Transcript Chapter 33 Plants

Chapter 33
Control Systems in Plants
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
 Soy protein is one of the few plant proteins that
provide all of the essential amino acids.
 Benefits of consuming soy include
– lowered risk of heart disease,
– high levels of antioxidants and fiber,
– low levels of fat, and
– lowering LDL (“bad cholesterol”) levels while maintaining
HDL levels.
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Introduction
 Soy contains phytoestrogens, hormones that can
reduce the symptoms of menopause in women and
can help
– reduce the risks of heart disease and
– sustain bone mass.
 However, high levels of estrogens appear to
increase the risk of
– breast cancer and
– ovarian cancer.
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Figure 33.0_1
Chapter 33: Big Ideas
Plant Hormones
Responses to Stimuli
Figure 33.0_2
PLANT HORMONES
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 Any growth response that results in plant organs
curving toward or away from stimuli is called a
tropism.
 The growth of a shoot in response to light is called
phototropism.
– Moving toward sunlight helps a growing plant use sunlight
to drive photosynthesis.
– Phototropism can result when the cells on the dark side of
a plant stem elongate faster than those on the light side.
Video: Phototropism
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Figure 33.1A
Figure 33.1B
Illuminated
side of shoot
Light
Shaded
side of
shoot
33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 Studies of plant responses to light led to the first
evidence of plant hormones, a chemical signal
– produced in one part of the body and
– transported to other parts,
– where it acts on target cells to change their functioning.
 Charles Darwin and his son Francis conducted
experiments that showed that the shoot tips of plants
controlled their ability to grow toward light.
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33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 The Darwins’ experiments
– 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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Figure 33.1C
Light
Control
1
2
Tip
removed
Tip covered
by opaque
cap
3
Tip covered
by transparent cap
Darwin and Darwin (1880)
4
Base covered
by opaque
shield
5
Tip
separated
by gelatin
block
6
Tip separated
by mica
Boysen-Jensen (1913)
Figure 33.1C_1
Light
Control
1
2
Tip
removed
Tip covered
by opaque
cap
3
4
Tip covered Base covered
by opaque
by transparent cap shield
Darwin and Darwin (1880)
33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
 Peter Boysen-Jensen later conducted experiments
that showed that chemical signals produced in shoot
tips were responsible for phototropism.
 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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Figure 33.1C_2
Light
5
Tip
separated
by gelatin
block
6
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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Figure 33.1D_s1
A chemical diffuses from the
shoot tip into the agar block.
Agar
1
Control
No light
The block
stimulates
growth.
Figure 33.1D_s2
A chemical diffuses from the
shoot tip into the agar block.
Agar
1
Control
No light
The block
stimulates
growth.
2 Offset blocks
stimulate
curved
growth.
Figure 33.1D_s3
A chemical diffuses from the
shoot tip into the agar block.
Agar
1
Control
No light
The block
stimulates
growth.
2 Offset blocks
stimulate
curved
growth.
3
Blocks with
no chemical
have no
effect.
33.2 Five major types of hormones regulate plant
growth and development
 Plant hormones
– are produced in very low concentrations but
– can have a profound effect on growth and development.
 The binding of hormones to cell-surface receptors
triggers a signal transduction pathway that
– amplifies the hormonal signal and
– leads to a response or responses within the cell.
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33.2 Five major types of hormones regulate plant
growth and development
 Plant biologists have identified five major types of
plant hormones.
– Other important hormones exist, but will not be discussed
here.
– Some of the hormones listed in Table 33.2 represent a
group of related hormones.
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33.2 Five major types of hormones regulate plant
growth and development
 As indicated in Table 33.2, each hormone has
multiple effects, depending on
– its site of action,
– its concentration, and
– the developmental stage of the plant.
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Table 33.2
33.3 Auxin stimulates the elongation of cells in
young shoots
 Auxin is the term for any chemical substance that
promotes seedling elongation.
 Indoleacetic acid (IAA) is the
– major natural auxin found in plants and
– type of auxin referred to in this chapter.
 Auxin is produced in apical meristems at the tips of
shoots.
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Figure 33.3A
33.3 Auxin stimulates the elongation of cells in
young shoots
 At different concentrations, auxin
– stimulates or inhibits the elongation of shoots and roots,
– may act by weakening cell walls, allowing them to stretch
when cells take up water,
– stimulates the development of vascular tissues and cell
division in the vascular cambium, promoting growth in
stem diameter, and
– is produced by developing seeds and promotes the
growth of fruit.
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Elongation
Inhibition Promotion
Figure 33.3B

Stems
0
Roots

0.9 g/L
1
108
106
104
102
Increasing auxin concentration (g/L)
102
Figure 33.3C
Enzyme that separates cross-linking molecules
CELL WALL
Cross-linking
molecule
4
2
Cellulose
microfibril
H2O
Plasma
Cell
membrane wall
H
H
H
H
H
H
Vacuole
3
H
Enzyme that
loosens
cell wall
H
1
H
Proton pump
(protein)
Plasma membrane
CYTOPLASM
Figure 33.3C_1
Enzyme that separates
cross-linking molecules
CELL WALL
Cross-linking
molecule
2
Cellulose
microfibril
H
H
H
H
H
H
3
H
Enzyme that
loosens
cell wall
H
1
H
Proton pump
(protein)
Plasma
membrane
CYTOPLASM
33.4 Cytokinins stimulate cell division
 Cytokinins
– promote cytokinesis, or cell division,
– are produced in actively growing organs such as roots,
embryos, and fruits, and
– move upward from roots through a plant,
– balancing the effects of auxin from apical meristems and
– causing lower buds to develop into branches.
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Figure 33.4
Terminal
bud
No terminal bud
33.5 Gibberellins affect stem elongation and have
numerous other effects
 Gibberellins
– promote cell elongation and cell division in stems and
leaves and
– were named for a genus of fungi that produce the same
chemical and cause “foolish seedling” disease, in which
rice seedlings grew so tall and spindly that they toppled
over before producing grain.
– 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.
 In some plants, gibberellins interact antagonistically
with abscisic acid.
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Figure 33.5A
Dwarf plant
(untreated)
Dwarf plant
treated with
gibberellins
Figure 33.5B
Figure 33.5C
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.
 ABA also acts as a “stress hormone,” causing
stomata to close when a plant is dehydrated.
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Figure 33.6
33.7 Ethylene triggers fruit ripening and other
aging processes
 Ethylene is a
– gaseous by-product of coal combustion and
– naturally occurring plant hormone.
 Plants produce ethylene, which triggers
– fruit ripening and
– programmed cell death.
 Ethylene is also produced in response to stresses
such as drought, flooding, injury, or infection.
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33.7 Ethylene triggers fruit ripening and other
aging processes
 A changing ratio of auxin to ethylene, triggered
mainly by shorter days, probably causes
– autumn color changes and
– the loss of leaves from deciduous trees.
 When an autumn leaf falls, the base of the leaf
separates from the stem.
– The separation region is called the abscission layer, and
– the leaf drops off when its weight splits the abscission
layer apart.
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Figure 33.7A
Figure 33.7B
Leaf
stalk
(petiole)
Stem
Protective layer Abscission layer
Stem
Leaf stalk
Figure 33.7B_1
Leaf
stalk
(petiole)
Stem
Figure 33.7B_2
Protective layer Abscission 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, and
– use as weed killers.
 Agricultural uses of plant hormones
– help keep food prices down and can benefit the
environment in aspects such as soil erosion, but
– may have dangerous side effects for humans and the
environment.
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Figure 33.8
Figure 33.8_UN
RESPONSES TO STIMULI
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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 is a response to light.
– Gravitropism is a response to gravity.
– Thigmotropism is a response to touch.
Video: Gravitropism
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Video: Mimosa Leaf
Figure 33.9A
Figure 33.9B
33.10 Plants have internal clocks
 Plants display rhythmic behavior including the
– opening and closing of stomata and
– folding and unfolding of leaves and flowers.
 A circadian rhythm
– is an innate biological cycle of about 24 hours and
– may persist even when an organism is sheltered from
environmental cues.
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33.10 Plants have internal clocks
 Research on a variety of organisms indicates that
circadian rhythms are controlled by internal
timekeepers known as biological clocks.
 Environmental cues such as light/dark cycles keep
biological clocks precisely synchronized.
 For most organisms, including plants, we know little
about
– where the clocks are located or
– what kinds of cells are involved.
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Figure 33.10
Noon
Midnight
33.11 Plants mark the seasons by measuring
photoperiod
 Biological clocks can influence seasonal events
including
– flowering,
– seed germination, and
– the onset of dormancy.
 The environmental stimulus plants most often use to
detect the time of year is called 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, such as chrysanthemums and
poinsettias
– generally flower in the late summer, fall, or winter
– when light periods shorten.
 Long-day plants, such as spinach, lettuce, and
many cereal grains
– generally flower in late spring or early summer
– when light periods lengthen.
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Figure 33.11
0
Time (hrs)
24
Plants bloom only
with a longer dark
period.
1
2
Flash of light
prevents flowering.
3
Light
Shortday
(longnight)
plants
Darkness
Flash of
light
Plants bloom
only with a
shorter dark
period.
4
5
Flash of light
induces
flowering.
6
Critical dark
period
Longday
(shortnight)
plants
Figure 33.11_1
0
Time (hrs)
24
Plants bloom only
with a longer dark
period.
1
2
Flash of light
prevents flowering.
3
Light
Darkness
Flash of
light
Shortday
(longnight)
plants
Figure 33.11_2
0
Time (hrs)
24
Plants bloom
only with a
shorter dark
period.
4
5
Flash of light
induces
flowering.
6
Critical dark
period
Longday
(shortnight)
plants
33.12 Phytochromes are light detectors that may
help set the biological clock
 Phytochromes
– are proteins with a light-absorbing component and
– may help plants set their biological clock and monitor
photoperiod.
 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.
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Figure 33.12A
Red
light
Pr
Pfr
Far-red
light
33.12 Phytochromes are light detectors 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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Figure 33.12B
0
Time (hrs)
24
1
R
2
R FR
3
RFRR
4
RFRRFR
Critical dark
period
Short-day
(long-night)
plant
Long-day
(short-night)
plant
33.13 EVOLUTION CONNECTION: Defenses
against herbivores and infectious microbes
have evolved in plants
 Herbivores are animals that mainly eat plants.
 Plants use chemicals to defend themselves against
herbivores and pathogens.
 Plants counter herbivores with
– physical defenses, such as thorns, and
– chemical defenses, such as distasteful or toxic
compounds.
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Figure 33.13A_s1
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
Figure 33.13A_s2
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
2
Signal
transduction
pathway
Figure 33.13A_s3
3
Synthesis
and release
of chemical
attractants
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
2
Signal
transduction
pathway
Figure 33.13A_s4
4
Wasp is attracted
3
Synthesis
and release
of chemical
attractants
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
2
Signal
transduction
pathway
Figure 33.13A_s5
5
4
Wasp is attracted
The
wasp
lays
eggs
3
Synthesis
and release
of chemical
attractants
Plant cell
1
Damage to plant
and chemical in
caterpillar saliva
2
Signal
transduction
pathway
Figure 33.13A_2
33.13 EVOLUTION CONNECTION: Defenses
against herbivores and infectious microbes
have evolved in plants
 Plants defend themselves against pathogens at
several levels.
– The first line of defense against infection is the physical
barrier of the plant’s epidermis.
– If that fails, plant cells damaged by infection
– seal off the infected areas and
– release microbe-killing chemicals that signal nearby cells to
mount a similar chemical defense.
– In addition, hormones trigger generalized defense responses in
other organs in the process of systemic acquired resistance.
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Figure 33.13B_s1
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
Avirulent
pathogen
Avr protein
Figure 33.13B_s2
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
Avirulent
pathogen
Avr protein
2
Signal
transduction
pathway
Figure 33.13B_s3
3
Enhanced
local
response
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
Avirulent
pathogen
Avr protein
2
Signal
transduction
pathway
Recognition between R and Avr proteins,
leading to a strong local response
Figure 33.13B_s4
3
Enhanced
local
response
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
4
Avirulent
pathogen
Avr protein
2
Hormones
Signal
transduction
pathway
Recognition between R and Avr proteins,
leading to a strong local response
Figure 33.13B_s5
5
3
Enhanced
local
response
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
4
Avirulent
pathogen
Avr protein
2
Hormones
Signal
transduction
pathway
Recognition between R and Avr proteins,
leading to a strong local response
Signal
transduction
pathway
Figure 33.13B_s6
5
3
Enhanced
local
response
1
Binding of the
pathogen’s Avr
protein to the
plant’s R protein R protein
6
4
Avirulent
pathogen
Avr protein
2
Signal
transduction
pathway
Hormones
Additional
defensive
chemicals
Signal
transduction
pathway
Recognition between R and Avr proteins, Systemic acquired
leading to a strong local response
resistance
You should now be able to
1. Describe the experiments and conclusions of the
phototropism research performed by the Darwins,
Boysen-Jensen, and Went.
2. Describe the functions of the five major types of
plant hormones.
3. Describe the uses of plant hormones in modern
agriculture and the ethical issues associated with
their use.
4. Define phototropism, gravitropism, and
thigmotropism.
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You should now be able to
5. Explain how biological clocks work and how they
influence the lives of plants.
6. Distinguish between short-day plants and long-day
plants.
7. Describe the roles of phytochromes in plants.
8. Explain how plants defend themselves against
herbivores.
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Figure 33.UN01
Gravity
Light
Phototropism
Gravitropism
Thigmotropism
Figure 33.UN02
Critical dark
period
Short-day
(long-night) plants
Critical dark
period
Long-day
(short-night) plants
Figure 33.UN03
(a)
enhances
(b)
(e)
opposes
(f)
stimulates
Cell
elongation
stimulates
inhibits
Leaf
abscission
stimulates
inhibits
(c)
Axillary
bud growth
stimulates
inhibits
opposes
(d)
(g)
Seed
dormancy
stimulates
opposes
(h)