Hydrogen Nanobubbles Generated In Situ from Nanoscale Zerovalent Iron with Water to Further Enhance Selenite Sequestration.

Gas nanobubbles used for water treatment and recovery give rise to great concern for their unique advantages of less byproducts, higher efficiency, and environmental friendliness. Nanoscale zerovalent iron (nZVI), which has also been widely explored in the field of environmental remediation, can generate gas hydrogen by direct reaction with water. Whether nanoscale hydrogen bubbles can be produced to enhance the pollution removal of the nZVI system is one significant concern involved. Herein, we report direct observations of in situ generation of hydrogen nanobubbles (HNBs) from nZVI in water. More importantly, the formed HNBs can enhance indeed the reduction of Se(IV) beyond the chemical reduction ascribed to Fe(0), especially in the anaerobic environment. The possible mechanism is that HNBs enhance the reducibility of the system and promote electron transport in the solution. This study demonstrates a unique function of HNBs combined with nZVI for the pollutant removal and a new approach for in situ HNB generation for potential applications in the fields of in situ remediation agriculture, biotechnology, medical treatment, health, etc.

Reactive oxygen species signaling is involved in melatonin-induced reduction of chlorothalonil residue in tomato leaves.

Pesticide overuse has led to serious global concerns regarding food safety and environmental pollution. Although the reduction of pesticide residue is critical, our knowledge about induced pesticide metabolism in plants remains fragmentary. Melatonin (N-acetyl-5-methoxytryptamine) is an effective stress-relieving agent in both animals and plants, but little is known about the melatonin signaling mechanism and its effect on pesticide metabolism in plants. Here, we found that exogenous melatonin treatment significantly reduced chlorothalonil residue by 41 % but suppression of endogenous melatonin accumulation increased chlorothalonil residue in tomato leaves. Moreover, melatonin increased photosynthesis, Fv/Fm, Calvin cycle enzyme activity, antioxidant enzyme activity, glutathione pool, and RESPIRATORY BURST HOMOLOG1 (RBOH1) expression in tomato leaves. However, the upregulation of RBOH1, CYP724B2, GST1, GST2, GSH and ABC, the increased glutathione concentrations and the activity of detoxification enzymes due to melatonin treatment were all significantly attenuated by the treatment with an NADPH oxidase inhibitor and a ROS scavenger, indicating a clear relationship between the reduction of pesticide residue and induction in detoxifying enzymes and genes upon melatonin treatment in an apoplastic H2O2-dependent manner. These results reveal that melatonin-induced reduction in chlorothalonil residue is mediated by H2O2 signaling in tomato leaves.

Overexpression of tomato RING E3 ubiquitin ligase gene SlRING1 confers cadmium tolerance by attenuating cadmium accumulation and oxidative stress.

Heavy metal pollution not only decreases crop yield and quality, but also affects human health via the food chain. Ubiquitination-dependent protein degradation is involved in plant growth, development, and environmental interaction, but the functions of ubiquitin-ligase (E3) genes are largely unknown in tomato (Solanum lycopersicum L.). Here, we functionally characterized a RING E3 ligase gene, SlRING1, which positively regulates cadmium (Cd) tolerance in tomato plants. An in vitro ubiquitination experiment shows that SlRING1 has E3 ubiquitin ligase activity. The determination of the subcellular localization reveals that SlRING1 is localized at both the plasma membrane and the nucleus. Overexpression of SlRING1 in tomato increased the chlorophyll content, the net photosynthetic rate, and the maximal photochemical efficiency of photosystem II (Fv/Fm), but reduced the levels of reactive oxygen species and relative electrolyte leakage under Cd stress. Moreover, SlRING1 overexpression increased the transcript levels of CATALASE (CAT), DEHYDROASCORBATE REDUCTASE (DHAR), MONODEHYDROASCORBATE REDUCTASE (MDHAR), GLUTATHIONE (GSH1), and PHYTOCHELATIN SYNTHASE (PCS), which contribute to the antioxidant and detoxification system. Crucially, SlRING1 overexpression also reduced the concentrations of Cd in both shoots and roots. Thus, SlRING1-overexpression-induced enhanced tolerance to Cd is ascribed to reduced Cd accumulation and alleviated oxidative stress. Our findings suggest that SlRING1 is a positive regulator of Cd tolerance, which can be a potential breeding target for improving heavy metal tolerance in horticultural crops.

Enhanced aggregation and sedimentation of nanoscale zero-valent iron (nZVI) with polyacrylamide modification.

Nanoscale zero-valent iron (nZVI) settled slowly and incompletely in a nano-iron reactor (NIR) in wastewater treatment, and the effluent quality and processing capacity of nZVI were degenerated. Herein, three types of polyacrylamide (PAM), anionic-APAM (nZVIAPAM), cationic-CPAM (nZVICPAM), and nonionic-NPAM (nZVINPAM)) were applied to modify the nZVI (nZVIPAM), which were proved to enhance aggregation and sedimentation in the gravity settling clarifier of NIR. PAM modification lead to aggregate by forming large agglomerates. The median sizes of aggregates were 32, 194, 168 and 133 µm respectively for nZVI, nZVICPAM, nZVINPAM, and nZVIAPAM. Under quiescent conditions, bare nZVI needed 5 min to reach sedimentation equilibrium, while nZVIPAM just within 1 min nZVICPAM settled more quickly and completely than nZVINPAM and nZVIAPAM. The Fe concentration in the dynamic flow NIR effluent could keep a low level for 8 h for nZVIPAM, while bare nZVI for 6 h. Iron concentration was 3.11, 0.037, 0.93, and 1.20 mg·L-1 for nZVI, nZVICPAM, nZVINPAM, and nZVIAPAM after 8-h-reaction. Meanwhile, the reactivity of nZVIPAM was kept much longer for lead removal in the NIR. Results demonstrated PAM modifications (especially CPAM) provided a reliable solution for nZVI aggregation and sedimentation in wastewater treatment.

Physiological and Defense Responses of Tea Plants to Elevated CO2: A Review.

Rising atmospheric carbon dioxide, an important driver of climate change, has multifarious effects on crop yields and quality. Despite tremendous progress in understanding the mechanisms of plant responses to elevated CO2, only a few studies have examined the CO2-enrichment effects on tea plants. Tea [Camellia sinensis (L.)], a non-deciduous woody perennial plant, operates massive physiologic, metabolic and transcriptional reprogramming to adapt to increasing CO2. Tea leaves elevate photosynthesis when grown at CO2-enriched environment which is attributed to increased maximum carboxylation rate of RuBisCO and maximum rates of RuBP regeneration. Elevated CO2-induced photosynthesis enhances the energy demand which triggers respiration. Stimulation of photosynthesis and respiration by elevated CO2 promotes biomass production. Moreover, elevated CO2 increases total carbon content, but it decreases total nitrogen content, leading to an increased ratio of carbon to nitrogen in tea leaves. Elevated CO2 alters the tea quality by differentially influencing the concentrations and biosynthetic gene expression of tea polyphenols, free amino acids, catechins, theanine, and caffeine. Signaling molecules salicylic acid and nitric oxide function in a hierarchy to mediate the elevated CO2-induced flavonoid biosynthesis in tea leaves. Despite enhanced synthesis of defense compounds, tea plant defense to some insects and pathogens is compromised under elevated CO2. Here we review the physiological and metabolic responses of tea plants to elevated CO2. In addition, the potential impacts of elevated CO2 on tea yield and defense responses are discussed. We also show research gaps and critical research areas relating to elevated CO2 and tea quality for future study.

Dopamine alleviates bisphenol A-induced phytotoxicity by enhancing antioxidant and detoxification potential in cucumber.

Bisphenol A (BPA) is an emerging organic pollutant, widely distributed in environment. Plants can uptake and metabolize BPA, but BPA accumulation induces phytotoxicity. In this study, we administered dopamine, a kind of catecholamines with strong antioxidative potential, to unveil its role in cucumber tolerance to BPA stress. The results showed that exposure to BPA (20 mg L-1) for 21 days significantly reduced growth and biomass accumulation in cucumber seedlings as revealed by decreased lengths and dry weights of shoots and roots. While BPA exposure decreased the chlorophyll content, cell viability and root activity, it remarkably increased reactive oxygen species (ROS) accumulation, electrolyte leakage and malondialdehyde (MDA) content, suggesting that BPA induced oxidative stress in cucumber. However, exogenous dopamine application significantly improved the photosynthetic pigment content, root cell viability, growth and biomass accumulation, and decreased the ROS and MDA levels by increasing the activity of antioxidant enzymes under BPA stress. Further analysis revealed that dopamine application significantly increased the glutathione content and the transcripts and activity of glutathione S-transferase under co-administration of dopamine and BPA compared with only BPA treatment. Moreover, dopamine decreased the BPA content in both leaves and roots, suggesting that dopamine promoted BPA metabolism by enhancing the glutathione-dependent detoxification. Our results show that dopamine has a positive role against BPA phytotoxicity and it may reduce the risks-associated with the dietary intake of BPA through consumption of vegetables.

Trichoderma asperellum reduces phoxim residue in roots by promoting plant detoxification potential in Solanum lycopersicum L.

Phoxim, a broad-spectrum organophosphate pesticide, is widely used in agriculture to control insect pests in vegetable crops as well as in farm mammals. However, the indiscriminate use of phoxim has increased its release into the environment, leading to the contamination of plant-based foods such as vegetables. In this study, we investigated the effect of Trichoderma asperellum (TM, an opportunistic fungus) on phoxim residue in tomato roots and explored the mechanisms of phoxim metabolism through analysis of detoxification enzymes and gene expression. Degradation kinetics of phoxim showed that TM inoculation rapidly and significantly reduced phoxim residues in tomato roots. Phoxim concentrations at 5d, 10d and 15d post treatment were 75.12, 65.71 and 77.45% lower in TM + phoxim than only phoxim treatment, respectively. The TM inoculation significantly increased the glutathione (GSH) content, the activity of glutathione S-transferase (GST) and the transcript levels of GSH, GST1, GST2 and GST3 in phoxim-treated roots. In addition, the activity of peroxidase and polyphenol peroxidase involved in the xenobiotic conversion also increased in TM + phoxim treatment. The expression of detoxification genes, such as CYP724B2, GR, ABC2 and GPX increased by 3.82, 3.08, 7.89 and 2.46 fold, respectively in TM + phoxim compared with only phoxim. Similarly, the content of ascorbate (AsA) and the ratio of AsA to dehydroascorbate increased by 45.16% and 57.34%, respectively in TM + phoxim-treated roots. Our results suggest that TM stimulates plant detoxification potential in all three phases (conversion, conjugation and sequestration) of xenobiotc metabolism, leading to a reduced phoxim residue in tomato roots.

Feasibility of nanoscale zero-valent iron (nZVI) for enhanced biological treatment of organic dyes.

Biodegradation of recalcitrant organic contaminants such as organic dyes is a fundamental challenge in wastewater treatment. We report herein the integration of nanoscale zero-valent iron (nZVI) with membrane bioreactors (nZVI-bio system) to achieve enhanced degradation of Congo red (CR) in wastewater. nZVI pretreatment converts the large and bio-recalcitrant CR molecules into smaller and more biodegradable organic compounds in continuous flow stirred tank reactors (CFSTR). A nZVI-bio system was experimented continuously for 52 d with a color removal efficiency of 99% and a reduction of chemical oxygen demand (COD) from 167 mg L-1 to less than 70 mg L-1. However, a conventional biotreatment system treating identical wastewater achieved color removal efficiency of just 30-70% and the COD reduction to 116 mg L-1. This suggests that integrated nZVI-bio system has potential for the treatment of recalcitrant organic dyes. On-line measurements of pH and redox potential in the CSFTR can be conveniently used to monitor and regulate treatment performance.

Highly dispersed core-shell iron nanoparticles decorating onto graphene nanosheets for superior Zn(II) wastewater treatment.

This study reports the preparation of highly dispersed nanoscale zerovalent iron (nZVI) with core-shell structure decorated onto graphene nanosheets (Gr-NS) to form nZVI-Gr-NS composite. Meanwhile, its excellent performance for concentrated Zn(II) wastewater treatment is also studied. The adsorption of Zn(II) onto nZVI-Gr-NS is well simulated by the pseudo-second-order model, which indicates the adsorption is the rate-controlling step. Moreover, the adsorption isotherms of Zn(II) on the nZVI-Gr-NS can fit well with the Langmuir model. The negative thermodynamic parameters (△GƟ, △HƟ, △SƟ) calculated from the temperature-dependent isotherms indicate that the sorption reaction of Zn(II) is an exothermic and spontaneous process. The high saturation magnetization (37.4 emu g-1) of the nZVI-Gr-NS makes separation of nZVI-Gr-NS-bound Zn(II) easily and quickly from aqueous solution. Most importantly, nZVI-Gr-NS composites not only remove Zn(II) but also spontaneously remove As, Se, and Cu ions from real smelting wastewater samples. This study provides a good solution for heavy metal removal in real wastewater.

Nanoencapsulation of arsenate with nanoscale zero-valent iron (nZVI): A 3D perspective.

The principal forces driving the efficient enrichment and encapsulation of arsenic (As) into nanoscale zero-valent iron (nZVI) are the disordered arrangement of the atoms and the gradient chemical potentials within the core-shell interface. The chemical compositions and the fine structure of nZVI are characterized with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), X-ray energy-dispersive spectroscopy (XEDS), electron energy loss spectroscopy (EELS), and high-resolution X-ray photoelectron spectroscopy (HR-XPS). Atomically resolved EELS at the oxygen K-edge unfolds that the Fe species in nZVI are well stratified from Fe(III) oxides in the outermost periphery to a mixed Fe(III)/Fe(II) interlayer, then Fe(II) oxide and the pure Fe(0) phase. Reactions between As(V) and nZVI suggest that a well-structured local redox gradient exists within the shell layer, which serves as a thermodynamically favorable conduit for electron transfer from the iron core to the surface-bound As(V). HR-XPS with ion sputtering shows that arsenic species shift from As(V), As(III)/As(V) to As(V)/As(III)/As(0) from the iron oxide shell-water interface to the Fe(0) core. Results reinforce previous work on the efficacy of nZVI for removing and remediating arsenic while the analytical TEM methods are also applicable to the study of environmental interfaces and surface chemistry.

Evolution of nanoscale zero-valent iron (nZVI) in water: Microscopic and spectroscopic evidence on the formation of nano- and micro-structured iron oxides.

Knowledge on the transformation of nanoscale zero-valent iron (nZVI) in water is essential to predict its surface chemistry including surface charge, colloidal stability and aggregation, reduction and sorption of organic contaminants, heavy metal ions and other pollutants in the environment. In this work, transmission electronic microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy are applied to study the compositional and structural evolution of nZVI under oxic and anoxic conditions. Under anoxic conditions, the core-shell structure of nZVI is well maintained even after 72h, and the corrosion products usually contain a mixture of wustite (FeO), goethite (α-FeOOH) and akaganeite (ß-FeOOH). Under oxic conditions, the core-shell structure quickly collapses to flakes or acicular-shaped structures with crystalline lepidocrocite (γ-FeOOH) as the primary end product. This work provides detailed information and fills an important knowledge gap on the physicochemical characteristics and structural evolution of engineered nanomaterials in the environment.

Transformation and composition evolution of nanoscale zero valent iron (nZVI) synthesized by borohydride reduction in static water.

The reactivity of nanoscale zero valent iron (nZVI) toward targeted contaminants is affected by the initial nZVI composition and the iron oxides formed during the aging process in aquatic systems. In this paper, the aging effects of nZVI, prepared using a borohydride reduction method in static water over a period of 90 days (d), are investigated. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy are used to characterize the corrosion products of nZVI. Results show that both the structures and the compositions of the corrosion products change with the process of aging. The products of nZVI aged for 5 d in static water media are mainly magnetite (Fe3O4) and maghemite (γ-Fe2O3), accompanied by lepidocrocite (γ-FeOOH). For products aged 10 d, XRD data show the formation of ferrihydrite and lepidocrocite. When aged up to 90 d, the products are mainly γ-FeOOH mixed with small amounts of Fe3O4 and γ-Fe2O3. Transmission electronic microscopy (TEM) images show that the core-shell structure forms into a hollow spherical shape after 30 d of aging in aquatic media. The results indicate first that iron ions in the Fe(0) core diffuse outwardly toward the shell, and hollowed-out iron oxide shells emerge. Then, the iron oxide shell collapses and becomes a flaky, acicular-shaped structure. The type and the crystal phase of second iron oxide minerals are vastly different at various aging times. This study helps to explain the patterns of occurrence of specific iron oxides in different natural conditions.

Arbuscular mycorrhizae improve low temperature tolerance in cucumber via alterations in H2O2 accumulation and ATPase activity.

The combined effects of arbuscular mycorrhizal fungi (AMF) and low temperature (LT) on cucumber plants were investigated with respect to biomass production, H2O2 accumulation, NADPH oxidase, ATPase activity and related gene expression. Mycorrhizal colonization ratio was gradually increased after AMF-inoculation. However, LT significantly decreased mycorrhizal colonization ability and mycorrhizal dependency. Regardless of temperature, the total fresh and dry mass, and root activity of AMF-inoculated plants were significantly higher than that of the non-AMF control. The H2O2 accumulation in AMF-inoculated roots was decreased by 42.44% compared with the control under LT. H2O2 predominantly accumulated on the cell walls of apoplast but was hardly detectable in the cytosol or organelles of roots. Again, NADPH oxidase activity involved in H2O2 production was significantly reduced by AMF inoculation under LT. AMF-inoculation remarkably increased the activities of P-type H(+)-ATPase, P-Ca(2+)-ATPase, V-type H(+)-ATPase, total ATPase activity, ATP concentration and plasma membrane protein content in the roots under LT. Additionally, ATP concentration and expression of plasma membrane ATPase genes were increased by AMF-inoculation. These results indicate that NADPH oxidase and ATPase might play an important role in AMF-mediated tolerance to chilling stress, thereby maintaining a lower H2O2 accumulation in the roots of cucumber.

Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM).

An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

[Skin prick test of inhalative allergens for patients with allergic rhinitis in Yichang].

OBJECTIVE: To investigate the allergens in patients with allergic rhinitis in Yichang, so that to find common allergens of Yichang and to provide statistic basis for a reasonable prevention and treatment to allergic rhinitis. METHOD: 1,979 patients with allergic rhinitis in Yichang were detected for allergens by skin prick test and the distribution of positive rates to inhaled allergens was compared between different genders and ages. RESULT: 1,545 (78.1%) of 1,979 suspected allergic rhinitis patients presented positive reaction. The positive rate in male was significantly higher than in female, and that in juvenile group was significantly higher than in adults. Among positive cases in inhalation group, the most common allergen was flour mite (80.4%), followed by house dust mite (64.9%), cockroach (13.3%) and artemisia pollen (8.2%). CONCLUSION: The study shows that the flour mite and house dust mite are the most common inhaled allergens causing allergic rhinitis in Yichang. We should pay more attention to the prevention and treatment for the juvenile patients.

[Research advances in endophytic fungi of mangrove].

Mangrove, a kind of special host plants, is a resource of abundant endophytic fungi. More than 200 species of endophytic fungi are isolated and identified from mangrove, being the second largest community of marine fungi. The reported endophytic fungi of mangrove are mainly Alternaria, Aspergillus, Cladosporium, Colletotrichum, Fusarium, Paecilomyces, Penicillium, Pestalotiopsis, Phoma, Phomopsis, Phyllosticta and Trichoderma. Most endophytic fungi have wide range of hosts, and a few only have single host. However, the composition and dominant species on each mangrove plant are different. The colonization of endophytic fungi always varies with different parts (leaves, twigs, stems) and age of host plants and with seasons. The endophytic fungi of mangrove can produce many kinds of metabolites with great potential for anti-microbial and anti-tumor medicinal use. In this paper, the research advances in biodiversity of endophytic fungi in mangrove, their distribution, biological and ecological function, and secondary metabolites were reviewed.