Application of nitric oxide and calcium nitrate enhances tolerance of wheat seedlings to salt stress

Nitric oxide and calcium are two kinds of signaling molecules that are the key secondary messenger. An experiment was conducted in saline culture solution to examine the cross-talk interactions of nitric oxide and calcium in common wheat under NaCl stress. Addition of 100 mM NaCl reduced plant growth, decreased the chlorophyll content and root activity, increased the reactive oxygen species (such as O2·-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{O}}_{2}^{ \cdot - } $$\end{document} and H2O2) level, lipid peroxidation and electrolyte leakage, and suppressed the activities of antioxidant enzymes in wheat seedlings. Moreover, high Na+ resulted in the deficiency of mineral nutrients. While addition of 0.10 mM sodium nitroprusside (a NO donor) and/or 17.50 mM Ca(NO3)2 (Na/Ca = 5) alleviated a decline in chlorophyll content, root activity and soluble sugar content, stimulated the activities of antioxidant enzymes such as superoxide dismutase, peroxidase and catalase and decreased the electrolyte leakage, lipid peroxidation, H2O2 content, O2·-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{O}}_{2}^{ \cdot - } $$\end{document} generation rate. Furthermore, the concentrations of potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe) and copper (Cu) concentrations in the leaves and roots of wheat were increased, indicating that application of Ca(NO3)2 facilitated the maintenance of ion homeostasis, while the exogenous NO improved the uptake of Ca. The results suggest that the nitric oxide and calcium are effective in alleviating the adverse effects of salt stress: the nitric oxide is more actively involved in antioxidant system while the calcium is more beneficial to ion homeostasis. When applied in combination, Ca(NO3)2 could counteract the toxicity of exogenous NO to the root, while the exogenous NO may promote the selectivity of uptake and transport of Ca2+.