Mingjing Ke

Evaluation of the toxic response induced by azoxystrobin in the non-target green alga Chlorella pyrenoidosa

The top-selling strobilurin, azoxystrobin (AZ), is a broad-spectrum fungicide that protects against many kinds of pathogenic fungi by preventing their ATP production. The extensive use of AZ can have negative consequences on non-target species and its effects and toxic mechanisms on algae are still poorly understood. In this work, Chlorella pyrenoidosa that had been grown in BG-11 medium was exposed to AZ (0.5-10xa0mgxa0L-1) for 10xa0d. The physiological and molecular responses of the algae to AZ treatment, including photosynthetic efficiency, lipid peroxidation level, antioxidant enzyme activities, as well as transcriptome-based analysis of gene expression, were examined to investigate the potential toxic mechanism. Results shows that the photosynthetic pigment (per cell) increased slightly after AZ treatments, indicating that the photosystem of C.xa0pyrenoidosa may have been strengthened. Glutathione and ascorbate contents were increased, and antioxidant enzyme activities were induced to relieve oxidative damage (e.g., from lipid peroxidation) in algae after AZ treatment. Transcriptome-based analysis of gene expression combined with physiological verification suggested that the 5xa0mgxa0L-1 AZ treatment did not inhibit ATP generation in C.xa0pyrenoidosa, but did significantly alter amino acid metabolism, especially in aspartate- and glutamine-related reactions. Moreover, perturbation of ascorbate synthesis, fat acid metabolism, and RNA translation was also observed, suggesting that AZ inhibits algal cell growth through multiple pathways. The identification of AZ-responsive genes in the eukaryotic alga C.xa0pyrenoidosa provides new insight into AZ stress responses in a non-target organism.

The interactive effects of diclofop-methyl and silver nanoparticles on Arabidopsis thaliana: Growth, photosynthesis and antioxidant system.

Diclofop-methyl (DM), a common post-emergence herbicide, is frequently used in agricultural production. Silver nanoparticles (AgNPs) are one of the most widely used nanoparticles, and as such, have been detected and monitored in several environmental systems. Here we investigated the interactive effects of DM and AgNPs on the physiological morphology, photosynthesis and antioxidant system of Arabidopsis thaliana. Our results demonstrated that a 1.0xa0mg/L DM treatment had no significant effect on the fresh weight of plant shoots and the content of total chlorophyll and anthocyanin. However, a 0.5xa0mg/L AgNPs treatment was found to significantly inhibit plant growth and chlorophyll synthesis, and was found to cause more severe oxidative damage in plants compared to the effects observed in a hydroponic suspension in which DM and AgNPs were jointly present. Meanwhile, the relative transcript levels of photosynthesis related genes (psbA, rbcL, pgrl1A and pgrl1B) in the combined group were found to be slightly increased compared to transcript levels in the AgNPs group, in order to maintain ATP generation at relatively normal levels in order to repair light damage. One explanation for these observed antagonistic effects was that the existence of DM affects the stability of AgNPs and reduced Ag+ release from AgNPs in the mixed solution. Thereupon, the Ag+-content was found to decrease in shoots and roots in the combined group by 15.2% and 9.4% respectively, compared to the AgNPs group. The coexistence of herbicides and nanomaterials in aquatic environments or soil systems will continue to exist due to their wide usages. Our current study highlights that the antagonistic effects between DM and AgNPs exerted a positive impact on A.xa0thaliana growth.

Impact of copper nanoparticles and ionic copper exposure on wheat (Triticum aestivum L.) root morphology and antioxidant response.

Copper nanoparticles (nCu) are widely used in industry and in daily life, due to their unique physical, chemical, and biological properties. Few studies have focused on nCu phytotoxicity, especially with regard to toxicity mechanisms in crop plants. The present study examined the effect of 15.6u202fμM nCu exposure on the root morphology, physiology, and gene transcription levels of wheat (Triticum aestivum L.), a major crop cultivated worldwide. The results obtained were compared with the effects of exposing wheat to an equivalent molar concentration of ionic Cu (Cu2+ released from CuSO4) and to control plants. The relative growth rate of roots decreased to approximately 60% and the formation of lateral roots was stimulated under nCu exposure, possibly due to the enhancement of nitrogen uptake and accumulation of auxin in lateral roots. The expression of four of the genes involved in the positive regulation of cell proliferation and negative regulation of programmed cell death decreased to 50% in the Cu2+ treatment compared to that of the control, while only one gene was down-regulated to about half of the control in nCu treatment. This explained the decreased root cell proliferation and higher extent of induced cell death in Cu2+- than in nCu-exposed plants. The increased methane dicarboxylic aldehyde accumulation (2.17-fold increase compared with the control) and decreased antioxidant enzyme activities (more than 50% decrease compared with the control) observed in the Cu2+ treatment in relation to the nCu treatment indicated higher oxidative stress in Cu2+- than in nCu-exposed plants. Antioxidant (e.g., proline) synthesis was pronouncedly induced by nCu to scavenge excess reactive oxygen species, alleviating phytotoxicity to wheat exposed to this form of Cu. Overall, oxidative stress and root growth inhibition were the main causes of nCu toxicity.

A comparison of the effects of copper nanoparticles and copper sulfate on Phaeodactylum tricornutum physiology and transcription

Copper nanoparticles (CuNPs) have been used in a broad range of applications. However, they are inevitably released into the marine environment, making it necessary to evaluate their potential effects on marine phytoplankton. In this study, the short-term (96h) effects of CuNPs and CuSO4 on Phacodactylum tricornutum growth, photosynthesis, reactive oxygen species production and transcription were assessed. It was found that high concentrations (40μM) of CuNPs and CuSO4 significantly inhibited the growth, photosynthesis and induced oxidative stress of P. tricornutum, while lower concentrations caused a hormetic response as indicated by a slight stimulation in algal growth. The high percentage of dissolved Cu (78-100%) in culture medium suggested that the dissolved Cu was the main driver of toxicity during CuNPs treatment. The algal cells upregulated electron transport chain-related genes to produce more energy and restore photosynthesis after 96h of treatment with CuNPs and CuSO4. This study delineates the cellular mechanism behind the toxicity of CuNPs and CuSO4 on marine diatoms.

Reproductive and endocrine-disrupting toxicity of Microcystis aeruginosa in female zebrafish.

Microcystis aeruginosa, a primary species in cyanobacterial blooms, is ubiquitously distributed in water. Microcystins (MCs) purified from M.xa0aeruginosa can exert reproductive toxicity in fish. However, the effects of M.xa0aeruginosa at environmentally relevant levels on the reproductive and endocrine systems of zebrafish are still unknown. The present study investigated the reproductive and endocrine-disrupting toxicity of M.xa0aeruginosa on female zebrafish (Danio rerio) by short-term exposure (96xa0h). After exposure, marked histological lesions in the liver or gonads, such as nuclear pyknosis and deformation, were observed, and the fertilization rate and hatchability of eggs spawned from treated females were both significantly lower than they were in females in the control group, suggesting the possibility of transgenerational effects of M.xa0aeruginosa exposure. Moreover, M.xa0aeruginosa exposure decreased the concentration of 17β-estradiol (E2) and testosterone (T) in female zebrafish. Interestingly, the vtg1 transcriptional level significantly decreased in the liver, whereas plasma vitellogenin (VTG) protein levels increased. The present findings indicate that M.xa0aeruginosa could modulate endocrine function by disrupting transcription of hypothalamic-pituitary-gonadal-liver (HPGL) axis-related genes, and impair the reproductive capacity of female zebrafish, suggesting that M.xa0aeruginosa causes potential adverse effects on fish reproduction in Microcystis bloom-contaminated aquatic environments.

Physiological and Molecular Response of Arabidopsis thaliana to CuO Nanoparticle (nCuO) Exposure

The widespread application of copper oxide nanoparticles (nCuO) results in ecological risk when nanoparticles enter the environment. This study clarifies the mechanism of nCuO toxicity in Arabidopsis thaliana seedlings via comparison with copper (Cu) ion bioeffects. Under the same culture conditions, Cu2+ ion exposure exerted a stronger inhibitory effect on plant fresh weight and growth and caused stronger oxidative disruption (measured by malondialdehyde, MDA) than nCuO exposure. The Cu2+ ions also showed a stronger induction effect than did nCuO on the activity of antioxidant enzymes and the transcription of antioxidant-related genes. Dissolved Cu2+ ions contributed a minority of the toxicity of nCuO, implying that nCuO itself showed relative strong phytotoxicity. The work presented here will help increase our understanding of the toxicity of metal nanoparticles in plants.

Phytotoxic effects of silver nanoparticles and silver ions to Arabidopsis thaliana as revealed by analysis of molecular responses and of metabolic pathways

The acute (3 days) and chronic (whole life history) responses of Arabidopsis thaliana following exposure to silver nanoparticles (AgNPs) and Ag+ ions (AgNO3) in respectively a hydroponic medium and in soil were studied. After 3u202fdays of hydroponic exposure, AgNPs (1.0 and 2.5u202fmg/L) exerted more severe inhibitory effects on plant (shoot and root) growth and photosynthesis than the same concentrations of Ag+ ions. In soil cultivation, the photoperiod, the autonomous, and the vernalization pathways were down-regulated to 0.15- to 0.5-fold of the control after 12.5u202fmg/kg AgNPs treatment. This exposure caused a decrease of approximately 25%-40% as compared to the control of the transcription of flowering key genes including AP1, LFY, FT and SOC1, and finally resulted in a delayed flowering time of 5u202fdays. Only autonomous and vernalization pathways were inhibited by Ag+ ion treatment and ultimately the time of flowering in treated plants was delayed by 3u202fdays. The energy production related metabolic pathways in the tricarboxylic acid cycle and in sugar metabolism were stimulated stronger by AgNPs than by Ag+ ion treatment, thus releasing more energy and accelerating the physiological metabolic responses against stress in the AgNPs treatment while subsequently reducing the plant growth and yield at the maturation stage. Importantly, shikimate-phenylpropanoid biosynthesis, and tryptophan and galactose metabolisms were regulated only by the AgNPs treatment, which was a specific effect of nanoparticles. This work provides a systematic understanding at the molecular, physiological as well as metabolic level of the effects of AgNPs and Ag+ ions in A. thaliana.

The combined toxicity effect of nanoplastics and glyphosate on Microcystis aeruginosa growth

Waste plastics can be degraded to nanoplastics (NPs, diameter<1u202fμm) by natural forces. NPs not only directly affect aquatic organisms but also adsorb other pollutants, causing combined pollution. Glyphosate is one of the most widely used herbicides and is commonly monitored in freshwater systems. In this study, the effects of the combined toxicity of polystyrene cationic amino-modified nanoparticles (nPS-NH2) and glyphosate on a blue-green alga, Microcystis aeruginosa, were investigated. Our results demonstrated that 5u202fmg/L glyphosate had a strong inhibitory effect on M.xa0aeruginosa (the 96-h inhibitory rate was 27%), while 5u202fmg/L nPS-NH2 had no apparent effect on the growth of M.xa0aeruginosa. Interestingly, nPS-NH2 combined with glyphosate showed antagonistic effects on the inhibition of algal growth because nPS-NH2 displayed a strong adsorption capacity for glyphosate, which significantly alleviated the inhibitory effect of glyphosate on M.xa0aeruginosa growth. However, the presence of glyphosate enhanced the stability of the dispersion system, which allowed more nPS-NH2 to adsorb on the surface of M.xa0aeruginosa and may result in greater enrichment of nPS-NH2 in the food chain to show potential repercussions to human life. Our current study provides a new theoretical basis for the combined effects of NPs and pesticide pollution.

Interacting effect of diclofop-methyl on the rice rhizosphere microbiome and denitrification

A better knowledge of the intertwined effects of herbicides on plant physiology and microbiome as well as nutrient biogeochemical cycles are needed for environmental management. Here we studied the influence of herbicide diclofop-methyl (DM) on the rice root microbiome and its relationship with N cycle. To do so, we exposed rice seedlings to 100u202fμg/L DM and studied rhizosphere microbiota using MiSeq-pyrosequencing, root exudation by GC-MS, and denitrification activity by 15N isotope-tracing and qRT-PCR. The richness and diversity of rhizosphere microorganisms, significantly increased after DM exposure combined with an increase in root exudation of amino acids, sugars, and fatty acids. Transcription of denitrification-related gene and denitrification rate increased significantly in the rice rhizosphere. Our results suggest that DM strongly influenced the root exudation of bacteria nutrients, which affected root microbiome community and potentially influenced N cycle in rice rhizosphere.

Investigation of Rhizospheric Microbial Communities in Wheat, Barley, and Two Rice Varieties at the Seedling Stage.

The plant rhizosphere microbiota plays multiple roles in plant growth. We investigated the taxonomic and functional variations in the rhizosphere microbial community, examining both prokaryotes and eukaryotes, of four crops at the seedling stage: wheat, barley, and two rice varieties ( indica and japonica) seeded in paddy soil. The diversity of rhizosphere communities in these four species was determined. Results showed that wheat and barley had much stronger selection effects than rice for the rhizosphere microbial community. Functional metagenomic profiling indicated that a series of sequences related to glycan, limonene, and pinene degradation pathways as well as some relatively rare functions related to N or S metabolism were enriched in the rhizosphere soil. We conclude that the four tested crops induced the formation of the microbial community with specific features that may influence the plant growth but stochastic processes also appreciably influenced the functional selection.