Plant Embryolgy

• Anther


  A structure in the flower that contains the pollen sacs
• Pollen


  The male reproductive cells produced in the anther
• Anther type


  • Number of microsporangia per anther
  • Microsporangia are typically tubular in shape and occur in pairs, which coalesce during development by the breakdown of the cell layers between them
  • Each pair of microsporangia is termed a THECA
• Bithecal/Tetrasporangiate


  Angiosperms with two thecae
• Monothecal/Bisporangiate


  Angiosperms with only one theca (e.g. Malvaceae, Cannacaea, Marantaceae and species of Salvia (Lamiceae))
• Anther wall development


  • Outer most cell layer is the ENDOTHECIUM, which typically consists of enlarged cells with secondary wall thickenings functioning in anther dehiscence
  • Innermost cell layer is the TAPETUM, which consists of metabolically active cells that function in the development of pollen grains
  • Early in development an anther contains two layers of cells, an outer epidermis and an inner layer of primary parietal cells
• Anther wall development


  Cells of the primary parietal layer divide tangentially (parallel to the outer surface) to give rise to two layers of cells, secondary parietal cells
• Types of anther wall development

  • Basic - Both secondary parietal cell layers divide to yield two middle layers
  • Dicotyledonous - Only the outer secondary parietal cell layer divides to yield the endothecium and a single middle layer
  • Monocotyledonous - Only the inner secondary parietal cell layer divides to yield the tapetum and a single middle layer
  • Reduced - The secondary parietal cells do not divide further and develop directly into the endothecium and tapetum
• Types of tapetum


  • Secretory - The tapetum remains intact with no breakdown of cell walls
  • Amoeboid (Plasmodial/Periplasmodial) - The tapetal cell walls break down, with release of the cytoplasm of the tapetal cells into the locule
• Types of endothecial cells

  • Girdling endothecium - The secondary wall thickenings form rings with cross bridges between them
  • Spiral endothecium - The secondary wall thickenings are spiral or helical in shape
• Ovule


  The immature seed, consisting of a stalk (funiculus), a megasporangium (also called the nucellus), and one or two surrounding integuments
• Micropyle


  The pore or canal within one or more integuments through which (in angiosperms) a pollen tube traverses prior to fertilization
• Micropylar region


  The region of the nucellus where the micropyle is located
• Chalazal region


  The region of the nucellus opposite the micropyle
• Raphe


  The region where the funiculus is adnate (or decurrent) to the nucellus
• Nucellus type


  • Crassinucellate - The parietal cell undergoes additional mitotic divisions, the products of which form an inner layer of nucellus cells
  • Tenuinucellate - The archeal cell does not divide and develops directly into the megasporocyte, the nucellus will generally be composed of a single layer of cells, the original outer layer
  • Pseudocrassinucellate - No parietal cell is formed, yet periclinal divisions occur in the single outer layer, forming an additional inner layer of nucellar cells
• Megasporogenesis


  The development of megaspores from the megasporocyte, the cell that undergoes meiosis
• Patterns of megasporogenesis


  • Monosporic - The four megaspores are produced, only one of them contributes to the female gametophyte
  • Bisporic - One of the binucleate cells, containing two megaspore nuclei, contributes to the female gametophyte
  • Tetraporic - All four haploid megaspore nuclei contribute to the female gametophyte
• Megagametogenesis


  The development of the female gametophyte from the haploid product(s) of meiosis
• Bitegmic


  Ovules with two integuments
• Unitegmic


  Ovules with one integument
• Ategmic


  Ovules that lack any integument
• Micropyle types


  • Amphistomal - In a typical, bitegmic angiosperm ovule, the micropyle is typically formed or delimited by both integments
  • Endostomal - The micropyle is delimited by only the inner integument (the outer one being foreshortened)
  • Exostomal - The micropyle is delimited by only the outer integument (the inner one being foreshortened)
  • Zig-zag - The micropylar pore of the outer integument is spatially displaced relative to the inner integument
  • Unistomal - The ovule is unitegmic
• Ovule types


  • Anatropous - Curvature during development results in displacement of the micropyle to a position adjacent to the funiculus base; a vasculature strand traverses from the base of the funiculus to the nucellar region opposite the micropyle
  • Orthotropous [atropous] - No curvature takes place during development; the micropyle is positioned opposite the funiculus base, and the vasculature traverses from the base of the funiculus to the chalazal nucellar region
  • Amphitropous - The nucellus is bent along both upper and lower sides
  • Campylotropous - The nucellus is bent only along the lower side
• Ana-amphitropous


  A vascular strand curves, traversing from the base of funiculus to the chalazal region of the nucellus; the nucellus is bent sharply in the middle along both the lower and upper sides, often with differentiated cells (called a "basal body") at the angle of the bend
• Ana-campylotropous


  Similar to the ana-amphitropous type in vasculature, differing in that the nucellus is bent only along the lower side, with no "basal body"
• Ortho-amphitropous


  The vasculature is straight, leading from the funiculus base to the middle of the nucellus; the nucellus is bent sharply in the middle along both the lower and upper sides
• Amphitropous ovule


  • Nucellus is bent only along the lower side
• Campylotropous ovule


  • Nucellus is bent only along the lower side
• Four ovule types


  • Ana-amphitropous
  • Ana-campylotropous
  • Ortho-amphitropous
  • Ortho-campylotropous
• Ana-amphitropous ovule


  1. Vascular strand curves, traversing from the base of funiculus to the chalazal region of the nucellus

  2. Nucellus is bent sharply in the middle along both the lower and upper sides

  3. Often has differentiated cells (called a "basal body") at the angle of the bend
• Ana-campylotropous ovule


  1. Similar to ana-amphitropous in vasculature

  2. Nucellus is bent only along the lower side

  3. No "basal body"
• Ortho-amphitropous ovule


  1. Vasculature is straight, leading from the funiculus base to the middle of the nucellus

  2. Nucellus is bent sharply in the middle along both the lower and upper sides

  3. Often has a "basal body" present
• Ortho-campylotropous ovule


  1. Similar to ortho-amphitropous

  2. Nucellar body is bent only along the lower side

  3. No "basal body"
• Ovule position


  • Epitropous (micropyle points distally)
  • Hypotropous (micropyle points proximally)
  • Pleurotropous (micropyle points to the side)
  • Heterotropous (varies in orientation)
• Epitropous ovule


  • Micropyle points distally
  • Can be further divided into epitropous-dorsal (raphe is dorsal) or epitropous-ventral (raphe is ventral)
• Hypotropous ovule


  • Micropyle points proximally
  • Can be further divided into hypotropous-dorsal (raphe is dorsal) or hypotropous-ventral (raphe is ventral)
• Pleurotropous ovule


  • Micropyle points to the side
  • Can be further divided into pleurotropous-dorsal (raphe is above) or pleurotropous-ventral (raphe is below)
• Obturator


  A protuberance of tissue, typically arising from the funiculus or placenta, that may develop at the base of the ovule
• Obturators may be typical of certain groups, e.g. the Euphorbiaceae