Fig. 7-0a

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Results
Shaded side
Control
Light
Boysen-Jensen
Illuminated side
Light
Darwin and Darwin
Mica (impermeable)
Gelatin (permeable)
Light
Opaque shield over curvature
Trans- parent cap
Opaque cap
Tip removed
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Results
Excised tip on agar cube
Growth-promoting chemical diffuses into agar cube
Control (agar cube lacking chemical)
Offset cubes
Control
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Cell wall-loosening enzymes cleave cross-linking p
olysaccharides.
CELL WALL
Low pH activates expansins.
H2O
Cell wall
Plasma membrane
H?
Acidity increases.
H?
H?
H?
H?
H?
H?
H?
Proton pump activity increases.
Nucleus
Cytoplasm
Vacuole
Plasma membrane
ATP
Sliding cellulose microfibrils allow cell to
elongate.
H?
CYTOPLASM
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• Grapes from control
• vine (left) and gibberellin-
• treated vine (right)

(a) Rosette form (left) and gibberellin-induced
bolting (right)
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Aleurone
Endosperm
?-amylase
Sugar
GA
GA
Water
Radicle
Scutellum (cotyledon)
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Red mangrove (Rhizophora mangle) seeds
Coleoptile
Maize mutant
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ein mutant
ctr mutant
(b) ctr mutant
(a) ein mutant
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0.5 mm
Abscission layer
Protective layer
Stem
Petiole
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(a) Before exposure to light
(b) After a weeks exposure to natural daylight
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1.0
436 nm
Refracting prism
0.8
0.6
Phototropic effectiveness
0.4
White light
0.2
0
400
450
500
550
650
600
700
Wavelength (nm)

• Light wavelengths below 500nm induce
• curvature.

• Blue light induces the most curvature
• of coleoptiles.

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Results
Dark
Red
Red
Far-red
Dark
Dark (control)
Red
Far-red
Dark
Red
Red
Far-red
Red
Far-red
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Responses to Pfr Seed germination Inhibition
of vertical growth and stimu- lation of
branching Setting internal clocks Control of
flowering
Red light
Pr
Pfr
Synthesis
Far-red light
Slow conversion in darkness (some species)
Enzymatic destruction
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Noon
1000 PM
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24 hours
(a) Short-day (long-night) plant
Darkness
Flash of light
Light
Critical dark period
(b) Long-day (short-night) plant
Flash of light
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24 hours
R
R
F
R
R
F
R
R
R
F
R
R
F
R
Short-day (long-night) plant
Long-day (short-night) plant
Critical dark period
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Statoliths
20 ?m
(a) Primary root of maize bending
gravitropically (LMs)
(b) Statoliths settling to the lowest sides
of root cap cells (LMs)
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(a) Unstimulated state (leaflets spread apart)
(b) Stimulated state (leaflets folded)
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Vascular cylinder
Air tubes
Epidermis
100 ?m
100 ?m
(a) Control root (aerated)
(b) Experimental root (nonaerated)
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Recruitment of parasitoid wasps that lay their
eggs within caterpillars
Synthesis and release of volatile attractants
Wounding
Chemical in saliva
Signal transduction pathway
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Infected tobacco leaf with lesions
Signal
Signal transduction pathway
Hypersensitive response
Signal transduction pathway
Acquired resistance
R protein
Avirulent pathogen
Avr effector protein
Systemic acquired resistance
R-Avr recognition and hypersensitive response