Transcript Slide 1

PLANT RESPONSES
US 8934 Relate
aspects of
plant responses
to
environmental
factors
Contents:
Environment
Plant Movements
Phototropism
Tropism Mechanism
Other Tropisms
AND
Nastic Responses
Hormones
Timing
AS 90716
Describe
animal
Behaviour and
Plant
Responses to
Environmental
factors
Plant Rhythms
Flowering
Phytochrome
More Phytochrome
Plant Relationships
ENVIRONMENT
The environment of an organism is made up of all of the factors
that affect it. A habitat is a zone with a certain range of factors,
such as a savannah.
An organism has adaptations that help it survive in its habitat.
The better adapted it is, the more chance it has of successful
reproduction – survival of the fittest.
Biotic Factors:
Abiotic Factors:
Intraspecific
Light
Competition
Water
Cooperation
Wind
Aggression
Humidity
Reproduction
Nutrients
Interspecific
Gravity
Competition
Temperature
Exploitation
Mutualism
Commensalism
PLANT RESPONSES
Plants can move to respond to the environment.
There are two types of movement…
TROPISMS are growth responses, and act in a direction
relative to the stimulus (positive or negative).
NASTIC RESPONSES are fast, reversible movements and
are non-directional.
The stimuli for
This is
growth may be:
called a:
For instance:
Light
Photo
the opening
and closing of
Water
Hydro
flowers during
Nasty
Gravity
Gravi/Geo
the day is a
or
type of…
Chemicals
Chemo
Tropism
Photonasty
Touch
Thigmo
Manual pg 178/9
Temperature
Thermo
PHOTOTROPISM
A well-studied example of a tropism is Phototropism. Many
experiments have been done using coleoptiles (growing
shoots).
What is the adaptive advantage of this response?
Increased light… more photosynthesis.
Check out some time-lapse footage of TROPISMS.
POSSIBLE TROPISM MECHANISM
An explanation for what is happening inside the plant is that a
hormone called auxin (or IAA – indoleacetic acid) controls the
elongation of cells.
Light breaks
down auxin on
the sunny side.
Cells on the shady side
elongate more – plant
bends.
Auxin sent out from
the tip – encourages
cell elongation.
Manual pg 180
AUXIN
Auxin has a number of functions, and
can affect different cells in different
ways.
Auxin naturally moves down the plant
due to gravity and so collects on the
lowest surfaces of stems and roots.
In the stem it promotes cell elongation,
leading to negative geotropism.
In the roots it inhibits elongation →
positive geotropism.
As it comes from the tip, the concentration decreases
down the plant. In high conc. It inhibits lateral buds, in
lower conc. It promotes the buds. This leads to apical
dominance.
Removing the tip of a plant makes it grow bushy.
OTHER TROPISMS
What is the advantage of this?
Stem: Gets light, PS, reproduce more
Roots: Gain water, nutrients, stability.
Name
Hydrotropism
Mechanism
Roots are positively
hydrotropic
Thigmotropism Some stems are positively
thigmotropic and grow
around other objects
Chemotropism Roots, either positive or
negative
Advantage
Collect more water
Increased light
without energy
output on structure
Gain or avoid
chemicals
Manual pg 181
NASTIC RESPONSES
They provide much faster response to a stimulus than tropisms.
They are often controlled by water (turgor) pressure.
Some examples are:
The opening and closing of stomata
Sleep movements (leaf droop at night time)
The opening and closing of flowers during the day
Check out some time-lapse footage of NASTIC RESPONSES
(esp. 1st three and last one - sunflower nutation)
Manual pg 182
HORMONES
Plant hormones (unlike animals’) can produce a number of
responses, many of which overlap, and interact with other
hormones to promote or inhibit them, depending on the conditions.
Some of the main aspects of each type…
Auxins (IAA)
Cytokinins
Gibberellins
Abscissic acid
(ABA)
Ethylene (Ethene)
Role
Promote cell
elongation in
stems, inhibit in
roots. (And
others)
Cell division,
lateral bud
growth.
Inhibits leaf
drop.
Stem
elongation.
Promotes leaf fall
abscission).
Inhibits some
other hormones,
and germination,
closes stomata in
drought.
Promotes fruit
ripening, abscission
of fruit leaves and
flowers.
Place Transport
Growing points
(tips)
Root tips,
unripe fruit
Growing
points (tips)
All over.
All over (aging /
damaged areas)
From shoot and
root tips to other
places by active
transport.
Through
Xylem and
Phloem
Through
Xylem and
Phloem
Through Xylem
and Phloem
Diffusion
Normal growth
Fast growth
Protection
Ripening
Manual pg 183/4
TIMING
Both plants and animals need to be able to detect time in order to
coordinate activities in appropriate conditions.
There are a number of environmental cues.
These include astronomically caused cycles, such as...
•
The earth orbiting the sun (seasons) “circannual”
•
The Moon orbiting the Earth (phases of the moon) “circalunar”
•
The Earth spinning on its axis (day/night) “circadian”
Manual pg 187
PLANT RHYTHMS
A plant’s “Biological Clock” is controlled by either:
endogenous factors (inside the plant – genetic)
exogenous factors (outside the plant) – environmental
Some circadian rhythms are: flower opening and closing, leaf tilt,
stomata opening and closing, and sun tracking.
Some seasonal rhythms are:
acclimation
dormancy
vernalisation
stratification
Find definitions for these on
page 196 of the manual.
Most seasonal rhythms are in response to temperature, moisture
or photoperiod.
Manual pg 195
FLOWERING
Flowering (as well as a number of other responses) is controlled by
the phytochrome system.
Leaf
Detects light
Flower bud
Begins
development
Message sent with
hormone called
Florigen (theoretically).
Phytochrome has 2 forms:
Fast with red light
(from the sun)
Pr
Pfr
Slow overnight
Pr is “phytochrome red”
Pfr is “phytochrome far-red”
PHYTOCHROME SYSTEM
Fast with red light
(from the sun)
After a long night
(winter) there will
be lots of Pr.
Pr
Fast with far red
light
Pfr
Slow overnight
After a short
night (summer)
there will still be
lots of Pfr left.
Pfr → Pr can also be achieved quickly (for experimental purposes)
by using far-red light (hence it’s name).
Pfr promotes flower growth in long-day (summer) plants.
Pfr inhibits flower growth in short-day (winter) plants.
Day neutral plants tend to flower all of the time.
Confused?
DON’T PANIC!
MORE ON PHYTOCHROME
Some experiments on the phytochrome system:
Long day
plant
Short day
plant
Manual pg 197-8
PLANT RELATIONSHIPS
Plants compete with other plants for resources, such as light,
water, and minerals. Plants can reduce competition by
producing chemicals that harm other species. This is called
allelopathy.
Some plants also protect themselves from herbivory by using
spines, waxy cuticles, hard seed coats, and divaricating habit.
They may also produce chemicals that are toxic or unpalatable
to animals. In response, some animals have produced a
resistance to these chemicals (coevolution).
Plants may also undergo commensalism, mutualism or
parasitism.
GERMINATION
Why don't tomato (and other) seeds germinate when they are still
in the fruit?
Perhaps there is some sort of chemical inhibition going on that
stops the seed growing until it has been eaten or the fruit has
rotted down.
The plant practical on tomato seed germination.
GERMINATION PRAC. RESULTS
%
Germ.
Ave.
seedling
length
(mm)
60
Average seedling length
Conc.
of
juice
50
40
30
20
0
100
50
5
100
27
10
80
13
15
90
7
20
90
10
120
25
100
5
100
30
40
5
80
50
30
2
75
10
1
100
0
0
10
0
0
5
10
15
20
25
30
50
75
100
50
75
100
% Germ.
Conc. of Juice
60
40
20
0
0
5
10
15
20
25
Conc. of juice
30