Differences in the Temporal Kinetics of the Metabolic Responses to Salinity Between the Salt-Tolerant Thellungiella salsuginea and the Salt-Sensitive Arabidopsis thaliana Reveal New Insights in Salt Tolerance Mechanisms

To unravel the mechanisms underpinning salt tolerance, different studies have attempted to determine the physiological and genetic variations behind the difference in salt tolerance between Arabidopsis thaliana and the salt-tolerant Thellungiella salsuginea (halophila). Most of these studies were limited to a specific duration of salt treatment and neglected the time response as a possible contributing factor to the higher salt tolerance exhibited by T. salsuginea. In this work, a comprehensive and detailed comparison of the response of the two species to high salinity was conducted at different times for up to ten days of salt treatment. T. salsuginea responded more rapidly and to a higher extent to adjust its metabolism and showed constitutive levels of anticipatory metabolism to salinity. T. salsuginea responded more rapidly in terms of maintaining light use efficiency, limiting the uptake of Na+, and increasing the accumulation of sugars and proline when exposed to salinity. T. salsuginea had much higher constitutive levels of metabolites, including malate, proline, and inositol, in comparison to A. thaliana. Interestingly, T. salsuginea showed a reduction in malate levels under salt treatment in contrast to A. thaliana. These results suggest that constitutive levels and the rapidity of the deployment of resistance mechanisms, together with metabolic plasticity, in response to salt stress are important adaptive traits for salt tolerance in plants.