Biology in Focus - Chapter 30

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



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


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


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


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


Video: Flower Time Lapse


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


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


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



Figure 30.3

Normal Arabidopsis flower

Abnormal Arabidopsis flower

Se

StCa

Pe

Se

Pe

Se

Pe

Pe


Figure 30.3a

Normal Arabidopsis flower

Se

StCa

Pe


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


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



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


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


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


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


This cell is partitioned into a multicellular female gametophyte, the embryo sac



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


Figure 30.5-2Carpel Anther

Ovary


Femalegametophyte(embryo sac)

Egg (n)

Antipodal cells

Synergids

Polar nucleiin central cell


Sperm(n)

Pollentube

Integuments

Survivingmegaspore(n)

Megasporangium(2n)

Pollengrains

Tube cellGenerative cellOvule with

megasporangium (2n) Male

gametophyte(in pollengrain) (n)

Microspore(n)


MEIOSIS

MEIOSIS

Key


Figure 30.5-3

Discharged sperm nuclei (n)

Carpel Anther

Ovary



Eggnucleus (n)

Egg (n)

Antipodal cells

Synergids



Sperm(n)

Pollentube

Integuments


Megasporangium(2n)

Style

Pollengrains

Sperm

StigmaPollen tube

Tube nucleus




Microspore(n)


MEIOSIS

FERTILIZATION

MEIOSIS

Key


Figure 30.5-4


Carpel Anther

Ovary

Seed

Germinatingseed

Seed coat (2n)Endosperm (3n)

Embryo (2n)



Nucleus ofdevelopingendosperm(3n)

Zygote (2n)Eggnucleus (n)

Egg (n)

Antipodal cells

Synergids



Key

MEIOSIS

FERTILIZATION

Sperm(n)

Pollentube

Integuments


Megasporangium(2n)

Style

Pollengrains

Sperm

StigmaPollen tube

Tube nucleus




MEIOSIS Microspore(n)



Figure 30.5a

Anther


Key

Tube cell

Generative cell

Male gametophyte

(in pollengrain) (n)

MEIOSIS Microspore(n)



Figure 30.5b


Key

OvaryMEIOSIS

Integuments


Megasporangium(2n)

Ovule withmegasporangium (2n)


Figure 30.5c


Key

Egg (n)

Antipodal cells

Synergids


Sperm(n)

Pollentube

Integuments


Megasporangium(2n)

Style

Pollengrains

Sperm

StigmaPollen tube

Tube nucleus



Figure 30.5d


Key


SeedSeed coat (2n)Endosperm (3n)

Embryo (2n)


Nucleus ofdevelopingendosperm(3n)

Zygote (2n)Eggnucleus (n)

Egg (n)

Antipodal cells

Synergids


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


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


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


Video: Bat Pollinating

Video: Bee Pollinating


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)


Figure 30.6aa

Hazel carpellateflower (carpels only)


Figure 30.6ab

Hazel staminateflower (stamens only)


Figure 30.6ac

Common dandelionunder normal light


Figure 30.6ad

Common dandelionunder ultravioletlight


Figure 30.6b

Pollination by bats or birds

Long-nosed batfeeding on cactusflower at night

Hummingbirddrinking nectar ofcolumbine flower


Figure 30.6ba

Long-nosed bat feeding on cactus flower at night


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


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”


Pollination by bats occurs in plants that produce light-colored, aromatic flowers


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


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)


Animation: Plant Fertilization


Figure 30.7-1

Polarnuclei

Pollengrain

Ovule

Two sperm

Egg

StigmaPollen tube

StyleOvary

Micropyle

Tubenucleus


Figure 30.7-2

Polarnuclei

Polarnuclei

Pollengrain

Ovule

Egg

Synergid

Two spermOvule

Two sperm

Egg

StigmaPollen tube

StyleOvary

Micropyle

Tubenucleus


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)


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


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


Animation: Seed Development


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


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



Figure 30.9Seed coat

Endosperm

RadicleHypocotyl

Epicotyl

Cotyledons

Seed coat

RadicleHypocotylEpicotyl

Cotyledons

Pericarp fusedwith seed coat


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


Figure 30.9a

Seed coat

RadicleHypocotyl

Epicotyl

Cotyledons

(a) Common garden bean, a eudicot with thick cotyledons


Figure 30.9b

EndospermSeed coat


Cotyledons

(b) Castor bean, a eudicot with thin cotyledons


Figure 30.9c

Pericarp fusedwith seed coat


Scutellum(cotyledon)

EndospermColeoptile

Coleorhiza

(c) Maize, a monocot

The seeds of some eudicots, such as castor beans, have 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


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


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


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


Video: Plant Time Lapse


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


Figure 30.10a

Radicle

Hypocotyl Epicotyl

Cotyledon

Foliage leaves

Seed coat

Cotyledon

HypocotylCotyledon

Hypocotyl

(a) Common garden bean


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


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


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


Animation: Fruit Development


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


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)


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


Fruit dispersal mechanisms include Water Wind Animals



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



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



Figure 30.12ab

Giant seed of the tropical Asian climbing gourdAlsomitra macrocarpa


Figure 30.12ac

Dandelion “seeds” (actually one-seeded fruits)Dandelion fruit


Figure 30.12ad

Winged fruit of a maple


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



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”


Figure 30.12ba

Fruit of puncture vine(Tribulus terrestris)


Figure 30.12bb

Squirrel hoarding seeds or fruitsunderground


Figure 30.12bc

Seeds dispersed in black bear feces


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


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



Figure 30.13

Asexual reproduction in aspen trees

Apomixis is the asexual production of seeds from a diploid cell


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


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


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



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


Figure 30.14aa

Staminate flowers


Figure 30.14ab

Carpellate flowers


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


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


Totipotency, Vegetative Reproduction, and Tissue Culture

Totipotent cells are able to asexually generate a clone of the original organism through cell division


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


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


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



Figure 30.15

Developing rootLaboratory cloning of a garlic plant

(c)(a) (b)

Plant tissue culture facilitates genetic engineering and the elimination of viruses


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



Figure 30.16


Figure 30.16a


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


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


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


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


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



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


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”


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


GMO opponents advocate for clear labeling of all GMO foods


Possible Effects on Nontarget Organisms

Many ecologists are concerned that the growing of GM crops might have unforeseen effects on nontarget organisms


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


Efforts are under way to prevent this by introducing Male sterility Apomixis Transgenes into chloroplast DNA (not transferred

by pollen) Strict self-pollination



Figure 30.UN01a


Figure 30.UN01b


Figure 30.UN02

Endospermnucleus (3n)(two polar nucleiplus sperm)

Zygote (2n)(egg plus sperm)

Biology in Focus - Chapter 30

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Transcript of Biology in Focus - Chapter 30