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Signal Transduction
CYTOPLASM
CELL
WALL
Plant hormones
1 Reception
2
Transduction
3 Response
Activation
of cellular
responses
Chapter 39
Relay molecules
Receptor
Hormone or
environmental
stimulus
Plasma membrane
Figure 39.4 An example of signal transduction in plants: the role of
phytochrome in the de-etiolation (greening) response (layer 1)
Etiolation and DeDe-etiolation
2 Transduction
1 Reception
3 Response
CYTOPLASM
NUCLEUS
cGMP
Plasma
membrane
Second messenger
produced
Specific
protein
kinase 1
activated
Phytochrome
activated
by light
Cell
wall
Light
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 39.4 An example of signal transduction in plants: the role of
phytochrome in the de-etiolation (greening) response (layer 2)
2 Transduction
1 Reception
3 Response
CYTOPLASM
Second messenger
produced
2 Transduction
1 Reception
3 Response
Transcription
factor 1
NUCLEUS
CYTOPLASM
NUCLEUS
cGMP
Plasma
membrane
Figure 39.4 An example of signal transduction in plants: the role of
phytochrome in the de-etiolation (greening) response (layer 3)
Specific
protein
kinase 1
activated
cGMP
Plasma
membrane
Second messenger
produced
Phytochrome
activated
by light
Specific
protein
kinase 1
activated
Phytochrome
activated
by light
Cell
wall
Specific
protein
kinase 2
activated
Light
P
Transcription
factor 2
P
Cell
wall
Specific
protein
kinase 2
activated
Transcription
Light
Translation
Ca2+ channel
opened
Ca2+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ca2+ channel
opened
De-etiolation
(greening)
response
proteins
Ca2+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1
Plants Raging Hormones
The discovery of phototropisms
Darwin and son
found that the top
of the plant played
an important role
Confirmed by
Boysen and Jensen
Auxin
Went
demonstrated
that the chemical
substance was
transferable and
named it
AUXIN
Produced in the embryo, apical meristems, young
leaves
Is transported down the stem
Cell elongation, lateral root formation , herbicide,
fruit development
Above describes the effect of auxin on strawberry development. The
achenes produce auxin.
auxin. When removed the strawberry does not develop
(Raven, 1992).
Cytokinin
Produced in the roots (moves upwards)
Cell division and differentiation, apical
dominance
Axillary buds
(a) Intact plant
“Stump” after
removal of
apical bud
Lateral branches
(b) Plant with apical bud removed
2
Gibberellins
Meristems, young leaves and embryos
Stem elongation, fruit growth, break dormancy
Brassinosteroids
Abscisic Acid (ABA)
Leaves, stems, roots, green fruit
Inhibits growth, stimulates seed dormancy and
drought tolerance
Seeds ,fruits, leaves, shoots, floral buds
Elongation and xylem differentiation
Ethylene
Ripening fruits, stem nodes, aging leaves and
flowers
Apoptosis, leaf abscission, fruit ripening, triple
response.
Coleoptile
3
LIGHT
Plants will respond differently changes in light
including: wavelength, duration, intensity,
direction
Two classes of photoreceptors
BlueBlue-light photoreceptors
Phytochromes
The structure of a phytochrome
How does a phytochrome work?
Biological Clocks and Circadian
Rhythms
Day length and Night length
Circadian Rhythms
Biological clocks
Noon
Short day plants
Long day plants
Neutral day
plants
Midnight
4
Figure 39.25 Positive gravitropism in roots: the
statolith hypothesis
Other stimuli
Statoliths
(a)
20 µm
(b)
Thigmomorphogenesis
Plant hormones will aid in dealing
with environmental stresses
Drought
Flooding
Salt
Heat stress
Cold stress
Herbivores
Pathogens
5
Coevolution of plants and their
pathogens
The control of plant resistance
6