Plants

1
Plants

• 9.4 Reproduction in Plants

2
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

3
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?

4
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 long-night) plants
  Poinsettia
• Others are long-day (ie short-night) plants Red
  clover
• Why does the length of night matter?

5
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

6
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

7
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.

8
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.

9
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.

10
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.

11
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

12
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.

13
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.

14
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.

15
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.

16
Pollination, fertilization, and seed dispersal

• Seeds can not move themselves, yet often travel
  long distances from the parent plant.
• Why?
• How?

17
Pollination, fertilization, and seed dispersal

• Seed dispersal
• Reduces the competition between offspring and
  parent.
• Helps spread the species.

18
The structure of seeds

• Draw the internal structure of a seed
• Label and annotate
• See page 434