Recently, plant secondary metabolites are considered as important sources of pharmaceuticals, food additives, flavours, cosmetics, and other industrial products. The accumulation of secondary metabolites in plant cell and organ cultures often occurs when cultures are subjected to varied kinds of stresses including elicitors or signal molecules. Application of exogenous jasmonic acid (JA) and methyl jasmonate (MJ) is responsible for the induction of reactive oxygen species (ROS) and subsequent defence mechanisms in cultured cells and organs. It is also responsible for the induction of signal transduction, the expression of many defence genes followed by the accumulation of secondary metabolites. In this review, the application of exogenous MJ elicitation strategies on the induction of defence mechanism and secondary metabolite accumulation in cell and organ cultures is introduced and discussed. The information presented here is useful for efficient large-scale production of plant secondary metabolites by the plant cell and organ cultures.

Centella asiatica (Apiaceae) is a tropical/subtropical medicinal plant, which contains a variety of triterpenoids, including madecassoside, asiaticoside, madecassic acid, and asiatic acid. In this study, we tested the efficiency of hairy root (HR) induction in C. asiatica from leaf and petiole explants. Leaves and petioles collected from C. asiatica plants were suspended in agro-stock for 30 min and co-cultured with Agrobacterium rhizogenes for 3 days to induce HR formation. The transformation efficiency of leaf and petiole explants was approximately 27% and 12%, respectively. A total of 36 HR lines were identified by PCR-based amplification of rol genes, and eight of these lines were selected for further analysis. Among all eight HR lines, the petiole-derived lines HP4 and HP2 displayed the highest growth index (37.8) and the highest triterpenoids concentration (46.57 mg∙g⁻¹), respectively. Although triterpenoid concentration was >2-fold higher in leaves than in petioles of C. asiatica plants, the accumulation of triterpenoids in petiole-derived HR cultures was 1.4-fold higher than that in leaf-derived HR cultures. Additionally, in both leaf- and petiole-derived HR cultures, terpenoid production was higher in HRs than in adventitious roots. These results demonstrate that the triterpenoid content in the explant does not affect the triterpenoid content in the resultant HRs. The HR culture of C. asiatica could be scaled up to enable the mass production of triterpenoids in bioreactors for the pharmaceutical and cosmetic industries.