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

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Abstract
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 Km 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.