scholarly journals Two Embryo-Sac Mother Cells in Lilium longiflorum

1907 ◽  
Vol 43 (6) ◽  
pp. 418-419
Author(s):  
Margaret C. Ferguson
Keyword(s):  
Embryo Sac ◽  
Lilium Longiflorum ◽  
Mother Cells

The time and duration of preleptotene chromosome condensation stage in Lilium hybrid cv. Black Beauty

1975 ◽  
Vol 188 (1093) ◽  
pp. 477-493 ◽  
Keyword(s):  
Maximum Degree ◽  
Meiotic Chromosome ◽  
Embryo Sac ◽  
Lilium Longiflorum ◽  
Chromosome Condensation ◽  
Late Prophase ◽  
Significant Function ◽  
Mother Cells ◽  
Black Beauty ◽  
Pairing Behaviour

A period of chromosome condensation followed by decondensation occurs between premeiotic interphase and leptotene in Lilium hybrid cv. ‘Black Beauty’. The duration of this period was estimated to be about 1.16 days in pollen mother cells (p. m. cs) of plants grown at 20 °C. Preleptotene chromosome condensation and contraction also occurred in embryo sac mother cells (e. m. cs) of ‘Black Beauty’. However, the maximum degree of chromosome contraction at the preleptotene condensation stage was much greater in p. m. cs than in e. m. cs. Moreover, the preleptotene condensation and decondensation stage was apparently shorter in e. m. cs (about 0.7 days) than in p. m. cs. The developmental behaviour of p. m. c. chromosomes during pre­leptotene condensation and decondensation was essentially the same as that described by Walters (1970, 1972) for the corresponding stages in Lilium longiflorum cv. ‘Croft’. A brief illustrated description is given of the appearance of p. m. cs at various stages of preleptotene chromosome condensation in both methylene blue stained anther sections, and in Feulgen stained anther squashes. ‘Black Beauty’ p. m. cs entered preleptotene chromosome condensation stage from G2 of premeiotic interphase having completed DNA synthesis. All the p. m. cs within an anther loculus underwent preleptotene chromo­some condensation stage with a degree of synchrony not less than that found at early first meiotic prophase. At maximum chromosome contration the diploid chromosome number (2 n = 24) could often be counted, but no evidence of association of chromosomes was seen. At this stage the appearance of the chromosomes was indistinguishable from that of late prophase or prometaphase chromosomes at mitosis. Thereafter chromo­somes underwent decondensation and elongation and eventually passed into leptotene without first entering any other stage. The nature and possible significance of preleptotene chromosome condensation and decondensation are discussed. The appearance and behaviour of chromosomes at preleptotene condensation stage is the same as that displayed by chromosomes at mitotic prophase. Similarly, the appearance and behaviour of chromosomes at preleptotene decondensation is indistinguishable from that normally seen at mitotic telophase. It is suggested, therefore, that preleptotene condensation and decondensation represent a true mitotic reversion in which metaphase and anaphase are omitted. In normal Lilium genotypes meiosis is initiated by p. m. cs at G2 of premeiotic interphase. In ‘Black Beauty’, however, the control regu­lating the initiation of meiosis apparently is effective later in the cell cycle and acts only after p. m. cs have entered mitotic prophase. It is concluded that preleptotene chromosome condensation stage has no effect on normal meiotic chromosome pairing behaviour and probably has no significant function. Two parallel threads (chromatids) are visible in chromosomes at preleptotene condensation stage while, in chromo­somes at leptotene, invariably only a single thread is seen. It is suggested, therefore, that chromosomes at maximum preleptotene condensation can­not enter a meiotic sequence without first undergoing a within-chromosomal reorganization of their chromatin, and that preleptotene chromo­some decondensation stage represents such a reorganization.

The floral morphology and embryology of Themeda australis (R. Br.) Stapf

1964 ◽  
Vol 12 (2) ◽  
pp. 157 ◽  
Author(s):  
PS Woodland
Keyword(s):  
Embryo Sac ◽  
Pollen Grains ◽  
Low Fertility ◽  
Linear Tetrad ◽  
Polygonum Type ◽  
Morphological Variations ◽  
Endosperm Formation ◽  
Secretory Type ◽  
Successive Cytokinesis ◽  
Mother Cells

A comparative study was carried out between diploid and tetraploid races of Themeda australis from Armidale and Cobar, respectively. Some morphological variations occur in both populations, but sporogenesis and gametogenesis are identical. The anther is tetrasporangiate and the development of its four-layered wall is described. The tapetum is of the secretory type and its cells become binucleate at the initiation of meiosis in the adjacent microspore mother cells which undergo successive cytokinesis. Microspore tetrads are usually isobilateral and the pollen grains are three-celled at dehiscence, which takes place by lateral longitudinal slits. The ovule is of a modified anatropous form and bitegmic, the broad micropyle being formed of both integuments. The single hypodermal archesporial cell develops directly into the megaspore mother cell and the nucellar epidermis undergoes periclinal and anticlinal divisions to form a conspicuous epistase. The chalaza1 megaspore of the linear tetrad gives rise to a Polygonum-type embryo sac. Material from the Armidale population showed one embryo sac per ovule, but two to five embryo sacs were present in that from Cobar. Embryogeny is typically graminaceous and endosperm formation is at first free-nuclear, later becoming cellular. Polyembryony follows fertilization of several embryo sacs within the same ovule. The reasons for low fertility of T. australis and poor germination of seeds are discussed.

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 Chiasma variation and control in pollen mother cells and embryo-sac mother cells of rye

1974 ◽  
Vol 23 (2) ◽  
pp. 185-190 ◽  
Author(s):  
E. D. G. Davies ◽  
G. H. Jones
Keyword(s):  
Embryo Sac ◽  
Genetic System ◽  
Chiasma Formation ◽  
Pollen Mother Cells ◽  
Controlling System ◽  
Mother Cells ◽  
And Control

SUMMARYMean chiasma frequencies and the amounts of between-bivalent chiasma variation were computed for pollen mother cells (p.m.c.) and embryo-sac mother cells (e.m.c.) of five distinct inbred rye lines. Despite the considerable differences for both these metrics shown by the different lines, very little variation was seen between p.m.c. and e.m.c. belonging to the same lines. It is concluded that chiasma formation in p.m.c. and e.m.c. of rye is governed and regulated by a single controlling system of genes and that variation in this genetic system is expressed identically in the two sexes.

scholarly journals Chromosome linkage in oenothera, with special reference to some F 1 hybrids

1929 ◽  
Vol 105 (736) ◽  
pp. 207-230 ◽  
Keyword(s):  
Embryo Sac ◽  
Reduction Division ◽  
Exact Nature ◽  
Chromosome Behaviour ◽  
Final Solution ◽  
Female Side ◽  
Chromosome Configuration ◽  
Pure Lines ◽  
Mother Cells ◽  
Derivatives Of

Oenothera has placed a large part in our initiation into many new fields of cytological and genetical research. Since ring-formation of chromosomes was first observed in this genus by Cleland a few years ago, it has become apparent as a characteristic of meiosis in several other Angiosperms, but whether these are entirely comparable to Oenothera is at present doubtful. It is to Oenothera that we look for the final solution of many of the difficulties encountered in any endeavour to correlate these phenomena with chromosome behaviour in more typical genera, for within the Onagra group are numerous inter-fertile species, each of which is characterised by its own particular chromosome configuration, which is constant throughout all the pollen mother-cells. Such rings are now known to occur also at reduction division in the embryo-sac mother-cell of a number of forms, and it has been found that similar configurations prevail on the male and female side in any particular species. This is observed by the author to be the ease in Oe. rubricalyx (unpublished) and similar conditions have been described by Håbansson (1928) in several other derivatives of Oe. Lamarckiana . It seemed that a systematic study of the linkage of the chromosomes in a number of pure lines and in the hybrids between them was desirable, in that it might throw some light on the exact nature of pairing and chromosome linkage. Some such hybrids have already been described by Cleland (1927). This paper will deal with the chromosome behaviour in a number of F 1 hybrids between pure lines in which the meiotic divisions have already been studied (Sheffield, 1927).

scholarly journals Studies on the Morphology, Ontogeny and Embryology of the Flowers of Hedycarya Arborea J.R. et G. Forst. (Subfamily Monimioideae) and Laurelia Novae-Zelandiae A. Cunn. (Subfamily Atherospermoideae) of the Family Monimiaceae

2021 ◽  
Author(s):  
◽  
Frederick Bruce Sampson
Keyword(s):  
Generative Cell ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Tetrad Stage ◽  
Pollen Mother Cells ◽  
The Family ◽  
Long Time ◽  
External Part ◽  
Mother Cells ◽  
And Function

<p>The inflorescences, flowers and the vascularization of floral parts of Hedycarya arborea and Laurelia novae-zelandiae were described and comparisons made with other members of the family in an attempt to determine the basic types of inflorescences, flowers and floral vascularization in the family. The vegetative, inflorescence and floral meristems of the two genera were compared. It was concluded that the vegetative apices of both had the tunica-corpus configuration typical of many other woody Ranales and other orders. The inflorescence apices were quite similar to the vegetative ones. The young floral apices are in a state of transition from a tunica-corpus to a mantle-core configuration and older floral apices had the mantle-core configuration, which is typical of the floral apices of many woody Ranales. Unusual features of the floral apices of Hedycarya and Laurelia were the lack of a pronounced rib meristem and the occurrence of relatively frequent divisions within vacuolate cells of the core. The ontogeny of the stamens of Hedycarya and Laurelia was described and comparisons were made. In both genera the micro-sporangium developed in a similar fashions: in Hedycarya 5-6 wall layers are formed inside the epidermis; in Laurelia there are 3-5 layers. Both genera had a typically thickened endothecium and a tapetum of the secretory type in which the tapetal cells become binucleate during the first meiotic division of the pollen mother cells. In Hedycarya the meiotic divisions of the pollen mother cells are of the successive type in which walls form by means of centrifugal cell plates Pollen grains remain in permanent tetrads in this genus. In Laurelia wall formation at the end of meiosis is of a modified simultaneous type, which may not have been hitherto described in the literature. Pollen grains are not in permanent tetrads. When the first division occurs in each microspore in Hedycarya, all four cells of a tetrad are at the same stage of division and the generative cell is cut off towards the distal face of the grain. Each microspore is in the two celled condition when shed. It was deduced that the generative cell is cut off against what represents a radial wall of the grain (with reference to the tetrad stage) in Laurelia. Pollen is shed in either the two or three celled condition. Comparisons were made with the development of microsporangia and male gametophytes in other woody Ranales. A study was made of the ontogeny, structure and function of the staminal appendages of Laurelia. It was found that the appendages function as nectaries, the nectar being predominantly sucrose. After a discussion of the various theories as to the morphological nature of the staminal appendages of the Laurales, it was concluded that they are morphologically staminodes. The carpels of Hedycarya and Laurelia have a basically similar ontogeny in which, as in the Lauraceae, the terminal stigmatic region develops from a solid terminal meristem in contrast to many woody Ranales in which the stigma-consists of crests which surround the external part of the cleft of the carpel. The ovules of Hedycarya and Laurelia resemble those of most other woody Ranales in being bitegmic, crassinucellate and anatropous with a monosporic 8-nucleate embryo sac of the Polygonum type. Both linear and T-shaped megaspore tetrads were found in the two genera. Laurelia has pseudocarps which develop after anthesis and enclose plumose achenes, but in Hedycarya the fruits are drupes. It was concluded that Laurelia and Hedycarya belong to two subfamilies which have been separated from each other for a long time and have undergone considerable evolution in different directions. It was also concluded that the Monimiaceae are closely related to the Lauraceae.</p>

Fine Structure of Meiotic Prophase Chromosomes in Lilium Longiflorum

1967 ◽  
Vol 25 ◽  
pp. 88-89
Author(s):  
Peter B. Moens
Keyword(s):  
Electron Microscopy ◽  
Drosophila Melanogaster ◽  
Meiotic Prophase ◽  
Lilium Longiflorum ◽  
Nurse Cells ◽  
Tomato Plants ◽  
Regional Conference ◽  
Mother Cells ◽  
European Regional ◽  
Dipteran Species

The presence of the tripartite ribbon within synapsed homologues has been reported for a large number of sexually reproducing organisms (over one hundred species, including fungi, plants, vertebrates and invertebrates). The absence of the ribbon in some species is associated with uncommon synaptic behaviour of meiotic prophase chromosomes (Drosophila melanogaster males, Drosophila melanogaster females homozygous for synapsis suppressing mutant C3G, and achiasmatic Dipteran species, reported by G. F. Meyer, 1964, Third European Regional Conference on Electron Microscopy). The tripartite ribbon, or synaptinemal complex, may therefore be assumed to be related to pairing of homologues at meiosis. The presence of the complexes and multi-complexes in non-meiotic cells such as insect obcyte nurse cells and spermatids suggests a somewhat broader function of the complexes. This is further supported by the occurrence of complexes in non-homologous paired chromosomes in the pollen mother cells of haploid tomato plants.

Nucleolus-associated telomere clustering and pairing precede meiotic chromosome synapsis in Arabidopsis thaliana

2001 ◽  
Vol 114 (23) ◽  
pp. 4207-4217 ◽  
Author(s):  
Susan J. Armstrong ◽  
F. Christopher H. Franklin ◽  
Gareth H. Jones
Keyword(s):  
Arabidopsis Thaliana ◽  
Meiotic Chromosome ◽  
In Situ Hybridisation ◽  
Embryo Sac ◽  
Early Prophase ◽  
Homologous Chromosomes ◽  
Chromosome Synapsis ◽  
Mother Cells ◽  
Telomere Signal

The intranuclear arrangements of centromeres and telomeres during meiotic interphase and early prophase I of meiosis in Arabidopsis thaliana were analysed by fluorescent in situ hybridisation to spread pollen mother cells and embryo-sac mother cells. Meiocyte identification, staging and progression were established by spreading and sectioning techniques, including various staining procedures and bromodeoxyuridine labeling of replicating DNA. Centromere regions of Arabidopsis are unpaired, widely dispersed and peripherally located in nuclei during meiotic interphase, and they remain unpaired and unassociated throughout leptotene. Eventually they associate pairwise during zygotene, as part of the nucleus-wide synapsis of homologous chromosomes. Telomeres, by contrast, show a persistent association with the nucleolus throughout meiotic interphase. Variation in telomere signal number indicates that telomeres undergo pairing during this interval, preceding the onset of general chromosome synapsis. During leptotene the paired telomeres lose their association with the nucleolus and become widely dispersed. As the chromosomes synapse during zygotene, the telomeres reveal a loose clustering within one hemisphere, which may represent a degenerate or relic bouquet configuration. We propose that in Arabidopsis the classical leptotene/zygotene bouquet is absent and is replaced functionally by nucleolus-associated telomere clustering.

TWO EMBRYO-SAC MOTHER-CELLS IN THE OVULE OF FRITILLARIA.

1910 ◽  
Vol 9 (6-7) ◽  
pp. 257-259
Keyword(s):  
Embryo Sac ◽  
Mother Cells
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