Transcript Photosynthesis

Chapter 27
Control of Growth
and Responses in
Plants
Outline
Plant Responses
Tropisms
Nastic Movements
Plant Hormones
Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Photoperiodism
Control of Growth
and Responses in
Plants
2
Plant Responses
Control of Growth
and Responses in
Plants
3
Tropisms
Plant growth toward or away from a unidirectional
stimulus is called a tropism
- Positive is towards stimulus
- Negative is away from stimulus
Phototropism - Light
Gravitropism - Gravity
Thigmotropism - Touch
Phototropism
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Phototropism
Control of Growth
and Responses in
Plants
5
Positive phototropism:
Occurs because cells on the shady side of the
stem elongate
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
Gravitropism
Control of Growth
and Responses in
Plants
When a plant is placed on its side, the stem
grows upward, opposite of the pull of gravity
Stems with root caps grow downward
Root cells contain statoliths
Auxin is responsible for:
Positive gravitropism of roots, and
Negative gravitropism of shoots
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Gravitropism
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Thigmotropism
Control of Growth
and Responses in
Plants
8
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
Coiling Response
9
Nastic Movements
Control of Growth
and Responses in
Plants
Nastic movements:
Do not involve growth and
Are not dependent on the stimulus direction
Seismonastic movements result from:
Touch
Shaking, or
Thermal stimulation
Sleep movements:
Occur daily in response to light and dark changes
Prayer Plant
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Seismonastic Movement
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Sleep Movement
12
Circadian Rhythms
Control of Growth
and Responses in
Plants
A 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
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Plant Hormones
Control of Growth
and Responses in
Plants
Almost all communication on a plant is done by
hormones
Synthesized in one part of the plant
Travels within phloem in response to the
appropriate stimulus
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Auxins
Control of Growth
and Responses in
Plants
15
Auxin is produced in shoot and apical meristem
and is found in young leaves and in flowers and
fruits
Apically produced auxin prevents the growth of
axillary buds
- Apical dominance
Weak solution of auxin applied to woody cutting
causes rapid growth of adventitious roots
- Promotes fruit growth
Apical Dominance
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Demonstrating Phototropism
17
How Auxins Work
Control of Growth
and Responses in
Plants
Auxins bind to plasma membrane receptors
Activated proton pumps H+ out of cell
Cell wall loosens
Turgor pressure increases due to the entry of
water
Cell enlarges
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Auxin Mode of Action
19
Gibberellins
Control of Growth
and Responses in
Plants
Gibberellins:
Growth promoting hormones
Bring about elongation of the resulting cells
Gibberellic acid
- Stem elongation
- Breaking of dormancy
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Effect of Gibberellins
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Gibberellic Acid:
Structure and Mode of Action
22
Cytokinins
Control of Growth
and Responses in
Plants
Cytokinins
A class of plant hormones that promote cell
division
Derivatives of adenine
- Prevent senescence
- Initiate growth
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Interaction of Hormones
24
Abscisic Acid
Control of Growth
and Responses in
Plants
25
Abscisic acid (ABA):
Initiates and maintains seed and bud dormancy,
and
Brings about closure of stomata
Produced by:
- Any “green tissue” with chloroplasts
- Monocot endosperm, and
- Roots
Abscisic Acid:
Control of Stoma Opening
26
Ethylene
Control of Growth
and Responses in
Plants
27
Ethylene is involved in abscission
Once abscission has begun:
- Ethylene stimulates certain enzymes
- Cause leaf, fruit, or flower to drop
Also ripens fruit by increasing activity of enzymes
that soften fruit
Functions of Ethylene
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Photoperiodism
Control of Growth
and Responses in
Plants
29
Photoperiodism:
Any physiological response prompted by changes
in day or night length
- Short-day plants
- Long-day plants
- Day-neutral plants
Some plants may require a specific sequence of
day lengths in order to flower
Photoperiodism and Flowering
30
Phytochrome
Control of Growth
and Responses in
Plants
Phytochrome is a blue-green leaf pigment that
alternately exists in two forms
Phytochrome red (Pr)
Phytochrome far-red (Pfr)
Conversion of forms allows a plant to detect
photoperiod changes
Also promotes seed germination and inhibits
stem elongation
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Phytochrome Conversion Cycle
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Phytochrome Control of Growth Pattern
33
Review
Plant Responses
Tropisms
Nastic Movements
Plant Hormones
Auxins
Gibberellins
Cytokinins
Abscisic Acid
Ethylene
Photoperiodism
Control of Growth
and Responses in
Plants
34
Ending Slide Chapter 27
Control of
Growth and
Responses in
Plants