The element contents in the compartments of root and leaf cells of soybean and cucumber plants grown for 8 d in a nutrient solution containing 50 mM NaCl, 25 mM CaCl2 or 50 mM NaCl+4.75 mM CaSO4 were examined by X‐ray microanalysis of freeze‐substituted dry sections. Sodium accumulated in the vacuoles rather than in the cytoplasm and apoplastic space in the root cells of the soybean plants, leading to the difficulty in the transport of Na to leaves in soybean. Salt injury of soybean is considered to be caused by the accumulation of Cl at high concentrations in all the compartments of root and leaf cells. In contrast, the accumulation of Na in the cytoplasm of the root and leaf cells might disturb the metabolism and lead to the occurrence of salt toxicity in cucumber plants, which are tolerant to Cl due to the stimulation of Cl accumulation in vacuoles when the Ca concentration was high in nutrient media.

Effects of the application of supplemental Ca on the growth and mineral content and on the ion concentration of the sap of individual plant parts were investigated in soybean and cucumber plants that were treated with 50 mM NaCl. Treatment with NaCl reduced the growth of both kinds of plants and also the photosynthetic rate of the first cucumber leaf and the first soybean trifoliolate leaf at 7 d after the treatment. Increase of the Ca concentration in the medium alleviated the reduction of growth and photosynthetic rate, and its effect was more conspicuous in cucumber than in soybean. In the plant parts that contained high amounts of Na and Cl but a low amount of K with the NaCl treatment, the application of supplemental Ca decreased the Na content, increased the K content but did not affect appreciably the uptake and translocation of Cl. Because increasing Ca concentrations in the medium affected the contents of cations such as Na and K, the ameliorative effect of Ca was considered to be remarkable in cucumber plants where a high Na content resulted in growth inhibition due to salinity. On the contrary, the effect of supplemental Ca application appeared to be weak in soybean plants because in these plants, Cl might induce growth inhibition due to salinity and the application of supplemental Ca did not affect substantially the Cl status. In the NaCl treatment, the decrease in the concentrations of anions other than Cl− was more conspicuous in soybean plants than in cucumber plants. Hence anion imbalance due to excess Cl− might induce growth inhibition in soybean. In cucumber plants, the total cation concentration was slightly changed whereas the Na+ concentration increased with the decrease in the K+ concentration by the NaCl treatment. Cation imbalance that was caused by increased Na+ concentration and decreased K+ and Mg2+ concentrations might be responsible for the growth inhibition in cucumber plants. Increase of the Ca concentration in the medium affected only slightly the occurrence of such imbalance of cations or anions in both kinds of plants.

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