Transcript document

Chapter 33
Control Systems in Plants
PowerPoint Lectures for
Biology: Concepts & Connections, Sixth Edition
Campbell, Reece, Taylor, Simon, and Dickey
Lecture by L. Brooke Stabler
Copyright © 2009 Pearson Education, Inc.
Introduction: What Are the Health Benefits
of Soy?
 Soy protein is one of the few plant proteins that
provide all of the essential amino acids
 Benefits of soy include
– It reduces the risk of heart disease
– It is rich in antioxidants and fiber
– It is low in fat and helps increase “good” cholesterol
(HDL) while reducing “bad” cholesterol (LDL)
– Soy contains phytoestrogens, hormones that can reduce
the symptoms of menopause in women
– More research into the use of phytohormones to treat
the symptoms of menopause is needed
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PLANT HORMONES
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 Phototropism is a phenomenon by which plants
grow toward a light source
 Phototropism occurs when the cells on the dark side
of a plant stem elongate faster than those on the
light side
 Charles Darwin and his son Francis conducted
experiments that showed that the shoot tips of
plants controlled their ability to grow toward light
 Peter Boysen-Jensen later conducted experiments
that showed that chemical signals produced in shoot
tips were responsible for phototropism
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
Video: Phototropism
Copyright © 2009 Pearson Education, Inc.
Shaded
side of
shoot
Light
Illuminated
side of
shoot
33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 The Darwins’ experiment
– When plant tips were removed, plants did not grow
toward light
– When plant tips were covered with an opaque cap, they
did not grow toward light
– When plant tips were covered with a clear tip, they did
grow toward light
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 Jensen’s experiment
– When a gelatin block that allowed chemical diffusion
was placed below the shoot tip, plants grew toward light
– When a mica block that prevented chemical diffusion
was placed below the shoot tip, plants did not grow
toward light
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Light
Control
1
2
Tip
removed
Tip covered
by opaque
cap
3
4
Tip covered Base
by transcovered
parent cap by opaque
shield
Darwin and Darwin (1880)
5
6
Tip separated by
gelatin
block
Tip separated
by mica
Boysen-Jensen (1913)
33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 A graduate student named Frits Went isolated the
chemical hormone responsible for phototropism
– Plant tips were placed on an agar block to allow the
chemical signal molecules to diffuse from the plant tip
to the agar
– When agar blocks containing chemical signals were
centered on the ends of “decapitated” plants, they grew
straight
– When agar blocks were offset to one side of the
“decapitated” plants, they bent away from the side with
the agar block
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
– Went concluded that a chemical produced in the shoot
tip was transferred down through the plant, and high
concentration of that chemical increased cell elongation
on the dark side of the plant
 The chemical signal responsible for phototropism is
a hormone that Went called auxin
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Shoot tip placed on agar
block. Chemical diffuses
from shoot tip into agar.
Agar
1
Control
No light
Block with
chemical
stimulates
growth.
Shoot tip placed on agar
block. Chemical diffuses
from shoot tip into agar.
Agar
1
Control
No light
Block with
chemical
stimulates
growth.
2
Offset blocks with
chemical stimulate
curved growth.
Shoot tip placed on agar
block. Chemical diffuses
from shoot tip into agar.
Agar
1
Control
No light
Block with
chemical
stimulates
growth.
3
2
Offset blocks with
chemical stimulate
curved growth.
Other controls:
Blocks with no
chemical have
no effect.
33.2 Five major types of hormones regulate plant
growth and development
 A hormone is a chemical signal that is produced in
one part of the body and transported to another,
where it triggers responses in target cells
 Binding of hormones to specific cellular receptors
triggers a signal transduction pathway
 Tiny amounts of hormone can have a big effect
Copyright © 2009 Pearson Education, Inc.
33.2 Five major types of hormones regulate plant
growth and development
 All aspects of plant growth and development are
affected by hormones
 There are five classes of plant hormones and each
class can have multiple effects on plant growth and
development
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
33.3 Auxin stimulates the elongation of cells in
young shoots
 Indoleacetic acid (IAA) is a naturally occurring
auxin that promotes seedling elongation
 Auxin is produced in shoot apical meristems and
transported downward through a plant
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33.3 Auxin stimulates the elongation of cells in
young shoots
 Concentration of auxin and site of activity are
important to auxin’s effects
– In moderate concentrations, auxin promotes cell
elongation in stems
– In high concentrations, auxin reduces cell elongation in
stems
– Auxins affects cell elongation in roots at lower
concentrations
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Elongation
Inhibition Promotion

Stems
0
Roots

0.9 g/L
1
104
106
102
108
Increasing auxin concentration (g/L)
102
33.3 Auxin stimulates the elongation of cells in
young shoots
 A hypothesis for the action of auxin
– Auxins stimulate plant cells to take up H+ ions, lowering
pH
– Acidity causes separation of cross linkages in cellulose
– As the cell takes up water, the cell elongates because of
weakening of the cellulose cell wall
– Auxins stimulate the plant to produce additional cell wall
material
– As pH decreases, the larger cell wall restabilizes
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1
Plasma
membrane
Cell
wall
Vacuole
H+
Proton
pump
(protein)
Cell wall
Cellulose
molecule
H+
2
H2O
3
Cell
elongation
Enzyme
Cytoplasm
Cellulose loosens;
cell can elongate Cellulose
molecule
Cross-linking
molecule
33.4 Cytokinins stimulate cell division
 Cytokinins promote cytokinesis, or cell division
 Cytokinins
– Are produced in actively growing organs such as roots,
embryos, and fruits
– Produced in roots move upward through the plant
– Retard aging in leaves and flowers
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33.4 Cytokinins stimulate cell division
 Cytokinins and auxins interact to control apical
dominance
– Auxins inhibit axillary bud growth, reducing lateral
branching
– Cytokinins counter the action of auxin by promoting
axillary bud growth
– The ratio of auxins to cytokinins controls axillary bud
growth
Copyright © 2009 Pearson Education, Inc.
Terminal bud
No terminal bud
33.5 Gibberellins affect stem elongation and have
numerous other effects
 Gibberellins are plant hormones that promote
stem elongation by increasing cell division and
elongation
 Gibberellins were named for a genus of fungi that
produce the same chemical and cause “foolish
seedling” disease
 There are more than 100 distinct gibberellins
produced primarily in roots and young leaves
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33.5 Gibberellins affect stem elongation and have
numerous other effects
 Gibberellins also promote fruit development and
seed germination
 Gibberellins act antagonistically against another
plant hormone called abscisic acid
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33.6 Abscisic acid inhibits many plant processes
 Abscisic acid (ABA) is a plant hormone that
inhibits growth
 High concentrations of ABA promote seed dormancy
– ABA must be removed for germination to occur
– The ratio of ABA to gibberellins controls germination
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33.6 Abscisic acid inhibits many plant processes
 ABA also influences plant water relations
– Accumulation of ABA in wilted leaves promotes stomatal
closure
– ABA produced in roots can signal low soil moisture
conditions and triggers plants to conserve water by
closing stomata
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33.7 Ethylene triggers fruit ripening and other
aging processes
 Ethylene is a gaseous by-product of natural gas
combustion and a naturally occurring plant hormone
 Plants produce ethylene in response to stresses such
as mechanical pressure, injury, infection, and
drought or flood
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33.7 Ethylene triggers fruit ripening and other
aging processes
 Ethylene promotes aging processes such as fruit
ripening and natural cell death
– It is used commercially to ripen fruits
– Growers inhibit ethylene production using CO2 to inhibit
ripening in stored fruit
 Ethylene promotes leaf abscission in fall by breaking
down cells at the base of the petiole
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1
3
2
Leaf
stalk
Stem
(twig)
Protective Abscission
layer
layer
Stem
Leaf stalk
33.8 CONNECTION: Plant hormones have many
agricultural uses
 Agricultural uses of plant hormones include
– Control of fruit production, ripening, and dropping
– Production of seedless fruits
– Use as weed killers
 Agricultural uses of plant hormones help keep food
prices down and benefit the environment
 Some consumers are concerned that synthetic plant
hormones may have dangerous side effects for
humans
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GROWTH RESPONSES AND
BIOLOGICAL RHYTHMS IN
PLANTS
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33.9 Tropisms orient plant growth toward or away
from environmental stimuli
 Tropisms are responses that cause plants to grow
in response to environmental stimuli
– Positive tropisms cause plants to grow toward a
stimulus
– Negative tropisms cause plants to grow away from a
stimulus
 Plants respond to various environmental stimuli
– Phototropism—response to light
– Gravitropism—response to gravity
– Thigmotropism—response to touch
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33.9 Tropisms orient plant growth toward or away
from environmental stimuli
Video: Gravitropism
Video: Mimosa Leaf
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33.10 Plants have internal clocks
 Circadian rhythms are innate biological cycles of
approximately 24 hours
 Both plants and animals have circadian rhythms
 Circadian rhythms are influenced by environmental
cues such as light, but they are controlled by
biological clocks
 The biological clocks of plants are likely the result of
rhythmic production of proteins that influence gene
expression
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Noon
Midnight
33.11 Plants mark the seasons by measuring
photoperiod
 Flowering, seed germination, and dormancy are all
seasonal phenomena in plants
 Plants detect season by measuring photoperiod,
the relative lengths of day and night
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33.11 Plants mark the seasons by measuring
photoperiod
 Plant flowering signals are determined by night
length
– Short-day plants flower when the dark period is
greater than some critical length
– Long-day plants flower when the dark period is
shorter than some critical length
– Experiments that altered light and dark periods were
used to determine that it is night length and not day
length that cues plants to flower
Copyright © 2009 Pearson Education, Inc.
2
4
3
5
6
Darkness
Flash
of light
Light
0
Short-day (long-night) plants
Long-day (short-night) plants
Critical night length
1
Time (hr)
24
2
3
24
Time (hr)
Darkness
Flash
of light
Light
0
Short-day (long-night) plants
Critical night length
1
5
6
24
Time (hr)
Darkness
Flash
of light
Light
0
Long-day (short-night) plants
Critical night length
4
33.12 Phytochrome is a light detector that may
help set the biological clock
 Phytochromes are proteins with a light-absorbing
component
 Phytochromes detect light in the red and far-red
wavelengths
– One form of phytochrome absorbs red light (Pr)
– One form detects far-red light (Pfr)
– When Pr absorbs light, it is converted into Pfr
– When Pfr absorbs light, it is converted into Pr
Copyright © 2009 Pearson Education, Inc.
33.12 Phytochrome is a light detector that may
help set the biological clock
– Pr is naturally produced during dark hours, while Pfr is
broken down
– The relative amounts of Pr and Pfr present in a plant
change as day length changes
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Rapid conversion
in daylight
Red
light
Pr
Pfr
Slow conversion
in darkness
Far-red
light
24
20
R
FR
R
FR
R
R
FR
R
FR
R
Time (hr)
16
12
8
4
1
2
3
0
Long-day (short-night) plant
4
Critical night length
Short-day (long-night) plant
33.13 TALKING ABOUT SCIENCE: Joanne
Chory studies the effects of light and
hormones in the model plant Arabidopsis
 Scientists often use small and easily manipulated species as
models to learn about biological processes
 Arabidopsis is a plant in the mustard family that has been
used extensively to study plant genetics and physiology
 Dr. Joanne Chory has used Arabidopsis to study genes that
control hormones and signal transduction pathways; her
work has many applications in science and agriculture
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PLANT DEFENSES
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33.14 EVOLUTION CONNECTION: Defenses
against herbivores and infectious microbes
have evolved in plants
 Herbivores are organisms that feed on plants; many
plant adaptations have evolved to defend against
herbivores
– Production of distasteful or poisonous compounds
– Symbioses with organisms that defend plants
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33.14 EVOLUTION CONNECTION: Defenses
against herbivores and infectious microbes
have evolved in plants
 Plants have also evolved defenses against
pathogens
– The epidermis is the first line of defense against
infection
– Chemical defenses offer a way to fight pathogens that
enter the plant
Copyright © 2009 Pearson Education, Inc.
1
Damage to plant
and chemical in
caterpillar saliva
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
Plant cell
2
Signal
transduction
pathway
3
1
Damage to plant
and chemical in
caterpillar saliva
Synthesis
and release
of chemical
attractants
Plant cell
2
Signal
transduction
pathway
4
Recruitment of wasp
3
1
Damage to plant
and chemical in
caterpillar saliva
Synthesis
and release
of chemical
attractants
Plant cell
2
Signal
transduction
pathway
5
Wasp
lays
eggs
4
Recruitment of wasp
3
1
Damage to plant
and chemical in
caterpillar saliva
Synthesis
and release
of chemical
attractants
Plant cell
2
Signal
transduction
pathway
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Avirulent
pathogen
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Avirulent
pathogen
2
Signal
transduction
pathway
3
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Avirulent
pathogen
Enhanced
local
response
2
Signal
transduction
pathway
R-Avr recognition leading to a
strong local response
3
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Enhanced
local
response
4
Avirulent
pathogen
2
Hormones
Signal
transduction
pathway
R-Avr recognition leading to a
strong local response
5
3
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Enhanced
local
response
4
Avirulent
pathogen
2
Hormones
Signal
transduction
pathway
R-Avr recognition leading to a
strong local response
Signal
transduction
pathway
5
3
1
Binding of
pathogen’s signal
molecule to
plant’s receptor
molecule
Enhanced
local
response
6
4
Avirulent
pathogen
Signal
transduction
pathway
2
Hormones
Additional
defensive
chemicals
Signal
transduction
pathway
R-Avr recognition leading to a
strong local response
Systemic acquired
resistance
33.15 TALKING ABOUT SCIENCE: Plant
biochemist Eloy Rodriguez studies how
animals use defensive chemicals made by
plants
 Animals may “medicate” themselves with chemicals
produced by plants
 Scientists observe which plants animals eat for
“medicinal” purposes and how much of each plant
they eat
Copyright © 2009 Pearson Education, Inc.
33.15 TALKING ABOUT SCIENCE: Plant
biochemist Eloy Rodriguez studies how
animals use defensive chemicals made by
plants
 Observation of such animal behavior has led
scientists to study how such chemicals might benefit
humans
– Plant chemicals can kill animal parasites
– Some may be useful for treatment of tumors
Copyright © 2009 Pearson Education, Inc.
Gravity
Light
Phototropism
Gravitropism
Thigmotropism
Critical night
length
Short-day (long-night) plants
Critical night
length
Long-day (short-night) plants
(a)
enhances
(b)
(e)
opposes
(f)
stimulates
Cell
elongation
stimulates
inhibits
inhibits
(c)
Axillary
bud growth
stimulates
inhibits
Leaf
abscission
Seed
dormancy
stimulates
stimulates
opposes
(d)
(g)
opposes
(h)
Chlorophyll fluorescence
6
5
4
3
2
1
0
25
30
35
40
45
Leaf temperature (ºC)
50
55
You should now be able to
1. Explain what hormones are and how they work
2. Describe the experiments that led to the discovery
of auxins
3. Name the five general classes of plant hormones
and describe the actions of each class
4. Explain what tropisms are and give examples of
different kinds of plant tropisms
Copyright © 2009 Pearson Education, Inc.
You should now be able to
5. Describe circadian rhythms and biological clocks;
recognize the innate basis of such rhythms and
how they are affected by environmental cues
6. Explain the difference between short-day and longday plants
7. Describe the experiments that led to the discovery
of the effects of night length on flowering
8. Explain how plants detect seasons using proteins
Copyright © 2009 Pearson Education, Inc.
You should now be able to
9.
Give examples of plant defenses that have
evolved to protect plants against herbivores and
pathogens
10. Explain how scientists can help treat human
diseases by studying the things that other animals
eat
Copyright © 2009 Pearson Education, Inc.