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© 2014 Pearson Education, Inc.

Results

Control

Light

Illuminated side

Shaded side

Boysen-Jensen

Light

Gelatin (permeable)

Mica (impermeable)

Opaque shield over curvature

Trans- parent cap

Opaque cap

Tip removed

Light

Darwin and Darwin

2

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Control

Results

Control (agar cube lacking chemical)

Offset cubes

Growth-promoting chemical diffuses into agar cube

Excised tip on agar cube

3

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CELL WALL

H+ H+

H+ H+

H+ H+

H+ H+

Cell wall-loosening enzymes cleave cross-linking polysaccharides.

Plasma membrane

Cell wall

H2O

Nucleus Cytoplasm Vacuole

Sliding cellulose microfibrils allow cell to elongate. CYTOPLASM H+

Plasma membrane ATP

Proton pump activity increases.

Acidity increases.

Low pH activates expansins.

3

2

1

5

4

5

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(a) Rosette form (left) and gibberellin-induced bolting (right)

(b)   Grapes from control vine (left) and gibberellin- treated vine (right)

6

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Aleurone Endosperm

Water

Scutellum (cotyledon)

Radicle

GA

GA

α-amylase Sugar

7

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Red mangrove (Rhizophora mangle) seeds

Coleoptile

Maize mutant 8

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ein mutant ctr mutant

(b) ctr mutant (a) ein mutant

9

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0.5 mm

Stem Petiole

Abscission layer Protective layer

10

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(a) Before exposure to light (b) After a week’s exposure to natural daylight

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(a)  Light wavelengths below 500nm induce curvature.

(b)  Blue light induces the most curvature of coleoptiles.

White light

Refracting prism

Wavelength (nm)

400 450 500 550 650 600 700

436 nm

Phot

otro

pic

effe

ctiv

enes

s 1.0

0.8

0.6

0.4

0.2

0

12

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Dark Red Red Far-red Dark

Dark (control)

Red Far-red Dark

Results

Red Red Far-red Red Far-red

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Red light

Pr Pfr

Far-red light

Enzymatic destruction

Slow conversion in darkness (some species)

Responses to Pfr: • Seed germination • Inhibition of vertical growth and stimu- lation of branching

• Setting internal clocks • Control of flowering

Synthesis

14

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Noon 10:00 PM

15

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(a) Short-day (long-night) plant

(b) Long-day (short-night) plant

Darkness Flash of light

Light Critical dark period

Flash of light

24 hours

16

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24 hours

Critical dark period

R F R R F R

R F R R

R F R

R

Short-day (long-night)

plant

Long-day (short-night)

plant 17

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(a) Primary root of maize bending gravitropically (LMs)

(b) Statoliths settling to the lowest sides of root cap cells (LMs)

Statoliths 20 µm

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(a) Unstimulated state (leaflets spread apart)

(b) Stimulated state (leaflets folded)

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(a) Control root (aerated) (b) Experimental root (nonaerated)

100 µm

Epidermis

100 µm

Air tubes

Vascular cylinder

22

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Wounding Chemical in saliva

Signal transduction pathway

Recruitment of parasitoid wasps that lay their eggs within caterpillars

Synthesis and release of volatile attractants

1 1

2

3

4

23

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Infected tobacco leaf with lesions

Signal transduction

pathway

Acquired resistance

Systemic acquired resistance

R protein

Avr effector protein

R-Avr recognition and hypersensitive response

Avirulent pathogen

Signal transduction pathway

Hypersensitive response

Signal 4

3 2

5

1

6

7

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