Freshwater scarcity and other abiotic factors, such as climate and soil salinity in the Near East and North Africa (NENA) region, are affecting crop production. Therefore, farmers are looking for salt-tolerant crops that can successfully be grown in these harsh environments using poor-quality groundwater. Barley is the main staple food crop for most of the countries of this region, including Tunisia. In this study, the AquaCrop model with a salinity module was used to evaluate the performance of two barley varieties contrasted for their resistance to salinity in three contrasted agro-climatic areas in Tunisia. These zones represent sub-humid, semi-arid, and arid climates. The model was calibrated and evaluated using field data collected from two cropping seasons (2012–14), then the calibrated model was used to develop different scenarios under irrigation with saline water from 5, 10 to 15 dS m⁻¹. The scenario results indicate that biomass and yield were reduced by 40% and 27% in the semi-arid region (KAI) by increasing the irrigation water salinity from 5 to 15 dS m⁻¹, respectively. For the salt-sensitive variety, the reductions in biomass and grain yield were about 70%, respectively, although overall biomass and yield in the arid region (MED) were lower than in the KAI area, mainly with increasing salinity levels. Under the same environmental conditions, biomass and yield reductions for the salt-tolerant barley variety were only 16% and 8%. For the salt-sensitive variety, the biomass and grain yield reductions in the MED area were about 12% and 43%, respectively, with a similar increase in the salinity levels. Similar trends were visible in water productivities. Interestingly, biomass, grain yield, and water productivity values for both barley varieties were comparable in the sub-humid region (BEJ) that does not suffer from salt stress. However, the results confirm the interest of cultivating a variety tolerant to salinity in environments subjected to salt stress. Therefore, farmers can grow both varieties in the rainfed of BEJ; however, in KAI and MED areas where irrigation is necessary for crop growth, the salt-tolerant barley variety should be preferred. Indeed, the water cost will be reduced by 49% through growing a tolerant variety irrigated with saline water of 15 dS m⁻¹.

The interaction between salinity and nitrogen metabolism has been investigated in two barley landraces, one tolerant (“100/1B”) and one susceptible to salinity (“Barley medenine”) from the Middle East and North Africa (MENA) region. Barley plants were exposed to 50 mM NaCl for 7 days; then, salinity was increased to 150 mM NaCl in the presence (10 mM) or limitation (1 mM) of ammonium as a nitrogen source. Upon salinity, “100/1B” was shown to support N assimilation by enhancing the glutamine synthetase (GS) and glutamine oxoglutarate aminotransferase (GOGAT) cycle under high N, and the stimulation of the glutamate dehydrogenase (GDH) pathway under low N treatment. In “Barley medenine”, salinity reduced the GS/GOGAT cycle, and increased GDH activity. Upon salinity, Heat Shock Proteins 70 and PEPC remained unchanged in “100/1B”, while they decreased in “Barley medenine”. The tolerance degree is a determining factor in enzymes’ occurrence and regulation: exposed to salinity, “100/1B” rapidly increased APX and PEPC activities, while this was delayed in “Barley medenine”. Salinity increased cyt-G6PDH levels in “100/1B”, while “Barley medenine” showed a decrease in G6PDH isoforms. Correlation analyses confirm GOGAT was related to G6PDH; GDH and APX with PEPC in “100/1B” under moderate salinity; severe salinity correlated GDH with G6PDH and PEPC. In “Barley medenine” under salinity, GOGAT was correlated with G6PDH, while APX showed a relation with PEPC. Therefore, specific enzymatic activities and occurrence can be used to determine stress responsiveness of different landraces. We suggest that the rapid increase in G6PDH, APX, and nitrogen assimilation enzymes activities represents an index of tolerance in “100/1B” and a stress symptom in “Barley medenine”.

This study aims to investigate the activities and expression of enzymes of primary metabolism and relate these data with the growth performance of three different durum wheat genotypes (Maali; YT13; and ON66) under osmotic stress. Growth traits—including plant height, dry weight (DW) and relative water content (RWC)—were measured to classify genotypes depending on their tolerance to stress. Several enzymes were investigated: Ascorbate peroxidase (APX), Glutamine Synthetase (GS), Glutamine dehydrogenase (GDH), Glutamate synthase (GOGAT), Glucose 6-phosphate dehydrogenase (G6PDH), and Phosphoenolpyruvate Carboxylase (PEPC). The expression of the cytosolic and plastidic glutamine synthetase (TaGS1 and TaGS2), high affinity nitrate transporters (TaNRT2.3) and Glutamate dehydrogenase (TaGDH) were also detected by qRT-PCR. The results indicated different growth performances among genotypes, indicating Maali and YT13 as tolerant genotypes and ON66 as a drought-susceptible variety. Data showed a decrease in PEPC and increase in APX activities under osmotic stress; a slight decrease in GS activity was observed, together with an increase in G6PDH in all genotypes; GS and NRT2 expressions changed in a similar pattern in the different genotypes. Interestingly, Maali and YT13 showed higher transcript abundance for GDH under stress compared to ON66, suggesting the implication of GDH in protective phenomena upon osmotic stress.