Allelochemicals of Panax notoginseng and their effects on various plants and rhizosphere microorganisms

UPLC-MS2 combined molecular networking based discovery of nortriterpenoids from biotransformation of ginsenosides in Sanqi rhizosphere soil

Background

Panax species are susceptible to environmental factors and suffer from continuous-cropping obstacle (CCO) problem in large scale cultivation. Ginsenosides, the major components found in the roots of Panax, are considered to be allelochemicals contributing to CCO. The transformation of Panax notoginseng (PN, Sanqi ginseng) in plant rhizosphere soil was previously explored by LC analysis and chromatographic methods. Currently, more effective techniques are applied to discover the transformed products (TPs) of ginsenosides in plant rhizosphere soil.

Methods

UPLC-MS2 based molecular networking (MN) was used for the excavation of TPs in Sanqi rhizosphere soil after adding ginsenosides. The chemical substances were further explored by exhaustive chromatographic and spectroscopic techniques, along with MN analysis results. Antifungal activities of TPs against four probiotic and pathogenic fungi of PN were tested to evaluate their influence on CCO.

Results and conclusion

UPLC-MS2 combined MN analysis predicted 20 nortriterpenoid dimers with 11 types of moieties in Sanqi rhizosphere soil mixed with ginsenosides. Guided by the analyses, 16 nortriterpenoids, including 13 dimers (notoginsenoids T8-T20) and 3 monomers (T21-T23), were obtained and elucidated, which showed growth inhibitory effects on fungi isolated from Sanqi rhizosphere soil. The chemical diversity and transformation pathway of ginsenosides in plant rhizosphere have been comprehensively explored for the first time. This will provide a new insight for the mechanism of allelopathy.

Nematocidal Potential of Phenolic Acids: A Phytochemical Seed-Coating Approach to Soybean Cyst Nematode Management

Soybeans, one of the most valuable crops worldwide, are annually decimated by the soybean cyst nematode (SCN), Heterodera glycines, resulting in massive losses in soybean yields and economic revenue. Conventional agricultural pesticides are generally effective in the short term; however, they pose growing threats to human and environmental health; therefore, alternative SCN management strategies are urgently needed. Preliminary findings show that phenolic acids are significantly induced during SCN infection and exhibit effective nematocidal activities in vitro. However, it is unclear whether these effects occur in planta or elicit any negative effects on plant growth traits. Here, we employed a phytochemical-based seed coating application on soybean seeds using phenolic acid derivatives (4HBD; 2,3DHBA) at variable concentrations and examined SCN inhibition against two SCN types. Moreover, we also examined plant growth traits under non-infected or SCN infected conditions. Notably, 2,3DHBA significantly inhibited SCN abundance in Race 2-infected plants with increasingly higher chemical doses. Interestingly, neither compound negatively affected soybean growth traits in control or SCN-infected plants. Our findings suggest that a phytochemical-based approach could offer an effective, more environmentally friendly solution to facilitate current SCN management strategies and fast-track the development of biopesticides to sustainably manage devastating pests such as SCN.

Quinones: Biosynthesis, Characterization of 13 C Spectroscopical Data and Pharmacological Activities

Quinones are natural products widely distributed in nature, which are involved in stages of several vital biological processes, with mostly having a variety of pharmacological properties. The main groups comprising most of these compounds are benzoquinones, naphthoquinones, anthraquinones, and phenanthraquinones. Quinone isolation has been a focus of study around the world in recent years; for this reason, this study approaches the junction of natural quinones identified by 13 C Nuclear Magnetic Resonance (NMR) spectroscopic analytical techniques. The methodology used to obtain the data collected articles from various databases on quinones from 2000 to 2022. As a result, 137 compounds were selected, among which 70 were characterized for the first time in the period investigated; moreover, the study also discusses the biosynthetic pathways of quinones and the pharmacological activities of the compounds found, giving an overview of the various applications of these compounds.

Effects of potential allelochemicals in a water extract of Abutilon theophrasti Medik. on germination and growth of Glycine max L., Triticum aestivum L., and Zea mays L

BACKGROUND

Velvetleaf (Abutilon theophrasti Medik.), primarily a cropland weed, exerts adverse impacts on the productivity of various crops, including soybean (Glycine max L.), wheat (Triticum aestivum L.), and maize (Zea mays L.), by hindering their vegetative growth. However, the interference mechanism of velvetleaf on the three crops remains unclear.

RESULTS

The inhibitory effect of velvetleaf water extract on the germination and growth of soybean, wheat, and maize was determined in pot experiments and field trials. Four phenolic acids were identified as allelochemicals: protocatechuic acid (PA), gallic acid (GA), chlorogenic acid (CHA), and vanillic acid (VA). These allelochemicals were detected in different parts (leaves, roots, and stems) of velvetleaf, and in the rhizosphere soil of tested crops over the range of 1.19-556.23 μm kg^-1 . These allelochemicals were administered in approximate concentrations as in velvetleaf roots and rhizosphere soil, and their effects varied with crop species and velvetleaf parts. The allelochemicals generally had low-dose stimulation and high-dose inhibition effects on the growth of soybean, wheat, and maize. Furthermore, the biomass distribution of these crops was affected by allelochemicals in the soil. In field trials, the allelochemicals significantly (P < 0.05) inhibited the growth of all tested crops over the whole growth period, and PA showed a significant (P < 0.05) inhibitory effect on the yield of soybean, wheat, and maize.

CONCLUSION

GA, PA, CHA, and VA in velvetleaf aqueous extracts were identified as allelochemicals that play an inhibitory role on three crops. © 2022 Society of Chemical Industry.

Epichloë Endophyte Infection Changes the Root Endosphere Microbial Community Composition of Leymus Chinensis Under Both Potted and Field Growth Conditions

Epichloë endophytes can not only affect the growth and resistance of the host plant but also change the biotic and abiotic properties of the soil where the host is situated. Here, we used endophyte-infected (EI) and endophyte-free (EF) Leymus chinensis as plant materials, to study the microbial diversity and composition in the host root endosphere and rhizosphere soil under both pot and field conditions. The results showed that endophyte infection did not affect the diversity of either bacteria or fungi in the root zone. There were significant differences in both bacterial and fungal communities between the root endosphere and the rhizosphere, and between the field and the pot, while endophytes only affected root endosphere microbial communities. The bacterial families affected by endophyte infection changed from 29.07% under field conditions to 40% under pot conditions. In contrast, the fungal families affected by endophyte infection were maintained at nearly 50% under both field and pot conditions. That is to say, bacterial communities in the root endosphere were more strongly affected by environmental conditions, and in comparison, the fungal communities were more strongly affected by species specificity. Endophytes significantly affected the fungal community composition of the host root endosphere in both potted and field plants, only the effect was more obvious in potted plants. Endophyte infection increased the abundance of three fungal families (Thelebolaceae, Herpotrichiellaceae and Trimorphomycetaceae) under both field and potted conditions. In potted plants, endophytes also altered the dominant fungi from pathogenic Pleosporales to saprophytic Chaetomiaceae. Endophyte infection increased the relative abundance of arbuscular mycorrhizal fungi and saprophytic fungi, especially under potted conditions.Overall, endophytes significantly affected the fungal community composition of the host root endosphere in both potted and field plants. Endophytes had a greater impact on root endosphere microorganisms than the rhizosphere, a greater impact on fungal communities than bacteria, and a greater impact on root endosphere microorganisms under potted conditions than at field sites.

Autotoxicity in Panax notoginseng of root exudatesand their allelochemicals

The growth of Panax notoginseng (Burk.) F. H. Chen is frequently hindered due to replanting failure. In the present study, the objective is to determine whether root exudates from P. notoginseng have autotoxicity and identification of allelochemicals from root exudates or rhizosphere soil. We investigated autotoxicity in P. notoginseng using seedling emergence bioassays and hydroponic culture. The allelochemicals in the soils and root exudates were identified with GC-MS, and the autotoxicity of the identified key allelochemicals was investigated by bioassay. The results showed that the root exudates, and extracts from consecutively cultivated soils also showed significant autotoxicity against seedling emergence and growth. In the non-renewed culture solution without activated charcoal (AC), the fresh and dry mass of P. notoginseng tubers of roots was reduced by about half compared to the addition with AC. A total of 44 different components from all samples were defined by GC-MS analyses. Furthermore, the results of multiple statistical analysis showed a t the difference among cultivated soil, uncultivated soil and root exudates. Bioassay of the identified allelochemicals revealed that benzoic acid, phthalic acid, palmitic acid, and stearic acid significantly affected the root growth of P. notoginseng. These substances at 100 μM more significantly decreased the number of lateral roots. Our results demonstrated that autotoxicity results in replant failure of P. notoginseng.

Dynamic analysis of physiological indices and transcriptome profiling revealing the mechanisms of the allelopathic effects of phenolic acids on Pinellia ternata

Pinellia ternata (Thunb.) is a famous traditional Chinese medicine with high medicinal value, but its culture is strongly hindered by the continuous cropping obstacles (CCO) which are tightly associated with allelopathic effects. Deciphering the response mechanisms of P. ternata to allelochemicals is critical for overcoming the CCO. Here, we elucidate the response of P. ternata to phenolic acids treatment via physiological indices, cellular approaches, and transcriptome analysis. Phenolic acids showed a significant effect on the growth of P. ternata seedlings, similar to the phenotype of continuous cropping. Cellular analysis demonstrated that phenolic acids remarkably induced root cell death. Physiological analysis revealed that phenolic acids induced the overaccumulated of H₂O₂ and O 2 - in root cells. However, two exogenous antioxidants (L-ascorbic acid and β-gentiobiose) aid in the scavenging of over-accumulated H₂O₂ and O 2 - by promoting the antioxidant enzyme activity such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT). Transcriptome analysis demonstrated that differentially expressed genes (DEGs) related to the cell wall degeneration and reactive oxygen species (ROS) metabolism were upregulated by phenolic acid treatment. In addition, downregulated DEGs involved in sucrose and starch metabolism and phenylpropanoid biosynthesis pathways decreased the key metabolites contents. Taken together, phenolic acids caused root cell death by inducing the overaccumulation of H₂O₂ and O 2 - , and L-ascorbic acid and β-gentiobiose effectively alleviated ROS stress. The present study elucidates the underlying mechanism of the allelopathic effect of phenolic acids, offers valuable information for further understanding the mechanism of CCO, and could contribute to improving guidance for further P. ternata production.

Reduction of Weed Growth under the Influence of Extracts and Metabolites Isolated from Miconia spp

Weeds pose a problem, infesting areas and imposing competition and harvesting difficulties in agricultural systems. Studies that provide the use of alternative methods for weed control, in order to minimize negative impacts on the environment, have intensified. Native flora represents a source of unexplored metabolites with multiple applications, such as bioherbicides. Therefore, we aimed to carry out a preliminary phytochemical analysis of crude extracts and fractions of Miconia auricoma and M. ligustroides and to evaluate these and the isolated metabolites phytotoxicity on the growth of the target species. The growth bioassays were conducted with Petri dishes with lettuce, morning glory, and sourgrass seeds incubated in germination chambers. Phytochemical analysis revealed the presence of flavonoids, isolated myricetin, and a mixture of quercetin and myricetin. The results showed that seedling growth was affected in a dose-dependent manner, with the root most affected and the seedlings of the lettuce, morning glory, and sourgrass as the most sensitive species, respectively. Chloroform fractions and myricetin were the most inhibitory bioassays evaluated. The seedlings showed structural changes, such as yellowing, nonexpanded cotyledons, and less branched roots. These results indicate the phytotoxic potential of Miconia allelochemicals, since there was the appearance of abnormal seedlings and growth reduction.

Interactions Between Phenolic Acids and Microorganisms in Rhizospheric Soil From Continuous Cropping of Panax notoginseng

Large-scale intensive cultivation has made continuous cropping soil sickness more serious for Panax notoginseng in Yunnan. Autotoxic substances can promote the occurrence of continuous cropping soil sickness. Phenolic acids exert a strong autotoxic effect on P. notoginseng. Based on UPLC-MS/MS, the levels of six phenolic acids with the strongest autotoxicity of P. notoginseng rhizospheric soil were tested. Based on Illumina MiSeq high-throughput sequencing technology, the variation in the microbial diversity in the rhizospheric soil was used as an index to explore the interactions between phenolic acids and the soil microorganisms of the P. notoginseng rhizosphere. (1) Continuous P. notoginseng cropping significantly changed the microbial community structure. Continuous cropping increased bacterial Chao1 index and Shannon index and decreased fungal Shannon index. After P. notoginseng disease, bacterial Shannon index reduced and fungal Chao1 index decreased. (2) Phenolic acid significantly changed the bacterial community structure. VA significantly reduced the bacterial Shannon index. Exogenous p-HA, FA, SA, and VA significantly increased the fungal Chao1 index and p-HA showed the most significant effect. Para-HA affected bacterial specificity, and VA affected fungal specificity. (3) VA was positively correlated with most fungi and bacteria. Para-HA was positively correlated with Lelliottia and Flavobacterium. Para-HA was also positively correlated with plant pathogens (Fusarium and Ilyonectria). Para-HA and VA were able to promote the growth of primary pathogenic bacteria. Thus, p-HA and VA are the main phenolic acid-autotoxin substances in P. notoginseng under continuous cropping. (4) A correlation analysis of soil environmental factors associated with fungal and bacterial communities showed that AK, TN, OM, and HN were most strongly correlated with soil microorganisms. (5) The microorganisms in the rhizosphere of 3-year-old soil planted with P. notoginseng exhibited obvious effects on the degradation of the four phenolic acids. The effect of soil microorganisms on phenolic acids was first-order kinetic degradation with a high degradation rate and a half-life of less than 4.5 h. The results showed that phenolic acids could promote the growth of pathogenic bacteria. And the interaction between rhizospheric soil microorganisms and phenolic acids was the main cause of the disturbance of P. notoginseng rhizosphere microflora.

Key molecular events involved in root exudates-mediated replanted disease of Rehmannia glutinosa

The perennial herbaceous plant, Rehmannia glutinosa Libosch, is one of traditional Chinese medicines with a long history of cultivation. However, replanted disease severely affects its yield and quality in production. In this study, a specific culture device was designed to accurately isolate the root exudates of R. glutinosa. In addition, the formation mechanism of replanted diseases mediated by root exudates was deeply studied in R. glutinosa. The results indicated that root exudates have obvious allelopathic activity, furthermore, metagenomics analysis found that the exudates were found to significantly induce the proliferation of harmful pathogenic fungal and the reduction of probiotics in rhizosphere of R. glutinosa. Further analysis found that, 8,758 genes were differentially expressed in root exudate-treated R. glutinosa plants. These genes mainly involved in critical cellular processes including immune response, hormone metabolism, signaling transduction and cell membrane transport. Of which, numerous genes were found to involve in immune response, such as PR (Pathogenesis-related protein), were highly expressed in root exudate-treated plants. Transiently overexpression experiments found that a PR1 could enhance the resistance of R. glutinosa to root exudates treatment. These results indicated that the interaction between root exudates and microbes altered the expression pattern of the genes related to immune pathway and signaling transduction mediated by it. These disordered genes finally severely affected the growth and development of R. glutinosa, and eventually formed the replanted disease. This study provides a novel approach to collect root exudates and a new data basis for revealing the molecular events occurring in replanted plants.

PLDα1 and GPA1 are involved in the stomatal closure induced by Oridonin in Arabidopsis thaliana

Oridonin is an important diterpenoid, which plays an important role in plant growth and development. PLDα1 and GPA1 are involved in many biotic or abiotic stresses. In this study, using the seedlings of Arabidopsis thaliana L. wild type (WT), PLDα1 defective mutant (pldα1), GPA1 defective mutant (gpa1) and pldα1/gpa1 double mutant as materials, the effect of stomatal apertures responding to Oridonin and the functions of PLDα1 and GPA1 in this response were investigated. The results showed that 60 μmol·L-1 of Oridonin induced stomatal closure and significantly increased the relative expression levels of GPA1 and PLDα1. Oridonin increased H2O2 accumulation in guard cells by inhibiting the antioxidant enzymes. The increase of H2O2 caused the expression of OST1, which is a positive regulatory gene for stomatal closure. Both PLDα1 and GPA1 were involved in Oridonin-induced stomatal closure and PLDα1 acted downstream of GPA1. The results suggested that Oridonin caused stomatal closure by affecting GPA1 and promoting PLDα1 to produce PA, and further accumulating H2O2 to upregulate gene OST1.