Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
Figure 38.2 An overview of angiosperm reproduction
Stamen
Anther
Stigma
Carpel
Germinated pollen grain
(n) (male gametophyte)
on stigma of carpel
Anther at
tip of stamen
Style
Ovary
Filament
Ovary (base of carpel)
Pollen tube
Ovule
Embryo sac (n)
(female gametophyte)
Sepal
Egg (n)
FERTILIZATION
Petal
Receptacle
Sperm (n)
Mature sporophyte Seed
plant (2n) with
(develops
flowers
from ovule)
(a) An idealized flower.
Key
Zygote
(2n)
Seed
Haploid (n)
Diploid (2n)
(a) Simplified angiosperm life cycle.
See Figure 30.10 for a more detailed
version of the life cycle, including meiosis.
Germinating
seed
Embryo (2n)
(sporophyte)
Simple fruit
(develops from ovary)
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
- No
- Complete – have all 4 floral parts – sepal, petal, carpel, stamen
- Incomplete – lack 1 or more parts
- Perfect flowers – have both stamen & carpels
- Imperfect flowers – missing either stamen or carpels
- Stamenate – have stamen
- Carpellate – have carpel
- Stamenate & carpellate on same plant – monoecious
- Stamenate & carpellate on different plant – dioecious
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
Figure 38.4 The development of angiosperm gametophytes
(pollen grains and embryo sacs)
(a) Development of a male gametophyte
(pollen grain). Pollen grains develop
within the microsporangia (pollen
sacs) of anthers at the tips of the
stamens.
Pollen sac
(microsporangium)
2 Each microsporocyte divides by
meiosis to produce
four haploid
microspores,
each of which
develops into
a pollen grain.
3 A pollen grain becomes a
mature male gametophyte
when its generative nucleus
divides and forms two sperm.
This usually occurs after a
pollen grain lands on the stigma
of a carpel and the pollen
tube begins to grow. (See
Figure 38.2b.)
1 Within the ovule’s
megasporangium
is a large diploid
Megacell called the
sporocyte
megasporocyte
Integuments
(megaspore
mother cell).
Micropyle
2 The megasporocyte divides by
Surviving
meiosis and gives
megaspore
rise to four haploid
Female gametophyte cells, but in most
species only one
(embryo sac)
of these survives
Antipodel
as the megaspore.
Cells (3)
Megasporangium
Microsporocyte
Ovule
MEIOSIS
MicroSpores (4)
Each of 4
microspores
MITOSIS
Generative
cell (well
form 2
sperm)
Male
Gametophyte
(pollen grain)
Polar
Nuclei (2)
Egg (1)
Integuments
Nucleus
of tube cell
20 m
75 m
Ovule
Ragweed
Pollen
grain
Key
To labels
Diploid (2n)
Haploid
Diploid (2n)
(n)
100 mm
100
1 Each one of the
microsporangia
contains diploid
microsporocytes
(microspore
mother cells).
(b) Development of a female gametophyte
(embryo sac). The embryo sac develops
within an ovule, itself enclosed by the
ovary at the base of a carpel.
Synergids (2)
Embryo
sac
3 Three mitotic divisions
of the megaspore form
the embryo sac, a
multicellular female
gametophyte. The
ovule now consists of
the embryo sac along
with the surrounding
integuments (protective
tissue).
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
4. How can plants prevent self-fertilization?
- Genetic adaptations – “S genes” – self-incompatibility – reject self
- Anatomical adaptations – pin & thrum flowers
Stigma
Stigma
Anther
With
pollen
Pin flower
Thrum flower
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
4. How can plants prevent self-fertilization?
5. How does double fertilization occur & why is this important?
Figure 38.6 Growth of the pollen tube and double fertilization
Pollen grain
1 If a pollen grain
germinates, a pollen tube
grows down the style
toward the ovary.
Polar
nuclei
Egg
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule (containing
female
Gametophyte, or
Embryo sac)
Micropyle
2 The pollen tube
discharges two sperm into
the female gametophyte
(embryo sac) within an ovule.
3 One sperm fertilizes
the egg, forming the zygote.
The other sperm combines with
the two polar nuclei of the embryo
sac’s large central cell, forming
a triploid cell that develops into
the nutritive tissue called
endosperm.
Ovule
Polar nuclei
Egg
Two sperm
about to be
discharged
Endosperm nucleus (3n)
(2 polar nuclei plus sperm)
Zygote (2n)
(egg plus sperm)
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
4. How can plants prevent self-fertilization?
5. How does double fertilization occur & why is this important?
6. What happens after fertilization?
- Development of an embryo
Figure 38.7 The development of a eudicot plant embryo
Ovule
Endosperm
nucleus
Integuments
Zygote
Zygote
Terminal cell
Basal cell
Proembryo
Suspensor
Basal cell
Cotyledons
Shoot
apex
Root
apex
Suspensor
Suspensor
Seed coat
Endosperm
Figure 38.8 Seed structure
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons. The
fleshy cotyledons store food absorbed from the endosperm before
the seed germinates.
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons. The narrow,
membranous cotyledons (shown in edge and flat views) absorb
food from the endosperm when the seed germinates.
Scutellum
(cotyledon)
Coleoptile
Coleorhiza
Pericarp fused
with seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
(c) Maize, a monocot. Like all monocots, maize has only one
cotyledon. Maize and other grasses have a large cotyledon called a
scutellum. The rudimentary shoot is sheathed in a structure called
the coleoptile, and the coleorhiza covers the young root.
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
4. How can plants prevent self-fertilization?
5. How does double fertilization occur & why is this important?
6. What happens after fertilization?
7. How do fruits develop?
Figure 38.9 Developmental origin of fruits
Carpels
Flower
Ovary
Stigma
Stamen
Stamen
Ovule
Raspberry flower
Pea flower
Carpel
(fruitlet)
Seed
Stigma
Ovary
Stamen
Pea fruit
(a) Simple fruit. A simple fruit
develops from a single carpel (or
several fused carpels) of one flower
(examples: pea, lemon, peanut).
Raspberry fruit
(b) Aggregate fruit. An aggregate fruit
develops from many separate
carpels of one flower (examples:
raspberry, blackberry, strawberry).
Pineapple inflorescence
Each
segment
develops
from the
carpel of
one flower
Pineapple fruit
(c) Multiple fruit. A multiple fruit
develops from many carpels
of many flowers (examples:
pineapple, fig).
Chapter 38: Angiosperm Reproduction & Biotechnology
1. Let’s review the life cycle of an angiosperm….
2. Can all plants self-fertilize?
3. How does pollen (male gametophyte) & the embryo sac (female
gametophyte) develop?
4. How can plants prevent self-fertilization?
5. How does double fertilization occur & why is this important?
6. What happens after fertilization?
7. How do fruits develop?
8. What happens during germination?
Figure 39.11 Gibberellins mobilize nutrients during the germination
of grain seeds
22 The aleurone responds by
synthesizing and secreting
digestive enzymes that
hydrolyze stored nutrients in
the endosperm. One example
is -amylase, which hydrolyzes
starch. (A similar enzyme in
our saliva helps in digesting
bread and other starchy foods.)
1 After a seed
imbibes water, the
embryo releases
gibberellin (GA)
as a signal to the
aleurone, the thin
outer layer of the
endosperm.
3 Sugars and other
nutrients absorbed
from the endosperm
by the scutellum
(cotyledon) are consumed
during growth of the
embryo into a seedling.
Aleurone
Endosperm
-amylase
GA
GA
Water
Radicle
Scutellum
(cotyledon)
Sugar
Figure 38.10 Two common types of seed germination
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean. In common garden
beans, straightening of a hook in the
hypocotyl pulls the cotyledons from the soil.
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize. In maize and other grasses, the shoot grows
straight Up through the tube of the coleoptile.