Ameliorating effects of exogenous Ca2+ on foxtail millet seedlings under salt stress

In the present study, we investigated whether Ca2+ application alleviates salinity-induced damage in foxtail millet (Setaria italica L.). We evaluated the stress-related ion balance, physiological activity and gene expression involved in plant defences against salinity exposure. Twenty-one-day-old foxtail millet was maintained in sand culture for 7 days and subjected to one of seven treatments: half-strength modified Hoagland solution (the control), 1.0% NaCl, 1.0% NaCl + 2.5 mM Ca2+, 1.0% NaCl + 5.0 mM Ca2+, 1.0% NaCl + 7.5 mM Ca2+, 1.0% NaCl + 10.0 mM Ca2+, 1.0% NaCl + 12.5 mM Ca2+. The addition of Ca2+ significantly increased shoot and root height and weight relative to calcium absent treatment and corrected the ion imbalance by increasing Ca2+, Mg2+ and K+, and decreasing Na+ in the leaves and roots. It increased chlorophyll content and root activity and decreased the relative electrolyte leakage in the roots and leaves. Calcium application significantly upregulated superoxide dismutase and catalase, increased total protein, and decreased malondialdehyde and H2O2. Finally, the addition of Ca2+ upregulated the expression of APX, SOD and CAT. It was found that 10.0 mM Ca2+ was the optimal concentration for alleviating salt stress injury in foxtail millet.