Cell cycle arrest mediated by Cd-induced DNA damage in Arabidopsis root tips

Accumulating evidence demonstrates that the aberrant expression of cell cycle regulation and DNA repair genes can result in abnormal cell proliferation and genomic instability in eukaryotic cells under different stresses. Herein, Arabidopsis thaliana (Arabidopsis) seedlings were grown hydroponically on 0.5 × MS media containing cadmium (Cd) at 0–2.5 mg L−1 for 5 d of treatment. Real time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed that expression of DNA damage repair and cell cycle regulation genes, including BRCA1, MRE11, WEE1, CDKA;1 and PCNA1, showed an inverted U-shaped dose-response. In contrast, notably reduced expression was observed for G1-to-S transition-related genes, Histone H4, E2Fa and PCNA2; DSB end processing, GR1; G2-to-M transition-related gene, CYCB1;1; and DNA mismatch repair, MSH2, MSH6 and MLH1 genes in root tips exposed to 0.125–2.5 mg/L Cd for 5 d. Flow cytometry (FCM) analysis revealed significant increases of cells with a 2C nuclear content and with a 4C and 8C nuclear content under Cd stresses of 0.125 and 1–2.5 mg L−1, respectively. Our results suggest that 0.125 mg L−1 Cd-induced DNA damage induced the marked G1/S arrest, leading to accelerated growth in root tips, while 1.0–2.5 mg L−1 Cd-induced DNA damage caused a notable G2/M arrest in root tips, leading to reduced growth in root tips. This may be a protective mechanism that prevents cells with damaged DNA from dividing under Cd stress

A Facile Synthesis of Polypyrrole/Carbon Nanotube Composites with Ultrathin, Uniform and Thickness-Tunable Polypyrrole Shells

An improved approach to assemble ultrathin and thickness-tunable polypyrrole (PPy) films onto multiwall carbon nanotubes (MWCNTs) has been investigated. A facile procedure is demonstrated for controlling the morphology and thickness of PPy film by adding ethanol in the reaction system and a possible mechanism of the coating formation process is proposed. The coated PPy films can be easily tuned by adding ethanol and adjusting a mass ratio of pyrrole to MWCNTs. Moreover, the thickness of PPy significantly influences the electronic conductivity and capacitive behavior of the PPy/MWCNT composites. The method may provide a facile strategy for tailoring the polymer coating on carbon nanotubes (CNTs) for carbon-based device applications

Cadmium-induced genomic instability in Arabidopsis: molecular toxicological biomarkers for early diagnosis of cadmium stress

Microsatellite instability (MSI) analysis, random-amplified polymorphic DNA (RAPD), and methylation-sensitive arbitrarily primed PCR (MSAP-PCR) are methods to evaluate the toxicity of environmental pollutants in stress-treated plants and human cancer cells. Here, we evaluate these techniques to screen for genetic and epigenetic alterations of Arabidopsis plantlets exposed to 0–5.0 mg L−1 cadmium (Cd) for 15 d. There was a substantial increase in RAPD polymorphism of 24.5, and in genomic methylation polymorphism of 30.5–34.5 at CpG and of 14.5–20 at CHG sites under Cd stress of 5.0 mg L−1 by RAPD and of 0.25–5.0 mg L−1 by MSAP-PCR, respectively. However, only a tiny increase of 1.5 loci by RAPD occurred under Cd stress of 4.0 mg L−1, and an additional high dose (8.0 mg L−1) resulted in one repeat by MSI analysis. MSAP-PCR detected the most significant epigenetic modifications in plantlets exposed to Cd stress, and the patterns of hypermethylation and polymorphisms were consistent with inverted U-shaped dose responses. The presence of genomic methylation polymorphism in Cd-treated seedlings, prior to the onset of RAPD polymorphism, MSI and obvious growth effects, suggests that these altered DNA methylation loci are the most sensitive biomarkers for early diagnosis and risk assessment of genotoxic effects of Cd pollution in ecotoxicology

The exposure of gadolinium at environmental relevant levels induced genotoxic effects in Arabidopsis thaliana (L.)

Rare Earth Elements (REEs) are increasingly being used in agriculture and are also used to produce high end technological devices, thereby increasing their anthropogenic presence in the environment. However, the ecotoxicological mechanism of REEs on organisms is not fully understood. In this study, the effects of gadolinium (Gd) addition on Arabidopsis thaliana (L.) were investigated at both physiological and molecular levels. Four treatments (0, 10, 50 and 200 μmol·L−1 Gd) were used in the exposure tests. Biomass, root length and chlorophyll content in shoots/roots were measured to investigate the plant’s physiological response to Gd stress. Random amplified polymorphic (RAPD)-Polymerase Chain Reaction (PCR) and methylation sensitive arbitrarily primed (MSAP)-PCR were used to investigate changes in genetic variation and DNA methylation of A. thaliana when exposed to Gd. At the physiological level, it was found that low concentration of Gd (10 μmol·L−1) could significantly increase the plant biomass and root length, while the growth of A. thaliana was significantly inhibited when exposed to 200 μmol·L−1 of Gd, yet the total soluble protein content in aerial plant parts increased significantly by 24.2% when compared to the control group. Among the 12 primers considered in the RAPD assessment, at the molecular level, only four primers revealed different patterns in their genomic DNA. Compared to the control group, the treatment with 50 μmol·L−1 of Gd was associated with lower polymorphism, while the treatment with 200 μmol·L−1 of Gd was associated with higher polymorphism. The polymorphism frequencies for the 50 μmol·L−1 of Gd and the 200 μmol·L−1 of Gd were 4.67% and 20.33%, respectively. The MSAP analysis revealed that the demethylation (D) type of Arabidopsis genomic DNA increased significantly under 10 and 50 μmol·L−1 of Gd, while the methylation (M) type was also significantly increased under 200 μmol·L−1 of Gd. Generally, the total methylation polymorphism (D+M) increased with an increase of Gd concentration. It was found that high concentrations of Gd appeared to cause DNA damage, but low concentrations of Gd (as low as 10 μmol·L−1) were associated with DNA methylation change. Further, it was verified by Real time Reverse Transcription PCR (RT-PCR) on the bands detected by the MSAP analysis, that the genes relative to processes including cell cycle, oxidative stress and apoptosis, appeared to be regulated by methylation under Gd stress. These findings reveal new insight regarding ecotoxicity mechanisms of REEs on plants

Toxic Effects of Two Representative Rare Earth Elements (La and Gd) on Danio rerio Based on Transcriptome Analysis

The expanding applications of rare earth elements (REEs) in various fields have raised concerns about their biosafety. However, previous studies are insufficient to elucidate their toxic effects and mechanisms of action and whether there are uniform or predictable toxicity patterns among REEs. Herein, we investigated the toxic effects of two representative REEs (lanthanum (La) and gadolinium (Gd)) on zebrafish (Danio rerio) through toxicity experiments and transcriptome analysis. The results of the toxicity experiments showed that the two REEs have similar lethality, with half-lethal concentrations (LC50) at micromolar levels and mixed toxicity showing additive effects. Differential expression gene screening and functional group enrichment analysis showed that La and Gd might affect the growth and development of Danio rerio by interfering with some biological molecules. The two REEs showed significant effects on the metabolic pathways of exogenous or endogenous substances, including glutathione sulfotransferase and acetaldehyde dehydrogenase. Moreover, some basic biological processes, such as DNA replication, the insulin signaling pathway, and the p53 signaling pathway, were significantly enriched. Overall, the toxicity patterns of La and Gd may affect some biological processes with different intensities; however, there are many similarities in their toxicity mechanisms and modes of action. The concentrations investigated in this study were comparable to those of REE residues at highly contaminated sites, thus mimicking the ecotoxicological effects at environmentally relevant concentrations

Clinicopathological features associated with lymph node metastasis in early gastric cancer: Analysis of a single-institution experience in China

BACKGROUND: An accurate assessment of potential lymph node metastasis is an important issue for the appropriate treatment of early gastric cancer. Minimizing the number of invasive procedures used in cancer therapy is critical for improving the patient’s quality of life