angiosperms

• Carpel


  Stigma + style + ovary
• Gynoecium


  One or a cluster of carpels
• Flower Anatomy
• Complete flower has gynoecium and androecium
• Incomplete flower can be carpellate or staminate
• Monoecious plant has both male and female flower(s) on same plant (e.g. soybean)
• Dioecious plant has male and female flowers on separate plants (e.g. cannabis)
• Microsporogenesis


  Pollen mother cells inside the four (4) pollen sacs (microsporocytes) of the anther undergo meiosis to produce unicellular haploid spores
• Microgametogenesis


  The unicellular haploid spores then undergo mitosis to produce 2-3 cell pollen (i.e. the microgametophyte)
• Each 2n mother cell gives a tetrad of n microspores
• The sterile cells in the anther provide nutrition of the developing microspores - this is the tapetum layer
• The tapetum adds a lipid rich coat to the pollen grain
• Each diploid pollen mother cell gives rise to a tetrad of haploid microspores
• The haploid microspore divides by mitosis to form 2-3 cell pollen (the microgametophyte) consisting of 1 large vegetative (tube) cell and 1-2 tiny generative cell(s) (develop into sperm)
• Vegetative cell


  Non-reproductive, will form pollen tube upon germination
• Generative cell


  Reproductive, divides to form the two sperm cells
• Microsporogenesis


  Formation of microspores (single-celled precursors of pollen grains) within the microsporangia, or pollen sacs, of the anther
• Microgametogenesis


  Later development of the microgametophyte by mitosis to the two/three-celled stage
• Pollen Formation Occurs by Two Consecutive Processes


  1. Microsporogenesis

  2. Microgametogenesis
• Microgametophyte


  Pollen grain
• The microgametophyte can divide again to produce a 3rd cell
• Megagametogenesis


  Mitosis (x3)
• Megagametophyte


  Embryo sac (the female gametophyte)
• The female gametophyte is an eight-nucleate, seven-celled structure
• Female gamete


  Egg cell used to reproduce offspring
• Functions of megagametophyte cells


  • Feed growing embryo
  • Synergids produce an attractant that guides the pollen tube to the female gametophyte
  • Egg cell is used to reproduce offspring
• The most common type of embryo sac is the Polygonum type (70%)
• Only two ancient lineages (<30%) (a) and (c) exhibit monosporic development (from a single megaspore). 3 of 4 megaspores disintegrate. (b) exhibits tetrasporic development (from four megaspore nuclei)
• One nucleus from each group migrates into the center of the eight-nucleate sac (the polar nuclei)
• Angiosperm gametophytes (haploid generation) are tiny in size
• The mature megagametophyte (embryo sac) is only 7 cells
• This is called double fertilization