sitl1 mutant reduces Na+ and Mg2+ uptake and root-to-shoot translocation
In order to investigate the mechanistic basis of salinity tolerance and the observed reduction in root development and leaf chlorophyll content, the ion concentrations of the sitl1 and WT plants grown for 1 week under 0 mM or 50 mM NaCl stress conditions were measured (Figure 5a-e). Under unstressed conditions, K content was increased by 1.38-fold and Mg was reduced by 0.61-fold, respectively, in the root ofsitl1 compared to that of WT (Figure 5a,b). Mg content in leaf tissues was also reduced by 0.76-fold in sitl1 , whereas, Na, Ca, and P content were not changed in both root and leaf tissues (Figure 5c-e). Under salinity stress conditions, K content was increased 1.75-fold, however, Mg and Na content were reduced 0.82-fold and 0.67-fold, respectively, in the root of sitl1 . Notably, significant reduction of Mg and Na content were observed in both roots and leaves of the sitl1 under 100 mM NaCl treatment (Figure 5b,c).
Next, we analyzed Mg, Na, and K concentrations in xylem sap (Figure 5a-e). The Mg and Na concentrations in xylem sap were significantly reduced 0.56-fold and 0.64-fold, respectively, compared to the WT, whereas K concentration in xylem sap was not changed under normal condition (Figure 5f-h). Mg and Na concentrations in xylem sap were also significantly lower in the sitl1 than in the WT under 100 mM NaCl stress (Figure 5f,g). Collectively, these results demonstrate that improved salinity tolerance, and reduced root growth and leaf chlorophyll content in sitl1 caused major changes to the Mg and Na content in both roots and leaves.