Week 2 | Day 3 | BIOA02

Week 2 | Day 3 | BIOA02

Two Mobile Life Cycle Stages

  1. Seed Dispersal Syndrome
  2. Pollination Syndrom
  3. Seed Dispersal Syndrome
  • Without seed dispersal adaptations, most seeds are deposited close to the mother plant
    • Parent-offspring competition for space & resources
    • Mating between closely related individuals, inbreeding depression

Ingenious Adaptations

  1. Explosive self-dispersal DIY: ballistochory
    • Shoots out seeds
    • Eg. Jewelweed (touch-me-not)
  2. Wind dispersal: anemochory
    • Hairs/wings that can float away with the wind easily
    • Eg. dandelions, winged maples
  3. Water dispersal: hydrochory
    • By water, usually only occurs in plants that live near water
    • Eg. sea bean, coconuts
  4. “External hitchhiking”: exozoochory
    • Stick to fur of larger animals (or even stick to birds)
    • Eg. Burdock
  5. “Internal hitchhiking”: endozoochory
    • Animals eat them
    • Actually may germinate less if it isn’t digested through an animal gut because it damages the seed just enough to let it grow
  6. Ant dispersal: myrmecochory
    • Elaiosomes: food for ants (etymology: elaios= oil, some= body)
      • Fleshy structure attached to seeds
      • Rich in lipids and proteins
    • Symbiotic relationship: plant gets seed dispersal, ant gets food
  7. Gravity: barochory & secondary dispersal by animals
    • Big, heavy seeds
    • Starch-rich, oil-rich = great food
    • Survive winter: seed caching
      • Some cashes are forgotten, tree seedling recruitment
      • Scatter hoarding: one or a few seeds per cache
      • Larder hoarding: many seeds per cache

Seed Anatomy (Angiosperms)

  • Contains plant embryo, covered with protective seed coat (testa)
    • Embryo gives enough food to give seedlings a start
  • Embryo: embryonic shoot, root (radicle) and cotyledons (embryonic leaves)
  • Food for embryo (endosperm) (Food for disperser)

Food for the embryo: endosperm

Endosperm: food storage cells inside seed; not part of embryo; developed through double fertilization (df)

Double fertilization (angiosperms only): parallel to fertilization of egg by pollen (to embryo), one pollen nucleus (1n) fertilizes the ‘central cell’ (2n) inside ovule to the endosperm (3n)