Angiosperm Reproduction and
Biotechnology
Chapter 38
p. 771-780
LE 38-2b
Germinated pollen grain
(n) (male gametophyte)
Anther
Ovary
Ovule
Embryo sac (n) (female
gametophyte)
Pollen
tube
FERTILIZATION
Egg (n)
Mature
Sperm (n)
sporophyte
plant (2n)
Zygote
(2n)
Seed
Key
Seed
Haploid (n)
Diploid (2n)
Germinating
seed
Simplified angiosperm life cycle
Embryo (2n)
(sporophyte)
Simple fruit
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 Cycle
Flower Blooming (time lapse)
LE 38-2a
Anther
Stamen
Filament
Stigma
Carpel
Style
Ovary
Sepal
Petal
Key
Haploid (n)
Diploid (2n)
Receptacle
An idealized flower
Flower Variations

Many flower variations have evolved
during the 140 million years of
angiosperm history




A) Symmetry: radial/bilateral
B) Ovary Location: superior/semiinferior/inferior
C) Floral Distribution: individual
flowers/inflourescence (clusters)
D) Reproductive Variations:
Monoecious: stamen & carpal on same flower
 Dioecious: stamen & carpal on different plants

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
LE 38-4
Development of a male gametophyte
(pollen grain)
Development of a female gametophyte
(embryo sac)
Pollen sac
(microsporangium)
Megasporangium
Microsporocyte
Ovule
MEIOSIS
Megasporocyte
Integuments
Micropyle
Microspores (4)
Surviving
megaspore
Each of 4
microspores
Female gametophyte
(embryo sac)
MITOSIS
Ovule
Generative
cell (will
form 2
sperm)
Male
gametophyte
(pollen grain)
Antipodal
cells (3)
Polar
nuclei (2)
Egg (1)
Integuments
Nucleus of
tube cell
Synergids (2)
20 µm
Key
to labels
Haploid (n)
Diploid (2n)
100 µm
75 µm
(LM)
Ragweed
pollen
grain
(colorized
SEM)
Embryo
sac
(LM)
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
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
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
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
Structure of Monocot Seed



Scutellum: thin, specialized
cotyledon that absorbs nutrients
during germination
Coleoptile: covers young shoot
Coleorhiza: covers young root
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)
Developmental Origin of Fruits
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
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
Seed Germination