Pulsed electric field stimulates plant secondary metabolism in suspension cultures ofTaxus chinensis

Symphonies of Growth: Unveiling the Impact of Sound Waves on Plant Physiology and Productivity

The application of sound wave technology to different plant species has revealed that variations in the Hz, sound pressure intensity, treatment duration, and type of setup of the sound source significantly impact the plant performance. A study conducted on cotton plants treated with Plant Acoustic Frequency Technology (PAFT) highlighted improvements across various growth metrics. In particular, the treated samples showed increases in the height, size of the fourth expanded leaf from the final one, count of branches carrying bolls, quantity of bolls, and weight of individual bolls. Another study showed how the impact of a 4 kHz sound stimulus positively promoted plant drought tolerance. In other cases, such as in transgenic rice plants, GUS expression was upregulated at 250 Hz but downregulated at 50 Hz. In the same way, sound frequencies have been found to enhance the osmotic potential, with the highest observed in samples treated with frequencies of 0.5 and 0.8 kHz compared to the control. Furthermore, a sound treatment with a frequency of 0.4 kHz and a sound pressure level (SPL) of 106 dB significantly increased the paddy rice germination index, as evidenced by an increase in the stem height and relative fresh weight. This paper presents a complete, rationalized and updated review of the literature on the effects of sound waves on the physiology and growth parameters of sound-treated plants.

The role of sound stimulation in production of plant secondary metabolites

Sound vibration is one of natural stimuli trigging physiological changes in plants. Recent studies showed that sound waves stimulated production of a variety of plant secondary metabolites, including flavonoids, in order to enhance seed germination, flowering, growth or defense. In this review, we examine the potential role of sound stimulation on the biosynthesis of secondary metabolites and the followed cascade of physiological changes in plants, from the perspective of transcriptional regulation and epigenetic regulation for the first time. A systematic summary showed that a wide range of factors may regulate the production of secondary metabolites, including plant species, growth stage, sound types, sound frequency, sound intensity level and exposure time, etc. Biochemical and physiological changes due to sound stimulation were thoroughly summarized as well, for secondary metabolites can also act as a free radical scavenger, or a hormone signaling molecule. We also discussed the limits of previous studies, and the future application of sound waves in biosynthesis of plant secondary metabolites.

Electrostimulation improves plant growth and modulates the flavonoid profile in aeroponic culture of Scutellaria baicalensis Georgi

Scutellaria baicalensis Georgi is a valuable medicinal plant of the Lamiaceae family. The roots, Scutellariae baicalensis radix, are valued in the traditional medicine of East Asia and are also listed in several pharmacopeias, such as the Chinese and European versions. The roots contain a high amount of flavones, such as baicalein, wogonin and their glucuronides, baicalin and wogonoside, respectively, with rare structures of unsubstituted B-ring. These major constituents are responsible for its pharmacological activity, mainly anti-inflammatory, antiviral, and antitumor, as well as BDZ-receptor modulating. There is a fast-growing demand for both the crude drug and the individual flavonoids obtained from it. However, the variability of content and composition of flavonoids in the roots is significant and affects pharmaceutical use, and little is known about the influence of various factors on root quality. In our experiments, we use aeroponics to determine the effect of electroporation as an abiotic stressor on plant growth, development, and root mass, as well as on its metabolic profile.

RESULTS

Electroporation significantly impacted plant growth and the content of flavonoids, especially baicalein and wogonin, depending on the treatment parameters. Concentrations of aglycones were increased in at least half of the treatment conditions. The greatest amounts (a 2.5-fold increase compared to controls) were recorded after applying an electrical field characterized by the following parameters: E = 3 kV/cm, t = 100 μs, and N = 10. In conclusion, electrostimulation is an innovative and efficient way to increase plant growth and yield in an aeroponic system, as well as modulate the profile and content of bioactive flavones in the roots. However, the fine-tuning of these parameters, such as the electrical field strength (E), length (t), and number (N) of impulses delivered, is of great importance. It was also shown that cultivation of the experimental plants in aeroponics had a positive impact on their survival and development while being a sustainable and efficient horticultural practice.

The Metabolite Content of the Post-Culture Medium of the Tree Fern Cyathea delgadii Sternb. Cell Suspension Cultured in the Presence of 2,4-D and BAP

The aim of this study was to demonstrate the metabolic profile of post-culture medium as an expression of cell suspension metabolic activity of the tree fern Cyathea delgadii Sternb. The molecular profile of the tree fern’s cell culture has been never described, according to our knowledge. The cell suspension was established using ½ MS medium supplemented with various concentrations of 2,4-D and BAP. The optimal concentrations were 2.0 mg·L−1 and 0.2 mg·L−1, respectively. The cell suspension initially showed an organized system of cell division and later unorganized cell proliferation. LC-MS and GC-MS were used to identify the chemical composition of the post-culture medium. The LC-MS analysis results suggested that the color of liquid medium could be due to the presence of flavonoid derivatives, as this group of compounds was represented by eight compounds. After GC-MS analysis based on retention indexes and thanks to mass spectra comparison, 130 natural products were recognized, belonging to various classes of primary and secondary metabolites.

Using the Strategy of Inducing and Genetically Transforming Plant Suspension Cells to Produce High Value-Added Bioactive Substances

Plants can produce many functional bioactive substances. The suspension cell system of plants can be constructed based on its characteristics to realize the large-scale production of valuable products. In this review, we mainly talk about the main strategies, elicitation, and genetic transformation to improve the yield of active substances by using this system. Meanwhile, we focus on the challenges hiding in the practical application and the future prospects and provide new ideas and the theoretical basis for obtaining numerous bioactive substances from plants.

In vitro production of sesquiterpenes by electro-elicitation in Gyrinops walla Gaetner calli and cell suspension cultures

Aloeswood or Agarwood has long been perfumery commodity traded between Mediterranean Region and Southeast Asia since ancient times. Oil or chips are obtained by destructive harvesting of several Thymeleaceous genera includes Aquilaria and Gonystylus and are expensive and highly demanded ingredients in the global market. The recent recovery of Gyrinops walla as a potential producer of market-quality agarwood in mature damaged woods and branches, the intense illicit felling and exportation G. walla leading to the verge of extinction from Sri Lankan flora. The sustainable utilization of G. walla undoubtedly enhances the foreign exchange of the country and the non-destructive utilization G. walla through biotechnology is the only option available for sustainable exploitation and conservation of the vulnerable G. walla species. An electro-elicitation apparatuses were designed and built to stimulate calli and cell suspensions. The elicited and calli and cell suspensions were harvested at different time periods to extract sesquiterpenes. Current intensities of 10 mA and 50 mA, and 0.1 mA were the optimum values for the induction of sesquiterpenes; γ-selinene, β-caryophyllene, α-cadinol and α-guaiene, production in both calli and cell suspension after 8 weeks and 6 hours, respectively. The findings of the study led to conclude the possibility of induction of production of sesquiterpenes through electro-elicitation of G. walla calli and cell suspension in an in vitro system for sustainable utilization and conservation endeavours.

Electric stimulation promotes growth, mineral uptake, and antioxidant accumulation in kale (Brassica oleracea var. acephala)

Several studies have demonstrated that electric treatment has a positive effect, respectively, on germination, root growth and post-harvest quality. Nevertheless, there is still a lack of research on the effect of electric treatment on growth characteristics and quality of whole plants. Here, we explored the effect of electric fields on two cultivars of kale (Brassica oleracea var. acephala). Three levels of electric current (10, 50, and 100 mA) were applied to the nutrient solution of hydroponically grown plants for three weeks. Kale plants subjected to the electric fields, particularly 50 mA, had higher fresh and dry weights than the control. The absence of an electric field in a Faraday cage caused a significant decrease in shoot and root growth compared with the natural electric field (control). Electrostimulation enhanced nutrient uptake by activating root hair formation and active ion transport. Plants grown under 50 mA contained 72% more calcium, 57% more total phenolic compounds, and had a 70% greater antioxidant capacity than the control. This work provides foundational information regarding the effects of electrical stimulus on plants, which could enable the development of innovative culture technologies to improve crop yields and quality.

Nanosecond pulsed electrical fields enhance product recovery in plant cell fermentation

The potential of pharmacologically active secondary plant metabolites is limited by the low yield from often rare plants, and the lack of economically feasible chemical synthesis of these complex compounds. Plant cell fermentation offers an alternative strategy to overcome these constraints. However, the efficiency of this approach is limited by intracellular sequestration of the products, such that continuous bioprocessing is not possible. As a precondition for such a, more attractive, continuous process, it is of great importance to stimulate the export of the product into the medium without impairing viability and, thus, the productivity of the cells. Using nicotine alkaloids of tobacco as a case study, an alternative strategy is explored, where nanosecond pulsed electric fields (nsPEFs) are applied for the efficient downstream recovery of the products. To maintain cell viability and allow for the further use of biomass, cells were exposed to strong (1-20 kV·cm^-1), but very short (10-100 ns) electric pulses, which leads to a temporary permeabilisation of cell membranes. Using two transgenic cell lines, where two key genes involved in the metabolism of the anti-Alzheimer compound nornicotine were overexpressed, we could show that this nsPEF treatment improved the partitioning of some nicotine alkaloids to the culture medium without impairing viability, nor the synthesis of alkaloids. However, this release was only partial and did not work for nornicotine. Thus, nsPEFs produced a fractionation of alkaloids. We explain this electrofractionation by a working model considering the differential intracellular compartmentalization of nicotineic alkaloids.

Electroporation in food processing and biorefinery

Electroporation is a method of treatment of plant tissue that due to its nonthermal nature enables preservation of the natural quality, colour and vitamin composition of food products. The range of processes where electroporation was shown to preserve quality, increase extract yield or optimize energy input into the process is overwhelming, though not exhausted; e.g. extraction of valuable compounds and juices, dehydration, cryopreservation, etc. Electroporation is--due to its antimicrobial action--a subject of research as one stage of the pasteurization or sterilization process, as well as a method of plant metabolism stimulation. This paper provides an overview of electroporation as applied to plant materials and electroporation applications in food processing, a quick summary of the basic technical aspects on the topic, and a brief discussion on perspectives for future research and development in the field. The paper is a review in the very broadest sense of the word, written with the purpose of orienting the interested newcomer to the field of electroporation applications in food technology towards the pertinent, highly relevant and more in-depth literature from the respective subdomains of electroporation research.

Enhanced production of fumigaclavine C by ultrasound stimulation in a two-stage culture of Aspergillus fumigatus CY018

Stimulation by physical means including ultrasound is important to cell morphology and the product yield. In this work, the effect of ultrasound on the production of fumigaclavine C (FC), a conidiation-associated alkaloid with strong anti-inflammatory activity, was investigated in a newly developed two-stage culture of Aspergillus fumigatus CY018. The optimum ultrasonication conditions consisted of exposing cultures (at 12h of growth phase) to 10-min repeated irradiation (4 times) with a 24-h interval at the fixed power (500 W). Under this condition, FC production reached 118.09 mg/L, which was 89% higher than the control and much higher than previous reported values. Morphological analysis demonstrated that mycelia morphology from ultrasonication was in the form smaller and looser pellets as compared to that of the control. In addition, conidia that is closely related to FC biosynthesis were significantly increased after ultrasound stimulation, with 3 folds of that from the control.

Exudation: an expanding technique for continuous production and release of secondary metabolites from plant cell suspension and hairy root cultures

This review addresses methods of obtaining secondary metabolites from plant cell suspension and hairy root cultures and their exudates, particularly the physiological mechanisms of secondary metabolites release and trafficking. The efficiency for product recovery of metabolites can be increased by various methods, based on the principle of continuous product release into the cultivation medium. The most common methods for metabolite recovery are elicitation, influencing membrane permeability, and in situ product removal. The biosynthetic pathways can be influenced by cultivation conditions, transformation, or application of elicitors. The membrane permeability can be altered through the application of chemical or physical treatments. Product removal can be greatly increased through a two-phase system and the introduction of absorbents into the cultivation medium. In this review, we describe some improved approaches that have proven useful in these efforts.

Metabolomic evaluation of pulsed electric field-induced stress on potato tissue

Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cell nucleae. Metabolic profiling of data obtained through GC/TOF-MS and UPLC/TOF-MS complemented with orthogonal projections to latent structures clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation.

Sub-lethal levels of electric current elicit the biosynthesis of plant secondary metabolites

Many secondary metabolites that are normally undetectable or in low amounts in healthy plant tissue are synthesized in high amounts in response to microbial infection. Various abiotic and biotic agents have been shown to mimic microorganisms and act as elicitors of the synthesis of these plant compounds. In the present study, sub-lethal levels of electric current are shown to elicit the biosynthesis of secondary metabolites in transgenic and non-transgenic plant tissue. The production of the phytoalexin (+)-pisatin by pea was used as the main model system. Non-transgenic pea hairy roots treated with 30-100 mA of electric current produced 13 times higher amounts of (+)-pisatin than did the non-elicited controls. Electrically elicited transgenic pea hairy root cultures blocked at various enzymatic steps in the (+)-pisatin biosynthetic pathway also accumulated intermediates preceding the blocked enzymatic step. Secondary metabolites not usually produced by pea accumulated in some of the transgenic root cultures after electric elicitation due to the diversion of the intermediates into new pathways. The amount of pisatin in the medium bathing the roots of electro-elicited roots of hydroponically cultivated pea plants was 10 times higher 24 h after elicitation than in the medium surrounding the roots of non-elicited control plants, showing not only that the electric current elicited (+)-pisatin biosynthesis but also that the (+)-pisatin was released from the roots. Seedlings, intact roots or cell suspension cultures of fenugreek (Trigonella foenum-graecum), barrel medic, (Medicago truncatula), Arabidopsis thaliana, red clover (Trifolium pratense) and chickpea (Cicer arietinum) also produced increased levels of secondary metabolites in response to electro-elicitation. On the basis of our results, electric current would appear to be a general elicitor of plant secondary metabolites and to have potential for application in both basic and commercial research.

The effect of heat shock on paclitaxel production in Taxus yunnanensis cell suspension cultures: role of abscisic acid pretreatment

The heat shock (HS) response is a conserved cellular defense mechanism to elevated temperatures, observed in cells from bacteria to human. It is characterized by the increased accumulation of HS proteins. This work examines the effect of HS on the secondary metabolite biosynthesis of cultured plant cells. Suspension cultures of Taxus yunnanensis cells, which produce the anticancer diterpenoid paclitaxel (Taxol), were heat shocked at 35-50 degrees C for 30-60 min. The results show that HS reduced cell viability and growth but significantly induced paclitaxel production. The HS-induced paclitaxel production depended on the intensity of HS and the physiological state of the cells. Abscisic acid (ABA)-pretreatment not only increased cell viability and growth upon HS but also improved HS-induced paclitaxel yield. The best culture phase to apply the HS was the late-exponential growth phase. Under the optimized condition, HS enhanced paclitaxel yield by sixfold to 6.8 mg/L. In addition, a prior mild-HS treatment also significantly increased HS-induced paclitaxel production. Furthermore, HS induced oxidative burst, the early event of plant defense response to pathogen attack and other stress challenge; the addition of putative inhibitors of lipoxygenase, a key enzyme for jasmonic acid biosynthesis, significantly inhibited HS-induced pacliatxel accumulation. The stimulation of secondary metabolite production by HS may be a result of HS-induced plant cell defense response.

Electrical stimulation of the energy metabolism in yeast cells using a planar Ti-Au-electrode interface

We report on the influence of dielectric pulse injection on the energy metabolism of yeast cells with a planar interdigitated electrode interface. The energy metabolism was measured via NADH fluorescence. The application of dielectric pulses results in a distinct decrease of the fluorescence, indicating a response of the energy metabolism of the yeast cells. The reduction of the NADH signal significantly depends on the pulse parameters, i.e., amplitude and width. Furthermore, the interface is used to detect electrical changes in the cell-electrolyte system, arising from glucose-induced oscillations in yeast cells and yeast extract, by dielectric spectroscopy at 10 kHz. These dielectric investigations revealed a beta(1)-dispersion for the system electrolyte/yeast cells as well as for the system electrolyte/yeast extract. In agreement with control measurements we obtained a glycolytic period of 45 s for yeast cells and of 11 min for yeast extract.

Responses of defense signals, biosynthetic gene transcription and taxoid biosynthesis to elicitation by a novel synthetic jasmonate in cell cultures ofTaxus chinensis

Recently novel synthetic jasmonate derivatives were shown to have very powerful stimulating effects on the biosynthesis of taxuyunnanine C (Tc) by Taxus chinensis cells (Biotech Bioeng, 86:595; ibid. 86: 809, 2004). To provide an insight into the elicitation mechanism of the newly synthesized elicitors, by taking 2-hydroxyethyl jasmonate (HEJ, at 100 microM) as a typical example, in this work the defense signals were detected and their influences on the expression of important genes in taxoid biosynthetic pathway were examined in cell cultures of T. chinensis. The oxidative burst (induced H2O2 production) was confirmed, and the induction of lipoxygenase (LOX) activity and intracellular jasmonate acid (JA) synthesis was found. The gene transcription of geranylgeranyl diphosphate synthase (GGPPs) and taxa-4(5),11(12)-diene synthase (TS) was up-regulated by HEJ elicitation compared to control. Inhibition of JA biosynthesis by a putative LOX inhibitor, ibuprofen (IBU), effectively depressed the HEJ-induced up-regulation of GGPPs and TS gene transcription levels. In contrast, the inhibition of H2O2 production by membrane NADPH oxidase inhibitor, diphenylene iodonium (DPI), did not affect the transcriptions of those genes. For the HEJ-induced Tc production, it was suppressed with addition of DPI or IBU. The results suggest that both H2O2 and JA signals were involved in HEJ-induced Tc biosynthesis, and JA mediated the induction of GGPPs and TS genes expression, but H2O2 was not essential to activate them. Finally, a signal transduction cascade from defense signal response to activated transcription of taxoid biosynthetic genes and enhanced Tc production is proposed.

Novel synthetic 2,6-dichloroisonicotinate derivatives as effective elicitors for inducing the biosynthesis of plant secondary metabolites

Two novel 2,6-dichloroisonicotinic acid (INA) derivatives [trifluoroethyl 2,6-dichloroisonicotinate (TFINA) and 2-(2,6-dichloro-pyridine-4-carbonyloxy)-ethyl jasmonate (DPCEJ)] were chemically synthesized and evaluated by bioassay as potential elicitors for inducing the biosynthesis of plant secondary metabolites. A suspension culture of Taxus chinensis, which stably produces a high level of bioactive taxuyunnanine C (Tc), was taken as a model plant cell system. A significant increase in Tc accumulation was observed in the presence of TFINA or DPCEJ. For example, addition of 100 microM TFINA or DPCEJ on day 7 led to a high Tc content of 21.6 +/- 2.0 or 27.7 +/- 1.0 mg g(-1) (on day 21), while the Tc content was 13.7 +/- 1.0 and 17.1 +/- 0.9 mg g(-1) for the control and that with addition of 100 microM INA, respectively. To the best of our knowledge, this is the first report on the use of synthetic INA derivatives for inducing the biosynthesis of plant secondary metabolites. The results indicate that the newly synthesized INA analogues can act as promising elicitors for secondary metabolism induction in plant cell cultures.

Plant cells: secondary metabolite heterogeneity and its manipulation

This chapter proposes the concept of rational manipulation of secondary metabolite heterogeneity in plant cell cultures. The heterogeneity of plant secondary metabolites is a very interesting and important issue because these structure-similar natural products have different biological activities. Both taxoids and ginsenosides are two kinds of preeminent examples in the enormous reservoir of pharmacologically valuable heterogeneous molecules in the plant kingdom. They are derived from the five-carbon precursor isopentenyl diphosphate, produced via the mevalonate or the non-mevalonate pathway. The diterpenoid backbone of taxoids is synthesized by taxadiene synthase and the triterpenoid backbone of ginsenosides is synthesized by dammarenediol synthase or beta-amyrin synthase. After various chemical decorations (oxidation, substitution, acylation, glycosylation, benzoylation, and so on) mediated by P450-dependent monooxygenases, glycosyltransferases, acyltransferases, benzoyltransferases, and other enzymes, the terpenoid backbones are converted into heterogeneous taxoids and ginsenosides with different bioactivities. Although detailed information about accumulation and regulation of individual taxoids or ginsenosides in plant cells is still lacking, remarkable progress has recently been made in the structure and bioactivity identification, biosynthetic pathway, manipulation of their heterogeneity by various methodologies including environmental factors, biotransformation, and metabolic engineering in cell/tissue cultures or in plants. Perspectives on a more rational and efficient process to manipulate production of desired plant secondary metabolites by means of metabolic engineering and "omics"-based approaches (e.g., functional genomics) are also discussed.

A novel synthetic fluoro-containing jasmonate derivative acts as a chemical inducing signal for plant secondary metabolism

A novel fluoro-containing jasmonate derivative was chemically synthesized and evaluated as a potential elicitor with respect to the induction of plant defense responses and the biosynthesis of plant secondary metabolites. A bioactive taxuyunnanine C (Tc)-producing cell line of Taxus chinensis was taken as a model plant cell system. The presence of novel synthesized pentafluoropropyl jasmonate (PFPJA) induced two early and important events in plant defense responses, including an oxidative burst and activation of L-phenylalanine ammonia lyase. In addition, PFPJA was found to significantly increase Tc accumulation, without any inhibition of cell growth. Moreover, Tc accumulation was increased more in the presence of PFPJA compared with methyl jasmonate (MJA) and previously reported trifluoroethyl jasmonate (TFEJA). For example, addition of 100 muM PFPJA on day 7 led to a high Tc content (38.2 +/- 0.3 mg/g) at day 21, while the Tc content was 29.3 +/- 0.3 mg/g and 34.9 +/- 0.9 mg/g with the addition of 100 microM MJA and TFEJA, respectively. Quantitative structure-activity analysis of fluoro-containing jasmonates suggests that the increase in the fluoro-groups introduced into the carboxyl side-chain of MJA resulted in a higher stimulatory activity for Tc biosynthesis, which corresponds well with the markedly increased lipophilicity after fluorine introduction. These results indicate that newly synthesized fluoro-containing PFPJA can act as a powerful chemical inducing signal for secondary metabolism in plant cell cultures.