Download CH 39 PPT Plant Response

Do plants feel like human?
PLANT SIGNAL TRANSDUCTION
an overview
• The Telegraph Plant
https://www.youtube.com/watch?v=J-fIKlcCbSU
• What Plants Talk About (Full Documentary)
https://www.youtube.com/watch?v=CrrSAc-vjG4
Oct. 15, 2015
Reception and Transduction
Signal transduction pathways
link signal reception to response
• Plants have cellular receptors that detect changes in their
environment
• For a stimulus to elicit a response, certain cells must have an
appropriate receptor
• Stimulation of the receptor initiates a specific signal transduction
pathway
• A potato left growing in darkness produces shoots that look
unhealthy and lacks elongated roots
Etiolated potato in response to light exposure is
good example of signal Transduction
• 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
• A potato’s response to light is an example of
cell-signal processing
• The stages are reception, transduction, and
response
• Internal and external signals are detected by receptors, proteins that
change in response to specific stimuli
• Second messengers transfer and amplify signals from receptors to
proteins that cause responses
Signal Transduction Pathways
Etiolation vs De-etiolation
1. Reception
2. Transduction
• Second Messengers
3. Response
A. Post-translational
modification:
involves modification of
existing proteins via the
phosphorylation (Protein
kinases) /dephosphorylation
(Protein phosphatases) of
specific amino acids
(a) Before exposure to light
(b) After a week’s exposure to
natural daylight
???
B. Transcriptional Regulation
– Specific transcription
factors bind directly to
specific regions of DNA
and control transcription of
genes
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https://www.youtube.com/watch
?v=1R_h4itoXYc
Plant Hormones in Signaling
Plant Hormones
• Hormones are chemical signals that coordinate different parts of
an organism
• In general, hormones control plant growth and development by
affecting the division, elongation, and differentiation of cells
• Plant hormones are produced in very low concentration, but a
minute amount can greatly affect growth and development of a
plant organ
Plant Hormones in Phototropism
Auxin (Indoleacetic acid, IAA)
1. Cell elongation
Asymmetrical distribution of auxin moving down from
coleoptile tip causes cells on darker side to elongate
faster
2. Lateral and Adventitious Root
Formation: Auxin is involved in
root formation and branching
3. Auxins as Herbicides: An
overdose of synthetic auxins can
kill eudicots
4. Other Effects of Auxin: Auxin
affects secondary growth by
inducing cell division in the
vascular cambium and
influencing differentiation of
secondary xylem
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The Role of Auxin in Cell Elongation
Cross-linking
polysaccharides
Cell wall–loosening
enzymes
– Growth regulators that stimulate
cytokinesis (cell division)
3 Expansins separate
microfibrils from crosslinking polysaccharides.
CELL WALL
4 Cleaving allows
microfibrils to slide.
Cellulose
microfibril
H2O
2 Cell wall
becomes
more acidic.
1 Auxin
increases
proton pump
activity.
Plasma
membrane
Plasma membrane
Nucleus
Cell
wall
Cytoplasm
Vacuole
CYTOPLASM
Cytokinins
– Cytokinins are produced in
actively growing tissues such as
roots, embryos, and fruits
Expansin
5 Cell can elongate.
– Cytokinins, auxin, and other
factors interact in the control of
apical dominance to suppress
development of axillary buds
– Cytokinins work together with
auxin to control cell division and
differentiation
– Cytokinins retard the aging of
some plant organs by inhibiting
protein breakdown, stimulating
RNA and protein synthesis, and
mobilizing nutrients from
surrounding tissues
Gibberellins
• Gibberellins have a variety of effects, such as stem
elongation, fruit growth, and seed germination
• Gibberellins stimulate growth of leaves and stems
Gibberellins in seed germination
1 Gibberellins (GA)
send signal to
aleurone.
2 Aleurone secretes
-amylase and other enzymes.
3 Sugars and other
nutrients are consumed.
• In stems, they stimulate cell elongation and cell division
Aleurone
• In many plants, both auxin and gibberellins must be present
for fruit to set
Endosperm
-amylase
Sugar
GA
• Gibberellins are used in spraying of Thompson seedless
grapes
GA
Water
Scutellum
(cotyledon)
Ethylene
Radicle
The Triple Response to Mechanical Stress
• Allows a growing shoot to avoid obstacles
• The triple response consists of a slowing of
stem elongation, a thickening of the stem, and
horizontal growth
• Plants produce ethylene in response to stresses such as
drought, flooding, mechanical pressure, injury, and infection
• The effects of ethylene include response to mechanical stress,
leaf abscission, and fruit ripening
0.00
0.10
0.20
0.40
0.80
Ethylene concentration (parts per million)
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ein mutant
ctr mutant
Ethylene in senescence
• Senescence is the programmed death of plant cells or organs
• A burst of ethylene is associated with senescence, the
programmed destruction of cells, organs, or whole plants
• Leaf Abscission
A change in the balance of auxin and ethylene controls leaf
abscission, the process that occurs in autumn when a leaf falls
• Fruit Ripening
A burst of ethylene production in a fruit triggers the ripening
process
(a) ein mutant
(b) ctr mutant
Ethylene-insensitive mutant
Triple response in air but do not respond
to inhibitors of ethylene synthesis
ABSCISSION
Abscisic Acid (ABA)
1. Slows growth
• Ethylene induce
leaf abscission.
2. Controls seed dormancy: Ratio of ABA to Gibberellins
0.5 mm
3. Drought Tolerance: ABA causes opening of potassium
channels in guard cells when plant begins to wilt
• Brassinosteroids
slow leaf
abscission.
• Promote xylem
differentiation
similar to auxin.
Protective layer
Stem
Strigolactones
Abscission layer
Petiole
Responses to Light are critical for plant success
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Stimulate seed
germination
Establish
mycorrhizal
associations
Help control apical
dominance
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Light cues many key events in plant
growth and development.
Photomorphogenesis: Effects of light on
plant
Plants detect not only presence of light
but also its direction, intensity, and
wavelength (color)
Action spectrum
Relative response of a process to different
wavelengths
Blue and Red light most important
Action spectra are useful in studying any
process that depends on light
Blue Light Photoreceptors
Phototropism
Opening of stomata
Hypocotyl elongation
Phytochromes (absorb red)
Seed germination
Shade avoidance
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Biological Clocks and Circadian Rhythms
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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
Circadian rhythms are cycles that are about 24 hours long and are governed
by an internal “clock”
Circadian rhythms can be entrained to exactly 24 hours by the day/night cycle
The clock may depend on synthesis of a protein regulated through feedback
control and may be common to all eukaryotes
The Effect of Light on the Biological Clock: Phytochrome conversion marks
sunrise and sunset, providing the biological clock with environmental cues
Photoperiodism and Responses to Seasons
• Photoperiod, the relative lengths of night and day, is the
environmental stimulus plants use most often to detect the time
of year.
• Photoperiodism is a physiological response to photoperiod.
• Photoperiodism and Control of Flowering.
- Short-day plants: Plants that flower when a light period is
shorter than a critical length.
- Long-day plants: Plants that flower when a light period is
longer than a certain number of
- Day-neutral plants is controlled by plant maturity, not
photoperiod.
Phytochromes in Photoperiodism
The critical night length
24 hours
(a) Short-day (long-night) plant
Darkness
Light
Critical
dark period
Flash
of
light
-Short-day plants are governed by
whether the critical night length
sets a minimum number of hours of
darkness
(b) Long-day (short-night) plant
-Long-day plants are governed by
whether the critical night length
sets a maximum number of hours
of darkness
Flash of light
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Red light can interrupt the nighttime portion of the photoperiod
Action spectra and photoreversibility experiments show that phytochrome is
the pigment that receives red light
A Flowering Hormone?
• Some plants flower after only a single exposure to
the required photoperiod
• Other plants need several successive days of the
required photoperiod
• The flowering signal, not yet chemically identified, is called
florigen.
• Florigen may be a macromolecule governed by the CONSTANS
gene.
• Still others need an environmental stimulus in
addition to the required photoperiod
– For example, vernalization is a pretreatment with
cold to induce flowering
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Plants respond to a wide
variety of stimuli other than light
Meristem Transition and Flowering
• For a bud to form a flower instead of a vegetative
shoot, meristem identity genes must first be
switched on
• Researchers seek to identify the signal transduction
pathways that link cues such as photoperiod and
hormonal changes to the gene expression required
for flowering
• Because of immobility, plants must adjust to a range of
environmental circumstances through developmental and
physiological mechanisms
• Gravitropism
• Thigmomorphogenesis
– Thigmotropism
• Environmental Stress
– Drought
– Flooding
– Salt
– Heat
– Cold
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
Statoliths
(a) Root gravitropic bending
• Thigmotropism: Growth response to touch e.g. vines and other
climbing plants
20 µm
(b) Statoliths settling
http://www.allposters.com/-sp/Twining-Stem-of-a-Morning-Glory-Plant-an-Example-ofThigmotropism-Ipomoea-Purpurea-Posters_i6012596_.htm
Transmission of electrical impulses: action potentials
• Thigmotropism is growth in response to touch
• It occurs in vines and other climbing plants
• Rapid leaf movements in response to
mechanical stimulation are examples of
transmission of electrical impulses called
action potentials
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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
ABIOTIC STRESSES
http://caps.ncbs.res.in/stifdb2/help.html
Drought and Flooding
• During 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
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Salt Stress
Salt can lower the water potential of the soil solution and reduce water uptake
Plants respond to salt stress by producing solutes tolerated at high
concentrations
This process keeps the water potential of cells more negative than that of the
soil solution
• Enzymatic destruction of root cortex cells creates air tubes that
help plants survive oxygen deprivation during flooding
Raffinose family of oligosaccharides
Salt-stress sensing and tolerance mechanisms
ROS signal transduction pathway under salt stress
Na+/H+ antiporter AtNHX1
NSCCs, nonselective cation channels;
ROS, reactive oxygen species;
CDPKs, calcium-dependent protein kinases;
CBLs, calcineurin B-like proteins;
CIPKs, CBL-interacting protein kinases;
AP2/ERF, APETALA2/ETHYLENE RESPONSE FACTOR;
bZIP, basic leucine zipper;
NHX, Na+ /H+ exchanger;
SOS, SALT OVERLY SENSITIVE.
SOS3 (Ca2+ -binding protein),
SOS2 (Suc nonfermenting- like) kinase
SOS1, plasma membrane Na+/H+ antiporter
Trends in Plant Science June 2014, Vol. 19, No. 6
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Model for the role of signaling factors in stomatal
closure and retrograde signaling during water stress
Illustration of the response of plants to water stress
Front. Plant Sci., 13 March 2014 | http://dx.doi.org/10.3389/fpls.2014.00086
Front. Plant Sci., 13 March 2014 | http://dx.doi.org/10.3389/fpls.2014.00086
Classes of genes that are induced by water-deficit stress
Heat and Cold Stress
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Excessive heat can denature a plant’s enzymes
Heat-shock proteins help protect other proteins from heat 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
https://ag.purdue.edu/hla/zhulab/Pages/default.aspx
http://www.intechopen.com/
Transcriptional network of abiotic stress responses
BIOTIC STRESSES
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Defenses Against Herbivores
• Herbivory, animals eating plants, is a stress that plants face in
any ecosystem
• Plants counter excessive herbivory with physical defenses such
as thorns and chemical defenses (Secondary compounds) such as
distasteful or toxic compounds
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Plants damaged by insects can release
volatile chemicals to warn other plants
of the same species
Methyljasmonic acid can activate the
expression of genes involved in plant
defenses
4 Recruitment of
parasitoid wasps
that lay their eggs
within caterpillars
3 Synthesis and
release of
volatile attractants
• Some plants even “recruit” predatory animals that help defend
against specific herbivores
1 Wounding
1 Chemical
in saliva
2 Signal transduction
pathway
Model of the signaling network for plant defense responses
Green Leaf Volatile (GLV) biosynthesis
Oral factors
- effectors
- elicitors
ACS, 1-aminocyclopropane-1-carboxylate (ACC) synthase;
Int. J. Mol. Sci. 2011, 12(6), 3723-3739; doi:10.3390/ijms12063723
CDPKs, Ca2+-dependent protein kinases;
GOX, glucose oxidase;
Chewing arthropods induce JA-dependent
JAs, jasmonates;
defense responses, whereas piercing-sucking
MAPK, mitogen-activated protein kinase;
arthropods frequently induce SA-dependent
ROS, reactive oxygen species;
defense responses.
SA, salicylic acid.
Green Leaf Volatiles (GLVs) are emitted during
herbivory, pathogen infection and abiotic stress
Int. J. Mol. Sci. 2013, 14(9), 17781-17811; doi:10.3390/ijms140917781
Defenses Against Pathogens
• A plant’s first line of defense against infection is the epidermis
and periderm
• If a pathogen penetrates the dermal tissue, the second line of
defense is a chemical attack that kills the pathogen and prevents
its spread
• This second defense system is enhanced by the inherited ability
to recognize certain pathogens
Int. J. Mol. Sci. 2013, 14(9), 17781-17811; doi:10.3390/ijms140917781
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Response to attacks by pathogens
1.
Plant and Microbial symbiosis
1st line of defense is periderm and
epidermis
2. Host-Pathogen Coevolution

Rhizobium-legume symbiosis
Virulent vs Avirulent
Plant-mycorrhizal symbiosis
3. Hypersensitive Response
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Cause cell and tissue death near
infection site to restrict spread of
pathogen
4. Systematic Acquired Resistance
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Plant wide expression of defense
genes in response to salicylic acid
Trends in Plant Science, March 2015, Vol. 20, No. 3
• Systemic acquired resistance causes
systemic expression of defense genes
and is a long-lasting response
Applied Soil Ecology 85 (2015) 94–113
• Salicylic acid is synthesized around
the infection site and is likely the
signal that triggers systemic acquired
resistance
•
https://www.youtube.com/watch?v=fl4NhK7AaDQ
https://www.youtube.com/watch?v=QYmrOrTM-FA
https://www.youtube.com/watch?v=GTH6Ja24SMw
Videos
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Signal Transduction Pathways
https://www.youtube.com/watch?v=HEbueHx_Xag
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Do Plants Respond to Music?
https://www.youtube.com/watch?v=o54o71wVa2c
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How Plants Communicate & Think
https://www.youtube.com/watch?v=CsJkNOEwFcI
Stuff They Don't Want You to Know - Plant Intelligence
https://www.youtube.com/watch?v=KLhgtqd1M2g
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Do Plants Respond to Pain?
https://www.youtube.com/watch?v=fGLABm7jJ-Y
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When Plants Talk
https://www.youtube.com/watch?v=GZqB2T9zz7E
Plants: Plants' solutions to life's challenges David Attenborough.
https://www.youtube.com/watch?v=yOiyHp_oUKA
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