female gametophyte

FEMALE GAMETOPHYTE

Development & Types

05/03/2023The Female Gametophyte 2

IND

EX The Female Gametophyte 03 Development of Female Gametophyte 04 Types of Female Gametophytes 14 Monosporic 16

Polygonum 17Oenothera19

Bisporic 21Allium 22Endymion 24

Tetrasporic 26Fritillaria 27


THE FEM

ALE G

AMETO

PHYTE

Chalaza

Nucellus

Integuments

Antipodal Cells (3n)Embryo SacSecondary Nuclei (2n)Egg Cell (n)

Synergids (2n)Egg Apparatus (3n)

Micropyle

Raphe

Funiculus


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

The ovule (female gametophyte), first arises as a tiny protuberance from the placenta, in the cavity of the ovary.

Ovary Cavity

Ovule Protuberance


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

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).

CE

ME

.Nucellus

MMC (2n)


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

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).

CE

ME

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Nucellus

Megaspores(n) each

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ME

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R

D

MMC (2n) Megaspores (n) each


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

Out of the four megaspores, three degenerate, forming caps, while one remains functional.

This functional megaspore is haploid (n).

CE

ME

.

Degenerated megaspores

Functional Megaspore (n)


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

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.

CE

ME

Nucellus

Embryo Sac . Nucleus


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

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.

CE

ME

Embryo Sac

.

Nuclei

.


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

Each daughter nuclei divides again, and result in four nuclei.

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ME

Embryo Sac

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. .

.


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

Each nuclei divides again, for the last time, and result in eight nuclei.

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ME

Embryo Sac

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. .

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..


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

One nuclei from each end, come to the centre, and fuse to form a diploid secondary nucleus.

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ME

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Secondary Nuclei (2n)


DEVELO

PMEN

T OF FEM

ALE G

AMETO

PHYTE

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. CE

ME

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Secondary Nucleus (2n)

Antipodal cells(n+n+n)

Synergids (n+n)

Egg Cell(n)


TYPES OF FEM

ALE G

AMETO

PHYTES

FemaleGametophyte

Monosporic2 subtypes

Polygonum

Oenothera

Bisporic2 subtypes

Allium Endymion

Tetrasporic7 subtypes

Fritillaria


TYPES OF FEM

ALE G

AMETO

PHYTE

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.


MO

NO

SPORIC

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


POLYG

ON

UM

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 Polygonum sp.,

thus it is referred to as the Polygonum type of Embryo sac development.


POLYG

ON

UM

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ME

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MMC

Meiosis I

Meiosis II

Degen.

Mitosis IMitosis IIMitosis

IIIRearrng.


OEN

OTH

ERA 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.


OEN

OTH

ERACE

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ME. .

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MMC

Meiosis I

Meiosis II

Degen.

Mitosis IMitosis II

Rearrng.


BISPORIC

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


ALLIUM

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

CE

ME

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:

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MMC

Meiosis I

Degen.

Mitosis IMitosis IIRearrng.


ENDYM

ION

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.


ENDYM

ION

CE

ME

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ME.

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...

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MMC

Meiosis I

Degen.

Mitosis IMitosis IIRearrng.


TETRASPORIC

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.


FRITILLARIA 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.


FRITILLARIACE

ME

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CE

ME

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CE

ME

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CE

ME.

…

MMC

Meiosis I

Meiosis II

Mitosis IMitosis IIMitosis

IIIRearrng.

CE

ME. .

……

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ME. .

..

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female gametophyte

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