Absorption and Transport of Sodium and Potassium in Squash

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Abstract
Although the roots of Cucurbita pepo accumulated Na from a solution of moderate concentration, Na concentrations in the leaves remained low. When Na was supplied to the leaves it moved to the roots. Steam girdling resulted in accumulation of Na above the girdle. Na administered to one side of a divided root system migrated to the other side. These results are in contrast to those for K, and are interpreted as showing that while Na is moving upward through the xylem it is being returned to the roots via living cells. Addition of CaC12 to a solution of Na and K phosphates resulted in increased accumulation of K in roots, tops, and xylem exudate. This Ca treatment depressed accumulation of Na in the roots of Na co-centration in the xylem exudate, but did not influence Na concentration in the tops of transpiring plants. These results can be accounted for in terms of a site of Ca influence at the plasmalemma, a high affinity Na carrier at the tonoplast, and alternative pathways for limited Na transport into the stele.