powerpoint presentation · concept 39.2: plant hormones help coordinate growth, development, and...
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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
Plant Responses to Internal and
External Signals
Chapter 39
Concept 39.1: Signal transduction pathways
link signal reception to response
• A potato left growing in darkness produces shoots that look unhealthy, and it lacks elongated roots
• These are morphological adaptations for growing in darkness, collectively called etiolation
• After exposure to light, a potato undergoes changes called de-etiolation, in which shoots and roots grow normally
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(a) Before exposure
to light
(b) After a week’s exposureto natural daylight
Figure 39.3
Reception
CELLWALL
2 31 Transduction
CYTOPLASM
Response
Relay proteins and
second messengers
Activationof cellularresponses
Receptor
Hormone orenvironmentalstimulus Plasma membrane
• A potato’s response to light is an example of cell-signal
processing
Figure 39.4-1
Reception1
CYTOPLASM
Plasmamembrane
Phytochrome
Cellwall
Light
• Internal and external signals are detected by receptors, proteins that change in response to specific stimuli
• In de-etiolation, the receptor is capable of detecting light
Reception
Figure 39.4-2
Reception 21 Transduction
CYTOPLASM
Plasmamembrane
Phytochrome
Cellwall
Light
cGMP
Secondmessenger
Ca2
Ca2 channel
Proteinkinase 1
Proteinkinase 2
• Second messengers transfer and amplify signals
from receptors to proteins that cause responses
Transduction
Figure 39.4-3
Reception 2 31 Transduction Response
CYTOPLASM
Plasmamembrane
Phytochrome
Cellwall
Light
cGMP
Secondmessenger
Ca2
Ca2 channel
Proteinkinase 1
Proteinkinase 2
Transcriptionfactor 1
Transcriptionfactor 2
NUCLEUS
Transcription
Translation
De-etiolation(greening)
response proteins
P
P
Response
• A signal transduction pathway leads to
regulation of one or more cellular activities
• In most cases, these responses to stimulation
involve increased activity of enzymes
• This can occur by transcriptional regulation or
post-translational changes to the protein
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Concept 39.2: Plant hormones help coordinate
growth, development, and responses to stimuli
• Plant hormones are chemical signals that modify or
control one or more specific physiological processes
within a plant
• Tropism: growth of a plant towards or away from a stimulus
• Positive tropism (growing towards stimulus)
• Negative tropism (growing away from stimulus)
• Thigmotropism: touch
• Geotropism or Gravitropism: gravity
• Phototropism: Light
• Photoperiodism: the physiological response to the photoperiod
• Photoperiod: environmental stimulus a plant uses to detect the time of year
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Biological Clocks and Circadian Rhythms
• Many plant processes oscillate during the day
• Many legumes lower their leaves in the evening
and raise them in the morning, even when kept
under constant light or dark conditions
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Noon Midnight
Photoperiodism and Control of Flowering
• Some processes, including flowering in many species, require a certain photoperiod
• Depends on length of night, not day
– Plants that flower when a light period is shorter than a critical length are called short-day plants
– Plants that flower when a light period is longer than a certain number of hours are called long-day plants
– Flowering in day-neutral plants is controlled by plant maturity, not photoperiod
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Figure 39.2124 hours
Light Flashoflight
Darkness
Criticaldark period
Flashof light
(b) Long-day(short-night) plant
(a) Short day(long-night) plant
Gravity• Response to gravity is known as gravitropism
• Roots show positive gravitropism; shoots show
negative gravitropism
• Plants may detect gravity by the settling of
statoliths, dense cytoplasmic components
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Primary root of maizebending gravitropically(LMs)
Statoliths settling tothe lowest sides ofroot cap cells (LMs)
Mechanical Stimuli
• The term thigmomorphogenesis refers to changes in form that result from mechanical disturbance
• Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls
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• Thigmotropism is growth in response to touch
• It occurs in vines and other climbing plants
• Another example of a touch specialist is the sensitive plant Mimosa pudica, which folds its leaflets and collapses in response to touch
• Rapid leaf movements in response to mechanical stimulation are examples of transmission of electrical impulses
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(a) Unstimulated state (b) Stimulated state
(c) Cross section of a leaflet pair in the stimulated state (LM)
Leafletsafterstimulation
Pulvinus(motororgan)
Side of pulvinuswith flaccid cells
Side of pulvinuswith turgid cells
Vein
0.5
m
Figure 39.26
A Survey of Plant Hormones
• Plant hormones are produced in very low
concentration, but a minute amount can greatly
affect growth and development of a plant organ
• In general, hormones control plant growth and
development by affecting the division,
elongation, and differentiation of cells
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Complete # 1-9
Auxin
• Effects
– controls cell division
& differentiation
– phototropism
• growth towards light
• asymmetrical distribution of auxin
• cells on darker side elongate faster
than cells on brighter side
– apical dominance
What do Gibberellin and ABA do?
Gibberellins
• Family of hormones
– over 100 different gibberellins identified
• Effects
– stem elongation
– fruit growth
– seed germination
plump grapes in grocery
stores have been treated
with gibberellin hormones
while on the vine
Abscisic acid (ABA)
• Effects
– slows growth
– seed dormancy
• high concentrations of abscisic acid
– germination only after ABA is inactivated or leeched out
• survival value:
seed will germinate only
under optimal conditions
– light, temperature, moisture
Complete #21-26
Ethylene• Hormone gas released by plant cells
• Effects
– fruit ripening
– leaf drop
• like in Autumn
• apoptosis
One bad apple spoils the whole bunch…
Fruit ripening
• Adaptation
– hard, tart fruit protects developing seed from herbivores
– ripe, sweet, soft fruit attracts animals to disperse seed
• Mechanism
– triggers ripening process• breakdown of cell wall
– softening
• conversion of starch to sugar
– sweetening
– positive feedback system• ethylene triggers ripening
• ripening stimulates more ethylene production
Figure 39.UN03
Environmental Stresses
• Environmental stresses have a potentially adverse effect on survival, growth, and reproduction
• Stresses can be abiotic (nonliving) or biotic (living)– Abiotic stresses include drought, flooding, salt stress,
heat stress, and cold stress
– Biotic stresses include herbivores and pathogens
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Abiotic Stresses
• Drought: plants reduce transpiration by closing stomata, slowing leaf growth, and reducing exposed surface area– Growth of shallow roots is inhibited, while deeper roots
continue to grow
• Flooding: Enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding
• Salt: increased salt in the soil can reduce water
uptake
– Plants respond to salt stress by producing solutes
tolerated at high concentrations
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Heat Stress• Excessive heat can denature a plant’s enzymes
• Heat-shock proteins help protect other proteins
from heat stress
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Cold Stress
• Cold temperatures decrease membrane fluidity
• Altering lipid composition of membranes is a
response to cold stress
• Freezing causes ice to form in a plant’s cell walls
and intercellular spaces
• Many plants, as well as other organisms, have
antifreeze proteins that prevent ice crystals from
growing and damaging cells
Figure 39.UN05
Quiz Tomorrow
• Explain water transport
• Explain stomata opening and closing
• Explain sugar transport
• Know the Hormones!
• Tropisms
• Short Day v. Long Day Plants