Calcium supply effects on wheat cultivars differing in salt resistance with special reference to leaf cytosol ion homeostasis

Salinity causes changes in cytosolic Ca²⁺, Ca²⁺]_cyt, Na⁺, Na⁺]_cyt and pH, pH_cyt, which induce specific reactions and signals. Reactions causing a rebalancing of the physiological homeostasis of the cytosol could result in plant resistance and growth. Two wheat cultivars, Triticum aestivum, Seds1 and Vinjett, were grown in nutrient solution for 7 days under moderate salinity (0 and 50 mM NaCl) with and without extra addition of 5 mM CaSO₄ to investigate the seedling‐ion homeostasis under salinity. In the leaf protoplasts Ca²⁺]_cyt, Na⁺]_cyt and pH_cyt were detected using acetoxymethyl esters of the ion‐specific dyes, Fura 2, SBFI and BCECF, respectively, and fluorescence microscopy. In addition, both cultivars were grown for 3 weeks at 0, 50 and 125 mM NaCl with, or without, extra addition of 5 mM CaSO₄ to detect overall Na⁺ and Ca²⁺ concentrations in leaves and salinity effects on dry weights. In both cultivars, salinity decreased Ca²⁺]_cyt, while at extra Ca²⁺ supplied, Ca²⁺]_cyt increased. The Ca²⁺]_cyt increase was accompanied by increase in the overall Ca²⁺ concentrations in leaves and decrease in the overall Na⁺ concentration. Moreover, irrespective of Ca²⁺ treatment under salinity, the cultivars reacted in different ways; Na⁺]_cyt significantly increased only in cv. Vinjett, while pH_cyt increased only in cv. Seds1. Even at rather high total Na⁺ concentrations, the cytosolic concentrations were kept low in both cultivars. It is discussed whether the increase of Ca²⁺]_cyt and pH_cyt can contribute to salt tolerance and if the cytosolic changes are due to changes in overall Ca²⁺ and Na⁺ concentrations.