how do plants respond to the environment?
TRANSCRIPT
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Plant Response to the Environment
Today�s topics: • Finish water transport
• Phloem pushes water and sugars from sources to sinks
• Plants are dynamic (but slow) • Time-lapse videos of plant
movements
• Plant hormones – Auxin – Gibberellin – Cytokinin – Ethylene – ABA – & others
10 November 2021
Movement in the Phloem
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2
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1
2
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Vessel (xylem)
Sieve tube (phloem)
Uptake of water
Unloading of sugar
Sink
Sucrose
H2O
H2O
Bul
k flo
w b
y ne
gativ
e pr
essu
re
H2O Sucrose
Bul
k flo
w b
y po
sitiv
e pr
essu
re
Osmotic pressure drives
bulk flow of water and
sugars
Source (leaf)
Active transport of sucrose
How do plants respond to the environment?
http://i.imgur.com/B9M7Wck.jpg
Link to �Plants in Motion� Videos http://plantsinmotion.bio.indiana.edu/plantmotion/starthere.html
(from another textbook) Auxin
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Figure 39.5
Control
Light
Shaded side
Illuminated side
Boysen-Jensen
Light
Light
Darwin and Darwin
Gelatin (permeable)
Mica (impermeable)
Tip removed
Opaque cap
Trans- parent cap
Opaque shield over curvature
RESULTS
Control
RESULTS
Excised tip on agar cube
Growth-promoting chemical diffuses into agar cube
Control (agar cube lacking chemical)
Offset cubes
Auxin causes shoot cells to
expand
Auxin and Cell Expansion
Acid-growth hypothesis
Figure 39.7
Cell wall before auxin activates proton pumps
Cellulose microfibrils
Nucleus Vacuoles PLANT CELL WALL
Cellulose microfibril Cross-linking polysaccharide
Loosening of cell wall, enabling elongation
Auxin increases activity of proton pumps.
H+
H+
H+
Low pH activates expansins (red).
H+ H+
Elon
gatio
n
H+
H+ H+
H+
H+
H+
H+
H+
Polysaccharides are cleaved by cell wall-loosening enzymes (purple), loosening the microfibrils (brown).
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Auxin Transport
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Gravitropism
http://botit.botany.wisc.edu/Interface/web-lessons/Physiology/pos_gravitropism.html
Effects depends on dosage and tissue Herbicide 2,4D is an Auxin Rooting powder is also an Auxin
Often, the Ratio
of hormones is important
http://users.ugent.be/~pdebergh/pri/pri4et07.htm
Auxin mg/l
Cytokinin mg/l
(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
Auxins and Cytokinins interact Auxins and Cytokinins interact
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Ethylene is a ripening hormone
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