Response to Signals in Plants
Chapter 39
Signal Transduction Pathway
1.
Receptors receive a
stimulus and activate the
secondary messengers
2.
Secondary messengers
______ the signal in other
proteins
3.
Cells respond to the signal
1. _____________ pathway
2. Transcriptional regulation
Signal Transduction Pathway
1.
Light signal activates
__________ receptor
which initiates two signal
transduction pathways
2.
Each transduction pathway
activates kinase protein
3.
Kinase proteins activate
the expression of genes
that result in a _______
(de-etiolation) response
2
1
3
Plant Hormones
Hormone: _____________ produced in one part of an organisms body, which
_______ another part of the body where it binds with a specific receptor and initiates
a response in target cells or tissues








Auxin (IAA)
Cytokinins
Gibberellins (GA)
Abscisic acid (ABA)
Ethylene
Brassinosteroids
Jasmonates
Strigolactones
Hormone: Auxin (IAA)
Primary location produced:


Shoot apical meristem
Young leaves
Major functions:





Stimulates _____________
Promotes lateral and adventitious
root formation
Regulates ______________
Phototropism and gravitropism
Promotes secondary growth
Polar Transport of Auxin
Auxin is transported from apex to shoot
Cell wall is _____


Auxin ion picks up H+
Diffuses across plasma membrane
Cytosol is _______



Auxin loses H+
Uses energy to pump out H+ to maintain pH
Leaves cell through carrier proteins
Cell Elongation in Response to Auxin
3
Low pH activates
__________, which
separate microfibrils
and polysaccharides
Hormone: Cytokinins
Primary location produced in plant:
 Roots
Major functions:
 Regulate _________ (cytokinesis) and influence pathway of differentiation






More cytokinins = development of shoot buds
More auxins = more root growth
Control apical dominance = apical bud __________________ of axillary buds
Promote lateral bud growth
Stimulate seed germination
Delays senescence (death or deterioration of plant parts)
Apical Dominance
Hormone: Gibberellins (GA)
Primary location produced in plant:



Apical meristems of roots and buds
Young leaves
Developing seeds
Major functions:




Stimulate ____________ and _________
Pollen development and tube growth
Promotes _____________ and
germination
Stimulates flowering and fruits (with auxin)
Gibberellins Role in Germination
1.
After being activated by
water, gibberellins are
released, which signal the
aleurone
2.
Aleurone releases
_____________, which
breakdown endosperm
3.
Nutrients provide energy
to developing embryo
Hormone: Abscisic acid (ABA)
Primary location produced in plant:

All plant cells
Major functions:




______ growth
Controls stomata under water stress
Promotes seed dormancy (counteracts gibberellins)
Promotes leaf senescence (programed death)
Hormone: Ethylene
Primary location produced in plant:

Most plant cells
Major functions:

Triple response of seedlings
1.
2.
3.



Slow stem elongation
Thickening of stem
Horizontal growth of stem
Promotes ______
___________ (detachment)
Senescence
Movement in Plants
Tropism: a directional growth
response toward or away from a stimuli
_____________: directional growth in
response to light

Caused by concentration of Auxin on
shaded side
Movement in Plants
Gravitropism: directional growth in
response to _____

Caused by sedimentation of _______ in
plant cells.
Movement in Plants

Thigmotropism: directional growth in response to _____
Plant Response to Light
Blue-light photoreceptors



Initiate phototropism
Opening of ______
Slowing of seed leaf stem (hypocotyl)
after seedling breaks ground
Plant Response to Light
Phytochromes (receptors that absorb mostly red-light)

De-etiolation (greening)

Seed germination

Triggered by accumulation
of red and far-red phytochromes

Red phytochrome (Pr)


Far-red phytochrome (Pfr)


______ growth
________ growth
Shade avoidance

Pr and Pfr ratio dictate growth
Responses to Pfr:
• Seed germination
• Inhibition of vertical
growth and stimulation
of branching
• Setting internal clocks
• Control of flowering
Daily and Seasonal Plant Responses

Circadian rhythms: around 24-hr cycles that are not directly controlled
by a known environmental variable

Photoperiodism: a physiological response to photoperiod (interval an
organism is exposed to light in a 24-hr period)


Flowering (short-day vs. long-day)
Critical night length
Short-day and Long-day Plants

Short-day plants: require
light period ______ than
some critical period

Long-day plants: require
light period _____ than
some critical period
Critical Night Length

Some plants require a critical
night length (ex. 12-hrs) to
flower

Flowering can be turned on or
off by activating the red (Pr)
and far-red (Pfr) phytocrome
receptors
Flowering Hormone

Flower inducing hormone
(______) can initiate flowering
in plants not-triggered by
photoperiod
Plant Response to Environmental Stresses
Drought stress

Reduce transpiration






Close _______
Release of __________
Inhibits growth of young leaves
Change leaf shape
Deeper root growth
Drop leaves
Dormant Encilia californica
Plant Response to Environmental Stresses
Oxygen deprivation


Formation of aerial root
_____ of root cortex cells to
create air tubes

Ethylene
Plant Response to Environmental Stresses
Salt Stress


Salt glands
Production of compatible
solutes

Maintain water potential
Plant Response to Environmental Stresses
Heat Stress

________ proteins

Chaperone proteins
Plant Response to Environmental Stresses
Cold Stress



Alter lipid concentration of membranes
Changes in solute concentration of
cytosol
________ proteins
Plant Response to Pathogens
PAMP triggered immunity


Pathogen-associated molecular patterns (PAMPs) =
________________ specific to certain pathogens
Effectors act to cripple host plants innate immune
response

R proteins
Hypersensitive response = localized ____
_______ near infection site

Lesions
Systemic acquired response = signaling
molecules activate defense system in entire
plant
Plant Response to Pathogens
1.
Pathogen effector binds with R protein in host
plant cell
2.
R protein initiates a signal transduction pathway
3.
__________________. Infected area is sealed
off, with cell walls reinforced. Anti-microbial
molecules are released and infected area dies.
4.
Infected cells release signaling molecule
5.
Signaling molecule transported throughout plant
6.
Signaling molecule initiates signal transduction
pathway
7.
_____________________. Plant cells produce
molecules that protect the cell from pathogens.
Plant Response to Herbivores
Herbivory: animals eating plants

Recruitment of _____________
Plant Response to Herbivores
Production of _______________


Tannins
Opium
Plant Response to Herbivores

Timing of flowering