Background and Objective: Verbena officinalis is a valuable medicinal plant known for its rich content of phenolic compounds, flavonoids, and other secondary metabolites, which contribute to its remarkable antioxidant and therapeutic properties. Despite its widespread use in traditional medicine, no study has simultaneously evaluated the changes in total phenolic content, total flavonoid content, and antioxidant activity among different plant organs across various phenological stages in the natural habitats of Golestan Province, Iran. Therefore, the present study was conducted to investigate the total phenolic content, total flavonoid content, and antioxidant activity of different organs of V. officinalis at different phenological stages in order to determine the most suitable harvesting stage and plant organ.
Materials and Methods: This field study was carried out in the natural habitat of Qaleh-Miran, Golestan Province, Iran. Wild vervain plants were randomly collected at three phenological stages: vegetative, flowering, and seed-setting. At each stage, leaves, stems, and roots were harvested separately. After washing, the samples were shade-dried under indirect light and manually ground into powder. Total phenolic content was determined using the Folin–Ciocalteu colorimetric assay, total flavonoid content by the aluminum chloride colorimetric method, and antioxidant activity using the DPPH free radical scavenging assay. In addition, the possibility of essential oil extraction from different plant organs at different phenological stages was evaluated using the hydrodistillation method with a Clevenger apparatus. The obtained data were analyzed using analysis of variance (ANOVA), followed by appropriate mean comparison tests.
Results: The results demonstrated that both phenological stage and plant organ had significant effects on total phenolic content, total flavonoid content, and antioxidant activity of wild V. officinalis. The highest total phenolic content (62.57 mg GAE g⁻¹ extract), total flavonoid content (16.29 mg QE g⁻¹ extract), and antioxidant activity (89.13% DPPH radical inhibition) were recorded in the leaves at the flowering stage. In contrast, the lowest total phenolic content (24.82 mg GAE g⁻¹ extract) was observed in the roots at the seed-setting stage, whereas the lowest total flavonoid content (0.75 mg QE g⁻¹ extract) and antioxidant activity (43.31% DPPH radical inhibition) were recorded in the roots at the vegetative stage.
These findings indicate that the accumulation of phenolic and flavonoid compounds increases with the transition to the flowering stage. No extractable essential oil was obtained under the conditions of the present study. Furthermore, indigenous knowledge surveys revealed that the leaves are the most frequently used medicinal part of the plant by local people, which is consistent with the phytochemical findings obtained in this study.
Conclusion: The findings of this study indicate that the flowering stage and the leaves are the most suitable harvesting stage and plant organs for obtaining the highest levels of bioactive compounds. These results can contribute to medicinal plant utilization programs, harvesting management, conservation, and the sustainable use of wild V. officinalis. Overall, this study demonstrated that phenological stage and plant organ play a decisive role in the accumulation of bioactive compounds in wild vervain and may significantly influence its medicinal quality. Therefore, selecting the appropriate harvesting stage and plant organ can improve the yield of biologically active constituents, optimize the utilization of this medicinal species, support the development of herbal products, and contribute to the conservation of its natural populations. In addition, the findings provide a valuable basis for future studies on other secondary metabolites and the biological activities of this species under different climatic conditions across Iran. |