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Journal articles on the topic 'Functional megaspore'
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1
Domaciuk, Marcin, Agata Leszczuk, Ewa Szczuka, Wioleta Kellmann-Sopyła, Justyna Koc, and Irena Giełwanowska. "Female sporogenesis in the native Antarctic grass Deschampsia antarctica Desv." Polish Polar Research 37, no. 2 (June 1, 2016): 289–302. http://dx.doi.org/10.1515/popore-2016-0016.
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Abstract The development of megasporocytes and the functional megaspore formation in Deschampsia antarctica were analyzed with the use of microscopic methods. A single archesporial cell was formed directly under the epidermis in the micropylar region of the ovule without producing a parietal cell. In successive stages of development, the meiocyte was transformed into a megaspore tetrad after meiosis. Most megaspores were arranged in a linear fashion, but some tetrads were T-shaped. Only one of the 60 analyzed ovules contained a cell in the direct proximity of the megasporocyte, which could be an aposporous initial. Most of the evaluated D. antarctica ovules featured monosporic embryo sacs of the Polygonum type. Approximately 30% of ovules contained numerous megaspores that were enlarged. The megaspores were located at chalazal and micropylar poles, and some ovules featured two megaspores – terminal and medial – in the chalazal region, or even three megaspores at the chalazal pole. In those cases, the micropylar megaspore was significantly smaller than the remaining megaspores, and it did not have the characteristic features of functional megaspores. Meiocytes and megaspores of D. antarctica contained polysaccharides that were detectable by PAS-reaction and aniline blue staining. Starch granules and cell walls of megasporocytes, megaspores and nucellar cells were PAS-positive. Fluorescent callose deposits were identified in the micropylar end of the megasporocytes. During meiosis and after its completion, thick callose deposits were also visible in the periclinal walls and in a small amount in the anticlinal walls of megaspores forming linear and T-shaped tetrads. Callose deposits fluorescence was not observed in the walls of the nucellar cells.
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Herd, Y. R., E. G. Cutter, and I. Watanabe. "An ultrastructural study of postmeiotic development in the megasporocarp of Azolla microphylla." Canadian Journal of Botany 64, no. 4 (April 1, 1986): 822–33. http://dx.doi.org/10.1139/b86-107.
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The development of megasporocarps of Azolla microphylla, after the retention of a single functional megaspore within the megasporangium, was studied by light and transmission electron microscopy, using material grown under controlled conditions. The young megaspore contained a thin layer of cytoplasm with various organelles and was bounded by a thin exine. It was surrounded by a dense periplasmodial tapetum, which consisted of a peripheral vacuolate region, containing degenerated megaspores, a middle region containing nuclei and large organelles such as amyloplasts and mitochondria, and an inner zone, invaginated round the spore, comprising microtubules, ribosomes, and coated vesicles. At a later stage the exine increased in thickness, and greater vacuolation occurred at the periphery of the periplasmodium. The endoperine was formed by deposition of granular material between the exine and the periplasmodium, and further granular material deposited in small vacuoles gave rise to the exoperine. The floats were formed from three (tapetal) membrane-bounded chambers, in which granular material gradually became organised to form the pseudocells. Characteristic exoperinal filaments were formed in channels in the periplasmodium, which was eventually completely used up in the formation of floats, collar, and megaspore wall, in which sporopollenin was probably present. The megaspore itself became engorged with cytoplasm and storage products such as lipid and starch. Cells of Anabaena with relatively thick walls were present between the megasporangial wall and the indusium.
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Norrmann, Guillermo A., and Camilo L. Quarín. "Permanent odd polyploidy in a grass (Andropogon ternatus)." Genome 29, no. 2 (April 1, 1987): 340–44. http://dx.doi.org/10.1139/g87-056.
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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.
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Yeung, Edward C., and Sandra K. Law. "Embryology of Epidendrum ibaguense. I. Ovule development." Canadian Journal of Botany 67, no. 8 (August 1, 1989): 2219–26. http://dx.doi.org/10.1139/b89-283.
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The orchids are unique among angiosperms in that ovule development is initiated after successful pollination. The monandrous orchid Epidendrum ibaguense has three placental ridges at anthesis. After pollination, mitotic activities result in the formation of a dichotomously branching system of outgrowths. The tip of each branch consists of five to six nucellar cells covered by the epidermis. A subterminal nucellar cell differentiates into the archesporial cell approximately 12 days after pollination. By day 18, it differentiates directly into a megasporocyte. The first meiotic cell division produces a dyad in which the micropylar cell begins prompt degeneration. The second meiotic cell division results in the formation of two megaspores of unequal size. The larger cell at the chalazal end will become the functional megaspore. Callose is present in the walls of the megasporocyte, the micropylar dyad cell, and the megaspore destined to degenerate. The development of the megagametophyte conforms to the Polygonum type. One of the chalazal nuclei delays its final mitotic division until fertilization, making it appear that only two antipodals are present. The mature ovules are bitegmic and have an anatropous orientation.
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Brukhin, Vladimir B., and Peter V. Bozhkov. "Female gametophyte development and embryogenesis in Taxus baccata L." Acta Societatis Botanicorum Poloniae 65, no. 1-2 (2014): 135–39. http://dx.doi.org/10.5586/asbp.1996.023.
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Crassinucellate ovules are initiated in <em>Taxus</em>, directly from the shoot apex. The rudimentary pollen chamber is formed in the nucellus. A linear tetrad of megaspores with a functional chalazal megaspore is formed. A free-nuclear stage is charac-teristic at the beginning of megagametophyte development. Archegonia without ventral canal cell are solitary or in complexes. The embryo has a very long suspensor even after maturation. Two types of polyembryony have been revealed: i) embryogenic redifferentiation of suspensor cells and ii) cleavage of embryonic region in the early embryo. In the northern temperate climate of St. Petersburg one month delay in development of reproductive structures has been noted.
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Núñez-Mariel, Citlali, E. Mark Engleman, and Judith Márquez-Guzmán. "Embriología de Pachycereus militaris (Audot) Hunt (Cactaceae)." Botanical Sciences, no. 68 (May 29, 2017): 5. http://dx.doi.org/10.17129/botsci.1632.
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This is a contribution to the embryology of cacti and to the definition of their reproductory structures. The development of anthers, ovules and seeds of Pachycereus militaris is described. The type of development of the anther wall is monocotyledonous. This may have taxonomic importance above the family level. The endothecium is formed by a single stratum and the pollen grains are tricolpate, spinulate and punctitegilate. A lineal triad of megaspores was observed. The functional megaspore is the chalazal one. It is proposed that the term campylotropous should be uti lized for describing the ovule type, while the term circinotropous should be reserved for the funicle. In contrast to the stated by other authors, this study suggests that the seeds of Pachycereus militaris should be considered as non-albuminous and non-perispermous.
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Gomez, Maria Dolores, Daniela Barro-Trastoy, Clara Fuster-Almunia, Pablo Tornero, Jose M. Alonso, and Miguel A. Perez-Amador. "Gibberellin-mediated RGA-LIKE1 degradation regulates embryo sac development in Arabidopsis." Journal of Experimental Botany 71, no. 22 (August 26, 2020): 7059–72. http://dx.doi.org/10.1093/jxb/eraa395.
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Abstract Ovule development is essential for plant survival, as it allows correct embryo and seed development upon fertilization. The female gametophyte is formed in the central area of the nucellus during ovule development, in a complex developmental programme that involves key regulatory genes and the plant hormones auxins and brassinosteroids. Here we provide novel evidence of the role of gibberellins (GAs) in the control of megagametogenesis and embryo sac development, via the GA-dependent degradation of RGA-LIKE1 (RGL1) in the ovule primordia. YPet-rgl1Δ17 plants, which express a dominant version of RGL1, showed reduced fertility, mainly due to altered embryo sac formation that varied from partial to total ablation. YPet-rgl1Δ17 ovules followed normal development of the megaspore mother cell, meiosis, and formation of the functional megaspore, but YPet-rgl1Δ17 plants had impaired mitotic divisions of the functional megaspore. This phenotype is RGL1-specific, as it is not observed in any other dominant mutants of the DELLA proteins. Expression analysis of YPet-rgl1Δ17 coupled to in situ localization of bioactive GAs in ovule primordia led us to propose a mechanism of GA-mediated RGL1 degradation that allows proper embryo sac development. Taken together, our data unravel a novel specific role of GAs in the control of female gametophyte development.
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Cheng, Chia-Yi, Dennis E. Mathews, G. Eric Schaller, and Joseph J. Kieber. "Cytokinin-dependent specification of the functional megaspore in the Arabidopsis female gametophyte." Plant Journal 73, no. 6 (January 18, 2013): 929–40. http://dx.doi.org/10.1111/tpj.12084.
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Folsom, M. W., and D. D. Cass. "Embryo sac development in soybean: ultrastructure of megasporogenesis and early megagametogenesis." Canadian Journal of Botany 67, no. 10 (October 1, 1989): 2841–49. http://dx.doi.org/10.1139/b89-365.
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The soybean ovule is bitegmic with the megasporocyte three to four cell layers beneath the nucellar epidermis. The megasporocyte is much larger than the surrounding nucellar cells, is connected to the nucellus by plasmodesmata, and at this stage exhibits a cytoplasmic density comparable with cells of the nucellus. After meiosis, the chalazal megaspore becomes functional in megagametogenesis. It alone retains plasmodesmatal connections to the nucellus. Chalazal megaspore expansion is accompanied by development of many small vacuoles having a uniform distribution. The first megaspore mitosis results in two nuclei lying on an axis parallel to the longitudinal axis of the embryo sac. Ultimately, these two nuclei are separated by a large vacuole. Numerous Golgi vesicles and proteinlike bodies are observed along the periphery of vacuoles in the 1-, 2-, and 4-nucleate embryo sacs. As the contents of vesicles and proteinlike bodies are observed deposited in vacuoles, it is probable that they both add osmotica to the vacuoles, thus promoting a water flux. We believe that the production of Golgi vesicles and putative protein bodies may be important in the formation and expansion of the large vacuole that appears to drive embryo sac expansion during early megagametogenesis in soybean. It is also believed that the timing to this vacuole's development has important developmental consequences.
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Cao, Ling, Sheng Wang, Prakash Venglat, Lihua Zhao, Yan Cheng, Shengjian Ye, Yuan Qin, Raju Datla, Yongming Zhou, and Hong Wang. "Arabidopsis ICK/KRP cyclin-dependent kinase inhibitors function to ensure the formation of one megaspore mother cell and one functional megaspore per ovule." PLOS Genetics 14, no. 3 (March 7, 2018): e1007230. http://dx.doi.org/10.1371/journal.pgen.1007230.
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Farquharson, Kathleen L. "Mirror, Mirror on the Wall: A Role for AGP18 in Functional Megaspore Selection." Plant Cell 25, no. 4 (April 2013): 1190. http://dx.doi.org/10.1105/tpc.113.250411.
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Ross, Cynthia M., and Michael J. Sumner. "Development of the unfertilized embryo sac and pollen tubes in the dwarf mistletoe Arceuthobium americanum (Viscaceae)." Canadian Journal of Botany 82, no. 11 (November 1, 2004): 1566–75. http://dx.doi.org/10.1139/b04-121.
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Megasporogenesis, embryo sac development, and pollen tubes in Arceuthobium americanum Nutt. ex Engelm. were investigated with light, fluorescence, and electron microscopy. The orthotropous ovular structure of A. americanum lacked integuments and possessed a nucellus that was largely continuous with and indistinguishable from the placenta; we coined this structure the placental–nucellar complex (PNC). Two megasporocytes became evident in the tenuinucellate PNC by mid-April, and had undergone bisporic megasporogenesis by mid-May. The upper cell from each dyad (distal to the base of the PNC) became a functional megaspore, although only one would develop into a seven-celled embryo sac. Like typical angiosperm embryo sacs, that of A. americanum possessed an egg cell having the ultrastructure reflective of a quiescent cell, and lacked cellulosic and (or) hemicellulosic wall material between the egg apparatus and central cell. However, the egg apparatus arose at the lower embryo sac pole, not at the upper as expected for an orthotropous ovule. A hypothetical model for the development of Arceuthobium ovules is the ancestral fusion and subsequent reduction of two anatropous ovules to form two embryo sacs within the PNC, of which only one completes development. The synergids have no role in pollen tube guidance, as tubes could be seen below each functional megaspore prior to megagametogenesis.Key words: Arceuthobium, embryo sac, megasporogenesis, mistletoe, pollen tubes, ultrastructure.
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Cass, D. D., D. J. Peteya, and B. L. Robertson. "Megagametophyte development in Hordeum vulgare. 1. Early megagametogenesis and the nature of cell wall formation." Canadian Journal of Botany 63, no. 12 (December 1, 1985): 2164–71. http://dx.doi.org/10.1139/b85-306.
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Megagametophyte development in barley (Hordeum vulgare 'Atsel') was studied using Nomarski-interference optics and transmission electron microscopy. Stages described include the functional megaspore to cell wall formation. Aspects of the transition from the free nuclear stage of the embryo sac to the cellular embryo sac indicate involvement of elongate cell plates associated with clusters of microtubules. Initial cell walls among micropylar and chalazal nuclei are composed of beads derived from dictyosome vesicles. Fusion of growing cell plates occurs, especially within the antipodal apparatus.
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Shen, Hailin, Zhendong Liu, Ke Yan, Liren Zou, Jinghui Wen, Yinshan Guo, Kun Li, and Xiuwu Guo. "Cytological Study of Gender Conversion in Amur Grape." Journal of the American Society for Horticultural Science 143, no. 4 (July 2018): 289–95. http://dx.doi.org/10.21273/jashs04408-18.
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Amur grape (Vitis amurensis) is a dioecious species. To elucidate the time of and reason for pistil abortion in male amur grape from the perspective of cytology, we observed the sections of pistil of a male line during its development using optical and transmission electron microscopes. The abnormity in the morphology of nucellar cell and the development of various organelles appeared before the abnormity of functional megaspore mitosis. Programmed cell death (PCD) of the nucellar cells might be an important reason for mitosis disorder, leading to the abortion of pistil in male flower. However, the abortion can be eliminated by forchlorfenuron treatment, resulting in the recovery of functional pistil in male amur grape. This study provides cytological information on the gender conversion mechanism in male amur grape, which can promote gender determination studies in Vitis species.
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Miegroet, Françoise Van, and Michel Dujardin. "Cytologie et histologie de la reproduction chez le Nymphaea heudelotii." Canadian Journal of Botany 70, no. 10 (October 1, 1992): 1991–96. http://dx.doi.org/10.1139/b92-247.
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The ontogenesis of reproductive cells has been cytologically analysed in Nymphaea heudelotii Planch., family Nymphaea-ceae, subclass Magnoliidae. Our observations of embryo sac development on sections differ from those made by Cook in 1906. Embryo sacs derive from a single functional megaspore and are four nucleate. After fertilization, the polar nucleus divides and successively generates two storage tissues that are located in two separate chambers. Nucellar tissue, which is filling up with starch inclusions, then insures a storage function. This species possesses 14 bivalents at meiosis and 14 somatic chromosomes at the first mitosis of the pollen grain. A reorganization of amyliferous organelle aggregates has also been observed in microsporocytes. Key words: reproduction, embryogenesis, microsporogenesis, megasporogenesis, Nymphaea.
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Barrales-López, Angelica, Lorenzo Guevara-Olvera, Eduardo Espitia-Rangel, Mario M. González-Chavira, Aurea Bernardino-Nicanor, Leopoldo Gonzalez-Cruz, Wilson Huanca-Mamani, and Gerardo Acosta-García. "Female gametogenesis and early seed development in Amaranthus hypochondriacus L." Botanical Sciences 96, no. 3 (September 14, 2018): 383. http://dx.doi.org/10.17129/botsci.1875.
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<p><strong>Background</strong>: Attention to amaranth grains has increased in recent years due to the nutritional value of their seed proteins, which have high levels of the amino acid lysine. However, there is no detailed study describing the stages of seed development in <em>Amaranthus hypochondriacus. </em></p><p><strong>Question</strong>: How are the developmental patterns of the female gametophyte and young seed in <em>Amaranthus hypochondriacus</em>?</p><p><strong>Species studied</strong>: <em>Amaranthus hypochondriacus</em> L ’Revancha’ (Amaranthaceae).</p><p><strong>Study site and years of study</strong>: Plants were growth and collected from 2014 to 2016, in a greenhouse at Instituto Tecnológico de Celaya, Guanajuato, Mexico.</p><p><strong>Methods: </strong>Glomerules were collected before pollination and two weeks after anthesis. The ovules at different development stages were fixed and cleared and were analyzed by light microscopy. A clearing protocol was used to observe the developmental stages during female gametogenesis and embryogenesis.</p><p><strong>Results: </strong>We observed that the <em>Amaranthus hypochondriacus</em> ovule has a campylotropous form. The female gametophyte showed a<em> Polygonum</em>-type pattern of development. We were also able to identify all the stages from the megaspore mother cell to the cotyledon embryo stage. After meiosis, the micropylar megaspore differentiates into the functional megaspore. The embryo did not show symmetric divisions, although the final pattern is similar to that of in eudicotyledons. The suspensor showed additional longitudinal divisions, giving rise to a 2-rowed suspensor, while the endosperm showed a helobial development.</p><p><strong>Conclusions: </strong>These results will be used as baseline to identify morphological changes during seed development and to develop new strategies to improve seed quality or increase the yield.</p>
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Hater, Friederike, Thomas Nakel, and Rita Groß-Hardt. "Reproductive Multitasking: The Female Gametophyte." Annual Review of Plant Biology 71, no. 1 (April 29, 2020): 517–46. http://dx.doi.org/10.1146/annurev-arplant-081519-035943.
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Fertilization of flowering plants requires the organization of complex tasks, many of which become integrated by the female gametophyte (FG). The FG is a few-celled haploid structure that orchestrates division of labor to coordinate successful interaction with the sperm cells and their transport vehicle, the pollen tube. As reproductive outcome is directly coupled to evolutionary success, the underlying mechanisms are under robust molecular control, including integrity check and repair mechanisms. Here, we review progress on understanding the development and function of the FG, starting with the functional megaspore, which represents the haploid founder cell of the FG. We highlight recent achievements that have greatly advanced our understanding of pollen tube attraction strategies and the mechanisms that regulate plant hybridization and gamete fusion. In addition, we discuss novel insights into plant polyploidization strategies that expand current concepts on the evolution of flowering plants.
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Carapetian, J., and EA Rupert. "Ovule and Female Gametophyte Development in Fertile and Sterile Safflower Plants (Carthamus tinctorius L.)." Australian Journal of Botany 37, no. 6 (1989): 519. http://dx.doi.org/10.1071/bt9890519.
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Development of safflower ovules and female gametophytes was compared in fertile and genetically sterile F2 and backcross segregants from the cross between 'US-10' and '57-147' genotypes. Fertile plants formed normal anatropous ovules with eight-nucleate embryo sacs, typical of the angiosperms. One week before anthesis, the eight-nucleate embryo sac is well developed and undergoes rapid elongation and expansion during the 24 h prior to anthesis, accompanied by a doubling in length of the florets. Sterile plants also formed normal ovules, but apparently with a delayed initiation of meiosis which was subsequently arrested at Metaphase I. Embryo sacs did not form in sterile florets except for rare observations of uninucleate embryo sacs which began to degenerate before anthesis. The integumentary tapetum which normally developed upon completion of meiosis in fertile plants, was well developed during Prophase I of megasporogenesis in sterile plants. This observation suggests that cell differentiation and development of this nutritive jacket is basically controlled by the age of the ovules rather than initiated by appearance of the functional megaspore. Failure of both female and male gametogenesis seems to result from interaction of three independently segregating genes.
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Shao, Fengxia, Sen Wang, Juan Chen, and Rongyan Hong. "Megasporogenesis, Microsporogenesis, and Development of Female and Male Gametophytes of Ziziphus jujuba Mill. ‘Zhongqiusucui’." HortScience 54, no. 10 (October 2019): 1686–93. http://dx.doi.org/10.21273/hortsci14237-19.
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To investigate whether reproductive disorders exist in the sexual reproduction of Ziziphus jujuba Mill. ‘Zhongqiusucui’ and to understand the reproductive biology of ‘Zhongqiusucui’ and genetic improvements in jujube trees, we used ‘Zhongqiusucui’ flowers at different developmental stages as materials and conducted field and microscopic observations on the developmental pattern of mega- and microsporogenesis, as well as on the development of male and female gametophytes. The results show the following. 1) From the inflorescence development stage to flowering, the grade 0 bud on the inflorescence exhibited an increase in horizontal diameter, longitudinal diameter, peduncle length, and bud weight, but the rates of increase were different. From day 1 to day 5 after the inflorescence had developed, floral buds mostly grew horizontally. Day 5 was the floral bud flattening stage. From day 6 to day 8 after the inflorescence had developed, floral buds mostly grew longitudinally, and day 8 was the floral bud enlarging stage. 2) The stamens of ‘Zhongqiusucui’ had five anthers, and there were four locules per anther. The anther wall consisted of epidermis, endothecium, one- to two-layered middle layer, and a secretory-type tapetum. In addition, the development of the anther wall belonged to the basic type. The cytokinesis of the microsporocytes was synchronous, the tetrads mostly arranged as a tetrahedron, and the mature pollen had three germ pores, three grooves, and was bicellular pollen. During meiosis, the microsporocytes in each locule were at the same phase and therefore exhibited synchrony. Among the different anthers in the same floral bud, as well as the four locules in the same anther, the microsporocytes had asynchronous meiosis. 3) The pistils in the ‘Zhongqiusucui’ had two ovaries, two anatropous ovules, inner and outer integument, crassinucellate tetrads formed by the meiosis of megasporocytes aligned linearly along the nucellus, megaspore at the chalazal end that developed into the functional megaspore, which underwent mitotic division three times and developed into the mature embryo sac containing seven cells and eight nuclei, and embryo sac development of the Polygonum type. 4) The external morphology of the ‘Zhongqiusucui’ floral buds correlated with the internal developmental stage of the male and female gametophyte. Therefore, the internal developmental progress of the stamen and pistil can be determined by the external morphological characteristics of the floral buds.
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Zaki, M., and J. Kuijt. "Ultrastructural studies on the embryo sac of Viscum minimum: II. Megagametogenesis." Canadian Journal of Botany 72, no. 11 (November 1, 1994): 1613–28. http://dx.doi.org/10.1139/b94-199.
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Embryo sac development of Viscum minimum was investigated using light and electron microscopy. Stages described involve uninucleate, binucleate, four-nucleate, and mature embryo sacs following cellularization. During the early stage of development, prior to mitosis, numerous small vacuoles are initiated in the cytoplasm of a uninucleate functional megaspore. The centrally located nucleus undergoes the first mitotic division and results in formation of two identical nuclei sharing a common cytoplasm. As the vacuole increases rapidly in size, the two nuclei become separated and move to opposite poles where the second mitotic division takes place. A remarkable elongation of the embryo sac is observed between the second and third mitotic division. Eventually, the embryo sac reaches its final length, two-thirds of the length of the ovary, at cellularization. Elongation of the embryo sac is closely related to the increase in vacuole size. Factors involved in vacuole formation and in the elongation of the embryo sac are discussed along with changes accompanying the transition from a sporophytic to a gametophytic pattern of development. Ultrastructural studies on the mature embryo sac, following cellularization, suggest that the egg cell is the least active cell in the megagametophyte. On the other hand, the synergids appear metabolically very active, being rich in plastids, mitochondria, dictyosomes, numerous vesicles, polysomes, and reserves. The central cell is the largest cell in the embryo sac. In a mature embryo sac the central cell has two adjacent nuclei, suggesting that fusion of the nuclei is completed following pollination and fertilization. The antipodals possess a complete set of organelles, numerous free and aggregated ribosomes, and endoplasmic reticulum. It is believed the antipodals play a significant nutritive role during the development of the embryo sac of V. minimum. Modification of the wall between antipodals and central cell and its role in nutrient transportations are discussed. Key words: embryo sac, embryogenesis, gametogenesis, megagametogenesis, mistletoes, ultrastructure.
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Kindiger, B., C. Curtis, and J. B. Beckett. "Adjacent II segregation products in B–A translocations of maize." Genome 34, no. 4 (August 1, 1991): 595–602. http://dx.doi.org/10.1139/g91-090.
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In maize (Zea mays L.), meiotic events in B–A translocations that cause the A chromosome to move to one pole and the A–B and B–A chromosomes to move to the opposite pole result in the production of balanced, functional microspores and megaspores. Meiotic events that allow other combinations of chromosomes to proceed to the two poles (A A–B and A B–A) lead to the production of both duplicate (A A–B) and deficient (B–A) spores. Microspores and often megaspores that are deficient for a segment of the A chromosome are expected to abort. Duplication-bearing gametes usually function through the egg but are less able to compete with the normal gametes in the pollen. Cytological data, and genetic data from pollen, kernel, and seedling counts, were used to identify the production of A A–B gametes by B–A translocation heterozygotes and hyperploids. Adjacent II segregation of the A and A–B chromosomes of B–A heterozygotes and hyperploids has been detected in stocks of several different B–A translocations. Some B–A translocations exhibited a frequency of adjacent II segregation as high as 23%.Key words: Zea mays, adjacent segregation, B chromosomes, translocation.
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Chen, Yong, Xiaofeng Wang, Liang Li, and Chengqi Ao. "The formation of integuments, megasporogenesis and megagametogenesis in Dendrobium catenatum, with special discussions on embryo sac types and section techniques." Botanica Serbica 45, no. 2 (2021): 177–84. http://dx.doi.org/10.2298/botserb2102177c.
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The formation of integuments, megasporogenesis and megagametogenesis in Dendrobium catenatum, an economically important orchid, are observed. After pollination, mitotic cell divisions of the placental epidermis result in the formation of a branching system of outgrowths. The tip of each branch consists of an archesporial cell derived from the differentiation of the terminal subepidermal nucellar cell. It differentiates directly into a megasporocyte. The first division of the meiosis of the megasporocyte produces a dyad approximately equal in size, in which the micropylar cell promptly degenerates. The second meiotic division of the remaining dyad cell results in the formation of two megaspores of unequal size. The larger chalazal cell becomes functional and eventually develops into a mature megagametophyte. The development of the megagametophyte conforms to the Monosporic Polygonum type. The final arrangement of the mature embryo sac conforms to a sevencelled/ eight-nucleate structure. The mature ovule is bitegmic, tenuinucellate and has an anatropous orientation. In the present study, we also discuss the differences between three main types of embryo sac development and the improvement of section techniques.
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Wang, Tiankang, Yixing Li, Shufeng Song, Mudan Qiu, Licheng Zhang, Chengxia Li, Hao Dong, Lei Li, Jianlong Wang, and Li Li. "EMBRYO SAC DEVELOPMENT 1 affects seed setting rate in rice by controlling embryo sac development." Plant Physiology 186, no. 2 (March 5, 2021): 1060–73. http://dx.doi.org/10.1093/plphys/kiab106.
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Abstract Seed setting rate is one of the critical factors that determine rice yield. Grain formation is a complex biological process, whose molecular mechanism is yet to be improved. Here we investigated the function of an OVATE family protein, Embryo Sac Development 1 (ESD1), in the regulation of seed setting rate in rice (Oryza sativa) by examining its loss-of-function mutants generated via clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated9 (Cas9) technology. ESD1 was predominantly expressed at Stage 6 of panicle development, especially in the ovules. esd1 mutants displayed reduced seed setting rates with normal stamen development and pollen tube growth but abnormal pistil group. Investigation of embryo sacs revealed that during the mitosis of functional megaspores, some egg cells degraded during differentiation in esd1 mutants, thereby hindering subsequent fertilization process and reducing seed setting rate. In addition, the transcriptional level of O. sativa anaphase-promoting complex 6, a reported embryo sac developing gene, was significantly reduced in esd1 mutants. These results support that ESD1 is an important modulator of ESD and seed setting rate in rice. Together, this finding demonstrates that ESD1 positively regulates the seed setting rate by controlling ESD in rice and has implications for the improvement of rice yield.
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Chavez, Dario J., and Paul M. Lyrene. "Interspecific Crosses and Backcrosses between Diploid Vaccinium darrowii and Tetraploid Southern Highbush Blueberry." Journal of the American Society for Horticultural Science 134, no. 2 (March 2009): 273–80. http://dx.doi.org/10.21273/jashs.134.2.273.
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Diploid Vaccinium darrowii Camp has been used in breeding tetraploid southern highbush blueberry (Vaccinium corymbosum L.) as a source of reduced chilling requirement, adaptation to hot, wet summers, and resistance to leaf diseases. V. darrowii in Florida is quite variable, but most crosses have involved only one V. darrowii clone, Fla. 4B. The use in breeding of a wider range of V. darrowii accessions would provide beneficial diversity in the blueberry cultivated gene pool. The purpose of this research was to determine the functional 2n gamete frequency of numerous V. darrowii genotypes when crossed with tetraploid V. corymbosum, and to study the pollen fertility and backcross ability of the interspecific (V. darrowii × V. corymbosum) hybrids to V. corymbosum. Crosses between diploid V. darrowii and tetraploid highbush blueberry cultivars had low fruit set compared with the V. darrowii × V. darrowii and highbush × highbush crosses. The unusually high number of hybrids per pollinated flower (HPF) in certain 4x-2x or 2x-4x crosses was attributed to high functional 2n gamete production in certain V. darrowii genotypes. Diploid Vaccinium fuscatum Aiton and diploid V. darrowii × V. fuscatum hybrids, when crossed with southern highbush blueberry cultivars, were equally productive of hybrids whether used as male or female parents. Variation in frequency of functional 2n gametes in V. darrowii, expressed as high HPF, was present within plants (megaspores vs. microspores) and among V. darrowii plants. Of the 114 interspecific (V. darrowii × V. corymbosum) hybrids studied, 106 had pollen stainability >50%. This indicated that most of these hybrids were tetraploid, because triploid blueberries, like most triploid plants, are highly sterile. Twenty-two V. darrowii × V. corymbosum hybrids were backcrossed to tetraploid highbush blueberry cultivars. Fruit set was variable, but large populations of vigorous hybrids were obtained. Lower fruit set was associated with hybrids that had lower pollen fertility. It should be possible to obtain plants of cultivar quality in a few generations of backcrosses.
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Steyn, E. M. A., A. E. Van Wyk, and G. F. Smith. "Ovule and seed structure in Scolopia zeyheri (Scolopieae), with notes on the embryology of Salicaceae." Bothalia 35, no. 2 (August 29, 2005): 175–83. http://dx.doi.org/10.4102/abc.v35i2.398.
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Scolopia zeyheri (Nees) Harv. is a widespread African tree and a member of the largest genus of the tropical Old World tribe Scolopieae (Salicaceae sensu lato). This light microscopic study is the first report on ovule and seed structure in the genus and the tribe. Ovules vary from four to six per ovary, are anatropous. crassinucellate. bitegmic and occur in an epitropous (rarely pleurotropous). median-parietal position in the unilocular, usually bicarpellate ovary. A very extensive nucellus cap. comprising nucellus epidermal derivatives and parietal tissue, characterizes the young ovule during mega- sporogenesis and megagametogenesis, but the chalazal nucellus is poorly developed. During meiosis. the micropvlar dyad cell degenerates early. The functional dyad cell forms two megaspores of which the chalazal one usually develops into a Polygonum-type embryo sac. At maturity, the micropylar end of the embryo sac is covered by the remnants of the nucellus epidermis, the parietal tissue having degenerated. The globular embryo has a short suspensor and lies in nuclear endosperm becoming cellular. The seed coat develops from both integuments, is tannimferous. has a glabrous surface with stomata and a single layer of exotegmic, longitudinal fibres.Results are compared with relevant information previously reported for genera in the tribes Flacourtieae. Samvdeae. Saliceae, Scyphostegiae and for Oncoha Forssk. (Salicaceae sensu lato). Embryologically Scolopia shows a number of ple- siomorphic features compared to other Salicaceae. For example, it lacks an extranucellar embryo sac. an apomorphic feature in many Salicaceae. A summary of ovule and seed characters in Salicaceae sensu lato is given and contrasted with data available for Achariaceae sensu lato. Embryological data broadly supports the reclassification of genera, traditionally referred to Flacourtiaceae. amongst Salicaceae sensu lato and Achariaceae sensu lato.
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Brzezicka, Emilia, and Małgorzata Kozieradzka-Kiszkurno. "Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae)." Protoplasma, November 14, 2020. http://dx.doi.org/10.1007/s00709-020-01584-z.
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AbstractThis article describes the development of female gametophyte in Sedum rupestre L. New embryological information about the processes of megasporogenesis and megagametogenesis provided in this paper expand the current knowledge about the embryology of the studied species. S. rupestre is characterized by monosporic megasporogenesis and the formation of Polygonum–type embryo sac. The process of megasporogenesis is initiated by one megaspore mother cell, resulting in the formation of a triad of cells after meiosis and cytokinesis. The functional megaspore, which is located chalazally, is a mononuclear cell present next to the megaspore in the centre of the triad. Only one of the two non-functional cells of the triad is binucleate, which occur at the micropylar pole. In this paper, we explain the functional ultrastructure of the female gametophytic cells in S. rupestre. Initially, the cytoplasm of the gametophytic cells does not differ from each other; however, during differentiation, the cells reveal different morphologies. The antipodals and the synergids gradually become organelle-rich and metabolically active. The antipodal cells participate in the absorption and transport of nutrients from the nucellar cells towards the megagametophyte. Their ultrastructure shows the presence of plasmodesmata with electron-dense material, which is characteristic of Crassulaceae, and wall ingrowths in the outer walls. The ultrastructure of synergid cells is characterized by the presence of filiform apparatus and cytoplasm with active dictyosomes, abundant profiles of endoplasmic reticulum and numerous vesicles, which agrees with their main function—the secretion of pollen tube attractants. Reported data can be used to resolve the current taxonomic problems within the genus Sedum ser. Rupestria.
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Chehregani, Abdilkarim, Fariba Mohsenzadeh, and Nayereh Tanaomi. "Comparative study of gametophyte development in the some species of the genus Onobrychis: Systematic significance of gametophyte futures." Biologia 66, no. 2 (January 1, 2011). http://dx.doi.org/10.2478/s11756-011-0007-4.
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AbstractMale and female gametophytes have special characters that show a great variety in different taxa. In this study, gametophytes of four species belonging to three sections of the genus Onobrychis Mill. were studied with light microscopy. Results showed that the ovular primordium is tetra-zonate and gives rise to an anatropous ovule. The archesporium may consist of one or more archeosporial cells, but only one of them undergoes meiosis, forming a linear or T-shaped tetrad. Normally, only a single megaspore is functional which is located in the chalazal position while the others degenerate very soon. The young ovule is hemi-anatropous but the mature is anatropous, crassinucellar and bitegmic; integuments form a zig-zag micropyle. A 7-celled embryo-sac is formed corresponding to the Polygonum type. Based on our results, the ovular variable characters are the form and condition of ovary, presence or absence of ovary peduncle, the number and condition of ovule in ovary, length and width of ovule, length and width of embryo sac, number of layers in outer integument, condition of megaspore, alignment pattern of the integuments, asymmetrical initiation of the outer integument, shape of tetrad with the presence of one functional megaspore and so on. The separator characters in male gametophyte are including tri-cellular pollen grains and the number of tapetum nuclei. According to our study the female gametophyte characters are more variable than male gametophyte. The present study provides the first report on embryological description in the genus Onobrychis and also in section Heliobrychis.
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Zhao, Lihua, Liping Liu, Yanhui Liu, Xianying Dou, Hanyang Cai, Mohammad Aslam, Zhimin Hou, et al. "Characterization of germline development and identification of genes associated with germline specification in pineapple." Horticulture Research 8, no. 1 (November 1, 2021). http://dx.doi.org/10.1038/s41438-021-00669-x.
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AbstractUnderstanding germline specification in plants could be advantageous for agricultural applications. In recent decades, substantial efforts have been made to understand germline specification in several plant species, including Arabidopsis, rice, and maize. However, our knowledge of germline specification in many agronomically important plant species remains obscure. Here, we characterized the female germline specification and subsequent female gametophyte development in pineapple using callose staining, cytological, and whole-mount immunolocalization analyses. We also determined the male germline specification and gametophyte developmental timeline and observed male meiotic behavior using chromosome spreading assays. Furthermore, we identified 229 genes that are preferentially expressed at the megaspore mother cell (MMC) stage during ovule development and 478 genes that are preferentially expressed at the pollen mother cell (PMC) stage of anther development using comparative transcriptomic analysis. The biological functions, associated regulatory pathways and expression patterns of these genes were also analyzed. Our study provides a convenient cytological reference for exploring pineapple germline development and a molecular basis for the future functional analysis of germline specification in related plant species.