The present work shows that Benlate could induce homozygosis when diploid Aspergillus nidulans strains were in a heterozygous condition. This effect was dependent on mitotic instability of the strains and was associated with non-repaired lesions on chromosomes.
Detailed researches were carried out on the comparative morphology, karyology and karyomorphology of C. longifolia Rob. Cytological studies reveal the presence of n = 42 chromosomes in three populations of Sidhra lake plants, which agrees with the count of Pundhir (1994) but differs from the report of n = 63 chromosomes recorded by Pundhir and Gautam (1994b). Occurrence of two chromosome numbers in direct multiple of its basic chromosome number (x = 7) in the different populations of same geographical locality leads the suspicion that Charophytes possess high potentiality of natural hybridization which induce polyploidization and may be responsible for the occurrence of higher variations found at morphological and cytological level. Brief cytotaxonomic status of C. longifolia in the light of present studies have also been discussed
Meiotic studies of Pollen Mother Cell (PMCs) and 4C DNA content from root tip cells of 8 species of Mammillaria of the family Cactaceae revealed significant interspecific variations in the genome. The haploid chromosome number n=11 was recorded in M asteriflora, M bella, M. bravoae, M brevispina, M. elongata, M klissingiana and M matudae. The chiasma frequency sig-nificantly varied from 22.25 to 24.28 per nucleus. The formation of univalent in some of the cells, spindle anomalies i.e. early or late separation leads to the formation of pentads, sexads or octads in stead of tetrad formation in the meiotic telophase II through differential pollen sterility from 10.31 to 22.83% in M elongata and M collinsii respectively. The 4C DNA amount of root tip cells varied significantly from 18.262 to 24.124 pg in M klissingiana and M brevispina respectively. Significant variation in DNA amount with gross or minor alteration of chiasma frequency leads to genetic drift among the species.
The meiotic process in F3BC1 and F4BC1 of crosess S. cereale (2n=28) × Triticale (2n=42) was analyzed. It was established that the variation of number of univalents per cell is heterogenous.The variation of total bivalent number, ring bivalents and rod bivalents per cell characters changes from homogeneous to strongly heterogenous. The homogeneous variation of the total number of chromosomes shows that the selection of stabilized tetraploids with rye cytoplasm can start first in F3BC1.
The present investigation deals with the morphological and cytological studies of caffeine treated plants of Trigonella foenum-graecum. The untreated plants being normal while the treated populations showed a number of meiotic abnormalities such as univalents, laggards, bridges, nondisjunction, stickiness, cytomixis and precocious movement of chromosomes etc. The spectrum of abnormalities increased with an increasing concentration of caffeine. Lower doses of caffeine exhibited stimulatory effect on plant height, number of branches, pods, and internodal length while the higher doses caused inhibitory effect on morphological characters. Observed abnormalities
A set of inbred lines and single-cross and double-cross maize hybrids grown on acid and corrected soil of the Brazilian Central Plateau were tested for meiotic behavior. Among them, five inbred lines and five double-cross hybrids presented plants exhibiting cells connected by cytoplasmic channels which in several cases showed the passage of chromatin material. All meiotic stages were affected on both soil types. Although the phenomenon occurred at low frequency, it was observed between cells within the same stage, in different stages, or even between meiocytes and tapetum cells. Two to several cells were involved simultaneously. Anucleate cells close to bi-or trinucleate cells were frequently observed as well as cells exhibiting aneuploidy or polyploidy, syncythia, mixoploidy and abnormal tetrads.
The cytological features including chromosome counts, karyotypic measurements and localizations of C-banding were investigated in two species of Sternbergia Waldst. and Kit. from Turkey. Chromosome lengths were ranged from 18.04 to 6.62, am in S. fisheriana (Herbert) Rupr. and from 23.56 to 8.73, am in S. candida Mathew and T. Baytop. The karyotype of S. fischeriana was consisted from three pairs of metacentric and seven pairs of subtelocentric chromosomes. The karyotype formula of S. candida was consisted from three metacentric, four subtelocentric and three acrocentric chromosomes. One B chromosome was observed in each species. Predominate and also very faint telomeric and some faint centromeric and proximal C-bands were observed in both species.
Cytogenetic analysis of peripheral blood lymphocytes was carried out in ten hypoprolific pigsfrom a farm located near Rio Cuarto National University, where sows gave birth to no more thanthree piglets in their later farrows. Blood samples from seven sows and one boar were obtained in a first instance. Animalsshowed a high frequency of chromosomal abnormalities (ranging from 19 to 32 per 100 cells scored). Chromosomal aberrations were mainly chromatid breaks, chromatid exchanges (triradials, quadriradials) and chromosome fragments. In addition, 15% of the metaphases showed chromosomal pulverization. A sow and its piglet were studied in a second sampling detecting only chromosome pulverization aberration type (80% of the cells scored in average). Chromosomal localizationof breaks was done with GTG banded metaphases. At least, eight chromosomes were involved, thehighest frequency of breaks was located in the longest telocentric (chromosome n° 13). “Chromosome pulverization” has been associated to virus infection. All studied adult animals werevaccinated against Swine Fever, Aujeszky disease is endemic for the region. Consequently, chromosomaldamage could be induced by subclinical viral infection. Chromosomal anomalies might be relatedto the reproductive impairment of pigs; however, further studies would be necessary to identifythe clastogenic agent.
The karyotype analysis in miners working for 5 to 10 years in uranium mines revealed the existence of a normal chromosomal complement in 75-90% from analysed metaphases cells. Polyploidy and aneuploidy are frequent. The polyploidy through endomitosis can be merelythe very consequence of culture stress rather than an “in situ” state; when such polyploid cells ap-pear “in situ”, they are subject of elimination process under the guidance of regulatory mechanisms. Many different chromosomal rearrangements have been seen, the most frequent being attraction of satellite chromosomes (i.e. nucleolus organizing regions, which contain ribosomal cistrons), centromeric fusions of Robertsonian type, involving acrocentric chromosomes, varying in number from 3 to 5, leading to the apperance of characteristic triradial or cross structures. A quite high frequency of chromosomal lacunae and breakages, peculiar SCE patterns, lampbrush-like metaphase chromosomes were encountered. It is difficult to make any correlation between the presence of such chromosomal rearrangements (i.e. modifications) and their clinical significance, but the evidence leads one to the conclusion that the environment of uranium mines is a potentially mutagenic one. It can not be ruled out that at least some chromosomal abnormalities are pathological.
Random amplified polymorphic DNA (RAPD) was used to study DNA variation in 123 green, doubled-haploid plants derived from anther culture of six barley cultivars, including 'Andre', 'Harrington', 'Hector', 'Moravian III', 'Morex' and 'Otis'. Polymorphic fragments were found among derived lines and between cultivar and derived lines with 16 of 22 primers studied. The frequencies of polymorphism varied between derived lines. Lines derived from Moravian III showed polymorphism with 13 primers, while Hector and Hector derived lines were monomorphic with 22 primers studied. This indicated that DNA may be modified during anther culture and the degree of variation depended on the genotype of each cultivar.
The genome of Lolium temulentum has 50% more DNA than the L. multiflorum genome. However, chiasma and trivalent frequencies are not significantly different between the autotriploids of the species but there are differences in the frequencies of the various types of trivalent. The data show that, irrespective of genome size, each set of three homologous chromosome arms is first allocated a chiasma ensuring a ring bivalent or chain trivalent then additional chiasmata convert either of these configurations into a frying pan or bird cage trivalent.
Two Scorpaniform species (Scorpaena brasiliensis and S. isthmensis) from the coast of Rio de Janeiro (Brazil), were cytogenetically analyzed by Giemsa staining, silver nitrate and mithramycin A staining, and C-banding. S. brasiliensis showed 2n=46 and FN= 60 and S. isthmensis showed 2n=40 and FN= 54. The NORs were located in the telomeric regions of the short arms of a submetacentric chromosome (pair 5 in S. isthmensis and pair 2 in S. brasiliensis). Size NOR heteromorphism was detected in S. brasiliensis. The constitutive heterochromatin patterns revealed the presence of small centromeric segments in almost all chromosomes in both species. In S. brasiliensis a conspicuous block was also observed in the NOR sites. The karyotypes described in this study show a significant chromosome divergence, mainly due to centric fusions and pericentric inversions.
Two species of Setaria verticillata and Eragrostis aegyptica from Egypt were carried out under cytogenetic investigation in this study. They are very common and widely spreed grass belong family poaceae, mostly distributed in Nile delta region. All accessions collected for each species show no significance variation in morphological measurements. Mitotic chromosome investigation shows that Setaria verticillata has 18 chromosomes (x = 9) as diploid species, where Eragrostis aegyptiaca has 40 chromosomes based on x =10 as tetroploid species. Karyotype structure of the two species shows degree of dissimilarity of the first species within chromosome set in the length and centromere position (show types of metacentric, submetacentric and telocentric). Chromosome set also shows satellite chromosome with probability of translocation in one pair of chromosomes. In contrast the second species shows a karyotype structure with high degree of homogeneity in length and centromere position (mostly metacentric). Parameters of meiotic division as chromosome association, chiasmata frequency and pollen fertility as well as seed set were investigated for the two species. Meiosis of Setaria verticillata recorded low chiasmata frequency, low pollen fertility low percentage of seed set and more frequent aberrated cells. This in contrast to Eragrostis aegyptiaca, where meiosis show, normal behaviour of chromosomes, low aberration, high fertility and seed set. The mitotic and meiotic results observe the cytogenetic situation of the two species. The results pointed to the genetic instability of Setaria verticillata and the probability of hybriditynature of the species through out breeding with near by another diploid species. On other hand the results insure the genetic stability of Eragrostis aegyptiaca and confirm its autotetraploid nature.
The nucleolonema of Raphanus sativus root-tip cells was studied with light and electron microscopy especially focusing on its three-dimensional structural organization. Its countour was very intricate and the thickness showed a large variation in air-dried specimens. It usually appeared to coil or meander. Serial ultrathin sectioning of the nucleolonema in its longitudinal orientation first revealed the stack of short nucleolonema fragments, then a pair of knobbly frames with space in-between, and again the stack of the short nucleolonema segments. On the other hand, transversal sections revealed 'c'-shaped segments with the change of their openings' orientation. Morphometry of the nucleolonema indicated two categories of the nucleolonema; each had an average thickness of 510 nm and 1.19 μm, respectively. Taken together, the thin nucleolonema may coil or fold to form the thick one. The fibrillar centers including DNA-containing structures were closely associated with the thin nucleolonema and intermittently arranged along the nucleolonema.
The pellicle is formed by the zygote-specific wall (Cavalier-Smith 1976), which is constructed to replace the vegetative cell wall shed before mating (Claes 1971). The zygotic cell wall is composed of a fibrous material, which contains hydroxyproline as a major amino acid, glucose as the most abundant sugar residue, and a (1-3) β-D-glucan as the major structural polysaccharide (Grief et al. 1987). At least six zygote specific peptides with molecular masses of 76 kDa, 120 kDa, 150 kDa and >200 kDa (A, B and C) have been identified as components of zygotic walls (Minami and Goodenough 1978). Zygote-specific cDNA clones, which encoded the extensin-like proteins ZSP-1 and ZSP-2 (Woessner and Goodenough 1989), have also been obtained in previous studies (Ferris and Goodenough 1987). However, no gene was characterized that played a role in cell adhesion for pellicle formation, in Chlamydomonas. To elucidate the relationships between the pellicle and these peptides and genes, a detailed time schedule of gene expression in pellicle formation needs to be constructed. The aims of this study are to clarify when the pellicle is formed, and to estimate when mRNA and proteins involved in pellicle formation are synthesized, by using transcription and translation inhibitors administered at various times after mating. The pellicle, filmy aggregate of zygotic cells formed in the green alga Chlamydomonas reinhardtii, was characterized as a model of inter-cellular adhesion. Pellicle formation was observed following treatment with inhibitors of transcription and translation in the gamate and at various times after mating. The pellicle forms between 2.5 and 3.5 hr after gamete mixing and is sensitive to cytoplasmic inhibitors of transcription and translation, when they are mixed with gametes or zygotes soon after mating. This indicates that the pellicle formation related gene (s) is (are) one of the early zygote-specific genes, and that transcription occurs within the first 20 min after gamete mixing. The protein (s) required for pellicle formation is (are) synthesized predominantly between 1 and 2 hr after mating, just before pellicle formation.
The preferential digestion of male-derived chloroplast-DNA (cp-DNA) and fusion of the cell nuclei were observed in zygotes of the alga Chlamydomonas reinhardtii, when transcription (actinomycin D) and translation (cycloheximide) inhibitors were given at various times after mating. The minimum periods required to complete cytoplasmic transcription and translation were estimated. Genes playing a role in uniparental inheritance are transcribed from the moment the gametes fuse until about 1 hr after mating, but fusion of the cell nuclei requires a longer period of gene expression. Observations of two cell types indicating the beginning and completion of the preferential digestion of male-derived cp-DNA suggested two possibilities. (1) Expression of additional genes after expression of the first zygotic genes is required to complete the process. (2) The presence of a continuous signal promoting cp-DNA digestion is necessary for completion.