Leaves micromorphology, chemical profile, and bioactivity of in vitro-propagated Nepeta cyrenaica (Lamiaceae)

Abstract

Introduction: The endemic species Nepeta cyrenaica Quézel & Zaffran, native to northeastern Libya, is valued as an important honey-bearing plant.

Objectives: This study was aimed to examine the micromorphology, phytochemistry, and bioactivity of in vitro-propagated N. cyrenaica for the first time.

Materials and methods: The leaf indumentum was examined using light and scanning electron microscopy and further characterised for histochemistry. The chemical composition of essential oil (EO) was performed using GC-MS analysis, while dichloromethane (DCM), methanol (ME), ethanol (ET), and aqueous (AQ) extracts were analysed using qualitative and quantitative LC/MS analyses. The antioxidant activities of EO and extracts were assessed using three parallel assays, while enzyme-inhibiting effects were evaluated against four enzymes.

Results: The leaves bear various types of glandular trichomes, with lipophilic secretion predominating. The main EO component of EO was 1,8-cineole. A considerable number of phenolics and iridoids were tentatively identified in the ME extract. Quantitative LC/MS analysis confirmed that ferulic acid, rosmarinic acid, and epigallocatechin gallate were present in the highest amount in the extracts, in which three iridoids were also quantified. Although the ME extract contained the highest amount of polyphenolics and iridoids, the DCM extract showed the best overall biological potential. Additionally, EO exerted the strongest acetylcholinesterase and tyrosinase inhibition.

Conclusion: This study demonstrated that the endemic N. cyrenaica can be efficiently grown under in vitro conditions, where it develops various glandular trichomes that are thought to secrete and/or accumulate bioactive compounds with valuable medicinal potential.