Transcript 09 Development

Angiosperm
Development
Embryogenesis

Establishes body
plan of the plant
Apical-based pattern
 Radial pattern


Accompanies seed
development
2
Formation of the Embryo

Early stages same in all angiosperms
Terminal cell == apical cell
 Basal cell anchors embryo at micropyle


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Polarity!
Divisions  embryo proper + suspensor
3
Primary Meristems

Protoderm

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Periclinal divisions (parallel to surface)
Procambiun
Ground meristem
4
Developmental Stages
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Globular stage (e-h) – precedes
cotyledon development
Globular Stage  Heart Stage (i)

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Monocots – cylindrical
Torpedo Stage (k-l)
Development becomes
restricted to meristems
5
Suspensor
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Supports development of embryo proper
Angiosperm suspensors metabolically active
Fern and gymnosperm suspensors – push embryo
into nutritive tissues
 Angiosperm suspensor – provides embryo with
nutrients and hormones


Short-lived

Gone by torpedo stage
7
Arabidopsis mutants

Source of mutations
that explain plant
development
Expose seed to
mutagen
 Mutants produce seed

8
Arabidopsis mutants
B – no apical meristem/cotyledons
C – no hypocotyl
D – no root
E – no apical and no basal portions
Which Genes Set Up Body Axes?

MONOPTEROS -- sets up apical-basal axis.

Codes for MONOPTEROS protein -- transcription
factor.
Auxin and Monopteros

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Auxin – hormone produced in meristem
Concentration gradient provides positional
information
Auxin triggers production of regulatory
transcription factors
specific to cells in the hypocotyl & roots
 Establishes positional axis

Mature Embryo & Seed

Embryo continually nourished during development
Perisperm (from nucellar tissue) within endosperm
 Cotyledons



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Funiculus detaches from ovule  nutritionally
closed system
Seed dessicates
Seed coat hardens
12
Mature Embryo


Axis bearing cotyledons
Opposite ends
Shoot apical meristem
 Root apical meristem

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Epicotyl – stemlike axis


Plumule – embryonic shoot & leaves
Hypocotyl – stemlike axis

Radicle
13
14
Endosperm & Perisperm

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Some seeds (e.g., beet) contain both
Endosperm – double fertilization
Perisperm – proliferation of nucellus
When endosperm absorbed – large cotyledons


Sunflower, walnut, pea, bean
Large amounts of endosperm – membranous
cotyledons
15
Dicot Seeds

When endosperm absorbed – large cotyledons


Sunflower, walnut, pea, bean
Large amounts of endosperm – membranous
cotyledons
16
Monocot Seeds

Grasses – massive cotyledon  scutellum
Both radicle & plumule sheathed
 Coleorhiza and coleoptile

17
Seed Germination


Embryo growth delayed while seed matures
Germination – resumption of embryo growth

Many factors
o
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Mature seeds typically dry

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External – water, oxygen and temperature
Imbibation for enzymatic activity
Cells that produced reserve materials now digest
Cell enlargement & cell division
Early germination anaerobic

Once seed coat ruptured – process is aerobic!
18
Seed Dormancy
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Physiologically immature embryo
After-ripening
Cold periods
 Digestion
 Fire
 Water

19
Embryo to Adult

First emergent structure – root
Anchors plant
 Absorbs water

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Primary root
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Branch or lateral roots
Adventitious roots

Shoot-borne roots
20
Epigeal & Hypogeal Germination
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Epigeal

Hypocotyl elongates  hook

Hook straightens  pulls cotyledons & plumule
Hypogeal

Epicotyl elongates  hook

Hook straightens  pulls plumule
21
Endosperm
Present
Endosperm
Absorbed into Cotyledons
Before Germination
1. Corn
(Monocot)
2. Pea
(Dicot)
Hypogeous:
Cotyledons
Not Emergent
Start
Seed
Development
Epigeous:
Cotyledons
Emergent
Germination
4. Onion
(Monocot)
Castor Bean
(Dicot)
3. Bean
(Dicot)
Type 1
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Hypogeous
Monocot
Highly
differentiated
embryo
Endosperm
absorbed
during
germination
Type 2
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Hypogeous
Dicot
Endosperm
absorbed well
before

germination
Cotyledons fill
seed
Type 3

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Epigeous
Dicot
Endosperm
absorbed
well before

germination
Cotyledons
fill seed
Type 4
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Epigeous
Monocot
Endosperm
absorbed during
germination
Type 4
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Epigeous
Dicot
Endosperm
absorbed
during
germination