lecture 8

• Endosperm


  • Nutritive tissue with paternal contribution
  • Sets up potential for interesting evolutionary dynamics and developmental genetic changes
  • A huge part of everyday life and the world's diet
• Angiosperms


  • Originated endosperm
  • Originated fruits
• Seed development


  1. Ovule becomes seed containing embryo and food supply

  2. Ovary becomes fruit containing seeds

  3. Seed germinates, embryo develops into plant
• Fruit


  • Mature ovary of a flower
  • Develops as the seeds do from the ovules inside it
  • Usually requires pollination
  • Ovary wall becomes the thickened wall of the fruit called the pericarp
  • Can be dry or fleshy or both
• Monocot vs Eudicot seeds


  • Monocot: Endosperm starts as liquid with loose nuclei, then cellularizes into starchy solid
  • Eudicot: Some maintain separate endosperm until germination, others have endosperm taken up by growing embryo and stored in cotyledons

  
• Monocot and eudicot embryos differ in the number of cotyledons (embryonic leaves)
• Three major angiosperm innovations


  • Flowers
  • Endosperm
  • Fruits
• Flower


  Pollination and protection
• Endosperm


  Seedling establishment
• Fruit


  Protection and dispersal
• Abiotic seed/fruit dispersal mechanisms


  • Wind
  • Water
  • Active propulsion
  • Whole plant movement
• Biotic seed/fruit dispersal mechanisms


  • Passive adherence
  • Passive consumption and excretion
  • Active nutrient provisioning
• Coevolution may be the solution to Darwin's "abominable mystery" of the rapid diversification of angiosperms
• Coevolution


  • Can specialize to specific individual or subsets of species within same class of pollinator
  • Different ways to specialize on the same exact pollinator species
  • Lineages that shifted to a new pollinator class or to animal-mediated dispersal produce new species at faster rates
• The Andean cloud forest endemic bellflowers produced 550 new species in just ~5 million years
• The second half of the lecture focuses on plant form and function, covering developmental processes, functional integration, sensing and responding to environmental cues, and diversity of plant cell types and tissues
• Cotyledon


  Embryonic leaf that stores food for the developing plant
• Pericarp


  Fruit wall
• Dispersal mechanisms


  • Animal
  • Wind
  • Water
• Growth


  • Increase in size of a tissue by cell division or cell elongation
• Determination


  Commitment of a cell to a particular fate or tissue identity
• Differentiation


  The process of expressing the characteristics of a particular cell fate or tissue identity
• Shoot apical meristem (SAM)


  • Primary site of cell division at the tip of the shoot
• Root apical meristem (RAM)


  • Primary site of cell division at the tip of the root
• Primary growth


  Tissue elongation
• Hypocotyl


  Embryonic shoot below the cotyledons
• Epicotyl


  Embryonic shoot above the cotyledons
• Radicle


  Embryonic root
• Coleoptile


  Protective covering that sheaths the emerging shoot in monocots
• Apical hook


  Bent shape of the hypocotyl that protects the shoot apical meristem as it emerges from the seed
• Eudicot germination


  1. Radicle emerges first

  2. Hypocotyl emerges bent in apical hook

  3. Shoot growth above ground
• Monocot germination


  1. Radicle emerges first

  2. Hypocotyl and cotyledon remain within seed

  3. Epicotyl emerges sheathed by coleoptile

  4. Shoot breaks through coleoptile

  
• Meristems contain self-renewing cells that divide to produce new cells while maintaining their undifferentiated state
• Descendant cells below/above the shoot/root apex become stem/root tissues
• In the shoot, new primordia form and begin differentiating on the sides of the apex that will become other structures