Salt Tolerance Is Not Associated With the Sodium Accumulation of Two Maize Hybrids

Abstract

In this report, we test the hypothesis that Na⁺ accumulation in the shoot in maize is negatively correlated with salt tolerance. Salt tolerance is defined as a percentage of the control on a dry weight basis. Two hybrids (Pioneer hybrid 3578 and Pioneer hybrid 3772) differing widely in Na⁺ accumulation were compared. Plants were treated with two types of salinity for 15 days (80 mol m-3 NaCl or 80 mol m^-3 NaCl plus 8.75 mol m^-3 CaCl₂). Ion concentrations (Na⁺, K⁺, Ca²⁺ and Cl^-) were measured in the roots, stalks, sheaths and leaves of plants harvested every third day. Ion concentrations were significantly affected by the treatments. Na⁺ and Cl^- concentrations increased with salinity treatments; K⁺ and Ca²⁺ concentrations decreased. Supplemental Ca²⁺ increased Ca²⁺ and decreased Na⁺ concentrations. Hybrid 3772 maintained very low Na⁺ concentrations in the shoots, whereas 3578 did not. The largest distinction between the hybrids was in the ability to transport Na⁺ to the shoot; hybrid 3578 transported Na⁺ at twice the rate of hybrid 3772. In general, ion transport to the shoot appeared to be a function of root ion concentration. This model could account for the effects of NaCl salinity and supplemental Ca²⁺ on ion transport, although Na⁺ transport was complicated by an apparent reabsorption mechanism in the root and mesocotyl. The lack of correlation of Na⁺ accumulation in the shoot and other ion parameters with growth indicated that the mineral nutrition of the plants was not correlated with salt tolerance. It was concluded that the growth response of maize to salinity was primarily affected by osmotic factors.