Secondary Association Of Bivalents Research Articles

Ionizing radiation mediated cytological manifestation in microsporogenesis of Brassica campestris L.(Brassicaceae)

Purpose of the present work is to investigate the mutagenic effects of ionizing radiations (gamma rays) on Brassica campestris L. accession no - IC363713. Homogeneous seeds of Brassica were irradiated at four doses of gamma rays i.e. 150 Gy, 300 Gy, 450 Gy and 600 Gy by the gamma-chamber type 60Co at the dose rate of 2 second/Gy. During microsporogenesis, meiotic analysis of young floral buds was carried out in irradiated as well as non-irradiated plant materials. Meiotic study clearly revealed the meiotic malfunctioning of pollen mother cells (PMCs) that had shared copious count of cytological abnormalities namely unorientation, stickiness, precocious movement or fragmentation, secondary association of bivalents, asynchronous division, laggards, tripolarity and chromatin bridge. These aberrations were found to be distributed in all the phases of male meiosis. However, this impairing during meiosis has found to be collinearly associated with doses i.e. inclining tendency of abnormality percentage alongwith increasing doses were registered. Perhaps aforementioned chromosomal aberrations may be introduced by asymmetrical distribution of chromatin material in PMCs, had definitely compromised with pollen fertility, resulting the increased frequency of pollen sterility. Hence, pollen fertility registered, simultaneously, a moderate to sharp fall depending upon the intensity of doses.

Cytological Studies in Some Members of Tribe Senecioneae (Asteraceae) from North and Central India

Cytological studies have been made of 12 species of tribe Senecioneae (Asteraceae) from north and central India. Of these, 3 species, namely S. grahami Hook. f. (n=10), S. kunthianus Wall ex DC. (n=20) and S. sexatilis Sensu Hook. f. (n=10), are counted for the first time. Additional and/or variable cytotypes are recorded for 2 species, namely S. nudicaulis Buch.-Ham D. Don. (n=5, 10) and S. rufinervis DC. (n=10). Existence of B-chromosomes has been recorded in S. krascheninnikovii Schischk. (n=10+0−2B). Two species, S. vulgaris L. (n=20) and S. krascheninnikovii Schischk. (n=10), are explored for the first time from India. Besides these, cytomorphological variabilities have been observed in S. rufinervis (2n=20, 40) and S. nudicaulis Buch-Ham ex D. Don (2n=10, 20 and 40). Great variation in morphological characteristic have been noticed in different accessions of S. laetus Edgew, however all the accessions are found to exist at 2n=40. Meiotic configurations in the form of multivalents and/or secondary association of bivalents are found in Gynura nepalensis DC., Senecio laetus Edgew, S. kunthianus Wall ex DC., S. krascheninnikovii Schischk. and S. nudicaulis Buch-Ham ex D. Don.

Cytogenetics, biogeography and biology ofSantolina ageratifoliaBarnades ex Asso (Asteraceae: Anthemideae)

Santolina ageratifolia Barnades ex Asso is a natural autohexaploid (2n = 6x = 54, 54 + 1B), endemic to Teruel Province, Spain and inhabits a substrate derived from sandstone, red limolite and quartzite. Three chromosome formulae are found: 30m + 12sm + 12st, present in 52% of the descendants (52 metaphase), 24m + 5m-1sm + 18sm + 6st in 39% of the descendants (39 metaphase) and 24m + 5m-1sm + 18sm + 6st + 1B in 9% of the descendants (9 metaphase). Chiasmata are mostly interstitial rather than terminal, giving rise to the formation of cruciform structures. The predominance of bivalent configurations in the meiosis and the exclusively bivalent formation in four individuals indicate that this species has a strong tendency towards diploidization. Secondary association of bivalents is observed in the number of 2, 4–6 chromosomes associated, the average being 4.21 ± 1.20 chromosomes. The variation in the chromosomal characteristics suggests chromosome translocation and/or inversions. This species is partially sterile, with a mean pollen fertility of 40.56% and a mean fructification of 34.24%. The frequencies of multivalents and pollen fertility have a strongly significant effect on fructification percentage. Phenotypic variation in habits is not correlated with karyotype characteristics. The cytogeography of the polyploid taxa of the Santolina rosmarinifolia aggregate is discussed.

Origin and Meiotic Behaviour of Two Multiple Interchange Trisomics in Pearl Millet (Pennisetum ameticanum L. Leeke).

Two multiple interchange trisomics one involving all the fifteen chromosomes and other at least seven chromosomes were isolated in the progeny of two tertiary interchange trisomics of pearl millet (Penninsetum americanum (2n=14)). The study of chromosome association of diakinesis in these multiple interchanges showed varying frequencies and type of multivalent formations followed by abnormalities in later stages of meiosis. Secondary association of bivalents was quite frequent in one of the interchange. Aneuploidy together with translocation as the probable cause of further chromosome interchanges has been discussed on the light of the present investigation.

Cytogenetical investigations in Rutaceae. II. Meiotic studies in three intergeneric hybrids of Citrus.

Meiotic studies were conducted in two Citrus-Poncirus and one Citrus-Fortunella intergeneric hybrids. Regular bivalent formation and equal distribution of chromsomes at different stages of meiosis indicated similarity between the genomes of Citrus-Poncirus and Citrus-Fortunella. Cytomixis and secondary association of bivalents indicated a hybrid and polyploid nature of these genera. The basic chromosome number of Citrus and allied genera was reconfirmed as n=3.

Cytogenetical studies in Petunia. I Secondary association of bivalents in Petunia parviflora Juss.

Secondary association of bivalents at M1 was observed in Petunia parviflora (2n=18); secondary polyploidy has been attributed to be the possible cause of secondary association.

Cytological investigation of the family Scrophulariaceae I. Limnophila R. Br.

The cytology of six taxa in five species of Limnophila viz. L. aromatica (n=17), L. hypericifolia (n=17), L. indica (n=17), L. chinensis (n=34), L. chinensis var. glabra (n=34) and L. conferta (n=34) has been studied. The chromosome numbers of these taxa except L. aromatica and L. indica are reported for the first time. 2n=34 in L. aromatica forms a new chromosome count. Secondary association of bi-valents has been encountered in L. aromatica and L. indica. On the basis of evi-dence from the secondary association, x=4 has been suggested to be the probable original basic chromosome number of the genus Limnophila. Somatic chromo-somes of all the six taxa have been studied and the karyotypes are characterized by small sized chromosomes.

Secondary association of bivalents in Cissus discolor Blume.

Secondary association of bivalents, in groups ranging from 2-6 was observed in PMCs of Cissus discolor (2n=48) at diplotene and metaphase I stages. Polyploidy and hybrid nature of the species have been attributed to be the possible causes of secondary association.

Cytotaxonomy of Malvaceae. III. Meiotic studies of Hibiscus, Abelmoschus, Azanza, Thespesia, Malachra, Urena and Pavonia.

The present investigation includes the meiotic study of 15 species belonging to the tribe Hibisceae and Ureneae of the family Malvaceae. Of which meiotic study of 7 species has been done for the first time. The meiosis is regular in most of the taxa. Few irregularities like laggards in anaphase and telophase I and II, irregular distribution at anaphase I and non-congressional bivalents, secondary association of bivalents at metaphase I are noticed in a few species. The occurrence of distinct bivalents in majority of the taxa studied, indicate that they represent ancient polyploids.

Cytological study ofTrilobachne cookei (Stapf) Schenck ex Henr. (Tribe Maydeae)

Meiotic studies were reported inTrilobachne cookei (Stapf) Schenck ex Henr. for the first time. Chromosome number was found to ben=10. This is not in agreement with one of the earlier reports of 2n=10 but confirms the more recent report of 2n=20. Several hundred cells were examined at various stages of meiosis in many plants. Meiosis was regular, and pollen fertility and seed set were high. But irregularities like univalents, aneuploid numbers, quadrivalents, secondary association of bivalents into groups, interlocking of bivalents, pseudocytomixis, bridges, laggards and micronuclei were found in a low proportion of the cells. Two pairs of satellited chromosomes were present in the somatic metaphase plates. These facts taken together with the previous report of 2n=10 indicate the probable tetraploid nature of the present material. Intergeneric crosses attempted betweenTrilobachne and maize, teosinte, tripsacum and job’s tears (some of the other members of the tribe Maydeae) did not succeed.

Meiotic abnormalities in Saccharum spontaneum

Meiosis was studied in several clones of Saccharum spontaneum with chromosome numbers ranging from 2n=40 to 2n=126. Abnormalities recorded include occurrence of univalents, pseudo bivalents, multivalents, heteromorphic or unequal bivalents, chromosome mosaicism, secondary association of bivalents, and complement fractionation. Their origin and importance are discussed.

Cytogenetical studies inSaccharum spontaneum

Karyotype and meiosis were studied in several clones ofSaccharum spontaneum with chromosome numbers 2n=40 to 2n=126. Differences in the karyotype was observed between different clones with the same chromosome number. Karyotype symmetry/asymmetry has been indicated. The number of chromosomes in different cells of the same plant varied in many clones at meiosis and first pollen grain mitosis. Occurrence of B chromosomes in pollen mother cells and pollen grains were noticed in a few clones. At meiosis univalents, heteromorphic bivalents, secondary association of bivalents, etc., were noticed and their importance discussed.

Cyto-genetical Investigations on <i>Lindenbergia indica</i> (Linn.) Kuntze and <i>Mazus japonicus</i> (Thunb.) Kuntze

In the present investigation, the chromosome numbers for Lindenbergia indica (n=15 and 2n=30) and Mazus japonicus (n=20 and 2n=40) have been reported. The karyotype analysis revealed the presence of 4 and 8 satellited chromosomes respectively in their somatic complements. The two taxa under consideration show marked difference between them as regard the morphology of somatic chromosomes. On the basis of length, these chromosomes fall under 2 broad classes in both taxa but in L. indica they are either short or very short (9 morphological types) while in M. japonicus they are either long or medium-sized (12 morphological types).In general, the meiotic cycle is normal except showing a few cases of minor anomalies. In addition, multivalent formation takes place in M. japonicus. Secondary association of bivalents could be encountered in both taxa. In L. indica, as in some other genera under the family, the maximum association is in four groups indicating the basic number for the family. The presence of some extra-nuclear bodies in the pollen mother cells could be noted. These take bright stain with crystal violet but are Feulgen-negative.The karyotypes of four species worked out by the present authors, have been analysed. Moreover, the range of size variation in somatic chromosomes within the family have been compared and taxa possessing chromosome numbers in multiples of 5 (gametic) or 10 (somatic) have been enlisted. The phylogenetic significances of the presence of diverse nature of karyotypes, participation of unequal bivalents in units of secondary association and also the occurrence of both consistent and inconsistent numbers of chromosomes in members of the family have been discussed.

Cytological Studies onMorus IndicaL. andMorus LaevigataWall

SUMMARYThe meiotic numbers of Morus indica L. and Morus laevigata Wall, were confirmed to be as n = 14 and n = 28 respectively. Secondary association of bivalents indicates 7 as basic number. In M. laevigata the following peculiarities were noted in its meiotic behaviour: I) presence of multivalents and laggers;II) irregular separation of chromosomes;III) unequal numbers of chromosomes in different PMCs.The allopolyploid nature of M. indica and polyploid state of M. laevigata have been suggested.

Cytological Studies on the GenusRusselia

SUMMARYIn the present paper, the morphology of the somatic chromosomes and meiotic behaviour of Russelia equisetiformis Schlecht et Cham, and R. coccinea (Linn.) Wettst. has been described in detail and discussed.The chromosome number is 2n = 20 and n = 10 in both species. The chromosomes in R. equisetiformis are larger in size and fall under nine types out of which two pairs (type A and type C) are satellifed. The somatic complement of the other species 'R. coccinea) however, has only one pair of satellited chromosomes (type A). The chromosomes, in this species can be classified in eight types only.The meiotic division is fairly normal in both species. A high degree of secondary association of bivalents has been observed and the maximum association was found to be 2(3) + 2(2) indicating the basic number as four only.Lack of synchronisation in the meiotic division in the anthers of a flower was found to be characteristic in the two species studied. The presence of non-chromatic extranuclear bodies, specia...