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Complex Structures and more Terrestrial Evolution, always close,…
Complex Structures and more Terrestrial Evolution
Vascularization
Evolutionary Origins
Tracheid Evolution
Early
water transport only
relatively long and wide
Cooksonia
Water-conducting cell
Evolution
Annular thickenings-----> Annular rings
lack lignified cell wall
BRYOPHYTES
(non-vascular)
Hydroids
no plasmodesmata
no lignin in cells
Hydrostatic support in stems
During Devonian
increase in Xylem content
increase in tracheid size
increase in tracheid reinforcement
Stepwise progression
True Tracheids
Snyapomorphic Trait
likely evolved once
lignified with ornamented walls
function:
water transport
support
tapered at end and narrow
Xylem
critical to success of embryophytic land plants
specialized tissue that moves water and nutrients from Roots to Leaves
Evolutionary Origins:
in the sporophyte of polysporangiophytes
lignified and thickened cells walls for support
Conifers
Torus-margo pit membrane
Margo region:
porus
water movement
tracheid to tracheid
Torus:
thickening in center of membrane
protects conduits from spread of air throughout Xylem
Prevents Cavitation
Tracheophytes
All have vascular tissue
Architecture is diverse
Cell Type Varies
Classifications
Pteridophytes:
Lycophytes
First True Forest
towering
Carboniferous age
ex. competition. lycophytes out competion
Ferns & Horsetails
Tracheids
some have vessel elements in rhizomes
pit membranes
Euphyllophytes:
Spermatophytes
Gymnosperms
Angiosperms
Vessel Elements
Homogenous pit membrane
partially digested primary wall protected by an overarching, secondary wall border
Large diameter
open digested end walls
Location:
grouped vessel to vessel
or sporadically along the full length of the vessel wall
lignified and thickened cell walls
Origin:
Changes with organ
Roots and Shoots
Early Rooting Systems
Early Origin:
Prior to colonization of land
Rhizoid based
Rhizoids
Functions:
anchorage
some with mineral uptake
Comprised of:
multicellular
projections
unicellular
Genes:
predate land plants
play role in root hair development
structural change associated with bilateral symmetry
Gametophytic filamentous structures from the gametophytes
elongate by tip growth
Rhizomorphs
elaborate dichotomous rooting system
Lateral Appendages:
Stigmarian Rootlets
Abscised during plant development leaving helically arranged circular scars
highly branched
covered in root hairs
Modern relative
Rhizophores
Similar to Roots:
does not contain:
Root cap
Stomata
Chlorophyll
Growth:
Gravitropic
Extant Species:
Lycophyte
Bifurcating
Root hairs
No Quiescent Center
Evolution
Shoot turned Root
Rhynie Chert Fossils:
Early Vascular Plants
Dichotomously branched parenchymatous axes or telomes
Early Devonian:
Zosterophyllophyta
Branches:
Erect
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Horizontal
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Evolution:
Roots of Extant Lycophytes and Euphyllophytes
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Homologous
Upright, prostrate stems, and downward root like stems
Root Transition
Early Roots
RHYNIE CHERT
Lycopsid Asteroxylon mackiei
lacked root cap
continuous epidermis over meristem surface (root tip)
Data gives reason to hypothesize that:
Roots were a late innovation to vascular plants
anticlinal divisions only
Early Devonian
Lycophyte Asteroxylon mackiei
Roots:
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This evidence suggests:
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Root Meristem
Compared to Shoot Apical Meristem:
Stem cells:
Production and Maintenance involve similar developmental patterns
Location:
QUIESCENT CENTER
RAM
Rarely divides
Backup plan
Maintains Initial cell #
ORGANIZING CENTER
SAM
Functionally Equivalent
Similar Genes/Classes co-opted for use in both types of Meristems
Similar genes across Plant Taxa
Cellular Organization of Tissue:
Quiescent Center
Epidermis
Cortex
Endodermis Pericylce
Provascular and Columella cell files
stem cell progenitors
Apical Root Meristem behind ROOT CAP
Open
Produces more cells and releases individual living border cells
Closed
releases sheets or groups of dead cells
Prior to root evolution plants had a low capacity for water uptake
Root Body Plan
General Root Plan
Root Cap
Derived from and protects
Extant Lycophytes and Euphyllophytes
protect underlying tissues
secrete mucilage
cells that slough
Endodermis
Water Transport
Casparian Band
Symplastic movement
active process
water travels through the cytoplasmic regions of cells, which are connected to each other by plasmodesmata to form a continuous system
enables:
water to move through cell membranes to be filtered
contribute to increases in size and complexity among land plant evolution
Prevents Apoplastic Movement
water moves through the extracellular spaces
passive process
Pericycle
Pluripotent
inside:
Lateral Roots
Originate
Functions:
Anchors plant body to its Substrate
Absorbs:
Water
Dissolved Minerals
Root Hairs
Hypotonic Soil Solution to Hypertonic Cells
Single Celled
Short lived
Delicate
Water and minerals absorbed
Cortex
Large storage area
Outermost layers may show:
Hypodermis
long cells
short cells
common in monocots
outermost cell layers of the cortex derived by periclinal divisions in outer ground meristem
Exodermis:
Casparian Strip
suberized lamella
protect against pathogen invasion and possibly root drying during times of stress
Bound by Endodermis and Epidermis
ROOT:
Highly differentiated multicellular axis
Only found in
Sporophytes of Vascular Plants
Main organ in Vascular plants
Organizational Diversity
Lycophytes
Selaginella example
Endarch Protoxylem
Stele
Roots:
Branch dichotomously at apical meristem
No Root Hairs
No Root Cap
Monocots
Roots:
Commonly:
Adventitious
Arise Endogenously from:
Stems
Leaves
Polyarch
Stele
Pith in center
Endodermis
Casparian Strip
Epidermis
Cortex (Surrounding)
Pericycle
Xylem
Phloem
Eudicots
Roots:
Epidermis
Cortex
Endodermis
Casparian Strip
Pericycle
Xylem
Phloem
NO pith
Stele:
often Polyarch
Diverse
varies among Taxa
Leaves
Phyllad Evolution
Vascular plant leaves have evolved multiple times from branching shoot systems
Concepts:
Initial Constraints:
Environmental Conditions:
Low Capacity for water uptake
High atmospheric global temperatures
Low Stomatal Densities
Consequences:
Burning of fully webbed leaves
Vascular embolism - Stem
Lacking efficient vascular transport in leaves
Origins:
Environmental Conditions
Declining atmospheric CO2 levels
Declining Global temperatures
Increase in Stomatal Densities
Increases in Vein Densities
Evolutionary significance:
Rise in stomatal density permitted:
greater evaporative cooling
rid of convective heat loss
Earliest Evidence of True Leaves:
Fossil Lycophytes
Microphylls/Lycophylls
Narrow
Elongated
Arise from:
intercalary meristem
Single vascular trace along center of blade
connects directly to stem
Optimal Light Interception
Indeterminate growth proceeded leaf development
Photosynthesis
Convergent Evolution:
Leaves has at least 5 independent origins:
Liverwort Gametophyte
Moss Gametophyte
Lycophyte Sporophyte
Monilophyte Sporophyte
Spermatophyte Sporophyte
Leafles precursors in each lineage point to:
Non-homology of sporophytic leaf types
Enation Theory
Lycophyte leaves arose by progressive elaboration of epidermal outgrowth
Vascular strands later enter
connects to protoxylem poles in stem
Evidence:
Asteroxylon Fossil
Extant Selaginella drussiana
Two adjacent epidermal cells growing to form opposite pairs
Zimmerman Telome Theory
Evolution of Euphylls
Independently from Lycophylls
Overtopping
Unequal branching
Primary
Side
Planation
Flattening of axes into 2 dimensional
Webbing
Develop thin tissue between axes of branches
branches become veins
becomes mesophyll
By Devonian, widespread
Tissue Types:
Chlorenchyma
Ground Tissue
Specialized Parenchyma cells
Contains Chloroplasts
Function: Photosynthesis
Arenchyma
Ground Tissue
Specialized Parenchyma cells
Air spaces from cell digestion
Additional functions in aquatic plants:
Buoyoncy
Main Function:
Gas Exchange
Collenchyma
Ground tissue
Thickened primary cell walls
Found in bundle sheath of veins in some species and stem edges
Celery
Main Function: Flexible support
Vascular Tissue
Xylem
Tracheids
water transport
Phloem
Sieve tube element/sieve cells
Albuminous cells/Companion cells
Photosynthate transport
In Veins
Epidermis
Dermal Tissue
Epidermal cells
Guard Cells
Often Cutenized
Main Function: Protecting the internal tissues
Monocot
Epidermis
Adaxial (outer)
Abaxial (towards stem)
Covered by Cuticle
Contains Stomata
Bulliform cells:
Helpful for the rolling and unrolling
Mesophyll
Veins
Surrounded by bundle sheaths
Eudicot
Epidermis
Dermal Tissue
Epidermal cells
Guard Cells
Cuticle
upper and lower
Mesophyll
Palisade
Photosynthesis
Spongy
Gas Exchange
Veins
Bundle sheath cells
Xylem on top
Phloem on bottom
Indeterminate Growth
Trait Evolution:
Apomorphy
derived novel trait
Synapomorphy/Homology
Apomorphy shared by 2 or more taxa
Autopomorphy
character newer than
Plesiomorphy
character older than
Homoplasy
trait has gained or lost independently in separate lineages during evolution
Convergent Evolution
species independently share different trait than inferred in LCA
Convergence
independent evolution of a similar trait in two or more taxa
Apical Meristem
Plant Cell Division
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Evolution
Ancestral
in charophytes
Indeterminate meristems
Iterate leaves in regular patterns aroud the stem
Optimizes light interception during photosynthesis
Transpiration
Water Potential
Components:
Pressure Potential:
effect that pressure has on potential
if water is under pressure, both pressure potential and water potential increase
Hydrostatic pressure exerted on water in a cell
Due to turgor pressure
due to water filling vacuole, cell wall pushes,
xylem cells:
negative pressure
Osmotic potential:
effect that solutes have on potential
adding solutes decreases waters free energy, so osmotic potential is ALWAYS negative
difference between the solution and pure solvent after solutes have been added
Matric potential:
adhesion to structures such as:
cell walls
membranes
soil particles
adhesion can only decrease waters free energy, so metric potential is ALWAYS negative
due to adhesion of molecules to non dissolved structures
ALWAYS negative
Significance
outside living systems
dry soils
very high in plants
Cohesion-Tension Theory:
Transpiration Stream
Water movement from soil to atmosphere
Follows relatively high to low moisture level
From less negative to more negative water potential
Process:
Water evaporates out of open stomata to drier atmosphere, creating water potential differential
stomata open shortly after daybreak
Close at times of stress
Stomata closed at night
Water potential gradient from
mesophyll
cells all the way back to
xylem
draws water to vein
Stomata open
water
evaporates
from
intercellular spaces
Starts the domino effect of water potentials
Water enters through root hair via osmosis due to hypotonic soil solution
water moves from hypotonic to hypertonic solutions
root hair greatly increase surface area
Under SATURATED Conditions
Water passes through Endodermis, filtering solution, preventing embolism and foreign invaders
Casparian strip of root endodermis
symplastic movement
Embolism:
air pocket
effect:
non-functioning tracheary element
Water pulled up stem under tension, in an unbroken column
As water diffuses out of Xylem in the leaves, cohesive forces pull water upward through the xylem from roots
Water in the uppermost tracheary elements must lift the weight of the entire water column
Tension is on these molecules
causes pressure potential to be NEGATIVE
Strong Gradient necessary to maintain water flow
Water remains unbroken due to Cohesion of water molecules
Cohesion
Water polarity
Adhesion
along cell wall
helps to fight gravity
Pressure Flow
Xylem
water moves from less negative water potential to more negative water potential
Water Potential Differential
less negative water potential
Phloem
more negative water potential
Water enters sieve tube due to water potential differential, creating turgor pressure
Assimilate/Photosynthate loaded into sieve tube elements with help of companion cells from source
Sugars transported as sucrose
actively transported into sieve elements
Decreases water potential of STE
Sources to sink
Materials moved to
sinks
Actively growing areas
Leaves
Fruits
Shoot apical meristem
Storage areas
Roots
Root apical meristem
always close
Photosynthate moves by bulk flow to nearest/strongest
sink
and is unloaded
sucrose actively transported from sieve tube
by companion cells
stored as starch
used in metabolism
Aerobic respiration
Osmosis
causes ^
Concept
Key Terms:
Supports Growth and Development
Depends on Taxonomic Group