Changes in growth, photosynthetic pigments and antioxidant system of Hordeum vulgare plant grown under salinity stress via signal molecules application

During two successive winter seasons (2018/2019 and 2019/2020) at the greenhouse of the National Research Centre, Dokki, Cairo, Egypt, a pot experiment was conducted to compare the physiological effect of arginine (l-arg) at 10, 20 and 30 mM and sodium nitroprusside (SNP) at 0.25, 0.50 and 0.75 mM on barley plants grown under salinity stress conditions. The results show that salinity stress (4 g NaCl/L) significantly decreased growth parameters, photosynthetic pigments, indole acetic acid (IAA), and nitrate reductase (NR) accompanied by significant increases in hydrogen peroxide (H₂O₂), malodialdehyde (MDA), lipoxygenase enzyme activity (LOX), activity of enzymatic antioxidant system {superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (ASP), glutathione reductase (GR)}, non- enzymatic antioxidant system (phenolic compound, glutathione, tocopherol), DPPH% and compatible solutes (proline, soluble protein and total soluble sugar) of barley plants. All applied treatments alleviated the harmful effect of salinity stress on growth of barely plant irrigated with saline solution by increasing photosynthetic pigments, IAA, NR, enzymatic antioxidant system, non- enzymatic antioxidant system and compatible solutes accompanied by significant decreases in H₂O₂, MDA, activity of LOX. It is worthy to mention that the intense effect was due to sodium nitroprusside at 0.50 mM in barley plant either irrigated with tap water or saline solution. Sodium nitroprusside at 0.50 mM significantly increased total photosynthetic pigments by 41%, IAA by 127%, NR by 22.18 %, SOD by 70.78%, CAT by 32.39%, POX by 46.45%, ASP by 25.25%, GR by 85.25 %, proline content by 43.98%, soluble protein by 39.80% and total soluble sugar by 34.19% respectively.