Transcript Angiosperm Reproduction

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 38
Angiosperm Reproduction
and Biotechnology
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Flowers of Deceit
• Insects help angiosperms to reproduce sexually
with distant members of their own species
– For example, male Campsoscolia wasps 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
© 2011 Pearson
Inc. Inc., publishing as Pearson Benjamin Cummings
Copyright
© 2008Education,
Pearson Education,
Figure 38.1
• Many angiosperms lure insects with nectar; both
plant and pollinator benefit
• Mutualistic symbioses are common between
plants and other species
• Angiosperms can reproduce sexually and
asexually
• Angiosperms are the most important group of
plants in terrestrial ecosystems and in agriculture
© 2011 Pearson
Inc. Inc., publishing as Pearson Benjamin Cummings
Copyright
© 2008Education,
Pearson Education,
Concept 38.1: Flowers, double fertilization,
and fruits are unique features of the
angiosperm life cycle
• Plant lifecycles 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
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Video: Flower Blooming (time lapse)
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• 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
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Video: Flower Plant Life Cycle (time lapse)
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Figure 38.2
Stamen
Anther
Filament
Petal
Carpel
Stigma
Style
Ovary
Germinated pollen grain (n)
(male gametophyte)
Ovary
Ovule
Embryo sac (n)
(female gametophyte)
Anther
Pollen tube
FERTILIZATION
Sepal
Egg (n)
Sperm (n)
Receptacle
(a) Structure of an
idealized flower
Key
Zygote
(2n)
Mature sporophyte
plant (2n)
Haploid (n)
Diploid (2n)
(b) Simplified angiosperm
life cycle
Germinating
seed
Seed
Seed
Simple
fruit
Embryo (2n)
(sporophyte)
Figure 38.2a
Stamen
Anther
Filament
Petal
Stigma Carpel
Style
Ovary
Sepal
Receptacle
(a) Structure of an idealized flower
Figure 38.2b
Anther
Germinated pollen grain (n)
(male gametophyte)
Ovary
Ovule
Embryo sac (n)
(female gametophyte)
Pollen tube
FERTILIZATION
Egg (n)
Sperm (n)
Key
Zygote
(2n)
Mature sporophyte
plant (2n)
Haploid (n)
Diploid (2n)
(b) Simplified angiosperm
life cycle
Germinating
seed
Seed
Seed
Simple
fruit
Embryo (2n)
(sporophyte)
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: sepals,
petals, stamens, and carpels
• Stamens and carpels are reproductive organs;
sepals and petals are sterile
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• A stamen consists of a filament topped by an
anther with pollen sacs that produce pollen
• 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
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• 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
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Development of Male Gametophytes in
Pollen Grains
• Pollen develops from 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
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• 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
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Video: Bee Pollinating
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Video: Bat Pollinating Agave Plant
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Figure 38.3
(a) Development of a male
gametophyte
(in pollen grain)
(b) Development of a female
gametophyte (embryo sac)
Microsporangium
(pollen sac)
Megasporangium
Microsporocyte
Ovule
MEIOSIS
Megasporocyte
Integuments
Microspores (4)
Micropyle
Surviving
megaspore
Each of 4
microspores
Ovule
Male
gametophyte
(in pollen grain)
Generative cell
(will form 2
sperm)
Antipodal cells (3)
Polar nuclei (2)
Egg (1)
Nucleus of tube cell
Integuments
20 m
(LM)
Key to labels
Haploid (n)
Diploid (2n)
100 m
75 m
Ragweed
pollen
grain
(colorized
SEM)
Synergids (2)
Embryo sac
(LM)
Female gametophyte
(embryo sac)
MITOSIS
Figure 38.3a
(a) Development of a male gametophyte
(in pollen grain)
Microsporangium
(pollen sac)
Microsporocyte
MEIOSIS
Microspores (4)
Each of 4
microspores
MITOSIS
Male
gametophyte
(in pollen grain)
Generative cell
(will form 2 sperm)
Nucleus of tube cell
20 m
Key to labels
75 m
(LM)
Ragweed pollen grain
(colorized SEM)
Haploid (n)
Diploid (2n)
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
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• This cell is partitioned into a multicellular female
gametophyte, the embryo sac
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Figure 38.3b
(b) Development of a female gametophyte
(embryo sac)
Megasporangium
Ovule
MEIOSIS
Megasporocyte
Integuments
Micropyle
Surviving
megaspore
Ovule
Antipodal cells (3)
Polar nuclei (2)
Egg (1)
Integuments
Synergids (2)
Haploid (n)
Diploid (2n)
100 m
Key to labels
Embryo sac
(LM)
Female gametophyte
(embryo sac)
MITOSIS
Figure 38.3c
Generative cell
(will form 2
sperm)
Nucleus of
tube cell
(LM)
75 m
Figure 38.3d
20 m
Ragweed pollen grain
(colorized SEM)
100 m
Figure 38.3e
Embryo sac
(LM)
Pollination
• In angiosperms, pollination is the transfer of
pollen from an anther to a stigma
• Pollination can be by wind, water, or animals
• Wind-pollinated species (e.g., grasses and many
trees) release large amounts of pollen
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Figure 38.4a
Abiotic Pollination by Wind
Pollination by Bees
Common dandelion
under normal light
Hazel staminate flowers
(stamens only)
Hazel carpellate
flower (carpels only)
Common dandelion
under ultraviolet light
Figure 38.4aa
Hazel staminate flowers (stamens only)
Figure 38.4ab
Hazel carpellate
flower (carpels only)
Figure 38.4ac
Common dandelion under
normal light
Figure 38.4ad
Common dandelion under
ultraviolet light
Figure 38.4b
Pollination by Moths
and Butterflies
Pollination by Flies
Pollination by Bats
Anther
Moth
Fly egg
Stigma
Moth on yucca flower
Blowfly on carrion
flower
Pollination by Birds
Hummingbird
drinking nectar of
columbine flower
Long-nosed bat feeding
on cactus flower at night
Figure 38.4ba
Anther
Moth
Stigma
Moth on yucca flower
Figure 38.4bb
Fly egg
Blowfly on carrion flower
Figure 38.4bc
Long-nosed bat feeding on
cactus flower at night
Figure 38.4bd
Hummingbird drinking nectar of columbine flower
Coevolution of Flower and Pollinator
• Coevolution is the evolution of interacting species
in response to changes in each other
• Many flowering plants have coevolved with
specific pollinators
• The shapes and sizes of flowers often correspond
to the pollen transporting parts of their animal
pollinators
– For example, Darwin correctly predicted a moth
with a 28 cm long tongue based on the
morphology of a particular flower
© 2011 Pearson Education, Inc.
Figure 38.5
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 Plant Fertilization endosperm
(3n)
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Animation: Plant Fertilization
Right-click slide / select “Play”
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Figure 38.6-1
1
Stigma
Pollen
grain
Pollen
tube
2 sperm
Style
Ovary
Ovule
Polar
nuclei
Egg
Micropyle
Figure 38.6-2
2
1
Stigma
Pollen
grain
Pollen
tube
Ovule
2 sperm
Polar
nuclei
Style
Ovary
Egg
Ovule
Synergid
Polar
nuclei
Egg
Micropyle
2 sperm
Figure 38.6-3
2
1
Stigma
Pollen
grain
Pollen
tube
Ovule
2 sperm
Polar
nuclei
Style
Ovary
Egg
Ovule
Synergid
Polar
nuclei
Egg
Micropyle
3
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
2 sperm
Zygote
(2n)
Seed Development, Form, and Function
• After double fertilization, each ovule develops into
a seed
• The ovary develops into a fruit enclosing the
seed(s)
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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
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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
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Animation: Seed Development
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Figure 38.7
Ovule
Proembryo
Endosperm
nucleus
Integuments
Zygote
Suspensor
Cotyledons
Basal
cell
Shoot
apex
Root
apex
Terminal cell
Basal cell
Zygote
Suspensor
Seed
coat
Endosperm
Figure 38.7a
Ovule
Endosperm
nucleus
Integuments
Zygote
Terminal cell
Basal cell
Zygote
Figure 38.7b
Proembryo
Suspensor
Cotyledons
Basal
cell
Shoot
apex
Root
apex
Suspensor
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
• A mature seed is only about 5–15% water
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• 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
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Figure 38.8
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)
Coleoptile
Coleorhiza
Pericarp fused
with seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
(c) Maize, a monocot
Figure 38.8a
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
• The seeds of some eudicots, such as castor
beans, have thin cotyledons
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Figure 38.8b
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
• 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
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Figure 38.8c
Scutellum
(cotyledon)
Coleoptile
Coleorhiza
(c) Maize, a monocot
Pericarp fused
with seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
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
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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
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• 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
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Figure 38.9
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
Figure 38.9a
Foliage leaves
Cotyledon
Hypocotyl
Cotyledon
Epicotyl
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
• In maize and other grasses, which are monocots,
the coleoptile pushes up through the soil
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Figure 38.9b
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
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
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Animation: Fruit Development
Right-click slide / select “Play”
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• Fruits are also classified by their development
– Simple, a single or several fused carpels
– Aggregate, a single flower with multiple separate
carpels
– Multiple, a group of flowers called an
inflorescence
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Figure 38.10
Stigma
Carpels
Stamen
Flower
Style
Petal
Ovary
Stamen
Sepal
Ovule
Stigma
Ovule
Pea flower
Raspberry flower
Carpel
(fruitlet)
Seed
Stigma
Ovary
Stamen
Pineapple
inflorescence
Each segment
develops
from the
carpel
of one
flower
Stamen
Ovary (in
receptacle)
Apple flower
Remains of
stamens and styles
Sepals
Seed
Pea fruit
(a) Simple fruit
Raspberry fruit
(b) Aggregate fruit
Pineapple fruit
(c) Multiple fruit
Receptacle
Apple fruit
(d) Accessory fruit
Figure 38.10a
Carpels
Stamen
Ovary
Stamen
Stigma
Ovule
Pea flower
Raspberry flower
Carpel
(fruitlet)
Seed
Stigma
Ovary
Stamen
Pea fruit
(a) Simple fruit
Raspberry fruit
(b) Aggregate fruit
Figure 38.10b
Stigma
Flower
Petal
Sepal
Ovule
Pineapple
inflorescence
Each segment
develops
from the
carpel
of one
flower
Style
Stamen
Ovary (in
receptacle)
Apple flower
Remains of
stamens and styles
Sepals
Seed
Pineapple fruit
(c) Multiple fruit
Receptacle
Apple fruit
(d) Accessory fruit
• An accessory fruit contains other floral parts in
addition to ovaries
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• Fruit dispersal mechanisms include
– Water
– Wind
– Animals
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Figure 38.11a
Dispersal by Wind
Dandelion fruit
Dandelion “seeds” (actually one-seeded fruits)
Tumbleweed
Winged seed of
the tropical Asian
climbing gourd
Alsomitra macrocarpa
Winged fruit of a maple
Dispersal by Water
Coconut seed embryo,
endosperm, and endocarp
inside buoyant husk
Figure 38.11aa
Coconut seed embryo,
endosperm, and endocarp
inside buoyant husk
Figure 38.11ab
Winged seed of the tropical Asian
climbing gourd Alsomitra macrocarpa
Figure 38.11ac
Dandelion fruit
Dandelion “seeds” (actually one-seeded fruits)
Figure 38.11ad
Winged fruit of a maple
Figure 38.11ae
Tumbleweed
Figure 38.11b
Dispersal by Animals
Fruit of puncture vine
(Tribulus terrestris)
Squirrel hoarding
seeds or fruits
underground
Ant carrying
seed with nutritious
“food body” to its
nest
Seeds dispersed in black bear feces
Figure 38.11ba
Fruit of puncture vine
(Tribulus terrestris)
Figure 38.11bb
Squirrel hoarding seeds or fruits
underground
Figure 38.11bc
Seeds dispersed in black bear feces
Figure 38.11bd
Ant carrying
seed with nutritious
“food body” to its
nest
Concept 38.2: 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
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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
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Figure 38.12
• Apomixis is the asexual production of seeds from
a diploid cell
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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
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• 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 38.13
(a) Staminate flowers (left) and carpellate flowers (right)
of a dioecious species
Stamens Styles
Styles
Thrum flower
(b) Thrum and pin flowers
Stamens
Pin flower
Figure 38.13a
Staminate flowers
• Others have stamens and carpels that mature at
different times or are arranged to prevent selfing
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Figure 38.13b
Carpellate flowers
Figure 38.13c
Stamens Styles
Styles
Thrum flower
Stamens
Pin flower
• 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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Vegetative Propagation and Agriculture
• Humans have devised methods for asexual
propagation of angiosperms
• Most methods are based on the ability of plants to
form adventitious roots or shoots
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Clones from Cuttings
• 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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Inc. Inc., publishing as Pearson Benjamin Cummings
Copyright
© 2008Education,
Pearson Education,
Grafting
• 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
create and clone novel plant varieties
• A callus of undifferentiated cells can sprout shoots
and roots in response to plant hormones
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Figure 38.14
(a)
(b)
(c)
Developing root
• Transgenic plants are genetically modified (GM)
to express a gene from another organism
• Protoplast fusion is used to create hybrid plants
by fusing protoplasts, plant cells with their cell
walls removed
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Figure 38.15
50 m
Concept 38.3: Humans modify crops by
breeding and genetic engineering
• Humans 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 a staple
in many developing countries
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Figure 38.16
Figure 38.16a
Figure 38.16b
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 from different
species or genera
• The grain triticale is derived from a successful
cross between wheat and rye
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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 GM
organisms in agriculture and industry
• Modern plant biotechnology is not limited to
transfer of genes between closely related species
or varieties of the same 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
– For example, “Golden Rice” is a transgenic variety
being developed to address vitamin A deficiencies
among the world’s poor
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Figure 38.17
Cassava roots harvested in Thailand
Reducing Fossil Fuel Dependency
• Biofuels are made by the fermentation and
distillation of plant materials such as cellulose
• Biofuels can be produced by rapidly growing crops
such as switchgrass and poplar
• Biofuels would reduce the net emission of CO2, a
greenhouse gas
• The environmental implications of biofuels are
controversial
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The Debate over Plant Biotechnology
• Some biologists are concerned about risks of
releasing GM organisms (GMOs) into the
environment
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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
corn
– Bt maize has less insect damage and lower
infection by Fusarium fungus that produces the
cancer-causing 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 underway to prevent this by
introducing
– Male sterility
– Apomixis
– Transgenes into chloroplast DNA (not
transferred by pollen)
– Strict self-pollination
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Figure 38.UN01
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Zygote (2n)
(egg plus sperm)
Figure 38.UN02