Effect of cisplatin on Allium cepa root meristem cells

Allium cepa root growth was retarded by cisplatin treatment in a dose-dependent manner. A decrease in the mitotic index (MI) and an increase in the number of interphase cells was seen in cisplatin treated root tips. An increase in the frequency of abnormal mitoses and chromosomal aberrations was also observed in cisplatin treated groups which indicates its genotoxic effect on plant cells. The endogenous glutathione (GSH) level in the root tips decreased significantly after cisplatin treatment which may favour its increased interaction with cellular DNA thereby developing enhanced chromosomal aberrations and affecting cell divisions and root growth. It is suggested that the decrease in endogenous GSH may be related to the development of cisplatin-mediated genotoxic effects in plants.     

Effect of onion (Allium cepa) root exudates on the hyphal growth of Gigaspora margarita

 The effect of root exudates from onions differing in P status on spore germination and hyphal growth of arbuscular mycorrhizal fungi was investigated. Onion (Allium cepa) was grown in solution culture at different phosphorus concentrations (0, 0.1, 1.0, 8.0 and 24.0 mg P l^–1) and root exudates were collected. When spores of the arbuscular mycorrhizal fungus, Gigaspora margarita were incubated with these root exudates, spore germination was only slightly affected but hyphal growth was greatly affected, particularly with exudates from P-deficient plants. This suggests that the P nutrition of host plants influences the composition of root exudates and thereby the hyphal growth of arbuscular mycorrhizal fungi. Accepted: 25 June 1995     

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

Sodium butyrate at 4 m M 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 m M 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.     

Cytotoxic effect of citrinin on relative division rate of Allium cepa root cells

Effect of different doses of citrinin, the secondary metabolite of Penicillium citrinum Thom, was investigated on Allium cepa root cells. A marked decrease in mitotic index was observed with the increased concentration of toxin. In controls the mitotic index was 16·2 which at a concentration of 400 ppb was reduced to the level of 4·7. Besides a decrease in mitotic index, several cytological abnormalities were also found, such as chromosome breakage, polyploidy, anaphase bridge, laggard, etc.     

Genotoxicity of five food preservatives tested on root tips of Allium cepa L

The effects of the food preservatives sodium benzoate (SB), boric acid (BA), citric acid (CA), potassium citrate (PC) and sodium citrate (SC) have been studied on root tips of Allium cepa L. Roots of A. cepa were treated with a series of concentrations, ranging from 20 to 100 ppm for 5, 10 and 20 h. The results indicate that these food preservatives reduced mitotic division in A. cepa compared with the respective control. Mitotic index values were generally decreased with increasing concentrations and longer treatment times. Additionally, variations in the percentage of mitotic stages were observed. The total percentage of aberrations generally increased with increasing concentrations of these chemicals and the longer period of treatment. Different abnormal mitotic figures were observed in all mitotic phases. Among these abnormalities were anaphase bridges, C-mitosis, micronuclei, lagging, stickiness, breaks and unequal distribution.     

Developmental profile of intracellular compatments during Allium cepa root cell germination

The efflux kinetics of ⁸⁶Rb from 24 hr preloaded Allium cepacv. Evergreen Long White Bunching root tip cells through thefirst 120 hr of germination have been documented. Estimatesof the percent of isotope, the calculated amount present andthe halftime of efflux of the three root cell compartments presentwere made. Of the total isotope present the % in the vacuoledecreased from maxima of 64% to 40% with germination time, whilethe % of the isotope in the cytoplasm remained uniform near39%. The free space increased maximally throughout germinationto 20% by 120 hr. Rb content, based on specific activity calculations,of the slowest, intermediate and fastest compartments was seento rise from low levels at 52 hr germination toward maximalvalues by 96 hr. Speculation as to when a germinating root becomesfunctionally mature was attempted by comparing the times ofonset of major macromolecule synthesis (DNA, RNA, protein) tothat of maximal Rb content. Stable mitotic and DNA syntheticindices occurred at the 10 mm (72 hr) stage with the initiationof major macromolecules syntheses occurring prior to 2 mm (40hr). ⁸⁶Rb efflux data suggests that the compartments do notcontain maximal amounts until the 22 mm (96 hr) stage. (Received December 26, 1978; )     

Inhibitory effect of adrenaline and hydrocortisone on the growth of Allium cepa roots

The roots of Allium cepa were allowed to grow in distilled water containing 10(-4) M adrenaline hydrochloride or 2 X 10(-3) M hydrocortisone sodium succinate. Adrenaline inhibited the growth of roots; they decreased in length, number and total dry weight. The total amount of DNA in the roots was reduced much less than that of extracellular root components after adrenaline. Also hydrocortisone treatment resulted in a considerable decrease of the length and dry weight of Allium cepa roots. Both DNA and extracellular root components were influenced.     

Genotoxicity of five food preservatives tested on root tips of Allium cepa L.

The effects of the food preservatives sodium benzoate (SB), boric acid (BA), citric acid (CA), potassium citrate (PC) and sodium citrate (SC) have been studied on root tips of Allium cepa L. Roots of A. cepa were treated with a series of concentrations, ranging from 20 to 100 ppm for 5, 10 and 20 h. The results indicate that these food preservatives reduced mitotic division in A. cepa compared with the respective control. Mitotic index values were generally decreased with increasing concentrations and longer treatment times. Additionally, variations in the percentage of mitotic stages were observed. The total percentage of aberrations generally increased with increasing concentrations of these chemicals and the longer period of treatment. Different abnormal mitotic figures were observed in all mitotic phases. Among these abnormalities were anaphase bridges, C-mitosis, micronuclei, lagging, stickiness, breaks and unequal distiribution.     

Sister chromatid exchanges in Allium cepa

Differential staining of sister chromatids with Giemsa after BrdU incorporation into DNA was performed in Allium cepa L. chromosomes. A treatment solution containing 10^–7 M FdU, 10^–4 M BrdU and 10^–6 M Urd was found to ensure BrdU incorporation without affecting cell cycle duration. After several procedures before staining the slides with Giemsa had been tested, treatment with the fluorochrome compound 33258 Hoechst, exposure to UV light and heating at 55° C in 0.5×SSC, were found to be essential for good differentiation. The distribution of SCEs per chromosome agrees with the expected Poisson distribution. The mean value of SCEs per chromosome occurring when cells were exposed to the treatment solution for two consecutive rounds of replication (=5.5) was double the mean value observed when cells were exposed to the same treatment for only one round of replication (=2.8). SCEs were found to occur more frequently in those chromosome regions corresponding neither to C-bands nor to late replicating DNA-rich regions. Finally, the occurrence of SCEs involving less than the width of a chromatid is discussed.     

Salt-induced abnormalities on root tip mitotic cells of Allium cepa: prevention by inositol pretreatment

Salt-induced growth reduction of plants is a well-known phenomenon which poses major problem in crop productivity in places where vast majority of land plants are affected by salt. In this report, studies were carried out to reveal the effect of salt injury on the cell division pattern in roots and the role of myo-inositol in preventing the salt-induced ion disequilibrium on the chromosome and DNA degradation in roots. Present study revealed induction of various chromosomal abnormalities on the root tip mitotic cells of Allium cepa by treatment with different concentrations of NaCl (0–500 mM) for 24 h as also the amelioration of such effect by prior treatment of the roots with different concentration of myo-inositol (0–300 mM). Results showed that a narrow albeit definite range of extracellular myo-inositol (100–150 mM) is effective in preventing internucleosomal fragmentation which is the early response in roots under salt stress. Transgenic tobacco plants overexpressing Oryza (OsINO1) as well as Porteresia (PcINO1) cytosolic l-myo-inositol-1-phosphate synthase coding genes can withstand and retain their chromosomal and DNA integrity in 100 mM NaCl solution and can subsequently prevent DNA fragmentation, caused by intracellular endonuclease activity at this salt concentration.     

Nuclear matrix network in Allium cepa

The presence of a nuclear matrix network in animal cells has been claimed by many workers in the last decade. The purpose of our study was to see whether a similar structure could be identified in the cells of higher plants. Our work revealed the presence of a fibrillar nonchromatinic network in Allium cepa nuclei. This could be impregnated with AgNO₃ in intact cells as well as in isolated matrices at the light microscope level. It was seen to be associated with the chromosomes from early to late prophase and also in telophase. Ultrastructurally a fibrillar network comparable to that reported earlier from animal cells was observed. This network remained associated with metaphase and anaphase chromosomes and could be digested with pepsin. Biochemical estimation of the isolated matrix revealed it to be made up mainly of proteins (more than 90%), traces of DNA (less than 1%) and a small quantity of RNA. SDS PAGE showed three polypeptide bands in the molecular weight range of 55,000–63,000 daltons.     

Effects of polyamines and polyamine biosynthetic inhibitors on mitotic activity of Allium cepa root tips

The genotoxic and cytotoxic effects of exogenous polyamines (PAs), putrescine (Put), spermidine (Spd), spermine (Spm) and PA biosynthetic inhibitors, alpha-difluoromethylornithine (DFMO), cyclohexilamine (CHA), methylglioxal bis-(guanylhydrazone) (MGBG) were investigated in the root meristems of Allium cepa L. The reduction of mitotic index and the induction of chromosomal aberrations such as bridges, stickiness, c-mitotic anaphases, micronuclei, endoredupliction by PAs and PA biosynthetic inhibitors were observed and these were used as evidence of genotoxicity and cytotoxicity.     

The effects of fungicide benomyl (benlate) on growth and mitosis in onion (Allium cepa L.) root apical meristem

In this study, the effects of benomyl, a systemic fungicide were investigated in the mitotic cell division in onion (Allium cepa) root tip cells during germination. For this aim, different concentrations (1, 2, 5, 10 and 20 mM) of benomyl solutions were used. All the concentrations used caused several abnormalities in mitotic cell divisions and the mitotic frequency in the onion root tip cells decreased as the concentration of benomyl solution increased. Based on our findings, it is reported that benomyl has some negative effects on mitotic divisions in onion root tip cells.     

Analysis of the cell cycle in the root meristem of Allium cepa under the influence of ledakrin

The influence of a polish anticancer drug on the cell cycle using Allium test was studied. Methods of aceto-orcein squash slides, curve of labelled mitoses after 3H-thymidine incubation and cytophotometrics after Feulgen's reaction were employed. Ledakrin acts strongly antimitotically, but it does not block the cell cycle completely. The cytostatic activity of ledakrin results from its action on the interphase. The phases G1 and S are prolonged while M is unchanged after 6h incubation with ledakrin. During postincubation in water without ledakrin it was noted, at the beginning, that the mitotic activity decreases and it is brought about the lengthening of S and G2 phases. The duration of the cell cycle phases returns to the control level during further postincubation. The results of analysis of chromatin aberrations and the micronucleus test point to a mutagenic effect of ledakrin.     

DNA replication stress induces deregulation of the cell cycle events in root meristems of Allium cepa

Background and Aims

Prolonged treatment of Allium cepa root meristems with changing concentrations of hydroxyurea (HU) results in either premature chromosome condensation or cell nuclei with an uncommon form of biphasic chromatin organization. The aim of the current study was to assess conditions that compromise cell cycle checkpoints and convert DNA replication stress into an abnormal course of mitosis.

Methods

Interphase-mitotic (IM) cells showing gradual changes of chromatin condensation were obtained following continuous 72 h treatment of seedlings with 0·75 mm HU (without renewal of the medium). HU-treated root meristems were analysed using histochemical stainings (DNA-DAPI/Feulgen; starch-iodide and DAB staining for H₂O₂ production), Western blotting [cyclin B-like (CBL) proteins] and immunochemistry (BrdU incorporation, detection of γ-H2AX and H3S10 phosphorylation).

Key Results

Continuous treatment of onion seedlings with a low concentration of HU results in shorter root meristems, enhanced production of H₂O₂, γ-phosphorylation of H2AX histones and accumulation of CBL proteins. HU-induced replication stress gives rise to axially elongated cells with half interphase/half mitotic structures (IM-cells) having both decondensed and condensed domains of chromatin. Long-term HU treatment results in cell nuclei resuming S phase with gradients of BrdU labelling. This suggests a polarized distribution of factors needed to re-initiate stalled replication forks. Furthermore, prolonged HU treatment extends both the relative time span and the spatial scale of H3S10 phosphorylation known in plants.

Conclusions

The minimum cell length and a threshold level of accumulated CBL proteins are both determining factors by which the nucleus attains commitment to induce an asynchronous course of chromosome condensation. Replication stress-induced alterations in an orderly route of the cell cycle events probably reflect a considerable reprogramming of metabolic functions of chromatin combined with gradients of morphological changes spread along the nucleus.