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Angiosperm Reproduction and Biotechnology
Chapter 38p. 771-780
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LE 38-2b
Haploid (n)Diploid (2n)
Key
Simplified angiosperm life cycle
Germinatingseed
Seed
Seed
Simple fruit
Embryo (2n)(sporophyte)
Zygote (2n)
FERTILIZATION
Egg (n)
Sperm (n)
Embryo sac (n) (femalegametophyte)
OvuleOvary
Germinated pollen grain(n) (male gametophyte)
Pollentube
Anther
Maturesporophyteplant (2n)
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Flower Structure
Flowers are the reproductive shoots of the angiosperm sporophyte Stamen: (“male parts”)
Anther: where pollen is produced Filament: supports anther
Carpal: (“female parts”) Ovary: contains ovules (hold female
gametophytes) Stigma: where pollen lands Style: encloses ovary & supports the stigma
Time Lapse of Flowering Plant Life CycleFlower Blooming (time lapse)
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LE 38-2a
Stamen Anther
Filament
An idealized flower
Receptacle
Petal
Carpel
Sepal
Ovary
Style
Stigma
Haploid (n)Diploid (2n)
Key
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Flower Variations
Many flower variations have evolved during the 140 million years of angiosperm history A) Symmetry: radial/bilateral B) Ovary Location:
superior/semi-inferior/inferior C) Floral Distribution: individual
flowers/inflourescence (clusters) D) Reproductive Variations:
Monoecious: stamen & carpal on same flower Dioecious: stamen & carpal on different plants
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Gametophyte Development and Pollination
Pollination is the transfer of pollen from an anther to a stigma Pollen grain produces a pollen tube that grows
down into the ovary and discharges sperm near the embryo sac
Pollen develops from microspores within the sporangia of anthers
Embryo sacs develop megaspores w/in ovules
Bat Pollinating Agave Plant Bee Pollinating
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LE 38-4Development of a male gametophyte(pollen grain)
Pollen sac(microsporangium)
Micro-sporocyte
Micro-spores (4)
Generativecell (willform 2sperm)
Each of 4microspores
Malegametophyte(pollen grain)
Nucleus oftube cell
MITOSIS
(LM)75 µm
Ragweedpollengrain(colorizedSEM)
20 µm
Keyto labels
Haploid (n)
Diploid (2n)
MEIOSIS
Development of a female gametophyte(embryo sac)
Mega-sporangium
Ovule
Embryosac
Female gametophyte(embryo sac)
Mega-sporocyte
Integuments
Survivingmegaspore
Micropyle
Ovule Antipodalcells (3)
Polarnuclei (2)
Egg (1)
Synergids (2)Integuments
(LM)100
µm
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Double Fertilization
The pollen tube discharges TWO sperm into the embryo sac One sperm fertilizes
the egg The other combines
with the polar nuclei of the embryo, giving rise to the food-storing endosperm
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From Ovule to Seed
After double fertilization, each ovule develops into a seed
The ovary develops into a fruit enclosing the seed(s)
Endosperm Development: Stores nutrients that can be used by the
seedling OR Exports its food reserves to the cotyledons
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Embryo Development
The first mitotic division of the zygote, splits it into a basal cell and a terminal cell Terminal cell →
embryo Basal Cell →
Suspensor → anchors & transports nutrients to embryo
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Structure of the Eudicot Seed 1) Seed Coat: hard, protective shell that
encloses embryo & provides food supply 2) Radicle: embryonic root 3) Embryonic Axis
Hypocotyl: below cotyledon attachment Epicotyl: above cotyledon attachment
Contains shoot tip & 2 mini leaves
4) Cotyledon: “meat” of seed; stores food
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Structure of Monocot Seed
Scutellum: thin, specialized cotyledon that absorbs nutrients during germination
Coleoptile: covers young shoot Coleorhiza: covers young root
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From Ovary to Fruit
A fruit develops from the ovary Protects enclosed seeds and aids in seed
dispersal by wind or animals Types:
1) Simple: derived from 1 carpal/several fused (i.e. peach, pea, nut)
2) Aggregate: results from single flower w/ 2+ carpals (i.e. raspberry)
3) Multiple: results from inflourescence (i.e. pineapple)
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Developmental Origin of Fruits
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Seed Germination
As a seed matures, it dehydrates and enters a phase called dormancy ↓ metabolic rate growth & development suspended
↑ chances germination will occur at time & place most advantageous for seedling
Environmental cues required to break dormancy Change in temp or lighting
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From Seed to Seedling
Germination depends on imbibition the uptake of water due to low water potential of
the dry seed 1) Radicle (embryonic root) emerges first 2) Shoot tip breaks through soil surface 3) In many eudicots, a hook forms in the
hypocotyl, and growth pushes the hook above ground
4) In maize & other grasses (monocots) coleoptile pushes up through soil
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