Download video slide

Chapter 38
Angiosperm Reproduction and
Biotechnology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• To Seed or Not to Seed
• The parasitic plant Rafflesia arnoldii
– Produces enormous flowers that can produce
up to 4 million seeds
Figure 38.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pollination enables gametes to come together
within a flower
• Dominant sporophyte of angiosperms
– Produces spores male gametophytes (pollen
grains)
– Produces female gametophytes (embryo sacs)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Angiosperm reproduction
Stigma
Anther
Stamen
Carpel
Germinated pollen grain
(n) (male gametophyte)
on stigma of carpel
Anther at
tip of stamen
Style
Filament
Ovary (base of carpel)
Ovary
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)
(b) Simplified angiosperm life cycle.
See Figure 30.10 for a more detailed
version of the life cycle, including meiosis.
Figure 38.2a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Germinating
seed
Embryo (2n)
(sporophyte)
Simple fruit
(develops from ovary)
Flowers
• Reproductive shoots of the angiosperm
sporophyte
• 4 floral organs: sepals, petals, stamens, and
carpels (pistil)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Many variations in floral structure
– Have evolved during the 140 million years of
angiosperm history
SYMMETRY
OVARY LOCATION
FLORAL DISTRIBUTION
Lupine inflorescence
Bilateral symmetry
(orchid)
Superior
ovary
Sunflower
inflorescence
Sepal
Semi-inferior ovary Inferior ovary
Radial symmetry
(daffodil)
Fused petals
REPRODUCTIVE VARIATIONS
Figure 38.3
Maize, a monoecious
species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Dioecious Sagittaria
latifolia (common
arrowhead)
Angiosperm Gametophyte Development and
Pollination
• Pollination: Transfer of pollen f/ anther to
stigma pollen tube grows down into the ovary
 discharges sperm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pollen
– Develops from microspores within
the sporangia of anthers
Pollen sac
(microsporangium)
(a) Development of a male gametophyte
(pollen grain)
1
Each one of the
microsporangia
contains diploid
microsporocytes
(microspore
mother cells).
Microsporocyte
MEIOSIS
Microspores (4)
2 Each microsporocyte divides by
meiosis to produce
four haploid
microspores,
each of which
develops into
a pollen grain.
Figure 38.4a
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.)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Each of 4
microspores
Generative
cell (will
form 2
sperm)
MITOSIS
Male
Gametophyte
(pollen grain)
Nucleus
of tube cell
20 m
75 m
Ragweed
pollen
grain
KEY
to labels
Haploid (2n)
Diploid (2n)
• Embryo sacs
– Develop from megaspores within ovules
(b) Development of a female gametophyte
(embryo sac)
Megasporangium
Ovule
MEIOSIS
Megasporocyte
Integuments
Micropyle
Surviving
megaspore
Female gametophyte
(embryo sac)
MITOSIS
Ovule
Antipodel
Cells (3)
Polar
Nuclei (2)
Egg (1)
Integuments
Haploid (2n)
Diploid (2n)
100 m
Key
to labels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Synergids (2)
1
Within the ovule’s
megasporangium
is a large diploid
cell called the
megasporocyte
(megaspore
mother cell).
2 The megasporocyte divides by
meiosis and gives rise to four
haploid cells, but in most
species only one of these
survives as the megaspore.
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).
Embryo
sac
Figure 38.4b
Mechanisms That Prevent Self-Fertilization
• Make it difficult for a flower to fertilize itself
Stigma
Stigma
Anther
with
pollen
Pin flower
Thrum flower
Figure 38.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The most common anti-selfing mechanism is
self-incompatibility (plant rejects own pollen)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• After fertilization, ovules develop into seeds
and ovaries into fruits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Double Fertilization
• Pollen germinates, produces a pollen tube 
discharges two sperm into the embryo sac
• One sperm fertilizes the egg
• Other sperm combines with the polar nuclei 
endosperm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Double fertilization
Pollen grain
Stigma
Pollen tube
1 If a pollen grain
germinates, a pollen tube
grows down the style
toward the ovary.
Polar
nuclei
Egg
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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ovule
Polar nuclei
Egg
Two sperm
about to be
discharged
Endosperm nucleus (3n)
(2 polar nuclei plus sperm)
Zygote (2n)
(egg plus sperm)
Figure 38.6
From Ovule to Seed
• After double fertilization
– Each ovule develops into a seed
– The ovary develops into a fruit enclosing the
seed(s)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Endosperm Development
• Monocots and some eudicots (dicots)
– Endosperm stores nutrients that can be used
by the seedling after germination
• In other eudicots
– The food reserves of the endosperm are
completely exported to the cotyledons
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Structure of the Mature Seed
• The embryo and its food supply
– Are enclosed by a hard, protective seed coat
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Bean, a eudicot
– The embryo consists of the hypocotyl, radicle,
and thick cotyledons
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.
Figure 38.8a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Castor beans (eudicot)
– Thin cotyledons
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Hypocotyl
Radicle
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.
Figure 38.8b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Monocot, e.g. corn
– Single cotyledon and coleoptile
Pericarp fused
with seed coat
Scutellum
(cotyledon)
Endosperm
Coleoptile
Epicotyl
Hypocotyl
Coleorhiza
(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.
Figure 38.8c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Radicle
From Ovary to Fruit
• A fruit
– Develops f/ ovary
– Protects seeds
– Aids in the dispersal of seeds by wind or
animals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Fruits classification
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).
Figure 38.9a–c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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).
Seed Germination
• As a seed matures
– It dehydrates and becomes dormant
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Dormancy increases the chances that
germination will occur at a time and place most
advantageous to the seedling
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
From Seed to Seedling
• Imbibition
– Uptake of water due to low water potential of
the dry seed
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Radicle (embryonic root)
– First organ to emerge from the germinating seed
• In eudicots (e.g. bean)
– A hook forms in the hypocotyl, and growth pushes
the hook above ground
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Hypocotyl
Cotyledon
Hypocotyl
Radicle
(a)
Figure 38.10a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Seed coat
Common garden bean. In common garden
beans, straightening of a hook in the
hypocotyl pulls the cotyledons from the soil.
• Monocots (e.g. corn)
– The coleoptile pushes upward through the soil
Foliage leaves
Coleoptile
Coleoptile
Radicle
Figure 38.10b
(b) Maize. In maize and other grasses, the shoot grows
straight up through the tube of the coleoptile.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Many angiosperm species
– Reproduce both asexually and sexually
• Sexual reproduction
– Genetic variation that makes evolutionary
adaptation possible
• Asexual reproduction
– Called vegetative reproduction clones
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Fragmentation (asexual)
– Separation of a parent into parts  whole
plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In some species
– The root system of a parent gives rise to
adventitious shoots that become separate
shoot systems
Figure 38.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Vegetative (Asexual) Propagation and Agriculture
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Clones from Cuttings
• Asexually reproduced from plant fragments
called cuttings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Grafting
• Twig or bud from one plant can be grafted onto
a closely related plant
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Test-Tube Cloning
• in vitro methods
– create and clone novel plant varieties
(a) Just a few parenchyma cells from a
carrot gave rise to this callus, a mass
of undifferentiated cells.
Figure 38.12a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) The callus differentiates into an entire
plant, with leaves, stems, and roots.
• Plant biotechnology
– Innovations in the use of plants to make
products of use to humans
– Genetically modified (GM) organisms in
agriculture and industry
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Artificial Selection
• Human intervention done for thousands of
years
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Maize (corn)
– Product of artificial selection
– Staple in many developing countries, but is a
poor source of protein
Figure 38.14
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Reducing World Hunger and Malnutrition
• Genetically modified (GM) plants
Genetically modified rice
Ordinary rice
Figure 38.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 38.16
The Debate over Plant Biotechnology
• Some biologists, particularly ecologists
– Concerned about the unknown risks
associated with the release of GMOs into the
environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Issues of Human Health
• Concern that genetic engineering may transfer
allergens to food
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Transgene Escape
• GM crops may introduce genes from a
transgenic crop into related weeds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Despite all the issues associated with GM
crops
– The benefits should be considered
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings