Lecture 24 Embryogenesis and Meristems

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Lecture 24 Embryogenesis and Meristems
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Motivation
http//plantsinmotion.bio.indiana.edu/plantmotion/
earlygrowth/germination/germ.html
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Embryogenesis

• Definitions
• Stages of embryo development
• Meristems root apical meristem
• shoot apical meristem
• Formation and maintenance of apical meristem

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Embryogenesis
- process that initiates plant development -
transforms a single-celled zygote into a
multicellular, microscopic, embryonic plant
(embryo) - generates a complex core structure,
the seedling
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Embryogenesis establishes essential features of a
mature plant
Embryogenesis does not directly generate tissue
and organs of the adult plant. Entire adult
plant morphology is generated by the activities
of apical meristems.
3 weeks
5 weeks
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Meristems in plant development
What are meristems? - Populations of small,
isodiametric cells (having equal dimensions on
all sides) with embryonic characteristics -
retain embryonic character indefinitely (stem
cells), because some meristematic cells do not
undergo differentiation Vegetative meristems
- form body of root or stem - continuously
regenerate themselves
Reproductive meristem - primary
inflorescence meristem - secondary
inflorescence meristem
Stem cell
Daughter cells
Committed cells
Differentiated cells
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Stages of Arabidopsis embryo development
Suspensor
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Embryogenesis is characterized by a precise
pattern of cell division
1-cell 2-cell 8-cell
early globular
early heart late heart torpedo
mature embryo
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Postembryonic development of Arabidopsis
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Embryogenesis requires specific gene expression
WT
mp
Hypocotyl and root are missing
Root meristem
Heart stage/triangular stage
MP MONOPTEROS is involved in auxin signal
transduction
Wild type
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Root apical meristem (RAM) - Root development
Root tip has four developmental zones Root
cap Meristematic zone Elongation zone Maturation
(Differentiation) zone
All root tissues are derived from a small number
of stem cells in RAM
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Model of lateral root formation
Stage 6

• Lateral roots arise form the
• pericycle in mature regions
• of the root
• Cell division in pericycle establish
• secondary meristems that grow
• out through the cortex and epidermis

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Shoot apical meristem (SAM)
Central zone (CZ) undifferentiated
cells Peripheral zone (PZ) formation of new
lateral organs Rib zone (RZ) formation of new
stem
Layer 1 (L1) Generates epidermis Layer 2 (L2)
Layer 3 (L3) Generate internal tissue
L1 L2 anticlinal cell divisions L3 randomly
oriented cell divisions
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Three types of leaf arrangements along the shoot
axis
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Sites of leaf formation on the stem are related
to auxin transport
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A transcription factor controls leaf development
WT
as mutant phenotype - crinkled asymmetric
leaves - abnormally arranged leaf veins -
serrations in the leaf lamina - multiple
midveins on leaves
The gene AS ASYMMETRIC LEAVES encodes a
transcription factor expressed in leaf primordia
and developing cotyledons
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Chimeric plants
A mutation in a gene essential for chloroplast
development occurred in some of the stem cells of
the meristem ? cells derived from these cells are
white Cells from other stem cells are normal and
green
English ivy