One of my college presentations on Botany. Describes in detail, the female gametophyte(situated inside a flower)

1. Female Gametophyte Development & Types

2. The Female Gametophyte 03 Development of Female Gametophyte 04 Types of Female Gametophytes 14 Monosporic 16 Polygonum 17 Oenothera 19 Bisporic 21 Allium 22 Endymion 24 Tetrasporic 26 Fritillaria 27 INDEX 12/9/2008 2 The Female Gametophyte

3. Chalaza Nucellus Integuments Antipodal Cells (3n) Embryo Sac The Female gametophyte Secondary Nuclei (2n) Egg Cell (n) Egg Apparatus (3n) Synergids (2n) Micropyle Raphe Funiculus 12/9/2008 3 The Female Gametophyte

4. The ovule (female gametophyte), first arises as a tiny protuberance from the placenta, in the cavity of the ovary. Development of female Gametophyte Ovary Cavity Ovule Protuberance 12/9/2008 4 The Female Gametophyte

5. As it matures, the ovule consists of a nutritive cellular mass known as Nucellus, protected by two integuments, and attached to the placenta by a funiculus. Even at an early stage, one cell becomes evident in the nucellus, which is known as the megaspore mother cell (MMC). MMC is diploid (2n). Development of female Gametophyte CE ME Nucellus . MMC (2n) 12/9/2008 5 The Female Gametophyte

6. The MMC then increases in size, and divides twice (meiotically) to form 4 megaspores, known as ‘linear tetrad’. The first division is a reduction division. The resultant megaspores are haploid (n). Development of female Gametophyte CE ME Nucellus CE ME CE ME . . . Megaspores (n) each . . . R . MMC (2n) Megaspores (n) each D 12/9/2008 6 The Female Gametophyte

7. Out of the four megaspores, three degenerate, forming caps, while one remains functional. This functional megaspore is haploid (n). CE ME Development of female Gametophyte Degenerated megaspores . Functional Megaspore (n) 12/9/2008 7 The Female Gametophyte

8. The functional megaspore, then grows rapidly, by absorbing nutrition from nucellus, and forms the embryo sac. The process of formation of Embryo Sac is known as Megasporogenesis. The Embryo sac consists of one nucleus. Development of female Gametophyte Nucellus CE ME Embryo Sac . Nucleus 12/9/2008 8 The Female Gametophyte

9. The nucleus divided into two daughter nuclei, which move towards the poles. The pole of the embryo sac, closer to the Chalaza, is the chalazal end, and the one closer to the Micropyle is the micropylar end. Development of female Gametophyte CE ME . Embryo Sac Nuclei . 12/9/2008 9 The Female Gametophyte

10. Each daughter nuclei divides again, and result in four nuclei. Development of female Gametophyte CE ME . . Embryo Sac . . 12/9/2008 10 The Female Gametophyte

11. Each nuclei divides again, for the last time, and result in eight nuclei. Development of female Gametophyte CE ME . . . . Embryo Sac . . . . 12/9/2008 11 The Female Gametophyte

12. One nuclei from each end, come to the centre, and fuse to form a diploid secondary nucleus. Development of female Gametophyte CE ME . . . . Secondary Nuclei (2n) . . . . 12/9/2008 12 The Female Gametophyte

13. The nuclei at the chalazal end, get surrounded by cytoplasm, and form three distinct, haploid, Antipodal cells. Similarly, the nuclei at the micropylar end, form the egg apparatus, consisting of two haploid synergids on either side of a large, central, haploid egg cell. This concludes the development of the female gametophyte. Development of female Gametophyte CE ME Antipodal cells(n+n+n) . . . : Secondary Nucleus (2n) . Egg Cell(n) . . Synergids (n+n) 12/9/2008 13 The Female Gametophyte

14. Types of Female Gametophytes 12/9/2008 14 The Female Gametophyte

15. The types of female gametophytes are distinguished by the number of megaspores involved in the formation of the embryo sac. Based on this criteria, there are three types of female gametophytes: MONOSPORIC BISPORIC TETRASPORIC Each type has more than one subtype. Some of the common ones are discussed further. types of female Gametophyte 12/9/2008 15 The Female Gametophyte

16. A Monosporic Embryo Sac (ES) is derived from a single haploid megaspore. All the nuclei in the Embryo Sac are genetically identical, as they develop from the same megaspore. There are two subtypes of Monosporic female gametophytes. They are the Polygonum Type Oenothera Type Monosporic 12/9/2008 16 The Female Gametophyte

17. It was first described by Stresberger in 1879. Here, ES is formed by the megaspore at the chalazal end, and the rest of the tetrad degenerates. The Embryo Sac is 8 nucleated, three antipodal cells are located at the chalazal end, a central diploid secondary nucleus exists, along with a micropylar egg apparatus, consisting of two synergids, and an egg cell. This type of ES is most common in Angiosperms. It was observed in the flowers of Polygonumsp., thus it is referred to as the Polygonum type of Embryo sac development. Polygonum 12/9/2008 17 The Female Gametophyte

18. 12/9/2008 18 The Female Gametophyte MMC Meiosis I Meiosis II Degen. CE ME CE ME CE ME . . . . . . . . Polygonum CE ME CE ME CE ME CE ME . . . . . . . . . . : . . . . . . . . . . Mitosis I Mitosis II Mitosis III Rearrng.

19. This type of ES was derived from the megaspore of the micropylar end of the spore tetrad. The ES comprises of and egg apparatus and a uninucleate central cell. This type of ES is a characteristic of Onagraceae family. Oenothera 12/9/2008 19 The Female Gametophyte

20. 12/9/2008 20 The Female Gametophyte MMC Meiosis I Meiosis II Degen. CE ME CE ME CE ME . . . . . . . . Oenothera CE ME CE ME . . . CE ME . . . . . . . Mitosis I Mitosis II Rearrng.

21. In the plant bearing Bisporic ES the first division is accomplished by wall formation so that a dyad is formed. One of the dyad cell undergoes the sec. division, whereas the other one degenerates. Both the megaspores contribute in the formation of mature Bisporic ES. Each megaspore nucleus undergoes two mitotic division , forming 8 nuclei. The final organization of the embryo sac is similar to the Polygonum type. In Bisporic type, the ES is derived from 2 meiotic products, so the nuclei belongs to two different genetic constitutions. Four nuclei are different from the other four. Bisporic ES is of 2 types: Allium Endymion Bisporic 12/9/2008 21 The Female Gametophyte

22. The ES is derived from the Chalazal Dyad, and is similar to that of Polygonum type. The mature ES consists of one binucleate central cell, three antipodal cells at the Chalazal end, and an egg apparatus at the micropylar end. Allium 12/9/2008 22 The Female Gametophyte

23. 12/9/2008 23 The Female Gametophyte MMC Meiosis I Degen. CE ME CE ME . . : . Allium CE ME CE ME . . . . . . . . . : . . . . . . . . . Mitosis I Mitosis II Rearrng.

24. The ES is derived from the Micropylar Dyad, and is similar to that of Polygonum type. The mature ES consists of one binucleate central cell, three antipodal cells at the Chalazal end, and an egg apparatus at the Micropylar end. Endymion 12/9/2008 24 The Female Gametophyte

25. 12/9/2008 25 The Female Gametophyte MMC Meiosis I Degen. CE ME CE ME . . : . Endymion CE ME CE ME . . . . . . . . . : . . . . . . . . . Mitosis I Mitosis II Rearrng.

26. In this group neither of the meiotic division is accompanied by wall formation , so that, at the end of Meiosis, all the four haploid nuclei remain in the common cytoplasm, forming a coenomegaspore, which takes part in the formation of mature ES. A Tetrasporic ES, is more heterogeneous, than a Bisporic ES because, all the four megaspores are involved in the formation of ES and are genetically different. There are 7 types of Tetrasporic ES. Tetrasporic 12/9/2008 26 The Female Gametophyte

27. After the nuclear fusion, both the nuclei of the coenomegaspore(1 haploid + 1 triploid) , divide twice, forming four nuclei at each pore. The mature ES, comprises of an egg apparatus of three haploid cells, three triploid antipodal cells, and a central cell with two polar nuclei, one haploid and one triploid. Fritillaria 12/9/2008 27 The Female Gametophyte

28. 12/9/2008 28 The Female Gametophyte MMC Meiosis I Meiosis II CE ME CE ME CE ME . . . . . . . Fritillaria CE ME CE ME … … CE ME … … … … … … … … . . . … . . . . . . . . Mitosis I Mitosis II Mitosis III Rearrng.

29. 12/9/2008 The Female Gametophyte 29 Rutwik