Effects of certain food dyes on chromosomes of Allium cepa

The effects of 4 permitted food dyes, i.e., fast green FCF, indigo carmine, orange G and tartrazine, and the non-permitted dye metanil yellow on chromosomes of Allium cepa are reported. A significant increase in polyploid cells was observed in all cases. High doses of these dyes induced chromosome breaks and micronucleus formation. Although all dyes produced mitotic aberrations, metanil yellow and fast green FCF showed comparatively stronger clastogenic activity.     

Interspecific hybrid between Allium cepa and Allium sativum

Summary Interspecific hybrids between Allium cepa and Allium sativum were obtained using the fertile clone A. sativum as the male parent. The nascent embryos which formed shortly in interspecific hybridization between A. cepa and A. sativum were rescued by ovule culture at an early stage. The zygotes or proembryos developed in Murashige and Skoog medium containing 5.7×10^-8 M indole-3-butyric acid (IBA). Once developed, the embryos were taken out of the ovule and cultured on embryo culture medium where they regenerated into whole plants. The hybridity of the plants obtained was examined by morphological observation, chromosome analysis, and ribosomal RNA gene analysis. The analyses proved that the plants were mature sexual hybrids between A. cepa and A. sativum. Each hybrid plant had keeled but fistulose leaves and formed a bulb resembling that of A. cepa. The hybrids produced not only S-propenyl-l-cysteine sulfoxide, which is the major flavor precursor in A. cepa, but also S-allyl-l-cysteine sulfoxide (alliin), which is characteristic of A. sativum.     

Identification and chromosomal location of tandemly repeated DNA sequences in Allium cepa

A 314-bp tandemly repeated DNA sequence, named pAc074, was characterized in Allium cepa by fluorescence in situ hybridization (FISH) analyses using random amplified fragment as probe. The nucleotide sequences of the clone pAc074 is partially homologous to the satellite DNA sequences, ACSAT1, ACSAT2, and ACSAT3, of A. cepa with 81%, 81% and 78% similarity, respectively. Our sequential C-banding and FISH with pAc074 probe also clearly showed a close relation between Cheterochromatin at telomeric region and pAc074 sequences on all the chromosomes except on chromosome 6. On the long arm of chromosome 7, pAc074 sequences appeared as interstitial band which did not correspond to C-heterochromatin bands. Instead, the C-heterochromatin bands corresponded with the 5S rDNA signals. This is the first evidence of simultaneous banding of the 5S rDNA and C-band in A. cepa.     

洋葱细胞核仁内DNA的结构变化及排布过程(英文)

以洋葱 (AlliumcepaL .)细胞为研究材料 ,应用DNA细胞化学特异染色方法 (NAMA_Ur)及常规电子显微镜技术 ,观察了洋葱细胞核仁FC(纤维中心 )内DNA的超微结构 ,发现FC内DNA存在着一个介于集缩到解集缩之间的变化过程 ,并揭示了DNA在核仁内的连续排布过程 ,即核仁外DNA经过核仁通道进入到FC后 ,继续沿FC的边缘或DFC(致密纤维成分 )与FC的交界处环绕FC而排布 ,再经FC之间的核仁通道 ,延伸到另外的FC区域     

Factors affecting the production of SCEs by maleic hydrazide in root-tip chromosomes of Allium cepa

We have investigated the influence of pH on the induction of chromatid-type aberrations and sister-chromatid exchanges (SCEs) by maleic hydrazide (MH) in root-tip cells of Allium cepa. For both cytogenetic endpoints, the lower the pH of the treatment solution, the higher were the frequencies of chromosome alterations detected at metaphase. We have further studied the persistence of lesions giving rise to SCEs during successive cell cycles, as well as the influence of BrdU concentration in the post-treatment medium on the yield of MH-induced SCEs. Our results suggest that the cytogenetic action of MH in many respects resembles that of bifunctional alkylating agents.     

DNA polymorphism in Allium cepa cytoplasms and its implications concerning the origin of onions

Summary Mitochondrial and chloroplast DNA was isolated from fertile and cytoplasmic male sterile cultivars of cultivated onions. Restriction fragment length polymorphism led to the distinction between cytoplasms S and M. Mitochondrial DNA patterns from S cytoplasms appeared dentical and characterized mostly male sterile lines. An open-pollinated variety was found to bear this cytoplasm and thought to be the origin of S types. Mitochondrial DNA patterns from M cytoplasms were subdivided into four types, M₁ and M₂ corresponding to normal N cytoplasm, M₃ and M₄ probably corresponding to T cytoplasms. S and M cytoplasms were also distinguished by chloroplast DNA restriction patterns. Our results confirm previous genetic distinction between S, N and T cytoplasms.     

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.     

The effect of lead on Allium cepa L.

The effect of lead on Allium cepa L. at concentrations of 0.1, 1.0, 10, 50, 100 and 200 ppm were studied. Analysis focused on root growth, frequency of mitosis in a meristematic zone, and chromosomal aberrations. It was observed that lead reduces root growth and the frequency of mitotic cells in meristematic zones, and increases the frequency of aberrant cells. The intensity of the effects is a function of lead 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.     

The mechanism of stomatal movement in Allium cepa L.

In the guard cells of Allium cepa leaves, no starch was found either when the stomata were open or closed. The lack of other soluble polysaccharides that could be hydrolyzed during the opening reaction of the stomata (Schnabl, Planta 1977, in press) leads to the question, how is the osmotic effect, which is the basis of the stomatal movement, achieved in Allium? It is shown in this paper, by histochemical and microprobe analyses, that in Allium — as in other plant species—the K⁺ concentration of the guard cells increases during stomatal opening. The charges of the K⁺ ions in the guard cells seem to be fully compensated by imported Cl^- ions. This could mean that if starch is present in the guard cells, as in the majority of plant species, its major role in the mechanism of stomatal movement is to deliver the cuunteranions for the imported K⁺ ions.     

BAC FISH analysis in Allium cepa.

Onion (Allium cepa L.; 1C=15,000 Mb) is an agriculturally important plant. The genome of onion has been extensively studied at the conventional cytogenetic level, but molecular analyses have lagged behind due to its large genome size. To overcome this bottleneck, a partial bacterial artificial chromosome (BAC) library of onion was constructed. The average insert size of the BAC library was about 100 kb. A total of 48,000 clones, corresponding to 0.32 genome equivalent, were obtained. Fluorescent in situ hybridization (FISH) screening resulted in identification of BAC clones localized on centromeric, telomeric, or several limited interstitial chromosomal regions, although most of the clones hybridized with entire chromosomes. The partial BAC library proved to be a useful resource for molecular cytogenetic studies of onion, and should be useful for further mapping and sequencing studies of important genes of this plant. BAC FISH screening is a powerful method for identification of molecular cytogenetic markers in large-genome plants.     

Extraction and identification of different prostaglandins in Allium cepa

Green onions (Allium cepa) were homogenized in a blender and extracted by normal extraction methods except that diethyl ether was used as the first extracting solvent. Different analytical procedures were used for the identification of the prostaglandins separated. TLC was applied using silica gel 60 F254 plates and a mixture of benzene, dioxane and acetic acid (20:10:1) as eluent, and the Rf values were compared with those of authentic samples. GC analysis on an SE 30 packed column and FID was applied; relative retention times of the onion extract components were measured and matched with authentic prostaglandin samples using cholesterol as an internal standard. GC-MS analyses using the same conditions adopted for GC analysis were conducted on a Finnigan MAT 112S instrument. Four peaks were identified. The prostaglandins identified were F1 alpha, E1, B1 and A2.     

Actin in the preprophase band of Allium cepa

F-actin has been identified in the preprophase band of Allium cepa. Cells attached to subbed slides were obtained from formaldehyde-fixed root tips digested in EGTA and Cellulysin. The air-dried cells were extracted in Triton X-100, treated with rhodamine-phalloidin, rinsed briefly in PBS, and viewed in the fluorescence microscope. Interphase cells contain a network of actin fibers that extends into all areas of the cytoplasm. During preprophase, the network is replaced by a band of fibers aligned in the position of the preprophase band. Colocalization of F-actin with rhodamine-phalloidin and microtubules with tubulin immunocytochemistry confirms that the two bands are coincident. The actin appears to comprise a thin layer of fibers next to the plasmalemma. Like the microtubule preprophase band, the actin band narrows as preprophase progresses and disappears by midprophase. Fluorescent actin bands are not seen in fixed cells pretreated with excess unlabeled phalloidin before staining. They are also absent in roots exposed to cytochalasins B and D before fixation, but preprophase band microtubules at all stages of aggregation are still present. Colchicine treatment leads to the loss of both preprophase band microtubules and actin. The possible function of preprophase band actin is discussed.     

The role of ethylene in photoperiodic control of bulbing in Allium cepa

Bulb formation in Allium cepa L. cv. Dorata di Parma, was promoted by ethylene (Ethrel 120 mg l⁻¹) treatments. Application of the antiethylene complex silverthiosulphate (0.01 m M ) inhibited ethylene-induced bulb formation, but did not affect photoperiod-induced bulb formation. When the inhibitor of ethylene biosynthesis, aminoethoxyvinylglycine, was applied at 0.04 to 4 mg l⁻¹ to onion plants under inductive photoperiodic conditions the bulb promotion was unaffected. Therefore, Ethrel-induced bulb formation does not appear to be related to endogenous control of bulbing.