Sodium-calcium interactions in two wheat species differing in salinity tolerance

Sodium/calcium interactions were compared in two species of wheat known to differ in sodium accumulation in the shoot and biomass reduction under saline conditions. Unidirectional uptake of Na-22 to the roots was measured in 5, 50, 100 and 150 mM NaCl with four levels of calcium activity. Translocation of sodium to the shoot was measured as Na-22 uptake over 7 days. The rate of sodium uptake into the roots did not vary between the salt-sensitive Triticum turgidum cv. Modoc and the tolerant Triticum aestivum cv. Kharchia, except at low calcium, when the rate of uptake was higher in Kharchia, and more sensitive to inhibition by additional calcium. The rate of translocation to the shoot was similar in both species, however the shoot:root ratio was higher in Kharchia and so the concentration of sodium, on a shoot fresh weight basis, was more dilute in Kharchia. There was no evidence for differences in sodium transport processes between the species which might confer differential salinity tolerance. Translocation of calcium to the shoot was measured as Ca-45 uptake in 5 and 150 mM NaCl with 4 levels of calcium activity. Translocation of calcium was more inhibited by sodium in the salt-sensitive Modoc, and this may reflect differences in calcium transport processes, which could account in part for the greater salt sensitivity of this species.