Apospory in Paspalum thunbergii

2004 ◽  
Vol 52 (1) ◽  
pp. 81 ◽  
Author(s):  
Guohua Ma ◽  
Xuelin Huang ◽  
Nanxian Zhao ◽  
Qiusheng Xu
Keyword(s):  
Chromosome Number ◽  
Developmental Stage ◽  
Pollen Viability ◽  
Paraffin Section ◽  
Embryo Sac ◽  
Low Frequency ◽  
The Other ◽  
Egg Cell ◽  
Successive Generations ◽  
Mother Cells

The cytology, development of aposporous embryo sac, pro-embryo and pseudogamy in Paspalum thunbergii Kunth ex Steud. was studied. P. thunbergii was found to be a tetraploid cytotype, with a chromosome number of 40. Meiosis of the pollen mother cells was irregular, pollen viability was low and multiporate pollens were often observed. Megasporogenesis began normally; however, the megaspore deteriorated at the developmental stage of tetrad, while one to five specific nucellar cells became active and began enlarging, and then developed into aposporous embryo sacs. The mature aposporous sacs usually had three nuclei characterised by one egg cell and two polar nuclei. The egg cell developed spontaneously to form pro-embryos prior to anthesis. When several aposporous sacs occurred in the same ovule, usually one sac near the micropyle was involved in pseudogamy, while the other sacs were not involved. Low frequency of twin-embryo seedlings was observed after seeds matured. Examination of three successive generations by paraffin-section and clearing methods revealed that no sexual sac was present. Therefore, the species P. thunbergii is considered to be an obligate apomict that reproduces by apospory.

scholarly journals Breeding Systems in tetraploid Rubus species

1966 ◽  
Vol 7 (2) ◽  
pp. 245-253 ◽  
Author(s):  
G. J. Dowrick
Keyword(s):  
Chromosome Number ◽  
Embryo Sac ◽  
Breeding Systems ◽  
Egg Cell ◽  
Breeding Behaviour ◽  
Rubus Species ◽  
Embryo Sac Formation ◽  
Mother Cells ◽  
Normal Meiosis

1. The breeding behaviour of the three tetraploid Rubus species R. caesius, R. calvatus and R. laciniatus (2n = 28) has been investigated.2. Megaspore mother cells of all three species always undergo a normal meiosis and embryo-sac formation is of the Polygonum type. Egg cells have fourteen chromosomes.3. There is no evidence for the production of either aposporic or diplosporic embryo-sacs as has previously been assumed.4. The proportion of sexual and apomictic progeny differs in the three species and, in R. laciniatus, varies according to the chromosome number of the pollinating parent.5. The apomictic progeny are produced by diploidization of the reduced egg cells. These diploidized egg cells can subsequently be fertilized in R. laciniatus.6. The versatility in the breeding behaviour of these species is explained on the basis that only one type of embryo-sac is formed and that the developmental behaviour of the egg cell is conditioned by the chromosome number of the pollinating parent. Apomixis in these species is not a consequence of a breakdown of meiosis.

Embryology of Myosoton and Stellaria and its taxonomic significance (Caryophyllaceae)

Phytotaxa ◽  
2017 ◽  
Vol 306 (2) ◽  
pp. 124
Author(s):  
LIU WANG ◽  
YUN-YUN ZHAO ◽  
JIA-XI LIU
Keyword(s):  
Paraffin Section ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Development Stage ◽  
Mature Stage ◽  
Taxonomic Significance ◽  
Systematic Relationship ◽  
Common Features ◽  
Mother Cells ◽  
Scanning Electron

The systematic relationship between the genera Myosoton and Stellaria is a currently controversial. In this study, we compared their embryological characteristics of these two taxa using conventional paraffin section techniques and scanning electron microscopy. The results obtained showed that Myosoton and Stellaria share some common features. They all have tetrasporangiate anthers with dicotyledonous wall, secretory tapetum, microspore mother cells with simultaneous cytokinesis, tetrahedral tetrad, 3-celled mature pollen grains, linear megaspore tetrad, monosporic polygonum embryo sac, ovary with axial placenta at early development stage, secondary free central placenta at mature stage, bitegmic, crassinucellate amphitropous ovule, micropyle formed from inner integument, caryophyllad embryogenesis, nuclear endosperm, and seed with perisperm. In addition, their seed morphologies are also very similar. Both have rounded, polygonal seed coat cells with upward protrudings, V-shaped margin of testa cells and cross-intercellular contacts. The embryological characteristics support that genus Myosoton should be merged into genus Stellaria.

Embryological studies in the compositae. IV. Sporogenesis, gametogenesis, and embryogeny in Brachycome ciliaris (Labill.) Less

1964 ◽  
Vol 12 (2) ◽  
pp. 142 ◽  
Author(s):  
GL Davis
Keyword(s):  
New South ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Egg Cell ◽  
Male Sterile ◽  
Morphological Variations ◽  
Secondary Nucleus ◽  
South Wales ◽  
Mother Cells ◽  
Antipodal Cells

Material of two varieties of Brachycome ciliaris was obtained from several localities in southern Queensland and western New South Wales, and no embryological differences were found between populations in spite of considerable morphological variations. The plant was highly male-sterile, and although development of the anthers was normal up to the formation of microspore mother cells, presumed meiotic abnormalities resulted in failure to form microspore tetrads except in one instance. The formation of plasmodial microspore mother cells and unreduced pollen grains is described and the occurrence of normal pollen grains in two capitula is recorded. In the ovule, meiosis is suppressed and the megaspore mother cell becomes vacuolate and functions directly as the uninucleate embryo sac. Three nuclear divisions precede the formation of an eight-nucleate embryo sac in which the antipodal cells undergo secondary multiplication. There is circumstantial evidence that the polar nuclei divide simultaneously to form the fist four endosperm nuclei and do not first fuse to form a secondary nucleus. The egg cell develops parthenogenetically and cleavages follow the asterad type of development. The eariy stages of embryogeny are completed before the opening of the florets.

Ultrastructural observations of the mature megagametophyte and the fertilization in wheat (Triticum aestivum)

1985 ◽  
Vol 63 (2) ◽  
pp. 163-178 ◽  
Author(s):  
Ruilin You ◽  
William A. Jensen
Keyword(s):  
Triticum Aestivum ◽  
Pollen Tube ◽  
Cell Walls ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Central Cell ◽  
The Other ◽  
Egg Cell ◽  
Filiform Apparatus ◽  
Egg Apparatus

The mature embryo sac of wheat contains an egg apparatus composed of an egg cell and two synergids at the micropylar end, a central cell with two large polar nuclei in the middle, and a mass of 20 to 30 antipodals at the chalazal end. A comparison was made of the ultrastructural features of the various cells of the embryo sac. The features included the position of the nucleus and vacuoles, the number, structure, and distribution of organelles, and the extent of the cell walls surrounding each cell. The pollen tube enters one synergid through the filiform apparatus from the micropyle. The penetration and discharge of the pollen tube causes the further degeneration of that synergid, which had already undergone changes before pollination. The second synergid does not change further in appearance following the penetration of the first by the pollen-altered tube. Half an hour after pollination at 20–25 °C, two male nuclei are seen in the cytoplasm of the egg and the central cell. At about 1 h after pollination, one sperm has made contact with the egg nucleus, while the other sperm is fusing with one of the polar nuclei.

THE DEVELOPMENT OF TWIN EMBRYO SACS, EMBRYOS, AND ENDOSPERM IN POA ARCTICA R. BR.

1941 ◽  
Vol 19c (5) ◽  
pp. 135-144 ◽  
Author(s):  
V. Engelbert
Keyword(s):  
Chromosome Number ◽  
Pollen Germination ◽  
The Other ◽  
Individual Development ◽  
Polar Cell ◽  
The Individual ◽  
Mother Cells

The origin and development of twin embryo sacs especially in P. arctica R. Br. were studied microscopically in sections of whole spikelets representing consecutive stages in development from the time of emergence of the panicle until after pollination. Twin embryo sacs usually develop, one originating from the innermost of a row of four macrospores with the reduced chromosome number, the other from an aposporous cell that originates in the nucellus, near the chalaza and behind the normal archespore. The individual development of the normal and aposporous embryo sacs from their respective mother cells is traced and the competition between them discussed. Both aposporous and normal egg cells develop parthenogenetically. Pollen germination appears to activate the aposporous polar cell to form endosperm which in turn nourishes the aposporous (2n) and (or) the "sexual" (n) embryo. The greatest number of plants originate from the aposporous embryo. A type of apospory was found in P. alpina L. from Greenland. The work of other investigators, especially on P. pratensis L. is reinterpreted in the light of these findings.

Permanent odd polyploidy in a grass (Andropogon ternatus)

Genome ◽  
1987 ◽  
Vol 29 (2) ◽  
pp. 340-344 ◽  
Author(s):  
Guillermo A. Norrmann ◽  
Camilo L. Quarín
Keyword(s):  
Meiotic Division ◽  
Daughter Cell ◽  
Diploid Species ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Sperm Nucleus ◽  
The Other ◽  
Breeding Systems ◽  
Egg Cell ◽  
Interspecific Crosses

Andropogon ternatus is a triploid species (2n = 3x = 30) with a striking process of microsporogenesis that leads to the formation of two kinds of pollen grains. One-half of the grains carry only one 10-chromosome genome and the other half carry two genomes. After the first meiotic division in the megaspore mother cell, the micropylar daughter cell always has two nuclei, each with 10 chromosomes (genomes S and T); the chalazal daugher cell has one 10-chromosome set (genome S) and undergoes the second meiotic division giving rise to two megaspores; the one closer to the chalaza is the functional megaspore, while the other degenerates. The two-nucleate micropylar daughter cell remains undivided and then degenerates. Thus, the embryo sac always develops from a megaspore with 10 chromosomes (genome S). The results of interspecific crosses with a taxonomically related diploid species (A. selloanus) as well as the study of pollen grain development suggest that the grains carrying nuclei with 20 chromosomes (genomes ST) are functional in the fertilization process, while those with 10-chromosome nuclei seem to be ineffective. Therefore, A. ternatus is a sexual triploid that accomplishes the stability of its odd polyploid level by transmitting one genome through the egg cell and two genomes through the sperm nucleus. This is the first report of permanent odd polyploidy for a species of the monocotyledons. Key words: Gramineae, Andropogon ternatus, odd polyploidy, female meiosis, breeding systems.

MEIOTIC ASSOCIATIONS IN BARLEY LINES WITH EIGHT PAIRS OF CHROMOSOMES AND THEIR HAPLOIDS

1976 ◽  
Vol 18 (4) ◽  
pp. 753-761 ◽  
Author(s):  
R. A. Finch ◽  
K. J. Kasha
Keyword(s):  
Extra Chromosome ◽  
Embryo Sac ◽  
Low Frequency ◽  
Chromosome 8 ◽  
Chromosome 7 ◽  
Chromosome 5 ◽  
Hordeum Vulgare L ◽  
Pairing Behavior ◽  
Mother Cells ◽  
Extra Fragment

Meiosis was studied in pollen mother cells and embryo sac mother cells of seven lines of eight-paired barley (Hordeum vulgare L.) in diploids (2n = 16) and their haploids (2n = 8). Translocation 5-7a, whose breakpoints are distal on chromosome 5 and in the satellite of chromosome 7, was found in all lines. The extra fragment chromosome (8) is a normal or translocation form of chromosome 5 deficient for terminal regions. In diploids, the extra chromosome behaves regularly at meiosis except for occasional univalent-formation and can form a symmetric ring bivalent, but it never forms chiasmata with other chromosomes. In haploids, however, it forms a low frequency of chiasmata with chromosome 5 but this frequency is reduced when the terminal region of chromosome 5 pairs homologously with the satellite region of 7. Based on the hypothesis used to explain chromosome pairing behavior, it should be possible to derive and identify additional eight-paired lines that would be useful for breeding.

scholarly journals Limitation of current probe design for oligo-cross-FISH, exemplified by chromosome evolution studies in duckweeds

Chromosoma ◽  
2021 ◽  
Vol 130 (1) ◽  
pp. 15-25
Author(s):  
Phuong T. N. Hoang ◽  
Jean-Marie Rouillard ◽  
Jiří Macas ◽  
Ivona Kubalová ◽  
Veit Schubert ◽  
...  
Keyword(s):  
Growth Rate ◽  
Chromosome Number ◽  
Chromosome Evolution ◽  
Sequence Similarity ◽  
Flowering Plants ◽  
The Other ◽  
Probe Design ◽  
Congeneric Species ◽  
Specific Design ◽  
Spirodela Polyrhiza

AbstractDuckweeds represent a small, free-floating aquatic family (Lemnaceae) of the monocot order Alismatales with the fastest growth rate among flowering plants. They comprise five genera (Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia) varying in genome size and chromosome number. Spirodela polyrhiza had the first sequenced duckweed genome. Cytogenetic maps are available for both species of the genus Spirodela (S. polyrhiza and S. intermedia). However, elucidation of chromosome homeology and evolutionary chromosome rearrangements by cross-FISH using Spirodela BAC probes to species of other duckweed genera has not been successful so far. We investigated the potential of chromosome-specific oligo-FISH probes to address these topics. We designed oligo-FISH probes specific for one S. intermedia and one S. polyrhiza chromosome (Fig. 1a). Our results show that these oligo-probes cross-hybridize with the homeologous regions of the other congeneric species, but are not suitable to uncover chromosomal homeology across duckweeds genera. This is most likely due to too low sequence similarity between the investigated genera and/or too low probe density on the target genomes. Finally, we suggest genus-specific design of oligo-probes to elucidate chromosome evolution across duckweed genera.

scholarly journals Nucleotide Variation at theCHALCONE ISOMERASELocus inArabidopsis thaliana

Genetics ◽  
2000 ◽  
Vol 155 (2) ◽  
pp. 863-872 ◽  
Author(s):  
Helmi Kuittinen ◽  
Montserrat Aguadé
Keyword(s):  
Nucleotide Diversity ◽  
Direct Relationship ◽  
Selective Sweep ◽  
Balancing Selection ◽  
Neutral Theory ◽  
Low Frequency ◽  
The Other ◽  
Nucleotide Variation ◽  
Rapid Population Growth ◽  
History Of

AbstractAn ~1.9-kb region encompassing the CHI gene, which encodes chalcone isomerase, was sequenced in 24 worldwide ecotypes of Arabidopsis thaliana (L.) Heynh. and in 1 ecotype of A. lyrata ssp. petraea. There was no evidence for dimorphism at the CHI region. A minimum of three recombination events was inferred in the history of the sampled ecotypes of the highly selfing A. thaliana. The estimated nucleotide diversity (θTOTAL = 0.004, θSIL = 0.005) was on the lower part of the range of the corresponding estimates for other gene regions. The skewness of the frequency spectrum toward an excess of low-frequency polymorphisms, together with the bell-shaped distribution of pairwise nucleotide differences at CHI, suggests that A. thaliana has recently experienced a rapid population growth. Although this pattern could also be explained by a recent selective sweep at the studied region, results from the other studied loci and from an AFLP survey seem to support the expansion hypothesis. Comparison of silent polymorphism and divergence at the CHI region and at the Adh1 and ChiA revealed in some cases a significant deviation of the direct relationship predicted by the neutral theory, which would be compatible with balancing selection acting at the latter regions.

Aspidistra revoluta, a new species from limestone areas in Chongqing, China

Phytotaxa ◽  
2016 ◽  
Vol 257 (3) ◽  
pp. 280 ◽  
Author(s):  
Hao Zhou ◽  
Si-rong Yi ◽  
Qi Gao ◽  
Jie Huang ◽  
Yu-jing Wei
Keyword(s):  
New Species ◽  
Chromosome Number ◽  
Average Length ◽  
Chromosome Complement ◽  
Pollen Grains ◽  
The Other ◽  
Morphological Comparison ◽  
Chongqing Municipality ◽  
Karyotype Asymmetry ◽  
A New Species

Aspidistra revoluta (Asparagaceae) is described and illustrated as a new species from limestone areas in southern Chongqing Municipality, China. The new species can be distinguished from the other Aspidistra species by its unique umbrella-like pistil with large revolute stigma lobes that bent downwards and touch the base of the perigone. A detailed morphological comparison among A. revoluta, A. nanchuanensis and A. carnosa is provided. The pollen grains of A. revoluta are subspherical and inaperturate, with verrucous exine. The chromosome number is 2n = 38, and the karyotype is formulated as 2n = 22m + 6sm + 10st. The average length of chromosome complement is 4.50 μm, and the karyotype asymmetry indexes A1 and A2 are respectively 0.37±0.03 and 0.49±0.01.

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