Pulicaria odora essential oil: a potential source of eco- friendly antioxidants and allelochemicals

Abstract

Several plants are potential sources of natural antioxidants and can also stimulate or inhibit the germination and growth of weeds due to the production of secondary metabolites. Pulicaria odora, medicinal and aromatic plant, spontane­ous and widespread in Morocco, is widely used by the local population for its medicinal properties. In this study, allelopathic effects and antioxidant activities of P. odora roots essential oil (EO), and the main components, at different concentrations were investigated. The EO was isolated by hydrodistillation using a Clevenger apparatus. GC analysis of the EO indicated the presence of 75 volatile compounds. Among them, two accounted for 89.96% of the oil. The EO was then subjected to column chromatography on silica gel. Two major constituents were isolated and identified by ¹H NMR, ¹³C NMR as isobutyric acid 2-isopropyl-4-methyl-phenylester (1), and 2-isopropyl-4-methylphenol (2). Following the results obtained by DPPH, H₂O_2, and FRAP methods, EO and its main components possess an interesting antioxidant effect.  The significantly (p<0.05) highest antioxidant properties were exhibited by the phenolic compound 2 followed by EO, whereas lowest from compound 1. The allelopathic effect of EO and its main components at different concentrations (7.81-500 μg/mL) was also tested against two forage species. Data obtained showed that EO, compounds 1 and 2 inhibited significantly (p<0.05) seeds growth of both tested plants (M. sativa and M. falcata). A dose-response relationship was found in seed germination and seedling growth inhibition of the two tested plants. Overall, phenolic component 2 exhibited the highest phytotoxicity. Compound 1 and EO have moderate phytotoxic effects on the growth of the two seeds essayed. In addition, results indicated that the phytotoxic effect of the EO (or its main compounds) also depended on the tested species.

Several plants are potential sources of natural antioxidants and can also stimulate or inhibit the germination and growth of weeds due to the production of secondary metabolites. Pulicaria odora, medicinal and aromatic plant, spontane­ous and widespread in Morocco, is widely used by the local population for its medicinal properties. In this study, allelopathic effects and antioxidant activities of P. odora roots essential oil (EO), and the main components, at different concentrations were investigated. The EO was isolated by hydrodistillation using a Clevenger apparatus. GC analysis of the EO indicated the presence of 75 volatile compounds. Among them, two accounted for 89.96% of the oil. The EO was then subjected to column chromatography on silica gel. Two major constituents were isolated and identified by ¹H NMR, ¹³C NMR as isobutyric acid 2-isopropyl-4-methyl-phenylester (1), and 2-isopropyl-4-methylphenol (2). Following the results obtained by DPPH, H₂O_2, and FRAP methods, EO and its main components possess an interesting antioxidant effect.  The significantly (p<0.05) highest antioxidant properties were exhibited by the phenolic compound 2 followed by EO, whereas lowest from compound 1. The allelopathic effect of EO and its main components at different concentrations (7.81-500 μg/mL) was also tested against two forage species. Data obtained showed that EO, compounds 1 and 2 inhibited significantly (p<0.05) seeds growth of both tested plants (M. sativa and M. falcata). A dose-response relationship was found in seed germination and seedling growth inhibition of the two tested plants. Overall, phenolic component 2 exhibited the highest phytotoxicity. Compound 1 and EO have moderate phytotoxic effects on the growth of the two seeds essayed. In addition, results indicated that the phytotoxic effect of the EO (or its main compounds) also depended on the tested species.