The present work aims to characterize native bacteria from the saline rhizosphere of Sulla carnosa and to identify promising rhizobacteria isolates able to ameliorate the salt tolerance of this species. Bacteria were screened in vitro for salt tolerance capacity and plant growth promoting characteristics (PGP). Selected NaCl-tolerant bacteria showing a high PGP potential were further characterized for plant promotion effects on the growth of S. carnosa under salt stress (200 mM NaCl). Three putative salt-tolerant strains that showed multiple PGP-traits identified as Acinetobacter sp. (Br3), Pseudomonas putida (Br18) and Curtobacterium sp. (Br20) were selected for inoculation study. In a greenhouse experiment, NaCl significantly disturbed physiological parameters in non-inoculated S. carnosa. In these plants, NaCl reduced growth, increased foliar proline and malondialdehyde concomitant to Na + shoot concentrations. However, bacterial inoculation with selected PGP isolates ameliorated significantly plant growth and alleviated salt-induced physiological disturbances. Hence, as compared to non-inoculated plants, inoculation provided a significant increase in dry biomass and increased photosynthetic efficiency and chlorophyll leaf content under saline condition. Additional analysis showed that microbial inoculation also enhanced total soluble sugars content and antioxidant enzymes activities thereby preventing reactive oxygen species (ROS)-induced oxidative damage in plants. These results suggest that the inoculation of NaCl-stressed plants with selected salt-tolerant PGPR inocula exert beneficial effects on plant growth by alleviating salt-induced toxicity stress on plant growth and development.

It has previously been shown that certain halophytes can grow and produce biomass despite of the contamination of their saline biotopes with toxic metals. This suggests that these plants are able to cope with both salinity and heavy metal constraints. NaCl is well tolerated by halophytes and apparently can modulate their responses to Cd. However, the underlying mechanisms remain unclear. This study explores the impact of NaCl on growth, Cd accumulation, and Cd speciation in tissues of the halophyte Sesuvium portulacastrum. Seedlings of S. portulacastrum were exposed during 1 month to 0, 25, and 50 μM Cd combined with low salinity (LS, 0.09 mM NaCl) or high salinity (HS, 200 mM NaCl) levels. Growth parameters and total tissue Cd concentrations were determined, in leaves, stems, and root. Moreover, Cd speciation in these organs was assessed by specific extraction procedures. Results showed that, at LS, Cd induced chlorosis and necrosis and drastically reduced plant growth. However, addition of 200 mM NaCl to Cd containing medium alleviated significantly Cd toxicity symptoms and restored plant growth. NaCl reduced the concentration of Cd in the shoots; nevertheless, due to maintenance of higher biomass under HS, the quantity of accumulated Cd was not modified. NaCl modified the chemical form of Cd in the tissues by increasing the proportion of Cd bound to pectates, proteins, and chloride suggesting that this change in speciation is involved in the positive impact of NaCl on Cd tolerance. We concluded that the tolerance of S. portulacastrum to Cd was enhanced by NaCl. This effect is rather governed by the modification of the speciation of the accumulated Cd than by the reduction of Cd absorption and translocation.