Root Apical Cells Research Articles

Plant chromosome polytenization contributes to suppression of root growth in high polyploids.

Autopolyploidization, which refers to a polyploidization via genome duplication without hybridization, promotes growth in autotetraploids, but suppresses growth in high polyploids (autohexaploids or auto-octoploids). The mechanism underlying this growth suppression (i.e. 'high-ploidy syndrome') has not been comprehensively characterized. In this study, we conducted a kinematic analysis of the root apical meristem cells in Arabidopsis thaliana autopolyploids (diploid, tetraploid, hexaploid, and octoploid) to determine the effects of the progression of genome duplication on root growth. The results of the root growth analysis showed that tetraploidization increases the cell volume, but decreases cell proliferation. However, cell proliferation and volume growth are suppressed in high polyploids. Whole-mount fluorescence in situ hybridization analysis revealed extensive chromosome polytenization in the region where cell proliferation does not usually occur in the roots of high polyploids, which is likely to be at least partly correlated with the suppression of endoreduplication. The study findings indicate that chromosome polytenization is important for the suppressed growth of high polyploids.

Cytogenotoxic effects of 3-epicaryoptin in Allium cepa L. root apical meristem cells.

Diterpenoid 3-epicaryoptin (C26H36O9) is abundant in the leaves of Clerodendrum inerme, a traditionally used medicinal plant, and has insect antifeedant activities. Here, we aim to explore the cytogenotoxic effects of compound 3-epicaryoptin in Allium cepa root apical meristem cells. 3-epicaryoptin (concentrations of 100, 150, and 200µgmL-1) and the standard compound colchicine (200µgmL-1) were applied to A. cepa roots for 2, 4, and 4 + 16h (4-h treatment followed by 16-h recovery). Cytogenotoxicity was analyzed by studying the root growth retardation (RGR), mitotic index (MI), and chromosomal aberrations. The result showed statistically significant (p < 0.01), concentration-dependent RGR effects of 3-epicaryoptin treatment compared with the negative control. A study of cell frequency in different phases of cell division observed a significant (p < 0.001) increase in the metaphase cell percentage (66.2 ± 0.58%, 150µgmL-1), which subsequently caused an increase in the frequency of MI (12.29 ± 0.34%, 150µgmL-1) at 4h of 3-epicaryoptin treatment and that was comparable with the colchicine action. The cytological study revealed that the 3-epicaryoptin treatment could induce different types of chromosomal abnormalities, such as colchicine-like metaphase, vagrant chromosomes, sticky chromosomes, anaphase bridge, lagging chromosomes, multipolar anaphase-telophase, and an increased frequency of micronuclei and polyploid cells. These findings indicate that 3-epicaryoptin is cytogenotoxic, and thus, C. inerme should be used with caution in traditional medicine.

From stress to responses: aluminium-induced signalling in the root apex.

Aluminium (Al) toxicity is one of the major constraints for crop growth and productivity in most of the acid soils worldwide. The primary lesion of Al toxicity is the rapid inhibition of root elongation. The root apex, especially the transition zone (TZ), has been identified as the major site of Al accumulation and injury. The signalling, in particular through phytohormones in the root apex TZ in response to Al stress, has been reported to play crucial roles in the regulation of Al-induced root growth inhibition. The binding of Al in the root apoplast is the initial event leading to inhibition of root elongation. Much progress has been made during recent years in understanding the molecular functions of cell wall modification and Al resistance-related genes in Al resistance or toxicity, and several signals including phytohormones, Ca2+, etc. have been reported to be involved in these processes. Here we summarize the recent advances in the understanding of Al-induced signalling and regulatory networks in the root apex involved in the regulation of Al-induced inhibition of root growth and Al toxicity/resistance. This knowledge provides novel insights into how Al-induced signals are recognized by root apical cells, transmitted from the apoplast to symplast, and finally initiate the defence system against Al. We conclude that the apoplast plays a decisive role in sensing and transmitting the Al-induced signals into the symplast, further stimulating a series of cellular responses (e.g. exudation of organic acid anions from roots) to adapt to the stress. We expect to stimulate new research by focusing on the signalling events in the root apex in response to Al stress, particularly taking into consideration the signal transduction between the meristem zone, TZ, and elongation zone and the apoplast and symplast.

Reference genes for quantitative Arabidopsis single molecule RNA fluorescence in situ hybridization.

Subcellular mRNA quantities and spatial distributions are fundamental for driving gene regulatory programmes. Single molecule RNA fluorescence in situ hybridization (smFISH) uses fluorescent probes to label individual mRNA molecules, thereby facilitating both localization and quantitative studies. Validated reference mRNAs function as positive controls and are required for calibration. Here we present selection criteria for the first set of Arabidopsis smFISH reference genes. Following sequence and transcript data assessments, four mRNA probe sets were selected for imaging. Transcript counts per cell, correlations with cell size, and corrected fluorescence intensities were all calculated for comparison. In addition to validating reference probe sets, we present sample preparation steps that can retain green fluorescent protein fluorescence, thereby providing a method for simultaneous RNA and protein detection. In summary, our reference gene analyses, modified protocol, and simplified quantification method together provide a firm foundation for future quantitative single molecule RNA studies in Arabidopsis root apical meristem cells.

Genotoxic Efficacy of Fruit Extract of Cestrum diurnum Using Allium cepa Assay

Onion (Allium cepa) root apical meristem cells were treated, for various exposure time, with various concentrations (0.1-0.4%) of fruit extract of Cestrum diurnum so as to assess its cyto-genotoxic potential. The treated root tips were fixed, stained and squashed; and mitotic anomalies observed under a light microscope. The micro-nuclei (MN) were observed at interphase and MN percentage calculated. The fluctuations in mitotic index (MI) and abnormality percentage were statistically co-related through ANOVA analyses with exposure periods and concentrations as random variables. Phytochemical analyses of fruit extract of C. diurnum were performed using standard methods. The MI was significantly reduced by all the treatments. Increase in concentration and exposure time significantly increased the anomaly percentage and frequency of MN induction as compared to the control. Phytochemical analysis revealed the presence of alkaloids, terpenoids, phenolic compounds, tannins, phytosterols, volatile oils, and saponins as secondary metabolites. C. diurnum fruit extract showed promising cyto-genotoxic effects on A. cepa root apical meristem cells. However, caution is essential for the safe administration of herbal preparations.

Cytotoxic and Micronuclei Inducing Effects of Petroleum Ether Fraction of Leaf Aqueous Extract of &lt;i&gt;Clerodendrum viscosum&lt;/i&gt; Vent. in &lt;i&gt;Allium cepa&lt;/i&gt; Root Tip Cells

Clerodendrum viscosum is a traditionally used medicinal plant. The present study aimed to analyze a detailed cytotoxic effect of the nonpolar petroleum ether fraction (AQPEF) of leaf aqueous extract of C. viscosum Vent. (LAECV) in Allium cepa root tip cells. The LAECV was fractionated with petroleum ether and tested for A. cepa toxicity at early hours (2 and 4 h treatment) at concentrations 0, 50, 100, 150 and 200 {micro}g mL-1. The highest aberrant cell percentage (10.45{+/-}0.46%) was scored from 150 {micro}g mL-1 followed by100 {micro}g mL-1 (8.75{+/-}0.26%) concentration at 4 h treated samples. The AQPEF treatment induced a significant (p<0.0001) increase in micronuclei frequency; 4.31{+/-}0.33, 5.08{+/-}0.13, 5.05{+/-}0.22 and 3.05{+/-}0.37% respectively at concentrations 50, 100, 150, and 200 {micro}g mL-1. The highest polyploid frequency (20.14{+/-}0.68 %) induced with 100 {micro}g mL-1 of AQPEF at 16 h recovery. 150 {micro}g mL-1 is the most effective concentration of AQPEF to decipher its activity similar to colchicine (150 {micro}g mL-1). In summary, the present study indicates petroleum ether is suitable for extraction of the active phytochemicals of LAECV having cytotoxic effects on A. cepa root tip cells. The AQPEF has colchicine like micronuclei, polyploidy, and mitotic abnormality inducing potentials in A. cepa root apical meristem cells.

The cytological and molecular investigation of the toxic effects of the herbicide Roundup on Cucumis sativus

In the current study, it is aimed to investigate the toxic effects of a widely used herbicide Roundup containing active ingredient glyphosate on cucumber (Cucumis sativus) by cytological and molecular investigation. Three different concentrations (0.6%, 1.2% and 2.4%) of Roundup were applied to cucumber for 48 and 72 hours. At the end of the application procedure, the germination percentage, mean root length, mitotic frequency and mitotic abnormalities, RAPD profiles and Genomic template stability (GTS) were determined in root apical meristematic cells. For RAPD PCR analysis 10 RAPD primers were used, 8 of them produced band patterns and it was found that 5 RAPD primers among them produced unique polymorphic band patterns and subsequently were used to produce a total of 24 bands. Observed percentage of polymorphism was 26%. The changes in RAPD profiles after Roundup treatment was included variations as gain and/or loss of bands compared with the control group. Genomic template stability changed in RAPD profiles at various Roundup concentrations.

AtNUF2 modulates spindle microtubule organization and chromosome segregation during mitosis.

The NDC80 complex is a conserved eukaryotic complex composed of four subunits (NUF2, SPC25, NDC80, and SPC24). In yeast and animal cells, the complex is located at the outer layer of the kinetochore, connecting the inner layer of the kinetochore and spindle microtubules (MTs) during cell division. In higher plants, the relationship of the NDC80 complex with MTs is still unclear. In this study, we characterized the biological function of AtNUF2, a subunit of the Arabidopsis NDC80 complex. We found that AtNUF2 is widely expressed in various organs, especially in different stages of embryonic development. It was verified that AtNUF2 co-localized with α-tubulin on MTs during mitosis by immunohistochemical assays. Mutation of AtNUF2 led to severe mitotic defects, not only in the embryo and endosperm, but also in seedlings, resulting in seed abortion and stagnating seedling growth. Furthermore, the biological function of AtNUF2 was studied using partially complemented nuf2-3/-DD45;ABI3pro::AtNUF2 (nuf2-3/-DA ) seedlings. The chromosome bridge and lagging chromatids occurred in nuf2-3/-DA root apical meristem cells, along with aberration of spindle MTs, resulting in blocked root growth. Meanwhile, the direct binding of AtNUF2 and AtSPC25 to MTs was determined by an MT co-sedimentation assay invitro. This study revealed the function of AtNUF2 in mitosis and the underlying mechanisms, modulating spindle MT organization and ensuring chromosome segregation during embryo, endosperm, and root development, laying the foundation for subsequent research of the NDC80 complex.

Anti-proliferating activity of some toxic and medicinal plants used by Wancho tribe of Arunachal Pradesh, India

Medicinal plants extend to show an imperative role in the rural healthcare system of developing countries, where herbal medicine has a continuous history of long use. Field studies were conducted following standard ethnobotanical techniques to collect information on the use of toxic and medicinal plants used by the Wancho tribe of Arunachal Pradesh. Vigna radiata was used as a plant model in this study to investigate the antiproliferative property of selected medicinal plant extracts. Green gram seedling root apical meristem cells were used to determine the inhibition of germination and slow growth. Different concentrations of plant extract (20, 50, 250 and 500 µg/ml) were treated in a test tube containing the green gram seeds (n=5) on time dependent manner. Colchicine (20 mg/ml) was used as a standard drug for the growth retardation of green gram seedlings, while the distilled water group served as negative control. Germination test of Vigna radiata L. was performed according to ISTA (International Rules for Seed Testing) rules. The present study concludes that the methanolic plant extracts of all the collected plants significantly inhibited the rate of seed germination and seedling growth at dose dependent manner. It signifies that the use of Phlogacanthus parviflorus and Mikania micrantha in high concentrations may be potentially therapeutic for inhibiting the cell cycle in eukaryotic organisms.

Identification of putative origin of Iris pumila L. karyotype

Aim. The study was aimed at cytogenetic analysis of Iris pumila, I. attica, and I. pseudopumila, comparative study of the karyotypes of these species, as well as identification of putative origin of I. pumila karyotype. Methods. Cytogenetic analysis of root apical meristem, determination of chromosome number in mitotic metaphase plates, anaphase analysis. Results. The chromosome numbers observed were 2n=32 for I. pumila plants from different localities in Ukraine and 2n=16 for I. attica and I. pseudopumila plants from Greece and Italy, respectively. Some of the plants were mixoploids, the smallest proportion of mixoploids was in I. pseudopumila (10.9%) and the largest in I.pumila from all studied populations (60-80%). Anaphase analysis showed the presence of chromosomal aberrations in 2.6% of cells in roots of I. pseudopumila seedlings. The highest level of structural chromosomal aberrations (9.2%) was found in root apical meristem cells of I. pumila seedlings. Conclusions. The chromosome number was established as 2n=32 for I.pumila plants and 2n=16 for I. attica and I. pseudopumila plants. The high level of mixoploidy (60–80% of mixoploid plants) and anaphase chromosomal aberrations (up to 9.2%) was found in apical meristem of I. pumila seedlings. The amphidipiloid nature of I. pumila was established; the karyotype of the species could be formed as a result of a combination of chromosome sets from hypothetical ancestral species I. attica and I. pseudopumila.&#x0D; Keywords: Iris pumila L., Iris attica Boiss. &amp; Heldr., Iris pseudopumila Tineo, chromosome number, amphidiploid, mixoploidy.

Chloroplast-Localized Protoporphyrinogen IX Oxidase1 Is Involved in the Mitotic Cell Cycle in Arabidopsis.

Protoporphyrinogen IX oxidase1 (PPO1) catalyzes the oxidation of protoporphyrinogen IX to form protoporphyrin IX in the plastid tetrapyrrole biosynthesis pathway and is also essential for plastid RNA editing in Arabidopsis thaliana. The Arabidopsis ppo1-1 mutation was previously shown to be seedling lethal; however, in this study, we showed that the heterozygous ppo1-1/+ mutant exhibited reproductive growth defects characterized by reduced silique length and seed set, as well as aborted pollen development. In this mutant, the second mitotic division was blocked during male gametogenesis, whereas female gametogenesis was impaired at the one-nucleate stage. Before perishing at the seedling stage, the homozygous ppo1-1 mutant displayed reduced hypocotyl and root length, increased levels of reactive oxygen species accumulation and elevated cell death, especially under light conditions. Wild-type seedlings treated with acifluorfen, a PPO1 inhibitor, showed similar phenotypes to the ppo1-1 mutants, and both plants possessed a high proportion of 2C nuclei and a low proportion of 8C nuclei compared with the untreated wild type. Genome-wide RNA-seq analysis showed that a number of genes, including cell cycle-related genes, were differentially regulated by PPO1. Consistently, PPO1 was highly expressed in the pollen, anther, pistil and root apical meristem cells actively undergoing cell division. Our study reveals a role for PPO1 involved in the mitotic cell cycle during gametogenesis and seedling development.

АНЕУПЛОИДИЯ ПРИ СКРЕЩИВАНИЯХ FRAGARIA × ANANASSA DUCH. × POTENTILLA ANSERINA L.

Taxonomic relationship between Fragaria L. and Potentilla L. representatives is actively discussed today in the context of phylogenetic analysis by molecular markers and hybridization results. According to the data published, crosses between F. х ananassa Duch. (8x) х P anserina L. (4x) produce haploids, parthenogenetic seedlings (8x) and aneuploids. No viable progenies have been obtained. Our long-standing research in F. х ananassa х P anserina hybridization was targeted at obtaining 8x agamospermic progenies and studying their genetic variability. In one of the experiments, when P. anserina pollen was used in crosses, along with 2n = 56 matromorphous seedlings, an absolutely sterile seedling No. 89-3 was produced, which insignificantly differed from F. х ananassa by its phenotype, thus matching the Fragaria type. Chromosome number in root apical meristem cells appeared to be 2n = 6x = 42, being intermediate between the crossed parental forms. The absence of any morphological traits of the pollen parent (P. anserine ) showed the need to make molecular genetic analysis in order to prove its hybrid origin. Methods. To trace its origin, the techniques of Polygalacturonase Inhibitor Proteins (PGIPs) PCR and Amplified Fragment Length Polymorphism (AFLP) PCR analysis of internal transcribed spacer (ITS) were applied to F. х ananassa х P anserina seedlings. The study showed that seedling No. 89-3 and the parthenogenetic progenies are identical and correspond to the mother form (F. х ananassa ). Hence, eliminating 14 chromosomes of F. х ananassa and 14 chromosomes of P. anserina during the first divisions of a zygote (2n = 70) should be considered as the most likely scenario for the 2n = 42 chromosome number development in the studied No. 89-3, so the genetic material of P. anserina was absent in the embryo’s somatic cells. Development of aneuploids and parthenogenetic seedlings (8x) in the crosses of F. х ananassa х P anserina makes it possible to study additional mechanisms of variability appearing in the Fragaria genus. Reproductive isolation of an aneuploid, due to its complete sterility, limits its use solely to a cover plant’s role. In addition, its herbage biomass may be used for making fermented tea.

Methyl jasmonate enhances salt tolerance of almond rootstocks by regulating endogenous phytohormones, antioxidant activity and gas-exchange

The effects of methyl jasmonate (MeJA) foliar application (0, 0.025, 0.050 and 0.075 mM) on the growth and physiological responses of two almond rootstocks (GF677 and bitter almond) exposed to various concentrations of NaCl in irrigation water (0, 50, 100 and 150 mM) were evaluated. 60 days after salt stress exposure, the mitotic index of root apical meristem cells as well as shoot and root growth, activity of main antioxidant enzymes, gas exchange parameters and contents of cytokinins and ABA were determined. Salt stress decreased the plants’ growth, particularly at higher levels. Application of MeJA in optimal concentrations of 0.025 to 0.05 mM alleviated the adverse effect of salt stress by increasing the photosynthetic rate, activity of antioxidant enzymes (APX, SOD and POX), root and shoot dry mass, as well as cell membrane integrity. Furthermore, MeJA application brought about a two-fold increase in the concentration of leaf cytokinins. This reposition of cytokinins was due to restriction of both the activity of cytokinin oxidase and gene expression of this enzyme. The MeJA mitigating effect on the growth of salt-stressed plants could be a result of the inhibition of cytokinin decline under salt stress. The results revealed the effective impact of endogenous cytokinins in protective and growth improvement effects of MeJA on almond rootstocks under salt stress.

Sanguinarine-induced oxidative stress and apoptosis-like programmed cell death(AL-PCD) in root meristem cells of Allium cepa

A vast number of studies on plant cell systems clearly indicate that various biotic and abiotic stresses give rise to the uncontrolled increase in the level of reactive oxygen species (ROS). Excess concentrations of ROS result in damage to proteins, lipids, carbohydrates, and DNA, which may lead, in consequence, to the apoptotic cell death. The current study investigates the effects of sanguinarine (SAN), a natural alkaloid derived from the roots of Sanguinaria canadensis, on root apical meristem cells of Allium cepa. It is shown that SAN treatment generated large amounts of hydrogen peroxide (H2O2) and superoxide anion (O2·−). Oxidative stress induced in SAN-treated cells was correlated with DNA fragmentation, formation of micronuclei (MN), altered and ‘degenerated’ chromatin structures characteristic of apoptosis-like programmed cell death (AL-PCD). The experiments with SAN + MG132 (a proteasome inhibitor engaged in Topo II-mediated formation of cleavable complexes) and SAN + ascorbic acid (AA; H2O2 scavenger) seem to suggest, however, that the high level of H2O2 is not the only factor responsible for changes observed at the chromatin level and for the consequent cell death. Our findings imply that Topo II-DNA covalent complexes and 26S proteasomes are also involved in SAN-induced DNA damage.

Arabidopsis protein disulfide isomerase-8 is a type I endoplasmic reticulum transmembrane protein with thiol-disulfide oxidase activity.

BackgroundIn eukaryotes, classical protein disulfide isomerases (PDIs) facilitate the oxidative folding of nascent secretory proteins in the endoplasmic reticulum by catalyzing the formation, breakage, and rearrangement of disulfide bonds. Terrestrial plants encode six structurally distinct subfamilies of PDIs. The novel PDI-B subfamily is unique to terrestrial plants, and in Arabidopsis is represented by a single member, PDI8. Unlike classical PDIs, which lack transmembrane domains (TMDs), PDI8 is unique in that it has a C-terminal TMD and a single N-terminal thioredoxin domain (instead of two). No PDI8 isoforms have been experimentally characterized to date. Here we describe the characterization of the membrane orientation, expression, sub-cellular localization, and biochemical function of this novel member of the PDI family.ResultsHistochemical staining of plants harboring a PDI8 promoter:β-glucuronidase (GUS) fusion revealed that the PDI8 promoter is highly active in young, expanding leaves, the guard cells of cotyledons, and in the vasculature of several organs, including roots, leaves, cotyledons, and flowers. Immunoelectron microscopy studies using a PDI8-specific antibody on root and shoot apical cells revealed that PDI8 localizes to the endoplasmic reticulum (ER). Transient expression of two PDI8 fusions to green fluorescent protein (spGFP-PDI8 and PDI8-GFP-KKED) in leaf mesophyll protoplasts also resulted in labeling of the ER. Protease-protection immunoblot analysis indicated that PDI8 is a type I membrane protein, with its catalytic domain facing the ER lumen. The lumenal portion of PDI8 was able to functionally complement the loss of the prokaryotic protein foldase, disulfide oxidase (DsbA), as demonstrated by the reconstitution of periplasmic alkaline phosphatase in Escherichia coli.ConclusionThe results indicate that PDI8 is a type I transmembrane protein with its catalytic domain facing the lumen of the ER and functions in the oxidation of cysteines to produce disulfide bonds. It likely plays a role in folding newly-synthesized secretory proteins as they translocate across the ER membrane into the lumen. These foundational results open the door to identifying the substrates of PDI8 to enable a more thorough understanding of its function in plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0869-2) contains supplementary material, which is available to authorized users.

Gen dan QTL Pengendali Toleransi Tanaman terhadap Keracunan Aluminium dan Aplikasinya untuk Pemuliaan Tanaman di Indonesia

&lt;p&gt;Genetic knowledge of loci controlling Al toxicity tolerance is the key for a successful breeding program in developing Al&lt;br /&gt;tolerant cultivars. Tolerance level of crop plants to Al toxicity is genetically controlled. The gene inheritance pattern is mainly&lt;br /&gt;resulted from intensive studies of cereal crops, such as wheat, sorghum, maize, and rice. The trait can be controlled by a&lt;br /&gt;single dominant gene, a single dominant gene with many alleles, a pair of dominant genes, or by many genes (QTL). The&lt;br /&gt;majority of the Al tolerance genes identified so far belongs to two independent groups of gene families, i.e. aluminumactivated&lt;br /&gt;malate transporter (ALMT) and multidrug and toxic compound extrusion (MATE), both encoding transport proteins&lt;br /&gt;involved in Al-activated organic acid release, mainly citrate and malate. The variations in Al toxicity tolerance phenotypes are&lt;br /&gt;strongly correlated with the expressions of such genes in the root apical cells. Many Al tolerance QTLs have been mapped in&lt;br /&gt;the genomes of various crop species and were found to be colocated with the ALMT and MATE genes. The genetic maps of&lt;br /&gt;the Al tolerance genes and QTLs facilitate breeding programs for developing Al-tolerant cultivars through marker-assisted&lt;br /&gt;breeding methods. Al tolerance genes that have been isolated from genetically unrelated species can be used in genetic&lt;br /&gt;transformation studies of crop genotypes sexually incompatible to the gene source genotypes. The application of these&lt;br /&gt;molecular breeding methods expedites breeding programs to develop crop cultivars tolerance to Al toxicity and acid soils.&lt;br /&gt;Genomic technologies by using next-generation sequencing and high-throughput genotyping system accelerate Al toxicity&lt;br /&gt;tolerance gene and QTL discoveries of various crop species. The modern genomic technologies also facilitate more&lt;br /&gt;comprehensive PGR characterization and utilization to accelerate identification and isolation of the Al tolerance genes and&lt;br /&gt;QTLs to be used in a more comprehensive breeding program to support national food self sufficiency and food security&lt;br /&gt;programs.&lt;/p&gt;

СРАВНИТЕЛЬНЫЙ АНАЛИЗ ЧАСТОТЫ ЦИТОГЕНЕТИЧЕСКИХ ЭФФЕКТОВ В АПИКАЛЬНОЙ МЕРИСТЕМЕ КОРЕШКОВ ПРОРОСТКОВ СОРТОВ ЯРОВОГО ЯЧМЕНЯ (HORDEUM VULGARE L.), КОНТРАСТНЫХ ПО УСТОЙЧИВОСТИ К СВИНЦУ

Cell division activity, frequencies and spectra of cytogenetical abnormalities were studied in the root apical meristem cells of spring barley seedlings ( Hordeum vulgare L.). Comparative analysis of aberration frequencies in cells of most sensitive or tolerant barley cultivars was made. Sensitive and tolerant cultivars of spring barley were chosen by testing of lead influence on 100 barley cultivars from the VIR collection. Significant differences between groups of sensitive and tolerant cultivars were shown in indexes received on intact seedlings: frequencies of aberrant cells (FAC), frequency of cytogenetical abnormalities on a dividing cell (FADC), frequency of cytogenetical disturbances on a cell with cytogenetical abnormalities (FAAC). Mechanisms of tolerance to lead and HM were discussed.

Localization sites of nuclear envelope SUN2-like proteins in root meristem cells of Allium cepa under hydroxyurea-induced DNA replication stress

Regardless of the DNA replication stress induced by low concentration of hydroxyurea (HU), root apical meristem cells of Allium cepa keep growing, and some of them override the DNA damage checkpoint mechanisms initiating either premature or an abnormal mitotic chromosome condensation. Prolonged incubation of onion seedlings with HU results in an increased level of immunodetectable proteins sharing epitopes with SUN2, one of the highly conserved elements linking nuclear envelope (NE) to the cyto- and nucleoskeletal structures. In addition to NE, phragmoplast and cell plate, our observations extend an array of subcellular compartments at which SUN2-like proteins (SUN2-LPs) are localized. These include cortical preprophase band of microtubules, centromeric regions of ana- and telophase chromosomes, and nuclear bodies (SUN2-NBs) polarly localized in interphase nuclei according to Rabl’s configuration. SUN2-NBs (distinct from fibrillarin-rich Cajal bodies) colocalize with late-replicating areas of heterochromatin and are thought to represent clustered centromeres. Three-dimensional spatial analysis of SUN2-NBs suggests their connections with NE. An enhanced expression and additional localization sites of SUN2-LPs may be correlated with a considerable reprogramming of cellular functions triggered in response to prolonged HU treatment.

The effects of anti-DNA topoisomerase II drugs, etoposide and ellipticine, are modified in root meristem cells of Allium cepa by MG132, an inhibitor of 26S proteasomes

DNA topoisomerase II (Topo II), a highly specialized nuclear enzyme, resolves various entanglement problems concerning DNA that arise during chromatin remodeling, transcription, S-phase replication, meiotic recombination, chromosome condensation and segregation during mitosis. The genotoxic effects of two Topo II inhibitors known as potent anti-cancer drugs, etoposide (ETO) and ellipticine (EPC), were assayed in root apical meristem cells of Allium cepa. Despite various types of molecular interactions between these drugs and DNA-Topo II complexes at the chromatin level, which have a profound negative impact on the genome integrity (production of double-strand breaks, chromosomal bridges and constrictions, lagging fragments of chromosomes and their uneven segregation to daughter cell nuclei), most of the elicited changes were apparently similar, regarding both their intensity and time characteristics. No essential changes between ETO- and EPC-treated onion roots were noticed in the frequency of G1-, S-, G2-and M-phase cells, nuclear morphology, chromosome structures, tubulin-microtubule systems, extended distribution of mitosis-specific phosphorylation sites of histone H3, and the induction of apoptosis-like programmed cell death (AL-PCD). However, the important difference between the effects induced by the ETO and EPC concerns their catalytic activities in the presence of MG132 (proteasome inhibitor engaged in Topo II-mediated formation of cleavage complexes) and relates to the time-variable changes in chromosomal aberrations and AL-PCD rates. This result implies that proteasome-dependent mechanisms may contribute to the course of physiological effects generated by DNA lesions under conditions that affect the ability of plant cells to resolve topological problems that associated with the nuclear metabolic activities.

Morphological and Anatomical Effects of the Herbicide Roundup onZea mays(Poaceae)

The toxicity of a widely used herbicide Roundup, which contains the active ingredient glyphosate, on sweet corn (Zea mays) was investigated. After the determination of EC50 value for root growth, three different concentrations as low (4 ml/L), medium (8 ml/L) and high dose (16 ml/L) were applied to plant samples for 48 and 72 h. At the end of the application period, samples were comparatively studied in terms of their root and leaf anatomy, the upper and lower surface of leaf stomata indexes as well as chlorophyll contents to obtain morphological and anatomical information. Each concentration of glyphosate caused severe toxic effects on Zea mays cells and the strongest toxic effect was observed at the concentration level of 16 ml/L. At the end of the application procedure, the measurements of the parts of the Z.mays root treated with Roundup, the upper and lower surface of leaf stomata indexes, chlorophyll and total carotenoid concentrations were determined in root apical meristematic cells by using squashing techniques.