Melatonin-Induced Stress Enhanced Biomass and Production of High-Value Secondary Cell Products in Submerged Adventitious Root Cultures of Stevia rebaudiana (Bert.)

Abstract

Stress is one of the important factors that directly or indirectly affects the plant architecture, biochemical pathways, and growth and development. Melatonin (MEL) is an important stress hormone; however, the exogenous addition of melatonin to culture media stimulates the defense mechanism and releases higher quantities of secondary metabolites. In this study, submerged adventitious root cultures (SARCs) of diabetically important Stevia rebaudiana were exposed to variable concentrations (0.5−5.0 mg/L) of MEL in combination with 0.5 mg/L naphthalene acetic acid (NAA) to investigate the biomass accumulation during growth kinetics with 07 days intervals for a period of 56 days. The effects of exogenous MEL on the biosynthesis of stevioside (Stev.), total phenolics content (TPC), total flavonoids content (TFC), total phenolics production (TPP), total flavonoids production (TFP), total polyphenolics content (TPPC), fresh and dry weight (FW & DW), and antioxidant potential were also studied. Most of the SARCs displayed lag, exponential, stationary, and decline phases with variable biomass accumulation. The maximum fresh (236.54 g/L) and dry biomass (28.64 g/L) was observed in SARCs exposed to 3.0 mg/L MEL and 0.5 mg/L NAA. The same combination of MEL and NAA also enhanced the accumulation of TPC (18.96 mg/g-DW), TFC (6.33 mg/g-DW), TPP (271.51 mg/L), TFP (90.64 mg/L), and TPPC (25.29 mg/g-DW). Similarly, the highest stevioside biosynthesis (91.45 mg/g-DW) and antioxidant potential (86.15%) were observed in SARCs exposed to 3.0 mg/L MEL and NAA. Moreover, a strong correlation was observed between the biomass and the contents of phenolics, flavonoids, antioxidants, and stevioside. These results suggest that MEL is one of multidimensional stress hormones that modulate the biosynthetic pathways to release higher quantities of metabolites of interest for various industrial applications.

Elicitors directed in vitro growth and production of stevioside and other secondary metabolites in Stevia rebaudiana (Bertoni) Bertoni

“…The concentration of secondary metabolites in the leaves of stevia varies significantly in heterogenous populations. Infertility and low viability of seeds, as well as poor performance of stem cuttings used in clonal propagation, are major issues limiting the production of homogenous population of Stevia 18 , 19 . Exposure of plants grown in vitro to biotic or abiotic elicitors has been shown to modulate the biosynthetic pathways for certain plant metabolites, often releasing higher quantities of valuable metabolites in less time 20 .…”

“…Elicitation is an effective tool to not only activate plant defence mechanisms, but to release highly valuable secondary metabolites such as those used in the pharmaceutical, agrochemical, bio-pesticide, cosmetic, and food additive industries 22 . The study of elicitor activity plays an important role in elucidating plant defence mechanisms, as well as the regulation and prospects for enhancing the production of valuable secondary metabolites 18 . The main aim of the study reported here is to report the effect of the potential elicitors gibberellic acid GA 3 (growth regulator), NaCl (ionic and osmotic stress), and polyethylene glycol (osmotic stress) on shoot morphogenesis, polyphenolics content, antioxidant activity, and proline and stevioside content in shoots of Stevia rebaudiana cultured in vitro.…”