GC-TOF-MS analysis reveals salt stress-responsive primary metabolites in Casuarina glauca tissues

Abstract

Casuarina glauca is a model actinorhizal plant characterized by its ability to establish symbiosis with nitrogen-fixing Frankia bacteria. This species is able to thrive under extreme salinity environments. C. glauca tolerance to high salinity has been previously associated with low tissue dehydration, osmotic adjustments, and high membrane integrity. However, the full characterization of this plant system and the identification of key elements involved in its salt stress tolerance could be significantly improved through a metabolomics approach. To date, very little information is available in the literature about the C. glauca metabolome. The present study investigates the impact of salt stress on the primary metabolome of nodulated (NOD+) and non-nodulated (KNO3+) C. glauca tissues (nodules, roots, and branchlets) and aims to identify salt-stress responsive metabolites in these two plant groups. Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) is a powerful tool to measure primary metabolites such as sugars, amino, and organic acids, involved in the regulation of plant developmental processes, and has contributed to better understand how plant metabolism readjusts in response to high salinity. GC-TOF-MS data reveals major metabolite divergences in amino acid metabolism, which are highly consistent with the previously reported impairment of symbiotic activity, as well as down-regulation of the transcriptional activity of the plant symbiotic genes in the NOD+ plants. Altogether, our results revealed that C. glauca plants can tolerate high levels of salinity through modifications in the levels of some neutral sugars, proline, and ornithine.