angiosperm reproduction

• Angiosperm Reproduction
• Bio 152: Introductory Biology II
• Dr. Huynh
• After this lecture you should be able to...
• Angiosperm reproduction: flowers, (double) fertilization, and fruits

  
• Pollen grains

  • Contain male gametophytes

  
• Pollen grain production

  1. Microsporangia (pollen sacs) enclose diploid microsporocytes, which undergo meiosis, producing 4 haploid microspores each

  2. Microspores undergo mitosis to produce two-celled male gametophytes called pollen

  
• Ovules

  • Contain female gametophytes
  • Ovary contains ovules
  • Megasporocyte undergoes meiosis, producing four haploid megaspores
  • One megaspore undergoes several rounds of mitosis to produce a female gametophyte with 8 nuclei
  • 1 egg cell & 2 polar nuclei

  
• Pollination

  Transfer of pollen from anther to stigma

  
• Pollination

  • Accomplished via wind, water, or animals
  • Coevolution: evolution of interacting species in response to changes in each other
• Double fertilization

  One sperm fertilizes the egg, and the other combines with polar nuclei, creating triploid food-storing endosperm (3n)
• Fertilized ovule develops into a seed; ovary develops into a fruit

  
• • Egg and sperm form zygote (2n); develops into multicellular embryo
  • Endosperm (3n) stores nutrients for embryo
  • Seed: embryo and endosperm are enclosed by a hard, protective coat, often inside of a fruit (derived from the ovary)

  
• Fruit

  Seed encasement that develops from the ovary; protects seeds and aids in dispersal

  
• Fruit types

  • Dry: ovary dries out at maturity
  • Fleshy: ovary becomes thick, soft, and sweet at maturity
• Seed dispersal by water

  • Coconut seed (embryo, endosperm, and endocarp inside buoyant husk)

  
• Seed dispersal by wind

  • Dandelion "seeds" (actually one-seeded fruits)
  • Giant seed of the tropical Asian climbing gourd Alsomitra macrocarpa
  • Tumbleweed
  • Winged fruit of a maple

  
• Seed dispersal by animals

  • Fruit of puncture vine (Tribulus terrestris)
  • Squirrel hoarding seeds or fruits underground
  • Ant carrying seed with attached "food body"
  • Seeds dispersed in black bear feces

  
• Seed dormancy

  • Adaptation where seeds enter a period of dormancy; increases chances that germination occurs at time and place advantageous to seedling
  • Breaking of dormancy requires environmental cues, such as temperature, moisture, or lighting changes
• Angiosperms can also reproduce asexually

  • Vegetative reproduction: the production of clones from a parent plant (e.g. stolons, rhizomes)
  • Fragmentation: separation of a parent plant into parts that develop into whole plants

  
• Vegetative reproduction facilitated or induced by humans

  • Many kinds of important plants are asexually reproduced from plant fragments called cuttings
  • A twig or bud can be grafted onto a plant of a closely related species or variety

  
• Self-fertilization

  • Some angiosperms can self-fertilize; ensures every ovule develops into a seed
  • Selfing can result in inbreeding depression
  • Many species have evolved mechanisms to prevent selfing (dioecious, monoecious, perfect vs imperfect flowers, stamens and carpels maturing at different times or physically arranged to prevent selfing)

  
• Asexual reproduction

  Beneficial to a successful plant in a stable environment; leaves species vulnerable to environmental change
• Sexual reproduction

  Generates genetic variation that makes evolutionary adaptation possible; most don't seedlings survive
• Humans can harness angiosperm reproduction to genetically alter crops