Transcript PLANT RESPONSES

PLANT RESPONSES
BEGINS
Hello there. I’m John Travolta and I
played the lead in Saturday night
fever. I will be leading the
investigation into how the plants
respond to the environment.
As you may understand, people
respond to my dancing, but I don’t
understand how a plant can respond
to anything. Plants, well they just sit
there.
Plants move John. They just move very
slowly. They can also grow in a particular
direction.
I know that plants grow in
certain directions. You know, like
plants grow toward the light.
Roots always grow into the
ground, but I don’t know how
the plant “knows” how to do it?
You have to first consider that plants do
not have a nervous system like animals.
The plant has to be able to co-ordinate
and respond to the environment. Plants
use HORMONES to exert this control.
Here are the plant hormones. Let’s take
a trip into yesterday to try to remember
the PLANT HORMONE CATEGORIES.
Plant Growth Hormones
Gibberellins
Auxins
Cytokinins
Plant Hormones Inhibition
Ethylene
Ascisic acid
Hey they’re playin’ my song.
Thanks to those Gibb brothers BEE
GEES for the music that made
Saturday Night Fever such a
success.
GIBBERELLINS
GIBB BROTHERS IS GIBBERELLINS
Otherwise know as the BEE GEES
Promote cell division
Promote cell elongation
Promote germination in
seedsHere we
go. I’m
dancin’
now.
Gibberellins cause the
foolish seedling disease or
rice. The rice grows a
taller thinner stalk due to a
fungus that causes more
Gibberellin to be released .
These stems cannot
support the weight of the
seed and topple over.
GIBBERELLINS
Gibberellins
• Family of hormones
– over 100 different gibberellins identified
• Effects
– stem elongation
– fruit growth
– seed germination
plump grapes in grocery
stores have been treated with
gibberellin hormones while on
the vine
AUXINS
We’re oxen.
AUXINS cause growth
Grow stems or roots
Cause plant to grow in
a direction
TROPISMS
We’ll talk about tropisms
later.
How do you like
me now. After
auxin exposure I
grow tall like the
plant toward the
light of the disco
ball.
Stem elongation at low concentrations, but
inhibit stem growth at higher concentrations by
causing ethylene to be released.
AUXINS
Auxin (IAA)
the application of
gibberellins or auxin
may induce the
development of
seedless fruit
• Effects
– controls cell division
& differentiation
– phototropism
Seedless grapes.
That’s what I
like.
• growth towards light
• asymmetrical distribution of auxin
• cells on darker side elongate faster
than cells on brighter side
– apical dominance
CYTOKININS
Cause cell growth
Effect is dependent upon how much
auxin is present Counter apical
dominance of auxin when present
Trimming hedges cuts off the terminal buds and
promotes axillary bud growth. It’s all controlled
by plant hormones. Terminal buds exhibit apical
dominance unless you remove them.
Cutting off the terminal buds means less auxin travels
through the plant to the roots. Without auxin, cytokinins
from the roots take over and cause lateral bud growth.
The plant grows bushier.
ABSCISIC ACID
Lookin’ at inhibitory hormones now
ABA is ABSCISIC ACID.
It is the aging hormone for plants
It keeps plant embryos dormant
Slows the rate of cell growth
Controls opening and closing of stomata
Forms winter buds
We are older now.
I ain’t
no
dancin’
queen
ABSCISIC ACID
Abscisic acid (ABA)
• Effects
– slows growth
– seed dormancy
• high concentrations of abscisic acid
– germination only after ABA is inactivated or leeched out
wash it off to get seeds to germinate
• survival value:
seed will germinate only
under optimal conditions
– light, temperature, moisture
ETHYLENE
Ethylene
Remember we
talked about
ethylene in my
carbon chemistry
lesson
• Hormone gas released by plant cells
• Effects
– fruit ripening
– leaf drop
• like in Autumn
• apoptosis
If you put fruit together that
is ripening, it produces
ethylene that enters the air
and ripens the other fruit
around it.
Where Found in Plant
Major Functions
Auxin
Embryo of seed, young leaves,
meristems of apical buds
Stimulates cell elongation; involved in
phototropism, gravitropism, apical domincance,
and vascular differentiation; inhibits abscission
prior to formation of abscission layer; stimulates
ethylene synthesis; stimualtes fruit development;
induces adventitious roots on cuttings
Cytokinin
Synthesized in roots and
transported to other organs
Stimulates cell division, reverse apical
dominance, involved in shoot growth, delay leaf
sequence
Ethylene
Tissues of ripening fruits, nodes
Stimulates fruit ripening, leaf and flower
of stems, senescent leaves and
senescence, and abscission
flowers
Abscisic Acid
Leaves, stems, green fruit
Stimulates stomatal closure
Gibberellin
Meristems of apical buds and
roots, young leaves, embryo
Stimulates shoot elongation, stimulates bolting
and flowering in biennials, regulates production
of hydrolytic enzymes in grains
Now let’s take a look at plant tropisms
POSITIVE TROPISM – Plant grows toward the
stimulus
NEGATIVE TROPISM – Plant grows away from the
stimulus
PHOTOTROPISM- plant response to light
Positive phototropism shoots
grow toward light
Negative phototropism roots
grow away from light.
Plants respond to gravity
GRAVITROPISM
Positive gravitropism roots grow
down with gravity.
Gravity detected by plant statoliths
Thigmotropisms involve growth in
response to touch.
THIGMOTROPISM- plants respond to
touch
Coiling results from differential growth of
tendrils of climbing plants
TURGOR movements of water can cause
movements of plants that respond in a
more rapid manner
Sensitive plant
Mimosa pudica
Plants can also respond to:
DROUGHT- adjust transpiration rates
FLOODING –root cells need oxygen, water deprives them of
it. Root cortex undergoes apoptosis to produce air tubes to
act as “snorkels”
SALT STRESS- - root cell permeability changes due to
production of organic solutes in roots.
HEAT STRESS -special proteins
COLD STRESS- increased lipids in membranes
HERBIVORE DEFENCE- compounds to attract predator
insects- bad tasting/toxic chemicals- needles..etc
SUNLIGHT TIME
Photoperiodism –response to day and night length.. coordinate seasonal events, flowering time for cross
pollination, seed germination, bud dormancy
Chromophore changes isomeric form from Pr to Pfr with
light exposure --But not far red light.
Short day plants flower as days get shorter – summer
flowers
Long day plants flower as days get longer– spring flowers
VERNALIZATION seed needs to be pretreated with cold
before seed germination.
Plant Circadian
Rhythms24hr cycle not
paced by environment.
Phytochrome and
cryptochrome blue-light
receptors adjust the cycle.
Short day plants are
really long night plants.
Don’t interrupt the
darkness or the plant
will not flower.
There is evidence of a
flowering hormone that
is yet to be chemically
identified.
PLANT RESPONSE
ENDS