Comparing the Mechanical Properties of Rice Cells and Protoplasts under PEG6000 Drought Stress Using Double Resonator Piezoelectric Cytometry.

Plant cells' ability to withstand abiotic stress is strongly linked to modifications in their mechanical characteristics. Nevertheless, the lack of a workable method for consistently tracking plant cells' mechanical properties severely restricts our comprehension of the mechanical alterations in plant cells under stress. In this study, we used the Double Resonator Piezoelectric Cytometry (DRPC) method to dynamically and non-invasively track changes in the surface stress (ΔS) generated and viscoelasticity (storage modulus G' and loss modulus G″) of protoplasts and suspension cells of rice under a drought stress of 5-25% PEG6000. The findings demonstrate that rice suspension cells and protoplasts react mechanically differently to 5-15% PEG6000 stress, implying distinct resistance mechanisms. However, neither of them can withstand 25% PEG6000 stress; they respond mechanically similarly to 25% PEG6000 stress. The results of DRPC are further corroborated by the morphological alterations of rice cells and protoplasts observed under an optical microscope. To sum up, the DRPC technique functions as a precise cellular mechanical sensor and offers novel research tools for the evaluation of plant cell adversity and differentiating between the mechanical reactions of cells and protoplasts under abiotic stress.

[High-level expression of anti FLAG tag antibody in plants].

Plant bioreactor is a new production platform for expression of recombinant protein, which is one of the cores of molecular farming. In this study, the anti DYKDDDDK (FLAG) antibody was recombinantly expressed in tobacco (Nicotiana benthamiana) and purified. FLAG antibody with high affinity was obtained after immunizing mice for several times and its sequence was determined. Based on this, virus vectors expressing heavy chain (HC) and light chain (LC) inoculated into Nicotiana benthamiana leaves by using Agrobacterium-mediated delivery. Accumulation of the HC and LC was analyzed by SDS/PAGE followed by Western blotting probed with specific antibodies from 2 to 9 days postinfiltration (dpi). Accumulation of the FLAG antibody displayed at 3 dpi, and reached a maximum at 5 dpi. It was estimated that 66 mg of antibody per kilogram of fresh leaves could be obtained. After separation and purification, the antibody was concentrated to 1 mg/mL. The 1:10 000 diluted antibody can probe with 1 ng/mL FLAG fused antigen well, indicating the high affinity of the FLAG antibody produced in plants. In conclusion, the plant bioreactor is able to produce high affinity FLAG antibodies, with the characteristics of simplicity, low cost and highly added value, which contains enormous potential for the rapid and abundant biosynthesis of antibodies.

Microbial community composition and cooccurrence patterns driven by co-contamination of arsenic and antimony in antimony-mining area.

In the current study, a typical Sb mine was selected to explore the microbial community composition and assembly driven by the cocontamination of As/Sb with geographic distance. Our results showed that environmental parameters, especially pH, TOC, nitrate, total and bioavailable As/Sb contents largely affected the microbial community diversity and composition. The total and bioavailable As/Sb levels were significantly positively correlated with the relative abundance of Zavarzinella, Thermosporothrix and Holophaga, while the pH presented a significant negative correlation with the three genera, potentially implying they are important taxonomic groups in acid-mining soils. The cooccurrence network analysis indicated the environmental stress dominated by pH and As/Sb co-contamination affected the microbial modularity and interaction. Meanwhile, Homogeneous selection (HoS, 26.4-49.3%), and drift and others (DR, 27.1∼40.2%) were the most important assembly processes for soil bacterial, and the importance of HoS decreased and the DR increased with geographic distance to the contamination source respectively. Soil pH, nutrient availability, total and bioavailable As/Sb contents significantly affected the HoS and DR processes. This study provides theoretical support for microbial remediation in metal(loid)-contaminated soils.

Safety evaluation of FAD2 RNAi transgenic Brassica napus L. based on microbial diversity and metabonomic analysis.

Oleic acid desaturase (FAD2) is the key enzyme that produces polyunsaturated fatty acids in rapeseed (Brassica napus L), which is one of the main oil crops. RNA interference (RNAi) is an emerging technique that provides new opportunities for the generation of new traits in plants. To increase oleic acid content and reduce linoleic and linolenic acid content in rapeseed, we constructed an ihpRNA plant expression vector of the FAD2 gene and obtained transgenic plants for multiple generations by stable inheritance. In this study, third-generation transgenic plants (T3), seventh-generation transgenic plants (T7), and wild-type plants (WT) were used. The differences in microbial community diversity between transgenic plants and wild-type plants and the up- and downregulation of rhizosphere metabolite contents were investigated. In conclusion, the results showed that the soil microbial community structure was stable, the general microbial community structure was not changed by the transgenic rhizosphere exudates, and no significant harmful root exudate of transgenic rapeseed on the environment was found through the microbial community and metabolomics analysis. This work may provide an understanding of the impact of RNAi on plant metabolites and a safety evaluation method for transgenic plants and a reference for rapeseed breeding.

Arsenic biotransformation genes and As transportation in soil-rice system affected by iron-oxidizing strain (Ochrobactrum sp.).

Arsenic (As) biotransformation in soil affects As biogeochemical cycling and is associated with As accumulation in rice. After inoculation with 1% iron-oxidizing bacteria (FeOB) in paddy soil, As speciation, As biotransformation genes in soil, As/Fe in Fe plaques, and As accumulation in rice were characterized. Compared with the control, the available As concentrations in soils decreased while amorphous and poorly crystalline Fe-Al oxidized As and crystalline Fe-Al oxidized As fractions increased of F (FeOB) and RF (rice and FeOB) treatments. Fe concentrations increased and positively correlated with As concentrations in Fe plaques on the rice root surface (***P < 0.001). Compared with R (rice), Monomethyl As (MMA), dimethyl As (DMA), arsenate (As(V)), and arsenite (As(III)) concentrations in rice plants showed a downwards trend of RF treatment. The As concentration in grains was below the National Standard for Food Safety (GB 2762-2017). A total of 16 As biotransformation genes in rhizosphere soils of different treatments (CK, F, R and RF were quantified by high-throughput qPCR (HT-qPCR). Compared with the control, the As(V) reduction and As transport genes abundance in other treatments increased respectively by 54.54%-69.17% and 54.63%-73.71%; the As(III) oxidation and As (de) methylation genes did not change significantly; however, several As(III) oxidation genes (aoxA, aoxB, aoxS, and arsH) increased. These results revealed that FeOB could reduce, transport As, and maybe also oxidize As. In addition, As(III) oxidation gene (aoxC) in rhizosphere soil was more abundant than in non-rhizosphere soil. It indicated that radial oxygen loss (ROL) promoted As(III) oxidation in rhizosphere soils. The results provide evidence for As biotransformation by ROL and FeOB in soil-rice system. ROL affects As oxidation and immobilization, and FeOB affects As reduction, transportation and may also affect As oxidation.

Arsenic Transformation in Soil-Rice System Affected by Iron-Oxidizing Strain (Ochrobactrum sp.) and Related Soil Metabolomics Analysis.

Iron-oxidizing bacteria (FeOB) could oxidize Fe(II) and mediate biomineralization, which provides the possibility for its potential application in arsenic (As) remediation. In the present study, a strain named Ochrobactrum EEELCW01 isolated previously, was inoculated into paddy soils to investigate the effect of FeOB inoculation on the As migration and transformation in paddy soils. The results showed that inoculation of Ochrobactrum sp. increased the proportion of As in iron-aluminum oxide binding fraction, which reduced the As bioavailability in paddy soils and effectively reduced the As accumulation in rice tissues. Moreover, the inoculation of iron oxidizing bacteria increased the abundance of KD4-96, Pedosphaeraceae and other bacteria in the soils, which could reduce the As toxicity in the soil through biotransformation. The abundance of metabolites such as carnosine, MG (0:0/14:0/0:0) and pantetheine 4'-phosphate increased in rhizosphere soils inoculated with FeOB, which indicated that the defense ability of soil-microorganism-plant system against peroxidation caused by As was enhanced. This study proved that FeOB have the potential application in remediation of As pollution in paddy soil, FeOB promotes the formation of iron oxide in paddy soil, and then adsorbed and coprecipitated with arsenic. On the other hand, the inoculation of Ochrobactrum sp. change soil microbial community structure and soil metabolism, increase the abundance of FeOB in soil, promote the biotransformation process of As in soil, and enhance the resistance of soil to peroxide pollution (As pollution).

Remediation of arsenic-contaminated paddy field by a new iron oxidizing strain (Ochrobactrum sp.) and iron-modified biochar.

Iron-oxidizing strain (FeOB) and iron modified biochars have been shown arsenic (As) remediation ability in the environment. However, due to the complicated soil environment, few field experiment has been conducted. The study was conducted to investigate the potential of iron modified biochar (BC-FeOS) and biomineralization by a new found FeOB to remediate As-contaminated paddy field. Compared with the control, the As contents of GB (BC-FeOS), GF (FeOB), GFN (FeOB and nitrogen fertilizer), GBF (BC-FeOS and FeOB) and GBFN (BC-FeOS, FeOB and nitrogen fertilizer) treatments in pore water decreased by 36.53%-80.03% and the microbial richness of iron-oxidizing bacteria in these treatments increased in soils at the rice maturation stage. The concentrations of available As of GB, GF, GFN, GBF and GBFN at the tillering stage were significantly decreased by 10.78%-55.48%. The concentrations of nonspecifically absorbed and specifically absorbed As fractions of GB, GF, GFN, GBF and GBFN in soils were decreased and the amorphous and poorly crystalline hydrated Fe and Al oxide-bound fraction was increased. Moreover, the As contents of GB, GF, GFN, GBF and GBFN in rice grains were significantly decreased (*P < 0.05) and the total As contents of GFN, GBF and GBFN were lower than the standard limit of the National Standard for Food Safety (GB 2762-2017). Compared with the other treatments, GBFN showed the greatest potential for the effective remediation of As-contaminated paddy fields.

Pithecellobium clypearia: Amelioration Effect on Imiquimod-Induced Psoriasis in Mice Based on a Tissue Metabonomic Analysis.

Pithecellobium clypearia Benth. (accepted name: Archidendron clypearia (Jack) I.C.Nielsen; Mimosaceae), a popular traditional Chinese medicine, has a significant anti-inflammatory effect. The crude water extract of the aerial part of P. clypearia has been clinically applied to treat upper respiratory tract infections, acute gastroenteritis, laryngitis, and pharyngitis. However, the therapeutic mechanism of ethanol fraction of water extract (ESW) of P. clypearia to treat psoriasis should be complemented. The aim of our research was to clarify the protective effects of ESW from P. clypearia against psoriasis-like skin inflammation induced by imiquimod (IMQ) in mice with efficacy indexes and target tissue (spleen and serum) metabolomics. The ingredient of ESW was analyzed by ultrahigh-performance liquid chromatography combined with tandem mass spectrometry (UHPLC-MS/MS) method. The imiquimod-induced psoriatic mouse model was employed to investigate the effect of ESW against psoriasis, where the treatment method was implemented for 6 days both topically (Gel at 5%) and orally (at 2.4 g/kg p.o.). Traditional pharmacodynamic indicators (phenotypic characteristics, psoriasis area and severity index (PASI) score, H&E staining, immunohistochemical staining, the thickness of epidermis, body weight change, and spleen index) were conducted to appraise the efficacy of ESW. Furthermore, a gas chromatography-mass spectrometer (GC-MS) coupled with multivariate analysis was integrated and applied to obtain serum and spleen metabolic profiles for clarifying metabolic regulatory mechanisms of ESW. The current study illustrated that ESW is composed mainly of gallic acid, ethyl gallate, quercitin, 7-O-galloyltricetiflavan, quercetin, and myricetin by UHPLC-MS/MS analysis. ESW could distinctly improve IMQ-induced psoriasis in mouse through reducing PASI score, alleviating tissue damage, restoring spleen index, and inhibiting proliferating cell nuclear antigen (PCNA) expression in psoriasis-like skin tissue. From the metabolomics study, 23 markers with significant changes are involved in eight main pathways in spleen and serum samples, including linoleic acid metabolism and glycine, serine, and threonine metabolism. The current study showed that ESW had obvious antipsoriasis effects on IMQ-induced psoriasis in mice, which might be attributed to regulating the dysfunction of differential biomarkers and related pathways. In summary, ESW of P. clypearia showed a favourable therapeutic effect on IMQ-induced psoriasis, and metabolomics provided insights into the mechanisms of ESW to the treatment of psoriasis.

An antifouling polymer for dynamic anti-protein adhesion analysis by a quartz crystal microbalance.

Nowadays, the non-specific adsorption of biomolecules is a key issue in numerous fields. Herein, an improved antifouling molecule was synthesized by grafting phenol with oligopoly (ethylene glycol), named (4-(2-(2-ethoxyethoxy) ethoxy) phenol (EEP). An ideal antifouling polymer coating (PEEP) was synthesized by the mechanism of electropolymerization of phenol. Quartz crystal microbalance (QCM), a sensitive mass sensor, was used to dynamically monitor both the modification and anti-protein adhesion (with bovine serum albumin as the model) process. Quantitatively, less proteins were observed to adhere to the modified electrode (277.8 ng for bare GCE and 8.88 ng for the modified GCE). Fourier transform infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), and electrochemical methods were used to study the coatings in detail. In this study, EEP was synthesized for the electrochemical preparation of an antifouling coating and characterized by QCM and electrochemical methods. The mild preparation environment (lower potential window and in phosphate buffered saline) and one-step method enable potential applications of PEEP in the field of biomaterials and biosensors.

Characteristics of Metabolites by Seed-Specific Inhibition of FAD2 in Brassica napus L.

Fatty acid desaturase-2 (FAD2) is a key enzyme in the production of polyunsaturated fatty acids in plants. RNAi technology can reduce the expression of FAD2 genes in Brassica napus seeds and acquire transgenic B. napus plants with a high oleic acid content, but the effect of seed-specific inhibition of FAD2 expression on B. napus seed metabolites is not clear. Here we use widely targeted metabolomics to investigate the metabolites of normal-oleic-acid rapeseed (OA) and high-oleic-acid rapeseed (HOA) seeds, resulting in a total of 726 metabolites being detected. Among them, 24 differential metabolites were significantly downregulated and 88 differential metabolites were significantly upregulated in HOA rapeseed. In further lipid profile experiments, more lipids in B. napus seeds were accurately quantified. The contents of glycolipids and phospholipids that contain C18:1 increased significantly and C18:2 decreased because FAD2 expression was inhibited. The changes in the expression of key genes in related pathways were also consistent with the changes in metabolites. The insertion site of the ihpRNA plant expression vector was reconfirmed through genomewide resequencing, and the transgenic event did not change the sequence of FAD2 genes. There was no significant difference in the germination rate and germination potential between OA and HOA rapeseed seeds because the seed-specific ihpRNA plant expression vector did not affect other stages of plant growth. This work provides a theoretical and practical guidance for subsequent molecular breeding of high OA B. napus.

Serum Metabolomic Profiling Reveals the Amelioration Effect of Methotrexate on Imiquimod-Induced Psoriasis in Mouse.

BACKGROUND: The imiquimod (IMQ)-induced psoriasis mouse model has been used as a model for pathogenic mechanism research, and methotrexate (MTX) is widely employed to treat various clinical manifestations of psoriasis. We explored the underlying pathogenesis of psoriasis and the treatment mechanism of the conventional drugs from the metabolic perspective of the psoriasis mouse model. METHODS: Male BALB/c mice were smeared IMQ for 7 days to induce treatment-resistant psoriasis and intragastrically administered 1 mg/kg MTX. We evaluated inflammation of psoriasis-like lesions and therapeutic effects of MTX based on histological changes and immunohistochemistry. Based on gas chromatography-mass spectrometer detection of serum samples, a comprehensive metabolomics analysis was carried out to identify alterations of metabolites. RESULTS: It was found that MTX ameliorated psoriatic lesions (representative erythema, scaling, and thickening) by inhibiting proliferation and differentiation of keratinocytes. Using multivariate statistical analysis to process metabolomics data, the results displayed alterations in serum metabolites among mice of the control group, IMQ group, and MTX group. Compared with group, psoriasis mice had the higher level of d-galactose and lower expression of myo-inositol, 9,12-octadecadienoic acid, and cholesterol. In contrast with the model set, serum levels of glycine, pyrrolidone carboxylic acid, d-galactose, and d-mannose were significantly decreased in the MTX group. CONCLUSION: The differential metabolites, reflecting the perturbation in the pathways of inositol phosphate metabolism; galactose metabolism; glyoxylate and dicarboxylate metabolism; glycine, serine, and threonine metabolism; and glutathione metabolism, may lead to the pathogenesis of psoriasis, and they are also related to the pharmacological treatment effect of MTX on psoriasis. This study established the foundation for further research on the mechanism and therapeutic targets of psoriasis.

A synthetic biology approach for consistent production of plant-made recombinant polyclonal antibodies against snake venom toxins.

Antivenoms developed from the plasma of hyperimmunized animals are the only effective treatment available against snakebite envenomation but shortage of supply contributes to the high morbidity and mortality toll of this tropical disease. We describe a synthetic biology approach to affordable and cost-effective antivenom production based on plant-made recombinant polyclonal antibodies (termed pluribodies). The strategy takes advantage of virus superinfection exclusion to induce the formation of somatic expression mosaics in agroinfiltrated plants, which enables the expression of complex antibody repertoires in a highly reproducible manner. Pluribodies developed using toxin-binding genetic information captured from peripheral blood lymphocytes of hyperimmunized camels recapitulated the overall binding activity of the immune response. Furthermore, an improved plant-made antivenom (plantivenom) was formulated using an in vitro selected pluribody against Bothrops asper snake venom toxins and has been shown to neutralize a wide range of toxin activities and provide protection against lethal venom doses in mice.

Do aeration conditions affect arsenic and phosphate accumulation and phosphate transporter expression in rice (Oryza sativa L.)?

Widespread contamination of rice with arsenic (As) has revealed a major exposure pathway to humans. The present study aimed to investigate the effects of oxygen in the rhizosphere on phosphate (P) transporter (for arsenate transportation) expressions, on As and P accumulation and As speciation in four rice genotypes. Oxygenation marginally increased root and shoot length. Total As concentrations in rice roots were dramatically reduced following aeration compared to stagnant treatments (p < 0.001). Aeration treatments significantly increased arsenate while reducing arsenite concentrations in roots (p < 0.001). Root arsenite concentrations were 1.5-2.5 times greater in stagnant than in aeration treatments. Total P concentrations in rice roots were dramatically increased following aeration compared to stagnant treatments. The relative abundance of phosphate transporter (inorganic phosphate transporter and phosphate/H+ symporter family protein) expressions showed downregulation in aeration treatments, particularly for SY-9586, XWX-17, and XWX-12 in inorganic phosphate transporter expressions and XWX-17 in phosphate/H+ symporter family protein expression (p < 0.05). The relative abundance of phosphate carrier protein expressions were relatively higher than the other phosphate transporters, showing upregulation in aeration treatments.

Effect of wetland plants and bacterial inoculation on dissipation of phenanthrene.

This study attempts to evaluate the capacity of wetland plants' ability to dissipate phenanthrene (PHE) under waterlogged conditions. The results indicate that Typha latifolia and Vetiveria zizanioides may efficiently degrade PHE, and were much more effective when under combined plant cultivation with the inoculation of Pseudomonas frederiksbergensis (ATCC BAA-257) . Concentrations of PHE declined from 200 to less than 52 mg kg-1 in all treatments with plant cultivation. At the end of the experimental period, PHE was undetectable in combined plant cultivation in the presence of bacteria inoculation. Microbial biomass C(carbon), N(nitrogen), and P(phosphate) were significantly different (p < 0.05) in the presence and absence of bacteria inoculation with bacteria inoculation significantly (p < 0.05) increased microbial biomass P. The presence of bacteria inoculation and different plant species significantly (p < 0.05) decreased the PHE concentrations in the microcosms. The inoculation of bacteria and release of exudates from plant roots further enhanced the dissipation of PHE in sand. Concentrations of citric and malic acids were decreased up to 69% in bacteria-inoculated treatments, showing large citric and malic acids serving as a food source and growth substrate for bacteria.

Cadmium, lead, and arsenic contamination in paddy soils of a mining area and their exposure effects on human HEPG2 and keratinocyte cell-lines.

A mining district in south China shows significant metal(loid) contamination in paddy fields. In the soils, average Pb, Cd and As concentrations were 460.1, 11.7 and 35.1mgkg-1 respectively, which were higher than the environmental quality standard for agricultural soils in China (GB15618-1995) and UK Clea Soil Guideline Value. The average contents of Pb, Cd and As in rice were 5.24, 1.1 and 0.7mgkg-1 respectively, which were about 25, 4.5 or 2.5 times greater than the limit values of the maximum safe contaminant concentration standard in food of China (GB 2762-2012), and about 25, 10 or 1 times greater than the limit values of FAO/WHO standard. The elevated contents of Pb, Cd and As detected in soils around the factories, indicated that their spatial distribution was influenced by anthropogenic activity, while greater concentrations of Cd in rice appeared in the northwest region of the factories, indicating that the spatial distribution of heavy metals was also affected by natural factors. As human exposure around mining districts is mainly through oral intake of food and dermal contact, the effects of these metals on the viability and MT protein of HepG2 and KERTr cells were investigated. The cell viability decreased with increasing metal concentrations. Co-exposure to heavy metals (Pb+Cd) increased the metals (Pb or Cd)-mediated MT protein induction in both human HepG2 and KERTr cells. Increased levels of MT protein will lead to greater risk of carcinogenic manifestations, and it is likely that chronic exposure to metals may increase the risk to human health. Nevertheless, when co-exposure to two or more metals occur (such as As+Pb), they may have an antagonistic effect thus reducing the toxic effects of each other. CAPSULE: Metal contaminations in paddy soils and rice were influenced by anthropogenic activity; metal co-exposure induced MT protein in human cells.

Oxic and anoxic conditions affect arsenic (As) accumulation and arsenite transporter expression in rice.

Arsenic (As) exposure from rice consumption has now become a global health issue. This study aimed to investigate the effects of rice rhizosphere oxic conditions on silicate transporter (responsible for arsenite transportation) expressions, and on As accumulation and speciation in four rice genotypes, including two hybrid genotypes (Xiangfengyou9, Shenyou9586) and two indica subspecies (Xiangwanxian17, Xiangwanxian12). Oxic and anoxic treatments have different effects on root length (p < 0.001) and weight (p < 0.05). Total As concentrations in roots were dramatically lower in oxic treatments (88.8-218 mg/kg), compared to anoxic treatments (147-243 mg/kg) (p < 0.001). Moreover, root and shoot arsenite concentrations in oxic treatments were lower than that in anoxic treatments in arsenite treatments. The relative abundance of silicate transporter expressions displayed a trend of down-regulation in oxic treatments compared to anoxic treatments, especially significantly different for Xiangwanxian17, Xiangwanxian12 in Lsi1 expressions (p < 0.05), Xiangfengyou9, Shenyou9586, Xiangwanxian17 in Lsi2 expressions (p < 0.05). However, there were no significant differences of transporter expressions in different As treatments and genotypes. It may be a possible reason for low As accumulation in rice growing aerobically compared to flooded condition and a potential route to reduce the health risk of As in rice.

Effect of silicate on arsenic fractionation in soils and its accumulation in rice plants.

Four rice genotypes, two hybrid and two indica, were selected to investigate the effects of silicate (Si) application on arsenic (As) accumulation and speciation in rice and As fractionation in soil. There were significant differences in root, straw and grain biomass among genotypes (p < 0.05), and Si application significantly increased root (p < 0.05) and grain biomass (p < 0.001). Silicate addition reduced the proportion of As associated with well-crystallized hydrous oxides of Fe and Al and residual phases, whilst increasing the proportions of specifically-sorbed As and As associated with amorphous and poorly-crystalline Fe and Al hydrous oxides. Furthermore, the results indicated that the fraction proportions of non-specifically sorbed, specifically-sorbed, and associated with amorphous and poorly-crystalline hydrous oxides of Fe and Al in rhizosphere soils, were greater than non-rhizosphere soils. Silicate application had a significant effect decreasing total As concentrations in root (p < 0.005), straw (p < 0.05) and husk (p < 0.001) of rice plants. The effect of Si on reducing As accumulation in rice leaves was revealed by SXRF. Indica genotypes transported and accumulated less As than hybrid genotypes. Both percentage and concentration of iAs were lower in indica genotype XFY-9 than in hybrid genotype XWX-12. Silicate reduced iAs and DMA by 21% and 58% in grain (polished) respectively. DMA may have a greater translocation capacity from straw to grain (polished) than inorganic As. The study provides the potential for understanding As uptake mechanisms in rice and mitigating the health risks posed by As contamination in paddy fields.

The effect of silicon on iron plaque formation and arsenic accumulation in rice genotypes with different radial oxygen loss (ROL).

Rice is one of the major pathways of arsenic (As) exposure in human food chain, threatening over half of the global population. Greenhouse pot experiments were conducted to examine the effects of Si application on iron (Fe) plaque formation, As uptake and rice grain As speciation in indica and hybrid rice genotypes with different radial oxygen loss (ROL) ability. The results demonstrated that Si significantly increased root and grain biomass. Indica genotypes with higher ROL induced greater Fe plaque formation, compared to hybrid genotypes and sequestered more As in Fe plaque. Silicon applications significantly increased Fe concentrations in iron plaque of different genotypes, but it decreased As concentrations in the roots, straws and husks by 28-35%, 15-35% and 32-57% respectively. In addition, it significantly reduced DMA accumulation in rice grains but not inorganic As accumulation. Rice of indica genotypes with higher ROL accumulated lower concentrations of inorganic As in grains than hybrid genotypes with lower ROL.

Effects of manganese on the microstructures of Chenopodium ambrosioides L., A manganese tolerant plant.

Chenopodium ambrosioides L. can tolerate high concentrations of manganese and has potential for its use in the revegetation of manganese mine tailings. Following a hydroponic investigation, transmission electron microscopy (TEM)-energy disperse spectroscopy (EDS) was used to study microstructure changes and the possible accumulation of Mn in leaf cells of C. ambrosioides in different Mn treatments (200, 1000, 10000 µmol·L(-1)). At 200 µmol·L(-1), the ultrastructure of C. ambrosioides was clearly visible without any obvious damage. At 1000 µmol·L(-1), the root, stem and leaf cells remained intact, and the organelles were clearly visible without any obvious damage. However, when the Mn concentration exceeded 1000 µmol·L(-1) the number of mitochondria in root cells decreased and the chloroplasts in stem cells showed a decrease in grana lamellae and osmiophilic granules. Compared to controls, treatment with 1000 µmol·L(-1) or 10000 µmol·L(-1) Mn over 30 days, gave rise to black agglomerations in the cells. At 10000 µmol·L(-1), Mn was observed to form acicular structures in leaf cells and intercellular spaces, which may be a form of tolerance and accumulation of Mn in C. ambrosioides. This study has furthered the understanding of Mn tolerance mechanisms in plants, and is potential for the revegetation of Mn-polluted soils.

Effects of silicon (Si) on arsenic (As) accumulation and speciation in rice (Oryza sativa L.) genotypes with different radial oxygen loss (ROL).

Arsenic (As) contamination of paddy soils has adversely affected the health of millions of people those consuming rice for staple food. The present study was aimed at investigating the effects of silicon (Si) fertilization on As uptake, speciation in rice plants with different radial oxygen loss (ROL). Six genotypes were planted in pot soils under greenhouse conditions until late tillering state. The results showed that the rates of ROL were higher in hybrid rice genotypes varying from 19.76 to 27 µmol O2 g(-1) root dry weight h(-1) than that in conventional indica rice genotypes varying from 9.55 to 15.41 µmol O2 g(-1) root dry weight h(-1). Si addition significantly increased straw biomass (p<0.005), but with no significant effects on root biomass. Si fertilization significantly reduced shoot and root total As concentrations (p<0.001) in six genotypes grown in 40 mg As/kg soil. Si addition decreased the inorganic As in shoots of 'Xiangfengyou-9' with lower ROL and 'Xiangwanxian-12' with higher ROL by 31% and 25% respectively and had the tendency to increase DMA concentrations. It is potential to reduce As contamination of rice efficiently by combining Si fertilization and selecting genotypes with high radial oxygen loss.