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Megagametogenesis

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Megagametogenesis is the process of maturation of the female gametophyte, or megagametophyte, in plants[1] During the process of megagametogenesis, the megaspore, which arises from megasporogenesis, develops into the embryo sac, which is where the female gamete is housed. [2] These megaspores then develop into the haploid female gametophytes.[3] This occurs within the ovule, which is housed inside the ovary[4]

The Process

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Refer to the figure above to observe the process of megagametogenesis, which is detailed below.





Prior to megagametogenesis, a developing embryo undergoes meiosis during a process called megasporogenesis. Next, three out of four megaspores disintegrate, leaving only the megaspore that will undergo the megagametogenesis.[5] The following steps are shown in Figure 1, and detailed below.

  1. The remaining megaspore undergoes a round of mitosis. This results in a structure with two nuclei, also called a binucleate embryo sac

2. The two nuclei migrate to opposite sides of the embryo sac

3. Each haploid nucleus then undergoes two rounds of mitosis which creates 4 haploid nuclei on each end of the embryo sac

4. One nucleus from each set of 4 migrates to the center of the embryo sac. These form the binucleate endosperm mother cell. This leaves three remaining nuclei on the micropylar end and three remaining nuclei on the antipodal end. The nuclei on the micropylar end is composed of an egg cell, two synergid cells, and the micropyle, an opening that allows the pollen tube to enter the structure[6]. The nuclei on the antipodal end are simply known as the antipodal cells.[7] These cells are involved with nourishing the embryo, but often undergo programmed cell death before fertilization occurs.[8]

5. Cell plates form around the antipodal nuclei, egg ell, and synergid cells[9]

Variations

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Plants exhibit three main types of megagametogenesis. The number of haploid nuclei in the functional megaspore that is involved in megagametogenesis is the main difference between these three types.[10]

Monosporic

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Bisporic megagaetogenesis is shown in the figure and outlined below.

The most common type of megagametogenesis, monosporic megagametogenesis, is outlined above. This type of megagemetogenesis only allows one megaspore to undergo megagametogenesis, while the other three undergo programmed cell death.[11]

Bisporic

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As the name implies, bisporic megagametogenesis involves two genetically different haploid nuclei.[12]

  1. These two nuclei undergo a round of mitosis
  2. Then, the nuclei on the micropylar end of the structure undergo a second round of mitosis
  3. Next, the nuclei rearrange to form a trinucleate endosperm mother cell and the characteristic arrangement of the micropylar end, with an egg cell and two synergid cells
  4. Cell plates form around the egg cell and synergid cells

Post Megagametogenesis

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Megagametogenesis creates the female gametophyte, which is an integral part of pollination, a very prominent process in plants. The male counterpart to megagametogenesis is called microgametogenesis. Microgametogenesis is the process of the formation of the male gametophyte. During pollination, the female gametophyte communicates with the pollen tube to ensure that it comes in contact with the ovule.[13] When contact is made, the pollen tube grows through the micropyle opening into a synergid cell, that dies when this occurs. The death of the synergid cell signals to the pollen tube to release the sperm.[14] This process creates the embryo, seed coat, and endosperm which, after pollination, will become crucial parts of the seed.[15]

Implications

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Pollination is an essential process of global crop production.[16] Its success is economically crucial for farmers.[17] Additionally, pollination success is required for global food security. Cereals, or the seeds of grain crops, are most important staple food to humans around the world. They make up 48% of the calories consumed by humans.[18]


  1. ^ "QuickGO". www.ebi.ac.uk. Retrieved 2019-02-28.
  2. ^ Drews, Gary N.; Koltunow, Anna M.G (2011-12-26). "The Female Gametophyte". The Arabidopsis Book / American Society of Plant Biologists. 9. doi:10.1199/tab.0155. ISSN 1543-8120. PMC 3268550. PMID 22303279.{{cite journal}}: CS1 maint: PMC format (link)
  3. ^ Drews, Gary N.; Koltunow, Anna M.G (2011-12-26). "The Female Gametophyte". The Arabidopsis Book / American Society of Plant Biologists. 9. doi:10.1199/tab.0155. ISSN 1543-8120. PMC 3268550. PMID 22303279.{{cite journal}}: CS1 maint: PMC format (link)
  4. ^ "ZFIN GO: Biological Process: embryo sac development". zfin.org. Retrieved 2019-03-21.
  5. ^ "ZFIN GO: Biological Process: embryo sac development". zfin.org. Retrieved 2019-03-21.
  6. ^ "ScienceDirect". www.sciencedirect.com. Retrieved 2019-04-19.
  7. ^ Song, Xiaoya; Yuan, Li; Sundaresan, Venkatesan (2014-12). "Antipodal cells persist through fertilization in the female gametophyte of Arabidopsis". Plant Reproduction. 27 (4): 197–203. doi:10.1007/s00497-014-0251-1. ISSN 2194-7961. PMID 25389024. {{cite journal}}: Check date values in: |date= (help)
  8. ^ "ZFIN GO: Biological Process: embryo sac development". zfin.org. Retrieved 2019-03-21.
  9. ^ Drews, Gary N.; Yadegari, Ramin (2004-06-01). "Female Gametophyte Development". The Plant Cell. 16 (suppl 1): S133–S141. doi:10.1105/tpc.018192. ISSN 1040-4651. PMID 15075395.
  10. ^ de Boer-de-Jeu, M. J. (1978-02-02). "Ultrastructural aspects of megasporogenesis and initiation of megagametogenesis in Lilium". Bulletin de la Société Botanique de France. Actualités Botaniques. 125 (1–2): 175–181. doi:10.1080/01811789.1978.10826321. ISSN 0181-1789.
  11. ^ "Plant Physiology, Sixth Edition". 6e.plantphys.net. Retrieved 2019-03-28.
  12. ^ Willemse, M. T. M.; van Went, J. L. (1984), Johri, Brij Mohan (ed.), "The Female Gametophyte", Embryology of Angiosperms, Springer Berlin Heidelberg, pp. 159–196, doi:10.1007/978-3-642-69302-1_4, ISBN 9783642693021, retrieved 2019-04-19
  13. ^ Drews, Gary N.; Yadegari, Ramin (2004-06-01). "Female Gametophyte Development". The Plant Cell. 16 (suppl 1): S133–S141. doi:10.1105/tpc.018192. ISSN 1040-4651. PMID 15075395.
  14. ^ Drews, Gary N.; Yadegari, Ramin (2004-06-01). "Female Gametophyte Development". The Plant Cell. 16 (suppl 1): S133–S141. doi:10.1105/tpc.018192. ISSN 1040-4651. PMID 15075395.
  15. ^ Drews, Gary N.; Yadegari, Ramin (2004-06-01). "Female Gametophyte Development". The Plant Cell. 16 (suppl 1): S133–S141. doi:10.1105/tpc.018192. ISSN 1040-4651. PMID 15075395.
  16. ^ Dormann, Carsten F.; Liebscher, Juliane; Seppelt, Ralf; Lautenbach, Sven (2012-04-26). "Spatial and Temporal Trends of Global Pollination Benefit". PLOS ONE. 7 (4): e35954. doi:10.1371/journal.pone.0035954. ISSN 1932-6203. PMC 3338563. PMID 22563427.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  17. ^ Dormann, Carsten F.; Liebscher, Juliane; Seppelt, Ralf; Lautenbach, Sven (2012-04-26). "Spatial and Temporal Trends of Global Pollination Benefit". PLOS ONE. 7 (4): e35954. doi:10.1371/journal.pone.0035954. ISSN 1932-6203. PMC 3338563. PMID 22563427.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  18. ^ Society, National Geographic (2011-09-21). "grain". National Geographic Society. Retrieved 2019-03-21.