Root Meristems Of Allium Cepa Research Articles

The Study of the Mutagenic Effects of Zinc Phosphide (a Raticide) and of Mitomycin C (an Alkylating Agent) in the Presence of Activated Waters.

Our cytogenetical investigations performed on root meristems of Allium cepa and human lymphocytes, in which some 1421 metaphase cells have been analysed, using conventional staining methods as well as C- banding with barium hydroxide and staining using SCE (sister chromatid exchange), have indicated that chromosomal aberrations arose with a rate which paralleled the time in which the mutagen acted, both in control and in experimental variants, using activated waters.It has been concluded that the activated waters do not exhibit a protective effect and their stimulating actions on seeds germination and plant growth must be performed on other way which has nothing in connection with radioprotection or repair processes.

Chromotoxic Effects of One Fungicide(Dithane M-45) and Two Insecticides(Aldrex-30 and Metacid-50).

Treatment of different concentrations of Dithane M-45, Aldrex-30 and Metacid-50 showed positive chromotoxic effects in Allium cepa root meristem. Effects included high lethality for cell division, clumping, bridges, fragments, cytomixis, disturbed polarity etc. Such genotoxic effects warrants frequent use of these chemicals.

Cytological Effects of Indian Medicinal Plants I. Mitotic effects of leaf homogenate of Tylophora indica L. on Allium cepa.

In the present investigation the cytological effects of leaf homogenate of T. indica on Allium cepa root meristem were studied. The lower concentration of leaf homogenate caused mitoactivation while higher ones were mitodepressive. The leaf homogenate induced both physiological (stickiness of chromosomes, lagging chromosomes, hyperploid cells, etc) and clastogenic (chromosome breaks, ring chromosome and chromatin bridges) type of aberrations. Recovery of roots with 24 hr over water after treatment with leaf homogenate was not enough for normalisation of pattern of cell division.

The probability of G 1 cells to enter into S increases with their size while S length decreases with cell enlargement in Allium cepa

The distribution of cell surface area projection (cell size) has been measured at birth and at initiation of DNA synthesis in steady-state populations of Allium cepa root meristems. The conditional probability, P( I G 1 ) , that initiation occurs given that the event of being in g 1 also occurs has been estimated from these data. p( I G 1 ) was found to increase when cells became larger. The distribution of G 1 duration has been constructed from indicated cell size distributions. The absolute frequencies of G 1 times showed a maximum in the zone of cells with short G 1 periods; about 14% of cells appear to enter into S with G 1 ∼- 1 h. These results suggest that the increase of p( I G 1 ) was due to cell enlargement and not to cell aging. By comparing the cell size distribution at initiation of S and at the end of this period, a drastic reduction of cell size variability during DNA replication was observed and both curves were seen as rather similar in shape although they obviously had different modal points. These observations support that there is a negative correlation between the initiation size and the duration of genome duplication, and that cells which initiate DNA synthesis with the same size have a similar replication time. From this hypothesis, a plot of S duration versus cell size at initiation of this period was constructed by comparing the distributions of cell size at start and end of replication; this plot was also consistent with the existence of a negative correlation between cell initiation size and S length.

Ag-NOR proteins and rDNA transcriptional activity in plant cells.

In this work we used Allium cepa root meristem cells in actively growing conditions and under treatment with the protein synthesis inhibitors cycloheximide (CHM) and puromycin. Morphological and quantitative results indicate that these drugs induce dramatic alterations in nucleolar structure reflected by a decrease of nucleolar size, much more evident under treatment with CHM, and by segregation of its main components. Quantitative analysis shows a decrease in NOR-silver staining after treatment with CHM, whereas in cells treated with puromycin NOR-silver staining remains constant. Our results reveal a decrease in the Ag-NOR proteins under conditions of diminished cell activity, suggesting a direct relationship between the quantity of Ag-NOR proteins and transcriptional activity. Using two-dimensional gel electrophoresis and NOR-silver staining in gels, we have characterized some proteins corresponding to molecular weights of 28 and 31 KD and pI of approximately 5.2. After treatment with CHM, reactivity of these proteins against NOR-silver staining is diminished. By means of a morphological study, analysis of NOR-silver staining, and of anti-DNA and RNAse-gold labeling, we have tried an approach to the nucleolar organization in plant cells. Our results suggest that the fibrillar component shows a reticular distribution where fibrillar centers, as described in animal cells, are not distinguished.

The size of quiescent centre in roots of Allium cepa L. grown with ascorbic acid.

Following ascorbic-acid treatment a large number of quiescent centre cells undergo DNA synthesis and, at the same time, the cell proliferation in the entire root meristem of Allium cepa is stimulated. The effects of ascorbic acid on dividing cells in the meristem proper and on the quiescent centre are long-lasting since they are obtained in both short- and long-term experiments. Whatever the time of treatment with ascorbic acid and whatever the starting size of the quiescent centre (450 or 1000 cells), there is always a minimum number of quiescent centre cells (90-100) which remain in the G1 phase.

Effects of the leaf extract of Ricinus communis on Allium cepa.

The cellular damage, in Allium cepa root meristem, induced by the leaf extract of Ricinus communis was investigated. Total percentage of abnormalities increased correspondingly with increasing concentrations of the extract from 0.5% to 3% with complete arrest of mitosis at 4% of the extract. The major abnormalities were heavy pycnosis, clumping of chromosomes, chromosome fragmentation, lagging, unequal segregation at anaphase, chromosomebridge, spindle arrest resulting in the scattering of chromosomes, disintegration of nuclear and chromatin materials, nuclear budding and multinucleation. The abnormalities were discussed in detail.

Cell cycle- and differentiation stage-dependent variation of dUTPase activity in higher plant cells

Deoxyuridine triphosphate nucleotidohydrolase (dUTPase), a key enzyme in pyrimidine nucleotide metabolism, specifically hydrolyzes deoxyuridine triphosphate (dUTP) to deoxyuridine monophosphate and inorganic pyrophosphate. This enzyme activity has been studied in cellular extracts from Allium cepa root meristem cells with two specific aims: (i) to determine how the properties of the plant enzyme compare with those of dUTPase purified from other sources, and (ii) to analyze the relationship between dUTPase activity and cell proliferation and cell differentiation. Plant dUTPase is highly specific for dUTP, with an apparent Km of 6 microM, is highly sensitive to EDTA and it is probably a metalloenzyme. Our results demonstrate the presence of high levels of dUTPase in both resting and proliferating root meristem cells. The enzyme activity appears to be tightly regulated during the cell cycle. dUTPase activity increases at the G1/S boundary, remains high throughout S phase, and shows almost undetectable levels during G1 and G2. We have also found that dUTPase activity in differentiated cells, located in the mature portion of the root, is barely detectable. Altogether our results indicate that dUTPase activity is modulated by the proliferation rate and that this activity progressively decreases as cells initiate their differentiation program.

An experimental approach to nucleolar organization in plant cells: A morphological, cytochemical and quantitative study

ABSTRACT We have used morphological, cytochemical and immunocytochemical techniques, along with transcription inhibitors, to try to understand the nucleolar organization in Allium cepa root meristem cells. Our results reveal that the fibrillar component shows intense staining after using the NOR-silver technique, and gold particle labelling after incubation with DNase-gold and RNase-gold complexes. These different techniques reveal a reticular structure of the fibrillar component, supported by a central axis that is circular in transverse section. These structures are usually considered to be fibrillar centres, but we have called them clear areas, since we find in their interior neither Ag-NOR proteins nor labelling after incubation with nuclease-gold or anti-DNA. Taking into account the specific localization of the Ag-NOR proteins, our cytochemical and quantitative results, after applying NOR-silver staining in nucleoli of control cells and cells treated with transcription inhibitors, help us to a better understanding of the mechanisms of action of these drugs. Our results support a structural and functional role for the Ag-NOR proteins throughout the course of transcription.

Cytological effects of Phosalone on root meristem of Allium cepa L.

The cytological effects of the organophosphorus pesticide, Phosalone were studied on root meristems of A. cepa. Different periods of treatment were carried out using different concentrations (0.25, 0.5, 0.75 and 1.0%) of the pesticide. Subsequent Knop's recovery was done for 96 hours after treatments of upto 24 hours and 48 hours. The pesticide induced mitostatic effects on root meristem cells, the mitotic index gradually decreasing with the increase in concentration and time of treatment. Mutagenic effect was noticed with abnormalities like chromosome breakage and erosion, sticky bridges, laggrads, multipolarity, polyploidy, clumping and pycnosis. There was a slow rise in the mitotic index after recovery for 48 hours and 96 hours of 24 hours and 48 hours treatments respectively. The percentage of total chromosomal abnormalities was found to have decreased fairly in the recovery set of 96 hours of 48 hours direct treatment, the percentage of total chromosomal abnormalities was found to increase in concentrations 0.25% and 0.75% and slightly to decrease in concentrations 0.50% and 1.0% respectively. Material treated with 0.75% and 1.0% Phosalone for 48 hours, failed to show marked recovery with death of roots.

Influence of a Static Magnetic Field on Mitosis in Meristematic Cells ofAllium Cepa

The influence of static magnetic fields on mitosis and their cytogenetic effects were investigated in root meristems of Allium cepa. Five experiments were performed. Roots were excised from a bulb growing in a nutritive solution; some were exposed to a magnetic field and others were used as controls. In four experiments, mitotic and phase indices and frequencies of anaphase bridges, chromosome losts and apolar mitoses were compared between both groups. In another experiment, effects on cell birth rate were evaluated. The magnetic field did not change the mitotic index, but increases of the prophase and/or metaphase indices joined to decreases of the anaphase and telophase indices were found. Cell birth rate was also increased. Slight cytogenetic effects were observed. The results suggest that magnetic fields shorten the duration of the anaphase-telophase in Allium.

Cytological effects of fungal metabolites produced by fungi isolated from Egyptian poultry feedstuffs.

The cytogenetic effects of fungal metabolites produced by 113 strains belonging to 36 fungal species and isolated form 5 substrates of commercial poultry feedstuffs were tested for their effect on the growing root meristems of Allium cepa. The fungal metabolites of Paecilomyces canescens, Aspergillus fumigatus, Syncephalastrum racemosum, Aspergillus terreus and Mucor hiemalis strongly suppressed cell division. Metabolites from other strains had less effect on cell division but permitted the appearance of several abnormalities through different mitotic stages. In general, chromosomal aberrations were more obvious with metabolites of Aspergillus species, Mucor circinelloides and Cladosporium cladosporioides. The mutagenic effects produced by these fungal metabolites reflect the risk that might take place through the consumption of these contaminated feedstuffs.

Carbaryl—A selective genotoxicant

Mutagenic effects of carbaryl, a contact insecticide with slight systemic properties, have been investigated employing histidine reversion assay in Salmonella typhimurium strains and in vivo chromosomal aberrations in root meristems of Allium cepa. A detailed investigation revealed that carbaryl did not enhance significantly the frequency of histidine revertants in any of the strains of Salmonella i.e. frameshift mutagen tester (TA98), base pair substitution tester strain (TA1535) and ochre mutant strain (TA102). The supplementation with S9 mix did not have any appreciable effect. S14 prepared from wheat seedlings also did not enhance the reversion frequency significantly. However, carbaryl induced both clastogenic and physiological types of chromosomal aberration. The spectrum of chromosomal aberrations included c-mitosis, stickiness, vagrant chromosomes, polyploidy multi-polarity, delayed anaphases, end to end joining of chromosomes, chromosome breaks, ring chromosomes and anaphase bridges. The frequency of chromosomal aberrations was reduced by transferring the carbaryl treated bulbs to distilled water for 24 and 48 h. Similarly, recovery in the mitotic index was noticed by such transfer. The differences between the two assays may be attributed to differences in the metabolism of the test organisms.

Ascorbic acid‐induced progression of quiescent centre cells from G1 to S phase

summaryQuiescent centre cells, which are known to have their cycle extended mostly in G, and to divide rarely, art‐stimulated to undergo DNA synthesis in root meristems of Allium cepa L. by treatment with ascorbic acid. The effect of ascorbic acid is dramatic: 21% of all the cells in the quiescent centre remain in the G, phase while 79% enter S phase. From a mean value of 2204 × 103μ3 in water‐grown roots, the volume of the quiescent centre drops to a mean value of 167 × 103μ3 following treatment with ascorbic acid. These results indicate that ascorbic‐acid stimulates not only the activity of the quiescent centre cells but also cell proliferation in the entire root meristem. The rate of cell progression through the cycle may be related to cellular ascorbic acid content.

Relationship between resumption of rRNA transport into cytoplasm after cold treatment and progression through the cell cycle in root meristem cells

Experiments with 3H-uridine incorporation have shown that cold treatment inhibits rRNA transport from nucleoli to the cytoplasm. The rate of rRNA transport during recovery after cold treatment has been investigated in root meristems of Secale cereale, Vicia faba and Allium cepa. Results obtained by use of autoradiographic and cytophotometric methods indicate that in each species nucleoli lose half their radioactivity after the first 2.5–3.0 hr postincubation at 20°C. Concomitantly the number of cells entering the S phase and mitosis increases.

The effect of butyrate on cell cycle progression in Allium cepa root meristems

Sodium butyrate at 4 mM and above blocked cell proliferation in root meristems of Allium cepa L. bulbs. Cytophotometric determinations in asynchronously growing cells, as well as cycle kinetics in synchronous binucleate cells. indicated that blocking took place at mid‐G1 and at, or close to, the S/G2 border. Cell progression through S phase and mitosis was little affected. The cell cycle blockage induced by 6 mM butyrate was reversible when the drug was applied for periods of time not exceeding 12 h. Butyrate did not affect nucleic acid and protein synthesis activities, though its action on the cell cycle ressembled that produced by translation inhibitors.

Cytological effects of herbicides and insecticides on Allium cepa root meristems.

Cytological effects of two herbicides viz., asulum and MSMA and two insecticides viz., chlorpyriphos and endosulfan were tested on Allium cepa root meristems. One hour pulse treatments were given with test solutions at different concentrations and allowed to different recovery periods in Hoagland's nutrient solution.Among the test pesticides MSMA was observed to be the most effective clastogenic as well as turbagenic agent followed by endosulfan, chlorpyriphos and asulum respectively in that order.

Cytogenetic activities of some fungicides.

The effect of 4 concentrations containing 4, 20, 100 and 500 ppm a.i. of the two fungicides dithane and denmart applied for 4 and 24 h. on mitotic activity and chromosomes in root meristems of Allium cepa has been investigated. Both compounds inhibited mitosis and resulted in the accumulation of metaphase configurations. High concentrations of dithane gave rise to lower prophase frequency, whereas those of denmart reduced the frequency of both anaphase and telophase. Both compounds exerted a weak C-mitotic activity, but induced chromosomal stickiness, breaks and bridges in a considerable proportion of dividing cells. Denmart also induced chromosome lagging, binucleated and multinucleated cells and micronuclei. In general dithane was more effective in inhibting mitosis, whereas denmart produced higher amount of chromosomal abnormalities than dithane. The significance of the cytogenetic effects of both fungicides is discussed.

Genotoxic effects of some organophosphorus pesticides. III. In vivo chromosomal aberration bioassay in root meristems of Allium and Hordeum.

The genotoxic effects of three organophosphorus pesticides viz. ekatin, fenitrothion, phorate and MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) employing in vivo chromosomal aberration bioassay in root meristems of Allium and Hordeum have been investigated. Both physiological type aberrations like C-mitosis, despiralization, lagging chromosomes, multipolar cells as well as clastogenic effects like chromosome breaks, ring chromosome, chromatin bridges and micronuclei were induced by these pesticides. The order of radiomimetic potential was found to be phorate>fenitrothion>ekatin. The root meristem of Allium cepa was found to be more sensitive.

Regulation of G2 by cell size contributes to maintaining cell size variability within certain limits in higher plants.

The variability of (1) surface area projection (size) at which cells terminate DNA replication, (2) the area at which they initiate mitosis, (3) the area at which they divide, (4) the duration of G2, and (5) the duration of G2 plus mitosis (in fact, prophase + metaphase + anaphase) has been estimated in steady-state cell populations of Allium cepa root meristems. The coefficient of variation of cell area at termination of DNA synthesis was found to be 14% while the coefficient of variation of cell area at mitosis initiation was 13%. As there is also a substantial variability of G2 (the coefficient of variation was estimated to be 38%), the combination of these data indicates that cell size regulation of G2 contributes to maintaining cell size variability (and therefore DNA concentration) within certain limits. Mitosis also varies but less than G2 (the coefficient of variation of G2 + mitosis was found to be 31%). As the coefficient of variation of cell area at division (14%) is hardly larger than the coefficient of variation of cell area at initiation of mitosis, it can be suggested that coordination between cell size and mitosis duration helps to avoid a significant increase in the variability of cell size at the end of the division cycle.