چكيده انگليسي :
Borage (Borago officinalis L.) is an important medicinal species, as it contains mucilages, phenolic compounds, alkaloids, and gama-linolenic acid. Salinity is one of the most serious environmental constraints to the plant growth, dry mass, and economic yield. Melatonin is a plant growth regulator with signaling and scavenging roles that improves the antioxidative capacity of the stressed plants. Calcium is a ubiquitous structural and signalling molecule with critical roles in signalling responses to different stresses. Beneficial roles of melatonin and calcium in mitigating salt stress-induced alterations in physiological, biochemical and growth attributes have been confirmed for a number of crop species, but not for borage. Hence, a pot experiment was conducted in which two borage genotypes were subjected either to non-saline (Control) or 100 mM NaCl (Salt), Salt + 100 µM melatonin (Salt+Mel), Salt + 5 mM Ca (Salt+Ca), Salt + Mel + 5 mM Ca (Salt+Mel+Ca), Control + Mel, Control + Ca, Control + Mel + Ca treatments in three replicates. Salt-exposed plants indicated increases in the malondialdehyde, H2O2, proline, root and leaf Na+, and total phenolic concentrations, Na+/K+, and electrolyte leakage, but decreases in the chlorophylls and carotenoids concentrations, catalase and ascorbate peroxidase activities, leaf relative water content, root and leaf K+ and Ca+2 concentrations, root and shoot fresh and dry masses, compared with the control plants. Amending the salt-stressed plants with external Ca, Mel, and Mel + Ca resulted in decreases in malondialdehyde, H2O2, root and leaf Na+ concentrations, Na+/K+, and electrolyte leakage, but increases in the chlorophylls and carotenoids, proline, total phenolic, root and leaf K+ and Ca+2 concentrations, catalase and ascorbate peroxidase activities, leaf relative water content, root and shoot fresh and dry masses, and root volume compared with the plants that had not received these amendments. Our findings indicated for the first time that while harmful effects of salt were not substantial, the amendment with signal molecules such as Mel and Ca alone or in combination was effective in mitigating the adverse effects of salt on the physiological, biochemical, and growth attributes of borage. The novel finding that these signal molecules increase the total phenolic concentration potentiates borage as a valuable source for adding to the natural antioxidative properties of the pharmaceutical and food products.
Keywords: Borago officinalis, salt stress, plant stress signaling, Na+/K+, phenolics
