Comparative salt tolerance analysis between Arabidopsis thaliana and Thellungiella halophila, with special emphasis on K+/Na+ selectivity and proline accumulation

The eco-physiology of salt tolerance, with an emphasis on K+ nutrition and proline accumulation, was investigated in the halophyte Thellungiella halophila and in both wild type and eskimo-1 mutant of the glycophyte Arabidopsis thaliana, which differ in their proline accumulation capacity. Plants cultivated in inert sand were challenged for 3 weeks with up to 500 mM NaCl. Low salinity significantly decreased A. thaliana growth, whereas growth restriction was significant only at salt concentrations equal to or exceeding 300 mM NaCl in T. halophila. Na+ content generally increased with the amount of salt added in the culture medium in both species, but T. halophila showed an ability to control Na+ accumulation in shoots. The analysis of the relationship between water and Na+ contents suggested an apoplastic sodium accumulation in both species; this trait was more pronounced in A. thaliana than in T. halophila. The better NaCl tolerance in the latter was associated with a better K+ supply, resulting in higher K+/Na+ ratios. It was also noteworthy that, despite highly accumulating proline, the A. thaliana eskimo-1 mutant was the most salt-sensitive species. Taken together, our findings indicate that salt tolerance may be partly linked to the plants’ ability to control Na+ influx and to ensure appropriate K+ nutrition, but is not linked to proline accumulation.