biology in focus - chapter 30
TRANSCRIPT
CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
30Reproduction and Domestication of Flowering Plants
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
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© 2014 Pearson Education, Inc.
Figure 30.1
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
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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
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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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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
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Video: Flower Time Lapse
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Figure 30.2
Stamen
Petal
Filament
Anther CarpelStigma
Ovary
Style
Ovule
Sepal
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
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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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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
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© 2014 Pearson Education, Inc.
Figure 30.3
Normal Arabidopsis flower
Abnormal Arabidopsis flower
Se
StCa
Pe
Se
Pe
Se
Pe
Pe
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Figure 30.3a
Normal Arabidopsis flower
Se
StCa
Pe
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Figure 30.3b
Abnormal Arabidopsis flower
Se
Pe
Se
Pe
Pe
The ABC hypothesis explains the formation of the four types of floral organs through the regulatory activity of three classes of organ identity genes
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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
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© 2014 Pearson Education, Inc.
Figure 30.4
(b) Side view of flowers with organ identity mutations
(a) A schematic diagram of the ABC hypothesis
Wild type Mutant lacking A
StamenCarpel
Petal
SepalMutant lacking B Mutant lacking C
StamensCarpels
PetalsSepals
Stamen
Carpel
Petal
Sepal
AB
C
C geneactivity B C
geneactivity
A B gene
activity
A geneactivity
Active genes:Whorls:
AB
CBB B
A A AC C C AB BB BAA A
A ACB
CBB B
C C CC C C A CA A AC C CA A
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Figure 30.4a
(a) A schematic diagram of the ABC hypothesis
StamensCarpels
PetalsSepals
Stamen
Carpel
Petal
Sepal
AB
C
C geneactivity B C
geneactivity
A B gene
activity
A geneactivity
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Figure 30.4ba
(b) Side view of flowers with organ identity mutationsWild type Mutant lacking A
StamenCarpel
Petal
Sepal
Active genes:
Whorls:
AB
CB B B
A A ACC C CBC
B B BCC CCC C
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Figure 30.4bb
Mutant lacking B Mutant lacking C
AB BB BAA A
A AA CA A AC C CA A
(b) Side view of flowers with organ identity mutations
Active genes:
Whorls:
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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© 2014 Pearson Education, Inc.
Figure 30.5-1Carpel Anther
Mature flower onsporophyte plant(2n)
Haploid (n)Diploid (2n)
Pollengrains
Tube cellGenerative cell
Male gametophyte
(in pollengrain) (n)
Microspore(n)
Microsporocytes (2n)Microsporangium
MEIOSIS
Key
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Figure 30.5-2Carpel Anther
Ovary
Mature flower onsporophyte plant(2n)
Femalegametophyte(embryo sac)
Egg (n)
Antipodal cells
Synergids
Polar nucleiin central cell
Haploid (n)Diploid (2n)
Sperm(n)
Pollentube
Integuments
Survivingmegaspore(n)
Megasporangium(2n)
Pollengrains
Tube cellGenerative cellOvule with
megasporangium (2n) Male
gametophyte(in pollengrain) (n)
Microspore(n)
Microsporocytes (2n)Microsporangium
MEIOSIS
MEIOSIS
Key
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Figure 30.5-3
Discharged sperm nuclei (n)
Carpel Anther
Ovary
Mature flower onsporophyte plant(2n)
Femalegametophyte(embryo sac)
Eggnucleus (n)
Egg (n)
Antipodal cells
Synergids
Polar nucleiin central cell
Haploid (n)Diploid (2n)
Sperm(n)
Pollentube
Integuments
Survivingmegaspore(n)
Megasporangium(2n)
Style
Pollengrains
Sperm
StigmaPollen tube
Tube nucleus
Tube cellGenerative cellOvule with
megasporangium (2n) Male
gametophyte(in pollengrain) (n)
Microspore(n)
Microsporocytes (2n)Microsporangium
MEIOSIS
FERTILIZATION
MEIOSIS
Key
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Figure 30.5-4
Discharged sperm nuclei (n)
Carpel Anther
Ovary
Seed
Germinatingseed
Seed coat (2n)Endosperm (3n)
Embryo (2n)
Mature flower onsporophyte plant(2n)
Femalegametophyte(embryo sac)
Nucleus ofdevelopingendosperm(3n)
Zygote (2n)Eggnucleus (n)
Egg (n)
Antipodal cells
Synergids
Polar nucleiin central cell
Haploid (n)Diploid (2n)
Key
MEIOSIS
FERTILIZATION
Sperm(n)
Pollentube
Integuments
Survivingmegaspore(n)
Megasporangium(2n)
Style
Pollengrains
Sperm
StigmaPollen tube
Tube nucleus
Tube cellGenerative cellOvule with
megasporangium (2n) Male
gametophyte(in pollengrain) (n)
MEIOSIS Microspore(n)
Microsporocytes (2n)Microsporangium
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Figure 30.5a
Anther
Haploid (n)Diploid (2n)
Key
Tube cell
Generative cell
Male gametophyte
(in pollengrain) (n)
MEIOSIS Microspore(n)
Microsporocytes (2n)Microsporangium
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Figure 30.5b
Haploid (n)Diploid (2n)
Key
OvaryMEIOSIS
Integuments
Survivingmegaspore(n)
Megasporangium(2n)
Ovule withmegasporangium (2n)
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Figure 30.5c
Haploid (n)Diploid (2n)
Key
Egg (n)
Antipodal cells
Synergids
Polar nucleiin central cell
Sperm(n)
Pollentube
Integuments
Survivingmegaspore(n)
Megasporangium(2n)
Style
Pollengrains
Sperm
StigmaPollen tube
Tube nucleus
Femalegametophyte(embryo sac)
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Figure 30.5d
Haploid (n)Diploid (2n)
Key
Discharged sperm nuclei (n)
SeedSeed coat (2n)Endosperm (3n)
Embryo (2n)
Femalegametophyte(embryo sac)
Nucleus ofdevelopingendosperm(3n)
Zygote (2n)Eggnucleus (n)
Egg (n)
Antipodal cells
Synergids
Polar nucleiin central cell
FERTILIZATION
Sperm(n)
Pollentube
Style
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
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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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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
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Video: Bat Pollinating
Video: Bee Pollinating
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Figure 30.6a
Abiotic pollination by wind Pollination by insects
Common dandelionunder ultravioletlight
Common dandelionunder normal light
Hazel staminateflower (stamens only)
Hazel carpellateflower (carpels only)
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Figure 30.6aa
Hazel carpellateflower (carpels only)
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Figure 30.6ab
Hazel staminateflower (stamens only)
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Figure 30.6ac
Common dandelionunder normal light
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Figure 30.6ad
Common dandelionunder ultravioletlight
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Figure 30.6b
Pollination by bats or birds
Long-nosed batfeeding on cactusflower at night
Hummingbirddrinking nectar ofcolumbine flower
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Figure 30.6ba
Long-nosed bat feeding on cactus flower at night
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Figure 30.6bb
Hummingbird drinking nectar of columbine flower
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
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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”
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Pollination by bats occurs in plants that produce light-colored, aromatic flowers
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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
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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)
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Animation: Plant Fertilization
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Figure 30.7-1
Polarnuclei
Pollengrain
Ovule
Two sperm
Egg
StigmaPollen tube
StyleOvary
Micropyle
Tubenucleus
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Figure 30.7-2
Polarnuclei
Polarnuclei
Pollengrain
Ovule
Egg
Synergid
Two spermOvule
Two sperm
Egg
StigmaPollen tube
StyleOvary
Micropyle
Tubenucleus
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Figure 30.7-3
Zygote (2n)(egg plussperm)
Endospermnucleus (3n)(two polar nucleiplus sperm)
Polarnuclei
Polarnuclei
Pollengrain
Ovule
Egg
Synergid
Two spermOvule
Two sperm
Egg
StigmaPollen tube
StyleOvary
Micropyle
Tubenucleus
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
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Figure 30.8
Ovule
Integuments
Zygote
Terminal cell
Suspensor
Seed coat
Proembryo
Endospermnucleus
Zygote
Basal cell
Basal cell
EndospermSuspensor
Root apexShoot apexCotyledons
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
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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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© 2014 Pearson Education, Inc.
Figure 30.9Seed coat
Endosperm
RadicleHypocotyl
Epicotyl
Cotyledons
Seed coat
RadicleHypocotylEpicotyl
Cotyledons
Pericarp fusedwith seed coat
RadicleHypocotylEpicotyl
Scutellum(cotyledon)
EndospermColeoptile
Coleorhiza
(c) Maize, a monocot
(a) Common garden bean, a eudicot with thick cotyledons
(b) Castor bean, a eudicot with thin cotyledons
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Figure 30.9a
Seed coat
RadicleHypocotyl
Epicotyl
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
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Figure 30.9b
EndospermSeed coat
RadicleHypocotylEpicotyl
Cotyledons
(b) Castor bean, a eudicot with thin cotyledons
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Figure 30.9c
Pericarp fusedwith seed coat
RadicleHypocotylEpicotyl
Scutellum(cotyledon)
EndospermColeoptile
Coleorhiza
(c) Maize, a monocot
The seeds of some eudicots, such as castor beans, have 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
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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
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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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Video: Plant Time Lapse
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Figure 30.10
Radicle
Hypocotyl Epicotyl
Cotyledon
Foliage leaves
Coleoptile
Seed coat
(b) Maize
Cotyledon
HypocotylCotyledon
Hypocotyl
Foliage leaves
Coleoptile
Radicle
(a) Common garden bean
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Figure 30.10a
Radicle
Hypocotyl Epicotyl
Cotyledon
Foliage leaves
Seed coat
Cotyledon
HypocotylCotyledon
Hypocotyl
(a) Common garden bean
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Figure 30.10b
Coleoptile
(b) Maize
Foliage leaves
Coleoptile
Radicle
In some monocots, such as maize and other grasses, the coleoptile pushes up through the soil
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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
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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
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Animation: Fruit Development
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Figure 30.11
(b) Aggregate fruit
Stamen
(a) Simple fruit (c) Multiple fruit (d) Accessory fruit
Stamen
Stamen
Ovary
Stigma
Stigma
Stigma
Ovary
Stamen
Ovary (inreceptacle)
OvuleOvule
Seed
Pea flower
Pea fruit
Raspberry flower
Carpels
Pineapple inflorescence
Raspberry fruit
Carpel(fruitlet)
Pineapple fruit Apple fruit
Each segmentdevelopsfrom thecarpelof oneflower
Flower StylePetal
Sepal
Apple flower
Sepals
Seed
Remains ofstamens and styles
Receptacle
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Figure 30.11a
(b) Aggregate fruit
Stamen
(a) Simple fruit
StamenOvary
Stigma
Stigma
Ovary
Stamen
Ovule
Seed
Pea flower
Pea fruit
Raspberry flower
Carpels
Raspberry fruit
Carpel(fruitlet)
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Figure 30.11b
(c) Multiple fruit (d) Accessory fruit
Stamen
Stigma
Ovary (inreceptacle)Ovule
Pineapple inflorescence
Pineapple fruit Apple fruit
Each segmentdevelopsfrom thecarpelof oneflower
Flower StylePetal
Sepal
Apple flower
Sepals
Seed
Remains ofstamens and styles
Receptacle
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 30.12a Dispersal by water
Coconut seedembryo, endosperm,and endocarp insidebuoyant husk
Giant seed ofthe tropical Asianclimbing gourdAlsomitra macrocarpa
Dispersal by wind
Dandelion “seeds” (actually one-seeded fruits)Dandelion fruit
TumbleweedWinged fruit of a maple
Dispersal by water occurs in buoyant seeds and fruits like coconut, which can survive for long periods at sea
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Figure 30.12aa
Coconut seed embryo, endosperm, and endocarp inside buoyant husk
Dispersal by wind occurs in seeds and fruits that have adaptations such as parachute or winglike structures
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Figure 30.12ab
Giant seed of the tropical Asian climbing gourdAlsomitra macrocarpa
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Figure 30.12ac
Dandelion “seeds” (actually one-seeded fruits)Dandelion fruit
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Figure 30.12ad
Winged fruit of a maple
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Figure 30.12ae
Tumbleweed
Dispersal by animals occurs in seeds and fruits that are edible or adapted to attach to an animal’s skin or fur
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Figure 30.12bDispersal by animals
Fruit of puncture vine(Tribulus terrestris)
Seeds dispersed in black bear feces
Squirrel hoarding seeds or fruitsunderground
Ant carrying seed withattached “food body”
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Figure 30.12ba
Fruit of puncture vine(Tribulus terrestris)
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Figure 30.12bb
Squirrel hoarding seeds or fruitsunderground
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Figure 30.12bc
Seeds dispersed in black bear feces
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Figure 30.12bd
Ant carrying seed withattached “food body”
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
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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 30.13
Asexual reproduction in aspen trees
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 30.14
(a) Staminate flowers (left) and carpellate flowers (right)of a dioecious species
(b) Thrum and pin flowersThrum flower Pin flower
StamensStamensStyles
Styles
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Figure 30.14aa
Staminate flowers
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Figure 30.14ab
Carpellate flowers
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Figure 30.14b
Thrum flower Pin flower
StamensStamensStyles
Styles
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
Developing rootLaboratory cloning of a garlic plant
(c)(a) (b)
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
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
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
Reducing Fossil Fuel Dependency
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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 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 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
Endospermnucleus (3n)(two polar nucleiplus sperm)
Zygote (2n)(egg plus sperm)