Chromosomal rearrangements are thought to play a role in speciation, adaptation and evolution. The effects of chromosomal rearrangements on gene expression have been reported in many species and their close relatives, and may illustrate the consequences of adaptation. To investigate the effects of chromosomal rearrangements on phenotypic changes directly, studies of experimentally induced rearrangements are required; they allow gene expression and epigenetic states to be compared between mutants and wild-types. We have developed an effective method for inducing chromosomal rearrangements with heavy-ion beam irradiation, which is a sort of ionizing radiation. Reconstruction of such rearrangements by genome editing will enable reproducible studies on the effects of chromosomal rearrangements. In the future, therefore, these techniques will usher in a new era in which researchers can create novel species with designer chromosomes.
Conventional karyotyping and detection of nucleolar organizer region (NOR) were performed on a tropical oyster, Crassostrea iredalei from Nakhon Si Thammarat province, Thailand. Chromosome preparations were made from gill tissues. Conventional Giemsa’s staining and Ag-NOR banding were performed. The results revealed that the chromosome number was 2n=20 and fundamental number (NF) was 40, the karyotype consisting of 12 large metacentric and eight medium metacentric chromosomes. The NORs were located terminally on the long arms of the chromosome pair 10.
Lycoris shaanxiensis Y. Xu & Z. B. Hu was a rare and endemic species to the southern Shanxi province, China. The chromosome number and karyotype of five populations of this species were described here. All plants of each population had 2n=30 chromosomes, but the karyotypical constitutions were different among populations. The karyotype formulae of this taxa was 2n=30=3m+10st+12t+5T for Huangbaocun population; 2n=30=3m+4st+18t+5T for Laoyu population; 2n=30=3m+8st+14t+5T for Shuangmingcun population; 2n=30=3m+6st+16t+5T for Jiangcun and Zudongcun populations. Based on chromosome analysis, it was suggested that L. shaanxiensis should be of hybrid origin and an allotriploid.
Several environmental and mutagenic factors lead to induce nuclear polymorphism like micronuclei (MN) and nuclear buds. MN are the disintegrated partitioned nuclear or chromosomal fragment. Their occurrence is indicator of genomic instability or chromosomal turmoil. Combined mutagenic treatment of gamma rays and ethyl methane sulphonate (EMS) was experienced to induce formation of MN and nuclear buds in cluster bean [Cyamopsis tetragonoloba (L.) Taub]. A considerable proportion of microcells was also encountered that display future fate of micronuclei in the cell. A peculiar correlation with this nuclear polymorphism was experienced on the presence of bridges and laggards at anaphase I and II stages. Frequency of bridges and laggards were collinear to the combined mutagenic action. Pollen viability was also examined through pollen fertility percentage to inculcate effects of the nuclear incineration on the viability of pollen and the results depicted a dose dependent decline in pollen fertility.
The cytotoxic effects of low doses (20 to 100 µM) of nickel ions (Ni) and cadmium ions (Cd) as well as antioxidative enzyme changes in Allium cepa roots were studied. Heavy metal induced oxidative damage showed significant reduction in root length, mitotic index, total protein content and catalase (CAT) activity and increased cell abnormality index as well as proline content. Enhanced antioxidative enzyme activities were noticed to minimize oxidative stress by increasing guaiacol peroxidase (GPX) activity of the tissue. The effect of toxicity was found to be dose dependent in antioxidative enzyme level and more pronounced in root systems. Evans blue uptake by the root cells showed the cell death parameter which served as an indicator of cytotoxicity. Recovery experiments till 48 h showed significant changes in antioxidative enzyme systems of the cells reverting back to normal. Treatment of Ni and Cd led to spindle abnormalities like multipolarity, sticky bridge in anaphase, early separation, clumping of chromosomes, late separation as well as direct chromosomal damage with chromosome break, chromosome erosion, laggard chromosomes. This experiment explains the role of reactive oxygen in heavy metal toxicity and their DNA damage, cell death and adaptive responses to genotoxic challenges of the cells amelioration.
Conventional staining and Ag-NORs banding techniques were applied on the chromosomes of hihgfin barb fish, Cyclocheilichthys armatus. Specimens were collected from the Chao Phraya River, Thailand. The mitotic chromosome preparations were directly obtained from kidney tissues of eight males and eight females. The results revealed that the diploid chromosome numbers of C. armatus was 2n=50 and the fundamental number (NF) was 94 in both males and females. The karyotype consists of four large metacentric, six large submetacentric, two large acrocentric, eight medium metacentric, 12 medium submetacentric, 12 medium acrocentric and six medium telocentric chromosomes. No sex chromosome was observed. Ag-NORs indicating NORs were clearly exhibited at the region adjacent to telomere of the short arm of some chromosomes. The NORs located on chromosomes of the metacentric chromosome pair 3 and the submetacentric chromosome pair 7. The karyotype formula of C. armatus is 2n=50=Lm4+Lsm6+La2+Mm8+Msm12+Ma12+Mt6. Cytogenetic data of cyprinid fishes can be used as the basic knowledge for enhancing the existing cytotaxonomic information and chromosome evolution of the Cyprinidae especially in the genus Cyclocheilichthys.
The various toxic chemicals used in painting of steel furniture are benzene, toluene, xylene and thinner. Of these, the cytotoxic effects of benzene and thinner were evaluated using root tip cells of Allium cepa. Chromosomal aberration assay was done and relative division rate (RDR) and mitotic index were calculated. An investigation of the root length was also carried out for 14 days in both control and after post treatment with benzene and thinner. Benzene and thinner showed positive cytotoxic effects on A. cepa root tips. Chromosomal abnormalities induced were early separation, exclusion, laggard, sticky bridge and persistent bridge. Both benzene and thinner also showed some positive effect on stimulation of cell division and growth of roots. These should not be deterred danger for crops on the basis of only cytotoxic effect. Thus, both cytotoxic and genotoxic effects should be assessed.
Twenty inter hybrids (IVHs) were raised in crossing among three sesame cultivars Sesamum indicum L. cv. Tilottama, Roma and Savitri following inter planting. Frequency of plants with crossed pods ranges from 0.00 to 5.00% among the lines. Percentage of crossed pods per plant varies 1.59 to 3.84% in Roma×Tilottama (RT) hybrids, 2.36 to 3.13% in Savitri×Roma (SR) and 2.17 to 5.56% in Savitri×Tilottama (ST). IVHs are screened at F1 based on seed coat color. Meiotic configurations assessed in parents and in F1 hybrids reveal high frequency of regular homologous pairing with 13II (Tilottama: 99.35%, Roma: 97.50%, Savitri: 97.37%; RT hybrids: 87.44% average, SR hybrid: 84.08% and ST: 89.29%) at metaphase I (MI) with near equal (13/13), anaphase I (AI) and relatively high pollen grain fertility. F2 segregation of selfed F1 progenies demonstrates intermediate dominance (1 : 2 : 1) of seed coat color of the studied sesame varieties. Based on seed yield/plant and fatty oil content, few promising IVHs are screened.
Adiantum philippense Linn. (Adiantaceae) is widely distributed in tropical, sub-tropical and warm temperate regions. Mostly apogamous triploid cytotype (2n=90) has been reported frequently from several localities in India. In the recent exploration of A. philippense species complex in Uttar Pradesh, India, the diploid (n=30) and tetraploid (n=60) cytotypes have been found. The morphological characters such as the lamina, pinna, spore size, and stoma were measured and compared. The clear difference was detected in spore size between the two cytotypes.
Cytogenetical studies were carried out on Colocasia esculenta (L.) Schott and five different karyotypes were observed, karyotype formula of each karyotype were 2n=28=L24m+M4sm, 2n=28=L14m+L2sm+M6m+M6sm, 2n=28=L22m+L6sm, 2n=28=L18m+M4m+M2sm+S2sm+S2sm and 2n=28=L8m+L4sm+M4m+M10sm+S2m. The karyotype of five strains had same chromosome number of 2n=28 and fundamental number (NF)=56. Therefore, all of the five strains had a symmetrical karyotype that consisted of metacentric and submetacentric chromosomes. The differences among karyotypes were caused by number of metacentric and submetacentric chromosomes. The chromosome number of C. esculenta had been reported, but this is the first report of karyotype variation among strains.
The current study report the chromosome counts for twelve species of tribe Epilobieae from the cold desert regions of north-west Himalaya. These chromosome counts add to our existing database and enlighten our understanding of the cytology and distribution pattern of the tribe. First chromosome counts for two species, Chamerion speciosum (Decne.) Holub (2n=4x=72) and Epilobium chitralense P. H. Raven (2n=2x=36) has been reported. These species showed 100% pollen fertility. All the chromosome counts (except C. speciosum) determined in this study from the north-west Himalaya are diploid 2n=2x=36, which is consistent with the proposed base number x=18 for the tribe Epilobieae. On the basis of study of available chromosome counts and existing literature, along with counts presented at this point, it is level-headed to conclude that 2n=36 is the most frequent chromosome number for this tribe with an established base chromosome number, x=18. We herein also discuss the cytogeographic distribution pattern of the tribe Epilobieae based on present as well as previous findings in the literature.
Triploid cytotypes of Polystichum squarrosum have been found from India. All accessions shared the same cytological status of 2n=123, the first ever record against the earlier reported diploid (2n=82) and tetraploid (2n=164) cytotypes from India. Individuals depicted highly abnormal meiotic behavior characterized by presence of univalents beside bivalents, unoriented chromosomes at metaphase I (MI), laggards, chromatin bridges at anaphase and telophase. Cytomixis at tetrad showing nuclear fusion between sporads is another noticeable phenomenon in this species. Triads, polyads and micronuclei at tetrad stage consequently lead to low spore fertility and formation of heterogenous spores. B-chromosomes were found in few cells in one of the accessions.
Male meiotic studies have been performed on three wild accessions of Arthraxon hispidus scored from Parvati valley and Solang valley of Kullu district in Himachal Pradesh. The accessions shared the same diploid chromosome number of 2n=30 and added a variable dysploid chromosome report for the species against the earlier reports of 2n=18, 36, 38, 40. Multiple chromosomal associations due to structural heterozygosity for reciprocal translocations involving four to six chromosomes seem to have increased the chiasma frequency in meiocytes. Owing to adjacent type orientation of multiple chromosomal associations coupled with some meiotic irregularities, the studied accessions also related with some pollen sterility.
Nucleolar organizer regions (NORs) and karyotype in the black lancer, Bagrichthys majusculus from Nakhon Phranom and Sing Buri provinces, Thailand, were investigated. The mitotic chromosome preparations were directly obtained from kidney tissues of eight male and eight female specimens. Conventional and Ag-NOR staining techniques were applied to the chromosomes. The chromosomes number of B. majusculus was 2n=50 and the fundamental number (NF) of all specimens was 96. The karyotype consists of six large metacentric, six large submetacentric, two large acrocentric, eight medium metacentric, 12 medium submetacentric, two medium acrocentric, six small metacentric, four small submetacentric and four small telocentric chromosomes. Sex chromosome was not observed. Moreover, the interstitial NORs were clearly observed at the long arm of the metacentric chromosome pair 1. The result revealed that a heteromorphic NOR type was appeared in one male and one female fish and other fish have homozygous NOR in the pair 1 chromosomes.
Male meiotic studies carried out on the plants of Fagopyrum acutatum (Polygonaceae) collected from the Parvati valley, Kullu district, Himachal Pradesh, India confirms the earlier chromosome reports of 2n=16 from outside of India. The presently recorded chromosome count of n=8 in pollen mother cells (PMCs) is the first ever report of a diploid cytotype for the species from India. The presently studied diploid individuals from the Parvati valley showed the presence of structural heterozygosity for reciprocal translocations. Analysis reveals that multiple associations of four to six chromosomes were noticed in 39–40% meiocytes. A few PMCs in the accession also depicted the presence of two to six univalent chromosomes which could be attributed to the hybrid nature of the taxon or due to synaptic irregularities in chromosomal pairing during meiosis. Consequent to multiple chromosomal associations and univalent chromosomes, the studied plants depicted some pollen sterility.
The present communication reports the first record of intraspecific euploid cytotypes (2x, 4x) in Arabis recta from the cold deserts of North-West Himalayas in India. The study included the detailed male meiosis, microsporogenesis, pollen fertility and morphometric parameters in the accessions of 2x and 4x cytotypes. Both the diploid and tetraploid cytotypes exhibited normal meiotic behaviour characterized by normal chromosome pairing, regular segregation of chromosomes and nearly cent percent fertility. The 2x and 4x cytotypes grow under similar extreme cold desert conditions on mountain slopes between 2800 to 4500 m altitudes. The 4x plants grow much taller and possessed much larger sized pubescent leaves. The two cytotypes could also be differentiated on the basis of size of stomata and pollen grains, which are significantly larger in the 4x compared to the 2x.
Male meiotic studies have been performed on plants basis in Deutzia staminea collected from three localities of Parvati valley, Kullu district, Himachal Pradesh, India. The scored accessions uniformly exhibited the diploid chromosome count of 2n=26 confirming the earlier reports from other regions of North-West Himalayas. The individuals studied from Gurthigarh showed perfectly normal meiosis, microsporogenesis and 100% pollen fertility. On the other hand, plants studied from Pulga and Malana showed the existence of multiple associations of chromosomes due to structural heterozygosity for reciprocal translocations. Analysis of 118 countable pollen mother cells (PMCs) showed that 17.8% meiocytes depicted multivalent of ring or chain type involving 2.87% of the chromosomes. Also these individuals showed the phenomenon of cytomixis (6.57% PMCs), chromatin stickiness, and abnormal spindle activity depicted in form of out of plate bivalents, chromatin bridges and laggards. The existence of some pollen sterility (15–29%) in diploid individuals seems to be the consequence of multivalents during metaphase I (MI) and cytomictically induced meiotic irregularities in the PMCs.
In the present study, 26 species belonging to 17 genera and five tribes of the family Asteraceae collected from natural habitats in cold deserts of the western Himalaya were analyzed on their meiotic events. The chromosome counts are reported for the first time in four species viz. Brachyactis roylei (n=9), Cousinia thomsonii (n=12), Erigeron umbrosus (n=9) and Waldheimia glabra (n=9). The euploid or aneuploid chromosome numbers are reported in Arctium lappa (n=17), Bellis perennis (n=5) and Saussurea heteromalla (n=8). The chromosome counts of n=9 in E. borealis is new to the Indian populations. The chromosome counts in the rest 18 species are new additions from the cold desserts of Lahaul-Spiti district of Himachal Pradesh. The present meiotic study also discloses meiotic abnormalities viz. chromosome stickiness, cytomixis, laggards, etc. leading to the hypo-/or hyperploid meiocytes. These abnormalities further may alter pollen viability by producing unreduced pollen grains and might be responsible for the disparity in the chromosome numbers.