Calcium alleviation of sodium toxicity in salt-treated Cyclocarya paliurus seedlings

Cyclocarya paliurus seedlings were cultured in a greenhouse under saline conditions in 50 L black plastic boxes containing Hoagland-Arnon nutrient solution. Plants were treated with a nutrient solution plus 85 mM NaCl and 0, 6, 12 or 18 mM Ca(NO3)2. Vegetative growth, leaf and root Na+ and Ca2+ concentrations were measured. Na+ toxicity symptoms were observed in plants non-treated with Ca2+. Shoot length was higher in Ca2+ treated plants, although shoot growth was reduced at 18 mM CaNO3, probably due to the high total ion concentration reached in the external solution. Ca2+ supply linearly increased leaf and root Ca2+concentration and decreased leaf Na+ concentration. However, there were no differences in root Na+concentration. Results indicate that Ca2+ may take part in the Na+ exclusion mechanism, mainly preventing Na+ transport to the shoot that may be an important ability for survival under saline conditions.   Key words: Cyclocarya paliurus, NaCl, sodium exclusion, calcium.