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The Plant Body
Today’s topics:
• Genetics of PlantDevelopment
– Flower Development
• Organization of stems androots– Xylem and Phloem
• Secondary growth
1 April 2009
Cell-Cell Signals
• e.g. Root Hair
Development
Genetic control of Flower
Development
Apetala
Class AAgamous
Class C
Pistillata
Class B
“ABC Model”
These genes allcode fortranscriptionfactors
Normal
Flower
Fig. 35-34Sepals
Petals
Stamens
Carpels (a) A schematic diagram of the ABC hypothesisA
A + B
gene
activity
BC
A gene
activity
B + C
gene
activity
C gene
activityCarpel
Petal
Stamen
Sepal
Activegenes:
Whorls:
Stamen
Carpel
Petal
Sepal
Wild type Mutant lacking A Mutant lacking B Mutant lacking C
A A A A
B B B B
C C C C
B B B B
C C C C C C C C A A A AC C C C A A A AB B B B
A A A A
(b) Side view of flowers with organ identity mutations
Which class of mutant is this?
Normal
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The evolutionary determination of sepal
and petal.
A CB2
B1
B3
MADS box genes and Plant
Evolution
http://www.biologie.uni-hamburg.de/b-online/e28_2/phylogeny.htm
The Plant Body
• All ofthese are
made ofthe same
cells andtissues
All Cells of the Plant Body
Originate in a Meristem
(a) Planes of cell division
Developingguard cells
Guard cell“mother cell”
Unspecializedepidermal cell
(b) Asymmetrical cell division
Pattern of cell division affects form
Cellulosemicrofibrils
Nucleus Vacuoles 5 !m
Microfibrils control cell wall expansion
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3
Major Tissue
Systems
• Dermal
• Ground
• Vascular
Dermaltissue
Groundtissue Vascular
tissue
Perforationplate
Vesselelement
Vessel elements, withperforated end walls Tracheids
Pits
Tracheids and vessels(colorized SEM)
Vessel Tracheids 100 !mVessels and Tracheids
Ground
Dermal
Keyto labels
Vascular
Root hair
Epidermis
Cortex Vascular cylinder
Zone ofdifferentiation
Zone ofelongation
Zone of celldivision
Apicalmeristem
Root cap
100 !m
Roots
Root with xylem and phloem in the center(typical of eudicots)
(a)
100 !m
Epidermis
Cortex
Endodermis
Vascularcylinder
Pericycle
Xylem
Phloem
Dermal
Ground
Vascular
Key
to labels
Root Cross Section
Shoot apical meristem Leaf primordia
Youngleaf
Developingvascularstrand
Axillary budmeristems
0.25 mm
Shoot GrowthSclerenchyma(fiber cells)
Phloem Xylem
Ground tissueconnecting
pith to cortex
Pith
CortexEpidermis
Vascularbundle
1 mm
Cross section of stem with vascular bundles forminga ring (typical of eudicots)
(a)
Dermal
Ground
Vascular
Keyto labels
Stem x.s.
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Secondary Growth
Fig. 35-19a3
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Primary and secondary growthin a two-year-old stem
(a)
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondaryxylem
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Growth
Cork
Bark
Most recent corkcambium
Layers ofperiderm
Vascular cambium Growth
Secondaryxylem
After one yearof growth
After two yearsof growth
Secondaryphloem
Vascularcambium
X X
X X
X
X
P P
P
P
C
C
C
C
C
The Vascular Cambium always produces
• Xylem toward the inside
• Phloem toward the outside
Annual Rings