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This study was conducted to investigate the response of four barley cultivars (Reyhan03, Yousef, Afzal, and Khatam) to salinity stress at 0 (control), 100, 200 and 300 mM levels as a factorial experiment, within the randomized complete block design in three replications in a greenhouse, using the Hoagland solution. The physiological and biochemical properties including dry weight and RWC, photosynthesis pigments, K⁺/Na⁺, osmotic adjustments (soluble sugars, glycine betaine, proline), hydrogen peroxide and antioxidants enzymes (catalase and peroxidase) in root and shoot of barley cultivars were evaluated in saline and non-saline conditions. To determine the relationship between growth performance and the physiological and biochemical properties, the correlation between the properties and causality analysis was examined. Results obtained from comparing the mean among the treatment combinations showed that the salinity stress reduced the dry weight, photosynthesis pigments, and K⁺/Na⁺, while it increased the soluble sugars, glycine betaine, proline, H₂O₂, catalase and peroxidase in the root and shoot of barley cultivars. Correlation analysis indicated that potassium in the shoot had the most positive and significant correlation coefficient (r= 0.86) with the dry matter of shoot. The stepwise regression analysis showed that the root dry weight, catalase of root and shoot, H₂O₂ of shoot and K⁺/Na⁺ of shoot contributed to the performance. Causality analysis revealed that the root dry weight, K⁺/Na⁺ of shoot, and catalase of shoot were highly important as they had a direct positive and significant impacts on the performance of shoot dry matter.

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Salinity stress is one of the most important environmental stresses that decrease crop growth and yield. Barley is an important crop known as the salt-tolerant plant in cereals. In this study, the salt stress-responsive root transcriptome of tolerant (Afzal) and susceptible (Yusef) cultivars was investigated. The sequencing of mRNA transcripts (termed RNA-Seq) was performed using the Illumina HiSeq platform after filtering for RNA with 3' polyadenylated tails to include only mRNA. The Tuxedo pipeline was used to identify the altered expression of transcripts. Sequencing results showed that, after initial trimming of the reads, more than 20 million reads (92%) remained for all samples, of which 88% were aligned with the barley genome. Bioinformatics analysis showed the altered genes expressions in various processes such as membrane antiporter and transporter activity, an antioxidant, wide range of kinase and phosphatase cascades, internal signal transduction, metabolism of carbohydrates, amino acids, and lipids, binding processes, response to plant hormones, catalytic activity, and cell wall organization. Gene network analysis revealed that key genes, including proteins involved in systemic acquired resistance, peroxidase family proteins, cyclin-dependent protein kinase, phosphatidylinositol kinase, auxin-carrying proteins, mannose 6 phosphate isomerase, helicases and transcription factors play an important role in salt tolerance. These data can be used as a valuable source in future studies for genetic manipulation of barley and development of salinity tolerant cultivars.