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

Abstract

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 5mM or 50mM 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 6h 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−.