Skip to main content

Chapter 39

Reproduction in plants

  • Most flowering plants display sexual reproduction
    • Two gametes fuse to produce offspring with a unique combination of genes
  • They undergo Alternation of Generations 
    • Two multicellular life cycle stages
    • diploid
      • Spore producing sporophyte
        • produces spores by meiosis
          • a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.
    • haploid
      • Gamete producing gametophyte
        • produces gametes by mitosis
          • a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
  • Egg is Female
  • Sperm is Male

Screenshot-from-2019-02-27-20-43-03.png

Evolutionary Trends in the Plant Kingdom

  • Sporophyte has become larger, more complex
    • Flowering plants
      • Sporophyte independent 
      • Dependent gametophyte is only a few cells contained within flowers
  • Gametophyte has become smaller, less complex
    • Moss
      • Sporophytes small and dependent on gametohyte (Dominant form)
  • Female
    • 7 cells
  • Male
    • 2-3 cells

Screenshot-from-2019-02-27-20-48-43.png

Flower and Sexual Cycle

  • Flowers
    • ONLY in angiosperms
    • All sizes, shapes, colors, and aromas
  • Essential process of Sexual reproduction occurs within flowers
    • Meiosis/cytokenesis
      • reduces chromosome number
    • Syngamy (fertilization)
      • restores chromosome number

"Ideal" Flower

  • Uses highly modified leaves arranged in whorls (circular) at the tip of a highly modified stem
  • A flower is a highly modified determinate (short term) shoot system

Screenshot-from-2019-02-27-21-31-46.png

  • Pedical, receptical, 4 sets of highly modified leaves are all 2N and part of the sporophyte generation
  • Pollen (sperm) and eggs of embryo sac are part of the 1N generation
  • Pedical
    • flower stalk
  • Recepticle
    • tip of modified stem with 4 whorls attached

Sexual Cycle

Screenshot-from-2019-02-27-21-34-37.png

Screenshot-from-2019-02-27-21-37-45.png

Male

  • Pollen formation
    • occurs within the anther of stamen
  • Anther
    • Bilobed with 2 pollen chambers per lobe

922bc112d7d7f455d12aa057c7c9ce47.jpg

  1. 2N microspore mother cell
  2. meiosis/cytokenesis
  3. 4 1N microspores
  4. Each: mitosis/cytokenesis
    unequal and incomplete
  5. 1N Generating cell
    1N Tubecell

Male Gametophyte

Screenshot-from-2019-02-27-22-15-33.png

Pollination

  • Transfer of pollen from the anther to the stigma
  • Self-pollination
    • Transfer with the same flower or between flowers on the same plant
                                                                •  
  • Cross-Pollination
    • Transfer between  flowers of other plants
Pollinating Agents

Mechanisms utilized for transfer of pollen

  1. Wind
    • small/lightweight pollen
  2. Water
    • Transfer with a few aquatic plants
  3. Animals
    • Majority of plants
    • Utilized as a "trick and reward" system
    • nectar, colors, and aromas to attract animals

Female

Ovule Development

  • Ovule
    • future seed
  • Enclosed within the ovary of pistol  (carpel)
  • One to many ovules per ovary
    • ovary will become fruit
  • Ovule attached to central axis or to wall of hollow fruit
    • always enclosed
    • angiosperms
  • within ovule is 1 large 2N cell
    • megaspore mother cell

20190227_222436.jpg

  1. 2N megaspore mother cell
  2. meisos/sytokenesis
  3. 4 1N Megaspores
  4. 3 degrade
  5. 2N Functional megaspore
  6. Series of 3 mitosis/cytokenesis cycles
    Incomplete and unqueal
  7. 7-celled embryo sac
    8 nuclei

Female gametophyte

 

embryo-sac.gif

Screenshot-from-2019-02-27-22-15-55.png

  • 1N Functional megaspore
    • 3 mitosis/cytokenesis divisions
  • One cell with 1 nucleus becomes 8 nuclei but only 7 cells

Embryo sac

  • 8 nuclei, 7 cell structure
  • female gametophyte
  • 3 antipodal cells (1N)
    • opposite end from micropyle
  • 1 central cell with 2 large 1N polar nuclei
  • 2 Synergids (1N)
    • Micropyle end on outside
  • 1 egg (1N)
    • Middle at micropyle end

Syngamy (fused gametes)

  • 1N egg + 1N sperm = 2N zygote (single fertilized egg)
  • Pollen grain germination
    • tube cells form pollen tube (delivers sperm)
    • generative cell divides by mitosis/cytokenesis to produce 2 sperm

Screenshot-from-2019-02-27-22-45-54.png

  • Pollen tube enters micropyle
    • digests tube cell nucleus
  • Pollen tube enters one synergid
    • releases it's content (sperm)
    • synergid ruptures
    • mycropyle closes

 

  • "Double fertilization" (double fusion)
    • 1N egg +1N sperm = 2N zygote
    • 1N sperm +2 1N polar nuclei = 3N primary endosperm cell

 

  • Post fertilization with ovule
  • 2N zygote grows by mitosis/cytokenesis into 2N multicellular embryo
  • 3N primary endosperm cell grows by mitosis/cytokenesis into 3N multicellular endosperm
    • nutrient tissue for embryo

 

  • Ovule/ovary with 2N zygote  mature/enlarges with sugars/H2O into a fruit (mature ovary) with enclosed seeds (mature ovules)
  • Seed dispersal (seeds enclosed withing a fruit)
  • agents
    • wind
    • water
    • animals - majority

Seed germination

  • Seed with 2N embryo enters period of dormancy
  • dormancy broken by a combination of internal (hormones) and external factors (environmental)
  • radical (first root) emerges and grows down
  • shoot emerges and grows up
Back to top