reproduction in plants

• Gametophyte


  Stage of the life cycle of a plant that is haploid; stage that produces gametes via mitosis; these gametes fuse to form a zygote that develops into a sporophyte
• Sporophyte


  Stage of the life cycle of a plant that is diploid; it is the most recognizable structure in most flowering plants; it produces haploid spores by meiosis in structures called sporangia
• Types of Life Cycles of Plants

  • Haplontic life cycle
  • Haplodiplontic life cycle
  • Diplontic life cycle
• Haplontic life cycle


  • Life cycle where the haploid stage (gametophyte) is multicellular and the only diploid stage is the fertilized egg cell
• Chara


  • Multicellular green alga related to higher plants because it has both chlorophyll a and b and produce plant starch
  • Its dominant stage is a multicellular haploid stage which produces gametes that eventually fuse to form unicellular zygotes
  • Each zygote then undergoes meiosis to become haploid, after which it undergoes mitosis to become the multicellular organism
• Haplodiplontic life cycle


  • Life cycle that includes multicellular diploid (sporophyte) and haploid (gametophyte) generations
• Moss


  • Has a multicellular haploid (gametophyte) stage that produces gametes
  • These gametes fuse to produce a zygote that undergoes mitosis to produce a multicellular sporophyte
  • Within a part of the sporophyte called the capsule, cells undergo meiosis to produce meiospores
  • These spores are eventually released and germinate by dividing mitotically to become a multicellular gametophyte
• Diplontic life cycle


  • Life cycle where the diploid stage (sporophyte)is multicellular and the haploid stage (gametophyte) is represented by the single-celled gametes
• Angiosperms


  Also known as flowering plants; group of plants that produce reproductive structures called flowers in their sporophyte stages
• Flower


  Reproductive structure in flowering plants; made up of four major whorls (Sepals, Petals, Stamen (Anther and Filament), Carpels(stigma, style, ovary and ovule))
• Sepals


  The outermost whorls of a flower; collectively called the calyx
• Petals


  Whorl inner to the sepals; may be brightly colored in some; collectively called the corolla
• Stamen


  Whorl inner to the petals; the male reproductive structure of the flower; bears the male sporangia (also known as microsporangia)
• Anther


  Part of the stamen that contains the microsporangia that develops into pollen grains
• Filament


  Part of the stamen that serves as the stalk of the anther
• Pistil or carpels


  Innermost whorl of the flower; the female reproductive structure of the flower; bears the female sporangia (also known as the megasporangia)
• Stigma


  Part of the pistil where the pollen grain derived from the microsporangium attaches during pollination
• Style


  Part of the pistil that serves as the stalk of the stigma; leads to the ovary
• Ovary


  Found at the base of the pistil; contains one or more ovules; eventually becomes the fruit
• Ovule


  Contains the female sporangia or megasporangia; eventually becomes the seed
• Types of flowers based on the presence of the whorls

  • Complete
  • Incomplete
• Types of flowers based on the presence of reproductive whorls

  • Perfect / Bisexual
  • Imperfect / Unisexual
• Imperfect / Unisexual

  A flower that has only either the stamens (staminate flower) or the carpels (carpellate flower)
• Monoecious plant


  A plant having perfect flowers or both staminate and carpellate flowers on the same individual
• Dioecious plant


  A plant having only either the staminate or carpellate flower
• Plant types based on the presence of reproductive structures

  • Monoecious
  • Dioecious
• Development in flowering plants


  Gametophyte - Development through gametogenesis
• Male gametophyte development


  1. Microsporangium in anther contains microsporocytes

  2. Each microsporocyte undergoes meiosis to produce 4 haploid microspores

  3. Each microspore develops into a pollen grain (containing 2 sperm nuclei and 1 tube nucleus)
• Female gametophyte development


  1. Megasporangium in ovule contains megasporocytes

  2. One megasporocyte undergoes meiosis to produce 4 haploid megaspores

  3. 3 megaspores degenerate

  4. Remaining megaspore divides mitotically 3 times to form 8-nucleate embryo sac
• Pollination


  Placement of pollen grain from anther to stigma of carpel
• Pollen grain


  • Immature male gametophyte developed in anther, derived from microsporocytes
  • Contains tube cell and generative cell
  • Tube cell develops into pollen tube, generative cell divides into 2 sperm nuclei
• Embryo sac


  • Female gametophyte in ovule, derived from megasporocyte
  • Mature embryo sac contains 8 nuclei that become real cells - 1 egg, 2 synergids, 2 polar cells, 3 antipodals
• Micropyle


  Opening in ovule integuments where pollen tube enters to reach embryo sac
• Endosperm


  Nutritive tissue derived from fusion of sperm nucleus and 2 polar nuclei, stores food for developing embryo
• Zygote


  Formed by fusion of egg and one sperm nucleus
• Double fertilization


  1. Pollen tube discharges 2 sperm cells into embryo sac

  2. One sperm fuses with egg to form zygote

  3. Other sperm fuses with polar nuclei to form endosperm
• Embryo development (embryogenesis)


  1. Zygote divides mitotically to form proembryo and suspensor

  2. Cotyledons appear on proembryo

  3. Proembryo elongates into embryo
• Maturation of ovary and ovule

  Ovary matures into fruit, ovule becomes seed which may become dormant
• Seed germination


  1. Seed undergoes imbibition to break dormancy

  2. Nutrients in endosperm/cotyledons digested and transferred to growing regions

  3. Primary meristems develop

  4. Radicle emerges

  5. Plumule breaks through soil surface
• Epigeal germination

  Cotyledon emerges above ground, exposing hypocotyl of plumule