right © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 33 Control Systems in Plants
May 13, 2015
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Chapter 33Chapter 33
Control Systems in Plants
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
What Are the Health Benefits of Soy?
• Soy protein
– Is one of the few plant proteins that contains all the essential amino acids
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• Phytoestrogens, a class of plant hormones
– Are found in soy
CH3
OH
HO HO
O OH
OHO
Estrogen (Estradiol) Phytoestrogen (Genistein)
Chemical structures of a humanestrogen and a plant phytoestrogen
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• Soy products contain isoflavones
– A type of phytoestrogen that may provide human health benefits
Soybeans
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PLANT HORMONES
33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone
• Plants exhibit phototropism
– The growth of shoots in response to light
Figure 33.1A
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• Microscopic observations of plants
– Indicate that a cellular mechanism underlies phototropism
Shaded side of shoot
Illuminated side of shoot
Light
Figure 33.1B
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Showing That Light Is Detected by the Shoot Tip
• Charles Darwin showed that the tip of a grass seedling detects light
– And transmits a signal down to the growing region of a shoot
Light
Control Tipremoved
Tip covered byopaque cap
Tip coveredby trans-parent cap
Base coveredby opaqueshield
Tip separatedby gelatinblock
Tip separatedby mica
Darwin and Darwin (1880) Boysen-Jensen (1913)
Figure 33.1C
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Isolating the Chemical Signal
• The hormone auxin
– Was determined to affect phototropism
– Promotes faster cell elongation on the shaded site of the shoot
Agar
Shoot tip placed on agar block.Chemical (later called auxin)diffuses from shoot tipinto agar.
Other controls:Blocks with nochemical haveno effect.
Offset blocks withchemical stimulatecurved growth.Control
Block withchemicalstimulatesgrowth.
No light
Figure 33.1D
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33.2 Five major types of hormones regulate plant growth and development
• Even in small amounts, plant hormones
– Trigger signal transduction pathways
– Regulate plant growth and development
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• The major types of plant hormones
Table 33.2
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33.3 Auxin stimulates the elongation of cells in young shoots
• Plants produce auxin (IAA)
– In the apical meristems at the tips of shoots
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• At different concentrations, auxin
– Stimulates or inhibits the elongation of shoots and roots
Figure 33.3A, B
Roots
Stems
0
0.9 g/L
10–8 10–6 10–4 10–2 1 102
Increasing auxin concentration (g/L)
Elo
ngat
ion
Inhi
bitio
n
Pro
mot
ion
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• Auxin may act by weakening cell walls
– Allowing them to stretch when cells take up water
Plasmamembrane
Cellwall H+
1
2H+
3H2O
Vacuole
Cellelongation
Cellulose loosens; cell can elongate
Cellulosemolecule
Cross-linkingmolecule
Enzyme
Cellulosemolecule
Cell wall
Cytoplasm
H+ pump(protein)
Figure 33.3C
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• Auxin promotes growth in stem diameter
– By stimulating the development of vascular tissues and cell division in vascular cambium
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33.4 Cytokinins stimulated cell division
• Cytokinins
– Are produced by growing roots, embryos, and fruits
– Promote cell division
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• Cytokinins from roots may balance the effects of auxin from apical meristems
– Causing lower buds to develop into branches
Figure 33.4
Terminal bud
No terminal bud
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33.5 Gibberellins affect stem elongation and have numerous other effects
• Gibberellins
– Stimulate the elongation of stems
Figure 33.5A
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• Gibberellins
– Stimulate the development of fruit
– Function in embryos in some of the early events of seed germination
Figure 33.5B
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33.6 Abscisic acid inhibits many plant processes
• Abscisic acid (ABA)
– Inhibits the germination of seeds
• The ratio of ABA to gibberellins
– Often determines whether a seed will remain dormant or germinate
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• Seeds of many plants remain dormant
– Until their ABA is inactivated or washed away
Figure 33.6
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• ABA also acts as a “stress hormone”
– Causing stomata to close when a plant is dehydrated
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33.7 Ethylene triggers fruit ripening and other aging processes
• As fruit cells age
– They give off ethylene, which triggers a variety of aging processes
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Fruit Ripening
• Ethylene
– Triggers fruit ripening
1
2
3
Figure 33.7A
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The Falling of Leaves
• A changing ratio of auxin to ethylene
– Is triggered by shorter days
– Probably causes autumn color changes and the loss of leaves from deciduous trees
Leafstalk
Stem(twig)
Abscissionlayer
Protectivelayer
Stem Leaf stalk
LM 2
0
Figure 33.7B
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CONNECTION
33.8 Plant hormones have many agricultural uses
• Farmers use auxin
– To delay or promote fruit drop
Figure 33.8
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• Auxins and gibberellins
– Are used to produce seedless fruits
• A synthetic auxin called 2,4-D
– Is used to kill weeds
– Has safety questions associated with its use