phytochrome and flowering auxin and cell expansion
TRANSCRIPT
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Phytochrome and Flowering
Today�s topics: • More about Hormones
• Apical dominance • Ripening • Dormancy
• Phytochrome • Red / Far red • Control of flowering • Shade avoidance
12 November 2021
Auxin and Cell Expansion
(a) Apical bud intact (not shown in photo)
(b) Apical bud removed
(c) Auxin added to decapitated stem
Axillary buds
Lateral branches
�Stump� after removal of apical bud
Auxin promotes apical dominance Control of Apical Dominance
Control of Apical Dominance Ethylene is a ripening hormone
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One bad apple CAN spoil the whole bunch . . .
Figure 39.14
(a) ein mutant (b) ctr mutant
ctr mutant ein mutant
Leaf abscision is controlled by the ratio of ethylene to auxin
0.5 mm
Protective layer
Stem Petiole
Abscission layer
ABA is a dormancy hormone
Seed Dormancy
Cold Tolerance
ABA Drought stress in roots causes stomata to
close
(a) Before exposure to light (b) After a week’s exposure to natural daylight
De-etiolation (greening response)
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Phytochrome pigment is activated by Red light Reception
CYTOPLASM
Plasma membrane
Phytochrome activated by light
Cell wall
Transduction Response Transcription factor 1 NUCLEUS
cGMP
Second messenger produced
Protein kinase 1
Transcription factor 2
P
Protein kinase 2
P
Transcription
Light Translation
Ca2+ channel opened
Ca2+
De-etiolation (greening) response proteins
1 2 3
You have seen other signaling pathways like this
Figure 39.16
Results
Red Dark Red Dark
Dark (control)
Red Dark
Data from H. Borthwick et al., A reversible photoreaction controlling seed germination, Proceedings of the National Academy of Sciences USA 38:662–666 (1952).
Far-red
Far-red Red Red Far-red Red Far-red
Phytochrome is a molecular switch that detects Red light
Far Red is just another color
Phytochrome
Chlorophyll
Red Far Red
Many plants us day length as a cue for flowering
Poinsettias are “short day” plants
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Fig. 39-21 24 hours
Light
Critical dark period
Flash of light
Darkness
(a) Short-day (long-night) plant
Flash of light
(b) Long-day (short-night) plant
Phytochrome measures
photoperiod
Plants actually measure the length
of night, not day
Fig. 39-22
24 hours
R
RFR
RFRR
RFRRFR
Critical dark period Short-day
(long-night) plant
Long-day (short-night)
plant
Phytochrome is a molecular switch that detects Red light
Leaves produce the flowering signal
Condition Number of plants that flowered
Short nights, intact plant
0/6
Long nights, intact plant
6/6
Long nights, all leaves removed
0/6
Long nights, all but one leaf removed
6/6
Leaves produce the flowering signal
Flowers No Flowers
Masked leaf has a long “night”
R/Fr ratio also used to detect neighbors
More Red
More Far Red