Jasmonic acid as a metabolic switch for eugenol biosynthesis and floral volatile enhancement in Ocimum basilicum

The present investigation elucidates the modulatory influence of exogenous jasmonic acid (JA) on the essential oil content and compositional dynamics of Ocimum basilicum L. (sweet basil) across critical ontogenetic stages—35, 50, and 65 days after sowing (DAS). Foliar treatments included JA at concentrations of 0.3 mM (JA 1), 0.6 mM (JA 2), and 0.9 mM (JA 3), alongside a control (2% ethanol in double-distilled water). At the highest tested concentration (0.9 mM; JA 3), markedly augmented the essential oil yield in both foliar and floral tissues, with maximum enhancement recorded in leaf tissues at 50 DAS and floral tissues at 65 DAS. Gas chromatography-mass spectrometry (GC-MS) profiling revealed a distinct dose- and stage-responsive upregulation in key phenylpropanoid constituents, notably eugenol and methyl eugenol. JA 3-treated leaves exhibited a striking enrichment of eugenol (22.57%) and methyl eugenol (7.21%) at 50 DAS, underscoring the pivotal role of JA in potentiating phenylpropanoid pathway flux. Simultaneously, monoterpenes such as thujene exhibited a marked decline under JA elicitation, suggesting a metabolic reallocation favouring specialized phenolic biosynthesis. The floral essential oil profile mirrored this trend, albeit with differential compound dominance and dose sensitivity, affirming a tissue-specific regulatory mechanism. Collectively, these findings substantiate the role of jasmonic acid as a potent biochemical elicitor, capable of enhancing both the quantitative and qualitative attributes of essential oil biosynthesis in sweet basil through transcriptional and metabolic reprogramming aligned with developmental cues.