Enhancement of Nitrate Uptake and Growth of Barley Seedlings by Calcium under Saline Conditions

The effect of Ca²⁺ on NO₃⁻ assimilation in young barley (Hordeum vulgare L. var CM 72) seedlings in the presence and absence of NaCl was studied. Calcium increased the activity of the NO₃⁻ transporter under saline conditions, but had little effect under nonsaline conditions. Calcium decreased the induction period for the NO₃⁻ transporter under both saline and nonsaline conditions but had little effect on its apparent K_m for NO₃⁻ both in the presence and absence of NaCl. The enhancement of NO₃⁻ transport by Ca²⁺ under saline conditions was dependent on the presence of Ca²⁺ in the uptake solution along with the salt, since Ca²⁺ had no effect when supplied before or after salinity stress. Although Mn²⁺ and Mg²⁺ enhanced NO₃⁻ uptake under saline conditions, neither was as effective as Ca²⁺. In longer studies, increasing the Ca²⁺ concentration in saline nutrient solutions resulted in increases in NO₃⁻ assimilation and seedling growth.