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Angiosperm Reproduction and Biotechnology
Chapter 38 Angiosperm Reproduction and Biotechnology
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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 Education, Inc. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Figure 38.1 Figure 38.1 Why is this wasp trying to mate with this flower?
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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 © 2011 Pearson Education, Inc. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 © 2011 Pearson Education, Inc.
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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 For the Discovery Video Plant Pollination, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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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
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Structure of an idealized flower
Figure 38.2a Stamen Stigma Carpel Anther Style Filament Ovary Sepal Petal Figure 38.2 An overview of angiosperm reproduction. Receptacle (a) Structure of an idealized flower
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Germinated pollen grain (n) (male gametophyte)
Figure 38.2b Anther Germinated pollen grain (n) (male gametophyte) Ovary Pollen tube Ovule Embryo sac (n) (female gametophyte) FERTILIZATION Egg (n) Sperm (n) Zygote (2n) Mature sporophyte plant (2n) Key Figure 38.2 An overview of angiosperm reproduction. Seed Haploid (n) Germinating seed Diploid (2n) Seed Embryo (2n) (sporophyte) (b) Simplified angiosperm life cycle Simple fruit
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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)
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Development of a male gametophyte (in pollen grain) (a)
Figure 38.3a Development of a male gametophyte (in pollen grain) (a) Microsporangium (pollen sac) Microsporocyte MEIOSIS Microspores (4) Each of 4 microspores MITOSIS Male gametophyte (in pollen grain) Generative cell (will form 2 sperm) Figure 38.3 The development of male and female gametophytes in angiosperms. Nucleus of tube cell 20 m Key to labels Ragweed pollen grain (colorized SEM) Haploid (n) 75 m (LM) Diploid (2n)
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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 © 2011 Pearson Education, Inc.
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This cell is partitioned into a multicellular female gametophyte, the embryo sac
© 2011 Pearson Education, Inc.
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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)
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Generative cell (will form 2 sperm) Nucleus of tube cell
Figure 38.3c Generative cell (will form 2 sperm) Nucleus of tube cell (LM) 75 m Figure 38.3 The development of male and female gametophytes in angiosperms.
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Ragweed pollen grain (colorized SEM)
Figure 38.3d 20 m Ragweed pollen grain (colorized SEM) Figure 38.3 The development of male and female gametophytes in angiosperms.
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Embryo sac (LM) 100 m Figure 38.3e
Figure 38.3 The development of male and female gametophytes in angiosperms.
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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 © 2011 Pearson Education, Inc.
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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
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Hazel staminate flowers (stamens only)
Figure 38.4aa Figure 38.4 Exploring: Flower Pollination Hazel staminate flowers (stamens only)
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Hazel carpellate flower (carpels only)
Figure 38.4ab Figure 38.4 Exploring: Flower Pollination Hazel carpellate flower (carpels only)
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Common dandelion under normal light
Figure 38.4ac Figure 38.4 Exploring: Flower Pollination Common dandelion under normal light
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Common dandelion under ultraviolet light
Figure 38.4ad Figure 38.4 Exploring: Flower Pollination Common dandelion under ultraviolet light
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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
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Anther Moth Stigma Moth on yucca flower Figure 38.4ba
Figure 38.4 Exploring: Flower Pollination Stigma Moth on yucca flower
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Blowfly on carrion flower
Figure 38.4bb Fly egg Figure 38.4 Exploring: Flower Pollination Blowfly on carrion flower
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Long-nosed bat feeding on cactus flower at night
Figure 38.4bc Figure 38.4 Exploring: Flower Pollination Long-nosed bat feeding on cactus flower at night
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Hummingbird drinking nectar of columbine flower
Figure 38.4bd Figure 38.4 Exploring: Flower Pollination Hummingbird drinking nectar of columbine flower
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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.
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Figure 38.5 Figure 38.5 Coevolution of a flower and an insect pollinator.
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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) © 2011 Pearson Education, Inc.
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Animation: Plant Fertilization Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
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1 Pollen grain Stigma Pollen tube 2 sperm Style Ovary Ovule
Figure 1 Pollen grain Stigma Pollen tube 2 sperm Style Ovary Ovule Polar nuclei Figure 38.6 Growth of the pollen tube and double fertilization. Egg Micropyle
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1 2 Pollen grain Stigma Pollen tube Ovule Polar nuclei 2 sperm Style
Figure 1 2 Pollen grain Stigma Pollen tube Ovule Polar nuclei 2 sperm Style Egg Ovary Ovule Synergid Polar nuclei Figure 38.6 Growth of the pollen tube and double fertilization. 2 sperm Egg Micropyle
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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
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Seed Development, Form, and Function
After double fertilization, each ovule develops into a seed The ovary develops into a fruit enclosing the seed(s) © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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Animation: Seed Development
Right-click slide / select “Play” © 2011 Pearson Education, Inc.
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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
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Ovule Endosperm nucleus Integuments Zygote Terminal cell Basal cell
Figure 38.7a Ovule Endosperm nucleus Integuments Zygote Figure 38.7 The development of a eudicot plant embryo. Terminal cell Basal cell Zygote
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Proembryo Suspensor Cotyledons Basal cell Shoot apex Root apex
Figure 38.7b Proembryo Suspensor Cotyledons Basal cell Shoot apex Root apex Seed coat Suspensor Figure 38.7 The development of a eudicot plant embryo. Endosperm
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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(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
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(a) Common garden bean, a eudicot with thick cotyledons
Figure 38.8a Seed coat Epicotyl Hypocotyl Radicle Cotyledons Figure 38.8 Seed structure. (a) Common garden bean, a eudicot with thick cotyledons
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The seeds of some eudicots, such as castor beans, have thin cotyledons
© 2011 Pearson Education, Inc.
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(b) Castor bean, a eudicot with thin cotyledons
Figure 38.8b Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle Figure 38.8 Seed structure. (b) Castor bean, a eudicot with thin cotyledons
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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 © 2011 Pearson Education, Inc.
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Scutellum (cotyledon) Pericarp fused with seed coat
Figure 38.8c Scutellum (cotyledon) Pericarp fused with seed coat Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle Figure 38.8 Seed structure. (c) Maize, a monocot
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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
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Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon
Figure 38.9a Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon Hypocotyl Hypocotyl Figure 38.9 Two common types of seed germination. Radicle Seed coat (a) Common garden bean
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In maize and other grasses, which are monocots, the coleoptile pushes up through the soil
© 2011 Pearson Education, Inc.
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Foliage leaves Coleoptile Coleoptile Radicle (b) Maize Figure 38.9b
Figure 38.9 Two common types of seed germination. Radicle (b) Maize
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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 © 2011 Pearson Education, Inc.
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Animation: Fruit Development Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
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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 © 2011 Pearson Education, Inc.
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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
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Carpels Stamen Ovary Stamen Stigma Ovule Pea flower Raspberry flower
Figure 38.10a Carpels Stamen Ovary Stamen Stigma Ovule Pea flower Raspberry flower Carpel (fruitlet) Stigma Seed Ovary Figure Developmental origin of fruits. Stamen Pea fruit Raspberry fruit (a) Simple fruit (b) Aggregate fruit
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Pineapple inflorescence
Figure 38.10b Stigma Style Flower Petal Stamen Sepal Ovary (in receptacle) Ovule Pineapple inflorescence Apple flower Remains of stamens and styles Each segment develops from the carpel of one flower Sepals Figure Developmental origin of fruits. Seed Receptacle Pineapple fruit Apple fruit (c) Multiple fruit (d) Accessory fruit
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An accessory fruit contains other floral parts in addition to ovaries
© 2011 Pearson Education, Inc.
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Fruit dispersal mechanisms include
Water Wind Animals © 2011 Pearson Education, Inc.
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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
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Coconut seed embryo, endosperm, and endocarp inside buoyant husk
Figure 38.11aa Coconut seed embryo, endosperm, and endocarp inside buoyant husk Figure Exploring: Fruit and Seed Dispersal
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Winged seed of the tropical Asian climbing gourd Alsomitra macrocarpa
Figure 38.11ab Figure Exploring: Fruit and Seed Dispersal Winged seed of the tropical Asian climbing gourd Alsomitra macrocarpa
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Dandelion “seeds” (actually one-seeded fruits)
Figure 38.11ac Dandelion fruit Figure Exploring: Fruit and Seed Dispersal Dandelion “seeds” (actually one-seeded fruits)
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Winged fruit of a maple Figure 38.11ad
Figure Exploring: Fruit and Seed Dispersal Winged fruit of a maple
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Figure 38.11ae Figure Exploring: Fruit and Seed Dispersal Tumbleweed
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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
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Fruit of puncture vine (Tribulus terrestris)
Figure 38.11ba Figure Exploring: Fruit and Seed Dispersal Fruit of puncture vine (Tribulus terrestris)
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Squirrel hoarding seeds or fruits underground
Figure 38.11bb Figure Exploring: Fruit and Seed Dispersal Squirrel hoarding seeds or fruits underground
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Seeds dispersed in black bear feces
Figure 38.11bc Figure Exploring: Fruit and Seed Dispersal Seeds dispersed in black bear feces
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Ant carrying seed with nutritious “food body” to its nest
Figure 38.11bd Ant carrying seed with nutritious “food body” to its nest Figure Exploring: Fruit and Seed Dispersal
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