Sodium, but not potassium, enhances root to leaf nitrate translocation in Swiss chard (Beta vulgaris var. cicla L.)

Salinity is known to reduce NO3- uptake in many plants. Our previous study found that the increasing NaCl concentrations in media enhanced NO3- uptake in leaves. Here, we investigated whether nitrate (NO3-) uptake by Swiss chard (Beta vulgaris var. cicla L.) was affected more by Na+ than by K+, and elucidated which NO3- uptake processes were related to the application of these ions in the culture medium. Plants were grown hydroponically and subjected to 5 mM or 50 mM of either K or Na treatments for 7 days: K5 (K 5, Na 0), K50 (K 50, Na 0), Na5 (K 0, Na 5), and Na50 (K 0, Na 50). The leaf NO3- concentration was significantly enhanced in the Na treatments compared with the K treatments. The ratio of leaf to root NO3- concentrations in K5 and Na5 were 0.46 and 1.59, respectively, which indicates that NO3- is translocated to the leaves in the Na treatments. The NO3- concentration in the xylem sap, collected 6 h after the start of the treatments, was significantly higher in Na50 than in the other treatments. These are the opposite of the results for Arabidopsis, which accumulates NO3- in its roots to increase its salinity tolerance. Our results suggest that Na but not K enhances NO3- uptake and transport to the leaves in Swiss chard and that its function may relate to xylem translocation of NO3-. (C) 2014 Elsevier B.V. All rights reserved.