Abstract
Sensitivity to Na and Cl was investigated in soybean (Glycine max L. Merill cv Fukuyutaka) and cucumber (Cucumis sativus L. cv Choujitu Ochiai Nigou) grown in modified Hoagland solution in a greenhouse. In the first experiment 21-d-old plants were treated with 25 and 50 mM NaCl, and 12.5 and 25 mM CaCl_2 for 11 d. Treatment with both the salts similarly reduced the growth of soybean while CaCl_2 treatment at both the concentrations failed to reduce the growth of cucumber but NaCl treatment did reduce it. In soybean plants treated with NaCl, Na concentration was greatly increased in roots and stem, and was not so much increased in leaves. Treatment with NaCl increased Na concentration in both roots and shoot of cucumber plants. Chloride concentration was increased in roots and shoot of soybean and cucumber plants by treatment with both the salts. In the second experiment 16-d-old cucumber plants were treated with NaCl, KCl, MgCl_2 and CaCl_2 at the Cl concentrations of 50 and 100 mM for 11 d. Treatment with 25 mM CaCl_2 slightly reduced plant growth because younger plants were used. When salts were added at a concentration of 100 mM Cl, CaCl_2 treatment reduced growth to 52% of the control plant while treatment with NaCl, KCl and MgCl_2 reduced it to 25% Chloride concentration was increased by treatment with any salt. It was the lowest in CaCl_2-treated plants. Treatment with NaCl, KCl and MgCl_2 greatly increased the concentration of each corresponding cation but CaCl_2 treatment only slightly increased Ca concentration. Leaf Cl concentration was higher than root Cl concentration in plants treated with NaCl, KCl and MgCl_2 while CaCl_2 treatment increased Cl concentration in roots rather than leaves. These results reveal that soybean shows severe sensitivity to Cl but is not so much affected by Na owing to its high ability to restrict the transport of Na to leaves and that cucumber is sensitive to Na but possesses substantial tolerance to Cl. It is considered that when large amounts of various salts are supplied the uptake of Ca which is smaller than the uptake of Na, K or Mg minimizes the effect of excess CaCl_2 in cucumber plants treated with CaCl_2.
