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Regulation of
Plant Growth and Development
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Growth in Animals
 Animals grow throughout the whole
organism

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many regions & tissues at different rates
Growth in Plants
 Specific regions of growth: meristems
stem cells: perpetually embryonic tissue
 regenerate new cells

 apical shoot meristem
 growth in length
 primary growth
 apical root meristem
 growth in length
 primary growth
 lateral meristem
 growth in girth
 secondary growth
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Apical meristems
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shoot
root
Root structure & growth
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protecting the meristem
Shoot growth
 Apical bud & primary
growth of shoot
region of stem growth
 axillary buds

 “waiting in the wings”
protecting the meristem
Young leaf
primordium
Apical meristem
Older leaf
primordium
Lateral bud
primordium
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Vascular tissue
Primary
xylem
Growth in woody plants
Primary
phloem
 Woody plants grow in
Epidermis
height from tip


Lateral
meristems
primary growth
apical meristem
 Woody plants grow in
diameter from sides


secondary growth
lateral meristems
Primary
phloem
Secondary
phloem
Secondary
Primary xylem
xylem
 vascular cambium
 makes 2° phloem & 2° xylem
 cork cambium
 makes bark
Annual
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growth
layers
Bark
Secondary growth
 Secondary growth

growth in diameter
 thickens & strengthens older part of tree

cork cambium makes bark
 growing ring around tree

vascular cambium makes xylem & phloem
 growing ring around tree
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Vascular cambium
Why are early
& late growth
different?
 Phloem produced to the outside
 Xylem produced to the inside
bark
cork
cambium
phloem
xylem
vascular
cambium
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late
early
last year’s xylem
cork cambium
Woody stem
How old is
this tree?
vascular cambium
late
early
3
2
1
xylem
phloem
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bark
Tree trunk anatomy
tree girdling
What does girdling
do
to a tree?
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Aaaargh!
Murderer!
Arborcide!
Plant hormones
 auxin
 gibberellins
 abscisic acid
 ethylene
 cytokinins
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Auxin (IAA)
 Effects
controls cell division
& differentiation
 phototropism

 growth towards light
 asymmetrical distribution of auxin
 cells on darker side elongate faster
than cells on brighter side

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apical dominance
Auxin on roots
Used as “rooting hormone”
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Cytokinins
-made in roots and travel upwards
Effect of cytokinins
and lack of auxin
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Gibberellins
 Family of hormones

over 100 different gibberellins identified
 Effects
stem elongation
 fruit growth
 seed germination

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plump grapes in grocery
stores have been treated
with gibberellin hormones
while on the vine
Gibberellins
- Made in apical meristems (roots and shoots) and
developing seeds
-shows effect of ‘”bolting” of flower producing stem
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Gibberellins
- Made in apical meristems (roots and shoots) and
developing seeds
-shows effect of ‘”bolting” of flower producing stem
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Abscisic acid (ABA)
 Effects
slows growth
 stimulates closing of
stomata (K+transport out of guard cells)
 seed dormancy

 high concentrations of abscisic acid
 germination only after ABA is inactivated or
leeched out
 survival value:
seed will germinate only
under optimal conditions
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 light, temperature, moisture
Ethylene
 Hormone gas released by plant cells
 Effects
fruit ripening
 leaf drop

 like in Autumn
 apoptosis
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Fruit ripening
 Adaptation


hard, tart fruit protects
developing seed from herbivores
ripe, sweet, soft fruit attracts
animals to disperse seed
 Mechanism

triggers ripening process
 breakdown of cell wall
 softening
 conversion of starch to sugar
 sweetening

positive feedback system
 ethylene triggers ripening
 ripening stimulates more ethylene production
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Tropisms
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Negative gravitropism
Positive gravitropism
Unequal distribution of organelles
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Thigmotropism
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Sudden movements caused by sudden release of K+
Response is transmitted to
other leaves via action
potentials
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Circadian
Rhythms
May be related
to cyclic
concentrations
in a transcription
factor
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Photoperiod and control of flowering
Relative length of day and night
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Red is most effective in interrupting flowering
A flash of far red can reverse the effect of red
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Phytochromes photoreceptors that function in a plants
response of flowering, germination
Have 2 forms: 1 absorbs red light (Pr), the other far red
light (Pfr)
Sunlight has high amount of red light
cytochrome in Pfr by sunset
Need minimum amount of night to covert back
to Fr to trigger flowering
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