Indirect regeneration of Withania somnifera and comparative analysis of withanolides in in vitro and greenhouse grown plants

Optimization of Elicitation Conditions to Enhance the Production of Potent Metabolite Withanolide from Withania somnifera (L.)

This study aimed at optimizing conditions for increased withanolide production in Withania somnifera. The elicitors used for the foliar spray on the aerial parts of the plant were salicylic acid, jasmonic acid, and chitosan for the enhancement of withanolides in Withania somnifera under different environmental regimes. Three different elicitors, i.e., chitosan, jasmonic acid and salicylic acid, were applied on the plants through foliar route every 15th day for 6 months, and later plants were used for sample preparation. Further, the elicitors were used in different concentration, i.e., jasmonic acid (50, 200 and 400 ppm), chitosan (10, 50 and 100 ppm) and salicylic acid (0.5, 1 and 2 ppm). The elicitors were sprayed on the foliar parts of the plant between 10:00-11:00 a.m. on application days. For elicitor spray, a calibrated sprayer was used. The withanolide A/withaferin A was quantified through HPLC. It was found that in an open environment, maximum withaferin A content, i.e., 0.570 mg/g (DW), was recorded with jasmonic acid (50 ppm) treatment in comparison to control (0.067 mg/g DW). Thus, there was an 8.5-fold increase in the withaferin A content. Maximum withanolide A content of 0.352 mg/g (DW) was recorded when chitosan (50 ppm) was sprayed, while in the control, withanolide A content was recorded to be 0.031 mg/g (DW); thus, chitosan application increased the production of withanolide A by 11.3-fold. Under controlled conditions, maximum withaferin A content of 1.659 mg/g (DW) was recorded when plants were sprayed with chitosan (100 ppm), which was 8.1 times greater than the control content of 0.203 mg/g (DW). Maximum withanolide A content of 0.460 mg/g (DW) was recorded when chitosan (100 ppm) was applied, whereas in the control, withanolide A content was found to be 0.061 mg/g (DW). Thus, foliar spraying of elicitors in very low concentrations can serve as a low-cost, eco-friendly, labor-intensive and elegant alternative approach that can be practiced by farmers for the enhancement, consistent production and improved yield of withanolide A/withaferin A. This can be a suitable way to enhance plant productivity, thus increasing the availability of withanolide A and withaferin A for the health and pharma industry.

Critical factors influencing in vitro propagation and modulation of important secondary metabolites in Withania somnifera (L.) dunal

Withania somnifera (L.) Dunal is a valuable medicinal plant in the Solanaceae family. It is commonly known as Ashwagandha and is widely distributed around the globe. It has multiple pharmacological properties owing to the existence of diverse secondary metabolites viz., withanolide A, withanolide D, withaferin A, and withanone. It is in great demand in the herbal industry because of its extensive use. In this background, the major challenge lies in the rapid multiplication of elite cultivars of W. somnifera in order to produce genetically and phytoconstituents uniform plant material for pharmaceutical industries. Thus it is necessary to explore various biotechnological approaches for the clonal mass propagation and synthesis of pharmaceutically important constituents in W. somnifera. Though there are several studies on in vitro propagation on W. somnifera, yet many factors that critically influence the in vitro response and withanolides production need to be fine-tuned in the pretext of the existing knowledge. The current review focuses on the advancements and prospects in biotechnological interventions to meet the worldwide demands for W. somnifera and its bioactive compounds. This update on in vitro studies on W. somnifera will be useful to many researchers, entrepreneurs, and herbal industries looking for its in vitro mass multiplication and scientific utilization.

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.

Hemidesmus indicus L. Br.: critical assessment of in vitro biotechnological advancements and perspectives

Hemidesmus indicus (L.) R. Br. ex Schult., commonly known as Indian sarsaparilla or Anantamul, is an ethnopharmacologically important medicinal plant from the family Apocynaceae. Biosynthesis of an array of bioactive compounds such as methoxybenzaldehydes and their derivatives has been accountable for its intensive medicinal attributes. Low seed setting, over-exploitation from natural habitat and a need for selection and preservation of elite germplasms yielding higher levels of bioactive compounds have led researchers to enquire the standardization of micropropagation techniques and quantitative estimation of phytochemicals from H. indicus. The present work aims to have a comprehensive account on micropropagation in H. indicus, a comparative estimation of biotic and abiotic factors, viz. elicitors and precursors playing a crucial role in H. indicus tissue culture, a critical appraisal of applied protocols to nullify embellished claims and a discussion on future perspectives. The review also highlights the comparative effect of different plant growth regulators as well as their combined role in rhizogenesis, callogenesis, base callus formation, callusing and somatic embryo-mediated indirect organogenesis, outcome of explant selection, contribution of abiotic (temperature, photoperiod, moisture, inorganic molecules) factors, role of carbon source, application of sterilization techniques and associated success rates, role of factors essential for acclimatization and secondary metabolite production, synthetic seed production and genetic transformation techniques. The compiled information along with individual study details, respective outcome and variability of reports will aid in proper assessment of cited standardized tissue culture protocols in H. indicus especially in relation to secondary metabolite production. Moreover, the assessment of applicability of different methodologies in this aspect will aid in the selection of high-yielding germplasms or chemotypes which is not only profitable for industrial application but also important for basic and applied preclinical and clinical research studies. KEY POINTS: • Critical and updated assessment on in vitro biotechnology in Hemidesmus indicus. • Biotechnological advancement via Agrobacterium-mediated transformation. • Key shortcomings and future research directions Graphical abstract Effect of biotic and abiotic factors on Micropropagation and secondary metabolite synthesis in Hemidesmus indicus.

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.

In Vitro Propagation and Conservation of Withania somnifera (Dunal) L

Plant tissue culture offers several techniques for rapid clonal propagation, germplasm conservation, regeneration of genetically manipulated superior clones, production of phyto-constituents, and ex vitro conservation of valuable phytodiversity. An improved and efficient micropropagation protocol for Withania somnifera (L.), a drug-producing medicinal plant, using juvenile explants (nodal explants) has been developed. Highest multiplication and subsequent elongation of shoots is observed on MS medium containing BA and NAA. The regenerated microshoots roots best on ½ MS medium containing NAA, established in earthen pots containing garden soil and are maintained in the greenhouse with 95 % survival rate. Genetic uniformity of micropropagated plants is confirmed by PCR-based DNA fingerprinting techniques, viz., RAPD and ISSR. No variation is observed in DNA fingerprinting patterns among the micropropagated plants, which are similar to that of the donor plant illustrating their genetic uniformity.

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.

Withania somnifera: Advances and Implementation of Molecular and Tissue Culture Techniques to Enhance Its Application

Withania somnifera, commonly known as Ashwagandha an important medicinal plant largely used in Ayurvedic and indigenous medicine for over 3,000 years. Being a medicinal plant, dried powder, crude extract as well as purified metabolies of the plant has shown promising therapeutic properties. Withanolides are the principal metabolites, responsible for the medicinal properties of the plant. Availability and amount of particular withanolides differ with tissue type and chemotype and its importance leads to identification characterization of several genes/ enzymes related to withanolide biosynthetic pathway. The modulation in withanolides can be achieved by controlling the environmental conditions like, different tissue culture techniques, altered media compositions, use of elicitors, etc. Among all the in vitro techniques, hairy root culture proved its importance at industrial scale, which also gets benefits due to more accumulation (amount and number) of withanolides in roots tissues of W. somnifera. Use of media compostion and elicitors further enhances the amount of withanolides in hairy roots. Another important modern day technique used for accumulation of desired secondary metabolites is modulating the gene expression by altering environmental conditions (use of different media composition, elicitors, etc.) or through genetic enginnering. Knowing the significance of the gene and the key enzymatic step of the pathway, modulation in withanolide contents can be achieved upto required amount in therapeutic industry. To accomplish maximum productivity through genetic enginnering different means of Withania transformation methods have been developed to obtain maximum transformation efficiency. These standardized transformation procedues have been used to overexpress/silence desired gene in W. somnifera to understand the outcome and succeed with enhanced metabolic production for the ultimate benefit of human race.

Free radical scavenging activity and comparative metabolic profiling of in vitro cultured and field grown Withania somnifera roots

Free radical scavenging activity (FRSA), total phenolic content (TPC), and total flavonoid content (TFC) of in vitro cultured and field grown Withania somnifera (Ashwagandha) roots were investigated. Withanolides analysis and comprehensive metabolic profiling between 100% methanol extracts of in vitro and field grown root tissues was performed using high performance thin layer chromatography (HPTLC) and gas chromatography-mass spectrometry (GC-MS), respectively. Significantly higher levels of FRSA, TPC, and TFC were observed in in-vitro cultured roots compared with field grown samples. In addition, 30 day-cultured in vitro root samples (1MIR) exhibited a significantly higher FRSA (IC₅₀ 81.01 μg/mL), TPC (118.91 mg GAE/g), and TFC (32.68 mg CE/g) compared with those in 45 day-cultured samples (1.5MIR). Total of 29 metabolites were identified in in vitro cultured and field grown roots by GC-MS analysis. The metabolites included alcohols, organic acids, purine, pyrimidine, sugars, and putrescine. Vanillic acid was only observed in the in vitro cultured root samples, and higher level of the vanillic acid was observed in 1MIR when compared to 1.5MIR. Therefore, it is suggested that 1MIR might serve as an alternative to field grown roots for the development of medicinal and functional food products.

In vitro propagation and withaferin A production in Withania ashwagandha, a rare medicinal plant of India

Withania ashwagandha, belonging to the family Solanaceae, is an important medicinal herb of India with restricted geographic distribution. It is a rich source of withaferin A (WA) and other bioactive withanolides. In the present study a rapid in vitro mass propagation protocol of W. ashwagandha was developed from nodal explants. Nodal explants were cultured on MS medium supplemented with various concentrations and combinations of plant growth regulators (PGRs). The highest number of regenerated shoots per ex-plant (33 ± 2.7) and highest WA (13.4 ± 1.15 mg/g of DW) production was obtained on MS medium supplemented with 5.0 μM 6-benzyladenine (BA) and 1.0 μM Kinetin (Kn). In vitro raised shoots were further rooted on half-strength MS medium containing 2.0 μM Indole-3-butyric acid (IBA) and analyzed for WA production. The rooted plantlets when transferred to poly bags in the greenhouse showed 90 % survival frequency. Levels of WA were higher in the in vitro and ex vitro derived shoot and root tissues as compared to field grown mother plants. In an attempt to further maximize WA production, shoot cultures were further grown in liquid MS medium supplemented with 5.0 μM 6-benzyladenine (BA) and 1.0 μM Kinetin (Kn). Root cultures were grown on half strength MS liquid medium fortified with 2.0 μM of IBA. WA production in the liquid cultures was significantly higher compared to the static composition of the same media. This protocol, first of its kind in this plant, can be successfully employed for conservation, proliferation and large-scale production of WA. The regenerated plants can also be used in traditional medicine as an alternative to naturally collected plants.

Establishment of an efficient and rapid method of multiple shoot regeneration and a comparative phenolics profile in in vitro and greenhouse-grown plants of Psophocarpus tetragonolobus (L.) DC

An in vitro method of multiple shoot induction and plant regeneration in Psophocarpus tetragonolobus (L.) DC was developed. Cotyledons, hypocotyls, epicotyls, internodal and young seedling leaves were used as explants. MS media supplemented with various concentrations of either thidiazuron (TDZ) or N6-benzylaminopurine (BAP) along with NAA or IAA combinations were used to determine their influence on multiple shoot induction. MS media supplemented with TDZ induced direct shoot regeneration when epicotyls and internodal segments were used as explants. TDZ at 3 mg L(-1) induced highest rate (89.2 ± 3.28%) of regeneration with (13.4 ± 2.04) shoots per explant. MS media supplemented with BAP in combination with NAA or IAA induced callus mediated regeneration when cotyledons and hypocotyls were used as explants. BAP (2.5 mg L(-1)) and IAA (0.2 mg L(-1)) induced highest rate (100 ± 2.66%) of regeneration with (23.2 ± 2.66) shoots per explant. Mature plants produced from regenerated shoots were transferred successfully to the greenhouse. In a comparative study, the phenolics contents of various parts of greenhouse-grown plants with that of in vitro-raised plants showed significant variations.

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.