1. Angiosperm Reproduction and Biotechnology
Chapter 38
Angiosperm Reproduction and Biotechnology
Pollination and seed dispersal are KEYS to ANGIOSPERM success!
Pollination enables gametes to come together within a flower
In angiosperms, the dominant sporophyte
Produces spores that develop within flowers into male gametophytes (pollen grains)
Produces female gametophytes (embryo sacs)

2. Fig. 38.2 - An Overview of Angiosperm Reproduction
Figure 38.2a, b
Anther at
tip of stamen
Filament
Anther
Stamen
Pollen tube
Germinated pollen grain
(n) (male gametophyte)
on stigma of carpel
Ovary (base of carpel)
Ovule
Embryo sac (n)
(female gametophyte)
FERTILIZATION
Egg (n)
Sperm (n)
Petal
Receptacle
Sepal
Style
Ovary
Key
Haploid (n)
Diploid (2n)
(a) An idealized flower.
(b) Simplified angiosperm life cycle. See Figure for a more detailed version of the life cycle, including meiosis.
Mature sporophyte
plant (2n) with
flowers
Seed
(develops
from ovule)
Zygote
(2n)
Embryo (2n)
(sporophyte)
Simple fruit
(develops from ovary)
Germinating
seed
Carpel
Stigma
Flowers are the reproductive shoots of the angiosperm sporophyte – they attract pollinators! The are composed of four floral organs: sepals, petals, stamens, and carpels that are attached to the stem at the receptacle. Stamens and carpels are the male and female reproductive organs. Sepals and petals are non-reproductive organs
Fertilization in a flower begins with pollination when one pollen grain containing three haploid nuclei, one tube nucleus, and two sperm nuclei lands on the sticky stigma of the flower.
The pollen grain absorbs moisture and sprouts, producing a pollen tube that burrows down the style into the ovary.
The two sperm nuclei travel down the pollen tube into the ovary.
Once inside the ovary, the two remaining sperm nuclei enter the ovule through the micropyle.
One sperm nucleus fertilizes the egg and becomes the embryo (2n).
The other sperm nucleus fertilizes the two polar bodies and becomes the triploid (3n) endosperm (food for growing embryo).
THIS PROCESS IS KNOWN AS DOUBLE FERTILIZATION because two fertilizations occur.
After fertilization, the ovule becomes the seed and the ripened ovary becomes the fruit.

3. Pollen – The Male Gametophyte
Pollen develops from microspores within the sporangia of anthers 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.)
Development of a male gametophyte
(pollen grain)
(a) 2
Each microsporo-
cyte divides by
meiosis to produce
four haploid
microspores,
each of which
develops into
a pollen grain.
Pollen sac
(microsporangium)
Micro-
sporocyte
spores (4)
Each of 4
microspores
Generative
cell (will
form 2
sperm)
Male
Gametophyte
Nucleus
of tube cell
Each one of the
microsporangia
contains diploid
microsporocytes
(microspore
mother cells). 1
75 m
20 m
Ragweed pollen grain
Figure 38.3a
MEIOSIS
MITOSIS
KEY to labels
Haploid (2n)
Diploid (2n)
Look at flower and find the ANTHER (male reproductive structure). Microsporangia contain diploid microsporocytes.
Microsporocytes divide by MEIOSIS to produce four haploid microspores – each one develops into a pollen grain.
Within a pollen grain, male gametophyte matures and forms TWO SPERM. This occurs AFTER a pollen grain lands on the sticky CARPEL of the flower and the pollen tube begins to grow.

4. Embryo Sacs – The Female Gametophyte
Embryo sacs develop from megaspores within ovules
Key
to labels
MITOSIS
MEIOSIS
Ovule
Integuments
Embryo
sac
Mega-
sporangium
sporocyte
Micropyle
Surviving
megaspore
Antipodel
Cells (3)
Polar
Nuclei (2)
Egg (1)
Synergids (2)
Development of a female gametophyte
(embryo sac)
(b)
Within the ovule’s
megasporangium
is a large diploid
cell called the
megasporocyte
(megaspore
mother cell). 1
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). 3
Female gametophyte
Diploid (2n)
Haploid (2n)
Figure 38.3b
100 m
The megasporocyte divides by
meiosis and gives rise to four
haploid cells, but in most
species only one of these
survives as the megaspore. 2
Within the ovule’s megasporangium is a large diploid cell called the megasporocyte.
The MEGASPOROCYTE divides by MEIOSIS to create FOUR HAPLOID CELLS (only one survives as megaspore).
The MEGASPORE divides by MITOSIS to form the embryo sac (female gametophyte). The ovule now consists of the embryo sac along with surrounding integuments.

5. Growth of the Pollen Tube and Double Fertilization
The pollen tube delivery of sperm to egg enables seeded plants to fertilize away from water!
Stigma
Polar
nuclei
Egg
Pollen grain
Pollen tube
2 sperm
Style
Ovary
Ovule (containing
female
gametophyte, or
embryo sac)
Micropyle
Ovule
Polar nuclei
Two sperm
about to be
discharged
Endosperm nucleus (3n)
(2 polar nuclei plus sperm)
Zygote (2n)
(egg plus sperm)
Figure 38.6
If a pollen grain
germinates, a pollen tube
grows down the style
toward the ovary. 1
The pollen tube
discharges two sperm into
the female gametophyte
(embryo sac) within an ovule. 2
After landing on a receptive stigma
A pollen grain germinates and produces a pollen tube that extends down between the cells of the style toward the ovary
The pollen tube then discharges two sperm into the embryo sac (double fertilization)
One sperm fertilizes the egg
The other sperm combines with the polar nuclei, giving rise to the food-storing endosperm
After fertilization, ovules develop into seeds and ovaries into fruits
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. 3

6. Development After Fertilization – From Ovule to Seed
After double fertilization - Each ovule develops into a seed
The ovary develops into a fruit enclosing the seed(s)
As the embryo develops from the zygote, the seed stockpiles proteins, oils, and starch (which is why seeds are such major nutritional sinks).

7. Mechanisms That Prevent Self-Fertilization
Many angiosperms have mechanisms that make it difficult or impossible for a flower to fertilize itself
Stigma
Stigma
Preventing Self Fertilization is KEY to angiosperm success:
Maintains/increases genetic diversity of the population
Avoids effects of inbreeding/more material for natural selection
Maintains Hybrid vigor
PIN and THRUM arrangement – produce two types of flowers on different individuals:
Pins have long styles and short stamens
Thrums have short styles and long stamens
Anther
with
pollen
Pin flower
Thrum flower
Figure 38.5

8. Self Incompatibility Prevents Self-Fertilization
Dioecious - in plant biology, having the male and female reproductive parts on different individuals of the same species, for example: staminate flowers (lacking carpels) and carpellate flowers (lacking stamens)
The most common anti-selfing mechanism in flowering plants is known as self-incompatibility, the ability of a plant to reject its own pollen
If a pollen grain from an anther happens to land on a stigma of a flower on the same plant, a biochemical block prevents the pollen from completing its development and fertilizing the egg.
Researchers are unraveling the molecular mechanisms that are involved in self-incompatibility
The plant’s response in analogous to our immune response – except is rejects self and accepts non-self
Some plants
Reject pollen that has an S-gene matching an allele in the stigma cells
Recognition of self pollen
Triggers a signal transduction pathway leading to a block in growth of a pollen tube

9. Structure of the Mature Seed
The embryo and its food supply are enclosed by a hard, protective seed coat
Endosperm- In angiosperms, a nutrient-rich tissue formed by the union of a sperm with two polar nuclei during double fertilization. The endosperm provides nourishment to the developing embryo in angiosperm seeds
Seed coat- A tough outer covering of a seed, formed from the outer coat of an ovule. In a flowering plant, the seed coat encloses and protects the embryo and endosperm
Hypocotyl- In an angiosperm embryo, the embryonic axis below the point of attachment of the cotyledon and above the radicle.
Radicle- embryonic root of a plant
Epicotyl- In an angiosperm embryo, the embryonic axis above the point of attachment of the cotyledons and below the first pair of miniature leaves

10. Cotyledons
A cotyledon "seed leaf“ is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling.
The number of cotyledons present is one characteristic used by botanists to classify the flowering plants (angiosperms). Species with one cotyledon are called "monocots“. Plants with two embryonic leaves are termed "dicots“.
In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct.
Cotyledons are formed during embryogenesis, along with the root and shoot meristems, and are therefore present in the seed prior to germination.
True leaves, however, are formed post-embryonically (i.e. after germination) from the shoot apical meristem, which is responsible for generating subsequent aerial portions of the plant.

11. Dicots
In a common garden bean (dicot) the embryo consists of the hypocotyl, radicle, and thick cotyledons
Figure 38.8a
(a) Common garden bean, a eudicot with thick cotyledons. The
fleshy cotyledons store food absorbed from the endosperm before
the seed germinates.
Seed coat
Radicle
Epicotyl
Hypocotyl
Cotyledons

12. Monocots
The embryo of a monocot has a single cotyledon, a coleoptile, and a coleorhiza
Figure 38.8c
(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.
Scutellum
(cotyledon)
Coleoptile
Coleorhiza
Pericarp fused
with seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
Coleoptile is a rudimentary shoot.
Coleorhiza covers the young root.

13. Dormancy Seed Germination
As a seed matures it dehydrates and enters a phase referred to as dormancy
Seed dormancy (adaptation for tough times) increases the chances that germination will occur at a time and place most advantageous to the seedling
The breaking of seed dormancy often requires environmental cues, such as temperature or lighting cues
An example of this is after extreme heats of forest fires or the extreme colds of winter
Dormant seeds can be viable and capable of germinating can vary from a few days to more than a few decades

14. Germination of seeds depends on the physical process called imbibition
From Seed to Seedling
Germination of seeds depends on the physical process called imbibition
The uptake of water due to low water potential of the dry seed

15. From Seed to Seedling - Germination
The radicle (1st embryonic root) is the first organ to emerge from the germinating seed
In many dicots a hook forms in the hypocotyl, and growth pushes the hook above ground
Figure 38.9a
Foliage leaves
Cotyledon
Hypocotyl
Radicle
Epicotyl
Seed coat
Common garden bean. In common garden
beans, straightening of a hook in the
hypocotyl pulls the cotyledons from the soil.
(a)

16. Germination in Monocots
Use a different method for breaking ground when they germinate
The coleoptile
Pushes upward through the soil and into the air
Figure 38.9b
Foliage leaves
Coleoptile
Radicle
Maize. In maize and other grasses, the shoot grows
straight up through the tube of the coleoptile.
(b)

17. Pineapple inflorescence
Types of Fruit
Fruits are classified into several types depending on their developmental origin
Carpels
Flower
Ovary
Stamen
Stigma
Stamen
Ovule
Pea flower
Raspberry flower
Pineapple inflorescence
Carpel
(fruitlet)
Each
segment
develops
from the
carpel of
one flower
Stigma
Seed
A fruit develops from the ovary and protects the enclosed seeds. It also aids in the dispersal of seeds by wind or animals. Fruits exist in different types:
Simple fruit- A fruit derived from a single carpel or several fused carpels
Aggregate fruit- A fruit derived from a single flower that has more than one carpel
Multiple fruit- A fruit derived from an inflorescence
Accessory fruit- A fruit, or assemblage of fruits, in which the fleshy parts are derived largely or entirely from tissues other than the ovary
Fruits usually ripen at about the same time that their seeds finish development
Ovary
Stamen
Pea fruit
Raspberry fruit
Pineapple fruit
Simple fruit. A simple fruit
develops from a single carpel (or
several fused carpels) of one flower
(examples: pea, lemon, peanut).
(a)
Aggregate fruit. An aggregate fruit
develops from many separate
carpels of one flower (examples:
raspberry, blackberry, strawberry).
(b)
Multiple fruit. A multiple fruit
develops from many carpels
of many flowers (examples:
pineapple, fig).
(c)
Figure 38.9a–c

18. Asexual Reproduction in Plants
Many flowering plants clone themselves by asexual reproduction
Many angiosperm species reproduce both asexually and sexually
Sexual reproduction generates the genetic variation that makes evolutionary adaptation possible
Asexual reproduction in plants is called vegetative reproduction

19. Mechanisms of Asexual Reproduction
Fragmentation
Is the separation of a parent plant into parts that develop into whole plants
Is one of the most common modes of asexual reproduction
Apomixis
Is the ability of some plant species to reproduce asexually without fertilization by a male gamete

20. Asexual Propagation – Clonal Species
In some species the root system of a single parent gives rise to many adventitious shoots that become separate shoot systems
This is known as vegetative reproduction – the collection of individuals are clones
Figure 38.11

21. Advantages & Disadvantages
With asexual reproduction there is no need for a pollinator
Asexual reproduction also allows a plant to pass on its entire genetic legacy unchanged by another parents genetic information
In the wild, only a small fraction of seeds (produced through sexual reproduction) can survive long enough to become parent plants themselves
But - sexual reproduction provides variation in offspring which can be advantageous in unstable environmental conditions
Sexual reproduction can allow for continuation of a species due to the great amount of variation that occurs in the offspring

22. Vegetative Propagation and Agriculture
Comparing Plant Propagation Methods
Method Procedure
Cuttings
A length of stem that includes lateral buds is cut from the parent plant and partially buried in soil or rooting mixture to take root.
A piece of stem is cut from the parent plant and attached to another plant.
A piece of lateral bud is cut from the parent plant and attached to another plant.
Grafting
Humans have devised various methods for asexual propagation of angiosperms
Budding