Arsenic accumulation and resistance mechanism in Panax notoginseng, a traditional rare medicinal herb

Physiological and metabolomic analyses reveal that Fe3O4 nanoparticles ameliorate cadmium and arsenic toxicity in Panax notoginseng

Heavy metal(loid)-contaminated available arable land seriously affects crop development and growth. Engineered nanomaterials have great potential in mitigating toxic metal(loid) stress in plants. However, there are few details of nanoparticles (NPs) involved in Panax notoginseng response to cadmium (Cd) and arsenic (As). Herein, integrating physiological and metabolomic analyses, we investigated the effects of Fe3O4 NPs on plant growth and Cd/As responses in P. notoginseng. Cd/As treatment caused severe growth inhibition. However, foliar application of Fe3O4 NPs increased beneficial elements in the roots and/or leaves, decreased Cd/As content by 10.38% and 20.41% in the roots, reduced membrane damage and regulated antioxidant enzyme activity, thereby alleviating Cd/As-induced growth inhibition, as indicated by increased shoot fresh weight (FW), the rootlet length and root FW by 40.14%, 15.74%, and 46.70% under Cd stress and promoted the shoot FW by 27.00% under As toxicity. Metabolomic analysis showed that 227 and 295 differentially accumulated metabolites (DAMs) were identified, and their accumulation patterns were classified into 8 and 6 clusters in the roots and leaves, respectively. Fe3O4 NPs altered metabolites significantly involved in key pathways, including amino sugar and nucleotide sugar metabolism, flavonoid biosynthesis and phenylalanine metabolism, thus mediating the trade-off between plant growth and defense under stress. Interestingly, Fe3O4 NPs recovered more Cd/As-induced DAMs to normal levels, further supporting that Fe3O4 NPs positively affected seedling growth under metal(loid)s stress. In addition, Fe3O4 NPs altered terpenoids when the seedlings were subjected to Cd/As stress, thus affecting their potential medicinal value. This study provides insights into using nanoparticles to improve potential active ingredients of medicinal plants in metal(loid)-contaminated areas.

Toxicological effects, residue levels and risks of endocrine-disrupting chemicals in Chinese medicine: a review

Traditional Chinese medicine (TCM) that is used worldwide possesses the satisfactory function of disease prevention, treatment and health care, and this natural medicine seems to be favored due to its low side effects. Endocrine disrupting chemicals (EDCs), which exist in all aspects of our lives, may interfere with the synthesis, action and metabolism of human sex steroid hormones, resulting in the development and fertility problems as well as obesity and the disturbance of energy homeostasis. From planting to processing, TCM may be polluted by various EDCs. Many studies pay attention to this problem, but there are still few reviews on the residues and toxicity risks of EDCs in TCM. In this paper, researches related to EDCs in TCM were screened. The possible contamination sources of TCM from planting to processing and its toxic effects were introduced. Moreover, the residues of metals, pesticides and other EDCs in TCM as well as the health risks of human exposure to EDCs through ingestion of TCM materials were reviewed.

Melatonin alleviates arsenite toxicity by decreasing the arsenic accumulation in cell protoplasts and increasing the antioxidant capacity in rice

Arsenic (As) is a common environmental pollutant that seriously interferes with the normal growth of organisms. There is an urgent need to take environment-safe and efficient strategies to mitigate As toxicity. Melatonin (MT) is a pleiotropic molecule that regulates plant growth and organ development and alleviates heavy metal stresses. The experiment aims to explore the mechanism of MT in reducing arsenite toxicity by hydroponic rice seedlings. The results showed that MT application reduced the As content in rice roots and shoots by 26.4% and 37.5%, respectively, and mainly decreased As content in the soluble fractions of the rice root cell. MT application also increased the As content of chelated-soluble pectin and alkali-soluble pectin in the cell wall by 14.7% and 74.4%, respectively. It promoted the generation of the functional group of the root cell walls by the FTIR analysis, indicating that MT may promote the fixation of As on the cell wall. Meanwhile, MT contributed to scavenging excess H₂O₂, reducing MDA content, and maintaining normal morphology of root cells by stimulating SOD, POD and CAT activities and increasing the level of GSH. The research deepens our understanding of how MT participates in maintaining redox homeostasis in rice cells, reducing As toxicity, and decreasing As concentration in rice seedlings, thereby providing more possibilities for reducing As accumulation in rice.

Potential use of arbuscular mycorrhizal fungi for simultaneous mitigation of arsenic and cadmium accumulation in rice

Rice polluted by metal(loid)s, especially arsenic (As) and cadmium (Cd), imposes serious health risks. Numerous studies have demonstrated that the obligate plant symbionts arbuscular mycorrhizal fungi (AMF) can reduce As and Cd concentrations in rice. The behaviours of metal(loid)s in the soil-rice-AMF system are of significant interest for scientists in the fields of plant biology, microbiology, agriculture, and environmental science. We review the mechanisms of As and Cd accumulation in rice with and without the involvement of AMF. In the context of the soil-rice-AMF system, we assess and discuss the role of AMF in affecting soil ion mobility, chemical forms, transport pathways (including the symplast and apoplast), and genotype variation. A potential strategy for AMF application in rice fields is considered, followed by future research directions to improve theoretical understanding and encourage field application.

Alteration in soil arsenic dynamics and toxicity to sunflower (Helianthus annuus L.) in response to phosphorus in different textured soils

Being analogue to arsenic (As), phosphorus (P) may affect As dynamics in soil and toxicity to plants depending upon many soil and plant factors. Two sets of experiments were conducted to determine the effect of P on As fractionation in soils, its accumulation by plants and subsequent impact on growth, yield and physiological characteristics of sunflower (Helianthus annuus L.). Experimental plan comprised of two As levels (60 and 120 mg As kg^-1 soil), four P (0-5-10-20 g phosphate rock kg^-1 soil) and three textural types (sandy, loamy and clayey) with three replications. Among different As fractions determined, labile, calcium-bound, organic matter-bound and residual As increased while iron-bound and aluminum-bound As decreased with increasing P in all the three textural types. Labile-As percentage increased in the presence of P by 16.9-48.0% at As60 while 36.0-68.1% at As120 in sandy, 19.1-64.0% at As60 while 11.5-52.3% at As120 in loamy, and 21.8-58.2% at As60 while 22.3-70.0% at As120 in clayey soil compared to respective As treatment without P. Arsenic accumulation in plant tissues at both contamination levels declined with P addition as evidenced by lower bioconcentration factor. Phosphorus mitigated the As-induced oxidative stress expressed in term of reduced hydrogen peroxide, malondialdehyde while increased glutathione, and consequently improved the achene yield. Although, P increased As solubility in soil but restricted its translocation to plant, leading to reversal of oxidative damage, and improved sunflower growth and yield in all the three soil textural types, more profound effect at highest P level and in sandy texture.

Impact of rhizosphere microorganisms on arsenic (As) transformation and accumulation in a traditional Chinese medical plant

Panax notoginseng is an important traditional medicinal plant, but the commercial value is threatened by root-rot disease caused by rhizosphere microbes and a potential health risk caused by plant arsenic (As) accumulation. Whether rhizospheric microbes isolated from P. notoginseng rhizosphere soil could impact As uptake and transport into P. notoginseng is not yet known. Among the three root-rot disease-causing pathogens Fusarium flocciferum (PG 1), Fusarium oxysporum (PG 2), and Fusarium solani (PG 3) and one root-rot disease biocontrol fungus Trichoderma koningiopsis (FC 1) and five biocontrol-exerting bacterial species Bacillus siamensis (BC 1), Delftia acidovorans (BC 2), Brevibacillus formosus (BC 3), Mortierella alpine (BC 4), and Bacillus subtilis (BC 5), one As-resistant pathogen and four biocontrol microorganisms with As-resistant ability were identified. The As-transforming ability of the identified fungi and bacteria was ranked in the order of FC 1 > PG 1 and BC 2 > BC 3 > BC 1, respectively. Then, the As-resistant biocontrol and pathogenic microbes were initiated to colonize the rhizosphere of 1-year-old P. notoginseng seedlings growing in artificially As(V)-contaminated soil to evaluate the impact of microbe inoculation on P. notoginseng As uptake and transport capacity. Concentration of As in P. notoginseng tissues decreased in the order of the sequence stem > root > leaf. Compared to treatment without colonization by microorganism, inoculation with microorganisms increased As root uptake efficiency and root As concentration, especially under treatment of inoculation by BC 2 and PG 1 + BC 2. As transport efficiency from root to stem decreased by inoculation with microorganism, especially under treatment with inoculation of BC 2 and PG 1 + BC 2. However, the impact of microorganism colonization on As stem to leaf transport efficiency was not obvious. In summary, inoculation with rhizosphere microbes may increase As accumulation in P. notoginseng root, especially when using bacteria with high As transformation ability. Therefore, it is necessary to evaluate the As transformation capacity before applying biological control microorganism to the rhizosphere of P. notoginseng.

Root cell wall chemistry remodelling enhanced arsenic fixation of a cabbage cultivar

The low- and high-arsenic (As) transferring cultivars (LTC and HTC) of cabbage showed significant differences in As uptake and distribution. We hypothesise that chemistry of root cell wall matrix plays a critical role. LTC and HTC were treated with As and grown for 60 days. As concentration and distribution at subcellular and cell wall component (pectin, hemicellulose and lignin) levels were determined. Remodelling enzymes (PME and PAL) and functional groups of cell wall were analysed. Results showed that shoot biomass of LTC was not affected by As. Less As was accumulated in shoot of LTC than HTC. LTC allocated more As in root and majority of As was deposited in cell wall. LTC had more hemicellulose 1 (HC1) and lignin, PME and PAL activities. The uronic acid contents of pectin, HC1 or HC2 were all positively (P < 0.05) correlated with As concentrations in each component, respectively. Chemistry of LTC root cell wall was remodelled in terms of changes in porosity, HC and lignin contents, and functional groups, which potentially exerted coupling effects on As entering and deposition. The LTC can restrain As in roots through changing characteristics of root cell wall matrix.

Arsenate-reducing bacteria affect As accumulation and tolerance in Salix atrocinerea

Arsenic (As)-reducing bacteria are able to influence As-speciation and, in this way, change As bio-availability. In consequence, this has an impact on As uptake by plants growing on polluted soil and on the effectiveness of the phytoremediation process. To be able to efficiently utilize these bacteria for As-phytoremediation in the field, a better understanding of the plant-bacterial interactions involved in As-tolerance or toxicity is needed. In this work, seedlings of a clone of Salix atrocinerea derived from a specimen naturally growing on an As-polluted brownfield were grown under gnotobiotic conditions exposed to As, and in the presence or absence of two of its field-associated and in vitro characterized plant growth-promoting (PGP) bacteria. The inoculation with Pantoea sp., induced a moderate reduction of AsV to AsIII in the exposure medium that, together with a coordinated plant response of As uptake, chelation and sequestration, increased As accumulation in roots; which is reflected into a higher phytostabilization. However, inoculation with Rhodococcus erythropolis due to a higher disproportionate reduction of AsV to AsIII in the medium caused less As accumulation in roots that non-bioaugmented plants and despite the lower As content, the concentrations of AsIII present in the medium and the damage suffered in roots and leaves, indicated that As tolerance mechanisms (such as prevention of AsIII uptake and efflux) did not occur in time to avoid physical disturbance and plants growth reduction. Interestingly, by two different metabolic pathways -coordinated by different key transporters mediating As uptake, tolerance, distribution and vacuolar accumulation at the roots- both bacteria limited As accumulation in Salix shoots. Our results provide for the first time a detailed insight in the plant-bacterial responses and physiological changes contributing to As tolerance in S. atrocinerea, that will facilitate the design of effective strategies for exploitation of plant-associated microorganisms for phytoremediation.

Phosphate transporters, PnPht1;1 and PnPht1;2 from Panax notoginseng enhance phosphate and arsenate acquisition

BACKGROUND

Panax notoginseng is a medicinally important Chinese herb with a long history of cultivation and clinical application. The planting area is mainly distributed in Wenshan Prefecture, where the quality and safety of P. notoginseng have been threatened by high concentration of arsenic (As) from the soil. The roles of phosphate (Pi) transporters involved in Pi acquisition and arsenate (AsV) tolerance were still unclear in this species.

RESULTS

In this study, two open reading frames (ORFs) of PnPht1;1 and PnPht1;2 separated from P. notoginseng were cloned based on RNA-seq, which encoded 527 and 541 amino acids, respectively. The results of relative expression levels showed that both genes responded to the Pi deficiency or As exposure, and were highly upregulated. Heterologous expression in Saccharomyces cerevisiae MB192 revealed that PnPht1;1 and PnPht1;2 performed optimally in complementing the yeast Pi-transport defect, particularly in PnPht1;2. Cells expressing PnPht1;2 had a stronger AsV tolerance than PnPht1;1-expressing cells, and accumulated less As in cells under a high-Pi concentration. Combining with the result of plasma membrane localization, these data confirmed that transporters PnPht1;1 and PnPht1;2 were putative high-affinity H+/H2PO4- symporters, mediating the uptake of Pi and AsV.

CONCLUSION

PnPht1;1 and PnPht1;2 encoded functional plasma membrane-localized transporter proteins that mediated a putative high-affinity Pi/H+ symport activity. Expression of PnPht1;1 or PnPht1;2 in mutant strains could enhance the uptake of Pi and AsV, that is probably responsible for the As accumulation in the roots of P. notoginseng.

Integrative response of arsenic uptake, speciation and detoxification by Salix atrocinerea

Despite arsenic (As) being very toxic with deleterious effects on metabolism, it can be tolerated and accumulated by some plants. General genetic mechanisms responsible for As tolerance in plants, including Salix species, have been described in transcriptomic analysis, but further experimental verification of the significance of particular transcripts is needed. In this study, a Salix atrocinerea clone, able to thrive in an As-contaminated brownfield, was grown hydroponically in controlled conditions under an As concentration similar to the bioavailable fraction of the contaminated area (18 mg kg^-1) for 30 days. At different time points, i.e. short-term and long-term exposure, biometric data, As accumulation, phytochelatin synthesis, non-protein thiol production and expression of target genes related to these processes were studied. Results showed that S. atrocinerea presents a great tolerance to As and accumulates up to 2400 mg As kg^-1 dry weight in roots and 25 mg As kg^-1 dry weight in leaves. Roots reduce As V to As III rapidly, with As III being the predominant form of As accumulated in root tissues, whereas in the leaves it is As V. After 1 d of As exposure, roots and leaves show de novo synthesis and an increase in non-protein thiols as compared to the control. Integrating these data on As accumulation in the plant and its speciation, non-protein thiol production and the kinetic gene expression of related target genes, a fundamental role is highlighted for these processes in As accumulation and tolerance in S. atrocinerea. As such, this study offers new insights in the plant tolerance mechanisms to As, which provides important knowledge for future application of high-biomass willow plants in phytoremediation of As-polluted soils.

Differential responses of growth, photosynthesis, oxidative stress, metals accumulation and NRAMP genes in contrasting Ricinus communis genotypes under arsenic stress

Effect of arsenate [As(V)] on biomass, photosynthetic rate, stomatal conductance, transpiration, oxidative stress, accumulation of As, Fe, Zn, Cu and Mn and expression of NRAMP genes was investigated in As(V) tolerant and sensitive genotypes of bioenergy crop Ricinus communis. As(V) treatments (100 and 200 μM) led to significant reduction in root and leaf biomass, photosynthetic rate, stomatal conductance and transpiration in GCH 2 and GCH 4 genotypes but no significant change or increase was observed in WM and DCH 177 genotypes. No significant difference was observed in hydrogen peroxide content and lipid peroxidation in As(V)-treated tolerant genotypes compared to control, whereas these parameters enhanced significantly in As(V)-treated sensitive genotypes. GCH 2 accumulated around two times As in leaves and showed significant reduction in concentration of Zn and Mn in the leaves and roots due to 200 μM As(V) treatment compared to WM. NRAMP genes are critical for uptake and distribution of essential divalent metal cations, photosynthesis and controlled production of reactive oxygen species in plants. RcNRAMP2, RcNRAMP3 and RcNRAMP5 genes showed differential expression in response to 200 μM As(V) in GCH 2 and WM suggesting that NRAMP genes are associated with differential responses of WM and GCH 2 genotypes to As(V) stress.

Heavy metal pollution and potential health risks of commercially available Chinese herbal medicines

A survey was conducted to investigate the pollution and health risks of copper (Cu), cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg) and zinc (Zn) in 60 Chinese herbal medicines (CHMs) collected from a market in Kunming City, Yunnan Province, China. Furthermore, eight CHMs (Cyathulae radix, Drynariae rhizoma, Peucedani radix, Homalomenae rhizoma, Dryopteris setosa, Polygonati rhizoma, Lilii bulbus, and Linderae radix) containing high Cd concentrations were selected to further analyse their Cd chemical forms. Additionally, the dissolution rates of six heavy metals in decoction liquid were also analysed for four CHMs (Typhonii rhizoma, Linderae radix, Homalomenae rhizoma, and Cyathulae radix), and the health risks of heavy metals in CHMs were evaluated. The results showed that the Cd, Hg and Cu concentrations in the 60 CHMs exceeded the limiting values of the "Green Trade Standards of Importing & Exporting Medicinal Plants & Preparations" (WM2-2001), with exceedance ratios of 38.8%, 8.3% and 1.7%, respectively. The majority of Cd was integrated with pectates and protein in CHMs, and the other five Cd chemical forms followed the order of water-soluble > insoluble heavy metal phosphates > oxalate > residual > inorganic form, indicating that Cd had relatively low bioactivity and toxicity. The average dissolution rates of Zn, Cu, Cd, Hg, As and Pb in the four CHMs were 47.4%, 33.8%, 20.5%, 6.1%, 5.4% and 4.8%, respectively. The calculation results of hazard quotients (HQs) for Cd and Hg showed that the CHMs did not pose a threat to human health.

Impacts of silicon addition on arsenic fractionation in soils and arsenic speciation in Panax notoginseng planted in soils contaminated with high levels of arsenic

Arsenic (As) is a well-known carcinogenic substance whose biological toxicity in soils and plants depends on its concentration and chemical forms. Silicon (Si) generally can alleviate biotic and abiotic stresses, including As stress. However, its effects vary depending on As chemical form, plant species and other factors. A pot experiment was performed to investigate the effects of Si addition on the content and forms of As in red soil and its uptake, transport and speciation in Panax notoginseng. The results showed that additions of 25 and 75 mg kg^-1 of Si both significantly decreased the concentrations of water-soluble As and exchangeable As in soil and therefore decreased the bioavailability of soil As. However, the As uptake by Panax notoginseng (PN) was increased, which resulted in increases in As concentration by 18.5% and 2.3% in roots and by 56.7% and 58.3% in shoots, respectively, when compared with the control. Arsenate (As(V)) was the dominant As species in all the treatment soils (99.8-100%), whereas arsenite (As(III)) was prevalent in plant roots (75.2-92.4%), shoots (74.1-87.9%) and leaves (73.9-84.3%). Si addition (25 and 75 mg kg^-1) significantly increased As(III) concentration in roots by 167.5% and 83.3%, respectively. Monomethylarsonic acid (MMA) was the only detected methylated As but at low concentrations (0.01-0.29 mg kg^-1) and only in PN leaves. Si addition (25 and 75 mg kg^-1) significantly increased the copy number of the arsenite methyltransferase (arsM) gene by 31.0% and 47.2% but did not increase the methylated As species content in PN leaves. The detected copy number of the arsM gene did not represent the capacity of soil to methylate As, and the sources of MMA in leaves need to be explored in further research.

Reducing Arsenic Concentration in Panax notoginseng via Contaminant Immobilization in Soil Using Fe-Ce Oxide

(Burk.) F.H. Chen, a valuable Chinese medicine, is currently confronted with arsenic (As) contamination in China due to soil pollution. Our previous research demonstrated that Fe(0) and zeolite had a certain inhibitory effect on As accumulation in . In order to further reduce As accumulation in the plant, a synthetic iron material (Fe-Ce oxide [FC]) with high As adsorption capacity was tested for As remediation. In the study, after FC was applied to the As-contaminated soil, was planted in the soil. The As leaching behavior of the treated soil and As accumulation in were evaluated. The results showed that FC immobilized As more effectively than Fe(0) and zeolite in soils with high As concentrations. When the FC dosage was 0.5 % (w/w), As concentration of root (the main medicinal part) decreased by 56%, and root biomass increased by 55%. Results indicated FC could reduce the non-specifically adsorbed As fraction (F1) and specifically adsorbed As fraction (F2) by 22 to 31% and 5 to 17%, respectively, thus reducing the toxicity characteristic leaching procedure leachable As concentration by 41 to 67%. The finding of an iron plaque coating on the plant root and its function as a barrier to As uptake by is reported here for the first time. The occurrence of iron plaque led to a reduction in As concentration in the phellem and xylem-phloem by 66 to 80% and 43 to 70%, respectively. Our findings will help in developing As contamination control in areas where is planted and set a foundation for a FC-based As immobilization technology.

Biodegradation of pentachloronitrobenzene by Cupriavidus sp. YNS-85 and its potential for remediation of contaminated soils

Pentachloronitrobenzene (PCNB) is a toxic chlorinated nitroaromatic compound. However, only a few bacteria have been reported to be able to utilize PCNB. In the present study, one pentachloronitrobenzene (PCNB)-degrading bacterium, Cupriavidus sp. YNS-85, was isolated from a contaminated Panax notoginseng plantation. The strain co-metabolized 200 mg L^-1 PCNB in aqueous solution with a removal rate of 73.8% after 5 days. The bacterium also degraded PCNB effectively under acid conditions (pH 4-6) and showed resistance to toxic trace elements (arsenic, copper, and cadmium). Its ability to utilize proposed PCNB intermediates as sole carbon sources was also confirmed. The soil microcosm experiment further demonstrated that bacterial bioaugmentation enhanced the removal of PCNB (37.8%) from soil and the accumulation of pentachloroaniline (89.3%) after 30 days. Soil enzyme activity and microbial community functional diversity were positively influenced after bioremediation. These findings indicate that Cupriavidus sp. YNS-85 may be a suitable inoculant for in situ bioremediation of PCNB-polluted sites, especially those with acid soils co-contaminated with heavy metal(loid)s.

Arsenic accumulation and speciation in rice grown in arsanilic acid-elevated paddy soil

P-arsanilic acid (AsA) is a emerging but less concerned contaminant used in animal feeding operations, for it can be degraded to more toxic metabolites after being excreted by animals. Rice is the staple food in many parts of the world, and also more efficient in accumulating arsenic (As) compared to other cereals. However, the uptake and transformation of AsA by rice is unclear. This study aimed to evaluate the potential risk of using AsA as a feed additive and using the AsA contaminated animal manure as a fertilizer. Five rice cultivars were grown in soil containing 100mg AsA/kg soil, after harvest, As species and their concentrations in different tissues were determined. Total As concentration of the hybrid rice cultivar was more than conventional rice cultivars for whole rice plant. For rice organs, the highest As concentration was found in roots. AsA could be absorbed by rice, partly degraded and converted to arsenite, monomethylarsonic acid, dimethylarsinic acid, arsenate. The number of As species and their concentrations in each cultivar were related to their genotypes. The soil containing 100mg AsA/kg or more is unsuitable for growing rice. The use of AsA and the disposal of animal manure requires detailed attention.

Illumina-based transcriptomic profiling of Panax notoginseng in response to arsenic stress

BACKGROUND

Panax notoginseng, a famous herbal medicine, has recently attracted great attention on its safety and quality since P. notoginseng can accumulate and tolerate As from growing environment. For the purpose of understanding As damage to the quality of P. notoginseng as well as corresponding tolerance mechanisms, genes involved in As stress response were identified using Illumina sequencing.

RESULTS

Totally 91,979,946 clean reads were generated and were de novo assembled into 172,355 unigenes. A total of 81,575 unigenes were annotated in at least one database for their functions, accounting for 47.34 %. By comparative analysis, 1725 differentially expressed genes (DEGs, 763 up-regulated/962 down-regulated) were identified between As stressed plant (HAs) and control plant (CK), among which 20 DEGs were further validated by real-time quantitative PCR (qRT-PCR). In the upstream and downstream steps of biosynthesis pathways of ginsenosides and flavonoids, 7 genes encoding key enzymes were down-regulated in HAs. Such down-regulations were also revealed in pathway enrichment analysis. Genes encoding transporters (transporters of ABC, MATE, sugar, oligopeptide, nitrate), genes related to hormone metabolism (ethylene, ABA, cytokinin) and genes related to arsenic accumulation (HXT, NRAMP, MT and GRX) were differentially expressed. The up-regulated genes included those of oxidative stress-related protein (GSTs, thioredoxin), transcription factors (HSFs, MYBs) and molecular chaperones (HSP).

CONCLUSIONS

The down-regulation of biosynthesis of ginsenoside and flavonoid indicated that As accumulation in P. notoginseng can cause not only safety hazard, but also qualitative losses. Aside from the results of arsenic content of seedling roots, the ability of P. notoginseng to over-accumulate arsenic can also be explained by the differential expression of genes of HXT, NRAMP, MT and GRX. To illustrate the detoxification mechanism of P. notoginseng, differential expression of genes encoding oxidative-related proteins, transcription factors, molecular chaperones, transporters and hormone were revealed in our study, which agreed with those reported in Arabidopsis to a certain extent, indicating P. notoginseng and Arabidopsis shared some common detoxification mechanisms in response to As stress. The longer As treatment in our study may account for the smaller quantity of related DEGs and smaller degree of expression differences of certain DEGs compared with those of Arabidopsis.

Soil-Plant Metal Relations in Panax notoginseng: An Ecosystem Health Risk Assessment

This study features a survey of the content of heavy metals (Pb, Cd, Cr, As, Hg and Cu) in root and cultivation soils of Panax notoginseng (P. notoginseng), carried out in China’s Yunnan Province. The average contents of Pb, Cd, Cr, As, Hg, and Cu in the soil were 61.6, 0.4, 102.4, 57.1, 0.3, and 35.1 mg·kg⁻¹, respectively. The heavy metals’ pollution indexes can be ranked as follows: As > Cd > Hg > Cu > Cr > Pb. The proportion of soil samples at slight, middle, strong, very strong, and extremely strong levels of potential environmental risk had values of 5.41%, 21.62%, 35.14%, 10.81%, and 27.03%, respectively. The potential environment risk index (RI) showed that 29.73% out of the total sample sites were above the level of strong and extremely strong. The ranges of Pb, Cd, Cr, As, Hg, and Cu content in tuber were 0.04–3.26, 0.04–0.33, 0.22–5.4, 0.10–1.8, 0.00–0.02, and 5.0–20.9 mg·kg⁻¹, respectively. In combination with P. notoginseng consumption data, the estimated heavy metal daily intakes (EDIs) were 0.08–0.23, 0.006–0.019, 0.17–0.52, 0.04–0.12, 0.001–0.002, and 0.59–1.77 μg·kg⁻¹·bw/day. All target hazard quotients (THQs) of individual elements and hazard indexes (HI) were less than one. The present study indicates that most of the P. notoginseng cultivation soil in the province of Yunnan presented slight and moderate ecological risk. Thus, more attention should be given to the heavy metals As, Cd, and Hg when selecting planting areas for the cultivation of P. notoginseng. Health risks associated with the intake of a single element or consumption of the combined metals through P. notoginseng are absent.

Jasmonic acid and methyl dihydrojasmonate enhance saponin biosynthesis as well as expression of functional genes in adventitious roots of Panax notoginseng F.H. Chen

Panax notoginseng, an important herbal medicine, has wide uses for its bioactive compounds and health function. In this work, we compared the content of saponin in cultivation and adventitious root. The total content of saponins in adventitious root (8.48 mg⋅g^-1 ) was found lower than in the native one (3-year-old) (34.34 mg⋅g^-1 ). To enhance the content of bioactive compounds, we applied elicitors jasmonic acid (JA) and methyl dihydrojasmonate (MDJ) to the adventitious root culture. It was observed that the highest total content of saponins (71.94 mg⋅g^-1 ) was achieved after treatment with 5 mg⋅L^-1 JA, which was 2.09-fold higher than native roots and 8.45-fold higher than the control group. The findings from high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry analysis showed that six new compounds were present after the treatment with the elicitors. Furthermore, we found that JA and MDJ significantly upregulated the expression of the geranyl diphosphate synthase, farnesyl diphosphate synthase, squalene synthase, squalene epoxidase, dammarenediol synthase, and CYP716A47 and CYP716A53v2 (CYP450 enzyme) genes; downregulated the expression of the cycloartenol synthase gene; and increased superoxide dismutase and peroxidase activities.

Reduction, methylation, and translocation of arsenic in Panax notoginseng grown under field conditions in arsenic-contaminated soils

Variations in arsenic (As) species in Panax notoginseng grown under field conditions remain understudied compared with those under greenhouse conditions. In the present study, soil and plant samples were collected from Wenshan Zhuang and Miao Autonomous Prefecture, Yunnan Province, which is the main production area of P. notoginseng in China, to identify As species in the soil and plant tissues and further assess effect of As toxic stress on As transformation and translocation in P. notoginseng. The results showed that arsenate (As(V)) was almost exclusively identified in the soil, while arsenite (As(III)) and monomethylarsonic acid (MMA) were detected in high proportions in plant tissues, suggesting that As(V) could be reduced and subsequently methylated in the plant body, mainly in the root. The reduction and methylation of As in the root of P. notoginseng were promoted by low As toxic stress, but were impeded by high As toxic stress. Arsenic(III) and MMA could rapidly translocate upwards in P. notoginseng. In addition, the translocation of total As, As(III), and MMA from the root to the rhizome was a response to As toxic stress, and the translocation rate increased with the increasing As concentration in the taproot. This study provides new insights into the detoxification mechanism of P. notoginseng grown in As-contaminated soils and the control of As during cultivation.

Nitrate reductase-mediated NO production enhances Cd accumulation in Panax notoginseng roots by affecting root cell wall properties

Panax notoginseng (Burk) F. H. Chen is a traditional medicinal herb in China. However, the high capacity of its roots to accumulate cadmium (Cd) poses a potential risk to human health. Although there is some evidence for the involvement of nitric oxide (NO) in mediating Cd toxicity, the origin of Cd-induced NO and its function in plant responses to Cd remain unknown. In this study, we examined NO synthesis and its role in Cd accumulation in P. notoginseng roots. Cd-induced NO production was significantly decreased by application of the nitrate reductase inhibitor tungstate but not the nitric oxide synthase inhibitor L-NAME (N(G)-methyl-l-arginine acetate), indicating that nitrate reductase is the major contributor to Cd-induced NO production in P. notoginseng roots. Under conditions of Cd stress, sodium nitroprusside (SNP, an NO donor) increased Cd accumulation in root cell walls but decreased Cd translocation to the shoot. In contrast, the NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and tungstate both significantly decreased NO-increased Cd retention in root cell walls. The amounts of hemicellulose 1 and pectin, together with pectin methylesterase activity, were increased with the addition of SNP but were decreased by cPTIO and tungstate. Furthermore, increases or decreases in hemicellulose 1 and pectin contents as well as pectin methylesterase activity fit well with the increased or decreased retention of Cd in the cell walls of P. notoginseng roots. The results suggest that nitrate reductase-mediated NO production enhances Cd retention in P. notoginseng roots by modulating the properties of the cell wall.

Cadmium transfer and detoxification mechanisms in a soil-mulberry-silkworm system: phytoremediation potential

Phytoremediation has been proven to be an environmentally sound alternative for the recovery of contaminated soils, and the economic profit that comes along with the process might stimulate its field use. This study investigated cadmium (Cd) transfer and detoxification mechanisms in a soil-mulberry-silkworm system to estimate the suitability of the mulberry and silkworm as an alternative method for the remediation of Cd-polluted soil; it also explored the underlying mechanisms regulating the trophic transfer of Cd. The results show that both the mulberry and silkworm have high Cd tolerance. The transfer factor suggests that the mulberry has high potential for Cd extraction from polluted soil. The subcellular distribution and chemical forms of Cd in mulberry leaves show that cell wall deposition and vacuolar compartmentalization play important role in Cd tolerance. In the presence of increasing Cd concentrations in silkworm food, detoxification mechanisms (excretion and homeostasis) were activated so that excess Cd was excreted in fecal balls, and metallothionein levels in the mid-gut, the posterior of the silk gland, and the fat body of silkworms were enhanced. And, the Cd concentrations in silk are at a low level, ranging from 0.02 to 0.21 mg kg(-1). Therefore, these mechanisms of detoxification can regulate Cd trophic transfer, and mulberry planting and silkworm breeding has high phytoremediation potential for Cd-contaminated soil.

Lead in the soil-mulberry (Morus alba L.)-silkworm (Bombyx mori) food chain: translocation and detoxification

The translocation of lead (Pb) in the soil-mulberry-silkworm food chain and the process of Pb detoxification in the mulberry-silkworm chain were investigated. The amount of Pb in mulberry, silkworm, feces and silk increased in a dose-responsive manner to the Pb contents in the soils. Mulberry roots sequestered most of the Pb, ranging from 230.78 to 1209.25 mg kg(-1). Over 92% of the Pb in the mulberry leaves was deposited in the cell wall, and 95.29-95.57% of the Pb in the mulberry leaves was integrated with oxalic acid, pectates and protein, and it had low bioavailability. The Pb concentrations in the silkworm feces were 4.50-4.64 times higher than those in the leaves. The synthesis of metallothioneins in three tissues of the silkworms was induced to achieve Pb homeostasis under Pb stress. These results indicated the mechanism involved in Pb transfer along the food chain was controlled by the detoxification of Pb in different trophic levels. Planting mulberry and rearing silkworm could be a promising approach for the remediation of Pb-polluted soils due to the Pb tolerance of mulberry and silkworm.

Effects of different cleaning treatments on heavy metal removal of Panax notoginseng (Burk) F. H. Chen

The quality and safety of Panax notoginseng products has become a focus of concern in recent years. Contamination with heavy metals is one of the important factors as to P. notoginseng safety. Cleaning treatments can remove dust, soil, impurities or even heavy metals and pesticide residues on agricultural products. But effects of cleaning treatments on the heavy metal content of P. notoginseng roots have still not been studied. In order to elucidate this issue, the effects of five different cleaning treatments (CK, no treatment; T1, warm water (50°C) washing; T2, tap water (10°C) washing; T3, drying followed by polishing; and T4, drying followed by tap water (10°C) washing) on P. notoginseng roots' heavy metal (Cu, Pb, Cd, As and Hg) contents were studied. The results showed that heavy metal (all five) content in the three parts all followed the order of hair root > rhizome > root tuber under the same treatment. Heavy metal removals were in the order of Hg > As > Pb > Cu > Cd. Removal efficiencies of the four treatments were in the order of T2 > T1 > T3 > T4. Treatments (T1-T4) could decrease the contents of heavy metal in P. notoginseng root significantly. Compared with the requirements of WM/T2-2004, P. notoginseng roots' heavy metal contents of Cu, Pb, As and Hg were safe under treatments T1 and T2. In conclusion, the cleaning process after production was necessary and could reduce the content of heavy metals significantly. Fresh P. notoginseng root washed with warm water (T2) was the most efficient treatment to remove heavy metal and should be applied in production.

Effects of nanoscale silica sol foliar application on arsenic uptake, distribution and oxidative damage defense in rice (Oryza sativa L.) under arsenic stress

Nanoscale silica sol foliar application reduced arsenic toxicity and accumulation in rice by enhancing its antioxidant defense capacity.

Arsenic stabilization by zero-valent iron, bauxite residue, and zeolite at a contaminated site planting Panax notoginseng

Panax notoginseng (Burk.) F.H. Chen, a rare traditional Chinese medicinal herb, is a widely used phytomedicine used all over the world. In recent years, the arsenic contamination of the herb and its relative products becomes a serious problem due to elevated soil As concentration. This study aimed to evaluate the effects of different types and dosages of amendments on As stabilization in soil and its uptake by P. notoginseng. Results showed that comparing to control treatment, the As concentrations of P. notoginseng declined by 49-63%, 43-61% and 52-66% in 0.25% zero-valent iron (Fe(0)), 0.5% bauxite residue, and 1% zeolite treatment, respectively; whereas the biomasses were elevated by 62-116%, 45-152% and 114-265%, respectively. The As(III) proportions of P. notoginseng increased by 8%, 9%, and 8%, and the transfer factors of As from root to shoot increased by 37%, 42% and 84% in the optimal treatments of Fe(0), bauxite residue, and zeolite. For soil As, all the three amendments could transform the non-specifically adsorbed As fraction to hydrous oxides Fe/Al fractions (by Fe(0) and red mud) or specifically adsorbed As fraction (by zeolite), therefore reduced the bioavailability of soil As. With a comprehensive consideration of stabilization efficiency, plant growth, environmental influence, and cost, Fe(0) appeared to be the best amendment, and zeolite could also be a good choice. In conclusion, this study was of significance in developing As contamination control in P. notoginseng planting areas, and even other areas for medicinal herb growing.