We report the first chromosome analysis and localization of the nucleolar organizer region of the Phayre's flying squirrel, Hylopetes phayrei (Blyth, 1985) from Thailand. After standard peripheral blood lymphocytes had been cultured at 37°C for 96 h in the presence of colchicine, the metaphase spreads were performed on microscopic slides and air-dried. Conventional staining, GTG-banding, high-resolution and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that the diploid chromosome number of H. phayrei was 2n = 38 and the fundamental number (NF) were 76 in both males and females. The karyotype has the presence of 2 large metacentric, 8 large submetacentric, 8 large acrocentric, 6 medium acrocentric, 6 small metacentric and 6 small acrocentric chromosomes. The X chromosome is a small submetacentric chromosome and the Y chromosome is a small acrocentric chromosome. From the GTG-banding and high-resolution techniques, the numbers of bands and locations in the H. phayrei are 182 and 234, respectively; each chromosome pair could be clearly differentiated. The Ag-NOR staining demonstrated that the three pairs of nucleolar organizer regions (NORs) were observed on the long arm regions of chromosome pairs 1, 5, and 14. The karyotype formula of H. phayrei could be deduced as: 2n (diploid) 38 = L2m+L8sm+L8a+M6a+S6m+S6a+sex-chromosomes
A new natural autotetraploid and the chromosomal characteristics of the dwarf snakehead fish (Channa gachua) from Kalasin, Nong Khai, Nong Bua Lam Phu and Udon Thani Provinces (four populations) in northeast Thailand were studied. Kidney cell samples were taken from 12 male and 12 female fish. Mitotic chromosome preparations were conducted using a blood cell culture technique as well as taken directly from kidney cells. Conventional and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that the autotetraploid chromosome number of C. gachua was 4n = 104, and the fundamental number (NF) was 112 in both sexes. The types of chromosomes were 4 large submetacentric, 2 large acrocentric, 16 large telocentric, 2 medium submetacentric, 68 medium telocentric and 12 small telocentric chromosomes. No strange-sized chromosomes related to sex were observed. The region adjacent to the centromere of chromosome pair 3 showed clearly observable secondary constriction (NORs). The karyotype formula for C. gachua is as follows: 4n (autotetraploid) 104 = L4sm+L2a+L16t+M2sm+M68t+S12t
We report the first polymorphism of nucleolar organizer regions (NORs) and karyological analysis of the banded langur (Presbytis femoralis) from Thailand. Blood samples were taken from two male and one female langurs. After standard peripheral blood lymphocytes had been cultured at 27°C for 96 h in the presence of colchicine, the metaphase spreads were performed on a microscopic slide and air-dried. Conventional, GTG-banding and high-resolution techniques were applied to stain the chromosome. The results showed that the diploid chromosome number of P. femoralis is 2n = 44, and the fundamental numbers (NF) of both sexes is 88. The types of autosomes are 20 large metacentric, 8 large submetacentric, 2 large acrocentric, 2 medium submetacentric, 4 small metacentric, 4 small submetacentric, and 2 small acrocentric chromosomes. The X chromosome is a large submetacentric chromosome and the Y chromosome is the smallest submetacentric chromosome. In addition, the long arm near the centromere of chromosome pair 17 showed clearly observable NORs. The result showed different sizes of NORs for heteromorphic chromosome pair 17 of all males and female. From the GTG-banding and high-resolution techniques, the number of bands on one set of haploid chromosomes in the P. femoralis are 264 and 332, respectively; each chromosome pair could be clearly differentiated. The karyotype formula for P. femoralis could be deduced as: 2n (diploid) 44 = L20m+L8sm+L2a+M2sm+S4m+S4sm+S2a+sex chromosomes
Four accessions of B. serrata, a threatened tree species of the Indian Thar desert, showed a gametic number of n = 22 in the form of either 22 bivalents or a combination of both bivalents and univalent, confirming the somatic chromosome number as 2n = 44. They were characterized by the presence of mixture of bivalents and univalents, however multivalent associations were completely lacking. The highest mean value (3.6) of univalents was found in B. serrata BSJO-26314-D, while the minimum number of univalents per cell (0.15) was recorded in B. serrata BSJO-26314-B. By and large, the univalents, wherever encountered, apparently behaved normally leading to equal distribution of chromosomes at anaphase I. Male meiosis in all the accessions showed that genetic diversity exists in the natural populations of B. serrata. A multidisciplinary approach for genome diagnostics with the use of various DNA-based marker systems might shed more light on existing intra-specific genetic variation in B. serrata.
To study the effects of high temperature on the meiosis of pollen mother cells (PMCs) and to determine their relationship with grain set, two in situ experiments were conducted between 2010 and 2012 on four wheat cultivars, Kauz, Montana, M6 and Chamran, under normal (normal cultivation) and terminal heat stress (late cultivation) conditions. Due to the delay in cultivation for the cultivars under stress conditions, their flowering stage faced heat stress at the end of the growing season, and therefore, a significant (p ≤ 0.05) increase was observed in meiotic abnormalities. Cytogenetic studies discovered that the meiosis in PMCs and the pollen development are strongly influenced by heat. Based on the results, abnormalities such as precocious chromosome migration to the poles, laggard chromosomes, micronuclei, absence of metaphase plate, pyknosis, abnormal cytokines, cytomixis and abnormal tetrad were observed in different cultivars. The sensitive cultivars, M6 and Montana, had the greatest percentages of meiotic abnormalities. The meiotic abnormalities showed a significant negative correlation with the number of kernels per spike under terminal heat stress conditions (r = −0.54, n =16, p ≤ 0.01). In other words, due to increasing meiosis abnormalities under terminal heat stress, the grain set was greatly reduced, especially in the susceptible cultivars. The result of this experiment showed that studying the meiosis in PMCs can be suggested as one of the research necessary to improve commercial heat-tolerant cultivars, and to some extent, as a method for screening tolerant lines in breeding programs.
Chromosome counts were carried out in root tip cells of Nesphostylis bracteata (Fabaceae), an endemic legume of Western Ghats, India. A diploid number of 2n =20 is reported here for the first time. The karyotype was found to be symmetrical with all chromosomes having a median region centromere. The chromosome length ranged from 1.50 to 2.69 µm.
The seeds of Eclipta alba have been successfully employed with different doses of X-ray irradiation to assess its effect on somatic chromosomes. The data obtained from the experimentally treated material have further been analysed with all the implications to understand the effects of radiation on the chromosome structure, behaviour and gene mutation. Although irradiation is known to induce chromosomal aberrations and mutation in many plants, its effect on Eclipta alba is not known. Data were obtained with regards to survival of seedlings and induced chromosomal anomalies in root tip cells. It may also be safely stated that experimental induction by physical means (X-rays) holds a clue to understanding the gene mutation and also the adaptability of the species in different environmental conditions. The result of experimental manipulation done as a part of the present investigation strengthens the contention that Eclipta alba in general is highly plastic and capable of forming populations through the adjustment of their genetic system.
This is the first study in which gynoeceum, megasporogenesis, megagametogenesis and female gametophyte of Gagea villosa were examined cytologically and histologically by using light microscopy techniques. Ovules of G. villosa are of anatropous, bitegmic and tenuinucellate type. Inner integument forms the micropyle. Embryo sac development is of bisporic Endymion type. Polar nuclei fuse before fertilization to form a secondary nucleus near the antipodals.
Microsporogenesis was analyzed in a rare intergeneric hybrid of sugarcane produced from a Sorghum×Saccharum cross. The original hybrid was found to be non-flowering. Some of the somaclones of this hybrid obtained by irradiating the callus at four Kr showed flowering. However, the somaclones were found to be male sterile. Here we report the occurrence of syncyte formation and subsequent chromatin degeneration in the somaclones of this hybrid. Syncytes were recorded in 58.3–85.7% pollen mother cells of somaclones that flowered. Meiosis progressed normally in microsporocytes till leptotene where the uninucleate cells appeared normal with loosely tangled, long thread-like chromosomes. Later, the whole nuclear mass divided into two or more groups, forming syncytes with multiple nuclei and micronuclei. Cytokinesis fractionated the syncyte into abnormal meiotic products. Degeneration of chromatin content was observed in both syncytes as well as in the uninucleate cells, resulting in anther sacs with fragmented chromatin mass. Complete pollen sterility resulted from these abnormalities. However, these plants were found to be female fertile and hybrids could be obtained by using it as a female parent in crosses with sugarcane.
Breakdown of soil urea yields ammonium ions or ammonia, which further converts to nitrite and nitrate due to nitrification. These breakdown products have severe toxic effects on the crop standing in the soil when present in high concentrations. Temporal changes in ammonium–nitrate ratio following urea application in soil and its consequent genotoxic effects were assessed. In an in vitro experiment, a treatment of different concentrations of urea was given to Allium cepa bulbs for different durations to optimize the concentration on the basis of root tip bioassay for minimum aberrations. Further, the effect of temporal changes in urea in the soil system was studied by a pot experiment in which urea was added to the soil at a rate of 200 mg N kg−1 soil (optimized from in vitro experiment). A regular intervals for four weeks, the roots from the onion bulbs were fixed and cytological analysis was done. Estimation of ammonium and nitrate was done on corresponding days. The cytological analysis of root tips harvested in both in vitro and pot experiments revealed dividing cells and different types of division anomalies. Variation was observed in the percentage of mitotic index and percentage of anomalous cells during the span of the experiments. In the case of the pot experiment, the abnormalities observed were of two distinct types (i) mitotic abnormalities, i.e., abnormalities in dividing cells, and (ii) interphase nuclear abnormalities. The varying ratio of ammonium and nitrate with respect to time has been considered as a possible reason for such variations in nuclear behaviour.
In this study, toxic effects of the lambda-cyhalothrin (LCT) in Allium cepa L. cells were investigated. Toxic effects were investigated by analyzing the leaf contents and the cytologic and antioxidant parameters. To this aim, different doses of LCT were applied to Allium cepa L. samples. As a result, all doses of LCT treatment significantly decreased the leaf pigments compared to the control. The activity of superoxide dismutase, catalase and MDA level showed a concentration–time dependent decrease after treatment. It was also found that LCT has a mitodepressive action on mitosis and produced clastogenic and aneugenic types of abnormalities in Allium cepa with decreased mitotic index depending on the dose of LCT. The data obtained in this study showed that plant bioassays can be used as an important indicator to detect possible genotoxicity of chemicals.
Micronuclei induction serves as an essential biomarker of radiation stress in a living system, and the simplicity of its detection technique has made it a widely used indicator of radiation damage. The present study was conducted to reveal the cytological dose–response of a few plant taxa, viz., Allium cepa var. aggregatum Linn., Allium sativum Linn., Chlorophytum comosum (Thunb.) Jacques and Eichhornia crassipes (Mart.) Solms, to low LET gamma radiation with special emphasis on the pattern of micronuclei induced across low and high dose regimes. A tri-phasic non-linear dose–response pattern was observed in the four taxa studied, characterised by a low dose linear segment, a plateau and a high dose linear segment. Despite a similar response trend, the critical doses where the phase transitions occurred varied amongst the plant taxa, giving an indication to their relative radiosensitivities. E. crassipes and A. sativum, with their lower critical doses for slope modifications of phase transitions, were concluded as being more radiosensitive as compared to C. comosum and A. cepa, which had relatively higher critical doses.
The genus Berberis belongs to the family Berberidaceae and includes mostly wild, important medicinal plants. Meiotic studies have been carried out for analyzing the genetic diversity in 11 populations covering four species from different selected parts of the Western Himalayas, such as Kashmir (Jammu and Kashmir) and the districts of Kangra and Sirmaur (Himachal Pradesh). The species being cytologically worked out for the first time worldwide include B. ceratophylla (2n = 28). Similarly, B. vulgaris (2n = 28), although worked out earlier from other countries, is being reported cytologically for the first time from India. The meiotic course in most of these populations has been observed to be normal except for a single population each of B. asiatica, B. ceratophylla and B. vulgaris marked with abnormal meiosis. Out of these three species, two (B. asiatica and B. vulgaris) are marked with cytomixis. These meiotic abnormalities lead to the production of heterogenous-sized fertile pollen grains and reduced pollen fertility.
Cyanophora paradoxa is an enigmatic biflagellate that may represent the first photosynthetic eukaryote morphologically. This alga has been widely studied as a model organism of primitive phototrophs. However, surface ornamentations of the vegetative cells have not been examined using ultra-high resolution field emission (FE) scanning electron microscopy (SEM). In the present study, C. paradoxa NIES-547 vegetative cells were examined using FE-SEM and compared with the data using conventional SEM. Our FE-SEM images demonstrated that the cell surface was ornamented with angular fenestrations framed by ridges. In contrast, conventional SEM did not reveal similar surface ornamentation. Transmission electron microscopy showed the ridge was formed by the edges of overlapping or attaching outermost plate vesicles at the cell periphery.