Reactive oxygen species and hormone signaling cascades in endophytic bacterium induced essential oil accumulation in Atractylodes lancea

Microbial regulation of plant secondary metabolites: Impact, mechanisms and prospects

Plant secondary metabolites possess a wide range of pharmacological activities and play crucial biological roles. They serve as both a defense response during pathogen attack and a valuable drug resource. The role of microorganisms in the regulation of plant secondary metabolism has been widely recognized. The addition of specific microorganisms can increase the synthesis of secondary metabolites, and their beneficial effects depend on environmental factors and plant-related microorganisms. This article summarizes the impact and regulatory mechanisms of different microorganisms on the main secondary metabolic products of plants. We emphasize the mechanisms by which microorganisms regulate hormone levels, nutrient absorption, the supply of precursor substances, and enzyme and gene expression to promote the accumulation of plant secondary metabolites. In addition, the possible negative feedback regulation of microorganisms is discussed. The identification of additional unknown microbes and other driving factors affecting plant secondary metabolism is essential. The prospects for further analysis of medicinal plant genomes and the establishment of a genetic operation system for plant secondary metabolism research are proposed. This study provides new ideas for the use of microbial resources for biological synthesis research and the improvement of crop anti-inverse traits for the use of microbial resources.

High-throughput sequencing-based analysis of the composition and diversity of the endophytic bacterial community in the roots of Dipsacus asperoides

This study employed Illumina high-throughput sequencing technology to investigate diversity and community structure of endophytic bacteria in wild D. asperoides growing in three distinct regions. The study analyzed the impact of region on endophytic bacteria, uncovered the core bacterial community, and furnished valuable insights for the screening of endophytic bacteria. This study identified 6,540 amplicon sequence variants (ASVs) coexisting with D. asperoides roots. These ASVs belong to 35 phyla, 84 classes, 204 orders, 365 families, and 708 genera. At the phylum level, the dominant phyla were Proteobacteria and Actinobacteria, while at the genus level, Acidothermus, Acidibacter, Bradyrhizobium, Frankia, and Pseudomonas emerged as the dominant genera. Furthermore, noticeable differences in endophytic bacterial communities were observed between the Yunnan and Guizhou regions. These findings can serve as a reference for the authentication of medicinal materials from various origins and the selection of active strains.

Electrochemistry of lyophilized blueberry and raspberry samples: ROS activation of the antioxidant ability of anthocyanins

An electrochemical study of lyophilized blueberry (Vaccinium corymbosum L.) and raspberry (Rubus idaeus L.) fruits was carried out using microparticulate deposits from ethanolic extracts of fruits in contact with different aqueous electrolytes. This voltammetry is dominated by the oxidation of anthocyanins. It was hypothesized that under conditions of electrochemical generation of reactive oxygen species (ROS), new anthocyanin-derived species with high antioxidant capacity are formed over a wide pH range. In the case of ROS-activated anthocyanins, electrochemical oxidation is associated with loss of sugar moieties. Experimental voltammetric and scanning electrochemical microscopy (SECM) imaging data consistent with this hypothesis are presented.

Use of biochar and a post-coagulation effluent as an adsorbent of malachite green, beneficial bacteria carrier, and seedling substrate for plants belonging to the poaceae family

Wastewater treatment plants produce solid and semi-solid sludge, which treatment minimises secondary environmental pollution because of wastewater treatment and obtaining new bioproducts. For this reason, in this paper, the co-pyrolysis of biogenic biomasses recovered from a biological reactor with immobilised fungal and bacterial biomass and a tertiary reactor with Chlorella sp. used for dye-contaminated wastewater treatment was carried out. Biogenic biomasses mixed with pine bark allowed the production and characterisation of two types of biochar. The raw material and biochar were on the "in vitro" germination of Lolium sp. seeds, followed by adsorption studies for malachite green (MG) dye using the raw material and the biochar. Results showed that using 60 mg L-1 of a cationic coagulant at pH 6.5 allowed for the recovery of more than 90% of the microalgae after 50 min of processing. Two biochar resulted: BC300, at pH 5.08 ± 0.08 and BC500, at pH 6.78 ± 0.01. The raw material and both biochars were co-inoculated with growth-promoting bacteria; their viabilities ranged from 1.7 × 106 ± 1.0 × 101 to 7.5 × 108 ± 6.0 × 102 CFU g-1 for total heterotrophic, nitrogen-fixing and phosphate-solubilising bacteria. Re-use tests on Lolium sp. seed germination showed that with the post-coagulation effluent, the germination was 100%, while with the biochar, with and without beneficial bacteria, the germination was 98 and 99%, respectively. Finally, BC500 adsorbed the highest percentage of malachite green at pH 4.0, obtaining qecal values of 0.5249 mg g-1 (R2: 0.9875) with the pseudo-second-order model.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03766-x.

The phenotypic variation mechanisms of Atractylodes lancea post-cultivation revealed by conjoint analysis of rhizomic transcriptome and metabolome

The wild Atractylodes lancea rhizomes have been traditionally used as herbal medicine. As the increasingly exhaustion of wild A. lancea, the artificial cultivation mainly contributed to the medicinal material production. However, besides the phenotypic variation of rhizome phenotypic trait alteration, the qualities of cultivated A. lancea decrease compared with the wild counterpart. To unveil the physiological and molecular mechanism beneath the phenotypic variation, GC-MS-based volatile organic compounds (VOCs) profiling and RNAseq-based transcriptome analysis were conducted. The volatile metabolomics profiling revealed 65 differentially accumulated metabolites (DAMs) while the transcriptomic profiling identified 12 009 differentially expressed unigenes (DEGs) post-cultivation. The volatile active compounds including atractylone, and eudesmol accumulated more in wild rhizome than in the cultivated counterpart, and several unigenes in terpene synthesis were downregulated under cultivated condition. Compared with the wild A. lancea rhizome, the contents of bioactive Jasmonic Acid (JAs) in cultivated A. lancea rhizome were higher, and evidences that JAs negatively regulate the terpenes biosynthesis in the cultivated A. lancea rhizome were also provided. The combinational omics analysis further indicated the high correlation between the ten cultivation-suppressed VOCs and the cultivation-altered genes for sesquiterpenoids biosynthesis in A. lancea. The network of the cultivation-altered transcription factors (TFs) and the ten VOCs suggested TFs (e.g. Arabidopsis ERF13 homologs and WRKY50) are involved in the regulation of terpenes biosynthesis. These results laid a theoretical basis for developing geo-herbalism medicinal plants with "high quality and optimal shape".

Mild shading promotes sesquiterpenoid synthesis and accumulation in Atractylodes lancea by regulating photosynthesis and phytohormones

Atractylodes lancea rhizome (AR) has high medicinal and economic value. A previous study has reported that the accumulation of sesquiterpenoids in AR has obvious advantages under bamboo canopy. A concrete shade value to promote the cultivation of high-quality AR has not been established. In this study, 80% shading was screened at six different light intensities (100%, 80%, 60%, 40%, 20%, 7%), and the mechanism was explored in terms of photosynthetic efficiency and phytohormones levels. The results indicated that the total sesquiterpenoid content of 80% mild shading increased by 58%, 52%, and 35%, respectively, compared to 100% strong light in seedling, expansion, and harvest stages and increased by 144%, 178%, and 94%, respectively, compared with 7% low light. The sesquiterpenoids hinesol and β-eudesmol contributed approximately 70% to the differential contribution ratio between mild shading and strong light (100%) or between mild shading and low light (7%). Furthermore, HMGR, DXR, and FPPS genes, which regulate sesquiterpenoid synthesis, were significantly upregulated in 80% mild shading. Transpiration rate; the intercellular CO₂ concentration; net photosynthetic rate; and levels of jasmonic acid, abscisic acid, and gibberellin were strongly correlated (r > 0.85) with sesquiterpenoid accumulation. Cis-acting elements responding to light and phytohormones were present within the promoter regions of HMGR, DXR, and FPPS. Therefore, 80% shading promotes the synthesis and accumulation of sesquiterpenoids in AR by regulating photosynthetic efficiency and phytohormone production, thereby promoting transcriptional expression.

Transcriptome sequencing and signal transduction for the enhanced tanshinone production in Salvia miltiorrhiza hairy roots induced by Trichoderma atroviride D16 polysaccharide fraction

Salvia miltiorrhiza Bunge. is commonly used to treat vascular diseases because of its activity ingredients, phenolic acids, and tanshinones. Polysaccharide fraction (PSF) extracted from Trichoderma atroviride D16 could promote tanshinone accumulation in S. miltiorrhiza hairy roots. Transcriptome sequencing was conducted to describe the global gene expression of PSF-treatment hairy roots, and data analyses showed enzymes of tanshinone biosynthetic pathways were up-regulated, and genes associated to signal molecules and transcription factors were responsive. Endogenous H2O2, abscisic acid, and nitric oxide contents were measured after PSF treatment, while tanshinone accumulations were measured with treatment of exogenous H2O2 or H2O2 inhibitor on PSF-treatment S. miltiorrhiza hairy roots. The results showed H2O2 was important in tanshinone biosynthesis caused by PSF and nitric oxide might be the downstream molecules of H2O2. Taken together, the study indicates that D16 PSF enhances the accumulation of tanshinones through enzymes of tanshinone biosynthetic pathways, signal molecules, and transcription factors.

Phytohormones and Transcriptome Analyses Revealed the Dynamics Involved in Spikelet Abortion and Inflorescence Development in Rice

Panicle degeneration, sometimes known as abortion, causes heavy losses in grain yield. However, the mechanism of naturally occurring panicle abortion is still elusive. In a previous study, we characterized a mutant, apical panicle abortion1331 (apa1331), exhibiting abortion in apical spikelets starting from the 6 cm stage of panicle development. In this study, we have quantified the five phytohormones, gibberellins (GA), auxins (IAA), abscisic acid (ABA), cytokinins (CTK), and brassinosteroids (BR), in the lower, middle, and upper parts of apa1331 and compared these with those exhibited in its wild type (WT). In apa331, the lower and middle parts of the panicle showed contrasting concentrations of all studied phytohormones, but highly significant changes in IAA and ABA, compared to the upper part of the panicle. A comparative transcriptome of apa1331 and WT apical spikelets was performed to explore genes causing the physiological basis of spikelet abortion. The differential expression analysis revealed a significant downregulation and upregulation of 1587 and 978 genes, respectively. Hierarchical clustering of differentially expressed genes (DEGs) revealed the correlation of gene ontology (GO) terms associated with antioxidant activity, peroxidase activity, and oxidoreductase activity. KEGG pathway analysis using parametric gene set enrichment analysis (PGSEA) revealed the downregulation of the biological processes, including cell wall polysaccharides and fatty acids derivatives, in apa1331 compared to its WT. Based on fold change (FC) value and high variation in expression during late inflorescence, early inflorescence, and antherdevelopment, we predicted a list of novel genes, which presumably can be the potential targets of inflorescence development. Our study not only provides novel insights into the role of the physiological dynamics involved in panicle abortion, but also highlights the potential targets involved in reproductive development.

Overcoming Multidrug Resistance in Salmonella spp. Isolates Obtained From the Swine Food Chain by Using Essential Oils: An in vitro Study

Antimicrobial resistance (AMR) is a global concern, and new approaches are needed to circumvent animal and food-borne resistant pathogens. Among the new strategies, the combination of antibiotics with natural compounds such as essential oils (EOs) could be an alternative to challenge bacterial resistance. The present study evaluates the phenotypic and genotypic antibiotic resistance of 36 Salmonella enterica (16 S. Typhimurium, 3 monophasic variant S. Typhimurium, 8 S. Enteritidis, 6 S. Rissen, 1 S. Typhi, and 2 S. Derby) strains, isolated from the swine production chain. The isolates displayed phenotypic resistance to gentamicin, amikacin, tobramycin, and tetracycline, while the resistance genes most commonly detected were parC, catA, nfsB, nfsA, blaTEM, tetA, and tetB. Then 31/36 Salmonella isolates were chosen to evaluate resistance to tetracycline and Thymus vulgaris, Eugenia caryophyllata, and Corydothymus capitatus EOs by determining minimum inhibitory concentrations (MICs). Finally, the synergistic effect between tetracycline and each EOs was evaluated by the checkerboard method, calculating the fractional inhibitory concentration (FIC) index. Among the EOs, C. capitatus displayed the best bioactivity in terms of MICs, with the lowest values (0.31 and 0.625 μl/ml). On the contrary, the strains showed the ability to grow in the presence of the maximum concentration of tetracycline employed (256 μg/ml). While not displaying a real synergism according to the FIC index, the combination of tetracycline compounds and the three EOs resulted in a significant reduction in the MIC values to tetracycline (4 μg/ml), suggesting a restoration of the susceptibility to the antibiotic in Salmonella spp.

Early stem growth mutation alters metabolic flux changes enhance sesquiterpenoids biosynthesis in Atractylodes lancea (Thunb.) DC

Atractylodes lancea (Thunb.) DC. is a well-known medicinal herb in China, containing abundant active components, including a variety of sesquiterpenoids. Owing to a shortage of wild resources, artificial cultivation has become the main breeding mode, leading to the germplasm degradation. In preliminary research, our research group found that a mutant tissue culture seedling of A. lancea is an excellent germplasm resource, characterized by early stem growth and higher sesquiterpenoid content than that of the wild type. In this study, the physiological and biochemical mechanisms underlying efficient sesquiterpenoids synthesis by this mutant A. lancea were systematically evaluated. The results showed that the photosynthetic efficiency, central carbon metabolism efficiency, and energy metabolism efficiency were significantly improved in mutant A. lancea compared with the wild type, and the content of endogenous hormones, such as gibberellin and jasmonic acid, changed significantly. In addition, levels of key metabolites and the expression level of key genes in the mevalonate and 2-C-methyl-d-erythritol-4-phosphate pathways were significantly higher in mutant type than in wild type, resulting in elevated sesquiterpenoid synthesis in the mutant. These physiological and biochemical properties explain the rapid growth and high sesquiterpenoid content of mutant A. lancea.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11240-022-02240-5.

Influence of tissue and geographic locality on culturable endophytic bacteria of Atractylodes macrocephala

The endophytic bacterial community and their diversity are closely related to the host's growth and development. This paper explores the culturable endophytic bacteria in the stems, leaves, roots and rhizomes of Atractylodes macrocephala (AM) of four localities (Yuqian, Wenxian, Pan'an and Pingjiang) and the potential correlation between the bacteria and plant bioactive compounds. A total of 118 endophytic bacteria belonging to 3 phyla, 5 classes, 11 orders, 26 families and 48 genera were isolated and identified from the four AM tissues. Among them, Bacillus was the dominant genus. In AM, the tissue type and locality influenced the endophytic bacterial community. Approximately 29.7 and 28.8% of the endophytic bacteria exhibited tissue specificity and geographic specificity, respectively. Furthermore, high-performance liquid chromatography revealed that the sesquiterpenoid (atractylenolide I, atractylenolide Ⅱ and atractylon) content was more in the rhizomes of Wenxian than in those of Pingjiang, Yuqian and Pan'an. The multiple linear regression was used to screen the bacterial strains related to the bioactive compounds of AM. The relative frequency of Microbacterium positively correlated with atractylenolide I and atractylon content in AM but negatively correlated with atractylenolide Ⅱ content. The study also provides a theoretical framework for future research on endophytic bacteria as alternative sources of secondary plant metabolites.

Beneficial Relationships Between Endophytic Bacteria and Medicinal Plants

Plants benefit extensively from endophytic bacteria, which live in host plant tissues exerting no harmful effects. Bacterial endophytes promote the growth of host plants and enhance their resistance toward various pathogens and environmental stresses. They can also regulate the synthesis of secondary metabolites with significant medicinal properties and produce various biological effects. This review summarizes recent studies on the relationships between bacterial endophytes and medicinal plants. Endophytic bacteria have numerous applications in agriculture, medicine, and other industries: improving plant growth, promoting resistance toward both biotic and abiotic stresses, and producing metabolites with medicinal potential. Their distribution and population structure are affected by their host plant's genetic characteristics and health and by the ecology of the surrounding environment. Understanding bacterial endophytes can help us use them more effectively and apply them to medicinal plants to improve yield and quality.

Medicinal Plants and Their Bacterial Microbiota: A Review on Antimicrobial Compounds Production for Plant and Human Health

Medicinal plants (MPs) have been used since antiquity in traditional and popular medicine, and they represent a very important source of bioactive molecules, including antibiotic, antiviral, and antifungal molecules. Such compounds are often of plant origin, but in some cases, an origin or a modification from plant microbiota has been shown. Actually, the research continues to report the production of bioactive molecules by plants, but the role of plant–endophytic interaction is emerging. Classic examples are mainly concerned with fungal endophytes; however, it has been recently shown that bacterial endophytes can also play an important role in influencing the plant metabolism related to the synthesis of bioactive compounds. In spite of this, a deep investigation on the power of MP bacterial endophytes is lacking. Here, an overview of the studies on MP bacterial microbiota and its role in the production of plant antimicrobial compounds contributing to prime host defense system and representing a huge resource for biotech and therapeutic applications is provided.

Molecular mechanisms in grass-Epichloë interactions: towards endophyte driven farming to improve plant fitness and immunity

All plants harbor many microbial species including bacteria and fungi in their tissues. The interactions between the plant and these microbes could be symbiotic, mutualistic, parasitic or commensalistic. Mutualistic microorganisms are endophytic in nature and are known to play a role in plant growth, development and fitness. Endophytes display complex diversity depending upon the agro-climatic conditions and this diversity could be exploited for crop improvement and sustainable agriculture. Plant-endophyte partnerships are highly specific, several genetic and molecular cascades play a key role in colonization of endophytes in host plants leading to rapid changes in host and endophyte metabolism. This results in the accumulation of secondary metabolites, which play an important role in plant defense against biotic and abiotic stress conditions. Alkaloids are one of the important class of metabolites produced by Epichloë genus and other related classes of endophytes and confer protection against insect and mammalian herbivory. In this context, this review discusses the evolutionary aspects of the Epichloë genus along with key molecular mechanisms determining the lifestyle of Epichloë endophytes in host system. Novel hypothesis is proposed to outline the initial cellular signaling events during colonization of Epichloë in cool season grasses. Complex clustering of alkaloid biosynthetic genes and molecular mechanisms involved in the production of alkaloids have been elaborated in detail. The natural defense and advantages of the endophyte derived metabolites have also been extensively discussed. Finally, this review highlights the importance of endophyte-arbitrated plant immunity to develop novel approaches for eco-friendly agriculture.

Bacterial endophytes from Lycoris radiata promote the accumulation of Amaryllidaceae alkaloids

Lycoris radiata is the major source of Amaryllidaceae alkaloids, having various medicinal activities. However, the low content of these alkaloids in planta limits their pharmaceutical development and utilization. In this study, the ability of bacterial endophytes to enhance the accumulation of five important Amaryllidaceae alkaloids was investigated. A total of 188 bacterial endophytes were isolated from L. radiata and their composition and diversity were analyzed. Fourteen ones were demonstrated to significantly increase the concentration of the alkaloids of interest in different organs, up to 11.1-fold over the control level, with no adverse influence on the plant growth. An additional 3 bacterial endophytes were found to significantly increase the dry weight of L. radiata with no adverse influence on the concentration of the alkaloids in planta, so the total yield of alkaloids in planta was increased up to 2.4-fold over the control level. Considering the plant growth-promoting abilities of these bacterial endophytes, it is speculated that the indole-3-acetic acid and siderophore secreted by them, combined with their nitrogen fixation ability, may contribute to the enhanced plant growth and the increased alkaloid accumulation in L. radiata. To our knowledge, this work is firstly defining the diversity of culturable bacterial endophytes in L. radiata and determining which species promoted the accumulation of Amaryllidaceae alkaloids. It provides several valuable bacterial inoculants that can be further applied to improve alkaloid production in L. radiata and broadens our understanding of the interactions between a medicinal plant and the bacterial endophytes.

Comparative Transcriptomics and Proteomics of Atractylodes lancea in Response to Endophytic Fungus Gilmaniella sp. AL12 Reveals Regulation in Plant Metabolism

The fungal endophyte Gilmaniella sp. AL12 can establish a beneficial association with the medicinal herb Atractylodes lancea, and improve plant growth and sesquiterpenoids accumulation, which is termed “double promotion.” Our previous studies have uncovered the underling primary mechanism based on some physiological evidences. However, a global understanding of gene or protein expression regulation in primary and secondary metabolism and related regulatory processes is still lacking. In this study, we employed transcriptomics and proteomics of Gilmaniella sp. AL12-inoculated and Gilmaniella sp. AL12-free plants to study the impact of endophyte inoculation at the transcriptional and translational levels. The results showed that plant genes involved in plant immunity and signaling were suppressed, similar to the plant response caused by some endophytic fungi and biotroph pathogen. The downregulated plant immunity may contribute to plant-endophyte beneficial interaction. Additionally, genes and proteins related to primary metabolism (carbon fixation, carbohydrate metabolism, and energy metabolism) tended to be upregulated after Gilmaniella sp. AL12 inoculation, which was consistent with our previous physiological evidences. And, Gilmaniella sp. AL12 upregulated genes involved in terpene skeleton biosynthesis, and upregulated genes annotated as β-farnesene synthase and β-caryophyllene synthase. Based on the above results, we proposed that endophyte-plant associations may improve production (biomass and sesquiterpenoids accumulation) by increasing the source (photosynthesis), expanding the sink (glycolysis and tricarboxylic acid cycle), and enhancing the metabolic flux (sesquiterpenoids biosynthesis pathway) in A. lancea. And, this study will help to further clarify plant-endophyte interactions.

Mutualistic fungus Phomopsis liquidambari increases root aerenchyma formation through auxin-mediated ethylene accumulation in rice (Oryza sativa L.)

The fungal endophyte Phomopsis liquidambari can improve nitrification rates and alter the abundance and composition of ammonia-oxidizers in the soil rhizosphere of rice. Aerenchyma is related to oxygen transport efficiency and contributes to the enhanced rhizospheric nitrification under flooding conditions. However, whether and how P. liquidambari affects aerenchyma formation is largely unknown. We therefore conducted pot and hydroponic experiments to investigate the changes of aerenchyma area, ethylene and indole-3-acetic acid (IAA) levels in rice with or without P. liquidambari infection. Our results showed that the larger aerenchyma area in rice roots with P. liquidambari inoculation was associated with markedly up-regulated expression of genes related to aerenchyma formation. Meanwhile, P. liquidambari inoculation substantially elevated root porosity (POR) and radial oxygen loss (ROL), leading to the enhancement of oxidation-reduction potential (ORP) under pot condition. Besides, P. liquidambari significantly increased IAA and ethylene levels in rice by stimulating the expression of genes involved in auxin and ethylene biosyntheses. Furthermore, auxin that partly acting upstream of ethylene signalling played an essential role in P. liquidambari-promoted aerenchyma formation. These results verified the direct contribution of P. liquidambari in promoting aerenchyma formation via the accumulation of IAA and ethylene in rice roots, which provides a constructive suggestion for improving hypoxia tolerance through plant-endophyte interactions.

Endophytic Pseudomonas induces metabolic flux changes that enhance medicinal sesquiterpenoid accumulation in Atractylodes lancea

The bacterial endophyte Pseudomonas fluorescens ALEB7B significantly enhances photosynthate accumulations in Atractylodes lancea. These carbohydrates are preferentially used by the host plant to synthesize secondary metabolites, rather than to increase plant biomass accumulation. Mechanisms underlying the allocation of endophyte-increased carbohydrate in different plant metabolic processes are largely unknown. We have studied how P. fluorescens ALEB7B enhances photosynthate accumulation and how bacterial elicitors regulate metabolic flux and increase medicinal sesquiterpenoid formation in A. lancea using the sterile tissue culture plantlets. P. fluorescens ALEB7B enhances plant photosynthate accumulation by synthesizing and secreting indole-3-acetic acid, which has been demonstrated using high-performance liquid chromatography analysis. The increased endogenous indole-3-acetic acid promotes plant root development and then assimilation. Increased carbohydrates provide the material basis for the formations of terpenoid hydrocarbon scaffolds, which has been proved using gas chromatography analysis. Further, protein and polysaccharide elicitors secreted by P. fluorescens ALEB7B have been separated and purified from the bacterial fermentation broth, which have been applied to A. lancea plantlets. Both elicitors can stimulate the conversions of terpenoid hydrocarbon scaffolds to oxygenous sesquiterpenoids, the active medicinal ingredients in A. lancea, by triggering the oxidative burst in planta. Moreover, this study separates an ABC transporter substrate-binding protein from protein elicitors secreted by P. fluorescens ALEB7B with an ÄKTA Prime Plus Purifier System and firstly shows that this protein is essential to induce oxygenous sesquiterpenoid accumulation in A. lancea. This study provides new perspectives for mechanisms of medicinal oxygenous terpenoid synthesis, which has important reference values to the cultivation of medicinal plants that have terpenoids as their active ingredients, such as Artemisia annua and Taxus chinensis.

In-vivo electrochemical monitoring of H2O2 production induced by root-inoculated endophytic bacteria in Agave tequilana leaves

A dual-function platinum disc microelectrode sensor was used for in-situ monitoring of H₂O₂ produced in A. tequilana leaves after inoculation of their endophytic bacteria (Enterobacter cloacae). Voltammetric experiments were carried out from 0.0 to -1.0V, a potential range where H₂O₂ is electrochemically reduced. A needle was used to create a small cavity in the upper epidermis of A. tequilana leaves, where the fabricated electrochemical sensor was inserted by using a manual three-dimensional micropositioner. Control experiments were performed with untreated plants and the obtained electrochemical results clearly proved the formation of H₂O₂ in the leaves of plants 3h after the E. cloacae inoculation, according to a mechanism involving endogenous signaling pathways. In order to compare the sensitivity of the microelectrode sensor, the presence of H₂O₂ was detected in the root hairs by 3,3-diaminobenzidine (DAB) stain 72h after bacterial inoculation. In-situ pH measurements were also carried out with a gold disc microelectrode modified with a film of iridium oxide and lower pH values were found in A. tequilana leaves treated with bacteria, which may indicate the plant produces acidic substances by biosynthesis of secondary metabolites. This microsensor could be an advantageous tool for further studies on the understanding of the mechanism of H₂O₂ production during the plant-endophyte interaction.