Elicitation of Submerged Adventitious Root Cultures of Stevia rebaudiana with Cuscuta reflexa for Production of Biomass and Secondary Metabolites

Stevia rebaudiana is an important medicinal plant that belongs to the Asteraceae family. The leaves of Stevia rebaudiana are a rich source of many health-promoting agents such as polyphenols, flavonoids, and steviol glycoside, which play a key role in controlling obesity and diabetes. New strategies such as the elicitation of culture media are needed to enhance the productivity of active components. Herein, the Cuscuta reflexa extracts were exploited as elicitors to enhance the productivity of active components. Cuscuta reflexa is one of the parasitic plants that has the ability to elongate very fast and cover the host plant. Consequently, it may be possible that the addition of Cuscuta reflexa extracts to adventitious root cultures (ADR) of Stevia rebaudiana may elongate the root more than control cultures to produce higher quantities of the desired secondary metabolites. Therefore, the main objective of the current study was to investigate the effect of Cuscuta reflexa extract as a biotic elicitor on the biomass accumulation and production of antioxidant secondary metabolite in submerged adventitious root cultures of Stevia rebaudiana. Ten different concentrations of Cuscuta reflexa were added to liquid media containing 0.5 mg/L naphthalene acetic acid (NAA). The growth kinetics of adventitious roots was investigated for a period of 49 days with an interval of 7 days. The maximum biomass accumulation (7.83 g/3 flasks) was observed on medium containing 10 mg/L extract of Cuscuta reflexa on day 49. As the concentration of extract increases in the culture media, the biomass gradually decreases after 49 days of inoculation. In this study, the higher total phenolics content (0.31 mg GAE/g-DW), total flavonoids content (0.22 mg QE/g-DW), and antioxidant activity (85.54%) were observed in 100 mg/L treated cultures. The higher concentration (100 mg/L) of Cuscuta reflexa extract considerably increased the total phenolics content (TPC), total phenolics production (TPP), total flavonoids content (TFC), total flavonoids production (TFP), total polyphenolics content (TPPC), and total polyphenolics production (TPPP). It was concluded that the extract of Cuscuta reflexa moderately improved biomass accumulation but enhanced the synthesis of phenolics, flavonoids, and antioxidant activities. Here, biomass’s independent production of secondary metabolites was observed with the addition of extract. The present study will be helpful to scale up adventitious roots culture into a bioreactor for the production of secondary metabolites rather than biomass accumulation in medicinally important Stevia rebaudiana.

Induction and evaluation of secondary metabolite and antioxidant activity in adventitious root of Codonopsis javanica

In this study, the effects of auxin (IBA, NAA), explants, and culture conditions (light/dark) on adventitious root induction of Codonopsis javanica were investigated. The results showed that dark conditions were more suitable for adventitious root induction than light conditions. All three types of explants (internodes, leaves, and nodes) induced adventitious roots, and the appropriate concentration of auxin was 0.5 mg/l IBA. After 4 weeks of incubation under dark conditions, the rooting percentage and number of roots/explant of internode, leaf, and node segments on media supplemented with 0.5 mg/l IBA were 100% and 33.87 roots, 97.78% and 23.48 roots, 100% and 25.20 roots, respectively. These adventitious roots were analysed for the presence of alkaloids, carbohydrates, saponin, fixed oils and fats, phenol, flavonoids, gum, and mucilage. The total polysaccharide content, total phenolic content, and the antioxidant activity (IC50) of C. javanica adventitious root biomass were 16.98%, 1.876 (mg GAE/g DW), and 2.44 (mg/ml), respectively. These results indicate that the adventitious roots of C. javanica contain bioactive compounds, which can be used as a material source for multiplication in large-scale systems.

Aerenchyma Formation in Adventitious Roots of Tall Fescue and Cocksfoot under Waterlogged Conditions

The formation of aerenchyma in adventitious roots is one of the most crucial adaptive traits for waterlogging tolerance in plants. Pasture grasses, like other crops, can be affected by waterlogging, and there is scope to improve tolerance through breeding. In this study, two summer-active cocksfoot (Dactylis glomerata L.) cultivars, Lazuly and Porto, and two summer-active tall fescue (Lolium arundinaceum Schreb., syn. Festuca arundinacea Schreb.) cultivars, Hummer and Quantum II MaxP, were selected to investigate the effects of waterlogging on root growth and morphological change. Cultivars were subjected to four periods of waterlogging treatments (7, 14, 21 and 28 days), while comparable plants were kept under free drained control conditions. The experiment was arranged as a split–split plot design, with waterlogging treatments (waterlogged, control) considered as main plots, time periods (days of waterlogging) as subplots and cultivars as sub-subplots. Plants began to show signs of waterlogging stress 14–21 days after the onset of waterlogging treatments. There were no significant differences in shoot biomass between the waterlogged and control plants of any cultivar. However, waterlogging significantly reduced root dry matter in all cultivars, with greater reduction in cocksfoot (56%) than in tall fescue (38%). Waterlogging also led to increased adventitious root and aerenchyma formation in both species. Cocksfoot cultivars showed a greater increase in adventitious roots, while tall fescue cultivars had a greater proportion of aerenchyma. Both cultivars within each species showed similar responses to waterlogging treatments. However, an extended screening program is needed to identify whether there are varietal differences within species, which could be used to discover genes related to aerenchyma or adventitious root formation (waterlogging tolerance) for use in breeding programs.