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.

We examined the effects of abiotic (methyl jasmonate [MeJA] and salicylic acid [SA]) and biotic (yeast extract and chitosan) elicitors for improvement of bioactive compounds production on adventitious root cultures in Polygonum multiflorum. The application of yeast extract resulted in significantly (p ≤ 0.05) higher dry root biomass (9.98 g/L) and relative growth rate versus the control. Cultures treated with abiotic elicitors showed higher percentage of dry weight than the other samples. Low concentrations of all elicitors (50 μM MeJA and SA, and 50 mg/L yeast extract) improved secondary metabolite production except for chitosan, whose performance was worse than that of the control. HPLC analysis of various bioactive compounds revealed significantly higher elicitation efficiency for MeJA than for the other treatments, with an approximately 2-fold increase in root dry weight (22.08 mg/g DW) under 50 μM MeJA treatment versus the control (10.35 mg/g DW). We also investigated the feasibility of scaling up the production process by comparing shake flask cultures with 3- and 5-L balloon type bubble bioreactors (BTBB) using 50 μM MeJA as an elicitor. Growth and metabolite accumulation increased in BTBB compared with shake flask cultures. We detected a non-significant difference in biomass productivity between 3 and 5-L BTBB, but the efficiency of bioactive compound accumulation decreased with increasing volume. These findings will be useful for developing a pilot-scale P. multiflorum adventitious root cultivation process for high biomass and bioactive compound production to meet the demands for natural ingredients by the pharmaceutical and cosmetic industries without affecting the natural habitat of this plant.

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Hairy root cultures (HRCs) are characterized by fast and unlimited root growth, and they have greater genetic stability than other cultivation methods. HRCs are known to accumulate phytochemical levels comparable to those of intact plant. In this study, HRCs of Polygonum multiflorum were established from leaf explants infected with Agrobacterium rhizogenes strain KCCM 11879. Over 60% of the explants showed hairy root induction after 21 days of cultivation on hormone-free MS (Murashige and Skoog Physiol Plant 15:473-479, 1962) medium; induced roots were confirmed by PCR using a rolC-specific primer. Of the six lines of HRCs selected for further analysis, line HR-01 performed best, producing a root biomass (105.2 g L of FW, 9.7 g L of DW), which is 10-fold higher than that of non-transgenic roots. The HR-01 line also showed a significant increase in its total phenolic content (26.64 mg g DW), while non-transgenic roots accumulated 8.36 mg g DW of total phenolic. The levels of phenolic compounds in the HRCs increased more than 2.5-fold following exposure to 50 μM methyl jasmonate for 5 days. Fourier transform infrared (FT-IR) spectroscopic analysis of bioactive accumulation in P. multiflorum enabled discrimination between hairy root and adventitious root cultures. Thus, it is evident from this study that HRCs could be an attractive proposition for large-scale production of root biomass and secondary metabolites of P. multiflorum in bioreactors.

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