Establishment of cell suspension cultures of Withania somnifera for the production of withanolide A

Enhancing Withanolide Production in the Withania Species: Advances in In Vitro Culture and Synthetic Biology Approaches

Withanolides are naturally occurring steroidal lactones found in certain species of the Withania genus, especially Withania somnifera (commonly known as Ashwagandha). These compounds have gained considerable attention due to their wide range of therapeutic properties and potential applications in modern medicine. To meet the rapidly growing demand for withanolides, innovative approaches such as in vitro culture techniques and synthetic biology offer promising solutions. In recent years, synthetic biology has enabled the production of engineered withanolides using heterologous systems, such as yeast and bacteria. Additionally, in vitro methods like cell suspension culture and hairy root culture have been employed to enhance withanolide production. Nevertheless, one of the primary obstacles to increasing the production of withanolides using these techniques has been the intricacy of the biosynthetic pathways for withanolides. The present article examines new developments in withanolide production through in vitro culture. A comprehensive summary of viable traditional methods for producing withanolide is also provided. The development of withanolide production in heterologous systems is examined and emphasized. The use of machine learning as a potent tool to model and improve the bioprocesses involved in the generation of withanolide is then discussed. In addition, the control and modification of the withanolide biosynthesis pathway by metabolic engineering mediated by CRISPR are discussed.

Influence of the Culture Conditions on Camellia sinensis Cell Cultures

Since the last century, it has been shown that dedifferentiated cells of Camellia sinensis can produce catechins and other secondary metabolites under in vitro conditions, with potential applications in the cosmetic, pharmaceutical and food industries. In this work, cell suspension cultures of a C. sinensis cell line (LSC-5Y) were established in a liquid medium in order to optimize the biomass productivity, catechin monomer (GC, EGC, C, EC, CG, and ECG) and alkaloid (TB and CAF) productivity. The following factors were evaluated: concentration of growth regulators (BA and IBA), inoculum size, age of the cell line, light exposure, and effect of biotic elicitors (MeJA and extracts of Ciborinia camelliae). GC, EGC, and ECG increased approximately 1.80-fold when the auxin IBA concentration was increased from 0.1 to 2.0 mg/L. In addition, better productivity of EGC, C, EC, and CAF was achieved by using inoculum densities between 50 and 100 g/L. Although lower inoculum densities (25 g/L) showed a higher growth rate (0.20 d-1), the use of inoculum densities higher than 25 g/L favors a 2-4-fold increase in total catechin (TC) productivity, with maximum productivity being reached after 21 days of culture. However, the cell line showed instability in TC productivity: in the short term (in three successive subcultures), the coefficient of variation was 32.80%, and catechin production capacity was 2.5 years with maximum productivity at 0.5 years. Finally, it was observed that ethanol, used as an elicitor solvent, has a strong elicitor effect capable of increasing the accumulation of catechins up to 5.24 times compared to the treatment without an elicitor.

An update on biotechnological intervention mediated by plant tissue culture to boost secondary metabolite production in medicinal and aromatic plants

Since prehistoric times, medicinal and aromatic plants (MAPs) have been employed for various therapeutic purposes due to their varied array of pharmaceutically relevant bioactive compounds, i.e. secondary metabolites. However, when secondary metabolites are isolated directly from MAPs, there is occasionally very poor yield and limited synthesis of secondary metabolites from particular tissues and certain developmental stages. Moreover, many MAPs species are in danger of extinction, especially those used in pharmaceuticals, as their natural populations are under pressure from overharvesting due to the excess demand for plant-based herbal remedies. The extensive use of these metabolites in a number of industrial and pharmaceutical industries has prompted a call for more research into increasing the output via optimization of large-scale production using plant tissue culture techniques. The potential of plant cells as sources of secondary metabolites can be exploited through a combination of product recovery technology research, targeted metabolite production, and in vitro culture establishment. The plant tissue culture approach provides low-cost, sustainable, continuous, and viable secondary metabolite production that is not affected by geographic or climatic factors. This study covers recent advancements in the induction of medicinally relevant metabolites, as well as the conservation and propagation of plants by advanced tissue culture technologies.

The impact of carbon source on cell growth and the production of bioactive compounds in cell suspensions of Hancornia speciosa Gomes

Belonging to the Brazilian flora, the species Hancornia speciosa (Gomes), known as mangabeira, has bioactive compounds of interest, such as flavonoids, xanthones, and proanthocyanidins. The objective of this study was to determine how the supplementation of sugars in culture medium affects the osmotic potential of the medium, as well as its influence on cell growth and on the concentration of phenolic compounds. For this purpose, after 90 days of subculture, 20 mL aliquots of the cultures were added to flasks containing 20 mL of medium with different sugars (glucose, fructose, sucrose, mannitol, and sorbitol) under a 16-h photoperiod with a spectral range between 400 and 700 nm of photosynthetically active radiation (45-55 μmol m-2 s-1) in a shaker at 110 rpm. After 30 days, the pH, electrical conductivity, osmotic potential, biomass accumulation, and concentrations of phenolic compounds were evaluated. Regardless of their concentration in the medium, the sugars sorbitol and mannitol provided more unfavorable conditions for water absorption at the cellular level, reducing the water potential of the medium. Sucrose favored greater water absorption and biomass accumulation. Among the various sugar concentrations, 3% (30 g/L) sucrose or glucose improved the accumulation of fresh and dry cell weight and the production of polyphenols such as chlorogenic acid, epicatechin, rosmarinic acid, hesperidin, rutin, and quercetin. In addition, they resulted in a higher osmotic potential of the medium and larger cells than other carbon sources. Despite the differences in cell size, no culture conditions compromised cell survival.

Biotechnological processes to obtain bioactive secondary metabolites from some Mexican medicinal plants

The consumption of medicinal plants has increased in recent decades due to the fact that they biosynthesize compounds with many biological activities; thus, some plant species with biological potential are being utilized as raw material by the industries for preparation of drugs, phytodrugs, or food supplements. This has the consequence of overexploitation and deforestation, which endangers plant species-of-interest. In recent years, alternatives have been sought to eradicate this problem. A solution that was given and is maintained is plant biotechnology, which favors the production of secondary metabolites (SMt) with important biological activity. Plant biotechnology allows us to increase the yield of a compound-of-interest, reduces its production times and costs, and allows constant and controlled production of the raw material, while aiding in the protection of medicinal plants that are found in danger of extinction. In the scientific literature, procuring the SMt by means of biotechnological processes is described, highlighting the study of five species from Mexican traditional medicine (Lopezia racemosa, Galphimia glauca, Cnidoscolus chayamansa, and Buddleja cordata), and the main biological activities are as follows: anti-inflammatory, hepatoprotector, neuroprotector, anxiolytic, antitumoral, antibacterial, and antioxidant, among others. KEY POINTS: • Secondary metabolites produce by biotechnology processes • Active secondary metabolites isolated from Mexican medicinal plants • Recent advances on the production of some bioactive secondary metabolites.

Ashwagandha: Advances in plant biotechnological approaches for propagation and production of bioactive compounds

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera is one of the most extensively delved Ayurvedic medicine. Apart from rejuvenation and increasing longevity, it has several other properties such as immunomodulation, anti-cancer, anti-stress and neuroprotection. Because of its prevailing use and increasing demand, it becomes prudent to scientifically evaluate and document both its propagation and production of desired phytoconstituents.

AIM OF THE STUDY

This review aims to highlight the research progress achieved on various biotechnological and tissue culture aspects of Withania somnifera and to cover up-to-date information regarding in-vitro propagation and production of withanolides.

MATERIALS AND METHODS

Significant published studies were identified for the years 2000-2018 using Elsevier-Science Direct, Pubmed and Google scholar and several research studies in our laboratory. Following keywords such as "plant extracts", "in vitro cultures", "callus and suspension culture", "micropropagation", "hairy root cultures" were used. Further, "Withania somnifera", "secondary metabolites specially withanolides", "molecular techniques" and "in vitro conservation" were used to cross-reference the keywords.

RESULTS

Ashwagandha comprises a broad spectrum of phytochemicals with a wide range of pharmacological properties. W. somnifera seeds have reduced viability and germination rates; thus, its regular cultivation method fails to achieve commercial demands mainly for the production of desired phytoconstituents. Cultivation of plant cells/tissues under in vitro conditions and development of various biotechnological strategies will help to build an attractive alternative to provide adequate quality and quantity raw materials. Recently, a large number of in vitro protocols has developed for W. somnifera not only for its propagation but for the production of secondary metabolites as well. Present work highlights a variety of biotechnological strategies both for prompt propagation and production of different bioactive secondary metabolites.

CONCLUSION

The present review focuses on the development and opportunities in various biotechnological approaches to accomplish the global demand of W. somnifera and its secondary metabolites. This review underlines the advances in plant biotechnological approaches for the propagation of W. somnifera and production of its bioactive compounds.

Development of a Cell Suspension Culture System for Promoting Alkaloid and Vinca Alkaloid Biosynthesis Using Endophytic Fungi Isolated from Local Catharanthus roseus

Cell and tissue cultures of Catharanthus roseus have been studied extensively as an alternative strategy to improve the production of valuable secondary metabolites. The purpose of this study was to produce C. roseus callus and suspension cell biomass of good quality and quantity to improve the total alkaloids and bis-indole alkaloids. The young stem derived-callus of C. roseus variety Quang Ninh (QN) was grown on MS medium supplemented with 1.5 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) plus 1.5 mg/L kinetin, and the growth rate increased by 67-fold after 20 days. The optimal conditions for maintaining the cell suspension culture were 150 mg/50 mL cell inoculum, a medium pH of 5.5 and a culture temperature of 25 °C. The low alkaloid content in the culture was compensated for by using endophytic fungi isolated from local C. roseus. Cell extracts of endophytic fungi—identified as Fusarium solani RN1 and Chaetomium funicola RN3—were found to significantly promote alkaloid accumulation. This elicitation also stimulated the accumulation of a tested bis-indole alkaloid, vinblastine. The findings are important for investigating the effects of fungal elicitors on the biosynthesis of vinblastine and vincristine, as well as other terpenoid indole alkaloids (TIAs), in C. roseus QN cell suspension cultures.

Preliminary study of the production of metabolites from in vitro cultures of C. ensiformis

BACKGROUND

Canavalia ensiformis is a legume native to Central and South America that has historically been a source of protein. Its main proteins, urease, and lectin have been extensively studied and are examples of bioactive compounds. In this work, the effect of pH and light effects on the growth of C. ensiformis were analyzed. Also, the bioactive compounds such as phenols, carotenoids, chlorophyll a/b, and the growth of callus biomass of C. ensiformis from the effect of different types of light treatments (red, blue and mixture) were evaluated. Likewise, the antioxidative activity of C. ensiformis extracts were studied and related to the production of bioactive compounds. For this, a culture of calluses obtained from seeds were carried out. For the light experiments, polypropylene boxes with red, blue, combination (1/3, 3/1 and 1/1 R-B, respectively) lights and white LED were used as control. In each treatment, three glass containers with 25 ml of MS salts containing 0.25 g of fresh callus were seeded.

RESULTS

The results have shown that the pH of the culture medium notably affects the increase in callogenic biomass. It shows that the pH of 5.5 shows better results in the callogenic growth of C. ensiformis with an average increase of 1.3051 g (198.04%), regarding the initial weight. It was found that the pH 5.5 and the 1/3 R-B LED combination had higher production of bioactive compounds and better antioxidant activity. At the same time, the red-light treatment was least effective.

CONCLUSIONS

It was possible to find the ideal conditions of important growth under conditions of pH and light of C. ensiformis. Likewise, it is evaluated whether the production of compounds of interest, such as phenolic compounds and carotenoids, occurs under these conditions. The highest production of calluses occurs in the 1/3 R-B LED combined light treatment, which showed a significant increase in biomass, followed by B. From this study, it could be demonstrated that C. ensiformis produces compounds such as phenols and carotenoids in vitro culture that are essential for the antioxidant activity of the plant.

Carbohydrates stimulated Amaryllidaceae alkaloids biosynthesis in Leucojum aestivum L. plants cultured in RITA® bioreactor

Background

Leucojum aestivum L. is an important medicinal plant which produces Amaryllidaceae alkaloids, especially galanthamine and lycorine. Research is currently exploring the possibility of producing these alkaloids using biotechnological methods, including in vitro cultures. The biosynthesis of alkaloids may be affected by the types and concentrations of carbohydrate sources used in the medium. In the present investigation we performed such studies on in vitro cultures of L. aestivum with a view to obtaining plant material of good quality, characterized, in particular, by a high content of valuable Amaryllidaceae alkaloids.

Methods

We examined the effects of various types of carbohydrate sources—sucrose, glucose, fructose and maltose—at different concentrations (30, 60 and 90 g/L)—on the quality of L. aestivum plants grown in the RITA^® bioreactor. The plants’ quality was assessed by their biomass increments, as well by as analysing photosynthetic pigments, endogenous sugar, phenolics and Amaryllidaceae alkaloid content. We also investigated the effect of sugars on the activity of the antioxidant enzymes catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD).

Results

The highest biomass increments were observed in plants cultivated in the medium containing 90 g/L sucrose. The highest CAT activity was noted in cultures growing in the medium supplemented with 90 g/L maltose, while the highest POD activity was observed in the presence of 90 g/L fructose and 60 g/L maltose. No differences in SOD activity were observed. Moreover, the sugars did not affect the contents of chlorophyll a and carotenoids, whereas the highest amount of chlorophyll b was recorded in plants growing in the medium with 60 g/L maltose. No statistically significant differences were observed in the contents of endogenous sugars and phenolics in any in vitro conditions. However, the addition of sugar had a decisive effect on the biosynthesis of the Amaryllidaceae alkaloids. The highest distribution of alkaloids occurred in plants cultured in the medium containing 60 g/L sucrose. Six Amaryllidaceae alkaloids were detected in the plant tissue. The addition of 30 g/L fructose in the medium resulted in the accumulation of five alkaloids, including ismine, which was not identified in other analysed tissues. The highest concentration of galanthamine was observed in plants cultured in the presence of 30 g/L fructose and 60 g/L sucrose (39.2 and 37.5 µg/g of dry weight (DW), respectively). The plants grown in the medium containing 60 g/L sucrose exhibited the highest lycorine content (1048 µg/g of DW).

Conclusions

The type and concentration of sugar used in the medium have an essential influence on the biosynthesis of Amaryllidaceae alkaloids in L. aestivum plants cultured in a RITA^® bioreactor. The results point to an interesting approach for commercial production of galanthamine and lycorine.

Innate endophytic fungus, Aspergillus terreus as biotic elicitor of withanolide A in root cell suspension cultures of Withania somnifera

In the present study, root cell suspension cultures of W. somnifera were elicited with mycelial extract (1% w/v) and culture filtrate (5% v/v) of their native endophytic fungus Aspergillus terreus 2aWF in shake flask. Culture filtrate of A. terreus 2aWF significantly elicits withanolide A at 6H (12.20 ± 0.52 µg/g FCB). However, with A. terreus 2aWF mycelial extract, withanolide A content was higher at 24H (10.29 µg/g FCB). Withanolide A content was maximum with salicylic acid (0.1 mM) treatment at 24H (8.3 ± 0.20 µg/g FCB). Further, expression analysis of withanolide pathway genes, hydrogen peroxide production, and lipid peroxidation was carried out after 48H of elicitation with 2aWF mycelial extract and culture filtrate. The expression levels of withanolides biosynthetic pathway genes, viz. HMGR, DXR, FPPS, SQS, SQE, CAS, SMT1, STE1 and CYP710A1 were quantified by real time PCR at 48H of elicitation. In all the treatments, the expression levels of key genes were significantly upregulated as compared to untreated suspension cells. Hydrogen peroxide was noticeably enhanced in SA, mycelia extract and culture filtrate, at 20% (115 ± 4.40 nM/g FCB), 42% (137.5 ± 3.62 nM/g FCB), and 27% (122.8 ± 1.25 nM/g FCB) respectively; however, lipid peroxidation was 0.288 ± 0.014, 0.305 ± 0.041 and 0.253 ± 0.007 (µM/gm FCB) respectively, higher than the control (0.201 ± 0.007 µM/gm FCB).

Metabolomic and biotechnological approaches to determine therapeutic potential of Withania somnifera (L.) Dunal: A review

BACKGROUND

Withania somnifera, a high value medicinal plant is a major source of pharmaceutically important active compounds withanolides. Withania somnifera has been used in ayurveda as health restorative and anabolic agent besides having anti-arthritic, antidepressant, anti-microbial, anti-inflammatory, anti-diabetic, anti-stress, neuroprotective and cardio-protective activities.

HYPOTHESIS/PURPOSE

The mining of the compound(s) of interest offers opportunity to identify desired attributes in the therapeutic area of interest. Metabolomic has become an important tool in the field of pharmacological and functional genomics of medicinal plants. The analysis supports the information regarding differential outline of the gene expression for increasing important withanolides viz. withanolide A and withaferin A in W. somnifera.

STUDY DESIGN

The bioinformatics and biotechnological approaches viz. tissue culture, genetic transformation, genomic, transcriptomic, proteomic, gene mining and metabolomic studies have opened new windows about engineering of withanolide production.

METHODS

Target and network analysis for maximum therapeutic potential of Withania somnifera have been determined by employing Genemania software for finding interactions among various human genes that are being affected by active constituents.

RESULTS

Some of the major bioactive compounds of Withania somnifera have been discussed on protein-protein, protein-DNA and genetic interactions with respect to gene and protein expression data, protein domains, metabolic profiling, root organ culture, genetic transformation and phenotypic screening profiles CONCLUSION: The implementation of latest bioinformatic tools in combination with biotechnological techniques for breeding platforms are important in conservation of medicinal plant species in danger. The current review is based on molecular and in vitro methodologies employed in W. somnifera for accepting their importance in the improvement of this valuable medicinal species.

Enhanced Production of Phenolic Compounds in Compact Callus Aggregate Suspension Cultures of Rhodiola imbricata Edgew

Rhodiola imbricata is a rare medicinal plant of the trans-Himalayan region of Ladakh. It is used for the treatment of numerous health ailments. Compact callus aggregate (CCA) suspension cultures of Rhodiola imbricata were established to counter extinction threats and for production of therapeutically valuable phenolic compounds to meet their increasing industrial demands. The present study also investigated the effect of jasmonic acid (JA) on production of phenolic compounds and bioactivities in CCA suspension cultures. CCA suspension cultures established in an optimized Murashige and Skoog medium supplemented with 30 g/l sucrose, 3 mg/l NAA, and 3 mg/l BAP showed maximum biomass accumulation (8.43 g/l DW) and highest salidroside production (3.37 mg/g DW). Upon 100 μM JA treatment, salidroside production (5.25 mg/g DW), total phenolic content (14.69 mg CHA/g DW), total flavonoid content (4.95 mg RE/g DW), and ascorbic acid content (17.93 mg/g DW) were significantly increased in cultures. In addition, DPPH-scavenging activity (56.32%) and total antioxidant capacity (60.45 mg QE/g DW) were significantly enhanced upon JA treatment, and this was positively correlated with increased accumulation of phenolic compounds. JA-elicited cultures exhibited highest antimicrobial activity against Escherichia coli. This is the first report describing the enhanced production of phenolic compounds and bioactivities from JA-elicited CCA suspension cultures of Rhodiola imbricata.

In vitro plant tissue culture: means for production of biological active compounds

MAIN CONCLUSION

Plant tissue culture as an important tool for the continuous production of active compounds including secondary metabolites and engineered molecules. Novel methods (gene editing, abiotic stress) can improve the technique. Humans have a long history of reliance on plants for a supply of food, shelter and, most importantly, medicine. Current-day pharmaceuticals are typically based on plant-derived metabolites, with new products being discovered constantly. Nevertheless, the consistent and uniform supply of plant pharmaceuticals has often been compromised. One alternative for the production of important plant active compounds is in vitro plant tissue culture, as it assures independence from geographical conditions by eliminating the need to rely on wild plants. Plant transformation also allows the further use of plants for the production of engineered compounds, such as vaccines and multiple pharmaceuticals. This review summarizes the important bioactive compounds currently produced by plant tissue culture and the fundamental methods and plants employed for their production.

Topical Delivery of Withania somnifera Crude Extracts in Niosomes and Solid Lipid Nanoparticles

BACKGROUND

Withania somnifera is a medicinal plant native to India and is known to have anticancer properties. It has been investigated for its anti-melanoma properties, and since melanoma presents on the skin, it is prudent to probe the use of W. somnifera in topical formulations. To enhance topical drug delivery and to allow for controlled release, the use of niosomes and solid lipid nanoparticles (SLNs) as delivery vesicles were explored.

OBJECTIVE

The objective of this study is to determine the stability and topical delivery of W. somnifera crude extracts encapsulated in niosomes and SLNs.

MATERIALS AND METHODS

Water, ethanol, and 50% ethanol crude extracts of W. somnifera were prepared using 24 h soxhlet extraction which were each encapsulated in niosomes and SLNs. Franz cell diffusion studies were conducted with the encapsulated extracts to determine the release and skin penetration of the phytomolecules, withaferin A, and withanolide A.

RESULTS

The niosome and SLN formulations had average sizes ranging from 165.9 ± 9.4 to 304.6 ± 52.4 nm with the 50% ethanol extract formulations having the largest size. A small particle size seemed to have correlated with a low encapsulation efficiency (EE) of withaferin A, but a high EE of withanolide A. There was a significant difference (P < 0.05) between the amount of withaferin A and withanolide A that were released from each of the formulations, but only the SLN formulations managed to deliver withaferin A to the stratum corneum-epidermis and epidermis-dermis layers of the skin.

CONCLUSION

SLNs and niosomes were able to encapsulate crude extracts of W. somnifera and release the marker compounds, withaferin A, and withanolide A, for delivery to certain layers in the skin.

SUMMARY

Withania somnifera crude extracts were prepared using ethanol, water, and 50% ethanol as solvents. These three extracts were then incorporated into niosomes and solid lipid nanoparticles (SLNs) for use in skin diffusion studies, thus resulting in six formulations (ethanol niosome, water niosome, 50% ethanol niosome, ethanol SLN, water SLN, and 50% ethanol SLN). The diffusion of two marker compounds (withaferin A and withanolide A) from the formulations into the skin was then determined. Abbreviations used: API: Active pharmaceutical ingredient, ANOVA: Analysis of variance, ED: Epidermis-dermis, HPLC: High-performance liquid chromatography, HLB: Hydrophilic-lipophilic balance, NMR: Nuclear magnetic resonance spectroscopy, PDI: Polydispersity index, SLN: Solid lipid nanoparticle, SD: Standard deviation, SCE: Stratum corneum-epidermis, TEM: Transmission electron microscopy.

Comparative study of withanolide production and the related transcriptional responses of biosynthetic genes in fungi elicited cell suspension culture of Withania somnifera in shake flask and bioreactor

Ashwagandha (Withania somnifera) is one of the most reputed medicinal plants in the traditional medicinal system. In this study, cell suspension culture of W. somnifera was elicited with cell homogenates of fungi (A. alternata, F. solani, V. dahliae and P. indica) in shake flask and the major withanolides like withanolide A, withaferin A and withanone were analysed. Simultaneously expression levels of key pathway genes from withanolides biosynthetic pathways were also checked via quantitative PCR in shake flask as well as in bioreactor. The results show that highest gene expression of 10.8, 5.8, 4.9, and 3.3 folds were observed with HMGR among all the expressed genes in cell suspension cultures with cell homogenates of 3% P. indica, 5% V. dahliae, 3% A. alternata and 3% F. solani, respectively, in comparison to the control in shake flask. Optimized concentration of cell homogenate of P. indica (3% v/v) was added to the growing culture in 5.0-l bioreactor under optimized up-scaling conditions and harvested after 22 days. The genes of MVA, MEP and withanolides biosynthetic pathways like HMGR, SS, SE, CAS, FPPS, DXR and DXS were up-regulated by 12.5, 4.9, 2.18, 4.65, 2.34, 1.89 and 1.4 folds, respectively in bioreactor. The enhancement of biomass (1.13 fold) and withanolides [withanolide A (1.7), withaferin A (1.5), and withanone (1.5) folds] in bioreactor in comparison to shake flask was also found to be in line with the up-regulation of genes of withanolide biosynthetic pathways.

Addressing Challenges to Enhance the Bioactives of Withania somnifera through Organ, Tissue, and Cell Culture Based Approaches

Withania somnifera is a highly valued medicinal plant in traditional home medicine and is known for a wide range of bioactivities. Its commercial cultivation is adversely affected by poor seed viability and germination. Infestation by various pests and pathogens, survival under unfavourable environmental conditions, narrow genetic base, and meager information regarding biosynthesis of secondary metabolites are some of the other existing challenges in the crop. Biotechnological interventions through organ, tissue, and cell culture provide promising options for addressing some of these issues. In vitro propagation facilitates conservation and sustainable utilization of the existing germplasms and broadening the genetic base. It would also provide means for efficient and rapid mass propagation of elite chemotypes and generating uniform plant material round the year for experimentation and industrial applications. The potential of in vitro cell/organ cultures for the production of therapeutically valuable compounds and their large-scale production in bioreactors has received significant attention in recent years. In vitro culture system further provides distinct advantage for studying various cellular and molecular processes leading to secondary metabolite accumulation and their regulation. Engineering plants through genetic transformation and development of hairy root culture system are powerful strategies for modulation of secondary metabolites. The present review highlights the developments and sketches current scenario in this field.

Enhanced Production of Anthraquinones and Phenolic Compounds and Biological Activities in the Cell Suspension Cultures of Polygonum multiflorum

Anthraquinones (AQs) and phenolic compounds are important phytochemicals that are biosynthesized in cell suspension cultures of Polygonum multiflorum. We wanted to optimize the effects of plant growth regulators (PGRs), media, sucrose, l-glutamine, jasmonic acid (JA), and salicylic acid (SA) for the production of phytochemicals and biomass accumulation in a cell suspension culture of P. multiflorum. The medium containing Murashige and Skoog (MS) salts and 4% sucrose supplemented with 1 mg/L 2,4-dichlorophenoxyacetic acid, 0.5 mg/L thidiazuron, and 100 µM l-glutamine at 28 days of cell suspension culture was suitable for biomass accumulation and AQ production. Maximum biomass accumulation (12.5 and 12.35 g fresh mass (FM); 3 and 2.93 g dry mass (DM)) and AQ production (emodin 295.20 and 282 mg/g DM; physcion 421.55 and 410.25 mg/g DM) were observed using 100 µM JA and SA, respectively. JA- and SA-elicited cell cultures showed several-fold higher biomass accumulation and AQ production than the control cell cultures. Furthermore, the cell suspension cultures effectively produced 23 phenolic compounds, such as flavonols and hydroxycinnamic and hydroxybenzoic acid derivatives. PGR-, JA-, and SA-elicited cell cultures produced a higher amount of AQs and phenolic compounds. Because of these metabolic changes, the antioxidant, antimicrobial, and anticancer activities were high in the PGR-, JA-, and SA-elicited cell cultures. The results showed that the elicitors (JA and SA) induced the enhancement of biomass accumulation and phytochemical (AQs and phenolic compounds) production as well as biological activities in the cell suspension cultures of P. multiflorum. This optimized protocol can be developed for large-scale biomass accumulation and production of phytochemicals (AQs and phenolic compounds) from cell suspension cultures, and the phytochemicals can be used for various biological activities.

Sucrose-enhanced biosynthesis of medicinally important antioxidant secondary metabolites in cell suspension cultures of Artemisia absinthium L

Natural products are gaining tremendous importance in pharmaceutical industry and attention has been focused on the applications of in vitro technologies to enhance yield and productivity of such products. In this study, we investigated the accumulation of biomass and antioxidant secondary metabolites in response to different carbohydrate sources (sucrose, maltose, fructose and glucose) and sucrose concentrations (1, 3, 5, 7 and 9 %). Moreover, the effects of 3 % repeated sucrose feeding (day-12, -18 and -24) were also investigated. The results showed the superiority of disaccharides over monosaccharides for maximum biomass and secondary metabolites accumulation. Comparable profiles for maximum biomass were observed in response to sucrose and maltose and initial sucrose concentrations of 3 and 5 %. Maximum total phenolic and total flavonoid contents were displayed by cultures treated with sucrose and maltose; however, initial sucrose concentrations of 5 and 7 % were optimum for both classes of metabolites, respectively. Following 3 % extra sucrose feeding, cultures fed on day-24 (late-log phase) showed higher biomass, total phenolic and total flavonoid contents as compared to control cultures. Highest antioxidant activity was exhibited by maltose-treated cultures. Moreover, sucrose-treated cultures displayed positive correlation of antioxidant activity with total phenolics and total flavonoids production. This work describes the stimulatory role of disaccharides and sucrose feeding strategy for higher accumulation of phenolics and flavonoids, which could be potentially scaled up to bioreactor level for the bulk production of these metabolites in suspension cultures of A. absinthium.

Chemical Elicitor-Induced Modulation of Antioxidant Metabolism and Enhancement of Secondary Metabolite Accumulation in Cell Suspension Cultures of Scrophularia kakudensis Franch

Scrophularia kakudensis is an important medicinal plant with pharmaceutically valuable secondary metabolites. To develop a sustainable source of naturaceuticals with vital therapeutic importance, a cell suspension culture was established in S. kakudensis for the first time. Friable calli were induced from the leaf explants cultured on a Murashige and Skoog (MS) medium containing 3.0 mg·L⁻¹ 6-benzyladenine (BA) in a combination with 2 mg·L⁻¹ 2,4-dichlorophenoxy acetic acid (2,4-D). From the callus cultures, a cell suspension culture was initiated and the cellular differentiation was investigated. In addition, the effect of biotic elicitors such as methyl jasmonate (MeJa), salicylic acid (SA), and sodium nitroprusside (SNP) on the accumulation of secondary metabolites and antioxidant properties was demonstrated. Among the elicitors, the MeJa elicited the accumulation of total phenols, flavonoids, and acacetin, a flavonoid compound with multiple pharmaceutical values. Similarly, the higher concentrations of the MeJa significantly modulated the activities of antioxidant enzymes and enhanced the scavenging potentials of free radicals of cell suspension extracts. Overall, the outcomes of this study can be utilized for the large scale production of pharmaceutically important secondary metabolites from S. kakudensis through cell suspension cultures.

A Decade of Molecular Understanding of Withanolide Biosynthesis and In vitro Studies in Withania somnifera (L.) Dunal: Prospects and Perspectives for Pathway Engineering

Withania somnifera, a multipurpose medicinal plant is a rich reservoir of pharmaceutically active triterpenoids that are steroidal lactones known as withanolides. Though the plant has been well-characterized in terms of phytochemical profiles as well as pharmaceutical activities, limited attempts have been made to decipher the biosynthetic route and identification of key regulatory genes involved in withanolide biosynthesis. This scenario limits biotechnological interventions for enhanced production of bioactive compounds. Nevertheless, recent emergent trends vis-à-vis, the exploration of genomic, transcriptomic, proteomic, metabolomics, and in vitro studies have opened new vistas regarding pathway engineering of withanolide production. During recent years, various strategic pathway genes have been characterized with significant amount of regulatory studies which allude toward development of molecular circuitries for production of key intermediates or end products in heterologous hosts. Another pivotal aspect covering redirection of metabolic flux for channelizing the precursor pool toward enhanced withanolide production has also been attained by deciphering decisive branch point(s) as robust targets for pathway modulation. With these perspectives, the current review provides a detailed overview of various studies undertaken by the authors and collated literature related to molecular and in vitro approaches employed in W. somnifera for understanding various molecular network interactions in entirety.

Transcriptome analysis reveals in vitro cultured Withania somnifera leaf and root tissues as a promising source for targeted withanolide biosynthesis

Background

The production of metabolites via in vitro culture is promoted by the availability of fully defined metabolic pathways. Withanolides, the major bioactive phytochemicals of Withania somnifera, have been well studied for their pharmacological activities. However, only a few attempts have been made to identify key candidate genes involved in withanolide biosynthesis. Understanding the steps involved in withanolide biosynthesis is essential for metabolic engineering of this plant to increase withanolide production.

Results

Transcriptome sequencing was performed on in vitro adventitious root and leaf tissues using the Illumina platform. We obtained a total of 177,156 assembled transcripts with an average unigene length of 1,033 bp. About 13% of the transcripts were unique to in vitro adventitious roots but no unique transcripts were observed in in vitro-grown leaves. A putative withanolide biosynthetic pathway was deduced by mapping the assembled transcripts to the KEGG database, and the expression of candidate withanolide biosynthesis genes -were validated by qRT PCR. The accumulation pattern of withaferin A and withanolide A varied according to the type of tissue and the culture period. Further, we demonstrated that in vitro leaf extracts exhibit anticancer activity against human gastric adenocarcinoma cell lines at sub G1 phase.

Conclusions

We report here a validated large-scale transcriptome data set and the potential biological activity of in vitro cultures of W. somnifera. This study provides important information to enhance tissue-specific expression and accumulation of secondary metabolites, paving the way for industrialization of in vitro cultures of W. somnifera.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1214-0) contains supplementary material, which is available to authorized users.

Enhanced biosynthesis of withanolides by elicitation and precursor feeding in cell suspension culture of Withania somnifera (L.) Dunal in shake-flask culture and bioreactor

The present study investigated the biosynthesis of major and minor withanolides of Withania somnifera in cell suspension culture using shake-flask culture and bioreactor by exploiting elicitation and precursor feeding strategies. Elicitors like cadmium chloride, aluminium chloride and chitosan, precursors such as cholesterol, mevalonic acid and squalene were examined. Maximum total withanolides detected [withanolide A (7606.75 mg), withanolide B (4826.05 mg), withaferin A (3732.81 mg), withanone (6538.65 mg), 12 deoxy withanstramonolide (3176.63 mg), withanoside IV (2623.21 mg) and withanoside V (2861.18 mg)] were achieved in the combined treatment of chitosan (100 mg/l) and squalene (6 mM) along with 1 mg/l picloram, 0.5 mg/l KN, 200 mg/l L-glutamine and 5% sucrose in culture at 4 h and 48 h exposure times respectively on 28^th day of culture in bioreactor. We obtained higher concentrations of total withanolides in shake-flask culture (2.13-fold) as well as bioreactor (1.66-fold) when compared to control treatments. This optimized protocol can be utilized for commercial level production of withanolides from suspension culture using industrial bioreactors in a short culture period.

Medicinal plant cell suspension cultures: pharmaceutical applications and high-yielding strategies for the desired secondary metabolites

The development of plant tissue (including organ and cell) cultures for the production of secondary metabolites has been underway for more than three decades. Plant cell cultures with the production of high-value secondary metabolites are promising potential alternative sources for the production of pharmaceutical agents of industrial importance. Medicinal plant cell suspension cultures (MPCSC), which are characterized with the feature of fermentation with plant cell totipotency, could be a promising alternative "chemical factory". However, low productivity becomes an inevitable obstacle limiting further commercialization of MPCSC and the application to large-scale production is still limited to a few processes. This review generalizes and analyzes the recent progress of this bioproduction platform for the provision of medicinal chemicals and outlines a range of trials taken or underway to increase product yields from MPCSC. The scale-up of MPCSC, which could lead to an unlimited supply of pharmaceuticals, including strategies to overcome and solution of the associated challenges, is discussed.

Enhancement of phenolics, resveratrol and antioxidant activity by nitrogen enrichment in cell suspension culture of Vitis vinifera

Ammonium nitrate (NH₄NO₃), an important nitrogen source (34% N), has been used as an elicitor to stimulate plant growth and development as well as induce secondary metabolites under controlled conditions. In the present paper, we investigated the enhancement of cell biomass, total phenolics, resveratrol levels, and antioxidant activity of Vitis vinifera cv. Pok Dum by nitrogen enrichment (MS medium supplemented with NH₄NO₃ at 0, 500, 1,000, 5,000 and 10,000 mg/L). The highest accumulations of biomass, phenolics and resveratrol contents were observed at 8.8-fold (86.6 g DW/L), 15.9-fold (71.91 mg GAE/g DW) and 5.6-fold (277.89 µg/g DW) by the 14th day, in the medium supplemented with 500 mg/L NH₄NO₃. Moreover, the antioxidant activities of cultured grape cells estimated by the DPPH^● and ABTS^●+ assay were positively correlated with phenolics and resveratrol, and the maximum activity was also observed in cultured cells with 500 mg/L NH₄NO₃ at 176.11 and 267.79 mmol TE/100 g DW, respectively.

Sustainable production of azadirachtin from differentiated in vitro cell lines of neem (Azadirachta indica)

Neem possesses immense medicinal properties and has immediate application as ecofriendly, biodegradable biopesticide. All these properties are because of a structurally complex bioactive compound Azadirachtin, mainly present in seeds. However, it could not be exploited to its full because of heterogeneity in compound production due to out-breeding in nature of the plant. This is the first elaborate report on systematic studies on azadirachtin biosynthesis where different redifferentiated and dedifferentiated in vitro cell lines of A. indica (neem), obtained from various explants, were utilized. All cell lines were found positive for the compound with significantly higher azadirachtin yield of 2330 µg /g DW was obtained from redifferentiated cell lines established from zygotic embryo cultures. The study, demonstrates the possibility of consistent biosynthesis of azadirachtin in bulk under optimal growth conditions.

Azadirachtin has high industrial demand due to its immediate application as an ecofriendly, biodegradable biopesticide and also due to its various other significant bioactivities. To date, the only commercially feasible way to produce azadirachtin is extraction from seeds, but their availability is very limited as the tree flowers only once a year and only one-third of the fruits are collected due to operational problems. Further, due to the strict out-breeding nature of the plant, the seeds are highly heterozygous, resulting in inconsistent metabolite production. Therefore, in the present study, to achieve sustainable production of azadirachtin, dedifferentiated and redifferentiated calli derived from various explants of neem—zygotic embryo, leaf and ovary—were investigated for their potential to biosynthesize azadirachtin. High-performance liquid chromatography analysis of the in vitro cell lines showed the presence of azadirachtin in all the samples tested, the content of which in cultured cells varied with explant source and cell differentiation response. The presence of azadirachtin in samples was further confirmed by positive electrospray ionization mass spectroscopy. The zygotic embryo cultures of neem accumulated much higher amounts of azadirachtin than leaf and ovary cultures. Furthermore, organized in vitro callus cultures (redifferentiated) supported higher azadirachtin biosynthesis, while unorganized callus cultures (dedifferentiated) supported the least. The maximum azadirachtin content of 2.33 mg g⁻¹ dry weight was obtained from redifferentiated immature zygotic embryo cultures.

A promising approach on biomass accumulation and withanolides production in cell suspension culture of Withania somnifera (L.) Dunal

Withanolide is one of the most extensively exploited steroidal lactones, which are biosynthesized in Withania somnifera. Its production from cell suspension culture was analyzed to defeat limitations coupled with its regular supply from the plant organs. In order to optimize the different factors for sustainable production of withanolides and biomass accumulations, different concentrations of auxins or cytokinins and their combinations, carbon sources, agitation speed, organic additives and seaweed extracts was studied in cell suspension culture. Maximum biomass accumulation (16.72 g fresh weight [FW] and 4.18 g dry weight [DW]) and withanolides production (withanolide A 7.21 mg/g DW, withanolide B 4.23 mg/g DW, withaferin A 3.88 mg/g DW and withanone 6.72 mg/g DW) were achieved in the treatment of Gracilaria edulis extract at 40 % level. Organic additive L-glutamine at 200 mg/l in combination with picloram (1 mg/l) and KN (0.5 mg/l) promoted growth characteristics (11.87 g FW and 2.96 g DW) and withanolides synthesis (withanolide A 5.04 mg/g DW, withanolide B 2.59 mg/g DW, withaferin A 2.36 mg/g DW and withanone 4.32 mg/g DW). Sucrose at 5 % level revolved out to be a superior carbon source yielded highest withanolides production (withanolide A 2.88 mg/g DW, withanolide B 1.48 mg/g DW, withaferin A 1.35 mg/g DW and withanone 2.47 mg/g DW), whereas biomass (7.28 g FW and 1.82 g DW) was gratefully increased at 2 % level of sucrose in cell suspension culture. This optimized protocol can be utilized for large scale cultivation of W. somnifera cells in industrial bioreactors for mass synthesis of major withanolides.

Influence of plant growth regulators on callus mediated regeneration and secondary metabolites synthesis in Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal, is an important medicinal plant being the source of extremely important compounds like withanolides and withaferin. Influence of different plant growth regulators (PGRs) were evaluated for induction of callus, callus mediated regeneration and production of secondary metabolites in them. Explants for callusing were collected from plants grown in vitro and maximum callusing (98 %) was obtained on MS medium supplemented with a combination of 2,4-dichlorophenoxy acetic acid (2,4-D) (0.5 mg l(-1)) and kinetin (KN) (0.2 mg l(-1)). Among different types of calli, best shoot regeneration was observed on green, compact calli produced on MS medium with a combination of 6-benzylamino purine (BAP) and indole butyric acid (IBA). MS medium supplemented with BAP (2 mg l(-1)) showed highest frequency (98 %) of shoot bud regeneration. The micro-shoots were efficiently rooted on MS media supplemented with 0.5 mg l(-1) IBA. Rooted plants were transferred to soil-vermi-compost (1:3; w/w) medium in greenhouse for acclimatization. Presence of withanolide A and withaferin A in calli was validated through high performance thin layer chromatography (HPTLC). It was interesting to observe that the PGRs showed significant influence on the secondary metabolites production in callus and 2,4-D having the least effect. Histological studies revealed the origin of shoot tip in the callus during regeneration.