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Plants
9.4 Reproduction in Plants
Flowering and Gene Expression
Flowering involves a change in gene
expression in the shoot apex.
Vegetative structures = roots, stems, and
leaves
When a seed germinates, the young plant is
in the VEGETATIVE PHASE.
Can last for weeks, months, years
Flowering and Gene Expression
Flowering involves a change in
gene expression in the shoot apex.
The change from vegetative to
REPRODUCTIVE PHASE is
marked by the production of the
parts of flowers instead of leaves
by the shoot apical meristems.
Flowers allow for sexual
reproduction.
What is sexual reproduction?
Why is it beneficial? What are its
challenges?
Flowering and Gene Expression
Flowering involves a change in
gene expression in the shoot apex.
What triggers the change from
vegetative to reproductive phase?
Temperature can play a role
Day length
More precisely it is the length of dark
period
Some plants are short-day (ie longnight) plants: Poinsettia
Others are long-day (ie short-night)
plants: Red clover
Why does the length of night
matter?
Flowering and Gene Expression
The switch to flowering is in
response to the length of light and
dark periods in many plants.
Light plays a role in the inhibition or
activation of genes that control
flowering.
Experiments have shown that plants
measure the length of dark periods.
A pigment in leaves of plants is used
to measure the dark…
Called phytochrome
Switches between two forms: PR and PFR
PFR is the active form
Receptor proteins in the cytoplasm are
able to bind PFR not PR
Flowering and Gene Expression
How does the plant use phytochrome
to measure the length of dark?
When PR absorbs red light it is
converted to PFR
When PFR absorbs far-red light it is
converted to PR
In normal sunlight, the red light is
more plentiful, so PR is rapidly
converted to PFR
However, PR is more stable, so in the
dark the PFR slowly converts back to
PR
Flowering and Gene Expression
In “long-day” plants, large amounts of
the PFR remain after the short night.
The binding of PFR to the receptor
promotes the transcription of a
“flowering time” gene (FT).
The FT mRNA is transported in the
phloem to the shoot apical meristem
In the meristem, it is translated into
FT protein.
The FT protein then binds to a
transcription factor.
This binding activates other genes
necessary for flowering to occur.
Flowering and Gene Expression
In “short-day” plants, the binding of
PFR to the receptor inhibits the
transcription of the “flowering time”
gene.
At the end of long nights, very little
PFR remains.
The inhibition fails.
The transcription and translation of
genes needed for flowering are
signalled.
QUESTION:
Contrast the control of flowering in short
and long day plants.
Mutualism between flowers and
pollinators
Most flowering plants use mutualistic
relationships with pollinators in sexual
reproduction.
Sexual reproduction requires the transfer of
pollen.
QUESTION:
List methods of pollen transfer.
State advantages and disadvantages of each.
Mutualism between flowers and
pollinators
Animals that transfer pollen are known as
“pollinators”.
Examples: birds, insects, rodents
Mutualism = a close association between
2 organisms where both organisms benefit.
Question:
Explain how both plants and animals benefit
from this relationship.
Parts of a flower
Draw your version
of the structure of
an animal pollinated
flower
Label and annotate
Discuss how this
structure aligns with
its function.
See pg 431
Pollination, fertilization, and seed
dispersal
Success in plant reproduction depends on
pollination, fertilization, and seed dispersal.
Pollination = is the process by which pollen
is transferred from the anther (male part) to
the stigma (female part) of the plant.
Pollination, fertilization, and seed
dispersal
when pollen has landed on the stigma of a
suitable flower of the same species, a chain
of events happens that ends in the making
of seeds:
A pollen grain grows a tiny tube, all the way
down the style to the ovary.
This pollen tube carries a male gamete to meet
the ovary in an ovule.
Pollination, fertilization, and seed
dispersal
Fertilization = the process during which two
gametes join and their chromosomes
combine, so that the fertilised cell contains a
normal complement of chromosomes.
Pollination, fertilization, and seed
dispersal
The fertilized ovule
goes on to form a
seed,
contains a food store
and an embryo that will
later grow into a new
plant.
The ovary develops
into a fruit to protect
the seed.
Pollination, fertilization, and seed
dispersal
Seeds can not move
themselves, yet often
travel long distances
from the parent plant.
Why?
How?
Pollination, fertilization, and seed
dispersal
Seed dispersal:
Reduces the
competition
between offspring
and parent.
Helps spread the
species.
The structure of seeds
Draw the internal structure of a seed
Label and annotate
See page 434