Evaluating salt tolerance mechanisms in two Tunisian barley landraces

Salt can be incredibly damaging to plants, impairing growth from germination to maturity. Salt disrupts the osmotic balance of plant cells whilst also causing oxidative damage, like other forms of environmental stress. This combination of osmotic and oxidative stress results in significant agricultural yield losses worldwide and this threat is increasing in arid and semi-arid areas due to rising global temperatures. For crop plants, increasing tolerance to salt will be crucial to ensure future food security.

The good news is that variation in salinity tolerance has already been found in several crop species. This is particularly evident in barley, with different genotypes displaying highly variable sensitivities to salt-stress. To overcome osmotic stress, tolerant genotypes tend to accumulate osmoprotectants like proline and soluble sugars. These osmoprotectants are the main actors of cellular osmotic adjustment used to maintain cytoplasmic water content. Oxidative stress on the other hand is partly balanced by antioxidant enzymatic scavenging compounds, such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT). It has been proposed that different isoforms of these antioxidant enzymes could be used as biochemical markers to breed for improved stress tolerance.

The regulation of growth in barley plants through osmotic adjustment, antioxidant genes expression, and enzymatic activities under salt stress. The color gradient indicates the level of involvement of the trait from low (light pink) to high (brown). Image credit: Ouertani *et al.*

In their new study published in AoBP, Ouertani et al. aimed to clarify the contributions of osmotic and oxidative stress components in leaves and roots of barley growth under salt stress. In the work, two Tunisian barley landraces contrasting in their sensitivity to salt-stress, Barrage Malleg (tolerant) and Saouef (sensitive), were subjected to severe salt stress. Seedlings were assessed for several growth traits, including proline and soluble sugar content, antioxidant enzyme (SOS, CAT and APX) activities and gene expression levels.

The results of the study showed that the salt tolerant landrace Barrage Malleg grew faster, accumulated more proline and soluble sugars, and had a stronger antioxidant system than Saouef when grown under extreme salinity. Stepwise regression analysis indicated that under severe salt stress the most important trait for barley growth was the copper/zinc-SOD gene expression level, suggesting that alleviating oxidative stress and maintaining cell osmotic homeostasis is a priority. Ouertani et al. hope that future research will build upon the findings of their work and provide a deeper understanding of the tolerance mechanisms afforded by copper/zinc-SOD expression, activity and related metabolism.