The karyotype of Haematobia irritans is reported along with data on nucleolar organizer regions (NORs). The karyotype (2n=10) is characterized by the presence of 3 metacentric and 2 submetacentric pairs and the absence of heteromorphic chromosomes. One of the submetacentric pairs seems to present a pericentromeric NOR. Among the Calyptrate, the horn fly is one of the few species that does not conform to the general rule of 2n=12.
A tetraploid variety of A. ampulacea was produced through colchiploidization by treatments in 0.15% and 0.20% colchicine for 7 to 20hr. The cytogenetics of the diploid and induced tetraploid were studied in order to determine the chromosome numbers and observe the meiotic behaviour. A. ampulacea diploid had a somatic chromosome complement of 18 chromosomes and regular 9 bivalents. The induced tetraploid had 36 somatic chromosomes and showed irregular meiosis characterized by the presence of quadrivalents and univalents at diakinesis and metaphase I with laggards and bridges at anaphse I. These differences in chromosomes numbers were reflected in plant size, length of spikes, number of spikelets and total seed production.
Artificial intersubspecific hybridization was carried out between (1) P. n. nesis Fruhstorfer, 1909 and P. n. japonica Shirôzu, 1952, known to be subspecies of P. napi (Linnaeus 1758). The chromosomes at Meiosis-I in the F1 hybrid males were investigated. All M-I cells of the 24 male F1 hybrids had a chromosome number n. 25. From the results of this experiment, a consideration was carried out of the relationship between P. n. japonica and nesis.
(1) The chromosomes of two species of the genus Mecopoda are described. (2) Mecopoda elongata has 2n=29 with 8 pairs of metacentric, 5 pairs of subacrocentric and one pair of acrocentric chromosomes. The karyotype of Mecopoda sp, consists of 2n=27 with all biarmed chromosomes- 8 pairs of metacentric, one pair of heteromorphic submetacentric with a secondary constriction in one homologue and 4 pairs of subacrocentric chromosomes. In both, the X chromosome is large and metacentric. (3) The basic karyotype of the genus Mecopoda is assumed to be 2n=31 with all acrocentric chromosomes and the karyotypes of M. elongata and Mecopoda sp. are considered to be derived from such a basic karyotype by the mechanisms of centric fusion and pericentric inverson. (4) The C-banded karyotype of Mecopoda sp. is presented showing the characteristic distribution of C-heterochromatin.
The diploid chromosome number of Oriental vole is 56, and all chromosome in the complement are acrocentrics. The Y chromosome is the smallest one. The C-banded karyotype reveals that the centromeric C-bands are abundant, and all chromosomes are C-bands positive, and Y chromosome is completely heterochromatin. The silver-stained karyotype has been studied. Five pairs of Ag-NORs were found in the terminal of Nos. 1, 2, 6, 14, 27, respectively, and the heteromorphism and association of Ag-NORs were also observed.
Analysis of 8 populations of 3 species of Echeandia echeandioides, E. tenuis and E. mexicana showed that all were diploid, chromosome counts were 2n=16, n=8 (x=8). Each species had a different karyotype. The three species also presented different cytotypes in all populations. However, the presence of the same cytotype in each population suggested that all populations originated from a single clone by vegetative reproduction. Cytotype variation was observed in heteromorphic pairs of metacentric, submetacentric, subtelocentric and chromosomes with satellite. The meiotic analysis had heterozygotic exchanges. MI analysis showed heteromorphic IIs and IVs. Al analysis displayed U-type chromatid exchange (3.91%-0.30%) and sub-chromatid aberrations (12.78%-1.91%). Lagging chromosomes were recorded in AI in 4 populations of E. echeandioides and E. tenuis. Ea mexicana did not present this type of aberration. Based on these results, we can suggest that exchanges had played an important role in the evolution of the genus.
The microsporogenesis process of one desynaptic mutant of Dactylis glomerata subsp. himalayensis (2n=2x=14) was investigated. Examination of prophase I provided clear evidence to classify the plant as a desynaptic mutant. As a consequence of the formation of univalents, the meiosis was frequently disturbed by such irregularities as defective congression, umbalanced chromosome segregation and development of micronuclei. Following different mechanisms of restitution unreduced microspores as well microspores with double the normal chromosome number were produced. It can be hypothesized that a large part of the pollen might be aneuploid and inadequate for fertilization. In any case, functional pollen was produced, a portion of which was certainly the unreduced type. The latter type is of particular interest for the role that it can have in the evolution of the genus Dactylis and for its potential application in the improvement of the cultivated species.
Chromosomes were counted in the preparation of gonad tissues from Cleopatra bulimoides collected from different localities around Qena City in Upper Egypt. The diploid chromosome number of this species was determined to be twenty eight (2n=28). The karyotype was made up of four metacentric, eight submetacentric and two telocentric chromosome pairs. Increased levels of polyploidy in the form of tetraploidy, pentaploidy, hexaploidy, heptaploidy and octaploidy were determined only in the specimens which have dark brown bands on their shells of this species. Shell measurements are also described in details. (These results are reported for the first time in Egypt.)
Seasonal pattern of cell division in a year in four deciduous (Albizzia lebbeck, Dalbergia sissoo, Tectona grandis and Terminalia crenulata) and three evergreen (Calophyllum inophyllum, Mangifera indica and Morinda tinctoria) plants is described in detail. The anticlinal division of fusiform initials were predominantly pseudotransverse although a few radial divisions in Dalbergia and lateral (or tangential) divisions in Albizzia were noticed. There was often a difference in the orientation of the anticlinal division spindles even in the adjacent fusiform initials in the different plants. The timing of both the periclinal and anticlinal and initial location of division were studied and recorded for all plants studied.
Data with respect to chiasma frequency, chiasma distribution, chromosome configurations at metaphase-I and frequecy of micronuclei and microcells at tetrad stage were collected from five varieties of A. porrum L. Mean chiasma frequency ranged from 30.14 and 30.5 per cell. Most of the chiasmata were either proximally or very-proximally localized. Cells at metaphase I usually showed normal bivalent configurations but univalents and quadrivalents were also observed.
Root tips of annual chrysanthemum were used for the study of radiation induced chromosomal aberrations at mitotic metaphase. This material has been found to have many advantages over the traditionally used ones, the most significant being the recovery of unusually large number of clear dividing cells and scorable chromosomal aberrations, facilitating authen-tic determination of dose-response and qualitative analysis of various categories of aberrations. This study offers a new cytogenetic system in which various theories of induced chromosomal aberrations can be tested.
The genus Parthenium contains plants which produce latex, although only P. argentatum produces the commercially important product, rubber, in sufficiently large quantities. Parthenium forms a natural polyploid series (Stebbins and Kodani 1944, Bergner 1944) and although many meiotic studies have been conducted, little mitotic karyological data has been published. This paper presents the first mitotic karyotype and idiogram of Parthenium argentatum (2n=36). In addition, a technique for production of well spread mitotic chromosome squashes is outlined.
Seven facultatively apomictic accessions of guineagrass (Panicum maximum) were studied cytologically for clarifying the mechanisms of seed-forming embryo development in poly-embryonic ovules. The continuous observations of ovules before and after anthesis under the condition of open-polination, indicate that 1) The first AESIC appeared is located dominantly in micropylar end (Chen and Kozono 1994), and the percentage of mature embryo sacs in micropylar end was higher than that in the other end; 2) The rates of the ovules contained developed embryo sacs in micropylar end at 4-days after anthesis were 33%-91% comparable to 0%-2% of that in the other ends; 3) The embryo of the developed sac in micropylar end, in final, became a seed-forming embryo, and in contrast, the other sacs, were crowded out to chalazal end and degenerated at 10 or more days after anthesis. From the above results, it can be concluded that the AESIC-derived embryo sac in micropylar end, in most of the cases, has temporal dominant in embryo sac mature, and has the positional dominant in fertilization and subsequent development of embryo sac when compared with the sacs in the other end in polyembryonic ovules. We, therefore, suggest that the degrees of sexuality or apomixis can be estimated based on the frequency of sexual and apomictic embryo sacs in the micropylar end by means of embryo sac analysis in present generation, even without progeny test. The other types of embryo sac development were also investigated and discussed.
In the present paper, karyotypes of Vicia venosa (Willd. ex Link) Maxim. and V. ramuliflora (Maxim.) Ohwi are reported. The karyotype formulae are as follows: V. venosa (Willd. ex Link) Maxim. 2n=12=2M+10sm; V. ramuliflora (Maxim.) Ohwi 2n=12=2M (2SAT)+8sm+2st and 2n=24=8m+16sm (2SAT). The karyotypes of the two species belong to “2A”. According to karyomorphology, tetraploid cytotype of V. ramuliflora distributed at alt. 2000-2400m in Mts. Changbaicould is an autopolyploid.
In this paper, chromosomes of two populations of so-called B. falcatum in Northeast China were investigated. Two cytotypes were found as follows: 2n=20 in plants from Pingdingshan, 2n=26 in plants from Wulimu. The chromosome complement of each cytotype was composed of large chromosomes and small chromosomes, showing bimodal variation in chromosome size. The number of the large chromosomes was constant to be four in them, while the number of the small chromosomes was sixteen in plants with 2n=20, twenty-two in plants with 2n=26.
The shoot apical meristem of a day-neutral desert ephemeral Pectis papposa was examined by SEM. Under axenic conditions with continuous light, seedlings grew very fast. Only 6 days after sowing, the shoot apical meristem formed the dome and produced three bracteal primordia after developing three sets of foliage leaves. This meant the flower initiation occurred at 6th day. It seems to be the fastest flowering plant ever investigated. The observation here brings the possibility to investigate whole the vegetative phase to elucidate the very beginning of the flower initiation.
The mammoth gene in Nicotiana tabacum causes the tobacco plant, which is otherwise day-neutral to flower under short photoperiodic conditions. The mammoth gene has been transferred to the genome of N. rustica through interspecific hybridization followed by repeated backcrossing to N. rustica. The expression and segregation of the mammoth gene was complex in the N. rustica genetic background. Plants with abnormal floral expressions and altered responses to environmental factors such as photoperiod and thermoperiod frequently appeared in the rustica-tabacum hybrid population. Three different flowering responses characterized the segregating populations. A small proportion of rustica-tabacum mammoth hybrids remained non flowering with continued vegetative growth for an indefinite period of time irrespective of photoperiod or thermoperiod. Nine percent of plants in the segregating backcross progeny expressed flower reversion phenomenon which was characterized by the appearance of terminal flowers with abnormal floral morphology, later reverting to normal inflorescence as in N. rustica. The remainder of the hybrid segregants were identical to N. rustica in floral morphology as well as in their responses to photoperiod. The segregation of plants with altered flowering expressions among the backcross progeny was highly heterogeneous. Cytological investigations were carried out both at mitosis and meiosis to find out whether the heterogeneous segregation of plants with altered flowering expressions could be related to abnormal chromosome segregations. The studies revealed variation in chromosome number at mitosis in flower revertant and non-flowering plants. The studies also revealed cytological aberrations in the hybrid progenies segregating for flower revertant and normal plants at meiosis. The results indicate that their genomes are at an unstable state and it was concluded that the heterogeneous segregation in the backcross hybrid progeny with altered responses to environmental factors and abnormal floral expressions may at least in part be due to chromosome instabilities.
The mammoth gene of Nicotiana tabacum has been transferred to N. rustica genome through interspecific hybridization followed by repeated backcrossing to N. rustica. Our previous studies have revealed that the expression and segregation of the mammoth gene was more complex in the N. rustica genetic background than in N. tabacum. Plants with abnormal floral expressions such as non flowering (NF) and flower revertants (FR) with altered responses to environmental factors such as photoperiod and thermoperiod frequently appeared in the backcross progeny of rustica-tabacum hybrids. The segregation of plants for FR and NF characters among the progeny was highly heterogeneous and chromosome instabilities were found both at mitosis and meiosis. Characterization of the genomic DNA of rustica-tabacum hybrid segregants (FR and NF) and the parental species (N. tabacum and N. rustica) was carried out in the present study using thermal denaturation and analytical density gradient analyses. Differences were observed in the DNA composition among the hybrid plants segregating for abnormal flowering expressions, FR and NF, as well as the parental species. Variation was observed in the mole fraction of 5-methyl deoxycytidine in the genomic DNA of the hybrid progenies and the parental species. Variation in the amount of satellite DNA fraction was also found between the hybrid plants, FR and NF and the recurrent parental species N. rustica. The differences in the buoyant densities, satellite DNA fraction, 5-methyl deoxycytidine contents between FR, NF and N. rustica suggests reorganization of genomes of the hybrid progenies following interspecific hybridization. The variation could result in part from the abnormal segregation of chromosomes and chromosome aberrations frequently found in the backcross progeny of rustica-tabacum hybrids at mitosis and meiosis.