Effects of water limitation on the production of key secondary metabolites with medicinal properties in <i>Plantago lanceolata</i> and <i>Tanacetum parthenium</i>

Plant secondary metabolites play vital roles in growth, defence, and human pharmacological applications, with medicinal plants historically used to treat diseases. However, climate-change-induced drought may threaten medicinal plants' growth and metabolite production. This study examines drought effects on two medicinal plants common in the UK: Plantago lanceolata and Tanacetum parthenium. Under glasshouse conditions, we compared growth, chlorophyll content, and photosystem II efficiency (Fv/Fm) in well-watered vs. low-watered plants. High-performance liquid chromatography (HPLC) measured the concentration of parthenolide in T. parthenium and verbascoside in P. lanceolata leaves, with both compounds being the two most abundant with medicinal relevance. Results showed significantly reduced growth for both species under drought, though photosynthetic performance remained unaffected. Parthenolide content in T. parthenium decreased with low water, while verbascoside in P. lanceolata showed no significant change. This study highlights drought’s impact on medicinal plants' growth and metabolite production, emphasizing the need for further research on environmental factors affecting secondary metabolites under climate change.