Higher plants undergo a variety of stresses and to combat those stresses they acclimatize themselves by producing diverse secondary metabolites. These secondary metabolites also have a wide range of industrial applications and hence they serve as candidates for commercialization. Owing to the constraints faced by natural plant extraction, plant cell/tissue culture has emerged as an alternative platform for the in vitro production of value added bioactive secondary metabolites. Implementation of several productivity enhancement strategies, including elicitation, can overcome the limitations faced by plant cell technology that hampers its extensive commercialization. Elicitation is a technique that involves exogenous addition of elicitors (abiotic or biotic) in the growth medium which consequently triggers stress response with concomitant enhancement in secondary metabolite production. Elicitor induced stress results in the activation of several defense-related genes or inactivation of non-defense-related genes, transient phosphorylation/dephosphorylation of proteins, expression of enzymes whose information can be used to ascertain the biosynthetic pathways of many secondary metabolites. Furthermore, integration of transcriptomics, proteomics and metabolomics with system biology can aid in discovery of novel genes, transcriptional factors and several biosynthetic pathways which in turn can serve as a valuable tool for metabolic engineering and gene manipulation for enhancing the yield and productivity of secondary metabolites.

Elicitation: a stimulation of stress in in vitro plant cell/tissue cultures for enhancement of secondary metabolite production

Citrus limon L. is an ingenious alternative medication and has a broad scope in managing several health conditions as part of natural remedies. Recently, medicinal plants have witnessed incredible consideration worldwide in the field of neuroscience for remedial intervention. The present work has investigated the phytochemical compounds and neuropharmacological potential of the seed extract of Citrus limon as a step to partially validate its formulations as nutraceuticals using an in vivo model. Diverse phytochemical groups such as alkaloids, glycosides, flavonoids, tannins, gums, saponins, steroids were qualitatively identified through colorimetric methods utilizing standard compounds. The neuropharmacological properties were studied in Swiss albino mice with the sleep time induced by thiopental sodium taken as an end-point, in standard hole cross, hole board, and open-field experiments at varying doses of 50 and 100 mg/kg body weight. Phytochemical screening showed that alkaloids, flavonoids, saponins, tannins, steroids, and glycosides are present in the aqueous extract of the seed. The extracts demonstrated a significant reduction in sleep onset and enhanced the sleep duration in a dose-dependent manner in thiopental sodium-induced sleeping time, along with a marked decrease in unconstrained locomotors and explorative properties in both hole cross and open field tests. Moreover, in the hole board study, the extracts minimized the count of head dips observed in the treated mice. The results shown in this study demonstrate that Citrus limon extracts have neuropharmacological properties that can be further examined for their potential role as an adjuvant with conventional medications or nutraceuticals.

https://www.imrpress.com/journal/JIN/21/1/10.31083/j.jin2101042/pdf

Citrus limon L. (lemon) seed extract shows neuro-modulatory activity in an in vivo thiopental-sodium sleep model by reducing the sleep onset and enhancing the sleep duration.

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.

https://www.mdpi.com/1422-0067/22/11/5710/pdf

Biochemistry of Terpenes and Recent Advances in Plant Protection.

The present study examines the neuropharmacological and antidiabetic properties of methanol leaves extract of Lannea coromandelica in animal models. This study is carried out by elevated plus-maze apparatus, motor coordination, thiopental sodium has an induction role in sleeping time, hole board, hole cross, open field, antidiabetic studies. Mice were treated doses of 100, 150, and 200 mg/kg body weight in elevated plus-maze apparatus and motor coordination; 100 and 200 mg/kg body weight in sleeping time, hole cross, hole board, and open field tests; and 200 and 400 mg/kg body weight in the antidiabetic activity test. Extraction specifies a significantly decreased time duration and sleeping time in a thiopental sodium-induced sleeping time test. The experimental extract decreased locomotor and exploratory behaviors of mice in the open-field and hole-cross tests compared to the effects of the control. Furthermore, the extract increased sleeping time with a dose-dependent onset of action. The hole-board test extract also demonstrated a reduced number of head dips. The findings showed that L. coromandelica has potential neuropharmacological effects. In addition, in alloxan-induced diabetic mice, leaves extract at 200 and 400 mg/kg body weight revealed significant antidiabetic properties and could be used to manage blood glucose levels with more research.

/pdf/neuropharmacological-and-antidiabetic-potential-of-lannea-1u7w8z58.pdf

Neuropharmacological and Antidiabetic Potential of Lannea coromandelica (Houtt.) Merr. Leaves Extract: An Experimental Analysis

Nutraceuticals are biologically active molecules present in foods; they can have beneficial effects on health, but they are not available in large enough quantities to perform this function. Plant metabolites, such as polyphenols, are widely diffused in the plant kingdom, where they play fundamental roles in plant development and interactions with the environment. Among these, flavonoids are of particular interest as they have significant effects on human health. In vitro and/or in vivo studies described flavonoids as essential nutrients for preventing several diseases. They display broad and promising bioactivities to fight cancer, inflammation, bacterial infections, as well as to reduce the severity of neurodegenerative and cardiovascular diseases or diabetes. Therefore, it is not surprising that interest in flavonoids has sharply increased in recent years. More than 23,000 scientific publications on flavonoids have described the potential anticancer activity of these natural molecules in the last decade. Studies, in vitro and in vivo, show that flavonoids exhibit anticancer properties, and many epidemiological studies confirm that dietary intake of flavonoids leads to a reduced risk of cancer. This review provides a glimpse of the mechanisms of action of flavonoids on cancer cells.

Flavonoids: A Myth or a Reality for Cancer Therapy?

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.

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

Bacopa monnieri has been used as a reputed drug in the Indian traditional ayurvedic system for centuries. This medicinal herb with important phytopharmaceuticals has been popularly known as “Brahmi”. In recent years, B. monnieri has been extensively studied for its bioactive constituents, constituents responsible for memory enhancing effect, and also its diverse other useful effects. It possesses many pharmacological activities such as antioxidant, gastrointestinal, endocrine, antimicrobial, anti-inflammatory etc. The plant has been also used for the treatment of neurological and neuropsychiatric diseases. Due to its multipurpose therapeutic potential, micropropagation using axillary meristems and de novo organogenesis has been extensively studied in the species and is being reviewed. High frequency direct shoot organogenesis can be induced in excised leaf and internode explants in the absence of exogenous phytohormones and the rate of induction is enhanced in the presence of exogenous cytokinins, supplements, growth regulators, etc. Using explants from tissue culture raised plants, direct shoot regeneration leading to production of more than 100 rooted plants/explant within 8–12 weeks period with 85%–100% survival in the field after acclimatization can be expected following optimized protocols. Bioreactor based micropropagation was found to increase the multiplication rate of shoot cultures for the commercial propagation of B. monnieri plants. The maximum content of bacosides has been recorded in shoot biomass using an airlift bioreactor system. Further studies for the biosynthesis of bacosides and other secondary metabolites need to be conducted in the species utilizing untransformed shoot cultures in bioreactors.

https://www.mdpi.com/2223-7747/9/4/411/pdf

In Vitro Propagation, Phytochemical and Neuropharmacological Profiles of Bacopa monnieri (L.) Wettst.: A Review

Induction of hairy roots by Agrobacterium rhizogenes and regeneration of Ri-transformed plants from such transgenic roots are reported in a large number of taxonomically diverse plant species Ri-transformed cultures (roots/calli/plants) have altered characteristics of their own compared to non-transformed ones Four rol genes (rolA, rolB, rolC, rolD) of T-DNA of Ri-plasmid are known to be responsible for these phenomena However, few attempts have been made to elucidate the role of individual rol genes on morphogenic ability In addition, the effect of wild-type A rhizogenes on the production of secondary metabolites is well studied in wide number of plant species The popularity of this research has never declined through time which explains its immense value and provides a hope for a promising future Based on such studies, several reviews have been written from time to time, explaining the ‘rol effect’ on secondary metabolite accumulation in medicinal plants and to discuss the advances in this field of research However, investigations dealing with the effect of individual rol genes are comparatively less and need further attention Therefore, in this chapter, we have discussed in detail the effects of each of the four rol genes individually or in combination on in vitro morphogenesis and secondary metabolite accumulation in medicinal plants

The Effects of rol Genes of Agrobacterium rhizogenes on Morphogenesis and Secondary Metabolite Accumulation in Medicinal Plants

Bacopa monnieri (Linn.) Wettst. (family Scrophulariaceae), a therapeutically important perennial herb, was transformed to study the stability of the effects associated with the insertion of a gene encoding β-cryptogein, a proteinaceous elicitor, either alone or in addition to the T-DNA genes in long-term in vitro culture as well as after transfer to the greenhouse. Plant lines BmAr-IXcrypt obtained via transformation by LBA 9402-crypt (pRi1855+pBin19++crypt) showed integration and expression of rolA, rolB, rolC, and rolD genes after 4 years of maintenance in vitro. The plant line BmAt-ncrypt obtained via transformation with A. tumefaciens strain LBA4404-crypt (harboring pBin19++crypt) as well as plant line BmAr-IXcrypt showed stable integration and expression of nptII gene and crypt gene even after transfer to greenhouse. The clones of Ri-crypt-transformed plants differed morphologically from Ri-transformed plants in that the typical “hairy root syndrome” was not observed in plants expressing crypt gene in the presence of rol genes. Except plant line BmAr-IXcrypt, none of the other transgenic plant lines showed any alteration in floral morphology and onset of flowering. The crypt-transformed plant lines (BmAr-IXcrypt and BmAt-ncrypt), maintained under long-term culture, showed significantly higher (p ≤ 0.05) amount of bacoside production in vitro (1.66- to 2.05-fold, with respect to non-transformed plants). In addition, accumulation of all the four bacosides was significantly higher (p ≤ 0.05) in crypt-transformed plants as compared to non-transformed plants grown for 1 year in greenhouse. Thus, the crypt-transformed plant lines of B. monnieri may be considered as the potential source for sustainable bioproduction of bacosides.

Effects associated with insertion of cryptogein gene utilizing Ri and Ti plasmids on morphology and secondary metabolites are stable in Bacopa monnieri-transformed plants grown in vitro and ex vitro

In the present study, high frequency regeneration has been obtained via de novo direct shoot organogenesis from leaf and internode explants in Murashige and Skoog (MS) basal medium without any phytohormone supplementation in Bacopa monnieri, an indigenous traditionally used medicinal herb. Leaves and internodes from different positions were excised from 4-weeks-old in vitro propagated B. monnieri plants and cultured on MS basal medium supplemented with 3% (w/v) sucrose and 0.75% (w/v) agar for 4 weeks. The induction of de novo shoot buds was observed at petiolar cut edges of leaf and both proximal and distal cut ends of internode explants within 10–15 days of culture. The first histological changes could be observed after 4–5 days, with meristematic activity of vascular bundles. Proliferation of epidermal cells gave rise to dome-shaped protuberances followed by shoot apical meristems formation and their vascular connections with explant tissues within 2 weeks of culture. However, a basipetal gradient of shoot regeneration from both types of explants collected along the branch axis was noticed after 4 weeks of culture. Leaf and internode explants near the basal region exhibited significantly higher number of shoot buds and micro shoots (8.8/leaf explant and 15/internode explant). Microshoots (7–12 micro shoots/leaf or internode explants) elongated (shoot length 8–9 cm) within 8 weeks on phytohormone free MS medium. Excised micro shoots rooted (100%) in hormone free MS medium within two weeks of culture. Rooted plants were then acclimatized and transferred to field with 95% survival. This protocol may be used for micropropagation, genetic transformation as well as a model system for evaluation of changes associated with acquisition of competence of differentiated cells in phytohormone free medium.

Sayantika Sarkar

Papers

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

In Vitro Propagation, Phytochemical and Neuropharmacological Profiles of Bacopa monnieri (L.) Wettst.: A Review

The Effects of rol Genes of Agrobacterium rhizogenes on Morphogenesis and Secondary Metabolite Accumulation in Medicinal Plants

Effects associated with insertion of cryptogein gene utilizing Ri and Ti plasmids on morphology and secondary metabolites are stable in Bacopa monnieri-transformed plants grown in vitro and ex vitro

Morpho-histological characterization and direct shoot organogenesis in two types of explants from Bacopa monnieri on unsupplemented basal medium