Establishment of hairy root cultures of Lactuca serriola and enhancement of phenolic metabolites through methyl jasmonate elicitation

Lactuca serriola is a wild lettuce species that synthesizes diverse phenolic compounds involved in plant defense and adaptation to environmental stress. Methyl jasmonate (MeJA), a key signaling molecule in plant defense, is known to regulate secondary metabolism by activating the phenylpropanoid pathway. In the present study, genetically stable hairy root cultures of L. serriola were established to investigate MeJA-induced metabolic reprogramming and its effects on phenolic accumulation and antioxidant defense responses. Hairy roots were induced using Agrobacterium rhizogenes strain ATCC 15834 and molecularly confirmed by PCR amplification of the rolC gene. The selected fast-growing hairy root line was treated with 0, 100, and 200 μM MeJA. MeJA significantly affected both growth and secondary metabolism. Although increasing MeJA concentrations reduced fresh and dry biomass, they promoted the accumulation of total phenolics and flavonoids. HPLC-DAD analysis further demonstrated significant increases in several phenolic metabolites, including caffeic acid, chlorogenic acid, p -coumaric acid, rosmarinic acid, and cinnamic acid. MeJA treatment also enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase, indicating activation of antioxidant defense systems associated with jasmonate-mediated stress responses and phenylpropanoid metabolism. This study provides the first comprehensive characterization of MeJA-induced phenolic metabolism in L. serriola hairy roots and demonstrates that MeJA effectively reprograms secondary metabolism toward enhanced phenolic biosynthesis. These findings advance our understanding of jasmonate-regulated defense metabolism in hairy roots while supporting the use of this in vitro system as a controlled platform for future studies and potential biotechnological production of specialized metabolites.