Agro-environmental and developmental regulation of the physiology and accumulation of bioactive secondary metabolites in Nepeta cataria L.
Creators: name: Nunes Gomes, Erik
Publisher: name: No Publisher Supplied
Year: 2024

description: Catnip (Nepeta cataria L.) is a plant in the Lamiaceae family mainly known for the production of nepetalactones, volatile monoterpenes with multiple applications in human and animal health. The most notorious biological activities attributed to nepetalactones are the behavioral effects they elicit in domestic cats and other felids, and the strong repellency against several arthropod species, including disease vectors. Nepetalactones and related compounds are biosynthesized in N. cataria via iridoid terpene pathway, a noncanonical pathway with unusual cyclization mechanisms involving specific enzymes such as G8H, 8HGO, ISY and NEPS. Some chemotypes of catnip can also produce essential oils with a characteristic lemon-like scent, mainly composed of monoterpenes geraniol, citronellol and citral and with little to no nepetalactones. These chemotypes are collectively known as lemon catnips (Nepeta cataria var. citriodora Dumoulin ex Lej.) and are not as extensively studied as their nepetalactone-rich counterparts. In addition to producing terpenes, both catnip and lemon catnip accumulate other important secondary metabolites, such as phenolic acids and flavones, which can also contribute to the biological activities attributed to the species. This dissertation addresses the influence of cultivation practices, genotypes, propagation methods, and harvesting regimes on the accumulation of important phytochemicals in N. cataria and N. cataria var. citriodora. Additionally, the transcriptional regulation of nepetalactone biosynthesis in catnip inflorescences is investigated and, lastly, the repellent effects of natural products from catnip and lemon catnip are assessed against the common bed bug (Cimex lectularius L.). Lemon catnip genotypes significantly varied regarding the stability of their chemical profile, while a commercial line was mainly composed of citronellol and geraniol across three harvests, newly selected lemon-scented genotypes only showed a traditional lemon catnip chemical profile after two successive harvests. Successive harvests also affected the chemical profile of nepetalactone-rich catnip cultivars CR3 and CR9. CR3 was less affected by successive harvests in terms of nepetalactone accumulation, producing predominantly the isomer E,Z-nepetalactone in its essential oil, while CR9 produced predominantly Z,E-nepetalactone in three out of the 4 successive harvests. Catnip cv. CR3 propagated via seeds produced more biomass and nepetalactones than plants propagated via stem cuttings. The propagation method also affected the phenological stages, with plants propagated vegetatively reaching flowering stage earlier. Inflorescences, and not leaves, are the main sites of accumulation of nepetalactones, flavones and free amino acids in N. cataria plants, while roots are the main site of rosmarinic acid and caffeic acid accumulation. Flower’s calyxes have significantly higher expression levels of G8H, 8HGO, NEPS1 and NEPS2 than leaves. Essential oils of catnip and lemon catnip and their mixture are as effective as DEET, the gold standard of repellents, at repelling bed bugs in vitro, and compounds geraniol and citronellol are the main bioactive molecules associated with lemon catnip repellency. This dissertation discusses the significance of these findings in terms of potential new uses of catnip and lemon catnip natural products as well as the ecophysiological mechanisms involved in their regulation in the species.