[2] Lecture 2

• Collective male reproductive parts of a flower

  Microsporophyll or androecium
• Collective female reproductive parts of a flower

  Megasporophyll or gynoecium
• Where male gametophytes are produced

  Anthers
• Where female gametophytes are produced

  Ovary, specifically in the ovule
• Male gametophyte = 2 – 3 cells

  Female gametophyte = 6 – 13 cells
• Label this pollen grain

  A) Generative Nucleus

  B) Pollen tube nucleus

  C) Pit

  D) Exine thick, outer sculptured wall

  E) Intine thin inner wall

  
• Label this ovary

  A) Raphe

  B) Hilum

  C) Funicle

  D) Chalaza

  E) Nucleus

  F) Antipodals

  G) Embryo Sac

  H) Secondary Nucleus

  I) Egg Cell

  J) Synergids

  K) Outer integument

  L) Micropyle

  M) Inner integument

  
• Microsporogenesis is the formation of microspores within the anther

  Microgametogenesis is complete upon the formation of sperm
• Microsporangia are found in the anther lobes (usually 4 per anther)
• Each microsporangium is surrounded by 4 wall layers:

  1. Epidermis
  2. Endothecium
  3. Middle layer
  4. Tapetum
• Innermost cell layer of the microsporangium

  Tapetum
• Tapetum

  • Nourishes developing pollen
  • Multinucleate cells
  • Produces enzymes like callase
  • Structural proteins - sporopollenin
• Microsporocytes

  • Microspore mother cells
  • Pollen mother cell
  • Diploid
  • Produced in the sporangia within the anther
• Microspore mother cells


  Microsporocytes
• Meiosis of microsporocyte results in 4 haploid microspores

  • Held together by callose wall
• Each micropore is surrounded by a callose wall
• Enzyme that dissolves callose

  Callase
• Angiosperms and gymnosperms are heterosporous

  • Microspores (male)
  • Megaspores (female)
• The action of anther walls is controlled by the endothecium
• Stage wherein flowers are open and fertile

  Anthesis
• Pollen Mitosis I

  • Asymmetric mitotic cell division
  • Generates the vegetative and generative cell
• The generative cell is engulfed within the cytoplasm of the vegetative cell
• Vegetative cell

  • Contains the bulk of the cytoplasm
  • Contains and nurtures the generative cell
  • Gives rise to the pollen tube
  • Arrests cell cycle in G1
• Gives rise to the pollen tube after pollination

  Vegetative cell
• The vegetative cell produces substances needed for pollination and pollen tube growth:

  1. Carbohydrates, lipids
  2. Transcripts or proteins for rapid pollen tube growth
  3. Osmoprotectants (disaccharides, proline, glycine-betaine)
• Identify the vegetative and generative cell

  A) Vegetative

  B) Generative

  
• Pollen Mitosis II

  • Generative cell located within the cytoplasm of the vegetative cell
  • Chromatin is condensed
  • Sperm cells are now within the cytoplasm of the vegetative cell

  
• Identify the stage of pollen mitosis:

  Pollen Mitosis II

  
• Bicellular pollen is shed when PMII occurs after pollination or in the pollen tube (60% of angiosperms)
• Tricellular pollen is shed when PMII occurs in the anther (40% of angiosperms)
• Exine – outer layer composed of sporopollenin

  Intine – inner layer composed of cellulose and pectin

  
• Uninucleate stage of pollen (1N)

  Microspore
• Pollen sacs (thecae)

  Microsporangium
• Entire stamen (2N)

  Microsporophyll
• The production of haploid microspores via meiosis

  Microsporogenesis
• T or F: Microsporogenesis is the production of gametes

  False
• Pollination occurs when pollen contacts the stigma
• The pollen tube grows through a germ pore in the pollen wall
• The pollen tube grows down through the style