AngiospermAngiospermDevelopmentDevelopment

EmbryogenesisEmbryogenesis

Establishes Establishes body plan of the body plan of the plantplant Apical-based Apical-based

patternpattern Radial patternRadial pattern

Accompanies Accompanies seed seed developmentdevelopment

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Formation of the EmbryoFormation of the Embryo Early stages same in all angiospermsEarly stages same in all angiosperms

Terminal cell == apical cellTerminal cell == apical cell Basal cell anchors embryo at micropyleBasal cell anchors embryo at micropyle

Polarity!Polarity! Divisions Divisions embryo proper + embryo proper +

suspensorsuspensor

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Primary MeristemsPrimary Meristems ProtodermProtoderm

Periclinal divisions (parallel to surface)Periclinal divisions (parallel to surface) ProcambiunProcambiun Ground meristemGround meristem

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Developmental Developmental StagesStages

Globular stage (e-h) – Globular stage (e-h) – precedes cotyledon precedes cotyledon developmentdevelopment

Globular Stage Globular Stage Heart Heart Stage (i)Stage (i) Monocots – cylindricalMonocots – cylindrical

Torpedo Stage (k-l)Torpedo Stage (k-l) Development becomes Development becomes

restricted to meristemsrestricted to meristems

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SuspensorSuspensor

Supports development of embryo properSupports development of embryo proper Angiosperm suspensors metabolically Angiosperm suspensors metabolically

activeactive Fern and gymnosperm suspensors – push Fern and gymnosperm suspensors – push

embryo into nutritive tissuesembryo into nutritive tissues Angiosperm suspensor – provides embryo Angiosperm suspensor – provides embryo

with nutrients and hormoneswith nutrients and hormones Short-livedShort-lived

Gone by torpedo stageGone by torpedo stage

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ArabidopsisArabidopsis mutants mutants Source of Source of

mutations that mutations that explain plant explain plant developmentdevelopment Expose seed to Expose seed to

mutagenmutagen Mutants produce Mutants produce

seedseed

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B – no apical meristem/cotyledonsC – no hypocotylD – no rootE – no apical and no basal portions

ArabidopsisArabidopsis mutants mutants

Which Genes Set Up Which Genes Set Up Body Axes?Body Axes?

MONOPTEROSMONOPTEROS -- sets up apical- -- sets up apical-basal axis.basal axis. Codes for MONOPTEROS protein -- Codes for MONOPTEROS protein --

transcription factor.transcription factor.

Auxin and MonopterosAuxin and Monopteros

Auxin – hormone produced in Auxin – hormone produced in meristemmeristem

Concentration gradient provides Concentration gradient provides positional informationpositional information

Auxin triggers production of Auxin triggers production of regulatory transcription factors regulatory transcription factors specific to cells in the hypocotyl & rootsspecific to cells in the hypocotyl & roots Establishes positional axisEstablishes positional axis

Mature Embryo & SeedMature Embryo & Seed Embryo continually nourished during Embryo continually nourished during

developmentdevelopment Perisperm (from nucellar tissue) within Perisperm (from nucellar tissue) within

endospermendosperm Cotyledons Cotyledons

Funiculus detaches from ovule Funiculus detaches from ovule nutritionally closed systemnutritionally closed system

Seed dessicatesSeed dessicates Seed coat hardensSeed coat hardens

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Mature EmbryoMature Embryo Axis bearing cotyledonsAxis bearing cotyledons Opposite endsOpposite ends

Shoot apical meristemShoot apical meristem Root apical meristemRoot apical meristem

Epicotyl – stemlike axisEpicotyl – stemlike axis Plumule – embryonic shoot & leavesPlumule – embryonic shoot & leaves

Hypocotyl – stemlike axisHypocotyl – stemlike axis Radicle Radicle

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Endosperm & PerispermEndosperm & Perisperm

Some seeds (e.g., beet) contain both Some seeds (e.g., beet) contain both Endosperm – double fertilizationEndosperm – double fertilization Perisperm – proliferation of nucellusPerisperm – proliferation of nucellus When endosperm absorbed – large When endosperm absorbed – large

cotyledonscotyledons Sunflower, walnut, pea, beanSunflower, walnut, pea, bean

Large amounts of endosperm – Large amounts of endosperm – membranous cotyledonsmembranous cotyledons

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Dicot SeedsDicot Seeds When endosperm absorbed – large When endosperm absorbed – large

cotyledonscotyledons Sunflower, walnut, pea, beanSunflower, walnut, pea, bean

Large amounts of endosperm – Large amounts of endosperm – membranous cotyledonsmembranous cotyledons

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Monocot SeedsMonocot Seeds Grasses – massive cotyledon Grasses – massive cotyledon

scutellumscutellum Both radicle & plumule sheathedBoth radicle & plumule sheathed Coleorhiza and coleoptileColeorhiza and coleoptile

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Seed GerminationSeed Germination Embryo growth delayed while seed maturesEmbryo growth delayed while seed matures Germination – resumption of embryo growthGermination – resumption of embryo growth

Many factorsMany factorso External – water, oxygen and temperatureExternal – water, oxygen and temperature

Mature seeds typically Mature seeds typically drydry Imbibation for enzymatic activityImbibation for enzymatic activity

Cells that produced reserve materials now Cells that produced reserve materials now digestdigest

Cell enlargement & cell divisionCell enlargement & cell division Early germination Early germination anaerobicanaerobic

Once seed coat ruptured – process is aerobic!Once seed coat ruptured – process is aerobic!

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Seed DormancySeed Dormancy

Physiologically immature embryoPhysiologically immature embryo After-ripeningAfter-ripening

Cold periodsCold periods DigestionDigestion FireFire Water Water

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Embryo to AdultEmbryo to Adult First emergent structure – rootFirst emergent structure – root

Anchors plantAnchors plant Absorbs waterAbsorbs water

Primary rootPrimary root Branch or lateral rootsBranch or lateral roots

Adventitious rootsAdventitious roots Shoot-borne rootsShoot-borne roots

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Epigeal & Hypogeal Epigeal & Hypogeal GerminationGermination

EpigealEpigeal HypocotylHypocotyl elongates elongates hook hook Hook straightens Hook straightens pulls cotyledons & pulls cotyledons &

plumuleplumule HypogealHypogeal

Epicotyl Epicotyl elongates elongates hook hook Hook straightens Hook straightens pulls plumule pulls plumule

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EndospermPresent

EndospermAbsorbed into CotyledonsBefore Germination

Epigeous:Cotyledons Emergent

Hypogeous:

Cotyledons Not Emergent

1. Corn(Monocot)

3. Bean(Dicot)

2. Pea(Dicot)

4. Onion(Monocot)

Castor Bean(Dicot)

GerminationStartSeed

Development

Type 1Type 1 HypogeousHypogeous MonocotMonocot Highly Highly

differentiatdifferentiated embryoed embryo

EndosperEndosperm m absorbed absorbed during during germinatiogerminationn

Type 2Type 2

HypogeousHypogeous DicotDicot Endosperm Endosperm

absorbed absorbed well well beforebefore germinationgermination

Cotyledons fill Cotyledons fill seedseed

Type 3Type 3 EpigeousEpigeous DicotDicot Endosperm Endosperm

absorbed absorbed well well before before germinationgermination

Cotyledons fill Cotyledons fill seedseed

Type 4Type 4

EpigeousEpigeous MonocotMonocot Endosperm Endosperm

absorbed absorbed duringduring germinationgermination

Type 4Type 4

EpigeousEpigeous DicotDicot Endosperm Endosperm

absorbed absorbed duringduring germinatiogerminationn