In vitro propagation, lactucin quantification, and antibacterial activity of Indian lettuce (Lactuca indica L.)

Lactuca indica L. (Asteraceae), a wild lettuce, is used as a vegetable and in traditional medicine. This study aims to establish in vitro propagation protocol and evaluate lactucin and antibacterial property from in vitro and natural plant tissues. Leaf blades and petioles were cultured in vitro on Murashige and Skoog (MS) medium supplemented with various concentrations of 6-benzylaminopurine (BAP) and 1.2 mg L–1 indoleacetic acid (IAA). Leaf petioles and a lower BAP concentration (0.5 mg L–1) were optimal for direct shoot induction, while the leaf blade and a higher BAP (4 mg L–1) concentration performed best for callus induction. When the callus was subcultured, 98.7% of samples regenerated plants on MS medium supplemented with 1.5 mg L–1 BAP and 0.5 mg L–1 IAA. MS medium containing 1 mg L–1 IAA was best for in vitro rooting. A high-performance liquid chromatography analysis of the in vitro samples revealed a higher amount of lactucin (sesquiterpene lactones) in the root than the callus and the leaf, whereas in naturally grown plants, higher lactucin amounts were obtained from the juvenile root followed by the root of the flowering plant and juvenile leaf as the lowest concentration. All tissue extracts showed antibacterial activity against Pseudomonas fuscovaginae (a rice pathogen) and Escherichia coli, which was directly proportional to amount of lactucin produced. This in vitro regeneration and phytochemical investigation will facilitate the further exploitation of this useful wild plant.