Transcript 04 GrowthDevelopment..

Chapter 16
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Growth form through
postembryonic processes
Animal form during embryogenesis
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Are there increases in complexity?
To what extent is growth coupled to
division, expansion & differentiation
How does the environment affect or
influence growth processes?
How are characteristic patterns genetically
controlled?
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Second set details nature of the underlying
mechanisms
How are characteristic growth patterns genetically
determined?
 How is development tied to external influences?
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Nutrients, energy, stress
 What mechanisms deal with external influences?
 What physical components involved & how do they work?
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Plants rigid anatomy compared to animals
Animal development characterized by cellular
migration
 Plant cells in inflexible/woody matrix
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Sporophyte development
Embryogenesis
 Germination/Vegetative development
 Reproductive development
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Process transforming the zygote into a
multicellular entity having a characteristic
organization
Within the ovule
 Predictable sequence
 Basic patterning – establishes polarity
 Cells differentiate positionally
 Concluding with changes allowing the embryo to
survive dormancy
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The breaking of the dormant state and the
beginning of vegetative growth
Many factors can trigger germination
 Early – stored reserves in the seed
 Meristematic activity
 Photomorphogenesis (ch. 17) – seedling
photosynthesizes
 Indeterminate growth
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Transition from vegetative to reproductive
Flowering (ch. 25)
 Fruit development
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Developmental processes by which basic plant
architecture established
Morphogenesis – elaboration of form
 Organogenesis – formation of functionally
organized structures
 Histogenesis – differentiation producing tissues
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Apical meristems – sustain indeterminate
growth
Development enables dormancy and
germination
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Arabidopsis – model organism
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Monocots -- weird.
Zygote (a)
Globular (b-d)
Heart (e-f)
Torpedo (g)
Mature (h)
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Polarity
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Apical-basal axis
Radial axis
Apical-basal begins with zygote
Apical cell -> nearly entire
embryo
Basal cell -> transient suspensor
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Apical cell
Apical region  cotyledons + apical meristem
 Middle region  hypocotyl, root, and meristem
 Hypophysis  quiescent center and root cap
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Lineage-dependent signaling
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Cell fate is fixed  fixed programs of development
Position-dependent signaling
Cell fate depends on position
BUT
 Cells have to have cues to signify position
 Cells have to assess their location
 Cells have to respond to that information
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Auxin important  tissue culture
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Embryogenic patterns in total absence of plant
Auxin deficient mutants morphologically
similar to normal plants with altered auxins
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TRIVIA!
GURKE – encodes acetyl-CoA carboxylase –
required for synthesis of very-long-chain fatty
acids and sphingolipids
 FACKEL – encodes a sterol C-14 reductase
 GNOM – guanine nucleotide exchange factor which
enables polar distribution of auxin
 MONOPTEROS – encodes an auxin response factor
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Radial patterning
Mechanism unknown
Work with Gibberellin mutants
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Meristems ≈ Stem Cells
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Mitotic potential persists
RAM/SAM – most important
 Intercalary meristems – meristems flanked by
differentiated tissues
 Marginal meristems – edges of developing
organs
 Meristemoids – superficial clusters of cells
(trichomes, stomata, etc.)
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Similarities
Initials – slow dividing & undetermined fate
 Are the underlying mechanisms the same?
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Differences
Lateral root formation back from root tip
 Leaves form at meristem – specialized terminology
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4 zones with distinct behaviors
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Root Cap
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Meristematic Zone
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Rapid and extensive cell elongation
Rate decreases with distance
Maturation Zone
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Initials that produce the root tissues
Elongation Zone
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Covers meristem; secreted mucigel
Perceives gravity
Cells acquire differentiated characteristics
Elongation/differentiation have ceased
Lateral organs form
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Quiescent Center – low rate of cell division
Close functional relationship between QC and
other initials – apparently
 SPECIES DEPENDANT!
 Removal of QC results in
abnormal division and
precocious differentiation
 QC -- auxin concentration maximum
 Derived from apical cell of hypophysis
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Auxin vs Cytokinin
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Auxin largely synthesized in shoot 
transported to root
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Promotes root growth
Cytokinin synthesized in root  transported to
shoot
Promotes shoot growth; suppresses roots
 Signaling begins in hypophysis
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Maintain sets of undetermined cells that
enable indeterminate growth
SAM – initials and undifferentiated derivatives
 Shoot apex – SAM plus developmentally
committed cells (e.g., most recently formed leaf
primordia)
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Species specific!
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Zones and layers
Central Zone – cluster of infrequently dividing
cells (c.f., QC)
 Peripheral Zone – dense;
incorporated into lateral organs
(e.g., leaves)
 Rib Zone – gives rise to internal
tissues
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Zones and Layers
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Tunica
L1  epidermis
 Anticlinal divisions
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Corpus
L2 & L3  internal tissues
 L2 – anticlinal
 L3 – randomly oriented
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Identities are position dependant
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L2 cell divides periclinally and in L1 becomes
epidermis
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Similar mechanisms maintain initials in
SAM and RAM
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Phyllotaxy
Position dependant mechanisms
 Auxins (remember Vi Hart?)
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Leaf initiation depends
on auxin accumulation
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Planar form of the leaf
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Distinct mechanisms for formation of lateral organs
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Root  series of periclinal divisions in pericycle  growth
in plane perpendicular to root
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Distinct mechanisms for formation of
lateral organs
Shoot  cells from several distinct layers
 Axillary meristems
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Pattern of branch formation directly related to
phyllotaxy
 Apical dominance (  Auxins)
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Senescence ≠ Necrosis
Senescence – energy-dependant developmental
process
 Necrosis – death brought about by physical
damage, poisons, or external injury
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Senescence – ordered degradation of cellular
contents; remobilization of nutrients
Associated with abscission
 Early senescence – nutrients mobilization
reversible
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Occurs variety of organs; in response to different cues
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Monocarpic senescence – senescence of entire plant after a
single reproductive cycle
Senescence of aerial shoots in herbaceous perennials
Seasonal leaf senescence
Sequential leaf senescence (leaves of an age die)
Senescence of fruits
Senescence of storage cotyledons
Senescence of floral organs
Senescence of specialized cell types (e.g., trichomes,
tracheids, vessel elements, etc.)
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Triggers
Reproductive processes
 Environmental cues  Day length; temperature
 Pathogens
 Hormonal control  ethylene; cytokinins
 Oxidative stress
 Metabolic status  sugar sensor hexokinase
 Macromolecule degredation
 Intrinsic developmental factors  age-related
 Programmed cell death  apoptosis
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Chloroplast first to degrade
Significant in terms on nutrient reallocation  N
 Releases potentially phototoxic chlorophyll
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Programmed cell death
Pathogens  necrotic lesions
 DNA replication errors
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Xylem trachery elements