Abstract
Salinity stress as a major agricultural limiting factor may influence the chemical composition and bioactivity of Rosmarinus officinallis L. essential oils and leaf extracts. The application of salicylic acid (SA) hormone may alleviate salinity stress by modifying the chemical composition, gene expression and bioactivity of plant secondary metabolites. In this study, SA was applied to enhance salinity tolerance in R. officinallis. R. officinallis plants were subjected to saline water every 2 days (640, 2,000, and 4,000 ppm NaCl) and 4 biweekly sprays of SA at 0, 100, 200, and 300 ppm for 8 weeks. Simulated salinity reduced all vegetative growth parameters such as plant height, plant branches and fresh and dry weights. However, SA treatments significantly enhanced these plant growth and morphological traits under salinity stress. Salinity affected specific major essential oils components causing reductions in α-pinene, β-pinene, and cineole along with sharp increases in linalool, camphor, borneol, and verbenone. SA applications at 100–300 ppm largely reversed the effects of salinity. Interestingly, SA treatments mitigated salinity stress effects by increasing the total phenolic, chlorophyll, carbohydrates, and proline contents of leaves along with decline in sodium and chloride. Importantly, this study also proved that SA may stimulate the antioxidant enzymatic mechanism pathway including catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) as well as increasing the non-enzymatic antioxidants such as free and total ascorbate in plants subjected to salinity. Quantitative real-time PCR analysis revealed that APX and 3 SOD genes showed higher levels in SA-treated rosemary under salinity stress, when compared to non-sprayed plants. Moreover, the expression level of selected genes conferring tolerance to salinity (bZIP62, DREB2, ERF3, and OLPb) were enhanced in SA-treated rosemary under salt stress, indicating that SA treatment resulted in the modulation of such genes expression which in turn enhanced rosemary tolerance to salinity stress.
Highlights
Salinity as abiotic stress is a permanent major threat to the agriculture industry worldwide and usually associated with morphological, physiological, and biochemical responses (Nazar et al, 2011; Gupta and Huang, 2014; Khan et al, 2014; AcostaMotos et al, 2017; Quan et al, 2017)
Some investigations indicated that plant secondary metabolites might be influenced by salicylic acid (SA) treatments such as the essential oils in Ocimum basilicum L. (Mirzajani et al, 2015), oleoresins in Pinus (Rodrigues and Fett-Neto, 2009), and triterpenes in Nigella (Elyasi et al, 2016)
The results showed that the ascorbate peroxidase (APX) and 3 superoxide dismutase (SOD) genes revealed higher levels in SA-treated rosemary under saline, with respect to non-sprayed plants (Figure 4), indicating the important roles of salicylic acid and antioxidant enzymes under abiotic stresses
Summary
Salinity as abiotic stress is a permanent major threat to the agriculture industry worldwide and usually associated with morphological (e.g., reduced growth and productivity), physiological (e.g., reduction of gas exchange parameters and homeostasis), and biochemical (e.g., oxidative stress with elevated reactive oxygen species content) responses (Nazar et al, 2011; Gupta and Huang, 2014; Khan et al, 2014; AcostaMotos et al, 2017; Quan et al, 2017). Several investigations indicated that salicylic acid influences gas exchange parameters and water composition (Stevens et al, 2006), increases phenolics accumulation (Kovácik et al, 2009), enhances the oxidative stress tolerance (Li et al, 2014), and may alleviate osmotic stress (Nazar et al, 2011). Some investigations indicated that plant secondary metabolites might be influenced by SA treatments such as the essential oils in Ocimum basilicum L. (Mirzajani et al, 2015), oleoresins in Pinus (Rodrigues and Fett-Neto, 2009), and triterpenes in Nigella (Elyasi et al, 2016)
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