Production of Plant Secondary Metabolites: Examples, Tips and Suggestions for Biotechnologists

Elsholtzia ciliata (Thunb.) Hyl. Extracts from Different Plant Parts: Phenolic Composition, Antioxidant, and Anti-Inflammatory Activities

Polyphenols play an important role on the health-promoting properties of humans. Plants belonging to Lamiaceae family are known as rich source of phenolic compounds. The current work aimed to evaluate the phenolic compounds, antioxidant, and anti-inflammatory activity of Elsholtzia ciliata (Thunb.) Hyl. ethanolic extracts from leaf, stem, flower, and whole herb. Twelve compounds were identified in ethanolic extracts using high-performance liquid chromatography (HPLC). The HPLC analysis revealed that chlorogenic acid, rosmarinic acid, and rutin were predominant compounds in ethanolicic extracts. Using HPLC-ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) post-column assay, avicularin, chlorogenic, and rosmarinic acids were identified as the predominant radical scavengers in all ethanolic extracts. All tested preparations significantly reduced the level of secretion of proinflammatory cytokines TNF-α, IL-6, and prostaglandin E2 induced by lipopolysaccharide treatment in mouse peritoneal macrophage cell culture. Stem and flower extracts were most efficient in reducing cytokine release, but leaf extract demonstrated stronger effect on prostaglandin E2 secretion. This is the first study exploring antioxidant efficiency by HPLC–ABTS post-column method and investigating anti-inflammatory activity of ethanolic extracts from E. ciliata different plant parts.

Combining Medicinal Plant In Vitro Culture with Machine Learning Technologies for Maximizing the Production of Phenolic Compounds

We combined machine learning and plant in vitro culture methodologies as a novel approach for unraveling the phytochemical potential of unexploited medicinal plants. In order to induce phenolic compound biosynthesis, the in vitro culture of three different species of Bryophyllum under nutritional stress was established. To optimize phenolic extraction, four solvents with different MeOH proportions were used, and total phenolic content (TPC), flavonoid content (FC) and radical-scavenging activity (RSA) were determined. All results were subjected to data modeling with the application of artificial neural networks to provide insight into the significant factors that influence such multifactorial processes. Our findings suggest that aerial parts accumulate a higher proportion of phenolic compounds and flavonoids in comparison to roots. TPC was increased under ammonium concentrations below 15 mM, and their extraction was maximum when using solvents with intermediate methanol proportions (55–85%). The same behavior was reported for RSA, and, conversely, FC was independent of culture media composition, and their extraction was enhanced using solvents with high methanol proportions (>85%). These findings confer a wide perspective about the relationship between abiotic stress and secondary metabolism and could serve as the starting point for the optimization of bioactive compound production at a biotechnological scale.

Isolation and characterization of nutrient dependent pyocyanin from Pseudomonas aeruginosa and its dye and agrochemical properties

Pyocyanin is a blue green phenazine pigment produced in large quantities by active cultures of Pseudomonas aeruginosa, with advantageous applications in medicine, agriculture and for the environment. Hence, in the present study, a potent bacterium was isolated from agricultural soil and was identified morphologically and by 16S rRNA sequencing as P. aeruginosa (isolate KU_BIO2). When the influence of nutrient supplements in both King’s A and Nutrient media as amended was investigated, an enhanced pyocyanin production of 2.56 µg ml⁻¹ was achieved in King’s A medium amended with soya bean followed by 1.702 µg ml⁻¹ of pyocyanin from the nutrient medium amended with sweet potato. Purified pyocyanin was characterized by UV-Vis Spectrophotometer and Fourier-Transform Infrared spectroscopy (FTIR). Furthermore, Liquid Chromatography Mass Spectrum (LCMS) and Nuclear Magnetic Resonance (NMR) confirmed its mass value at 211 and as N-CH₃ protons resonating at 3.363 ppm as a singlet respectively. The isolated pyocyanin displayed remarkable dye property by inducing color change in cotton cloth from white to pink. Lastly, the antifungal activity of test pyocyanin showed inhibition of growth of rice blast fungus, Magnaporthe grisea and bacterial blight of rice, Xanthomonas oryzae at concentrations of 150 and 200 ppm, respectively. Thus, this investigation provides evidence for diverse actions of pyocyanin which are nutrient dependent and are capable of acting on a large scale, by utilizing microbes existing in agriculture wastes, and thus could be used as an alternative source in the making of natural textile dyes with strong durability and a broad spectrum of ecofriendly agrochemicals.

Transgenesis as a Tool for the Efficient Production of Selected Secondary Metabolites from in Vitro Plant Cultures

The plant kingdom abounds in countless species with potential medical uses. Many of them contain valuable secondary metabolites belonging to different classes and demonstrating anticancer, anti-inflammatory, antioxidant, antimicrobial or antidiabetic properties. Many of these metabolites, e.g., paclitaxel, vinblastine, betulinic acid, chlorogenic acid or ferrulic acid, have potential applications in medicine. Additionally, these compounds have many therapeutic and health-promoting properties. The growing demand for these plant secondary metabolites forces the use of new green biotechnology tools to create new, more productive in vitro transgenic plant cultures. These procedures have yielded many promising results, and transgenic cultures have been found to be safe, efficient and cost-effective sources of valuable secondary metabolites for medicine and industry. This review focuses on the use of various in vitro plant culture systems for the production of secondary metabolites.

Boosting the Synthesis of Pharmaceutically Active Abietane Diterpenes in S. sclarea Hairy Roots by Engineering the GGPPS and CPPS Genes

Abietane diterpenoids (ADs), synthesized in the roots of different Salvia species, such as aethiopinone, 1-oxoaethiopinone, salvipisone, and ferruginol, have a variety of known biological activities. We have shown that aethiopinone has promising cytotoxic activity against several human tumor cell lines, including the breast adenocarcinoma MCF7, HeLa, epithelial carcinoma, prostate adenocarcinoma PC3, and human melanoma A375. The low content of these compounds in natural sources, and the limited possibility to synthesize them chemically at low cost, prompted us to optimize the production of abietane diterpenoids by targeting genes of the methylerythritol phosphate (MEP) pathway, from which they are derived. Here, we report our current and ongoing efforts to boost the metabolic flux towards this interesting class of compounds in Salvia sclarea hairy roots (HRs). Silencing the gene encoding the ent-copalyl-diphosphate synthase gene (entCPPS), acting at the lateral geranylgeranyl pyrophosphate (GGPP) competitive gibberellin route, enhanced the content of aethiopinone and other ADs in S. sclarea HRs, indicating indirectly that the GGPP pool is a metabolic constraint to the accumulation of ADs. This was confirmed by overexpressing the GGPPS gene (geranyl-geranyl diphosphate synthase) which triggered also a significant 8-fold increase of abietane diterpene content above the basal constitutive level, with a major boosting effect on aethiopinone accumulation in S. sclarea HRs. A significant accumulation of aethiopinone and other AD compounds was also achieved by overexpressing the CPPS gene (copalyl diphosphate synthase) pointing to this biosynthetic step as another potential metabolic target for optimizing the biosynthesis of this class of compounds. However, by co-expressing of GGPPS and CPPS genes, albeit significant, the increase of abietane diterpenoids was less effective than that obtained by overexpressing the two genes individually. Taken together, the results presented here add novel and instrumental knowledge to a rational design of a hairy root-based platform to yield reliable amounts of aethiopinone and other ADs for a deeper understanding of their molecular pharmacological targets and potential future commercialization.

Green and facile synthesis of water-soluble carbon dots from ethanolic shallot extract for chromium ion sensing in milk, fruit juices, and wastewater samples

Self-functionalized carbon dots (CDs) were prepared from ethanolic shallot extract to obtain a total phenolic precursor.

Vegetable Additives in Food Packaging Polymeric Materials

Plants are the most abundant bioresources, providing valuable materials that can be used as additives in polymeric materials, such as lignocellulosic fibers, nano-cellulose, or lignin, as well as plant extracts containing bioactive phenolic and flavonoid compounds used in the healthcare, pharmaceutical, cosmetic, and nutraceutical industries. The incorporation of additives into polymeric materials improves their properties to make them suitable for multiple applications. Efforts are made to incorporate into the raw polymers various natural biobased and biodegradable additives with a low environmental fingerprint, such as by-products, biomass, plant extracts, etc. In this review we will illustrate in the first part recent examples of lignocellulosic materials, lignin, and nano-cellulose as reinforcements or fillers in various polymer matrices and in the second part various applications of plant extracts as active ingredients in food packaging materials based on polysaccharide matrices (chitosan/starch/alginate).

Improving Phenolic Total Content and Monoterpene in Mentha x piperita by Using Salicylic Acid or Methyl Jasmonate Combined with Rhizobacteria Inoculation

The effects of plant inoculation with plant growth-promoting rhizobacteria (PGPR) and those resulting from the exogenous application of salicylic acid (SA) or methyl jasmonte (MeJA) on total phenolic content (TPC) and monoterpenes in Mentha x piperita plants were investigated. Although the PGPR inoculation response has been studied for many plant species, the combination of PGPR and exogenous phytohormones has not been investigated in aromatic plant species. The exogenous application of SA produced an increase in TPC that, in general, was of a similar level when applied alone as when combined with PGPR. This increase in TPC was correlated with an increase in the activity of the enzyme phenylalanine ammonia lyase (PAL). Also, the application of MeJA at different concentrations in combination with inoculation with PGPR produced an increase in TPC, which was more relevant at 4 mM, with a synergism effect being observed. With respect to the main monoterpene concentrations present in peppermint essential oil (EO), it was observed that SA or MeJA application produced a significant increase similar to that of the combination with rhizobacteria. However, when plants were exposed to 2 mM MeJA and inoculated, an important increase was produced in the concentration on menthol, pulegone, linalool, limonene, and menthone concentrations. Rhizobacteria inoculation, the treatment with SA and MeJA, and the combination of both were found to affect the amount of the main monoterpenes present in the EO of M. piperita. For this reason, the expressions of genes related to the biosynthesis of monoterpene were evaluated, with this expression being positively affected by MeJA application and PGPR inoculation, but was not modified by SA application. Our results demonstrate that MeJA or SA application combined with inoculation with PGPR constitutes an advantageous management practice for improving the production of secondary metabolites from M. piperita.

Plant Fibers and Phenolics: A Review on Their Synthesis, Analysis and Combined Use for Biomaterials with New Properties

Devising environmental-friendly processes in biotechnology is a priority in the current economic scenario. We are witnessing a constant and steady push towards finding sustainable solutions to societal challenges by promoting innovation-driven activities minimizing the environmental impact and valorizing natural resources. In bioeconomy, plants are among the most important renewable sources of both fibers (woody and cellulosic) and phytochemicals, which find applications in many industrial sectors, spanning from the textile, to the biocomposite, medical, nutraceutical, and pharma sectors. Given the key role of plants as natural sources of (macro)molecules, we here provide a compendium on the use of plant fibers functionalized/impregnated with phytochemicals (in particular phenolic extracts). The goal is to review the various applications of natural fibers functionalized with plant phenolics and to valorize those plants that are source of both fibers and phytochemicals.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

Current Advances on the Extraction and Identification of Bioactive Components of Sage (Salvia spp.)

Common sage (Salvia spp., with the most common species Salvia officinalis L., Lamiaceae) is an important medicinal and aromatic plant, with antioxidant, antimicrobial, anti-inflammatory and anticancer properties. The polyphenolic compounds are mainly responsible for its diverse biological activity. Many different methods for extraction and identification of sage bioactive compounds, using various solvents, have been developed in recent years. The total phenolic content is usually measured and identified by various technical methodologies with different sensitivity and specificity. In this aspect, the present review is aimed to critically summarize and discuss various technical approaches for the extraction and identification of sage bioactive components in order to point out the more appropriate approaches of them.

SuCComBase: a manually curated repository of plant sulfur-containing compounds

Plants produce a wide range of secondary metabolites that play important roles in plant defense and immunity, their interaction with the environment and symbiotic associations. Sulfur-containing compounds (SCCs) are a group of important secondary metabolites produced in members of the Brassicales order. SCCs constitute various groups of phytochemicals, but not much is known about them. Findings from previous studies on SCCs were scattered in published literatures, hence SuCComBase was developed to store all molecular information related to the biosynthesis of SCCs. Information that includes genes, proteins and compounds that are involved in the SCC biosynthetic pathway was manually identified from databases and published scientific literatures. Sets of co-expression data was analyzed to search for other possible (previously unknown) genes that might be involved in the biosynthesis of SCC. These genes were named as potential SCC-related encoding genes. A total of 147 known and 92 putative Arabidopsis thaliana SCC-related genes from literatures were used to identify other potential SCC-related encoding genes. We identified 778 potential SCC-related encoding genes, 4026 homologs to the SCC-related encoding genes and 116 SCCs as shown on SuCComBase homepage. Data entries are searchable from the Main page, Search, Browse and Datasets tabs. Users can easily download all data stored in SuCComBase. All publications related to SCCs are also indexed in SuCComBase, which is currently the first and only database dedicated to plant SCCs. SuCComBase aims to become a manually curated and au fait knowledge-based repository for plant SCCs.

Transcriptomic Analysis of Orange Fruit Treated with Pomegranate Peel Extract (PGE)

A Pomegranate Peel Extract (PGE) has been proposed as a natural antifungal substance with a wide range of activity against plant diseases. Previous studies showed that the extract has a direct antimicrobial activity and can elicit resistance responses in plant host tissues. In the present study, the transcriptomic response of orange fruit toward PGE treatments was evaluated. RNA-seq analyses, conducted on wounded fruits 0, 6, and 24 h after PGE applications, showed a significantly different transcriptome in treated oranges as compared to control samples. The majority (273) of the deferentially expressed genes (DEGs) were highly up-regulated compared to only 8 genes that were down-regulated. Gene Ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis showed the involvement of 1233 gene ontology (GO) terms and 35 KEGG metabolic pathways. Among these, important defense pathways were induced and antibiotic biosynthesis was the most enriched one. These findings may explain the underlying preventive and curative activity of PGE against plant diseases.

Cherry Extract from Prunus avium L. to Improve the Resistance of Endothelial Cells to Oxidative Stress: Mucoadhesive Chitosan vs. Poly(lactic-co-glycolic acid) Nanoparticles

Polyphenolic compounds contained in cherry extract (CE) are well known for their antioxidant and anti-inflammatory properties. Unfortunately, most of these natural compounds have low oral bioavailability, reducing their widespread use. Here, different concentrations of polyphenol-rich CE from Tuscany (Italy), encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), were compared with those encapsulated in two NP types, different from each other in terms of mucoadhesivity, obtained with chitosan derivatives (Ch-der), regarding CE gastrointestinal (GI) permeability and protective effect on oxidative stress. Different NP systems were physico-chemically characterized, and the antioxidant GI permeability was evaluated in a triple-cell co-culture model (Caco-2/HT29-MTX/Raji B), resembling the intestine. PLGA NPs efficiently entrapped CE (up to 840 µg gallic acid equivalent (GAE)/mL) without altering size (210 nm), polydispersity index (0.05), or zeta potential (−10.7 mV). Such NPs promoted permeation of encapsulated CE at a CE polyphenolic concentration of at least 2 µg GAE/mL. More mucoadhesive NPs from Ch-der, coded quaternary ammonium S-protected thiolated chitosan (QA-Ch-S-pro) NP, promoted CE GI permeation of 0.5 µg GAE/mL. At higher concentrations of Ch-der polymers, the resulting NPs containing CE were toxic toward Caco-2 and HT29-MTX cells. CE protected human umbilical vein endothelial cells (HUVECs) from oxidative stress and maintained its activity when entrapped in PLGA NPs. CE encapsulated in QA-Ch-S-pro NP protected HUVECs from oxidative stress, even more effectively than non-encapsulated CE. Furthermore, mucoadhesive NPs from Ch-der were more effective antioxidant protectors than PLGA NPs, but less cytotoxic PLGA NPs could be more useful when comparatively high therapeutic antioxidant doses are needed.

Ancient Tomato (Solanum lycopersicum L.) Varieties of Tuscany Have High Contents of Bioactive Compounds

The Tuscan Region has a vast repertoire of ancient plants that have been recovered across the territory over the years. These plants thrive in an environment characterized by minimal human intervention and are thus the result of the process of adaptation to the territory of origin. In this work, we focused on the quantification of bioactive compounds in ancient tomato varieties. More specifically, we quantified polyphenols, flavonoids, carotenoids, and vitamin C in eight local Tuscan tomato varieties and found higher contents with respect to those in commercial tomatoes Polyphenol and antioxidant compounds in ancient varieties reported a two- and, in some instances, three-fold increase in concentration, compared to the commercial counterparts. Interestingly, the data relative to the carotenoids did not show any significant differences when comparing the ancient varieties with the commercial ones, a finding confirming the market selection criterion based on color. On a longer-term perspective, this study aims at drawing attention to the importance of preserving autochthonous natural plant biodiversity and towards promoting research on local varieties. We believe that this study will pave the way to the valorization of local plant biodiversity and promote an extended use of products in the nutraceutical sector derived from vegetables.

Profile of Thin-Layer Chromatography and UV-Vis Spectrophotometry of Akar Kuning Stem Extract (Arcangelisia flava)

This study aims to obtain the profile of Thin-Layer Chromatography (TLC) and Ultraviolet-Visible (UV-Vis) spectrophotometry from ethanol extract of akar kuning stems (Arcangelisia flava) from Central Kalimantan. The TLC method is used with the orientation phase of the combination of polar-non-polar solvents resulting from orientation, while ethanol is used as the solvent for UV-Vis spectrophotometers. TLC results showed the formation of 3 stains on a combination of polar solvents chloroform : methanol : water while in a non-polar solvent combination n-hexane : ethyl acetate did not show any stains. Comparison of retention factor (Rf) values show the best combination of polar solvents to separate stains at a ratio of 5 : 2 : 1, respectively. Separation in 2-dimensional TLC with polar solvents showed a similar pattern with 1-dimensional separation in the form of 3 stains. UV-Vis spectrophotometer results showed 4 main peaks with wavelength 227.2; 267.4; 345.2; and 425.3 nm, respectively. The profile of the peak formed is very similar to that shown by berberine, one of the main metabolites of akar kuning. TLC and UV-Vis spectrophotometers profiles obtained are expected to support further research using akar kuning stems, especially those from Central Kalimantan.

Mediterranean Wild Edible Plants: Weeds or "New Functional Crops"?

The Mediterranean basin is a biodiversity hotspot of wild edible species, and their therapeutic and culinary uses have long been documented. Owing to the growing demand for wild edible species, there are increasing concerns about the safety, standardization, quality, and availability of products derived from these species collected in the wild. An efficient cultivation method for the species having promising nutraceutical values is highly desirable. In this backdrop, a hydroponic system could be considered as a reproducible and efficient agronomic practice to maximize yield, and also to selectively stimulate the biosynthesis of targeted metabolites. The aim of this report is to review the phytochemical and toxic compounds of some potentially interesting Mediterranean wild edible species. Herein, after a deep analysis of the literature, information on the main bioactive compounds, and some possibly toxic molecules, from fifteen wild edible species have been compiled. The traditional recipes prepared with these species are also listed. In addition, preliminary data about the performance of some selected species are also reported. In particular, germination tests performed on six selected species revealed that there are differences among the species, but not with crop species. “Domestication” of wild species seems a promising approach for exploiting these “new functional foods”.

Influence of different Agrobacterium rhizogenes strains on hairy root induction and analysis of phenolic and flavonoid compounds in marshmallow (Althaea officinalis L.)

Hairy roots were induced in Althea officinalis using Agrobacterium rhizogenes, strains A4, A13, ATCC15834, and ATCC15834(GUS). The leaf, petiole and shoot explants of marshmallow were used for the hairy roots induction. When hairy roots appeared, cultures were established in MS (Murashige and Skoog) liquid medium without growth regulators. Hairy roots in explants appeared 5-12 days after inoculation. Maximum transformation frequency of 83% was observed on shoot explants with ATCC15834 strain. Among the strains, ATCC15834(GUS) strain showed better potential in the mass production of hairy roots in the hormone-free liquid medium after 50 days of culturing. The highest total phenolic and flavonoids content was found at 1.57 ± 0.1 mg/g dry weight in A13 strain and 3.47 ± 0.3 mg/g in A4 strain, respectively. Secondary metabolite content of hairy roots was found to be strain-specific.

Agrobiotechnology Goes Wild: Ancient Local Varieties as Sources of Bioactives

The identification and use of species that have best adapted to their growth territory is of paramount importance to preserve biodiversity while promoting sustainable agricultural practices. Parameters including resistance to natural conditions (biotic and abiotic risk factors), biomass and fruit productivity, and phytochemical content with nutraceutical potential, could be used as quantitative markers of the adaptability of plants to wild environments characterized by minimal human impact. Ancient varieties, which are plant varieties growing in regional territories and not destined for market distribution, are a source of unique genetic characters derived from many years of adaptation to the original territory. These plants are often more resistant to biotic and abiotic stresses. In addition, these varieties have a high phytochemical (also known as bioactives) content considered health-beneficial. Notably, the content of these compounds is often lower in commercial cultivars. The use of selected territorial varieties according to the cultivation area represents an opportunity in the agricultural sector in terms of biodiversity preservation, environmental sustainability, and valorization of the final products. Our survey highlights the nutraceutical potential of ancient local varieties and stresses the importance of holistic studies (-omics) to investigate their physiology and secondary metabolism.

Functional Molecules in Locally-Adapted Crops: The Case Study of Tomatoes, Onions, and Sweet Cherry Fruits From Tuscany in Italy

The human diet is characterized by highly energetic molecules, but it also requires non-energetic compounds that are equally useful for cell functioning and for preserving the organism's health status. These "functional" molecules are represented by a wide variety of plant secondary metabolites, such as terpenoids, vitamins and polyphenols with antioxidant power. Widespread commercial crop varieties often contain scarce levels of functional molecules, because they have been mostly selected for productivity, rather than for the content of secondary metabolites. Different scenarios (global economic situation, foreseeable environmental changes) are pushing farmers to review the use of high yield crops and to focus on the valorization of locally-adapted plants. This renewed interest is strengthened by the growing need of consumers for functional foods with beneficial effects on human health and by the willingness to promote sustainable low-input agricultural practices exploiting local climate, soil, water, and (micro)biota. Here, we want to discuss a specific case study concerning locally-adapted crops in Tuscany (Italy). Analyses of nutraceutical molecules in locally-grown crop varieties (namely tomatoes, sweet cherries and onions) have shown that they are characterized by substantially higher functional molecule contents than commercial varieties. Our goal is to promote the high-throughput study of locally-adapted varieties to understand, in a medium-term perspective, whether the cultivation of such plants is a valuable support for the diet and an adequate local economic resource. Such plants can provide a boost to the regional economy, by diversifying the local crop-market landscape. Moreover, the exploitation of locally-grown plants results in the manufacture of fully-traceable products (from the raw bioresource to the finished product) with a "0 km" concept that minimizes the C footprint.