WITHDRAWN: HKT1;5 transporter gene expression and NHX-type Na+/H+ exchanger activity regulate adaptation of Echinacea species to salt stress

Abstract

Sodium (Na+) toxicity, as one of the main physiological threats to plant growth, may be used for maintaining cell turgor and solute concentrations. Salt-sensitive Echinacea purpurea and Echinacea angustifolia were compared regarding the mechanisms of Na+ uptake, exclusion, energetics, and expression of SOS1, NHX, and HKT1 transporter genes. The species differed in strategies to control Na+ concentration. Echinacea purpurea increased the xylem Na+ concentration upon exposure to 60 mM NaCl by increasing the activity of a high-affinity K+ transporter HKT1;5 and a Na+/H+ exchanger NHX. Echinacea angustifolia decreased the Na+ concentration in leaf sap at the beginning of salinity stress but could not maintain it for long. Higher net Na+ uptake was found in E. angustifolia than E. purpurea, whereas stronger activity of root-cell plasma membrane Na+/H+ (SOS1) exchanger was found in E. purpurea than E. angustifolia. It appeared that passive root entry of Na+ was limited in E. purpurea under salinity stress due to the SOS1-mediated Na+ exclusion. In conclusion, E. purpurea and E. angustifolia possess mechanisms to utilize rather than exclude Na+ as a means of adapting to the salinity stress.