Auxin - Herscher CUSD #2
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Transcript Auxin - Herscher CUSD #2
Growth Responses and Regulation of Growth
CHAPTER 11
GROWTH & DEVELOPMENT
Growth- the increase in size of a plant
Development- the gradual changes over the life
of the plant
Both are controlled by
Genetics
Hormones
(ex. Auxins, gibberellin…)
Environment (ex. Tropism)
WHAT ARE HORMONES?
Organic compounds that act as chemical
signals between cells
Regulate growth & development
5 MAJOR CLASSES OF PLANT HORMONES
5.
Auxin
Gibberellin
Cytokinin
Ethylene
Abscisic Acid
Basically, these are just signaling molecules
1.
2.
3.
4.
AUXIN
Hormone involved in
Stem
elongation
Apical
dominance (inhibition of lateral growth)
Encourages
Helps
root formation on cuttings
plant grow towards light
Targets
cells that are not reached by light (in shade)
Responsible
for Phototropism
Animation
AUXIN AND PHOTOTROPISM
Coleoptile = the
first leaf of a
monocot seedling
AUXIN AND ROOT DEVELOPMENT
Control
(roots placed in water)
LOW AUXIN
CONCENTRATION
HIGH AUXIN
CONCENTRATION
GIBBERELLIN
Hormone involved in
Stem
elongation
Flowering
Seed
germination
EFFECTS OF GIBBERELIN
CYTOKININ
Hormone involved in
REQUIRED
Delay
FOR CELL DIVISION!!!
of senescence (aging)
Interacts
with auxin in the control of apical
dominance (encouraging primary growth)
HORMONES AND TISSUE CULTURE
CYTOKININ AND
SENESCENCE
ETHYLENE
A gaseous plant hormone involved in
Leaf
abscissions (the normal falling off of
leaves/fruits/flowers)
Ripens
fruits
Weakening
Leaf
cell walls during autumn
senescence (aging)
ETHYLENE AND FRUIT RIPENING
ABSCISIC ACID
Plant Hormone involved in
Dormancy
(temporary state of arrest/growth does
not occur)
Response
Ex.
to stress
Drought – triggers closing of stomata
PHOTOPERIODISM
The response of a plant to the relative lengths of
daylight and darkness (such as flowering)
Short-day plants (long night)
Flower
when the night length is = or > ~ 12 hours
Late Summer or fall
Intermediate-day plants
Do
not flower when day is either too long or too short
Spring or Fall
Long-day plants (short night)
Flower
when night length is = or < 12 hours
Late spring or summer
Day-neutral plants
photoperiod
does not affect flowering
TEMPERATURE AND REPRODUCTION
Vernalization
The
low-temp requirement for flowering in some
plant species
Some plants need to be exposed to low temp for
several weeks for flowering to occur after seeds
germinate and grow
Example of plant with low T requirement:
Winter
Wheat:
planted in fall and germinates.
Seedlings exposed to cold winter
Flower after resuming growth in spring
TEMPERATURE REQUIREMENTS
TROPISM
A tropism is a directional growth response
Permanent change in position
3 types of tropism
Phototropism
- Stimulus photo = “light”
Gravitropism – Stimulus grav = “weight”
Thigmotropism – Stimulus thigmo = “touch”
TROPISMS
PHOTOTROPISM
Directional
GRAVITROPISM
Plant
growth of a plant caused by light
growth in response to direction of gravity
THIGMOTROPISM
Growth
in response to contact with a solid object