## 3 Discussion
As expected, the increase of NaCl in the environment led to an increase in the content of Na in the _H. portulacoides_ leaves and roots. This is normally associated with salt stress biomarkers due to the direct correlation between the accumulation of Na in the cell and plant salt toxicity [44; 45]. Besides, the increasing Na concentration in the medium will directly compete with other essential ions like K, resulting in the impairment of cellular functions regulated by potassium, such as enzyme activation, protein production, and photosynthesis [46; 47]. Nonetheless, our results, at mild salinity stress, showed that PGPR induced a significant reduction of the Na and Cl concentrations present in the roots, as well as a significant increase of the K and Ca contents in the leaf tissues. This may explain the significantly lower Na content found in the leaves of inoculated plants. This reveals superior maintenance of ionic homeostasis, indicated by the K: Na ratio in the tissues of inoculated plants. The increase of the Ca concentration in the leaves could serve as an ionic balance mechanism, allowing the cell membrane to maintain the K/Na selectivity [43]. The uptake of K and Ca due to PGPR inoculation has been demonstrated to result in the up-regulation of the antioxidant system and mitigation of salt stress-induced oxidative effects [48]. Furthermore, it has been described that rhizosphere inoculation by such halotolerant bacteria species may confer salt tolerance through sequestering Na\({}^{+}\) into vacuoles, expelling Na\({}^{+}\) from roots, and through the exertion of modulating attributes of the ion transporters involved [49; 50]. Leaf osmotic regulation is of crucial importance in salt stress plants [51]. The increased presence of organic osmolytes is a widespread plant strategy to prevent stress-induced damage to cellular organelles [52]. In halophyte plants, to counteract soil salinity, an accumulation of L-proline in leaf tissues is commonly observed. In addition to its osmoprotectant potential [53; 54], this amino acid is considered to play a pivotal role in the protection of cellular membrane structures, the activities of ROS scavenging enzymes, and the maintenance of leaf water content [55]. The proline content in leaves of _Hallimione portulacoides_ increased with increasing NaCl stress. This increase and concomitant leaf L-proline content were more pronounced in inoculated plants as compared to non-treated plants. The effect of the greater proline availability was clearly expressed in the leaf's relative water content, at 600 mM NaCl. It is also known that, as a nitrogen-containing amino acid, proline expression is enhanced when nitrogen is available, this relationship may be considered an important parameter explaining the more pronounced increase of proline concentration found in the inoculated samples [56; 57]. Regarding the pigment profiles, it was clear that _H. portulacoides_ plants were affected by the rise in salt concentration, revealing a salinity-induced shift in the metabolic activity from photo-harvesting to photoprotection. The role of the xanthophyll cycle in the photoprotection of PSII is a well-characterized energy dissipation mechanism commonly observed in all plants [58; 59]. The de-epoxidation state (DES) of luminal violaxanthin cycle pigments was found to be one of the most effective mechanisms for the dissipation of excess light energy, reducing the overload of energy within light-harvesting complexes (LHCs) [60; 61; 62]. Even though an increase of the de-epoxidation occurred at the highest test NaCl concentration, significant differences induced by bacterial inoculation were not found. However, the concentration of zeaxanthin was found to be significantly higher in the bio-augmented plants, at 0 mM and 400 mM NaCl. Zeaxanthin is characterized by having an important photoprotective role. It was found to enhance heat release. This parameter can be measured as non-photochemical quenching (NPQ) of excitation energy [63; 64]. Lutein plays a quasi-opposite role.