Abstract
We have analysed the salt tolerance of two endemic halophytes of the genus Limonium, with high conservation value. In the present study, seed germination and growth parameters as well as different biomarkers—photosynthetic pigments, mono and divalent ion contents—associated to salt stress were evaluated in response to high levels of NaCl. The study was completed with an untargeted metabolomics analysis of the primary compounds including carbohydrates, phosphoric and organic acids, and amino acids, identified by using a gas chromatography and mass spectrometry platform. Limonium albuferae proved to be more salt-tolerant than L. doufourii, both at the germination stage and during vegetative growth. The degradation of photosynthetic pigments and the increase of Na+/K+ ratio under salt stress were more accentuated in the less tolerant second species. The metabolomics analysis unravelled several differences between the two species. The higher salt tolerance of L. albuferae may rely on its specific accumulation of fructose and glucose under high salinity conditions, the first considered as a major osmolyte in this genus. In addition, L. albuferae showed steady levels of citric and malic acids, whereas the glutamate family pathway was strongly activated under stress in both species, leading to the accumulation of proline (Pro) and γ-aminobutyric acid (GABA).
Highlights
Final germination percentages after 30 days of incubation were very high in the controls for the two species, 95% in L. albuferae and 98% in L. dufourii
The lower values corresponded to seeds that had been pre-incubated with 150 mM NaCl, whereas the higher germination percentages were measured for those recovered from the 300, 450, and 600 mM NaCl plates, without statistically significant differences between these pre-treatments (Figure 1)
The germination study indicated that both species behave as halophytes, their germination being enhanced after one month of exposure to salt concentrations
Summary
The Mediterranean basin is one of the regions in the world with the greatest plant diversity [5] and is rich in saline habitats. Within this region, the Spanish territory of the Iberian Peninsula and the Balearic Islands contain several major hotspots of plant diversity [6,7]; besides, this area holds an extensive list of endemic and threatened species [8,9]. Limonium is one of the genera with more conservationist relevance in Spain, including 74 species listed in the Spanish Red List of Threatened Vascular Plants [8], according to IUCN (International Union for Conservation of Nature) Criteria [16]
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