## 4. Discussion
The results relating to the chlorophyll contents showed that the salinity stress led to a significant reduction in the chlorophyll contents [42; 43; 44]. This decrease could be due to high osmotic stress resulting in reduced assimilation of essential minerals [45]. A deficiency in these minerals, especially N, could lead to inhibition of the formation of chlorophyll molecules [44]. Additionally, a high concentration of salts in the leaves could cause overproduction of reactive oxygen species (ROS) and destroy all protein components of the chloroplast [43]. On the other hand, inoculation of PGPR resulted in an improvement in the chlorophyll and carotenoid contents compared with the respective uninoculated controls. Improvement by PGPRs of the chlorophyll content in many plants cultivated under abiotic stress conditions had been previously described [35; 46]. It was noted that for the different treatments the multi-strain combination showed a significant improvement in the chlorophyll and carotenoid contents compared to the other isolates and the uninoculated controls [47]. Application of a multi-strain consortium could be due to increased solubilization and mobilization of minerals. Plants can also protect themselves from salt stress by accumulating compatible solutes such as sugars and amino acids for intercellular osmotic adjustment or by synthesizing antioxidant enzymes, which decrease excessive ROS and maintain membrane stability [48]. The highest chlorophyll and carotenoid contents were recorded in the cases inoculated by the different combinations in soils 1 and 2. However in soil 3, despite its low salinity compared to soil 2, the chlorophyll and carotenoids contents were lower and similar for the different treatments excepted for OR15 strain which seemed to improve the carotenoid content. These results confirmed that factors affecting plant yield are not only limited to chlorophyll content and that photosynthetic efficiency is also linked to a range of factors [49]. Under salinity stress in soil 2, the BR5 strain caused a strong increase in the chlorophyll content which could be due to the halotolerant nature of this strain reducing the sodium accumulation which was associated with higher chlorophyll content. The reduction of chlorophyll is possibly related to the sensitivity of one of the stages of its biosynthesis to sodium chloride. The latter affects the chlorophyll b biosynthesis pathway less [50]. Analysis of the total soluble sugars content revealed that the saline stress significantly increased the quantity of these molecules in the plant, essentially at the root level, in the case of soils 2 and 3. The accumulation of total sugars in salt-stressed plants is a means of osmotic adjustment. These molecules play a vital role in osmoprotectant and carbon storage. Their accumulation induced by salt stress was further enhanced by PGPR. However, this was variable depending on the type of treatment. It was significantly increased by inoculation with RB13 or BR5 + RB13, OR15 + RB13, or BR5 + OR15 + RB13 co-inoculations. The increase in total sugars in stressed inoculated plants had been attributed to higher photosynthesis and starch degradation [51]. Therefore, an increase in the total sugars content following inoculation or co-inoculation with PGPRs significantly contributes to the growth of plants against salt stress by modulating defense strategies. An increase in protein content was recorded in plants inoculated with PGPRs. Inoculation improved protein content, which may be due to a decrease in the effect of salinity by PGPR strains and an increase in N uptake by the plant, which is an important protein constituent. The increase in antioxidant activity reduces the damage of proteins and amino acids. Many studies reported that PGPR-induced increase in leaf protein content in cereals and legumes [52]. Saline stress tolerance mechanisms often include the accumulation of proline. In our study, foliar and root proline concentrations were high in plants grown in saline soil (soil 2).