female gametophyte

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Female Gametophyt

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Female Gametophyt

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FEMALE GAMETOPHYTE

Female Gametophyte

Central cell with 2 polar nuclei

Female Gametophyte

Egg apparatus• one egg cell• two synergids

Female Gametophyte

Chalazal End * 3 antipodal cells

Development Of Embryo Sac

Begins with elongation of functional megaspore.

Elongation is largely in micropylar chalazal axis

•Non-Vacuolated megaspore

cytoplasm later developed with small sized vacuoles.• In later period they may fuse

together to form large sized vacuoles.

Stages In Megagametogen

esis

Megaspore after first-meiotic mitosis•A large central vacuole now appears between the two daughter nuclei.

•On further expansion of vacuole the nuclei are pushed towards opposite poles of the cell.

Four Nucleate Stage

Both the nuclei

divide twice,

forming 4 nuclei at

each pole

Eight Nucleate

Stage

Again divides to form 8 nucleate stage

3 + 2 + 3 Distribution

•All the 8 nuclei are in a common cytoplas - m•Soon after this division cell elongates and gains the sac like appearance

Mature Embryo Sac

• 3 – celled egg apparatus•3 – antipodal cell•Large central cell with Secondary nucleus

Mature Embryo Sac

•

Types Of Embryo Sac

• Monosporic Embryo Sac• Bisporic Embryo Sac• Tetrasporic Embryo Sac

Depending upon the number of megaspore nuclei involved in the formation of Eembryo Sac

Monosporic Embryo Sac

FeaturesIt is derived from only one of the four

megaspores.Al the nuclei are genetically

identical, because they are derived through mitoses of a single nucleus.

Types Of Monosporic Embryo Sac

Polygonum It is formed by the chalazal megaspore

of the tetrad & is 8 nucleate. It Consists,* 3 celled egg apparatus* 3 antipodal cells* binucleate central cell.

Types Of Monosporic Embryo Sac

Oenothera type It is formed by the micropylar

megaspore of the tetrad & is 4 nucleate. It Consists,

* 3 celled egg apparatus* uninucleate central cell.

Types Of Bisporic Embryo Sac

Features Formation of dyad cell. Among 2 one undergoes 2nd meiotic division and other one degenerates. Bisporic is derived from 2 meiotic products and their nuclei belongs to 2 different genetic constitutions.

Types Of Bisporic Embryo Sac

Allium Type The embryo sac is derrived from the chalazal dyad cell.

EndymionThe embryo sac is derrived from the micropylar

dyad cell.

Types Of Tetrasporic Embryo SacNo wall formation takes

place. Hence at the end of meiosis all the 4 haploid nuclei in a common cytoplas - m forming coenomegaspore.

All the 4 nuclei of the coenomega -spore take part in the formatio n of embryo sac. Due to the meiosis all nucleus are genetically different.

Tetrasporic – Adoxa Type

Embryo sac is 8 nucleate & formed after the post-meiotic mitosis.

Tetrasporic – Plumbago type

Only one post meiotic mitosis occurs. The mature embryo sac consists an - Egg cell

- 4 nucleate central cell

Other 3 nuclei are cut off as peripheral cell.

Tetrasporic – Penea Type

Due to 2 post-meiotic motises in the coenomegaspore 16 nuclei are formed. It consists 4 groups of 3 cell each,

- one at the micropylar end- one at the chalazal end- two arranged laterally

Remaining 4 behaves as polar Egg apparatus – micropylar triad

Tetrasporic – Peperomia Type

The embryo sac is 16 nucleate . The organization of mature sac is

- Ony one egg and synergids- six peripheral cells- central cell with 8 polar nuclei

Tetrasporic - Drusa

It is also 16 nucleate. It consists

- 3 celled egg apparatus- 2 polar nuclei- 11 antipodal cells

Tetrasporic – Fritillaria

After the nuclear fusion both nuclei of the coenomegaspore( one 1N and one 2N) divide twice forming 4 nuclei at each pole. The mature embryo sac comprises an

- egg apparatus of 3 1N cells.- 3 triploid antipodal cells- Central cell with 2 polar nuclei one

1N and one 2N

Tetrasporic – Plumbagella Type

After a nuclear division of each nucleus 4 nuclei are formed. Two at micropylar and 2 at the chalazal end. One of the haploid nuclei at the micropylar forms egg and other one acts as upper polar nucleus

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