Abstract Plant secondary metabolites provide a unique basis for medications, flavorings, and industrial biochemicals. These metabolites frequently accumulate in plants exposed to environmental stressors (e.g., drought stress), as a mechanism for adaptation and resistance. Plectranthus amboinicus (Lour.) Spreng is a semi-succulent Lamiaceae species valued for its curative properties and essential oil, the concentration of which is heavily impacted by irrigation levels. This investigation reveals a novel study into the physiological and molecular mechanisms of P. amboinicus by correlating field capacity (FC) levels with metabolite accumulation and specific gene expression. We examined the impact of six irrigation levels (0, 20, 40, 60, 80 and 100%; denoted as FC-0 to FC-100) on growth, essential oil (EO) yield, and carvacrol biosynthesis during the 2022 and 2023 seasons. Data revealed that plants subjected to the FC-0 exhibited the lowest growth parameters. However, these plants also presented a higher essential oil percentage and carvacrol concentrations, in addition to an increase in polyphenols and antioxidant enzymes, with greater oxidative substances accumulation (H 2 O 2 and MDA). Moreover, these plants presented higher gene expression of CYP71D178 and CYP71D180 genes. While increasing water level caused an increase in growth parameters, with a decline in the antioxidant activity. Increasing the water level to FC-100 increased the essential oil by approximately four fold but resulted in a decline in carvacrol content as compared to FC-0. Generally, water deficiency reduces crop yield, whereas irrigation increases plant productivity. However, in medicinal and aromatic plants, the relationship is distinct; in Plectranthus amboinicus, water deficiency showed a strong positive correlation with the secondary metabolite’s generation. In conclusion, the current report provides for the first time a molecular framework for P. amboinicus by depicting the expression patterns of CYP71D178 and CYP71D180. We revealed that these genes elaborate as the primary molecular shifts regulating carvacrol biosynthesis influenced by specific irrigation levels.
El-Sheshtawy et al. (Tue,) studied this question.