Effective elicitors and process strategies for enhancement of secondary metabolite production in hairy root cultures

Modifications in gene expression and phenolic compounds content by methyl jasmonate and fungal elicitors in Ficus carica. Cv. Siah hairy root cultures

BACKGROUND

One of the most effective strategies to increase phytochemicals production in plant cultures is elicitation. In the present study, we studied the effect of abiotic and biotic elicitors on the growth, key biosynthetic genes expression, antioxidant capacity, and phenolic compounds content in Rhizobium (Agrobacterium) rhizogenes-induced hairy roots cultures of Ficus carica cv. Siah.

METHODS

The elicitors included methyl jasmonate (MeJA) as abiotic elicitor, culture filtrate and cell extract of fungus Piriformospora indica as biotic elicitors were prepared to use. The cultures of F. carica hairy roots were exposed to elicitores at different time points. After elicitation treatments, hairy roots were collected, and evaluated for growth index, total phenolic (TPC) and flavonoids (TFC) content, antioxidant activity (2,2-diphenyl-1-picrylhydrazyl, DPPH and ferric ion reducing antioxidant power, FRAP assays), expression level of key phenolic/flavonoid biosynthesis genes, and high-performance liquid chromatography (HPLC) analysis of some main phenolic compounds in comparison to control.

RESULTS

Elicitation positively or negatively affected the growth, content of phenolic/flavonoid compounds and DPPH and FRAP antioxidant activities of hairy roots cultures in depending of elicitor concentration and exposure time. The maximum expression level of chalcone synthase (CHS: 55.1), flavonoid 3'-hydroxylase (F3'H: 34.33) genes and transcription factors MYB3 (32.22), Basic helix-loop-helix (bHLH: 45.73) was induced by MeJA elicitation, whereas the maximum expression level of phenylalanine ammonia-lyase (PAL: 26.72) and UDP-glucose flavonoid 3-O-glucosyltransferase (UFGT: 27.57) genes was obtained after P. indica culture filtrate elicitation. The P. indica elicitation also caused greatest increase in the content of gallic acid (5848 µg/g), caffeic acid (508.2 µg/g), rutin (43.5 µg/g), quercetin (341 µg/g), and apigenin (1167 µg/g) phenolic compounds.

CONCLUSIONS

This study support that elicitation of F. carica cv. Siah hairy roots can be considered as an effective biotechnological method for improved phenolic/flavonoid compounds production, and of course this approach requires further research.

Hairy root culture: a potent method for improved secondary metabolite production of Solanaceous plants

Secondary metabolites synthesized by the Solanaceous plants are of major therapeutic and pharmaceutical importance, many of which are commonly obtained from the roots of these plants. 'Hairy roots', mirroring the same phytochemical pattern of the corresponding root of the parent plant with higher growth rate and productivity, are therefore extensively studied as an effective alternative for the in vitro production of these metabolites. Hairy roots are the transformed roots, generated from the infection site of the wounded plants with Agrobacterium rhizogenes. With their fast growth, being free from pathogen and herbicide contamination, genetic stability, and autotrophic nature for plant hormones, hairy roots are considered as useful bioproduction systems for specialized metabolites. Lately, several elicitation methods have been employed to enhance the accumulation of these compounds in the hairy root cultures for both small and large-scale production. Nevertheless, in the latter case, the cultivation of hairy roots in bioreactors should still be optimized. Hairy roots can also be utilized for metabolic engineering of the regulatory genes in the metabolic pathways leading to enhanced production of metabolites. The present study summarizes the updated and modern biotechnological aspects for enhanced production of secondary metabolites in the hairy root cultures of the plants of Solanaceae and their respective importance.

Methyl jasmonate and salicylic acid as powerful elicitors for enhancing the production of secondary metabolites in medicinal plants: an updated review

Plant secondary metabolites are bioactive scaffolds that are crucial for plant survival in the environment and to maintain a defense mechanism from predators. These compounds are generally present in plants at a minimal level and interestingly, they are found to have a wide variety of therapeutic values for humans. Several medicinal plants are used for pharmaceutical purposes due to their affordability, fewer adverse effects, and vital role in traditional remedies. Owing to this reason, these plants are exploited at a high range worldwide and therefore many medicinal plants are on the threatened list. There is a need of the hour to tackle this major problem, one effective approach called elicitation can be used to enhance the level of existing and novel plant bioactive compounds using different types of elicitors namely biotic and abiotic. This process can be generally achieved by in vitro and in vivo experiments. The current comprehensive review provides an overview of biotic and abiotic elicitation strategies used in medicinal plants, as well as their effects on secondary metabolites enhancement. Further, this review mainly deals with the enhancement of biomass and biosynthesis of different bioactive compounds by methyl jasmonate (MeJA) and salicylic acid (SA) as elicitors of wide medicinal plants in in vitro by using different cultures. The present review was suggested as a significant groundwork for peers working with medicinal plants by applying elicitation strategies along with advanced biotechnological approaches.

Enhanced Production of Active Photosynthetic and Biochemical Molecules in Silybum marianum L. Using Biotic and Abiotic Elicitors in Hydroponic Culture

Elicitors are stressors that activate secondary pathways that lead to the increased production of bioactive molecules in plants. Different elicitors including the fungus Aspergillus niger (0.2 g/L), methyl jasmonate (MeJA, 100 µM/L), and silver nanoparticles (1 µg/L) were added, individually and in combination, in a hydroponic medium. The application of these elicitors in hydroponic culture significantly increased the concentration of photosynthetic pigments and total phenolic contents. The treatment with MeJA (methyl jasmonate) (100 µM/L) and the co-treatment of MeJA and AgNPs (silver nanoparticles) (100 µM/L + 1 µg/L) exhibited the highest chlorophyll a (29 µg g^-1 FW) and chlorophyll b (33.6 µg g^-1 FW) contents, respectively. The elicitor MeJA (100 µM/L) gave a substantial rise in chlorophyll a and b and total chlorophyll contents. Likewise, a significant rise in carotenoid contents (9 µg/g FW) was also observed when subjected to meJA (100 µM/L). For the phenolic content, the treatment with meJA (100 µM/L) proved to be very effective. Nevertheless, the highest production (431 µg/g FW) was observed when treated with AgNPs (1 µg/L). The treatments with various elicitors in this study had a significant effect on flavonoid and lignin content. The highest concentration of flavonoids and lignin was observed when MeJA (100 mM) was used as an elicitor, following a 72-h treatment period. Hence, for different plant metabolites, the treatment with meJA (100 µM/L) and a co-treatment of MeJA and AgNPs (100 µM/L + 1 µg/L) under prolonged exposure times of 120-144 h proved to be the most promising in the accretion of valuable bioactive molecules. The study opens new insights into the use of these elicitors, individually or in combination, by using different concentrations and compositions.

A Multifaceted Review of Eurycoma longifolia Nutraceutical Bioactives: Production, Extraction, and Analysis in Drugs and Biofluids

Eurycoma longifolia Jack (known as Tongkat Ali) is a popular traditional herbal medicine, native to southeast Asia, that is well-known for its aphrodisiac as well as several other effects. Mostly, the root extract of E. longifolia is used as a folk medicine for sexual dysfunction, aging, anxiety, exercise recovery, fever, increased energy, and osteoporosis. These health effects led to the inclusion of E. longifolia in dietary supplements, particularly for bodybuilding purposes. These effects are mediated by a myriad of bioactive compounds belonging to quassinoids, canthin-6-one alkaloids, tirucallane triterpenes, squalene derivatives, and bioactive steroids. Among these phytoconstituents, quassinoids account for a large portion of E. longifolia root phytochemicals. Of these ingredients, eurycomanone, the major quassinoid in E. longifolia extract, accounts to a large extent for its health effects. This review capitalizes on the novel trends toward the production of E. longifolia bioactives using biotechnology and extraction optimization for best yields and recovery. Alongside, novel extraction methods, i.e., green techniques, of E. longifolia bioactives are described. Further, an overview of the different analytical approaches for the quality control assessment of E. longifolia plant material and nutraceuticals is presented alongside studies in body fluids to determine its pharmacokinetics and efficacy level. Such a compilation of analytical methods will help ensure safety and efficacy of that major drug.

Improving galegine production in transformed hairy roots of Galega officinalis L. via elicitation

Galega officinalis L. is an herbaceous legume used to treat symptoms associated with hyperglycemia or diabetes mellitus because of its dominant alkaloid, galegine. In this study, we induced hairy roots in this plant using Rhizobium rhizogenes strain A4, and investigated the effect of type, concentration, and duration of elicitor application on galegine content and some phytochemical characteristics in the hairy roots. Hence, the best growing hairy root line in terms of growth rate was selected and subcultured for treatment with elicitors. Then, at the end of the log phase of growth, chitosan (100, 200, and 400 mg/L), salicylic acid (100, 200, and 300 mM), and ultrasound (1, 2, and 4 min) were applied to hairy roots culture medium. High-performance liquid chromatography (HPLC) showed that the content of galegine was significantly increased after elicitation compared with the control. Thus, the highest content of galegine (14.55 mg/g FW) was obtained 2 days after elicitation when ultrasonic waves were applied to the hairy root culture medium for 4 min. Also, elicitation resulted in a significant increase in the content of total phenol, flavonoid, H₂O₂ and MDA compared with the control. So that the highest total flavonoid content was obtained in hairy roots that were treated with ultrasonic waves for 4 min and harvested 2 days after elicitation; while, application of 400 mg/L chitosan for 4 days resulted in the highest total phenol (16.84 mg/g FW).

Chemical Elicitors-Induced Variation in Cellular Biomass, Biosynthesis of Secondary Cell Products, and Antioxidant System in Callus Cultures of Fagonia indica

Fagonia indica is a rich source of pharmacologically active compounds. The variation in the metabolites of interest is one of the major issues in wild plants due to different environmental factors. The addition of chemical elicitors is one of the effective strategies to trigger the biosynthetic pathways for the release of a higher quantity of bioactive compounds. Therefore, this study was designed to investigate the effects of chemical elicitors, aluminum chloride (AlCl₃) and cadmium chloride (CdCl₂), on the biosynthesis of secondary metabolites, biomass, and the antioxidant system in callus cultures of F. indica. Among various treatments applied, AlCl₃ (0.1 mM concentration) improved the highest in biomass accumulation (fresh weight (FW): 404.72 g/L) as compared to the control (FW: 269.85 g/L). The exposure of cultures to AlCl₃ (0.01 mM) enhanced the accumulation of secondary metabolites, and the total phenolic contents (TPCs: 7.74 mg/g DW) and total flavonoid contents (TFCs: 1.07 mg/g DW) were higher than those of cultures exposed to CdCl₂ (0.01 mM) with content levels (TPC: 5.60 and TFC: 0.97 mg/g) as compared to the control (TPC: 4.16 and TFC: 0.42 mg/g DW). Likewise, AlCl₃ and CdCl₂ also promoted the free radical scavenging activity (FRSA; 89.4% and 90%, respectively) at a concentration of 0.01 mM, as compared to the control (65.48%). For instance, the quantification of metabolites via high-performance liquid chromatography (HPLC) revealed an optimum production of myricetin (1.20 mg/g), apigenin (0.83 mg/g), isorhamnetin (0.70 mg/g), and kaempferol (0.64 mg/g). Cultures grown in the presence of AlCl₃ triggered higher quantities of secondary metabolites than those grown in the presence of CdCl₂ (0.79, 0.74, 0.57, and 0.67 mg/g). Moreover, AlCl₃ at 0.1 mM enhanced the biosynthesis of superoxide dismutase (SOD: 0.08 nM/min/mg-FW) and peroxidase enzymes (POD: 2.37 nM/min/mg-FW), while CdCl₂ resulted in an SOD activity up to 0.06 nM/min/mg-FW and POD: 2.72 nM/min/mg-FW. From these results, it is clear that AlCl₃ is a better elicitor in terms of a higher and uniform productivity of biomass, secondary cell products, and antioxidant enzymes compared to CdCl₂ and the control. It is possible to scale the current strategy to a bioreactor for a higher productivity of metabolites of interest for various pharmaceutical industries.

Application of Hairy Root Culture for Bioactive Compounds Production in Medicinal Plants

Medicinal plants are rich sources of natural bioactive compounds used to treat many diseases. With the development of the health industry, the market demands for Chinese medicine have been rapidly increasing in recent years. However, over-utilization of herbal plants would cause serious ecological problems. Therefore, an effective approach should be developed to produce the pharmaceutically important natural drugs. Hairy root culture induced by Agrobacterium rhizogenes has been considered to be an effective tool to produce secondary metabolites that are originally biosynthesized in the roots or even in the aerial organs of mature plants. This review aims to summarize current progress on medicinal plant hairy root culture for bioactive compounds production. It presents the stimulating effects of various biotic and abiotic elicitors on the accumulation of secondary metabolites. Synergetic effects by combination of different elicitors or with other strategies are also included. Besides, the transgenic system has promising prospects to increase bioactive compounds content by introducing their biosynthetic or regulatory genes into medicinal plant hairy root. It offers great potential to further increase secondary metabolites yield by the integration of manipulating pathway genes with elicitors and other strategies. Then advances on two valuable pharmaceuticals production in the hairy root cultures are illustrated in detail. Finally, successful production of bioactive compounds by hairy root culture in bioreactors are introduced.

Biochemistry of Terpenes and Recent Advances in Plant Protection

Biodiversity is adversely affected by the growing levels of synthetic chemicals released into the environment due to agricultural activities. This has been the driving force for embracing sustainable agriculture. Plant secondary metabolites offer promising alternatives for protecting plants against microbes, feeding herbivores, and weeds. Terpenes are the largest among PSMs and have been extensively studied for their potential as antimicrobial, insecticidal, and weed control agents. They also attract natural enemies of pests and beneficial insects, such as pollinators and dispersers. However, most of these research findings are shelved and fail to pass beyond the laboratory and greenhouse stages. This review provides an overview of terpenes, types, biosynthesis, and their roles in protecting plants against microbial pathogens, insect pests, and weeds to rekindle the debate on using terpenes for the development of environmentally friendly biopesticides and herbicides.

The effect of salt stress on the production of apocarotenoids and the expression of genes related to their biosynthesis in saffron

Saffron stigmas are widely used as food additives and as traditional medicine in Iran and many other countries. The unique taste, flavor and pharmaceutical properties of saffron stigmas are due to the presence of three apocarotenoids secondary metabolites crocin, picrocrocin and safranal. There is limited knowledge about the effect of environmental stresses on the metabolism of apocarotenoids in saffron. We analyzed the content of crocin and picrocrocin and the expression of key genes of apocarotenoid biosynthesis pathways (CsCCD2, CsCCD4, CsUGT2, CsCHY-β and CsLCYB) in saffron plants exposed to moderate (90 mM) and high (150 mM) salt (NaCl) concentrations. Measuring ion concentrations in leaves showed an increased accumulation of Na⁺ and decreased uptake of K⁺ in salt treated compared to control plants indicating an effective salt stress. HPLC analysis of apocarotenoids revealed that crocin production was significantly halted (P < 0.05) with increasing salt concentration while picrocrocin level did not change with moderate salt but significantly dropped by high salt concentration. Real-time PCR analysis revealed a progressive decrease in transcript levels of CsUGT2 and CsLCYB genes with increasing salt concentration (P < 0.05). The expression of CsCCD2 and CsCHY-β tolerated moderate salt concentration but significantly downregulated with high salt concentration. CsCCD4 however responded differently to salt concentration being decreased with moderate salt but increased at higher salt concentration. Our result suggested that salt stress had an adverse effect on the production of saffron apocarotenoids and it is likely influencing the quality of saffron stigma produced.

UV-C mediated accumulation of pharmacologically significant phytochemicals under light regimes in in vitro culture of Fagonia indica (L.)

Fagonia indica (L.) is an important medicinal plant with multitude of therapeutic potentials. Such application has been attributed to the presence of various pharmacological important phytochemicals. However, the inadequate biosynthesis of such metabolites in intact plants has hampered scalable production. Thus, herein, we have established an in vitro based elicitation strategy to enhance such metabolites in callus culture of F. indica. Cultures were exposed to various doses of UV radiation (UV-C) and grown in different photoperiod regimes and their impact was evaluated on biomass accumulation, biosynthesis of phytochemicals along antioxidant expression. Cultures grown under photoperiod (16L/8D h) after exposure to UV-C (5.4 kJ/m²) accumulated optimal biomass (438.3 g/L FW; 16.4 g/L DW), phenolics contents (TPC: 11.8 μgGAE/mg) and flavonoids contents (TFC: 4.05 μgQE/mg). Similarly, HPLC quantification revealed that total production (6.967 μg/mg DW) of phytochemicals wherein kaempferol (1.377 μg/mg DW), apigenin (1.057 μg/mg DW), myricetin (1.022 μg/mg DW) and isorhamnetin (1.022 μg/mg DW) were recorded highly accumulated compounds in cultures at UV-C (5.4 kJ/m²) dose than other UV-C radiations and light regimes.. The antioxidants activities examined as DPPH (92.8%), FRAP (182.3 µM TEAC) and ABTS (489.1 µM TEAC) were also recorded highly expressed by cultures under photoperiod after treatment with UV-C dose 5.4 kJ/m². Moreover, same cultures also expressed maximum % inhibition towards phospholipase A2 (sPLA2: 35.8%), lipoxygenase (15-LOX: 43.3%) and cyclooxygenases (COX-1: 55.3% and COX-2: 39.9%) with 1.0-, 1.3-, 1.3- and 2.8-fold increased levels as compared with control, respectively. Hence, findings suggest that light and UV can synergistically improve the metabolism of F. indica and could be used to produce such valuable metabolites on commercial scale.

Hairy Root Cultures-A Versatile Tool With Multiple Applications

Hairy roots derived from the infection of a plant by Rhizobium rhizogenes (previously referred to as Agrobacterium rhizogenes) bacteria, can be obtained from a wide variety of plants and allow the production of highly diverse molecules. Hairy roots are able to produce and secrete complex active glycoproteins from a large spectrum of organisms. They are also adequate to express plant natural biosynthesis pathways required to produce specialized metabolites and can benefit from the new genetic tools available to facilitate an optimized production of tailor-made molecules. This adaptability has positioned hairy root platforms as major biotechnological tools. Researchers and industries have contributed to their advancement, which represents new alternatives from classical systems to produce complex molecules. Now these expression systems are ready to be used by different industries like pharmaceutical, cosmetics, and food sectors due to the development of fully controlled large-scale bioreactors. This review aims to describe the evolution of hairy root generation and culture methods and to highlight the possibilities offered by hairy roots in terms of feasibility and perspectives.

Carbohydrate polymers exhibit great potential as effective elicitors in organic agriculture: A review

Some carbohydrate polymers, usually oligosaccharides or polysaccharides, have great potential as an elicitor of plant defense. However, due to the complexity and diversity of poly- and oligosaccharide structure, the molecular mechanisms and structure-activity relationships of carbohydrate elicitors are still not well understood, which hinders the application of carbohydrate elicitors in agriculture. This review introduces the mechanisms of carbohydrate elicitor perception and signaling in plants. The structure and activity relationships of main poly- and oligosaccharides studied for the control of plant diseases are discussed and summarized. Additionally, the effects of carbohydrate elicitors on the secondary metabolite production are also summarized.

Cell Suspensions of Cannabis sativa (var. Futura): Effect of Elicitation on Metabolite Content and Antioxidant Activity

Cannabis sativa L. is one of the most-studied species for its phytochemistry due to the abundance of secondary metabolites, including cannabinoids, terpenes and phenolic compounds. In the last decade, fiber-type hemp varieties have received interest for the production of many specialized secondary metabolites derived from the phenylpropanoid pathway. The interest in these molecules is due to their antioxidant activity. Since secondary metabolite synthesis occurs at a very low level in plants, the aim of this study was to develop a strategy to increase the production of such compounds and to elucidate the biochemical pathways involved. Therefore, cell suspensions of industrial hemp (C. sativa L. var. Futura) were produced, and an advantageous elicitation strategy (methyl jasmonate, MeJA) in combination with precursor feeding (tyrosine, Tyr) was developed. The activity and expression of phenylalanine ammonia-lyase (PAL) and tyrosine aminotransferase (TAT) increased upon treatment. Through ¹H-NMR analyses, some aromatic compounds were identified, including, for the first time, 4-hydroxyphenylpyruvate (4-HPP) in addition to tyrosol. The 4-day MeJA+Tyr elicited samples showed a 51% increase in the in vitro assay (2,2-diphenyl-1-picrylhydrazyl, DPPH) radical scavenging activity relative to the control and a 80% increase in the cellular antioxidant activity estimated on an ex vivo model of human erythrocytes. Our results outline the active metabolic pathways and the antioxidant properties of hemp cell extracts under the effect of specific elicitors.

Elicitation: A biotechnological tool for enhanced production of secondary metabolites in hairy root cultures

Elicitation is a possible aid to overcome various difficulties associated with the large-scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator-free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor-specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.

Effect of Aspergillus flavus Fungal Elicitor on the Production of Terpenoid Indole Alkaloids in Catharanthus roseus Cambial Meristematic Cells

This study reported the inducing effect of Aspergillus flavus fungal elicitor on biosynthesis of terpenoid indole alkaloids (TIAs) in Catharanthus roseus cambial meristematic cells (CMCs) and its inducing mechanism. According to the results determined by HPLC and HPLC-MS/MS, the optimal condition of the A. flavus elicitor was as follows: after suspension culture of C. roseus CMCs for 6 day, 25 mg/L A. flavus mycelium elicitor were added, and the CMC suspensions were further cultured for another 48 h. In this condition, the contents of vindoline, catharanthine, and ajmaline were 1.45-, 3.29-, and 2.14-times as high as those of the control group, respectively. Transcriptome analysis showed that D4H, G10H, GES, IRS, LAMT, SGD, STR, TDC, and ORCA3 were involved in the regulation of this induction process. The results of qRT-PCR indicated that the increasing accumulations of vindoline, catharanthine, and ajmaline in C. roseus CMCs were correlated with the increasing expression of the above genes. Therefore, A. flavus fungal elicitor could enhance the TIA production of C. roseus CMCs, which might be used as an alternative biotechnological resource for obtaining bioactive alkaloids.

Hairy Root Cultures of Eurycoma longifolia and Production of Anti-inflammatory 9-Methoxycanthin-6-one

The content of bioactive alkaloid 9-methoxycanthin-6-one in the roots of Eurycoma longifolia is rather small. In the current study, a high yield of 9-methoxycanthin-6-one was obtained from transgenic hairy roots (1.139 ± 0.20% dry weight, DW) compared to wild roots (0.164 ± 0.25% DW) of E. longifolia. Three liquid basal media supplemented with 3% sucrose were tested for the growth and accumulation of 9-methoxycanthin-6-one. The fastest growth was obtained in the Shenck and Hildebrandt (SH) medium while the highest 9-methoxycanthin-6-one content was observed in McCown's woody plant (WP) medium. In this study, compared to controls, the production of 9-methoxycanthin-6-one was increased by the maximum of 2.6 and 4.0 times after the addition of jasmonic acid and yeast extract, respectively, into hairy root cultures. In addition, pro-inflammatory cytokines IL-6 and TNF-α were significantly inhibited by 9-methoxycanthin-6-one in lipopolysaccharide-stimulated murine RAW264.7 cells, peritoneal macrophages and human THP-1 macrophages These results suggest that the elicited hairy root culture of E. longifolia is an alternative system for the production of an abundant source of anti-inflammatory 9-methoxycanthin-6-one.

Variations in Bioactive Content in Different Tomato Trusses due to Elicitor Effects

The tomato fruit is rich in bioactive compounds with antioxidant activity, the levels of which can vary over time in response to biotic and abiotic factors, including the application of elicitors. We investigated the effects of foliar spray of methyl jasmonate (MeJ), salicylic acid (SA), nitric oxide (NO), and hydrogen peroxide (H2O2) on tomato plants every 15 days until the end of cultivation. We measured the levels of bioactive compounds, antioxidant activity, and physiological parameters in three distinct trusses. With the exception of plant length, the elicitors had no effects on physiological parameters, whereas they did have an effect on lycopene content, bioactive compound levels, and antioxidant activity in the three sampled trusses. A strong correlation between bioactive compounds and antioxidant activity was found for the elicitors, particularly MeJ. Our results indicate that certain bioactive compounds and their antioxidant activities vary not only between trusses but also based on the specific elicitor used.

Enhanced biosynthesis of saponins by coronatine in cell suspension culture of Kalopanax septemlobus

Kalopanax septemlobus is a medicinal woody species of the family Araliaceae, and the pharmaceutical properties of saponins obtained from K. septemlobus suggest that K. septemlobus has the potential to be a crude drug and dietary health supplement. In this study, we established cell suspension culture of K. septemlobus to develop a sustainable source of natura-ceuticals. Friable calli were used for establishing cell suspension culture. The maximum amount of total saponins (1.56 mg/60 ml suspension) was obtained during the 15th day of incubation, whereas the maximum capacity of saponin production was reached after day 6 (0.42 μg/mg of fresh weight). The total saponin production in the cell suspension of K. septemlobus was significantly increased by coronatine (COR) at 160% at a dose of 1 μM compared with the mock-treated control, whereas methyl jasmonate treated cells exhibited less increase in total saponin level as compared to the COR-treated cells. In addition, the elicitation of COR strongly induced the expression of beta-amyrin synthase, thus resulting in the accumulation of oleanolic acid (2.369 ± 0.98 μg/mg of extract), a precursor for oleanane-type triterpene saponins. These results indicate that COR is an efficient elicitor for inducing phytochemicals in cell suspension culture and that it provides the possibility for producing saponins of K. septemlobus using cell suspension culture.

Promotion of phenolic compounds production in Salvia miltiorrhiza hairy roots by six strains of rhizosphere bacteria

Salvia miltiorrhiza Bunge is an important herb for the treatment of cerebrovascular and cardiovascular diseases with bioactive compounds (phenolic acids and tanshinones). Abundant studies showed that tanshinones could be stimulated by biotic and abiotic stresses, but limited information is available on biosynthesis of phenolic acids promoted by biotic stresses. The aim of the present work was to isolate and identify rhizosphere bacteria which stimulated phenolic compound in Salvia miltiorrhiza hairy roots and investigated the internal mechanism, providing a potential means to enhance content of pharmaceuticals in S. miltiorrhiza. The results showed that six bacteria, namely, HYR1, HYR26, SCR22, 14DSR23, DS6, and LNHR13, belonging to the genus Pseudomonas and Pantoea, significantly promoted the growth and content of major phenolic acids, RA and SAB. Bacteria LNHR13 was the most effective one, with the contents of RA and SAB reaching ∼2.5-fold (30.1 mg/g DW) and ∼2.3-fold (48.3 mg/g DW) as those of the control, respectively. Phytohormones and polysaccharides produced by bacteria showed potential responsibility for the growth and biosynthesis of secondary metabolites of S. miltiorrhiza. Meanwhile, we found that the more abundant the types and contents of phytohormones, the stronger their stimulating effect on the content of salvianolic acids.

Metabolomics reveals biotic and abiotic elicitor effects on the soft coral Sarcophyton ehrenbergi terpenoid content

The effects of six biotic and abiotic elicitors, i.e. MeJA (methyl jasmonate), SA (salicylic acid), ZnCl2, glutathione and β-glucan BG (fungal elicitor), and wounding, on the secondary metabolite accumulation in the soft coral Sarcophyton ehrenbergi were assessed. Upon elicitation, metabolites were extracted and analysed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Except for MeJA, no differences in photosynthetic efficiency were observed after treatments, suggesting the absence of a remarkable stress on primary production. Chemometric analyses of UPLC-MS data showed clear segregation of SA and ZnCl2 elicited samples at 24 and 48 h post elicitation. Levels of acetylated diterpene and sterol viz., sarcophytonolide I and cholesteryl acetate, was increased in ZnCl2 and SA groups, respectively, suggesting an activation of specific acetyl transferases. Post elicitation, sarcophytonolide I level increased 132 and 17-folds at 48 h in 0.1 mM SA and 1 mM ZnCl2 groups, respectively. Interestingly, decrease in sarcophine, a major diterpene was observed only in response to ZnCl2, whereas no change was observed in sesquiterpene content following treatments. To the best of our knowledge, this study provides the first documentation for elicitation effects on a soft corals secondary metabolome and suggests that SA could be applied to increase diterpenoid levels in corals.

Target-directed discovery and production of pharmaceuticals in transgenic mutant plant cells

Plants are a source of complex bioactive compounds, with value as pharmaceuticals, or leads for synthetic modification. Many of these secondary metabolites have evolved as defenses against competing organisms and their pharmaceutical value is "accidental", resulting from homology between target proteins in these competitors, and human molecular therapeutic targets. Here we show that it is possible to use mutation and selection of plant cells to re-direct their "evolution" toward metabolites that interact with the therapeutic target proteins themselves. This is achieved by expressing the human target protein in plant cells, and selecting mutants for survival based on the interaction of their metabolome with this target. This report describes the successful evolution of hairy root cultures of a Lobelia species toward increased biosynthesis of metabolites that inhibit the human dopamine transporter protein. Many of the resulting selected mutants are overproducing the active metabolite found in the wild-type plant, but others overproduce active metabolites that are not readily detectable in non-mutants. This technology can access the whole genomic capability of a plant species to biosynthesize metabolites with a specific target. It has potential value as a novel platform for plant drug discovery and production, or as a means of optimizing the therapeutic value of medicinal plant extracts.

Ultraviolet Radiation-Elicited Enhancement of Isoflavonoid Accumulation, Biosynthetic Gene Expression, and Antioxidant Activity in Astragalus membranaceus Hairy Root Cultures

In this work, Astragalus membranaceus hairy root cultures (AMHRCs) were exposed to ultraviolet radiation (UV-A, UV-B, and UV-C) for promoting isoflavonoid accumulation. The optimum enhancement for isoflavonoid production was achieved in 34-day-old AMHRCs elicited by 86.4 kJ/m(2) of UV-B. The resulting isoflavonoid yield was 533.54 ± 13.61 μg/g dry weight (DW), which was 2.29-fold higher relative to control (232.93 ± 3.08 μg/g DW). UV-B up-regulated the transcriptional expressions of all investigated genes involved in isoflavonoid biosynthetic pathway. PAL and C4H were found to be two potential key genes that controlled isoflavonoid biosynthesis. Moreover, a significant increase was noted in antioxidant activity of extracts from UV-B-elicited AMHRCs (IC50 values = 0.85 and 1.08 mg/mL) in comparison with control (1.38 and 1.71 mg/mL). Overall, this study offered a feasible elicitation strategy to enhance isoflavonoid accumulation in AMHRCs and also provided a basis for metabolic engineering of isoflavonoid biosynthesis in the future.