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• Ovary & ovule structure• Megaspore development• Female gametophyte development• Endosperm & embryo development

Female Gametophyte Development Objectives

Megasporogenesis, Megagametogenesis & Ovule Development

Ovary

Ovary Wall

Ovules

Ovule

Funiculus

Ovule & Megasporangium Structure

Ovuliferous scale

Pine ovule

Integument

Megasporangium

Megasporangium in a spike moss (Selaginella)

Ginkgo ovules

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Ovule Structure

Micropylarend

Chalazal end

Megasporogenesis

Micropyle

MegaporogenesisMeiosis I

Meiosis II

Meiosis I Megaspore Mother Cell Meiosis I Megaspore Mother Cell

Meiosis II Haploid megaspore nuclei Meiosis II Haploid megaspore nuclei

Migration and fusion of 3 megaspore nuclei to chalazal end

Micropylarnucleus (n) dividing

Chalazalnucleus (3n) dividing

Early stages of megagametogenesis

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MegagametogenesisLilium megagametogenesis

1. Megaspore segregation3. First Mitosis of micropylar and chalazalnuclei produces 2 cells at both ends

2. Nuclear fusion of micropylar and chalazal nuclei

4. Second mitosis micropylar nuclei 5. Second mitosis chalazal nuclei

Polar nucleus (3n) at chalazal end

Antipodal cell (3n) Antipodal cells (3n)

Megagametophyte =

Embryo Sac

2n

1n 1n

1n

1n

Meiosis

3n

3n

3n

3n

3n

3n

3n

1n

1n

1n

1n

1n

1n

3n

3n

3n

3n

1n1n

1n

Tetrasporic Development in Lilium

1n

2n

1n 1n

1n

1n

Meiosis

1n

1n

1n

1n

1n

1n

1n

1n

1n

1n

1n1n

1n

Monosporic Development in Polygonum

1n

Three megaspores degenerate

1n

1n

1n

1n

1n

1n

1n

1n

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Angiosperm Female Gametophyte Development

1. Megasporogenesis produces megaspores

2. Megaspore produces female gametophyte

Female gametophyte = embryo sac

3. Embryo sac produces an egg cell

Types of embryo sac development

1. Monosporic – Polygonum type– 1 functional megaspore– 7celled, 8 nucleate embryo sac– All haploid cells

2. Tetrasporic – Lilium type– 4 functional megaspores– 7 celled, 8 nucleate embryo sac– Haploid: egg cell, synergids + 1 polar cell nucleus– Triploid: 3 antipodal nuclei + 1 polar cell nucleus

Embryo Sac Structure

3 Antipodal cells

1 central cell with 2 nuclei

1 egg cell

2 synergid cellsEgg Apparatus

Zygote

Polar nuclei

Double Fertilization in Angiosperms

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Double Fertilization = Two Fusions

Sperm Nucleus

Egg Cell

1n polar nucleus

Sperm nucleus3n polar nucleus

Fertilization of egg cell Sperm fusion with central cell nuclei - Lilium

Zygote Endosperm

Early Endosperm Development

Endosperm

1. Definition

2. Functions1. Support Embryo Development2. Support Seedling Development after Germination

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Endosperm Presence in Mature Seed

1. Transient Endosperm – absent in seed1. Many Dicots

1. e.g. Soybean, Peanut, Phaseolus, Lettuce

2. Persistent endosperm – present in seed1. Endospermic Dicots: Castor bean,

Fenugreek, Carob, Locust 2. Most Monocots

Modes of Endosperm development

1. Free Nuclear Endosperm - Karyokinesis Only A. Cellularization From PeripheryB. Limited Cellularization around Embryo C. No Cellularization

2. Cellular Endosperm - Karyokinesis followed by CytokinesisA. Normal Cell Replication

3. Helobial Endosperm (some Monocots) Large Micropylar Cell Free Nuclear Division CellularizationSmall Chalazal Cell Limited Karyokinesis No Cellularization

Free-Nuclear Endosperm FormationDuring Pea Seed Development

Cellular Endosperm Formation in Barley

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Monocot endosperm Cellular & persistent

Variation in endosperm distribution within a mature seed

Dicot endosperm Free-nuclear & transient

Endosperm

Mature Embryo

Root Apical Meristem

Shoot Apical Meristem

Embryonic Axis HypocotylRadicle

Cotyledons

Embryogenesis: Proembryo formation

2 - celled8 – celled(octant) 16 - celled

16-celled Proembryo

Protoderm

Hypophysis

Separate Upper & Lower Tiers

Suspensor

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Early Heart-shaped stage & Histogenesis

Cotyledon primordiaProtoderm

Ground Meristem

Procambium

Hypophysis

Shoot apical meristem

Embryogenesis: Later Stages

Heart Torpedo Bent cotyledon Walking Stick

Cotyledons

Apical-Basal Organization during

Embryogenesis

Apical cells cotyledons & Shoot Apical Meristem

Central cells stem, hypocotyl, root and root apical meristem

Hypophysis Columella of root cap & Quiescent Center

Octant Stage

Radial Organization during Embryogenesis

VascularTissue System

Fundamental Tissue System

Dermal Tissue System

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Plant EmbryogenesisStages of embryo development

1. 2 16 cell globular proembryo2. Heart Torpedo Walking Stick Bent Cotyledon

Polarity established during development1. Zygote Terminal cell & basal cell2. Transition from radial to bilateral symmetry3. Establish a longitudinal axis: shoot - root4. Establish a radial axis: core to circumference5. Establish apical meristems

1. Shoot2. Root

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