absorption and translocation of sodium by maize seedlings.

The absorption and subsequent distribution of sodium and potassium has been examined in maize seedlings in short-term experiments using sodium-22 and potassium-42. The absorption and translocation of sodium by different segments of intact seedlings was also investigated. Although absorption of potassium exceeded that of sodium by a factor of about 50, there was no evidence that the entry of sodium was confined to a small region of the root. Determinations of the relative quantities of sodium and potassium in the xylem exudate of detached roots showed that the ratio of sodium to potassium decreased with increasing length of the root. These results suggested that upward movement of sodium in the xylem vessels was progressively reduced towards the basal part of the root. This conclusion was supported by microautoradiographs, which showed that although the concentration of sodium within the endodermis was greater than that in the cortex, there was an apparent decrease in the sodium content of the major xylem vessels at the basal end of the root.