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Plant Growth and Development II
"It is at the edge of a petal that love awaits.”
...William Carlos Williams
Patterns of Development
ZygoteZygote EmbryoEmbryoCotyledonsHypocotyl
Root
CotyledonsHypocotyl
Root
SAMSAM
RAMRAM
apical/basal, axial
embryogenesis
primarygrowth
SAMSAM Cell Differentiation
Cell Differentiation
Leaf Primordia
Leaf Primordia
Stem Tissues
Stem Tissues
1o Growth1o Growth
primarygrowth
RAMRAM RootTissues
RootTissues
? ? ?
Structure/Function
?
?
1o Growth1o Growth
2o Growth2o Growth
2o Growth2o Growth
Today
• How do plant organs, tissues and cells develop?
– Examine Plant Growth,
primary growth,• secondary growth,• cell elongation• molecular development.
Lateral Meristems...
…provide for secondary growth by producing secondary vascular tissue and periderm (secondary dermal tissue).
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.
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
Assignment
Be able to construct a tree from a seedling using these meristems,
- at the tissue level.
…same w/ root, w/o periderm.
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.
Plant Cell Walls
Cell Morphology
Mechanical and Structural
Water Relations
Plant Morphology Pathogen Defense
Bulk Flow
Biochemistry
Cell Wall Synthesis
MicrotubulesMovie
Cell Expansion
Primary Walls:
Less ordered, allows general enlargement. Secondary Walls:More ordered, restricts general enlargement, often lignified
(wood).
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.
Acid-GrowthHypothesis
ATP hydrolases (ATPases)
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.
know this
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.
• 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.
Model Organisms
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.
Arabisopsis thaliana+ 26,000 Genes
Genetics: analysis of mutant phenotypes,
Reverse Genetics: analysis of mutant genotypes,
Genomics: use of DNA sequence for all aspects of plant growth, development, evolution, ecology...
Pattern Formation
GNOM: signal transduction gene
lacks apical-basal axisHomeotic Gene
KNOTTED gene expression results in the differentiation of
cells into vasculature.