In all, ten Ipomoea spp. have been karyomorphologically analysed. The data from the present studies analysed in terms of chromosome number, absolute chromatin length, centromeric index, T. F. % and representative chromosome types tend to indicate the various degrees of overlap establishing close relationships between the species. The genus Ipomoea has been suggested to be a natural assemblage showing a reticulate evolution. The splitting of Ipomoea spp. into distinct subgenera on morphological ground (Hooker 1885) or into separate genera on the basis of pollen exine character (Hallier 1893) does not find support from karyomorphology which is a better biological character.
The karyotypic studies in ten varieties of Lens culinaris revealed that in all of them, the somatic chromosome number was uniform (2n=14). However, the varieties differed considerably among themselves in the total chromatin length, arm-ratio and position of centromere. There was a remarkable variation in terms of their symmetrical and asymmetrical karyotypes. With the help of D2-statistics, all the ten varieties were grouped into six clusters which underlined the possibilities of breeding among themselves for producing desirable recombinations. There was no direct correlation between the seed size and total chromatin length. Some small seeded varieties registered higher values of total chromatin length than those of large seeded forms. This clearly pointed out the fact that the small seeded forms might have given rise to the large seeded forms in cultivation. During this process, the total chromatin length has reduced by the deletion of the non-essential part of the chromatin material. There was no record of SAT-chromosomes in any of the varieties under study which suggested that these varieties were comparatively more evolved than those possessing SAT-chromosomes.
Detailed cytological studies have been made on Coix gigantea which often occurs as a weed in paddy fields of South India. This cyto-type shows the aneuploid chromosome numbers of n=6 and 2n=12. All the six bivalents are homologous showing complete pairing during meiosis. The pachytene studies show significant similarities between the IInd and Vth pair of chromosomes. The Ist and VIth pair show terminal knobs. The cytological evidence indicates the relationship of this cyto-type (2n=12) with the other cyto-types of C. gigantea, but its origin is obscure. This plant could survive in the paddy fields as it exhibits mimicry together with a short life-cycle. A wide collection fom different regions of South India and detailed cytological analysis might help us to understand its phylogenetic relationships.
Cytology of populations of three species of Crinum from South India is reported such as C. asiaticum, C. giganteum and C. moorei. All the species are diploids and x=11 basic, with C. asiaticum occurring here as triploid cytotype also. C. giganteum and C. moorei showed intraspecific aneuploidy, 2n=22 and 23 in the former and 2n=22, 21 and 20 in the latter. Meiotic behaviour and karyomorphology of the triploid C. asiaticum is suggestive of its autrotriploid nature. Karyotypes of all the taxa are relatively asymmetrical and graded, C. asiaticum exhibiting more asymmetry (3 B) and C. giganteum the least (2 B). The extent of chromosome numerical and structural difference noticed in the different populations of C. giganteum is pointed out to have some bearing on the plant morphological differences evident in the species complex. The disputed systematic treatment of the tribe Crineae is considered in the light of cytological data, and the evidence appears to favour Hutchinson's approach.
The mutachromosomal and mutagenic effects of water soluble extracts of different forms of tobacco preparations used in India, were observed on the plant system Allium cepa in vivo. The four forms of tobacco tested prepared by different processing methods. Mitotic index indicated that certain concentrations of tobacco extracts were mitogenic in Allium cells. The abnormalities recorded were stickiness, somatic bridge formation, diplochromatid and clumping. The mode of processing did not appear to make any appreciable change in affecting cell and chromosome division.
A detail analysis of somatic chromosomes from the brain and imaginary disc cells of the Uzifly, Exorista bombycis a parasitoid of the mulberry silkworm Bombyx mori (Lepidoptera: Bombycidae) is presented. The karyotype is established to have 5 pairs of submetacentric autosomes in a graded series and a pair of sex chromsomes which are homomorphic in female and heteromorphic in male. The acrocentric X-chromosome is the smallest element and the Y is submetacentric and is larger than the X-chromosome. This is unique to this species. The karyotype of this species is compared with those of other cytologically known Dipterans and discussed.
Apart from normal cell division, unequal cytokinetic divisions leading to formation of enucleate cells also occur in Cyclotella meneghiniana f. unipunctata. Migration of daughter nuclei and cell-plate formation seem to be independent mechanisms. Silica deposition on the walls of enucleate cells indicates neither complete cytokinesis nor mitosis are prerequisites for silicification.
A new antimalarial compound 8-aminoquinoline derivative, N1-(3-acetyl-4-5-dihydro-2-furanyl)-N4-(6-methoxy-8-quinolinyl), 1, 4-pentanediamine, Central Drug Research Institute code No. 80/53, has been evaluated for the in vivo genotoxicity assay as measured by the sister chromatid exchange and chromosome aberrations in bone marrow cells of mice. The trend tests for the evidence of dose response effects for both SCE and CA were negative. No significant increase in SCE or CA were observed for this compound when compared with respective negative controls. Thus, the present study indicates that the antimalarial compound 80/53 was not genotoxic in vivo in bone marrow cells of mice.
Detailed karyological and meiotic studies have been carried out in the diploid species of Gloriosa L. with somatic number 2n=22 chromosomes. This taxon G. lutea Hort. is morphologically distinct with linear and crisped monocolored chrome yellow perianth having pale orange seeds. It is distinct in its cytology and the karyotypic peculiarity with the formula 2n=22=2A'nm+2NM+4N'nm+12T'nm+2SM which supports its tendency of isolation as diploid species. Meiosis is highly irregular with first and second division stages showing large number of laggards. Univalents and multivalents are of common occurrence with high frequency of quadrivalents reflects on genomic instability.
Genetic stability, using cytological techniques, has been assessed in regenerated plantlets of Allium tuberosum (Alliaceae) in four culture passages and after their field establishment. Karyological studies of the regenerants indicated that majority (>90%) of the cells had shown normal complements and variants if any, were found to be restricted to a small proportion of cells. Aneusomaty, polyploidy and structural alterations were some of the variations recorded. Meiotic analysis of regenerated plants revealed that by and large they do not differ from the control plants and all the parameters (associations, chiasma frequency, terminalization coefficient and pollen stainability) showed no significant change when compared to control plants. However, quadrivalent range and frequency showed a considerable reduction in regenerated plants and factors responsible for this were discussed in detail. Efficacy of cytological techniques in confirming the genetic stability of regenerated plants has been demonstrated.
The relation between the numbers of B-chromosomes and C-bands was examined in 7 populations of Allium schoenoprasum from eastern North America. Correlations between those two variables were positive and significant both over all plants studied (n=68) and for population means (n=7). However, excluding either the two populations devoid of B-chromosomes or all plants without B-chromosomes, these correlations were not significant. Within the 5 populations possessing B-chromosomes, correlations between C-bands and B-chromosomes ranged from 0.47 to -0.50, but none reached significance levels. These results are discussed in relation with those reported for Ornithogalum montanum, where a strong negative association between numbers of B-chromosomes and Q-bands has been reported.
Therapeutic dose of vitamin B12 causes significant decrease in the incidence of Malathioninduced mitoinhibition and clastogeny in onion root-tip and bonemarrow cells of mice. Vitamin B12 alone does not produce any changes in division rate or clastogeny. The probable mechanism (s) involved in antigenotoxic effect of vitamin B12 have been discussed.
2C nuclear DNA contents were determined for 52 clones of four commercially important Mentha species viz., M. piperita, M. viridis, M. spicata and M. cardiaca. A three fold variation in 2C DNA content was detected which ranged from 2.83 pg in M. viridis to 8.73 pg in M. cardiaca. However, 2C DNA content per genome in the Mentha species was 4.64 fold. The observed significant decrease in proportionate amount of DNA values at higher ploidy may be attributed to its adaptive advantage. 2C nuclear DNA content did not show any relationship either with total chromosome length of the complement or nuclear volume.
The cytogenetic analysis of 13 specimens (9 males and 4 females) of Pseudotocinclus tietensis showed that this species has 2n=54 chromosomes (26M+20SM+6ST) plus one heteromorphic pair (SM/M) in the males and one homomorphic pair (SM/SM) in the females. Ag-NORs are located interstitially on the long arm of the largest metacentric pair and a small amount of constitutive heterochromatin is present in the karyotypes. The occurrence of a heteromorphic pair in the males is demonstrable by the presence of one extra C-banded block in the Y chromosome. The presence of one heterochromatin block distinguishing the sexual chromosomes suggests that this species presents a very primitive mechanism of sex chromosome differentiation.
Callus tissues were established from hypocotyl segments of Vicia faba in Schenk and Hildebrandt's Medium (SH) and subcultured in modified SH media containing magnesium sulphate in different concentrations (400mg/l, 600mg/l, 800mg/l, 1000mg/l and 1200mg/l). The callus cells in primary cultures were diploid. Only rarely cells showing chromosome break or clumping of chromosomes were observed. Calli subcultured in medium containing magnesium sulphate in different concentrations showed mixoploidy, chromosome breakage and chromosome clumping.
The occurrence of premature chromosome condensation (PPC) was demonstrated in cytological preparations developed in two out of five specimens of a fish, Eigenmannia virescens, 2n=38, analysed after a period they were maintained in laboratory conditions. Those specimens in which PCC occurred and tetraploid cells had come about by cell fusions were invariably infested with a ciliate protozoan, Ichthyophthirius multifiliis. It is speculated that in some way the infestation of fish with this organism may cause cell fusions in the body of the hosts resulting into PCC and tetraploidy.
The chromosomes of the Arabian camel or the one humped camel, Camelus dromedarius, L. have been studied using cell cultures of peripheral blood lymphocytes. Using C-banding technique, the diploid chromosome number for the C. dromedarius was found to be 74, with a karyotype consisting of 62 acrocentric, 8 metacentric and 2 submetacentric autosomes. The X chromosome is large, metacentric and the Y chromosome is a small metacentric sex chromosome. The fundamental number has been calculated to be 86 chromosomes.
Cytomorphological studies on H. muticus tetrasomics (2n+2=30), isolated from among the selfed progeny of autotriploids, and their diploid (2n=28) counterpart inbred CIMAP/NP-41 were carried out. The overall morphology of both the tetrasomics was similar to that of diploid except reduction in plant height, number of primary branches, pollen fertility and seed set per capsule and increase in leaf area per leaf. The four homologous chromosomes formed either a quadrivalent or two bivalents at diakinesis/metaphase I in majority of the PMCs in both the tetrasomics. Other associations like II+2Is, III+I and rarely 4Is were also observed in decreasing order. The mean frequencies of chromosome associations in terasomics were 0.48 IV, 0.11 III, 13.73 II and 0.27 I. Gametes with variable number of chromosomes ranging between n-1 and n+3 were produced as a result of 3-1 and 2-2 disjunction of quadrivalent. The differences in morphological features, meiotic behaviour, pollen fertility and seed set in the two tetrasomics suggested the involvement of different chromosomes in tetrasomy.
Chloroplast-nuclei of male origin in the zygotes of Chlamydomonas are known to be digested after mating. This preferential digestion was inhibited by UV irradiation. An action spectrum for the inhibition of preferential digestion showed that maximum inhibition occurred between 260-265nm. Preferential digestion was greatly inhibited during 10min after mating when the zygotes were exposed to a UV pulse (254nm, 1min). This inhibition was largely overcome by subsequent incubation in visible light. These results suggest that the genes involved in maternal inheritance function within the first 10 min after mating.
Population diversity of an understorey aroid, Schismatoglottis irrorata, was analyzed based on the proportion of individuals with and without B chromosomes. The number of B chromosomes varied not only among individuals but also within the same root tip. They were considered not to be active genetically. Statistic tests indicate that isolated populations significantly differed regarding their B chromosome proportions, which might have arisen from the founder effect and the genetic drift by geographical isolation.