Meiotic analysis of haploid and doubled haploid forms of Nicotiana otophora and N. tabacum

Detailed meiotic studies were conducted on anther-derived haploids of Nicotiana otophora (n = 12) and N. tabacum (n = 24). At midpachytene stages the non-homologous chromosomes apparently remain unpaired. However, since the spreading of chromosomes at this stage was poor, the possible partial pairing, if any, between non-homologues could not be determined with certainty. One to two univalents rarely exhibited partial foldback pairing involving a single arm or the intercalary regions of the same chromosome. — At diakinesis the bivalent-like structures ranged from 0–2 in Otophora and 0–7 per cell in Tabacum haploids. The bivalent-like configurations (mostly rod types with chromatin connections of varying thickness) observed at meta-anaphase I varied from 0 to 1 and 0 to 5 per cell in haploids of Otophora and Tabacum respectively. The various types of secondary associations of univalents at meta-anaphase I were also studied in different haploids. — The probable origin and significance of bivalent-like configurations and secondary associations observed in Nicotiana haploids is briefly discussed. Based on our results, it is concluded that there is very little intra- or intergenomic pairing, if any, in Nicotiana haploids studied. — The meiotic behavior of chromosomes in doubled haploids (N. tabacum) obtained by leaf mid-rib culture, root culture and spontaneous chromosome doubling was remarkably regular with a stable chromosome number of 2n = 48. The meiotic stability of the doubled haploids permits using these materials directly in the breeding program.Contribution from the Department of Agronomy, University of Kentucky. The investigation reported in this paper (72-3-51) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.     

Haploid meiosis and its bearing on the phylogeny of pearl millet,Pennisetum typhoides stapf et hubb.

Meiotic chromosome associations in a spontaneously originated haploid plant of pearl millet have been studied and their phyletic significance discussed. Chromosome pairing could be observed at pachytene and diplotene. Out of a total of 285 PMC's studied at diakinesis-metaphase 1, 43 showed one bivalent and 7 had two bivalents per cell. Both rod- and ring-bivalents were observed. Apart from synapsis accompanied by chiasma formation, close associations of univalent chromosomes were observed. Out of 150 cells without true bivalents, 41 showed 1 s-s association and five, 2 s-s pairs per cell. On the basis of the realization of a maximum of two bivalents per cell, as also of a maximum of 2 s-s pairs, it has been inferred that the chromosome complement ofP. typhoides (n=7) has evolved from a basic set ofn=5 chromosomes. Other available evidence supporting this inference is also discussed.     

Meiosis in haploid barley — An interpretation of non-homologous chromosome associations

Detailed meiotic studies were conducted on ten haploid plants representing six different genotypes of barley (Hordeum vulgare, 2n=14). At pachytene stages the non-homologous chromosomes were observed to pair as intimately as homologous chromosomes in many cells. Foldback pairing, involving single chromosomes, and multivalent associations were common. At diplotene, up to 4 chiasmatalike structures were observed in paired chromosomes but it is not likely that they resulted from crossing over. At diakinesis the bivalent frequency mean was from 1 to 1.3 per cell whereas by metaphase I the paired associations were rare with a single rod bivalent being observed in 3 to 5% of the cells. The frequencies of various types of secondary associations at metaphase were also recorded. — The origin and significance of bivalents and secondary associations in haploids is reviewed and discussed. Caution is urged in the interpretation that low levels of chromosome pairing in haploids is evidence of homology. It is concluded that very little chromosome duplication is likely to be found within the haploid set of barley chromosomes and that the basic chromosome number is seven.     

Medicago murex with 2n=16 and 2n=14 chromosome complements

Contrary to the generally held view, M. murex Willd. was found to be of 2n=14 constitution in the great majority of accessions. The 2n= 16 type, though distributed sparsely over a wide area, is most likely a relic. Chromosome studies at pachytene indicate that the 2n=14 type probably arose from the 2n=16 type by translocation of the chromosomal material of the smallest chromosome in the 2n=16 complement to one of the longer chromosomes, with loss of the centromere of the small chromosome. The total chromosome lengths of the two types thus remained not significantly different, which is in line with the few small morphological differences which were detectable between the two types. Of considerably phylogenetic interest was the finding of complete inter-sterility of the two M. murex types. Neither M. aculeata 2n= 16 nor M. constricta 2n=14 could be crossed with M. murex of the same chromosome number. Inviable hybrids were obtained on crossing M. murex 2n= 16 with M. turbinata 2n=16. The spiny vs. spineless pod character was investigated in the 2n=16 type and found to be inherited on a monofactorial basis.     

BIOSYSTEMATIC INVESTIGATIONS IN THE GENUS AGROPYRON. I. CYTOLOGICAL STUDIES OF SPECIES KARYOTYPES

Schulz -Schaeffer , Jurgen (Montana State Coll., Bozeman), and Peter Jurasits . Biosystematic investigations in the genus Agropyron. I. Cytological studies of species karyotypes. Amer. Jour. Bot. 49(9): 940–953. Illus. 1962.—Twenty-five species of the genus Agropyron are analyzed cytologically in this presentation. Accession numbers, names of collectors, locations where seed was collected, and observed chromosome numbers are listed. Chromosome numbers of A. panormitanum (2n = 28), A. lolioides (2n = 58), A. brachyphyllum (2n = 42), A. ciliatiflorum (2n = 28), A. kosanini (2n = 56), A. pseudorepens (2n = 28), A. squamosum (2n = 42), and A. subulatum (2n = 56) are reported. No previous counts in these species are known to the authors. Chromosome counts of A. caespitosum (2n = 42) and A. elongatiforme (2n = 58), deviate from previous reports. Idiograms of all species and photomicrographs of mitotic metaphase root tip cells of 14 species are presented. The distribution of 11 satellite-chromosome types in 25 Agropyron species is shown in Table 2. The proportions of these 11 satellite-chromosome types are recorded in Table 3. The significance of these satellite chromosomes as indicator chromosomes for genome relationships is discussed together with the pertinent literature.     

Morphology of the pachytene chromosomes of the Indian diploidSolanum nigrum L.

The pachytene chromosome morphology of a locally occurring diploid form ofSolanum nigrum L. (n=12) was studied. The pachytene chromosomes are charaterised by the presence of (1) chromatic and achromatic segments, (2) distinct centromeres and (3) macrochromomeres (telomeres) terminating the chromosome arms. The twelve bivalents are identified individually and described.     

Characterization of Some Chromosomal Aberrations in Regenerated Rice Plants (<Emphasis Type="Italic">Oryza sativa</Emphasis>)

Somaclonal variation was studied in two Iranian land races of O. sativa spp. japonica var Hassani and O. sativa spp. indica var Sadridomsiah and 2000 plants of each cultivar were cytogenetically examined in two steps. In the first step, chromosome counts of root tips was used to detect ploidy levels and aneuploids of regenerated plants. In the second step, chromosomal aberrations were characterized by pachytene analysis of PMC’s. Ploidy levels were seen between n and 4n (haploids to tetraploids) in both cultivars with diploid resource (2n = 2x = 24). The total rate of variation for Hassani (japonica) was 13.7% including 10.8% for changes in chromosome number (ploidy levels and aneuploids) and 2.9% for chromosomal aberrations such as deficiency. A total rate of variation for Sadridomsiah (indica) was 15.6% including 12.4% for change in numbers and 3.2% for aberrations in construction. Most of important cytological mutations were observed in various chromosomes among regenerated plants of cultivars. Neither nullisomics nor inversions were distinguished in any samples.     

INTERSPECIFIC HYBRIDIZATION IN HAPLOPAPPUS AND ITS BEARING ON CHROMOSOME EVOLUTION IN THE BLEPHARODON SECTION

Jackson , R. C. (U. Kansas, Lawrence.) Interspecific hybridization in Haplopappus and its bearing on chromosome evolution in the Blepharodon section. Amer. Jour. Bot. 49 (2) : 119–132. Illus. 1962.—Cytological analyses of interspecific hybrids between H. gracilis (n = 2) and H. spinulosus ssp. australis (n = 8) indicate that ssp. australis is a segmental allotetraploid, derived from past hybridization between 2 taxa with chromosome numbers of n = 4. Analysis of hybrids between H. gracilis (n = 2) and H. ravenii (n = 4), a previously undescribed species, has shown that the chromosome segments of these 2 species are almost completely homologous. Differential contraction is suggested as the explanation for the disappearance in late pachytene of presumed non-homologous segments which were evident in some cells at early pachytene. The pairing relationship of gracilis and ravenii chromosomes at pachytene and later prophase I stages of meiosis indicates that gracilis has evolved from ravenii by an aneuploid reduction process similar to that described for Crepis. The close morphological relationship of the 2 species adds further support to this proposition. Data from the cytological analysis of both interspecific hybrids indicate that x = 4 is the basic chromosome number for the Blepharodon section of Haplopappus.     

Recombination of R-D chromosome in pollen plants cultured from hybrid of 6x Triticale x common wheat

Summary Ninety-three pollen plants derived from the hybrid F₁ of 6x Triticale x common wheat were observed cytologically. The rye chromosomes presented in these plants were identified by Giemsa-banding. Pollen plants having chromosome constitution 2n = 24 in haploids and 2n=46 in diploids were found to be predominant. The chromosome distributions of the R and D genome are different. R chromosomes distributed randomly and tended to full combination in offspring, but D chromosomes distributed non-randomly and tended to maintain intact.     

Cytological evidence on the origin of sweet potato

Summary The results of intensive meiotic studies, particularly of the karyology and chromosomal homology at the pachytene stage, in the sweet potato (Ipomoea batatas L.), which is a hexaploid (2 n = 90), have thrown considerable light on its origin and genome relationships. Using suitable criteria, such as relative length of chromosomes, centromere position, chromomere pattern, absence of light staining segments in one of the arms, presence of telochromomere etc., 40 of the 45 haploid chromosome complement at pachytene were identified and assigned to 19 chromosomal types. Among these types, eight were present singly; in six of the types, chromosomes were present in duplicate, and in two types, in triplicate. The occurrence of higher multivalent chromosomal associations such as hexavalents and pentavalents, in addition to the quadrivalents already reported, was recorded for the first time at the pachytene and metaphase I stages. The hexavalents at pachytene were resolved into three distinct types based on the morphology of the participating chromosomes. A maximum number of nine quadrivalents at the metaphase I stage and four in the incompletely analyzed pachytene nuclei were recorded. The constituent chromosomes of three of the quadrivalents at pachytene stage were identified. From these observations, it is suggested that (i) the three parental genomes are partly homologous (ii) two of the genomes show closer homology to one another than to the third and (iii) the three genomes differ with respect to one or more of the eight chromosomal types occurring singly. The available information rules out an autopolyploid origin for sweet potato and suggests that the parental genomes are from closely related taxa. The advantages are emphasized of pursuing similar studies in other American Ipomoea species to unravel their relationship with the sweet potato. Among other meiotic irregularities, a translocated chromosome and a chromosome carrying inversion were detected at the pachytene stage and the possible role they may play in varietal differentiation is discussed.     

Meiosis in gray voles of the subgenus <Emphasis Type="Italic">Microtus</Emphasis> (Rodentia,Arvicolinae) and in their hybrids

The results of light and electron microscopic (EM) studies of meiosis in Microtus arvalis males of the karyoform “arvalis” (2n = 46, NFa = 80), in hybrids between the chromosomal forms arvalis and obscurus (2n = 46, NFa = 68), in M. rossiaemeridionalis voles (2n = 54, NFa = 54), and in a hybrid between the species M. rossiaemeridionalis and kermanensis (2n = 54, NFa = 54) are presented. SC (synaptonemal complex) karyotypes of the parental forms and the hybrids were constructed on the basis of measurements of the length of autosomal SCs revealed by the EM analysis in spermatocytes at the stage of middle pachytene. The SC karyotypes of M. arvalis and the hybrids ♀ obscurus × ♂ arvalis consist of 22 synaptonemal complexes of autosomal bivalents and the axial elements of the synaptonemal complexes of the sex chromosomes X and Y. The SC karyotypes of M. rossiaemeridionalis and the hybrid M. rossiaemeridionalis × M. kermanensis consist of 26 synaptonemal complexes of autosomal bivalents and a sex bivalent; they differ only in the length of the Y chromosome axis (Y chromosome in the hybrid was inherited from M. kermanensis). Asynaptic configurations of the autosomal SCs were not observed in the hybrids. The SC axial elements of the X and Y chromosomes in the parental forms and in the hybrids were located close to each other throughout pachytene, but they did not form a synaptic region. The normal synapsis in sterile hybrids (M. rossiaemeridionalis × M. kermanensis) and the behavior of the sex chromosomes in meiosis in fertile and sterile hybrids are discussed in the context of specific features of meiosis and reproductive isolation.     

Genome relationships between Hordeum procerum (6x) and H. lechleri (6x)

Investigations on the meiotic behaviour of chromosomes in interspecific hybrids (2n=6x=42) between Hordeum lechleri (6x) and H. procerum (6x) and in their component haploids have been utilized to assess the nature of pairing and the extent of genome homology between the two species. In the F₁ hybrids an average of 25 (60%) chromosomes associated at metaphase I, mostly as bivalents. A majority (60%) of the pollen mother cells (PMCs) in H. procerum haploids (2n=3x=21) displayed 21 univalents and even in the remainder, a maximum of two rod bivalents were formed resulting in an average of 0.52 bivalents per cell. In haploids of H. lechleri (2n=3x=21) however, 30% of chromosomes pair. The sum of the chromosomal associations in the component haploids represents only 17% of the complement, far below the observed frequency (60%) in the hybrids. Thus, the pairing displayed in hybrids between H. lechleri and H. procerum was mostly allosyndetic and suggestive of two genomes being common in these species.In haploid H. procerum 1/3 of the PMCs displayed a tripolar organisation of chromosomes leading to triad and hexad formation after divisions I and II respectively. The significance of hexad formation in the trihaploid H. procerum and a possible suppression of homoeologous pairing in H. procerum haploids are discussed.     

Flexible chromosome painting based on multiplex PCR of oligonucleotides and its application for comparative chromosome analyses in Cucumis

Chromosome painting is a powerful technique for chromosome and genome studies. We developed a flexible chromosome painting technique based on multiplex PCR of a synthetic oligonucleotide (oligo) library in cucumber (Cucumis sativus L., 2n = 14). Each oligo in the library was associated with a universal as well as nested specific primers for amplification, which allow the generation of different probes from the same oligo library. We were also able to generate double‐stranded labelled oligos, which produced much stronger signals than single‐stranded labelled oligos, by amplification using fluorophore‐conjugated primer pairs. Oligos covering cucumber chromosome 1 (Chr1) and chromosome 4 (Chr4) consisting of eight segments were synthesized in one library. Different oligo probes generated from the library painted the corresponding chromosomes/segments unambiguously, especially on pachytene chromosomes. This technique was then applied to study the homoeologous relationships among cucumber, C. hystrix and C. melo chromosomes based on cross‐species chromosome painting using Chr4 probes. We demonstrated that the probe was feasible to detect interspecies chromosome homoeologous relationships and chromosomal rearrangement events. Based on its advantages and great convenience, we anticipate that this flexible oligo‐painting technique has great potential for the studies of the structure, organization, and evolution of chromosomes in any species with a sequenced genome.     

A chromosome-specific estimate of transmission of heterozygosity by 2n gametes in potato

Polyploid plants are formed when numerically unreduced (2n) gametes participate in fertilization. Based on cytological and genetic analyses, modes of 2n gamete formation have been determined for a number of plant species. Gametes formed by a first-division restitution (FDR) mechanism contain nonsister chromatids near the centromere, whereas those formed by second-division restitution (SDR) contain sister chromatids. These mechanisms differ in the proportion of heterozygous loci they transmit intact to offspring. This paper estimates the transmission of heterozygosity on an individual chromosome basis through pachytene analysis of chromosomes of haploids (2n = 2x = 24) of Solanum tuberosum Andigena Group (2n = 4x = 48), a South American cultivated potato. Transmission of heterozygosity by FDR and SDR 2n gametes was calculated for 6 different cytogenetic assumptions. FDR was more than twice as effective as SDR in transmission of heterozygosity under all 6 scenarios. Rates of transmission of heterozygosity were similar in each situation. Transmission of heterozygosity by FDR was also compared with transmission of heterozygosity by tetrasomic inheritance and found to be approximately 50% more effective.     

Polyploidy and Evolution in Wild and CultivatedDahliaSpecies

Observations on the chromosomes of nine species ofDahliaCav.(Asteraceae, Heliantheae—Coreopsidinae) show that somehave 2n=32, others 2n=64, with a third group having both chromosomenumbers in the same taxon. Karyotype investigations showed thatthe chromosomes can be divided into groups of 14 metacentricsplus two submetacentrics per set of 16 chromosomes.In situhybridizationusing an rRNA gene probe indicated that the 2n=32 species haveeight hybridization sites whilst the 2n=64 species have 16 sites.Silver nitrate staining of these regions showed that not allof these nucleolar organizers are active. Meiotic analysis atmetaphase I and pachytene, by synaptonemal complex spreading,shows that the 2n=32 species have exclusive bivalent formationwhereas the 2n=64 species have small numbers of univalents plusquadrivalents in addition to bivalents. This study proposesthatDahliaspecies with 2n=32 are allotetraploids whereas thosespecies and chromosome races with 2n=64 are their autopolyploidderivatives. We suggest that a bivalent-promoting mechanismin the 2n=32 species may account for their meiotic behaviouras their component genomes appear so similar, and that thismechanism is also responsible for the low number of quadrivalentsin the 2n=64 taxa.Copyright 1998 Annals of Botany Comapny Chromosome pairing,Dahlia, in situhybridization, karyotype analysis, polyploidy, synaptonemal complex analysis     

Localization of chromosome regions in potoroo nuclei (<Emphasis Type="Italic"> Potorous tridactylus </Emphasis>Marsupialia: Potoroinae)

Chromosome paints of the rat kangaroo ( Aepyprymnus rufuscens, 2n =32) were used to define chromosome regions in the long nosed potoroo ( Potorous tridactylus, 2n =12 female, 13 male) karyotype and localize these regions in three-dimensionally preserved nuclei of the potoroo to test the hypothesis that marsupial chromosomes have a radial distribution. In human nuclei chromosomes are distributed in a proposed radial fashion. Gene-rich chromosomes in the human interphase nucleus are preferentially located in the central area while gene-poor chromosomes are found more at the periphery of the nucleus; this feature is conserved in primates and chicken. Chromosome ordering in nuclei of P. tridactylus is related to their size and centromere position. Its relationship with replication patterns in interphase nuclei and metaphase was studied. In addition it was observed that the nucleus was not a smooth entity but had projections occupied by specific chromosome regions. Edited by: R. Allshire     

ORIGIN OF TRIPSACUM ANDERSONII (GRAMINEAE)

Tripsacum andersonii Gray (Gramineae) is a species with 2n = 64 chromosomes. Chromosome behaviour during meiosis of microsporogenesis suggests that the species combines three homologous haploid Tripsacum genomes of x = 18 (54 chromosomes), and an alien haploid genome of x = 10 chromosomes. Cytogenetic studies indicate that T. andersonii originated as a hybrid between a species of Tripsacum (2n = 36) and a species of Zea (2n = 20). Comparative morphology and flavonoid chemistry fail to identify the Zea species involved in this intergeneric hybrid. Chromosome morphology suggests that it was either Z. mays L. subsp. mays (domesticated maize) or subspecies mexicana (Schrad.) Iltis (annual teosinte). The Tripsacum parent probably was T. latifolium Hitchc. of Central America. It resembles T. andersonii in vegetative morphology. Tripsacum maizar Hernandez et Randolph and T. laxum Nash, which resemble T. andersonii in flavonoid chemistry, are eliminated as possible parents on the basis of growth habit and the morphology of their hybrids with maize.     

The pachytene chromosomes of Ipomoea crassicaulis

Summary The detailed morphology of the pachytene chromosomes and microsporogenesis have been studied in a diploid (2 n=30) American species, Ipomoea crassicaulis (Bth) B. L. Robinson. Idiogram of the pachytene chromosomes is presented and taking advantage of the extreme precision that pachytene analysis can lend, karyological characteristics of the haploid complement have been worked out in detail and individual chromosomes are identified. The course of meiosis was normal and over ninety five percent of pollen were found stainable. The urgent need for extending similar studies to other taxa in this economically important genus for unravelling phyletic relationships has been stressed.

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Zusammenfassung Bei der diploiden amerikanischen Ipomoea crassicaulis (Bth) B.L. Robinson (2 n=30) wird die Morphologie der Pachytänchromosomen und die Mikrosporogenese untersucht. Das Idiogramm der Pachytänchromosomen wird aufgestellt und unter Ausnutzung der großen Präzisionsmöglichkeit der Pachytänanalyse werden die charakteristischen Daten des haploiden Chromosomensatzes erarbeitet und alle Chromosomen identifiziert. Die Meiose verläuft normal und liefert zu mehr als 95% guten Pollen. Die Notwendigkeit umfassender ähnlicher Untersuchungen bei anderen taxonomischen Einheiten aus dieser wirtschaftlich wichtigen Gattung zwecks Klärung phylogenetischer Beziehungen wird nachdrücklich hervorgehoben.

     

MEIOSIS WITH TELOMERIC PAIRING IN A HAPLOID OF TRITICUM MONOCOCCUM (x = 7)

In the microsporocytes of a haploid of Trilicum monococcum (x = 7), foldback and other nonhomologous pairing was observed at pachytene. At the diplotene equivalent stage of meiosis, nonhomologous chromosomes were connected by their telomeres in associations involving two to seven chromosomes. Telomeric connections were Feulgen-positive for DNA and were disjoined by metaphase I. These connections may have resulted from earlier base-pairing of repeated sequences of guanine-rich telomere overhangs of nonhomologous chromosomes. Recent molecular studies of several widely divergent organisms have shown that all telomeres of nonhomologous chromosomes in a genome are identical, and telomere structure is conserved among widely divergent eukaryotes. Chromosome distribution at anaphase I fitted theoretical expectations of random movement of each of the seven chromosomes to one or the other of the two poles as did pollen fertility (stainability) resulting from such distribution. A single bivalent in 3.78% of the metaphase I cells provided evidence for a duplication in the genome of Triticum monococcum.     

Features of Crossability, Haploidy and Polyembryony in Hybrid Combinations between Cultivated Barley Hordeum vulgare L. (2n = 14) and Wheat-Rye Substitution Lines Triticum aestivum L., Cultivar Saratovskaya 29/Secale cereale L., Cultivar Onokhoiskaya

The role of individual chromosomes of rye in the manifestation of crossability and seedling development in hybrid combinations between cultivated barley Hordeum vulgare L., cultivar Nepolegayushchii (2n = 14) and five wheat-rye substitution lines Triticum aestivum L., cultivar Saratovskaya 29/Secale cereale L., cultivar Onokhoiskaya (2n = 40 wheat + 2 rye chromosomes). Crossability, which was measured by two parameters—frequency of set grains and frequency of grains with embryos—was shown to be significantly affected by each of the five rye chromosomes examined: 1R, 2R, 3R, 5R, and 6R; the development of barley haploids was affected by rye chromosomes 1R, 3R, and 5R. We were the first to demonstrate that polyembryony could be induced by mutual effects of barley cytoplasm and rye chromosome 1R. Possible mechanisms controlling the development of haploids and twins in hybrid combinations H. vulgare × T. aestivum/S. cereale are discussed. The conclusion is drawn that hybrid combinations between cultivated barley and wheat-rye substitution lines can serve as new models for studying incompatibility mechanisms in distant crosses and genetic control of parthenogenesis.__________Translated from Genetika, Vol. 41, No. 6, 2005, pp. 784–792.Original Russian Text Copyright © 2005 by Pershina, Belova, Devyatkina, Rakovtseva, Kravtsova, Shchapova.