Plant Growth and Development II

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Plant Growth and Development II

• "It is at the edge of a petal that love awaits.
• ...William Carlos Williams

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Patterns of Development
Zygote
Embryo
Cotyledons Hypocotyl
SAM
Cell Differentiation
1o Growth
RAM
Root Tissues
1o Growth
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Today(continue)

• How do plant organs, tissues and cells develop?
• Examine Plant Growth,
• primary growth,
• secondary growth,
• cell elongation
• How is Plant Cell Differentiation Studied,
• discovering the process by which a cell acquires
  metabolic, structural and functional properties.

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Lateral Meristems...

• provide for secondary growth by producing
  secondary vascular tissue and periderm (secondary
  dermal tissue).

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Secondary Growth of Stems

• Two Lateral Meristems,
• Vascular cambium produces secondary vascular
  tissue,
• Cork cambium produces tissue (periderm) that
  replaces the epidermis,
• Secondary phloem and periderm comprise bark.

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Vascular Cambium
Fig. 35.20
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Secondary Growth Year 1
Fig. 35.21
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Lateral Meristem Cells
Fusiform initials meristematic cells that give
rise to xylem and phloem.
Ray initials meristematic cells that give rise
to (primarily) parenchyma cells that serve as
radial connections.
Tangential Section
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Secondary Growth Year 2
Fig. 35.21
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Secondary Growth
Fig. 35.21
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Secondary Growth
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Assignment
Be able to construct a tree from a seedling using
these meristems, - at the tissue level.
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Growth / Differentiation

• Growth,
• the irreversible increase in size that (in
  plants) almost always results from both cell
  division and cell enlargement,
• Differentiation,
• the process by which a cell acquires metabolic,
  structural and functional properties distinct
  from those of its progenitor.

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Cell Division / Cell Walls / Cell Growth
Fig. 35.10c
Fig. 12.8
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Plane of Division
Fig 35.28
Fig 35.27
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Plant Cell Walls
Cell Morphology
Water Relations
Bulk Flow
Biochemistry
Plant Morphology
Cell Morphology
Mechanical and Structural
Pathogen Defense
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Cellulose / Cell Walls
Fig. 5.8
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Cell Wall Synthesis
Fig 35.29
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Cell Expansion
Biased Microfibril Distribution allows for
directional growth. Turgor water potential is
lowered in the cell, allowing water uptake. The
force of the water pressure drives cell
expansion.
Secondary Walls More ordered, restricts general
enlargement, often lignified (wood).
Primary Walls Less ordered, allows general
enlargement.
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Acid-Growth Hypothesis
1. Plasma Membrane H-ATPases acidify the
apoplast (cell wall).
2. Cell wall loosening enzymes are activated.
3. Electrochemical gradient drives solutes into
the cell, - lowers osmotic potential, H2O?
4. Vacuolar ATPase provides membrane potential
for transport of solutes into the vacuole, etc.
etc.
ATP hydrolases (ATPases)
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Developmental Biology

• Modern approach is driven primarily by the
  study of genetics,
• primarily through the study of mutants, organisms
  blocked in specific developmental pathways,
• Model Organisms.

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Model Organisms

• Ease of cultivation,
• Rapid Reproduction,
• Small size,
• Fecund (large brood size),
• Mutants are available and easy to identify,
• Scientifically relevant (ecologically, organ
  system, etc.)
• Extant Literature, co-ordinated research emphasis.

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Arabisopsis thalianaThale cress/Mouse Ear Cress

• Arabidopsis is a plant belonging to the Mustard
  family, Cruciferae. Arabidopsis' agronomic value
  is as a Model Organism,
• weedy world-wide distribution and easily grown
  in the lab.
• self-fertilizing it is easy to generate and
  maintain genetic stocks.
• lifecycle about 42 days at 200 C and continuous
  light.
• fecundity up to 50,000 seeds per plant.
• mutable yes, lots of ways.
• literature 9718 journal articles (PubMed)
• - 1000 devoted labs.
• Arabidopsis is THE plant model organism with
  over 7000 full-time scientists devoted to
  understanding the growth and development of this
  organism, and the extension of this knowledge to
  other plants and organisms.

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Arabisopsis thaliana 26,000 Genes
Genetics analysis of mutant phenotypes, Reverse
Genetics analysis of mutant genotypes, Genomics
use of DNA sequence to all aspects of plant
growth, development, evolution, ecology...
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Cell Growth
FASS gene not cloned
fass Mutant cortical microtubules do not
organize.
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Pattern Formation
lacks apical-basal axis
GNOM guanine nucleotide exchange factor
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Shoot Development Begins at the Shoot Apical
Meristem
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Maintenance of the Meristem

• CLAVATA and WUSCHEL protein interactions
  constitute a tightly regulated control mechanism
  to maintain and delimit the meristem,
• wuschel Mutant Meristem Disappears
• clavata Mutant Enlarges Meristem
• WUSCHEL Gene Maintains the Meristem
• CLAVATA Mutant Delimits the Meristem

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Clavatas Molecular Mechanism

• clavata 1, 2 and 3 mutants have identical
  phenotypes of enlarged meristems
• CLAVATA3 protein acts as a signal molecule on
  the two-component clavata receptor, constituted
  by CLAVATA 1 and 2
• The clavata receptor is a leucine rich repeat
  (lrr) serine/threonine kinase receptor.

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Clavata Phenotypes
Clavata phenotype mutant
wt phenotype
CLAVATA turned off during development results in
determinant growth, I.e. a leaf.
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Transport

• Friday

Quiz Through Chapter 36, 748 - 754