Crithmum maritimum (sea fennel) withstands high salinity, and to better understand how different protective mechanisms against salinity are activated, young seedlings were exposed to increasing concentrations of NaCl (0 to 512 mM) over six weeks. Plant survival and chlorophyll content were reduced at > 85 mM NaCl and growth was affected at ≥ 341 mM NaCl. Relative water content fell and Na + accumulated more in leaves than in roots. Induction of Na + /H + antiporter expression reached a maximum at 427 mM NaCl in both tissues. Salinity induced the accumulation of proline, soluble sugars and glycine betaine. All three accumulated to higher levels in leaves than roots and greatest accumulation was after 6 weeks and the highest salt concentrations. Hydrogen peroxide levels fell with increasing salinity in leaves, while ascorbic acid and catalase activity rose. Overall, the most dramatic changes occurred after six weeks of saline stress but different mechanisms were activated at different salinity thresholds and in the two tissues. Key salinity thresholds in the response of Crithmum maritimum to salinity stress are identified activating different mechanisms. At 85 mM NaCl roots reach osmotic adjustment, at 171 mM further osmolyte protection mechanisms are activated, at 256 mM NaCl leaves reach osmotic adjustment, at 341 mM plant growth is affected and at the highest salinity tested, 512 mM, protective mechanisms are affected in leaves but not in roots.

No abstract

Understanding how halophytes survive high soil salinity in realistic long-term experiments is important for strategies to mitigate the effects of increasing soil salinity worldwide. Protective mechanisms in halophytes enabling survival include sequestration of salt via Na+/H+ antiporters, synthesis and accumulation of osmolytes, and activation of protective mechanisms against reactive oxygen species (ROS). Protective mechanisms elicited by a single step-up to a range of NaCl treatments (34–256 mM) in two populations of the halophyte Atriplex halimus L. from contrasting environments (arid steppe and saline coastline) were compared over 6 weeks. The coastal population survived significantly better at high salinity compared with the steppe population, although in both populations, salinity inhibited growth. Increased Na+ and K+ concentration was accompanied by higher induction of Na+/H+ antiporter gene expression in coastal than in steppe population leaves. Osmolytes increased more significantly in the coastal than in the steppe population with greater induction of choline mono-oxygenase gene expression. Activation of ROS scavenging mechanisms was greater in coastal than in steppe plants. Differential responses found through time, in different salt concentrations, and between leaves and roots indicate a finely tuned response. Sharp changes in responses at 171 mM NaCl indicate that different mechanisms may be invoked at different stress levels.

L’extraction des huiles essentielles a été effectuée par hydrodistillation à partir des feuilles de Tetraclinis articulata et Thymus vulgaris. Les rendements obtenus en huiles essentielles sont 2,70 % pour Thymus vulgaris et 1,10 % pour Tetraclinis articulata. L’analyse chimique révèle que les huiles essentielles de Thymus vulgaris appartiennent au chémotype Thymus vulgaris à carvacrol (48,56 %) et les huiles essentielles de Teraclinis articulata sont de chémotype Tetraclinis articulata à camphre (28,03 %). Les résultats de l’activité antifongique des huiles essentielles des feuilles de Thymus vulgaris et Tetraclinis articulata montrent un fort pouvoir inhibiteur sur la croissance mycélienne radiale d’Aspergillus flavus, de Penicillium digitatum et de Fusarium sp. Ils montrent également que l’activité antifongique augmente avec l’augmentation de la concentration des huiles essentielles testées. Celles-ci peuvent être utilisées comme agents antifongiques potentiels contre les champignons pathogènes.