Uptake and distribution of calcium, magnesium and potassium in cucumber of different age

Uptake and distribution of Ca+, Mg2+ and K2+ were investigated in plants of cucumber (Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 mM Ca2+, 2.0 mM Mg2+ and 2.0 mM K+. The + concentration was about the same in roots and shoots, while the Ca2+ and Mg2+ concentrations were low in roots compared to shoots. The K+ concentration decreased with increasing leaf age, while the Ca2+ and Mg2+ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21‐day‐old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca2+ (45Ca) uptake. Transport of Ca2+ increased to leaves above and below the excision point and total Ca2+ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites.