ovary & ovule structure • megaspore development • female ... · pdf fileginkgo...
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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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