Chapter 22 Early Development of the Plant Body

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Chapter 22Early Development of the Plant
Body
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Outline

• Intro
• Formation of embryo
• Mature embryo and seed
• Seed germination and dormancy
• Seed to adult plant

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Intro

• Embryogenesis formation of embryo
• est. body plan of 2 superimposed patterns
• apical-basal pattern
• longitudinal axis
• radial pattern
• concentric rings
• Embryogenesis followed by
  seed development
• seed embryo S stores coat
• func.
• survive adverse cond.
• facilitate dispersal

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Formation of the Embryo

• Lee-Deanes Talk

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Maturation of the Seed

• Maturation
• nutrients/S deposited in endosperm/perisperm/cotyl
  edons during embyrogenesis
• funiculus separates from ovule
• ovule is independent
• seed desiccates
• seedcoat hardens
• hilum micropyle scar after funiculus separates

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The Seed

• Embryonic axis
• root and shoot apical meristems
• epicotyl stem-like axis above cotyledons
• hypocotyl stem-like axis below cotyledons
• plumule embryonic shoot
• radicle embryonic root
• hypocotyl-root axis axis
  below cotyledons
  including root

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The Seed

• Endosperm/perisperm absorbed by embryo and used
  to produce large/fleshy cotyledons or not
• Dicots 2 cotyledons
• sunflowers/peas/beans
• endosperm S transferred, thick cotyledons
• castor bean
• S remains in endosperm, thin cotyledons

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The Seed

• Cotyledon absorbs digested endosperm
• S transferred to growing embryo
• Monocots 1 cotyledon
• scutellum cotyledon in grains
• colerhiza protective sheath covering
  radicle
• coleoptile protective sheath covering
  plumule

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Dormancy and Germination

• Dormancy period of arrested growth/development
• dormant seeds wont germinate
• even when external conditions are favorable
• dispersal, favorable conditions (Death Valley)
• Germination resumption of growth
• factors affecting germination
• internal physiologically immature
• external water, O2, temperature, light
• dormant seeds have 5-20 moisture content
• imbibition uptake of water (metabolism,
  seedcoat rupture)
• Enzymes activated for digestion of S reserves
• anaerobic then aerobic upon rupture
• Temp. btwn 5-45C
• species specific

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Dormancy and Germination

• After-ripening series of biochem. changes
  necessary prior to germination
• stratification exposure to cold temperatures
  before germination
• delays germination until favorable temps
• scarification degradation of seeds before
  germination
• via acids/leaching/mechanical damage
• dispersal
• natural mechanisms of stratification/scarification
  
• requirements linked to ecological problems in
  habitat

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Germination and Seedling Development

• 1st step radicle emerges, absorbs water
• 1º root (taproot) grows and develops lateral
  roots
• 1º root typically short lived in monocots
• adventitious roots develop
• Seedling feeds off cotyledons/endosperm until
  capable of maintaining itself

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Seedling Emergence from Soil

• Epigeous seed germination hypocotyl elongates
  and pulls cotyledons above ground

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Seedling Emergence from Soil

• Hypogeous seed germination epicotyl elongates
  and cotyledons stays below ground