Transcript Chapter 26: pp. 473 - 492 Copyright © The McGraw-Hill Companies, Inc.

Chapter 26: pp. 473 - 492
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
10th Edition
Sylvia S. Mader
Flowering Plants: Control
of Growth Responses
BIOLOGY
curving of stem
© Kim Taylor/Bruce Coleman, Inc.
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
1
Outline

Plant Hormones






Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Plant Responses



Tropisms
Nastic Movements
Photoperiodism
2
Plant Hormones

Flowering plants respond to environmental
stimuli



Stimuli include light, gravity, carbon dioxide levels,
pathogen infection, drought, and touch.
Response to stimuli leads to the survival of the
species.
The responses can be:

Short term


Stomata open and close in response to light levels.
Long term

The response to gravity causes downward growth of the
root and the upward growth of the stem.
3
Plant Hormones

Hormones
Enable plant cells to communicate
 Are synthesized in one part of the plant
 Travel within phloem or from cell to cell in
response to the appropriate stimulus

4
Plant Hormones

Mechanism that brings about a response
occurs at the cellular level.



Receptors containing pigment components
respond to light.

Phytochrome has a region that is sensitive to red light.

Phototropin has a region that is sensitive to blue light.
A transduction pathway, sometimes involving a
second messenger, initiates the response.
Cellular response occurs as a result.
5
Signal Transduction in Plants
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defense
hormones
hormone-binding site
3
blue light
signal
2
Receptor: Molecule in
the plasma membrane,
cytoplasm, or nucleus
that receives signal and
becomes activated.
Transduction pathway: A series
of relay proteins that amplify and
convert the original signal into one
that affects cellular machinery .
activated
phototropin
auxin
Response: Most often
a change in gene expression
or a cellular process affects
plant growth and development.
relay
proteins
Defense
responses
auxin carrier
Responses
include bending
of stem
1
activated
auxin receptor
Cytoplasm
Gene
expression
changes
Nucleus
Responses
include growth
of roots
6
Plant Hormones: Auxins

Auxins



Produced in shoot apical meristem
Found in young leaves, flowers, and fruits
Effects of auxin on growth and development

Apically produced auxin prevents the growth of axillary
buds




Apical dominance
Promotes growth of roots and fruit
Prevents loss of leaves and fruit
Promotes positive phototropism of stems
7
Demonstrating Phototropism
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1. Coleoptile tip is
intact.
2. Coleoptile tip is
removed.
3. Tips are placed on
agar, and auxin
diffuses into the agar.
4. Agar block is placed
to one side of the
coleoptile.
5. Curvature occurs
beneath the block.
8
How Auxins Cause Stems to Bend
When a stem is exposed to unidirectional
light, auxin moves to the shady sides
 Auxin binds to plasma membrane
receptors; the complex leads to the
activation of a proton pump
 Activated proton pumps H+ out of cell

Cell wall loosens
 Turgor pressure increases due to the entry of
water
 Cell enlarges

9
Expansion of the Cell Wall
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cellulose fiber
in cell wall
auxin
nucleus
H+
H+
enzyme
(inactive)
H+
H+
chloroplast
1
Cytoplasm
H+
H+
H+
active
enzyme
H2O
H+
2
turgor
turgor
3
10
Plant Hormones: Gibberellins
Gibberellins are growth-promoting
hormones
 Gibberellins cause stem elongation


There are about 70 gibberellins
Each differ slightly chemically
 The most common is gibberellic acid


When gibberellic acid is applied externally
to plants:
Stems become elongated
 Dormancy of buds and seeds is broken

11
Gibberellins Cause Stem Elongation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
b.
a: © Robert E. Lyons/Visuals Unlimited; b: © Sylvan Whittwer/Visuals Unlimited
12
Plant Hormones: Cytokinins





The cytokinins are a class of hormones that
promote cell division.
Cytokinins are found in dividing tissues of roots,
in seeds, and in fruits.
Cytokinins have been used to prolong the life of
flower cuttings as well as vegetables in storage.
Auxin and cytokinins interact.
Cytokinins prevent senescence.
13
Interaction of Hormones
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a.
b.
c.
d.
Courtesy Alan Darvill and Stefan Eberhard, Complex Carbohydrate Research Center, University of Georgia
14
Plant Hormones: Abscisic Acid
Abscisic acid (ABA) is produced by any
“green tissue” (i.e., tissue containing
chloroplasts).
 Abscisic acid is sometimes called the
stress hormone.

Initiates and maintains seed and bud
dormancy.
 Brings about the closure of stomata.

15
Dormancy and Winter
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© John Solden/Visuals Unlimited.
16
Dormancy and Germination
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plant Cell by Donald R. McCarthy. Copyright 1989 by American Society of Plant Biologists. Reproduced with permission of American Society of Plant
Biologists in the format Textbook via Copyright Clearance Center
17
Abscisic Acid Promotes Closure of Stomata
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inside
outside
H2O
K+
K+
K+
Ca2+
ABA
Open stoma
Guard cell plasma
membrane
Closed stoma
18
Ethylene


Ethylene (H2C = CH2) is a gas formed from the amino
acid methionine.
Effects of ethylene

Abscission


Ripening of fruits




Ethylene stimulates certain enzymes, such as cellulase, which
helps cause leaf, fruit, or flower drop
Increases the activity of enzymes, such as cellulase, that
soften fruits
It also promotes the activity of enzymes that produce the flavor
and smell of ripened fruits.
Axillary bud inhibition
Suppression of stem and root elongation
19
Ethylene and Abscission
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
No abscission
© Kingsley Stern
Abscission
20
Ethylene and Fruit Ripening
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
gene for ethylene
biosynthesis enzyme
ripe tomatoes
harvested
DNA
transcription
mRNA
translation
functional
enzyme for
ethylene
biosynthesis
ethylene synthesis (in plant)
green tomatoes
harvested
no ethylene
synthesis
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Science Focus

Arabidopsis thaliana



A small flowering plant related to cabbage and
mustard plants
Has no commercial value
It has become a model organism for the study of
plant molecular genetics, including signal
transduction.




It is small, so many hundreds of plants can be grown
in a small amount of space.
Generation time is short – 5-6 weeks until maturity.
It normally self-pollinates, but it can easily be crosspollinated.
The number of base pairs in its DNA is relatively small.
22
Overall Appearance of Arabidopsis thaliana
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Arabidopsis thaliana
b. Arabidopsis thaliana (enlarged drawing)
(Normal, Mutated center, Right): Courtesy Elliot Meyerowitz/California Institute of Technology
23
Arabidopsis Mutants
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Arabidopsis flower
A flat of Arabidopsis
Mutated flower
Mutated flower
Lab
(Normal, Mutated center, Right): Courtesy Elliot Meyerowitz/California Institute of Technology; B(Flat): © Inga Spence/Visuals Unlimited;
B(Lab): © Vo Trung Dung/Corbis Sygma
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Plant Responses: Tropisms

Tropisms

Plant growth toward or away from a
unidirectional stimulus is called a tropism
Positive tropism is growth toward the stimulus
 Negative tropism is growth away from the stimulus

Gravitropism - movement in response to
gravity
 Phototropism - movement in response to light
 Thigmotropism - movement in response to
touch

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Gravitropism

When a plant is placed on its side, the stem
grows upward, opposite of the pull of
gravity


Negative gravitropism
Stems with root caps grow downward
Positive gravitropism
 Response depends on sensors called statoliths


Auxin may be responsible for:
Positive gravitropism of roots, and
 Negative gravitropism of shoots

26
Gravitropism
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a.
gravity
b.
c.
25 mm
a: © Kingsley Stern; b: Courtesy Malcolm Wilkins, Glascow University; c: © BioPhot
27
Phototropism

Positive phototropism of stems
Occurs because cells on the shady side of the
stem elongate due to the presence of auxin.
 A pigment related to riboflavin thought to act as
a photoreceptor when phototropism occurs.

Auxin migrates to shady side of stem
 Shady sides elongate faster than bright side

28
Phototropin
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1
cytoplasm
blue light
2
3
blue light
phot
blue light
phot
ADP
transduction
pathway
phot
P
plasma
membrane
ATP
ATP
29
Thigmotropism

Unusual growth due to contact with solid
objects is called thigmotropism


Coiling of tendrils
Thigmomorphogenesis occurs when the
entire plant responds to the presence of
environmental stimuli
Wind
 Rain

30
Coiling Response
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© John D. Cunningham/Visuals Unlimited
31
Nastic Movements



Nastic movements:

Do not involve growth and

Are not dependent on the stimulus direction
Turgor movements result from touch, shaking, or
thermal stimulation.

Mimosa pudica

Venus flytrap
Sleep movements:

Occur daily in response to light and dark changes

Prayer Plant
32
Turgor Movement
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pulvinus
Before
vascular tissue
cell retaining
turgor
cell losing
turgor
After
© John Kaprielian/Photo Researchers, Inc.6
33
Circadian Rhythms

Circadian rhythms:

Biological rhythms with a 24-hour cycle

Tend to be persistent

Rhythm is maintained in the absence of
environmental stimuli

Caused by a biological clock
34
Sleep Movements and
Circadian Rhythms
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prayer plant (morning)
Prayer plant (night)
a.
Morning glory (morning)
b.
Morning glory (night)
Circadian Rhythm
flowers
open
flowers
close
Period
(about 24 hours)
0
12
24
36
48
Time (hours)
c.
(Top, both): © Tom McHugh/Photo Researchers, Inc.(Bottom left): © BIOS A. Thais/Peter Arnold, Inc.; (Bottom right): © BIOS Pierre Huguet/Peter Arnold, Inc.
35
Photoperiodism

Photoperiodism:

Any physiological response prompted by
changes in day or night length
Photoperiodism influences flowering in
some plants.
 Photoperiodism requires participation of a
biological clock and a plant photoreceptor
called phytochrome.

36
Phytochrome

Phytochrome is a blue-green leaf pigment
that alternately exists in two forms
Phytochrome red (Pr) is inactive
 Phytochrome far-red (Pfr) is active

Conversion of forms allows a plant to
detect photoperiod changes
 Also promotes seed germination and
inhibits stem elongation

37
Phytochrome Conversion Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
lightsensitive
region
red light
far-red light
kinase
inactive Pr
active Pfr
38
Phytochrome Control of Shoot Elongation
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a. Normal growth
b. Etiolation
© Grant Heilman Photography
39
Flowering

Flowering plants can be divided into three
groups based on their flowering status.
Short-day plants flower when the day length is
shorter than a critical length.
 Long-day plants flower when the day length is
longer than a critical length.
 Day-neutral plants are not dependent on day
length for flowering.


Some plants may require a specific
sequence of day lengths in order to flower.
40
Photoperiodism and Flowering
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cocklebur
Clover
night
flash of light
24
hours
critical
length
day
flower
flower
1
2
a. Short-day (long-night) plant
3
4
flower
5
6
b. Long-day (short-night) plant
41
Flowering Plants Respond to
the Biotic Environment

Plants are always under attack by herbivores and
parasites.
 Physical and Chemical Defenses


Cuticle-covered epidermis and bark
Secondary metabolites







Tannins
Alkaloids
Cyanogenic glycosides
Wound responses
Hypersensitive response
Indirect defenses
Mutualistic relationships with animals
42
Plant Predators and Parasites
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Alfalfa plant bug
Fungus infection
Monarch caterpillar and butterfly
(Bug): USDA/Agricultural Research Service, photo by Scott Bauer; (Fungus): © Kingsley Stern; (Caterpillar):
© Frans Lanting/Minden Pictures; (Butterfly): © Dwight Kuhn
43
Wound Response in Tomato
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
systemin
cytoplasm
lipase
wounded
leaf
systemin
release
membranebound
receptor
proteinase
inhibitors
membrane
lipids
salicylic acid
jasmonic acid
transduction pathway
nucleus
activation of
proteinase
inhibitor genes
44
Review

Plant Hormones






Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Plant Responses



Tropisms
Nastic Movements
Photoperiodism
45
Chapter 26: pp. 473 - 492
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
10th Edition
Sylvia S. Mader
Flowering Plants: Control
of Growth Responses
BIOLOGY
curving of stem
© Kim Taylor/Bruce Coleman, Inc.
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
46