Aluminum can induce alterations in the cellular localization and expression of three major nucleolar proteins in root tip cells of Allium cepa var. agrogarum L

Epigenetic modifications of 45S rDNA associates with the disruption of nucleolar organisation during Cd stress response in Pakchoi

The role of the nucleolus in Pakchoi response to Cd stress remains largely unknown. In this work, we focus on exploring the underling mechanism between nucleolus disruption and epigenetic modification in Cd stressed-Pakchoi. Our results indicated that the proportion of nucleolus disruption, decondensation of 45 S rDNA chromatin, and a simultaneous increase in 5' external transcribed spacer region (ETS) transcription were observed with increasing Cd concentration, accompanied by genome-wide alterations in the levels of histone acetylation and methylation. Further results showed that Cd treatment exhibited a significant increase in H3K9ac, H4K5ac, and H3K9me2 levels occurred in promoter regions of the 45 S rDNA. Additionally, DNA methylation assays in the 45 S rDNA promoter region revealed that individual site-specific hypomethylation may be engaged in the activation of 45 S rDNA transcription. Our study provides some molecular mechanisms for the linkage between Cd stress, rDNA epigenetic modifications, and nucleolus disintegration in plants.

Biomonitoring of surface water quality in the Chopim River within the Conservation Unit Campos de Palmas Wildlife Refuge, southern Brazil

The Campos de Palmas Wildlife Refuge (RVS-CP) is a full protection conservation unit (CU) formed by private properties. The present study aimed to use the bioindicators Allium cepa L. (cytotoxicity and mutagenicity tests) and Eisenia fetida (avoidance test) to assess the quality of surface water of the Chopim River within the RVS-CP area and its surroundings during the four seasons of the year. To do so, water samples were collected at five points, four inside the RVS-CP area and a fifth point outside thereof. Samples from all sampling points had cytotoxic effect on A. cepa in at least one season of the year. Such a finding may be related to inadequate management practices (without land-use control) in the areas surrounding the sampling points such as forestry, native fields, pastures, agriculture, and housing areas. As for the animal bioindicator (E. fetida), only points 1 (in the winter) and 5 (in the autumn) were toxic. Concerning mutagenicity, points 1 and 4 (in the spring), 1 and 2 (in the summer), and 3 (in the autumn) showed mutagenic effect on A. cepa meristematic cells, therefore only within the RVS-CP area. Overall, these results show that biomonitoring can be an ally of the residents of the RVS-CP area in controlling management practices, aiming to bring together economic support and conservation of resources, especially water.

Evaluation of the raw water quality: physicochemical and toxicological approaches

Environmental degradation has increased, mainly as a result of anthropogenic effects arising from population, industrial and agricultural growth. Water pollution is a problem that affects health, safety and welfare of the whole biota which shares the same environment. In Goiânia and metropolitan region, the main water body is the Meia Ponte River that is used for the abstraction of water, disposal of treated wastewater and effluents. In addition, this river receives wastewater from urban and rural areas. The aim in this present study was to evaluate the quality of raw water by some physical, chemical and toxicological tests. The physicochemical results found high levels of turbidity, conductivity, aluminum, phosphorus and metal iron, manganese, copper and lithium when compared to the standards of the Brazilian legislation. The values found of toxicity demonstrated a high degree of cytotoxicity and genotoxicity. Therefore, it was concluded that the Meia Ponte River has been undergoing constant environmental degradation, causing the poor quality of its waters. Thus, measures for the prevention and recovery should be adopted for the maintenance of the Meia Ponte River.

Nucleolar alterations are reliable parameters to determine the cytogenotoxicity of environmental pollutants

Pollution generated by deposition of industrial activity waste in the environment without due care can lead to serious environmental consequences. Bioassays in higher plants are means of understanding the cytogenotoxic effects of these substances. In the present work, Allium cepa L. was used as a model species to assess nucleolar changes induced by environmental pollutants. The substances used were Methyl Methane Sulfonate (MMS), cadmium (Cd), Spent Potliner (SPL) and the herbicide Atrazine. Water was used as a negative control. The silver-stained nucleolar organizer region (AgNOR) assay was used making it possible to evaluate how nucleolar parameters (number of nucleoli per nucleus and nucleoli area) behave when facing stress caused by such pollutants. The results obtained showed a variation in the observed parameters: an increase in the number of nucleoli in the treated cells and tendency to a reduction in nucleolar area, indicating that the tested pollutants may have impaired nucleolar activity. In addition, it was possible to establish a relationship between the behavior of the nucleolus with other changes as plantlet growth, cell proliferation, and DNA damage.

BMH-21 inhibits viability and induces apoptosis by p53-dependent nucleolar stress responses in SKOV3 ovarian cancer cells

The nucleolus is a stress sensor associated with cell cycle progression and apoptosis. Studies have shown that nucleolar stress is positively correlated with apoptosis in breast, prostate and lung cancer cells. However, the role and function of nucleolar stress in ovarian cancer has not been reported. In this study, we found that the nucleolar stress inducer BMH-21 inhibited viability of SKOV3 ovarian cancer cells in a dose-dependent manner. Furthermore, BMH-21 induced the expression of nucleolar stress marker proteins (nucleolin, nucleophosmin and fibrillarin) and promoted the nuclear export of these proteins. BMH-21 also decreased MDM2 proto-oncogene expression and increased protein levels of the tumor suppressor p53 and p53 phosphorylated at serine 15 (p‑p53‑Ser15), which contributed to increased expression of the downstream apoptosis-related protein BCL2 associated X (BAX) and activation of caspase-3. Taken together, these data provide the first reported evidence that induction of p53-dependent nucleolar stress by BMH-21 induces apoptosis in ovarian cancer. Our data suggest that nucleolar stress might be a pathway suitable for targeting in ovarian cancer.

Copper-induced root growth inhibition of Allium cepa var. agrogarum L. involves disturbances in cell division and DNA damage

Copper (Cu) is considered to be an indispensable microelement for plants. Excessive Cu, however, is toxic and disturbs several processes in the plant. The present study addressed the effects of ionic Cu (2.0 µM and 8.0 µM) on mitosis, the microtubule cytoskeleton, and DNA in root tip cells of Allium cepa var. agrogarum L. to better understand Cu toxicity on plant root systems. The results indicated that Cu accumulated in roots and that root growth was inhibited dramatically in Cu treatment groups. Chromosomal aberrations (for example, C-mitosis, chromosome bridges, chromosome stickiness, and micronucleus) were observed, and the mitotic index decreased during Cu treatments at different concentrations. Microtubules were one of the target sites of Cu toxicity in root tip meristematic cells, and Cu exposure substantially impaired microtubule arrangements. The content of α-tubulin decreased following 36 h of exposure to 2.0 µM or 8.0 µM of Cu in comparison with the control group. Copper increased DNA damage and suppressed cell cycle progression. The above toxic effects became more serious with increasing Cu concentration and prolonged exposure time.

Accumulation and cellular toxicity of aluminum in seedling of Pinus massoniana

BACKGROUND

Masson pine (Pinus massoniana) is one of the most important timber species with adaptable, fast growing, versatile advantages in southern China. Despite considerable research efforts, the cellular and molecular mechanisms of A1 toxicity and resistance in P. massoniana are still poorly understood. The effects of Al on uptake and translocation of Al and other minerals, cell division and nucleolus in P. massoniana were investigated.

RESULTS

The results indicated that Al accumulated mainly in the roots, and small amounts were transported to aboveground organs. In the presence of Al, the contents of Mg and Fe in stems increased and decreased in roots. Accumulation of Mn in the organs was inhibited significantly. Evidence from cellular experiments showed that Al had an inhibitory effect on the root growth at all concentrations (10⁻⁵ - 10⁻² M) used. Chromosome fragments, chromosome bridges, C-mitosis and chromosome stickiness were induced during mitosis in the root tip cells. Al induced the formation of abnormal microtubule (MT) arrays, consisting of discontinuous wavy MTs or short MT fragments at the cell periphery. MT organization and function of the mitotic spindle and phragmoplast were severely disturbed. The nucleolus did not disaggregate normally and still remained its characteristic structure during metaphase. Nucleolar particles containing argyrophilic proteins were accumulated and leached out from the nucleus to the cytoplasm. Evidence confirmed that these proteins contained nucleophosmin (B23), nucleolin (C23) and fibrillarin. Western immunoblot analysis revealed that the contents of three nucleolar proteins increased significantly.

CONCLUSION

Based on the information provided in this article, it is concluded that root tips of plants are the most sensitive organ to environmental stresses and the accumulation of Al ions primarily is in roots of P. massoniana, and small amounts of Al are transported to aboveground. Root apical meristems play a key role in the immediate reaction to stress factors by activating signal cascades to the other plant organs. Al induces a series of the cellular toxic changes concerning with cell division and nucleolus. The data presented above can be also used as valuable and early markers in cellular changes induced by metals for the evaluation of metal contamination.

Effects of lead on the morphology and structure of the nucleolus in the root tip meristematic cells of Allium cepa L

To study the toxic mechanisms of lead (Pb) in plants, the effects of Pb on the morphology and structure of the nucleolus in root tip meristematic cells of Allium cepa var. agrogarum L. were investigated. Fluorescence labeling, silver-stained indirect immunofluorescent microscopy and western blotting were used. Fluorescence labeling showed that Pb ions were localized in the meristematic cells and the uptake and accumulation of Pb increased with treatment time. At low concentrations of Pb (1-10 μM) there were persistent nucleoli in some cells during mitosis, and at high concentration (100 μM) many of the nucleolar organizing regions were localized on sticky chromosomes in metaphase and anaphase cells. Pb induced the release of particles containing argyrophilic proteins to be released from the nucleus into the cytoplasm. These proteins contained nucleophosmin and nucleolin. Pb also caused the extrusion of fibrillarin from the nucleus into the cytoplasm. Western blotting demonstrated the increased expression of these three major nucleolar proteins under Pb stress.