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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
30
Reproduction and
Domestication of
Flowering Plants
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Overview: Flowers of Deceit
 Insects help angiosperms to reproduce sexually
with distant members of their own species
 For example, male long-horned bees (Eucera
longicornis) mistake Ophrys flowers for females and
attempt to mate with them
 The flower is pollinated in the process
 Unusually, the flower does not produce nectar and
the male receives no benefit
© 2014 Pearson Education, Inc.
Figure 30.1
© 2014 Pearson Education, Inc.
 Many angiosperms lure insects with nectar or pollen;
both plant and pollinator benefit
 Participation in mutually beneficial relationships with
other organisms is common in the plant kingdom
 Angiosperms can reproduce sexually and asexually
 Angiosperms are the most important group of plants
in terrestrial ecosystems and in agriculture
© 2014 Pearson Education, Inc.
Concept 30.1: Flowers, double fertilization, and
fruits are unique features of the angiosperm life
cycle
 Plant life cycles are characterized by the alternation
between a multicellular haploid (n) generation and a
multicellular diploid (2n) generation
 Diploid sporophytes (2n) produce spores (n) by
meiosis; these grow into haploid gametophytes (n)
 Gametophytes produce haploid gametes (n) by
mitosis; fertilization of gametes produces a
sporophyte
© 2014 Pearson Education, Inc.
 In angiosperms, the sporophyte is the dominant
generation, the large plant that we see
 The gametophytes are reduced in size and depend
on the sporophyte for nutrients
 The angiosperm life cycle is characterized by “three
Fs”: flowers, double fertilization, and fruits
© 2014 Pearson Education, Inc.
Flower Structure and Function
 Flowers are the reproductive shoots of the
angiosperm sporophyte; they attach to a part of the
stem called the receptacle
 Flowers consist of four floral organs: carpels,
stamens, petals, and sepals
 Carpels and stamens are reproductive organs;
sepals and petals are sterile
Video: Flower Time Lapse
© 2014 Pearson Education, Inc.
Figure 30.2
Stamen
Stigma
Carpel
Anther
Style
Filament
Ovary
Petal
Sepal
Ovule
© 2014 Pearson Education, Inc.
 A carpel has a long style with a stigma on which
pollen may land
 At the base of the style is an ovary containing one
or more ovules
 A single carpel or group of fused carpels is called a
pistil
 A stamen consists of a filament topped by an anther
with pollen sacs that produce pollen
© 2014 Pearson Education, Inc.
 Complete flowers contain all four floral organs
 Incomplete flowers lack one or more floral organs,
for example, stamens or carpels
 Clusters of flowers are called inflorescences
© 2014 Pearson Education, Inc.
Flower Formation
 Flowers of a given plant species typically appear
synchronously, promoting outbreeding
 The transition from vegetative to reproductive growth
is triggered by environmental cues and internal
signals
 Floral organization is regulated by the products of
floral identity genes
 Mutations in these genes cause abnormal floral
development
© 2014 Pearson Education, Inc.
Figure 30.3
Pe
Ca
St
Se
Pe
Se
Normal Arabidopsis flower
Pe
Pe
Se
Abnormal Arabidopsis flower
© 2014 Pearson Education, Inc.
Figure 30.3a
Ca
St
Pe
Se
Normal Arabidopsis flower
© 2014 Pearson Education, Inc.
Figure 30.3b
Pe
Se
Pe
Pe
Se
Abnormal Arabidopsis flower
© 2014 Pearson Education, Inc.
 The ABC hypothesis explains the formation of the
four types of floral organs through the regulatory
activity of three classes of organ identity genes
© 2014 Pearson Education, Inc.
 Each class of organ identity genes is switched on in
two specific whorls of the floral meristem
 A genes are switched on in the two outer whorls
(sepals and petals)
 B genes are switched on in the two middle whorls
(petals and stamens)
 C genes are switched on in the two inner whorls
(stamens and carpels)
 Individuals lacking A, B, or C gene activity will
develop abnormal patterns of floral organs
© 2014 Pearson Education, Inc.
Figure 30.4
Sepals
Petals
A
B
Stamens
Carpels
C
AB
gene
activity
BC
gene
activity
C gene
activity
Carpel
(a) A schematic diagram
of the ABC hypothesis
Petal
Stamen
A gene
activity
Sepal
Active
genes:
B B
BB
AACCCC AA
BB
B B
CCCCCC CC
AACCCC AA
AA
AA
ABBAAB BA
Mutant lacking A
Mutant lacking B
Mutant lacking C
Whorls:
Carpel
Stamen
Petal
Sepal
Wild type
(b) Side view of flowers with organ identity mutations
© 2014 Pearson Education, Inc.
Figure 30.4a
Sepals
Petals
A
B
(a) A schematic diagram
of the ABC hypothesis
Stamens
Carpels
C
AB
gene
activity
BC
gene
activity
A gene
activity
C gene
activity
Carpel
Petal
Stamen
Sepal
© 2014 Pearson Education, Inc.
Figure 30.4ba
Active
genes:
BB
B B
A AC CCC AA
BB
BB
CCCCCCCC
Whorls:
Carpel
Stamen
Petal
Sepal
Wild type
Mutant lacking A
(b) Side view of flowers with organ identity mutations
© 2014 Pearson Education, Inc.
Figure 30.4bb
Active
genes:
A A C CC C A A
AA
AA
ABBAABBA
Mutant lacking B
Mutant lacking C
Whorls:
(b) Side view of flowers with organ identity mutations
© 2014 Pearson Education, Inc.
Development of Female Gametophytes (Embryo
Sacs)
 The embryo sac, or female gametophyte, develops
within the ovule
 Within an ovule, two integuments surround a
megasporangium
 One cell in the megasporangium undergoes
meiosis, producing four megaspores, only one of
which survives
 The megaspore divides, producing a large cell with
eight nuclei
© 2014 Pearson Education, Inc.
 This cell is partitioned into a multicellular female
gametophyte, the embryo sac
© 2014 Pearson Education, Inc.
Figure 30.5-1
Carpel
Mature flower on
sporophyte plant
(2n)
Anther
Microsporangium
Microsporocytes (2n)
MEIOSIS
Microspore
(n)
Generative cell
Tube cell
Male
gametophyte
(in pollen
grain) (n)
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Pollen
grains
Figure 30.5-2
Carpel
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore
(n)
Ovule with
megasporangium (2n)
Ovary
MEIOSIS
Male
gametophyte
(in pollen
grain) (n)
Megasporangium
(2n)
Surviving
megaspore
(n)
Female
gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
in central cell
Synergids
Egg (n)
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Integuments
Pollen
tube
Sperm
(n)
Generative cell
Tube cell
Pollen
grains
Figure 30.5-3
Carpel
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore
(n)
Ovule with
megasporangium (2n)
Ovary
MEIOSIS
Generative cell
Tube cell
Male
gametophyte
(in pollen
grain) (n)
Megasporangium
(2n)
Surviving
megaspore
(n)
Female
gametophyte
(embryo sac)
Antipodal cells
Polar nuclei
in central cell
Synergids
Egg (n)
Egg
nucleus (n)
Integuments
Pollen
tube
Sperm
(n)
FERTILIZATION
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Discharged sperm nuclei (n)
Pollen
grains
Stigma
Pollen tube
Sperm
Tube nucleus
Style
Figure 30.5-4
Carpel
Microsporangium
Microsporocytes (2n)
Anther
Mature flower on
sporophyte plant
(2n)
MEIOSIS
Microspore
(n)
Ovule with
megasporangium (2n)
Ovary
Germinating
seed
MEIOSIS
Generative cell
Tube cell
Male
gametophyte
(in pollen
grain) (n)
Megasporangium
(2n)
Embryo (2n)
Endosperm (3n) Seed
Seed coat (2n)
Female
gametophyte
(embryo sac)
Zygote (2n)
Nucleus of
developing
endosperm
(3n)
Surviving
megaspore
(n)
Antipodal cells
Polar nuclei
in central cell
Synergids
Egg (n)
Egg
nucleus (n)
Integuments
Pollen
tube
Sperm
(n)
FERTILIZATION
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Discharged sperm nuclei (n)
Pollen
grains
Stigma
Pollen tube
Sperm
Tube nucleus
Style
Figure 30.5a
Anther
Microsporangium
Microsporocytes (2n)
MEIOSIS
Microspore
(n)
Generative
cell
Tube cell
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Male
gametophyte
(in pollen
grain) (n)
Figure 30.5b
Ovule with
megasporangium (2n)
Ovary
MEIOSIS
Megasporangium
(2n)
Key
Haploid (n)
Diploid (2n)
Surviving
megaspore
(n)
Integuments
© 2014 Pearson Education, Inc.
Figure 30.5c
Pollen
grains
Megasporangium
(2n)
Surviving
megaspore
(n)
Female
gametophyte
(embryo sac)
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Antipodal cells
Polar nuclei
in central cell
Synergids
Egg (n)
Integuments
Pollen
tube
Sperm
(n)
Stigma
Pollen tube
Sperm
Tube
nucleus
Style
Figure 30.5d
Nucleus of
developing
endosperm
(3n)
Embryo (2n)
Endosperm (3n) Seed
Seed coat (2n)
Antipodal cells
Female
Polar nuclei
gametophyte
in central cell
(embryo sac)
Synergids
Zygote (2n)
Egg (n)
Egg
nucleus (n)
Style
Pollen
tube
Sperm
(n)
FERTILIZATION
Key
Haploid (n)
Diploid (2n)
© 2014 Pearson Education, Inc.
Discharged sperm nuclei (n)
Development of Male Gametophytes in Pollen
Grains
 Pollen develops from haploid microspores within
the microsporangia, or pollen sacs, of anthers
 Each microspore undergoes mitosis to produce two
cells: the generative cell and the tube cell
 A pollen grain consists of the two-celled male
gametophyte and the spore wall
© 2014 Pearson Education, Inc.
 If pollination succeeds, a pollen grain produces a
pollen tube that grows down into the ovary and
discharges two sperm cells near the embryo sac
© 2014 Pearson Education, Inc.
Pollination
 In angiosperms, pollination is the transfer of pollen
from an anther to a stigma
 Pollination can be by wind, water, or animals
 Most angiosperms depend on insects, birds, or other
animal pollinators
Video: Bat Pollinating
Video: Bee Pollinating
© 2014 Pearson Education, Inc.
Figure 30.6a
Abiotic pollination by wind
Pollination by insects
Common dandelion
under normal light
Hazel staminate
flower (stamens only)
Hazel carpellate
flower (carpels only)
© 2014 Pearson Education, Inc.
Common dandelion
under ultraviolet
light
Figure 30.6aa
Hazel carpellate
flower (carpels
only)
© 2014 Pearson Education, Inc.
Figure 30.6ab
Hazel staminate
flower (stamens only)
© 2014 Pearson Education, Inc.
Figure 30.6ac
Common dandelion
under normal light
© 2014 Pearson Education, Inc.
Figure 30.6ad
Common dandelion
under ultraviolet
light
© 2014 Pearson Education, Inc.
Figure 30.6b
Pollination by bats or birds
Long-nosed bat
feeding on cactus
flower at night
Hummingbird
drinking nectar of
columbine flower
© 2014 Pearson Education, Inc.
Figure 30.6ba
Long-nosed bat feeding on cactus flower
at night
© 2014 Pearson Education, Inc.
Figure 30.6bb
Hummingbird drinking nectar of columbine flower
© 2014 Pearson Education, Inc.
 Abiotic pollination by wind occurs in angiosperms
including grasses and many trees
 Wind-pollinated angiosperms tend to produce small,
inconspicuous flowers that lack nectar or scent and
release large amounts of pollen
© 2014 Pearson Education, Inc.
 Pollination by insects including bees, moths,
butterflies, flies, and beetles occurs in about 65% of
all angiosperms
 Bees are the most important pollinators
 Floral adaptations to attract bees include
 Production of nectar
 Sweet fragrance
 Brightly colored petals
 “Nectar guides”
© 2014 Pearson Education, Inc.
 Pollination by bats occurs in plants that produce
light-colored, aromatic flowers
© 2014 Pearson Education, Inc.
 Pollination by birds occurs in plants that produce
large, bright red or yellow flowers with little odor and
large quantities of nectar
 The petals of bird-pollinated flowers are often fused
into a floral tube
© 2014 Pearson Education, Inc.
Double Fertilization
 After landing on a receptive stigma, a pollen grain
produces a pollen tube that extends between the
cells of the style toward the ovary
 Double fertilization results from the discharge of
two sperm from the pollen tube into the embryo sac
 One sperm fertilizes the egg, and the other
combines with the polar nuclei, giving rise to the
triploid food-storing endosperm (3n)
Animation: Plant Fertilization
© 2014 Pearson Education, Inc.
Figure 30.7-1
Stigma
Pollen tube
Pollen
grain
Two sperm
Tube
nucleus
Style
Ovary
Ovule
Polar
nuclei
Egg
Micropyle
© 2014 Pearson Education, Inc.
Figure 30.7-2
Stigma
Pollen tube
Pollen
grain
Ovule
Two sperm
Tube
nucleus
Polar
nuclei
Style
Egg
Ovary
Polar Synergid
nuclei
Two sperm
Egg
Ovule
Micropyle
© 2014 Pearson Education, Inc.
Figure 30.7-3
Stigma
Pollen tube
Pollen
grain
Ovule
Two sperm
Tube
nucleus
Polar
nuclei
Style
Egg
Ovary
Polar Synergid
nuclei
Two sperm
Egg
Ovule
Micropyle
© 2014 Pearson Education, Inc.
Endosperm
nucleus (3n)
(two polar nuclei
plus sperm)
Zygote (2n)
(egg plus
sperm)
Seed Development, Form, and Function
 After double fertilization, each ovule develops into a
seed
 The ovary develops into a fruit enclosing the seed(s)
© 2014 Pearson Education, Inc.
Endosperm Development
 Endosperm development usually precedes embryo
development
 In most monocots and some eudicots, endosperm
stores nutrients that can be used by the seedling
 In other eudicots, the food reserves of the
endosperm are exported to the cotyledons
© 2014 Pearson Education, Inc.
Embryo Development
 The first mitotic division of the zygote splits the
fertilized egg into a basal cell and a terminal cell
 The basal cell produces a multicellular suspensor,
which anchors the embryo to the parent plant
 The terminal cell gives rise to most of the embryo
 The cotyledons form and the embryo elongates
Animation: Seed Development
© 2014 Pearson Education, Inc.
Figure 30.8
Ovule
Endosperm
nucleus
Zygote
Integuments
Zygote
Terminal cell
Basal cell
Proembryo
Suspensor
Basal cell
Cotyledons
Shoot apex
Root apex
Suspensor
© 2014 Pearson Education, Inc.
Seed coat
Endosperm
Structure of the Mature Seed
 The embryo and its food supply are enclosed by a
hard, protective seed coat
 The seed enters a state of dormancy, wherein it
stops growing and slows metabolism
 A mature seed is only about 5–15% water
© 2014 Pearson Education, Inc.
 In some eudicots, such as the common garden
bean, the embryo consists of the embryonic axis
attached to two thick cotyledons (seed leaves)
 Below the cotyledons the embryonic axis is called
the hypocotyl and terminates in the radicle
(embryonic root); above the cotyledons it is called
the epicotyl
 The plumule comprises the epicotyl, young leaves,
and shoot apical meristem
© 2014 Pearson Education, Inc.
Figure 30.9
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
Scutellum
(cotyledon)
Pericarp fused
with seed coat
Coleoptile
Endosperm
Epicotyl
Hypocotyl
Coleorhiza
(c) Maize, a monocot
© 2014 Pearson Education, Inc.
Radicle
Figure 30.9a
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
© 2014 Pearson Education, Inc.
Figure 30.9b
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
© 2014 Pearson Education, Inc.
Figure 30.9c
Scutellum
(cotyledon)
Pericarp fused
with seed coat
Coleoptile
Endosperm
Epicotyl
Hypocotyl
Coleorhiza
(c) Maize, a monocot
© 2014 Pearson Education, Inc.
Radicle
 The seeds of some eudicots, such as castor
beans, have thin cotyledons
© 2014 Pearson Education, Inc.
 A monocot embryo has one cotyledon
 Grasses, such as maize and wheat, have a special
cotyledon called a scutellum
 Two sheathes enclose the embryo of a grass seed:
a coleoptile covering the young shoot and a
coleorhiza covering the young root
© 2014 Pearson Education, Inc.
Seed Dormancy: An Adaptation for Tough Times
 Seed dormancy 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
changes
© 2014 Pearson Education, Inc.
Seed Germination and Seedling Development
 Germination depends on imbibition, the uptake of
water due to low water potential of the dry seed
 The radicle (embryonic root) emerges first
 Next, the shoot tip breaks through the soil surface
© 2014 Pearson Education, Inc.
 In many eudicots, a hook forms in the hypocotyl,
and growth pushes the hook above ground
 Light causes the hook to straighten and pull the
cotyledons and shoot tip up
Video: Plant Time Lapse
© 2014 Pearson Education, Inc.
Figure 30.10
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
© 2014 Pearson Education, Inc.
Cotyledon
Figure 30.10a
Foliage leaves
Cotyledon
Hypocotyl
Epicotyl
Cotyledon
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
© 2014 Pearson Education, Inc.
Hypocotyl
Cotyledon
Figure 30.10b
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
© 2014 Pearson Education, Inc.
 In some monocots, such as maize and other
grasses, the coleoptile pushes up through the soil
© 2014 Pearson Education, Inc.
Fruit Form and Function
 A fruit develops from the ovary
 It protects the enclosed seeds and aids in seed
dispersal by wind or animals
 A fruit may be classified as dry, if the ovary dries
out at maturity, or fleshy, if the ovary becomes thick,
soft, and sweet at maturity
© 2014 Pearson Education, Inc.
 Fruits are also classified by their developmental
origins
 Simple, from a single or several fused carpels
 Aggregate, from a single flower with multiple
separate carpels
 Multiple, from a group of flowers called an
inflorescence
Animation: Fruit Development
© 2014 Pearson Education, Inc.
Figure 30.11
Carpels
Stamen
Flower
Stigma
Style
Petal
Ovary
Stamen
Sepal
Ovule
Stigma
Pea flower
Ovule
Raspberry flower
Carpel
(fruitlet)
Stigma
Seed
Ovary
Ovary (in
receptacle)
Apple flower
Pineapple inflorescence
Each segment
develops
from the
carpel
of one
flower
Stamen
Remains of
stamens and styles
Sepals
Stamen
Seed
Pea fruit
(a) Simple fruit
© 2014 Pearson Education, Inc.
Raspberry fruit
(b) Aggregate fruit
Pineapple fruit
(c) Multiple fruit
Receptacle
Apple fruit
(d) Accessory fruit
Figure 30.11a
Carpels
Stamen
Ovary
Stamen
Stigma
Pea flower
Ovule
Raspberry flower
Carpel
(fruitlet)
Seed
Stigma
Ovary
Stamen
Pea fruit
(a) Simple fruit
© 2014 Pearson Education, Inc.
Raspberry fruit
(b) Aggregate fruit
Figure 30.11b
Flower
Petal
Stigma
Sepal
Ovule
Pineapple inflorescence
Each segment
develops
from the
carpel
of one
flower
(c) Multiple fruit
© 2014 Pearson Education, Inc.
Stamen
Ovary (in
receptacle)
Apple flower
Remains of
stamens and styles
Sepals
Seed
Pineapple fruit
Style
Receptacle
Apple fruit
(d) Accessory fruit
 An accessory fruit contains other floral parts in
addition to ovaries
© 2014 Pearson Education, Inc.
 Fruit dispersal mechanisms include
 Water
 Wind
 Animals
© 2014 Pearson Education, Inc.
Figure 30.12a
Dispersal by water
Dispersal by wind
Giant seed of
the tropical Asian
climbing gourd
Alsomitra macrocarpa
Winged fruit of a maple
© 2014 Pearson Education, Inc.
Coconut seed
embryo, endosperm,
and endocarp inside
buoyant husk
Dandelion fruit
Dandelion “seeds” (actually one-seeded fruits)
Tumbleweed
 Dispersal by water occurs in buoyant seeds and
fruits like coconut, which can survive for long
periods at sea
© 2014 Pearson Education, Inc.
Figure 30.12aa
Coconut seed embryo,
endosperm, and endocarp
inside buoyant husk
© 2014 Pearson Education, Inc.
 Dispersal by wind occurs in seeds and fruits that
have adaptations such as parachute or winglike
structures
© 2014 Pearson Education, Inc.
Figure 30.12ab
Giant seed of the tropical
Asian climbing gourd
Alsomitra macrocarpa
© 2014 Pearson Education, Inc.
Figure 30.12ac
Dandelion fruit
Dandelion “seeds” (actually one-seeded fruits)
© 2014 Pearson Education, Inc.
Figure 30.12ad
Winged fruit of a maple
© 2014 Pearson Education, Inc.
Figure 30.12ae
Tumbleweed
© 2014 Pearson Education, Inc.
 Dispersal by animals occurs in seeds and fruits
that are edible or adapted to attach to an animal’s
skin or fur
© 2014 Pearson Education, Inc.
Figure 30.12b
Dispersal by animals
Fruit of puncture vine
(Tribulus terrestris)
Squirrel hoarding seeds or fruits
underground
Ant carrying seed with
attached “food body”
Seeds dispersed in black bear feces
© 2014 Pearson Education, Inc.
Figure 30.12ba
Fruit of puncture vine
(Tribulus terrestris)
© 2014 Pearson Education, Inc.
Figure 30.12bb
Squirrel hoarding seeds or fruits
underground
© 2014 Pearson Education, Inc.
Figure 30.12bc
Seeds dispersed in black bear feces
© 2014 Pearson Education, Inc.
Figure 30.12bd
Ant carrying seed with
attached “food body”
© 2014 Pearson Education, Inc.
Concept 30.2: Flowering plants reproduce
sexually, asexually, or both
 Many angiosperm species reproduce both asexually
and sexually
 Sexual reproduction results in offspring that are
genetically different from their parents
 Asexual reproduction results in a clone of
genetically identical organisms
© 2014 Pearson Education, Inc.
Mechanisms of Asexual Reproduction
 Fragmentation, separation of a parent plant into
parts that develop into whole plants, is a very
common type of asexual reproduction
 In some species, a parent plant’s root system gives
rise to adventitious shoots that become separate
shoot systems
© 2014 Pearson Education, Inc.
Figure 30.13
Asexual reproduction in aspen trees
© 2014 Pearson Education, Inc.
 Apomixis is the asexual production of seeds from a
diploid cell
© 2014 Pearson Education, Inc.
Advantages and Disadvantages of Asexual Versus
Sexual Reproduction
 Asexual reproduction is also called vegetative
reproduction
 Asexual reproduction can be beneficial to a
successful plant in a stable environment
 However, a clone of plants is vulnerable to local
extinction if there is an environmental change
© 2014 Pearson Education, Inc.
 Sexual reproduction generates genetic variation that
makes evolutionary adaptation possible
 However, only a fraction of seedlings survive
 Some flowers can self-fertilize to ensure that every
ovule will develop into a seed
 Many species have evolved mechanisms to prevent
selfing
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Mechanisms That Prevent Self-Fertilization
 Many angiosperms have mechanisms that make it
difficult or impossible for a flower to self-fertilize
 Dioecious species have staminate and carpellate
flowers on separate plants
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Figure 30.14
(a) Staminate flowers (left) and carpellate flowers (right)
of a dioecious species
Stamens Styles
Styles
Thrum flower
(b) Thrum and pin flowers
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Stamens
Pin flower
Figure 30.14aa
Staminate flowers
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Figure 30.14ab
Carpellate flowers
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Figure 30.14b
Stamens Styles
Styles
Thrum flower
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Stamens
Pin flower
 Others have stamens and carpels that mature at
different times or are arranged to prevent selfing
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 The most common is self-incompatibility, a plant’s
ability to reject its own pollen
 Researchers are unraveling the molecular
mechanisms involved in self-incompatibility
 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
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Totipotency, Vegetative Reproduction, and
Tissue Culture
 Totipotent cells are able to asexually generate a
clone of the original organism through cell division
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Vegetative Propagation and Grafting
 When vegetative reproduction is induced by
humans it is called vegetative propagation
 Many kinds of plants are asexually reproduced
from plant fragments called cuttings
 A callus is a mass of dividing undifferentiated cells
that forms where a stem is cut and produces
adventitious roots
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 A twig or bud can be grafted onto a plant of a
closely related species or variety
 The stock provides the root system
 The scion is grafted onto the stock
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Test-Tube Cloning and Related Techniques
 Plant biologists have adopted in vitro methods to
clone plants for research or horticulture
 Small fragments of the parent plant are cultured on
artificial medium
 A callus of undifferentiated cells can sprout shoots
and roots in response to plant hormones
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Figure 30.15
(a)
(b)
(c)
Laboratory cloning of a garlic plant
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Developing root
 Plant tissue culture facilitates genetic engineering
and the elimination of viruses
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Concept 30.3: People modify crops through
breeding and genetic engineering
 People have intervened in the reproduction and
genetic makeup of plants for thousands of years
 Hybridization is common in nature and has been
used by breeders to introduce new genes
 Maize, a product of artificial selection, is unable to
persist in nature
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Figure 30.16
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Figure 30.16a
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Figure 30.16b
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Plant Breeding
 Mutations can arise spontaneously or can be
induced by breeders
 Plants with beneficial mutations are used in
breeding experiments
 Desirable traits can be introduced by hybridizing
wild species with domestic varieties within the same
species or genus
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Plant Biotechnology and Genetic Engineering
 Plant biotechnology has two meanings
 In a general sense, it refers to innovations in the use
of plants to make useful products
 In a specific sense, it refers to use of genetically
modified (GM) organisms in agriculture and industry
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 Modern plant biotechnology is not limited to transfer
of genes between closely related species or genera
 Transgenic organisms are genetically modified to
express a gene from another species
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Reducing World Hunger and Malnutrition
 Genetically modified plants may increase the quality
and quantity of food worldwide
 Transgenic crops have been developed that
 Produce proteins to defend them against insect pests
 Tolerate herbicides
 Resist specific diseases
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 Nutritional quality of plants is being improved
 “Golden Rice” is a transgenic variety being
developed to address vitamin A deficiencies among
the world’s poor
 Transgenic cassava has enriched levels of nutrients
and reduced levels of cyanide-producing chemicals
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Figure 30.17
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Reducing Fossil Fuel Dependency
 Biofuels are derived from living biomass, the total
mass of organic matter in a group of organisms
 Biofuels would reduce the net emission of CO2, a
greenhouse gas
 Biofuels can be produced through the fermentation
and distillation of plant materials such as cellulose
from rapidly growing crops including switchgrass
and poplar
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The Debate over Plant Biotechnology
 Some biologists are concerned about releasing GM
organisms (GMOs) into the environment
 The concern originates from the unstoppable
nature of the “experiment”
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Issues of Human Health
 One concern is that genetic engineering may
transfer allergens from a gene source to a plant
used for food
 Some GMOs have health benefits
 For example, maize that produces the Bt toxin has
90% less of a cancer-causing toxin than non-Bt
maize
 Bt maize has less insect damage and lower infection
by Fusarium fungus that produces the cancercausing toxin
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 GMO opponents advocate for clear labeling of all
GMO foods
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Possible Effects on Nontarget Organisms
 Many ecologists are concerned that the growing of
GM crops might have unforeseen effects on
nontarget organisms
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Addressing the Problem of Transgene Escape
 Perhaps the most serious concern is the possibility
of introduced genes escaping into related weeds
through crop-to-weed hybridization
 This could result in “superweeds” that would be
resistant to many herbicides
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 Efforts are under way to prevent this by
introducing
 Male sterility
 Apomixis
 Transgenes into chloroplast DNA (not transferred
by pollen)
 Strict self-pollination
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Figure 30.UN01a
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Figure 30.UN01b
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Figure 30.UN02
Endosperm
nucleus (3n)
(two polar nuclei
plus sperm)
Zygote (2n)
(egg plus sperm)
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