Arbuscular mycorrhiza differentially affects synthesis of essential oils in coriander and dill

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.

Variability in Chemical Composition and Biochemical Activities of Mentha x piperita L. Essential Oil, in Response to Mycorrhizal Symbiosis and Heavy Metal Stress

The present paper highlights the effect of Pb/Cd-stress and/or mycorrhizal colonization by Glomus Intraradices on yield, chemical composition, cytotoxicity and antimicrobial activity of Mentha x piperita L. essential oil. Our findings showed that mycorrhizal colonization could be used to improve the essential oil yield of M. x piperita, either in non-stressed or Pb/Cd-stressed plants. GC-MS analysis revealed three chemotypes: linalool/pulegone (32.6/30.8 %) chemotype in essential oils of non-mycorrhizal Pb-stressed plants, menthone/menthyl acetate (30.3/25.1 %) chemotype in essential oils of non-mycorrhizal Cd-stressed plants and menthol (44.6 %) chemotype in essential oils of non-mycorrhizal non-stressed plants, mycorrhizal non-stressed plants and mycorrhizal Pb/Cd-stressed plants. The cytotoxicity of M. x piperita essential oil, evaluated by brine shrimp lethality bioassay, was increased in presence of Pb/Cd-stress (from 379.58 to 72.84 μm/mL) and decreased in mycorrhizal plants (from 379.58 to 482.32 μm/mL). The antimicrobial activity of M. x piperita essential oil, evaluated by disc diffusion method and determination of Minimum Inhibitory Concentration against ten microorganisms, was enhanced by the mycorrhizal colonization and deceased by the Pb/Cd-stress. In conclusion, the inoculation of medicinal plants with mycorrhizal fungi is a real avenue for alleviating abiotic stress and/or increasing the quantity and quality of secondary metabolites in terms of biological activities.

Influence of drought stress and mycorrhizal (Funneliformis mosseae) symbiosis on growth parameters, chlorophyll fluorescence, antioxidant activity, and essential oil composition of summer savory (Satureja hortensis L.) plants

Introduction

Drought stress unfavorably influences the growth and physiological traits of plants in the arid and semi-arid regions of the world. This study aimed to determine the effects of arbuscular mycorrhiza fungi (AMF; Funneliformis mosseae) inoculation on the physiological and biochemical responses of summer savory (Satureja hortensis L.) under different irrigation regimes.

Methods

The first factor was different irrigation regimes, including no drought stress (100% field capacity; FC), moderate drought stress (60% FC), and severe drought stress (30% FC); the second factor included the plants without AMF (AMF₀) and with AMF inoculation (AMF₁).

Results

The results showed that better values, higher plant height, shoot mass (fresh and dry weight), relative water content (RWC), membrane stability index (MSI), photosynthesis pigments, Fv, Fm, Fv/Fm, and total soluble proteins were obtained in the plants inoculated with AMF. The highest values were obtained for plants with no drought stress, then the plants subjected to AMF₁ under 60% FC, and the lowest ones for plants under 30% FC without AMF inoculation. Thus, these properties are reduced under moderate and severe drought stress. At the same time, the utmost activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and the highest malondialdehyde (MDA), H₂O₂, proline, and antioxidant activity (TAA) were achieved for 30% FC + AMF₀. It was also found that AMF inoculation improved essential oil (EO) composition, also as EO obtained from plants under drought stress. Carvacrol (50.84-60.03%) was the dominant component in EO; γ-terpinene (19.03-27.33%), p-cymene, α-terpinene, and myrcene, were recognized as other important components in EO. The higher carvacrol and γ-terpinene contents were obtained from summer savory plants with AMF inoculation and the lowest for plants without AMF and under 30% FC.

Conclusion

According to the present findings, using AMF inoculation could be a sustainable and eco-friendly approach to improve physiological and biochemical characteristics and the essential oil quality of summer savory plants under water shortage conditions.

Optimizing Antioxidant Activity and Phytochemical Properties of Peppermint (Mentha piperita L.) by Integrative Application of Biofertilizer and Stress-Modulating Nanoparticles under Drought Stress Conditions

Drought stress (DS) negatively affects plant growth, productivity, and quality in semi-arid and arid regions. Nowadays, application of biofertilizers and stress-modulating nanoparticles (NPs) improves plant performance under stressful conditions. The study evaluated the impacts of arbuscular mycorrhizal fungi (Myco-Root) and TiO₂ NPs on the nutrient uptake, dry yield, essential oil (EO) productivity, and EO quality of peppermint (Mentha piperita L.) under different irrigation regimes. The treatments included three irrigation regimes containing irrigation after 20% (I₂₀, well-watered), 40% (I₄₀, mild DS), and 60% (I₆₀, severe DS) maximum allowable depletion (MAD) percentage of the soil's available water as well as four fertilizer sources contain no fertilization (control), Myco-Root biofertilizer, TiO₂ NPs, and an integrative application of Myco-Root + TiO₂ NPs. The results demonstrated that the highest (195.72 g m^-2) and the lowest dry yield (78.76 g m^-2) of peppermint was obtained in well-watered conditions with integrative application of Myco-Root + TiO₂ NPs and severe drought stress (I₆₀) without fertilization, respectively. The dry yield of peppermint was reduced by 27.7 and 53.4% in mild (I₄₀) and severe drought stress (I₆₀), respectively. The maximum EO content (1.49%) and EO yield (2.30 g m^-2) was recorded in mild drought stress (I₄₀) treated with Myco-Root + TiO₂ NPs. Based on the GC-MS and GC-FID analysis, 29 constituents were identified in peppermint EO, with the major constituents being menthol (38.99-52%), menthone (12.72-20.13%), 1,8-cineole (6.55-7.84%), and neo-menthol (3.14-4.52%), respectively. The maximum content of menthol, 1,8-cineole, and neo-menthol was obtained under mild drought stress (I₄₀) fertilized with Myco-Root + TiO₂ NPs. The results indicate that the integrative application of Myco-Root + TiO₂ NPs could be used as an alternative method of using chemical fertilizers in sustainable agricultural systems for improving the EO quantity and quality of peppermint grown under drought stress conditions.

Arbuscular mycorrhizal fungi: Effects on secondary metabolite accumulation of traditional Chinese medicines

Traditional Chinese medicine (TCM) has played a pivotal role in maintaining the health of people, and the intrinsic quality of TCM is directly related to the clinical efficacy. The medicinal ingredients of TCM are derived from the secondary metabolites of plant metabolism and are also the result of the coordination of various physiological activities in plants. Arbuscular mycorrhizal fungi (AMF) are among the most ubiquitous plant mutualists that enhance the growth and yield of plants by facilitating the uptake of nutrients and water. Symbiosis of AMF with higher plants promotes growth and helps in the accumulation of secondary metabolites. However, there is still no systematic analysis and summation of their roles in the application of TCM, biosynthesis and accumulation of active substances of herbs, as well as the mechanisms. AMF directly or indirectly affect the accumulation of secondary metabolites of TCM, which is the focus of this review. First, in this review, the effects of AMF symbiosis on the content of different secondary metabolites in TCM, such as phenolic acids, flavonoids, alkaloids and terpenoids, are summarized. Moreover, the mechanism of AMF regulating the synthesis of secondary metabolites was also considered, in combination with the establishment of mycorrhizal symbionts, response mechanisms of plant hormones, nutritional elements and expression of key enzyme their activities. Finally, combined with the current application prospects for AMF in TCM, future in-depth research is planned, thus providing a reference for improving the quality of TCM. In this manuscript, we review the research status of AMF in promoting the accumulation of secondary metabolites in TCM to provide new ideas and methods for improving the quality of TCM.

Mixed consortium of microbial inoculants improves yield and essential oil profile of coriander

Coriander (Coriandrum sativum L.), one of the oldest spice plants globally, has wide usage, mainly owing to its essential oil content. This study investigated the effects of rhizobacteria, mycorrhizae, and their combination on the yield and essential oil profile of coriander. The treatments resulted in statistically higher yield properties and essential oil values than the control. The effects of the microorganism treatments on the yield characteristics were not statistically different. However, the treatments significantly affected the essential oil content and yield. While the arbuscular mycorrhizal fungi and combined application of the microorganisms were statistically equal, arbuscular mycorrhizal fungi had a higher value in essential oil content and yield by 0.75% and 11.8 L ha^-1, respectively. The combined application resulted in higher values of linalool (9.47%) and γ-terpinene (6.75%), the components with the highest rate in the essential oil composition. The principal component analysis highlighted the importance of the combined application on the crucial components. In the light of the results, beneficial microorganism treatments were considered significant for yield and essential oil enhancement. Therefore, the wide use of these treatments will highly contribute to coriander cultivation.

Arbuscular mycorrhizal Fungi and Changes in Primary and Secondary Metabolites

Medicinal and aromatic plants (MAPs) are able to synthesize a diverse group of secondary metabolites (SMs) such as terpenoids or terpenes, steroids, phenolics, and alkaloids with a broad range of therapeutic and pharmacological potentials. Extensive use of MAPs in various industries makes it important to re-evaluate their research, development, production, and use. In intensive agricultural systems, increasing plant productivity is highly dependent on the application of chemical inputs. Extreme use of chemical or synthetic fertilizers, especially higher doses of N fertilization, decrease the yield of bioactive compounds in MAPs. The plant-soil microbial interaction is an eco-friendly strategy to decrease the demand of chemical fertilizers. Arbuscular mycorrhizal fungi (AMF), belongs to phylum Glomeromycota, can form mutualistic symbiotic associations with more than 80% of plant species. The AMF-plant symbiotic association, in addition to increasing nutrient and water uptake, reprograms the metabolic pathways of plants and changes the concentration of primary and secondary metabolites of medicinal and aromatic plants. The major findings reported that inoculation of AMF with MAPs enhanced secondary metabolites directly by increasing nutrient and water uptake and also improving photosynthesis capacity or indirectly by stimulating SMs' biosynthetic pathways through changes in phytohormonal concentrations and production of signaling molecules. Overall, the AMF-MAPs symbiotic association can be used as new eco-friendly technologies in sustainable agricultural systems for improving the quantity and quality of MAPs.

Arbuscular mycorrhizal fungi and production of secondary metabolites in medicinal plants

Medicinal plants are an important source of therapeutic compounds used in the treatment of many diseases since ancient times. Interestingly, they form associations with numerous microorganisms developing as endophytes or symbionts in different parts of the plants. Within the soil, arbuscular mycorrhizal fungi (AMF) are the most prevalent symbiotic microorganisms forming associations with more than 70% of vascular plants. In the last decade, a number of studies have reported the positive effects of AMF on improving the production and accumulation of important active compounds in medicinal plants.In this work, we reviewed the literature on the effects of AMF on the production of secondary metabolites in medicinal plants. The major findings are as follows: AMF impact the production of secondary metabolites either directly by increasing plant biomass or indirectly by stimulating secondary metabolite biosynthetic pathways. The magnitude of the impact differs depending on the plant genotype, the AMF strain, and the environmental context (e.g., light, time of harvesting). Different methods of cultivation are used for the production of secondary metabolites by medicinal plants (e.g., greenhouse, aeroponics, hydroponics, in vitro and hairy root cultures) which also are compatible with AMF. In conclusion, the inoculation of medicinal plants with AMF is a real avenue for increasing the quantity and quality of secondary metabolites of pharmacological, medical, and cosmetic interest.

Laser Light Treatment Improves the Mineral Composition, Essential Oil Production and Antimicrobial Activity of Mycorrhizal Treated Pelargoniumgraveolens

Pelargonium graveolens, rose-scented geranium, is commonly used in the perfume industry. P. graveolens is enriched with essential oils, phenolics, flavonoids, which account for its tremendous biological activities. Laser light treatment and arbuscular mycorrhizal fungi (AMF) inoculation can further enhance the phytochemical content in a significant manner. In this study, we aimed to explore the synergistic impact of these two factors on P. graveolens. For this, we used four groups of surface-sterilized seeds: (1) control group1 (non-irradiated; non-colonized group); (2) control group2 (mycorrhizal colonized group); (3) helium-neon (He-Ne) laser-irradiated group; (4) mycorrhizal colonization coupled with He-Ne laser-irradiation group. Treated seeds were growing in artificial soil inculcated with Rhizophagus irregularis MUCL 41833, in a climate-controlled chamber. After 6 weeks, P. graveolens plants were checked for their phytochemical content and antibacterial potential. Laser light application improved the mycorrhizal colonization in P. graveolens plants which subsequently increased biomass accumulation, minerals uptake, and biological value of P. graveolens. The increase in the biological value was evident by the increase in the essential oils production. The concomitant application of laser light and mycorrhizal colonization also boosted the antimicrobial activity of P. graveolens. These results suggest that AMF co-treatment with laser light could be used as a promising approach to enhance the metabolic content and yield of P. graveolens for industrial and pharmaceutical use.

Yield, Essential Oil and Quality Performances of Artemisia dracunculus, Hyssopus officinalis and Lavandula angustifolia as Affected by Arbuscular Mycorrhizal Fungi under Organic Management

Utilization of arbuscular mycorrhizal fungi (AMF) for enhancing growth and development as well as production of essential oil in aromatic plants has been increasingly drawing research interest. In order to assess the AMF effects on different aromatic species, an open-field experiment was carried out using Artemisia dracunculus (tarragon), Lavandula angustifolia (lavender) and Hyssopus officinalis (hyssop). AMF stimulated the growth of tarragon and lavender plants, whereas hyssop showed a slight developmental slowing; nonetheless, a significant increase in essential oil content in the three species was seen. AMF application increased the biomass of A. dracunculus and H. officinalis by 20–35%. No differences in antioxidant activity and phenolics content were recorded at harvest between the control and AMF-inoculated plants, but the latter showed a significant increase in antioxidant status upon storage at high temperature and humidity compared to the untreated control. The enhancement of abiotic stress resistance during storage in plants inoculated with AMF was the highest in A. dracunculus, and the lowest in H. officinalis, while the untreated control plants showed a significant decrease in phenolics, ascorbic acid and chlorophyll content, as well as antioxidant activity, upon the abiotic stress. AMF inoculation differentially affected the mineral composition, increasing the accumulation of Se, I and Zn in A. dracunculus, and decreasing the levels of heavy metals and Co, Fe, Li, Mn in H. officinalis. Based on the outcome of the present research, AMF inoculation resulted in a significant enhancement of the overall performances of A. dracunculus, L. angustifolia and H. officinalis, and also in the improvement of plant antioxidant status upon storage in stress conditions.

Responses of Vitis vinifera cv. Cabernet Sauvignon roots to the arbuscular mycorrhizal fungus Funneliformis mosseae and the plant growth-promoting rhizobacterium Ensifer meliloti include changes in volatile organic compounds

Arbuscular mycorrhizal (AM) fungi and plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that may associate with grapevine roots, improving stress tolerance, growth, and nutrition. AM fungi and PGPR enhance the production of plant secondary metabolites, including volatile organic compounds (VOCs) that play a key role in the interaction of plants with the environment and are involved in defence mechanisms. The aim of this study was to analyse the effects of an AM fungus and a rhizobacterium on plant growth and VOCs in Vitis vinifera cv. Cabernet Sauvignon roots to gain insight into the potential role of plant-rhizosphere microorganisms in vine growth and defence. Grapevines were inoculated or not with the AM fungus Funneliformis mosseae IN101 and/or the plant growth-promoting rhizobacterium Ensifer meliloti TSA41. Both microbial strains enhanced plant growth. Fifty-eight VOCs extracted from ground roots were identified using headspace solid-phase microextraction coupled to gas chromatography/mass spectrometry. VOCs were induced by F. mosseae IN101, increasing up to 87% compared with control plants. Monoterpenes were strongly enhanced by F. mosseae IN101, increasing up to 113% compared with control plants. Interestingly, monoterpene alcohols related to plant defence, such as myrtenol, p-cymen-7-ol, and p-mentha-1.8-dien-7-ol were increased. By contrast, E. meliloti TSA41 did not significantly affect VOCs. The knowledge of the effects of AM fungi and PGPR on grapevine VOCs may contribute to an integrated and sustainable management of vineyards.

Arbuscular mycorrhizal fungi altered the hypericin, pseudohypericin, and hyperforin content in flowers of Hypericum perforatum grown under contrasting P availability in a highly organic substrate

St. John's Wort (Hypericum perforatum) is a perennial herb able to produce water-soluble active ingredients (a.i.), mostly in flowers, with a wide range of medicinal and biotechnological uses. However, information about the ability of arbuscular mycorrhizal fungi (AMF) to affect its biomass accumulation, flower production, and concentration of a.i. under contrasting nutrient availability is still scarce. In the present experiment, we evaluated the role of AMF on growth, flower production, and concentration of bioactive secondary metabolites (hypericin, pseudohypericin, and hyperforin) of H. perforatum under contrasting P availability. AMF stimulated the production of aboveground biomass under low P conditions and increased the production of root biomass. AMF almost halved the number of flowers per plant by means of a reduction of the number of flower-bearing stems per plant under high P availability and through a lower number of flowers per stem in the low-P treatment. Flower hyperforin concentration was 17.5% lower in mycorrhizal than in non-mycorrhizal plants. On the contrary, pseudohypericin and hypericin concentrations increased by 166.8 and 279.2%, respectively, with AMF under low P availability, whereas no effect of AMF was found under high P availability. These results have implications for modulating the secondary metabolite production of H. perforatum. However, further studies are needed to evaluate the competition for photosynthates between AMF and flowers at different nutrient availabilities for both plant and AM fungus.

Terpenoids in plant and arbuscular mycorrhiza-reinforced defence against herbivorous insects

BACKGROUND

Plants, though sessile, employ various strategies to defend themselves against herbivorous insects and convey signals of an impending herbivore attack to other plant(s). Strategies include the production of volatiles that include terpenoids and the formation of symbiotic associations with fungi, such as arbuscular mycorrhiza (AM). This constitutes a two-pronged above-ground/below-ground attack-defence strategy against insect herbivores.

SCOPE

Terpenoids represent an important constituent of herbivore-induced plant volatiles that deter herbivores and/or attract their predators. Terpenoids serve as airborne signals that can induce defence responses in systemic undamaged parts of the plant and also prime defence responses in neighbouring plants. Colonization of roots by AM fungi is known to influence secondary metabolism in plants; this includes alteration of the concentration and composition of terpenoids, which can boost both direct and indirect plant defence against herbivorous insects. Enhanced nutrient uptake facilitated by AM, changes in plant morphology and physiology and increased transcription levels of certain genes involved in the terpenoid biosynthesis pathway result in alterations in plant terpenoid profiles. The common mycorrhizal networks of external hyphae have added a dimension to the two-pronged plant defence strategy. These act as conduits to transfer defence signals and terpenoids.

CONCLUSION

Improved understanding of the roles of terpenoids in plant and AM defences against herbivory and of interplant signalling in natural communities has significant implications for sustainable management of pests in agricultural ecosystems.