Fertility and aneuploidy in autopolyploidAnthoxanthum

An autopolyploid series comprising 2x, 3x and 4x was obtained by colchicining the diploid speciesA. ovatum Lag. The autotriploid, used as seed and pollen parent, was back-crossed to diploid and tetraploid. No significant overall difference was observed in fertility, but there was a tendency for particular pair crosses to the diploid as female parent to show higher levels of seed-setting. This may be associated with the relatively large proportion of haploid pollen that functions when the triploid is used as the male parent.The effectiveness, in part, of the freely liberated pollen of autotriploidAnthoxanthum in producing progeny, contrasts with the total failure of manually liberated allotriploidDactylis pollen. Triploid sterility may well relate to degree of hybridity.Genetic unbalance induced by aneuploidy was considered to be more relevant than the genetic ratio in seeds, as an explanation of the type of interploid progeny obtained inAnthoxanthum.Cytological material in this paper was submitted by the junior author in partial satisfaction of the requirements for the degree of M.Sc. in the University of Wales.     

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.     

Occurrence of aneuploid progenies from an asynaptic amphidiploid ofScilla scilloides (lindley) druce II. Mechanism of production of the various aneuploid progenies

The mechanism of production of the various aneuploid progenies was clarified in the asynaptic amphidiploid plants (2n=34+4f+2F, AABB) ofScilla scilloides. Its asynaptic nature and chromosomal stickiness lead to the unequal segregation at anaphase I (AI) in PMC's. The observed values in 18 segregation patterns, 17:17 to 0: 34, were different from the expected values estimated from random segregation of chromosomes. Nevertheless, the preferential transmission of special chromosomes among genomes A (x=8=a₁−a₈) and B (x=9=b₁−b₉) had not occurred. As the result of unequal segregation, the pollen grains with various chromosome numbers were observed. Almost all of the 200 pollen grains contained chromosome numbers more than 17 (range 8 to 34). The observed values of each chromosome number were roughly similar to the expected values of containing the complete set of genome A or B in the random distribution without preferential segregation of chromosomes at AI. The difference between the index of polien mitosis and the pollen fertility was significant in the Wilcoxon matched-pairs signed rank test and suggested the selection for some genomically unbalanced pollen grains during maturation. Consequently, viable pollen grains with various chromosome constitutions are a few (mean pollen fertility of 5.8%) but might produce many aneuploids by self- and cross-pollination.     

CYTOLOGY AND REPRODUCTIVE CHARACTERISTICS IN PENNISETUM SETACEUM

A green ecotype of fountaingrass, Pennisetum setaceum (Forsk.) Chiov., was found to be triploid (3x = 27) with 9 II + 9 I at metaphase I. Meiotic behavior of the bivalents was normal, but the univalents lagged and divided precociously at anaphase I. The univalent halves lagged at anaphase II and were distributed at random. Micronuclei were common, and stainable pollen was approximately 40%. The green type produced four progeny with 54 chromosomes. A purple strain of P. setaceum was found to be hexaploid (6x = 54) with varying chromosomal associations. Meiotic behavior was highly irregular and stainable pollen was almost zero. Megasporogenesis was initiated in both types, but the megaspores degenerated and nucellar and integument cells developed into four-nucleate, aposporous embryo sacs. Following self-pollination, the green type set approximately 10% seed and the purple type set 0.05% seed. Purple fountaingrass set as high as 18% seed following the application of pollen from Pennisetum ciliare (L.) Link (4x = 36), exemplifying a rare form of pseudogamy between two species. Improvement of P. setaceum through a standard breeding program appears unlikely.     

Some events of mitosis and cytokinesis in the generative cell of Ornithogalum virens L.

The organization of the microtubule (Mt) cytoskeleton during mitosis and cytokinesis of the generative cell (GC) in Ornithogalum virens L. (bicellular pollen type, chromosome number, n = 3) from prophase to telophase/sperm formation was investigated by localization of -tubulin immunofluorescence using a conventional fluorescence microscope and a confocal laser scanning microscope. Chromosomes were visualized with DNA-binding fluorochrome dyes (ethidium bromide and 46-diamino-2-phenyl-indole). The GC of O. virens is characterized by G2/M transition within the pollen grain and not in the pollen tube as occurs in the majority of species with bicellular pollen. It was found that prophase in the GC starts before anthesis and prometaphase takes place after 10 min of pollen germination. The prophase Mts are organized into three prominent bundles, located near the generative nucleus. The number of these Mt bundles is the same as the number of GC chromosomes, a relation which has not previously been considered in other species. The most evident feature in the prophase/ prometaphase transition of O. virens GC is a direct rapid rearrangement of Mt bundles into a network which appears to interact with kinetochores and form a typical prometaphase Mt organization. The metaphase chromosomes are arranged into a conventional equatorial plate, and not in tandem as is thought to be characteristic of GC metaphase. The metaphase spindle consists of kinetochore fibres and a few interzonal fibres which form dispersed poles. Anaphase is characterized by a significant elongation of the mitotic spindle concomitant with the extension of the distance between the opposite poles. At anaphase the diffuse poles converge. Cytokinesis is realized by cell plate formation in the equatorial plane of the GC. The phragmoplast Mts between two future sperm nuclei appear after Mts of the mitotic spindle have disappeared.Abbreviations DAPI 46-diamino-2-phenyl-indole - GC generative cell - GN generative nucleus - Mt microtubule This research was made possible in part due to TEMPUS Programme and Global Network for Cell and Molecular Biology UNESCO grants to Magorzata Bana. The experimental part of the work was done in Siena University. M. Banas is very grateful to Prof. Mauro Cresti and his group for scientific interest, offering the excellent laboratory facilities, and kind reception.     

CYTOLOGICAL ANALYSIS OF ANTHURIUM ANDRAEANUM (ARACEAE), ITS RELATED TAXA AND THEIR HYBRIDS

Karyotypes and meiotic configurations of Anthurium andraeanum and closely related taxa were analyzed. The karyotypes of A. andraeanum, A. caperatum, A. formosum, A. kamemotoanum, A. lindenianum, A. roseospadix, A. cf. sanctifidense, A. subsignatum, A. garagaranum, and an unidentified Anthurium sp. commonly consisted of four large metacentric or submetacentric chromosomes, two fairly large acrocentric chromosomes, two satellite chromosomes, and 22 smaller chromosomes. Variation in the karyotypes of A. nymphaeifolium and A. ochranthum suggested chromosomal rearrangement in the genus. All taxa showed 15 pairs of chromosomes at prometaphase I of meiosis in pollen mother cells. Four large chromosomes appeared as ring bivalents, and the rest of the chromosomes appeared as either ring or rod bivalents. Regular bivalent formation at prometaphase I of meiosis in pollen mother cells of species hybrids suggested close genomic relationships among parental taxa. On the other hand, reduction of pollen fertility estimated by pollen stainability in those hybrids suggested genetic divergence of species.     

A study of hybridisation involving the sweet potato and related species

Overwhelming evidence points to an American origin for the sweet potato Ipomoea batatas (L.) Lam. Attempts have been made to identify related diploid species from Mexico, and to use these in hybridisation experiments with I. batatas. The sweet potato is a poor seed setter but abundant bloom occurs in Jamaica very late in the year. Attempts at hybridisation between I. batatas (2n=90) and I. trichocarpa (Elliott) (2n=30) or I. gracilis (2n=30) has been tolerably successful. A very high degree of self-incompatibility was demonstrated in all three species investigated but successful crosses were made using different plants of I. trichocarpa. An investigation of pollen viability showed that in all cases pollen could germinate but pollen tube growth was abnormal in incompatible pollinations. I. trichocarpa hybridised readily with I. batatas when the former was used as female parent. Embryo development in such a cross proceeded slowly, and stopped before cotyledon formation. No viable seeds were obtained. A comparison of embryo development in hybrid and normal seeds brought to light anomalies in development and structure of endosperm and maternal tissue in the hybrid.     

Relationship between indoor and outdoor airborne fungal spores, pollen, and (1→3)-β-D-glucan in homes without visible mold growth

In this exploratory study, indoor and outdoor airborne fungal spores, pollen, and (1→3)-β-D-glucan levels were determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected in five Cincinnati area homes that had no visible mold growth. The total count of fungal spores and pollen in the collected samples was conducted under the microscope and Limulus Amebocyte Lysate (LAL) chromogenic assay method was utilized for the determination of the (1→3)-β-D-glucan concentration. For the combined number concentration of fungal spores and pollen, the indoor and outdoor geometric mean values were 573 and 6,435 m⁻³, respectively, with a geometric mean of the Indoor/Outdoor (I/O) ratio of .09. The geometric means of indoor and outdoor (1→3)-β-D-glucan concentrations were .92 and 6.44 ng m⁻³, respectively, with a geometric mean of the I/O ratio equal to .14. The I/O ratio of (1→3)-β-D-glucan concentration was found to be marginally greater than that calculated based on the combined number concentration of fungal spores and pollen. This suggests that (1→3)-β-D-glucan data are affected not only by intact spores and pollen grains but also by the airborne fragments of fungi, pollen, and plant material, which are ignored by traditional enumeration methodologies. Since the (1→3)-β-D-glucan level may elucidate the total exposure to fungal spores, pollen, and fungal fragments, its I/O ratio may be used as a risk marker for mold and pollen exposure in indoor environments.     

Chromosome elimination in Paspalum subciliatum (Notata group)

 This paper reports the occurrence of chromosome elimination during microsporogenesis in a Brazilian accession of Paspalum subciliatum. The accession was tetraploid (2n=4x=40) and meiosis was normal until diakinesis, with 20 regularly distributed bivalents. Starting at metaphase I, meiosis was very peculiar. In this phase, while ten bivalents were clustered in the equatorial plate, the other ten were still dispersed in the cytoplasm. In anaphase I the chromosomes showed different abilities to migrate to the poles. While one genome reached the poles in telophase I, the laggard was in metaphase or anaphase and was engulfed by extra nuclei. In the second division, behavior was the same. Our results show clear asynchrony in cell cycle, especially in some meiotic phases. Unfortunately we cannot explain the causes of the phenomenon, but this event shows once more that chromosome elimination serves as an incompatibility barrier preventing divergent genomes from coexisting in the same cellular system. The chromosome elimination affected pollen fertility but did not impair seed viability. Received: 22 April 1998 / Revision accepted: 2 September 1998     

Tetraploid hybrids from crosses between diploid and tetraploidDactylis and their significance

Chromosome counts on the progeny of crosses between diploid and tetraploid races ofDactylis show that tetraploid hybrids are produced as well as the expected triploids. The relative proportions of 4x and 3x hybrids vary greatly in different crosses, and the data suggest that parental geno-type influences the result. Overall, the frquencies of 3x and 4x hybrids are about equal, with no indication of a difference between the reciprocal 2x×4x and 4x×2x cross-combinations except perhaps in the case of diploids and autotetraploids of the same subspecies. Rare triploid hybrids are found in crosses between diploid subspecies ofDactylis. The mechanisms by which a diploid plant could donate two genomes to its offspring are discussed in relation to theDactylis situation, and the evolutionary significance of 4x hybrids formed in this way is considered.     

Studies on triploid Allium triquetrum

This work describes the relationship between the univalents seen at metaphase I and the distribution of dyads at anaphase I in the pollen mother cells of triploid Allium triquetrum. The orientation of the centromeres within the trivalents and bivalents at metaphase I towards the two poles of the pollen mother cells is random. The distribution of polar univalents towards the two poles at metaphase I is also random, as is the distribution of dyads at anaphase I in low univalent frequency collections. However, in a high univalent frequency collection, the distribution of dyads at anaphase I is non-random. There is an excess of cells with the most equal dyad distribution (13–14) and a paucity of cells with a 12–15 distribution. In low univalent frequency collections, the equatorial univalents are believed to remain in the equatorial region during anaphase I and are seen as laggards at late anaphase I. The remaining chromosomes move according to the metaphase I orientation of their centromeres to give a random distribution of dyads at anaphase I. In high univalent frequency collections it is argued that the non-random dyad distribution seen at anaphase I is the result of non-random movement of some of the equatorial univalents away from the equatorial region during anaphase I. The remaining equatorial univalents remain in the equatorial region and are seen as laggards at late anaphase I.     

Further studies on polyploid amphibians (Ceratophrydidawe)

Odontophrynus cultripes Reinhardt and Lutken, 1862 has 22 chromosomes in its diploid complement. Spermatocyte I contained 11 ring bivalents and metaphase II exhibited 11 chromosomes. Odontophrynus americanus (Duméril and Bibron) 1882 has 44 chromosomes in somatic as well as germ cells, these can be sorted into 11 groups of homologues. Metaphase I showed varying numbers of quadrivalents and metaphase II exhibited 22 dyads. Ceratophrys dorsata Wied., 1824 has 104 chromosomes in somatic and germ cells; these 104 chromosomes comprise 8 each of 13 kinds of homologues. The spermatocyte I contained ring octovalents and other multivalents, and metaphase II 52 chromosomes. The above findings indicate that evolution by polyploidization occurred in South American frogs belonging to the family Ceratophrydidae.This work was supported by a grant (GM-14577-01) from the National Institute of General Medical Sciences U. S. Public Health Service.     

Study on Genetic Behaviour of B Chromosomes at Meiosis in Agropyron Gaertn

The chromosomal behaviour at meiosis in pollen mother cells of 33 sample materials from 4 species in Agropyron Gaerm. distributed over various regions in China were observed. We. found that B chromosomes were mainly-present in A. mongolicum Keng (2n=2x=14) and were absent in the tetraploid ,A. cristarum (L.) Gaertn. (2n=4x=28) and ,A. michnoi Roshev. (2n=4x=28). Of all A. desertorum (Fisch.) Schult. (2n=4x=28) populations, they were present in 40%. The pairing between even numbers of B chromosomes usually occured at diakinesis where as uneven numbers of B chromosomes at metaphase 1. B chromosomes at anaphase I separated at random. The Fagging Bs tended to reach two poles by chromatids through precocious division of Bs. The pairing and chiasma frequencies between A chromosomes were increased by the larger numbers of Bs. The relationship between B chromosomes and species ploidy, the homeology among Bs, etc were discussed.     

Cytotaxonomische Beiträge zurTaraxacum-Flora der Türkei

A new triploid microspecies ofTaraxacum from sect.Erythrocarpa is described:Taraxacum erzincanense Doll. In addition, 2x 3x, and 4x chromosome numbers, pollen conditions and chorological facts are reported for serveral other rare Oriental microspecies.

     

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.     

A cytogenetic method for stacking gene pairs in common wheat

The potential for non-reciprocal Robertsonian translocations of wheat (Triticum aestivum L.) to assist in the stacking of genes was assessed from a study of their cytological and genetic behaviour. To obtain translocations, a double monosomic (3B+5A; 2n=40=19ii+2i) was crossed reciprocally with a contrasting disomic. Individuals inheriting a broken monosome were identified from the loss of one arm-specific DNA marker coupled with retention of a marker for the opposite arm. No double breaks (potential translocations) were found in 180 cross progeny recovered from pollen of the double monosomic but two instances (loss of 5AL plus 3BS; loss of 5AL plus 3BL) were found in 251 progeny recovered from ovules. Meiotic pairing and multi-color genome-specific fluorescence in situ hybridization (mcGISH) showed that each plant with a double break contained one translocated chromosome between the A and B genomes that had rejoined at the centromere and that formed a trivalent (19ii + 1iii) in about 83% of PMC. Most trivalents (approximately 92%) aligned at metaphase in a V configuration (alternate disjunction) while the rest aligned in linear I (adjacent disjunction) or ambiguous L configurations. Genetic analysis of a testcross of these fusion monosomics showed that this preferential co-orientation of the trivalent influenced the assortment of the chromosome arms involved. Loci that were located in the hemizygous ends of the V trivalent showed strong quasi-linkage in that most ovules from the female testcross carried relevant DNA markers either from both standard chromosomes or from neither. This shows that, in most cases, the two standard chromosomes assorted to the same pole while the fused monosome segregated to the opposite pole. For heterozygous loci (present both on the fusion monosome and the standard chromosomes) assortment was either independent or showed partial linkage to the hemizygous arm depending on the reported recombination distance from centromere. Marker assortment was further distorted in male testcrosses and in doubled haploids (made from the fusion monosomics by the maize method) by the strong selective advantage of pollen or haploids that inherited the standard chromosomes rather than the deficiencies. This genetic data shows that under the combined influence of alternate disjunction and natural selection, progeny of fusion monosomics will revert to the standard disomic arrangement, fixing the gene content of both hemizygous arms in the process. Thus, any pair of genes could be targeted for joint fixation by isolating the fusion monosome that will link them temporarily in a segregating population.     

Effect of genetic background on trisomy in ryegrass

Six primary trisomics of ryegrass, Lolium perenne L., were studied in perennial and perennial x annual hybrid backgrounds. Chromosome association at meiotic metaphase I and chiasma number per cell of the individual trisomes did not differ in the two genetic backgrounds. Hybrid trisomies showed wider variation in morphology, and had higher pollen fertility than the perennial trisomics and disomics. — It is concluded that the transfer of perennial ryegrass chromosomes and segments into annual ryegrass can be accomplished without any serious consequence on the cytological stability of the reconstituted genome.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

Ultrastructure of meiosis in the mossRhynchostegium serrulatum I. Prophasic microtubules and spindle dynamics

Summary An extensive system of microtubules develops during meiotic prophase in the mossRhynchostegium serrulatum (Hedw.)Jaeg. &Sauerb. Development of the cytoskeleton can be traced to early prophase when the nucleus is acentric and the single plastid divides into four plastids. The cytoskeletal microtubules are associated with equidistant positioning of the four plastids at the distal tetrad poles and with migration of the nucleus to a central position in the sporocyte. The cytoskeleton, which interconnects plastids and encloses the nucleus, contributes to the establishment of moss sporocyte polarity. Just prior to metaphase I evidence of the prophase cytoskeleton is lost as the bipolar metaphase I spindle develops in association with discrete polar organizers located in opposite cleavage furrows between plastids.