Effect of salinity stress on the physiological characteristics, phenolic compounds and antioxidant activity of Thymus vulgaris L. and Thymus daenensis Celak

Salinity stress is one of the most important challenges in agriculture systems. The present work was aimed to evaluated the effects of saline irrigation, using different NaCl concentrations (0, 30, 60, and 90 mM), on growth, physiological characteristics, phenolic compounds, and antioxidant activity of Thymus vulgaris and Thymus daenensis, that are two of the most important medicinal and aromatic plants in Iran. An analytical method based on HPLC-DAD has been developed to identify the main metabolites (mainly phenolic compounds) in thyme extracts. The results indicated that concentrations of 60 and 90 mM NaCl significantly decreased the plant dry matter production by about 28 and 40% in T. vulgaris and 34 and 39% in T. daenensis, respectively, compared with untreated plants. Application of NaCl also induced an increase in Na+content in shoots and leaves while the K+ and Ca2+contents decreased with the salinity stress. Total phenolic content increased by around 20% after the application of 60 mM NaCl, compared with control plants. Also, an increase in leaf flavonoid content by 38.6% and 36.6% was observed in plants grown under salt stress conditions after the application of 60 and 90 mM NaCl, respectively. Both investigated species were rich in phenolic acids, flavonoids, and phenolic monoterpenes. Cinnamic acid was the major constituent in both species. This compound increased by 31.4% in T. vulgaris treated with 60 mM NaCl compared with the control. Concentrations of 60 and 90 mM NaCl increased significantly the amount of gallic and rosmarinic acids in T. vulgaris (25 and 31.6%, respectively) and T. daenensis (20.4 and 27.6%, respectively). On the other hand, the mentioned NaCl concentrations did not significantly change the content of caffeic, syringic, and vanillic acids in T. vulgaris. Interestingly, the higher amount of chlorogenic acid (increase of 4.4%) in T. vulgaris was found under control condition, whereas in T. daenensis this compound increased when salinity stress intensified. The main outcome of the present study was the en- hancement of thyme phenolic content under salt stress treatments. Furthermore, salinity stress significantly influenced the antioxidant activities of plant extracts and may be recommended as an appropriate approach to enhance the antioxidant capacity of medicinal plants. In conclusion, the obtained data demonstrated that salinity stress decreased significantly the yield of both species, whereas improved the phenolic contents and antioxidant capacity of thyme plants

Effect of salinity stress on the physiological characteristics, phenolic compounds and antioxidant activity of Thymus vulgaris L. and Thymus daenensis Celak

Salinity stress is one of the most important challenges in agriculture systems. The present work was aimed to evaluated the effects of saline irrigation, using different NaCl concentrations (0, 30, 60, and 90 mM), on growth, physiological characteristics, phenolic compounds, and antioxidant activity of Thymus vulgaris and Thymus daenensis, that are two of the most important medicinal and aromatic plants in Iran. An analytical method based on HPLC-DAD has been developed to identify the main metabolites (mainly phenolic compounds) in thyme extracts. The results indicated that concentrations of 60 and 90 mM NaCl significantly decreased the plant dry matter production by about 28 and 40% in T. vulgaris and 34 and 39% in T. daenensis, respectively, compared with untreated plants. Application of NaCl also induced an increase in Na+content in shoots and leaves while the K+ and Ca2+contents decreased with the salinity stress. Total phenolic content increased by around 20% after the application of 60 mM NaCl, compared with control plants. Also, an increase in leaf flavonoid content by 38.6% and 36.6% was observed in plants grown under salt stress conditions after the application of 60 and 90 mM NaCl, respectively. Both investigated species were rich in phenolic acids, flavonoids, and phenolic monoterpenes. Cinnamic acid was the major constituent in both species. This compound increased by 31.4% in T. vulgaris treated with 60 mM NaCl compared with the control. Concentrations of 60 and 90 mM NaCl increased significantly the amount of gallic and rosmarinic acids in T. vulgaris (25 and 31.6%, respectively) and T. daenensis (20.4 and 27.6%, respectively). On the other hand, the mentioned NaCl concentrations did not significantly change the content of caffeic, syringic, and vanillic acids in T. vulgaris. Interestingly, the higher amount of chlorogenic acid (increase of 4.4%) in T. vulgaris was found under control condition, whereas in T. daenensis this compound increased when salinity stress intensified. The main outcome of the present study was the en- hancement of thyme phenolic content under salt stress treatments. Furthermore, salinity stress significantly influenced the antioxidant activities of plant extracts and may be recommended as an appropriate approach to enhance the antioxidant capacity of medicinal plants. In conclusion, the obtained data demonstrated that salinity stress decreased significantly the yield of both species, whereas improved the phenolic contents and antioxidant capacity of thyme plants

Natural diversity in phenolic components and antioxidant properties of oregano (Origanum vulgare L.) accessions, grown under the same conditions

Oregano (Origanum vulgare L.) is a rich source of biologically active components such as phenolic compounds. Here, seven pot grown O. vulgare accessions belonging to three subspecies (subsp. virens, subsp. vulgare and subsp. gracile) were investigated for their content in sixteen bioactive phenolic compounds as well as their antioxidant capacities (DPPH• and FRAP tests), total phenolic content (TPC) and total flavonoid content (TFC) in order to identify the most suitable ones on an industrial level. HPLC analyses showed that rosmarinic acid (659.6–1646.9 mg/100 g DW) was by far the most abundant constituent, followed by luteolin (46.5–345.4 mg/100 g DW), chicoric acid (36.3–212.5 mg/100 g DW), coumarin (65.7–193.9 mg/100 g DW) and quercetin (10.6–106.1 mg/100 g DW), with variability in concentration depending on the accession and subspecies. The highest level of rosmarinic acid and TPC was obtained from Ardabil accession (subsp. virens). There was a significant and positive correlation between rosmarinic acid and antioxidant activity (r = 0.46). TFC significantly correlated to TPC (r = 0.57) as well as to chicoric acid (r = 0.73). Cluster (CA) and principal component (PCA) analyses classified the investigated accessions in three different groups. Such natural variabilities in phenolics provide the possibility of using elite plants for nutraceutical and pharmaceutical industries and domestication of highly antioxidative accessions of oregano

Application of combined fertilizers improves biomass, essential oil yield, aroma profile, and antioxidant properties of Thymus daenensis Celak

Thymus daenensis Celak., also known as denaian thyme, is an endemic and endangered medicinal herb, having valuable therapeutic properties in the Iranian traditional medicine. In the present study, a two years’ field experiment was conducted to study the influence of organic and inorganic fertilizers on biomass, essential oil yield, essential oil content and compositions and antioxidant activity of denaian thyme in southwest of Iran. The treatments were: no fertilizer (control), chemical fertilizer (CF; NPK at 100-150-100 kg ha-18 ), cow manure, vermicompost (VC) and combined fertilizers (chemical fertilizer + cow manure + vermicompost). Application of combined fertilizers significantly increased the biomass and essential oil yield of denaian thyme as compared with control, in the first and second year, by 39.61% and 68.62%, respectively. Application of fertilizers, however, significantly affected the essential oil compositions of the plants in both growing years. The essential oil of T. daenensis was rich in the phenolic monoterpene thymol. The highest amount of thymol was obtained under application of combined fertilizers in both years. The antioxidant activity of T. daenensis methanolic extracts, evaluated by the DPPH assay, increased (10.41% compared with control) under application of combined fertilizers in the second year. In both years, the N content of the soil increased after treatment with combined fertilizers (around 43% higher over the control). Alike, soil fertility parameters such as P and K showed a marked improvement in all treatments over the control. Results of this study showed that the combined application offertilizers enhanced biomass and essential oil yield and improved the soil characteristics, antioxidant properties and aroma profile