1. Angiosperm Reproduction and Biotechnology
Chapter 38
Angiosperm Reproduction and Biotechnology

2. 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
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. Figure 38.1
Figure 38.1 Why is this wasp trying to mate with this flower?

4. Mutualistic symbioses are common between plants and other species
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
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. 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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6. 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
For the Discovery Video Plant Pollination, go to Animation and Video Files.
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7. Germinated pollen grain (n) (male gametophyte) Stamen Stigma Carpel
Figure 38.2
Anther
Germinated pollen grain (n) (male gametophyte)
Stamen
Stigma
Carpel
Anther
Style
Ovary
Filament
Ovary
Pollen tube
Ovule
Embryo sac (n) (female gametophyte)
Sepal
FERTILIZATION
Petal
Egg (n)
Sperm (n)
Receptacle
Mature sporophyte plant (2n)
Zygote (2n)
(a)
Structure of an idealized flower
Key
Haploid (n)
Seed
Germinating seed
Figure 38.2 An overview of angiosperm reproduction.
Diploid (2n)
Seed
Embryo (2n) (sporophyte)
Simplified angiosperm life cycle
(b)
Simple fruit

8. 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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9. A carpel has a long style with a stigma on which pollen may land
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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10. 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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11. 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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12. 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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13. Female gametophyte (embryo sac)
Figure 38.3
Development of a male gametophyte (in pollen grain)
(a)
(b)
Development of a female gametophyte (embryo sac)
Microsporangium (pollen sac)
Megasporangium
Microsporocyte
Ovule
Megasporocyte
MEIOSIS
Integuments
Microspores (4)
Micropyle
Surviving megaspore
Each of 4 microspores
MITOSIS
Ovule
Antipodal cells (3)
Male gametophyte (in pollen grain)
Generative cell (will form 2 sperm)
Figure 38.3 The development of male and female gametophytes in angiosperms.
Polar nuclei (2)
Female gametophyte (embryo sac)
Egg (1)
Nucleus of tube cell
Integuments
Synergids (2)
20 m
Ragweed pollen grain (colorized SEM)
Key to labels
Embryo sac
Haploid (n)
75 m
100 m
(LM)
Diploid (2n)
(LM)

14. 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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15. This cell is partitioned into a multicellular female gametophyte, the embryo sac
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16. Female gametophyte (embryo sac)
Figure 38.3b
(b)
Development of a female gametophyte (embryo sac)
Megasporangium
Ovule
Megasporocyte
MEIOSIS
Integuments
Micropyle
Surviving megaspore
MITOSIS
Ovule
Antipodal cells (3)
Figure 38.3 The development of male and female gametophytes in angiosperms.
Polar nuclei (2)
Female gametophyte (embryo sac)
Egg (1)
Integuments
Synergids (2)
Key to labels
Embryo sac
Haploid (n)
100 m
Diploid (2n)
(LM)

17. 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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18. Abiotic Pollination by Wind Pollination by Bees
Figure 38.4a
Abiotic Pollination by Wind
Pollination by Bees
Common dandelion under normal light
Hazel staminate flowers (stamens only)
Figure 38.4 Exploring: Flower Pollination
Hazel carpellate flower (carpels only)
Common dandelion under ultraviolet light

19. Pollination by Moths and Butterflies Pollination by Flies
Figure 38.4b
Pollination by Moths and Butterflies
Pollination by Flies
Pollination by Bats
Anther
Moth
Fly egg
Stigma
Blowfly on carrion flower
Long-nosed bat feeding on cactus flower at night
Moth on yucca flower
Pollination by Birds
Figure 38.4 Exploring: Flower Pollination
Hummingbird drinking nectar of columbine flower

20. 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
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21. Figure 38.5
Figure 38.5 Coevolution of a flower and an insect pollinator.

22. 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)
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23. Endosperm nucleus (3n) (2 polar nuclei plus sperm)
Figure 1 2 3
Pollen grain
Stigma
Endosperm nucleus (3n) (2 polar nuclei plus sperm)
Pollen tube
Ovule
Polar nuclei
2 sperm
Style
Egg
Ovary
Zygote (2n)
Ovule
Synergid
Polar nuclei
Figure 38.6 Growth of the pollen tube and double fertilization.
2 sperm
Egg
Micropyle

24. 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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25. 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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26. 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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27. Ovule Proembryo Endosperm nucleus Suspensor Integuments Cotyledons
Figure 38.7
Ovule
Proembryo
Endosperm nucleus
Suspensor
Integuments
Cotyledons
Zygote
Basal cell
Shoot apex
Root apex
Seed coat
Suspensor
Terminal cell
Figure 38.7 The development of a eudicot plant embryo.
Basal cell
Endosperm
Zygote

28. 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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29. 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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30. (a) Common garden bean, a eudicot with thick cotyledons
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
Figure 38.8 Seed structure.
Scutellum (cotyledon)
Pericarp fused with seed coat
Endosperm
Coleoptile
Epicotyl
Hypocotyl
Coleorhiza
Radicle
(c) Maize, a monocot

31. The seeds of some eudicots, such as castor beans, have thin cotyledons
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32. 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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33. 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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34. 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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35. 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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36. Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon
Figure 38.9
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
Foliage leaves
Figure 38.9 Two common types of seed germination.
Coleoptile
Coleoptile
Radicle
(b) Maize

37. In maize and other grasses, which are monocots, the coleoptile pushes up through the soil
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38. 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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39. 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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40. Pineapple inflorescence
Figure 38.10
Stigma
Style
Carpels
Stamen
Flower
Petal
Ovary
Stamen
Stamen
Sepal
Stigma
Ovary (in receptacle)
Ovule
Ovule
Pea flower
Raspberry flower
Pineapple inflorescence
Apple flower
Each segment develops from the carpel of one flower
Remains of stamens and styles
Carpel (fruitlet)
Stigma
Sepals
Seed
Ovary
Figure Developmental origin of fruits.
Stamen
Seed
Receptacle
Pea fruit
Raspberry fruit
Pineapple fruit
Apple fruit
(a) Simple fruit
(b) Aggregate fruit
(c) Multiple fruit
(d) Accessory fruit

41. An accessory fruit contains other floral parts in addition to ovaries
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42. Fruit dispersal mechanisms include
Water
Wind
Animals
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43. Dispersal by Wind Dispersal by Water Dandelion fruit Tumbleweed
Figure 38.11a
Dispersal by Wind
Dandelion fruit
Tumbleweed
Dandelion “seeds” (actually one-seeded fruits)
Winged seed of the tropical Asian climbing gourd Alsomitra macrocarpa
Winged fruit of a maple
Dispersal by Water
Figure Exploring: Fruit and Seed Dispersal
Coconut seed embryo, endosperm, and endocarp inside buoyant husk

44. Dispersal by Animals Fruit of puncture vine (Tribulus terrestris)
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
Figure Exploring: Fruit and Seed Dispersal
Seeds dispersed in black bear feces