Transcript 1d. Plantstaxonomy,reprod,response

Plant hormones
 auxins
 gibberellins
 abscisic acid
 ethylene
 cytokinins
 brassicosteroids
AP Biology
2005-2006
Response to light: Phototropism
 Growth towards light
 Hormone: Auxin
asymmetrical distribution of auxin
 cells on darker side elongate faster
than cells on brighter side

AP Biology
2005-2006
Apical dominance
 Controls cell division &
differentiation

axillary buds do no grow while
apical bud exerts control
shoot
root
AP Biology
2005-2006
Gibberellins
 Family of hormones

over 100 different gibberellins identified
 Effects
stem elongation
 fruit growth
 seed germination

AP Biology
plump grapes in grocery
stores have been treated
with gibberellin hormones
while on the vine
2005-2006
Abscisic acid (ABA)
 Effects
slows growth
 seed dormancy

 high concentrations of Abscisic acid
 germination only after ABA is inactivated down
or leeched out
 survival value:
seed will germinate only
under optimal conditions
 light, temperature, moisture

AP Biology
drought tolerance
 rapid stomate closing
2005-2006
Ethylene
 Ethylene is a hormone gas released by
plant cells
 Multiple effects

response to mechanical stress
 triple response
 slow stem elongation
 thickening of stem
 curvature to stem growth

leaf drop (like in Fall)
 apoptosis

AP Biology
fruit ripening
2005-2006
Apoptosis & Leaf drop
 Ethylene & auxin

many events in plants
involve apoptosis
(pre-programmed cell
death)
 death of annual plant
after flowering
 differentiation of
xylem vessels
What is the
evolutionary
advantage of
loss of leaves
in autumn?
 loss of cytosol
 shedding of autumn
leaves
AP Biology
2005-2006
Fruit ripening
 Adaptation


hard, tart fruit protects
developing seed from herbivores
ripe, sweet, soft fruit attracts
animals to disperse seed
 Ethylene

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
AP Biology
2005-2006
Applications
 Truth in folk wisdom!

one bad apple spoils the whole bunch
 ripening apple releases ethylene to speed
ripening of fruit nearby
 Ripen green bananas by bagging them

with an apple
Climate control storage of apples

AP Biology
high CO2 storage = reduces ethylene
production
2005-2006
Flowering Response
 Triggered by photoperiod


relative lengths of day & night
night length—“critical period”— is trigger
Plant is
sensitive to
red light
exposure
What is the
evolutionary
advantage of
photoperiodism?
AP Biology
Short-day plants
Long-day plants
Synchronizes
plant responses
to 2005-2006
season
Circadian rhythms
 Internal (endogenous) 24-hour cycles
4 O’clock
Noon
Midnight
Morning glory
AP Biology
2005-2006
Response to gravity
 How does a sprouting shoot “know” to grow towards
the surface from underground?

environmental
cues?
 roots = positive
gravitropism
 shoots = negative
gravitropism
 settling of statoliths
(dense starch
grains) may
detect gravity
AP Biology
2005-2006
Response to touch
 Thigmotropism
Mimosa (Sensitive plant)
closes leaves in response to
touch
AP Biology
Caused by changes in
osmotic pressure =
rapid loss of K+ =
rapid loss of H2O =
loss of turgor in cells
2005-2006
Plant defenses
 Defenses against herbivores
AP Biology
2005-2006
Plant defenses
 Defenses against herbivores
coevolution
Parasitoid wasp larvae
emerging from a caterpillar
AP Biology
2005-2006