Plant Tissues
Angiosperms – flowering plants
• The angiosperms are seed-bearing
vascular plants
• In terms of distribution and diversity, they
are the most successful plants on Earth
• The structure and function of this plant
group help explain its success
Monocots and Dicots – same
tissues, different features
1 cotyledon
4 or 5 floral
parts
3 floral
parts
Parallel veins
1 pore
Vascular
bundles
in ring
2 cotyledons
Netlike veins
3 pores
Vascular
bundles
dispersed
Flowering
Plant Life
Cycle
Diploid
Double fertilization
Haploid
pollination
Two
sperms
enter
ovule
Meiosis
microspores
Female gametophyte
Meiosis
Mitosis
without
cytoplasmic
division
Plant Life Histories
• Annuals complete life cycle in one growing season
• Biennials live for two seasons; flowers form in second
season
• Perennials grow and produce seeds year after year
Meristems – Where Tissues Originate
• Regions where cell divisions produce plant growth
• Apical meristems
– Responsible for primary growth (length)
• Lateral meristems
– Responsible for secondary growth (width)
Apical Meristems
Lengthen shoots and roots:
StemAM and RootAM
activity at
meristems
Cells that form at apical
meristems:
protoderm  epidermis
ground meristem  ground
tissues
procambium  primary
vascular tissues
new cells
elongate
and start to
differentiate
into primary
tissues
Lateral Meristems
Increases girth of older roots and stems
Cylindrical arrays of cells
vascular cambium  secondary vascular tissues
periderm  cork cambium
thickening
Plant Tissue Systems
• Ground tissue system
• Vascular tissue system
EPIDERMIS
• Dermal tissue system
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
Ground Tissue
• fills space b/t dermis & vascular
Parenchyma:
Primary
metabolic
(photosynthesis)
function
– Found in roots, stems & leaves
– Least specialized, thin flexible walls, don’t divide unless
specializing, respire, store food & water
Schlerenchyma: support w/ thick 2o wall strengthened
by lignin
– Found in stems & leaves
generally lack protoplasts
– Very rigid cell wall, dead at maturity, cannot lengthen
scaffolding “fibers” & “Sclereids”
Collenchyma:
child support
– Found in stems and leaves
– Grow and elongate with stems and leaves they support,
flexible in young parts of plant
Morphology of three simple tissue types
parenchyma
collenchyma
sclerenchyma
Simple Tissues
Complex Tissues
Made up of
only one
type of cell
Composed of a
mix of cell
types
Parenchyma
Collenchyma
Sclerenchyma
Xylem
Phloem
Epidermis
Vascular Tissue
Phloem: Phood conduction, carries products of photosynthesis to
non-photo cells
– Found in roots, stems, leaves
– Sieve cells, albuminous cells, companion cells, parenchyma
– Gymnospersm: sieve, angiosperms, sieve-tube members, connected
vertically by sieve plates
– Alive at maturity
Xylem:
–
–
–
–
–
provides water & ion transport from roots to leaves
Vessel elements, tracheids, fibers, wood parenchymal
tracheids & vessel members, thick w/ secondary wall with lignin
Dead at maturity
Seedless vascular & gymnosperms have tracheids w/ tapered ends
Angiospersm have both tracheids and vessel members wh are
continuous
Xylem
• Conducts water
and dissolved
minerals
• Conducting cells
are dead and
hollow at maturity
tracheids
vessel
member
Phloem: A Complex Vascular
Tissue
sieve plate
• Transports sugars
• Main conducting
cells are sievetube members
• Companion cells
assist in the
loading of sugars
sieve-tube
member
companion
cell
Epidermis:
A Complex Plant Tissue
- Covers and protects plant surfaces
- Secretes a waxy, waterproof
cuticle
- In plants with secondary growth,
periderm replaces epidermis
- protection, increase absorption
area in roots, reduces H2O loss in
stem & leaves,
- Regulates gas exchange in leaves
Signaling between Plants and Pathogens
Shoot and Root Systems:
Not independent
Shoot system
- produces sugars
by photosynthesis
- carries out
reproduction
water &
minerals
Root system
- anchors the plant
- penetrates the soil and
absorbs water and minerals
- stores food
sugar
SHOOT SYSTEM
ROOT SYSTEM
shoot apical
meristem
Shoot
Development
cortex
procambrium
protoderm procambrium
pith
ground meristem
primary xylem
primary phloem
Roots also have meristems
Leaf Gross Structure-Adapted for Photosynthesis
• Leaves are usually thin
– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in, oxygen out
• Leaves are arranged to capture sunlight
– Are held perpendicular to rays of sun
DICOT one another
– Arrange so they don’t shade
MONOCOT
petiole
axillary
bud
blade
node
sheath
blade
node
Leaf Structure
UPPER
EPIDERMIS
cuticle
PALISADE
MESOPHYLL
xylem
SPONGY
MESOPHYLL
phloem
LOWER
EPIDERMIS
O2
CO2
one stoma
Mesophyll: Photosynthetic Tissue
• A type of parenchyma tissue
• Cells have chloroplasts
• Two layers in dicots
– Palisade mesophyll
– Spongy mesophyll
Collenchyma
Parenchyma
Leaf Veins: Vascular Bundles
• Xylem and phloem –
often strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
Internal Structure of a
Dicot Stem
- Outermost layer is epidermis
- Cortex lies beneath epidermis
- Ring of vascular bundles
separates the cortex from the pith
- The pith lies in the center of the
stem
Internal
Structure
of a
Monocot
Stem
• The vascular bundles
are distributed
throughout the ground
tissue
• No division of ground
tissue into cortex and
pith
Dicots
Monocots
Ground tissue
system
Dermal tissue
system
Vascular tissue
system
Dicots and Monocots have different stem and root anatomies
Stems
Monocot stems differ
from dicot stems in
that they lack
secondary growth
• No vascular cambium
nor cork cambium
• Stems usually
uniform in diameter
• Scattered vascular
bundles (not in a ring
like dicot stems)
The Translocation of Phloem
•
•
•
the process of moving
photosynthetic product through the
phloem
In angiosperms, the specialized cells
that transport food in the plant are
called sieve-tube members,
arranged end to end to form large
sieve tubes
Phloem sap is very different from
xylem sap
– sugar (sucrose) can be concentrated
up to 30% by weight
•
Phloem transport is bidirectional
– Phloem moves from a sugar source
(a place where sugar is produce by
photosynthesis or by the breakdown
of sugars) to a sugar sink (an organ
which consumes or stores sugar)
– What are some organs which would
be sugar sinks?
Transport in Plants:
The Pressure Flow Model , 2
Root Systems
Root Structure
• Root cap covers tip
• Apical meristem
produces the cap
• Cell divisions and
elongation at the
apical meristem
cause the root to
lengthen
epidermis
endodermis
cortex
pericycle
root
hair
phloem
xylem
• Farther up, cells
differentiate and
mature
root apical
meristem
root cap
Primary Root Growth
Root Cap
•Secretes polysaccharide slime that lubricates the soil
•Constantly sloughed off and replaced
Apical Meristem
•Region of rapid cell division of undifferentiated cells
•Most cell division is directed away from the root cap
Quiescent Center
•Populations of cells in apical meristem which reproduce much more
slowly than other meristematic cells
•Resistant to radiation and chemical damage
•Possibly a reserve which can be called into action if the apical meristem
becomes damaged
The Zone of Cell Division - Primary Meristems
•Three areas just above the apical meristem that continue to divide for
some time
•Protoderm
•Ground meristem
•Procambium
The Zone of Elongation
•Cells elongate up to ten times their original length
•This growth pushes the root further downward into the soil
The Zone of Maturation
•Region of the root where completely functional cells are found
Internal Structure of a Root
• Outermost layer is epidermis
• Root cortex is beneath the epidermis
• Endodermis, then pericycle surround the vascular
cylinder
• In some plants, there is a central pith
Root Anatomy - Dicot Roots
Epidermis
•
Dermal tissue
•
Protection of the root
Cortex
•
Ground tissue
•
Storage of photosynthetic products
•
Active in the uptake of water and minerals
Endodermis
•
cylinder once cell thick that forms a boundary between the
cortex and the stele contains the casparian strip,
Pericycle
•
found just inside of the endodermis
•
may become meristematic
•
responsible for the formation of lateral roots
Vascular Tissue
•
Xylem and Phloem
Root Anatomy - Monocot Roots
Epidermis
•
Dermal tissue
•
Protection of the root
Cortex
•
Ground tissue
•
Storage of photosynthetic products
•
Active in the uptake of water and minerals
Endodermis
•
cylinder once cell thick that forms a boundary between the
cortex and the stele even more distinct than dicot counterpart
contains the casparian strip,
Pericycle
•
monocot roots rarely branch, but can, and this branch will
originate from the pericycle
Vascular Tissue
•
Xylem and Phloem
•
Forms a ring near center of plant
Pith
•
Center most region of root
Root Hairs and Lateral Roots
• Both increase the surface area of
a root system
• Root hairs are tiny extensions of
epidermal cells
• Lateral roots arise from the
pericycle and must push through
the cortex and epidermis to reach
the soil
•
Root of a single rye plant (fibrous system) measure
and counted 6400 roots w/ 12.5 million root hairs =
250 km, dist from Memphis, TN to Atlanta, GA
new
lateral
root
Symplastic Movement
• Movement of water and solutes through the continuous
connection of cytoplasm (though plasmodesmata)
• No crossing of the plasma membrane (once it is in the
symplast)
Apoplastic Movement
• Movement of water and solutes through the cell walls and the
intercellular spaces
• No crossing of the plasma membrane
• More rapid - less resistance to the flow of water
Net flow in
whole plants
Fig. 39.12b
Ascent of xylem sap
•transpirational pull
•flow from greater to lower
water concentration
•relies on cohesion &
adhesion of water
–cavitation breaks chain of
water molecules
Fig. 39.11
The availability of soil water and minerals
Long-distance transport of water from roots to leaves
Net flow in
whole plants
Key Concepts:
• Diffusion: movement
of molecules from
high to low
concentration.
• Osmosis: diffusion of
water across a semipermeable
membrane.
• Mass or bulk flow:
movement of fluid
due to pressure or
gravity differences.
Long-distance movement of water
• Plants mostly obtain water & minerals from soil.
• Water moves up the xylem by bulk flow.
• Movement of water depends on transpiration pull, cohesion &
adhesion of water molecules, capillary forces, and strong cell
walls.
Other mechanisms of water transport not as
important:
• Diffusion (note mosses, etc.)
• Capillary forces (cohesions & adhesion)
• Osmotic pressure (guttation)
Fig. 39.11
Water – pushed or pulled?
• Pushing of the xylem sap occurs via
root pressure – root cells expend
energy to pump mineral into the
xylem. Minerals accumulate in the
xylem sap lowering water potential
there. Thus water flows into the
xylem, generating a positive
pressure that pushes fluid up the
xylem.
Guttation – from root
pressure
availability
of soilsap
waterup
andaminerals
But root pressureThe
can
only push
few meters and many plants generate no
root pressure at all. How does water
reach leaves of 100 m tall trees?
Xylem sap is pulled up the plant via
transpirational pull. Leaves actually
generate the negative pressure
necessary to bring water to them.
Long-distance transport of water from roots to leaves
• The transport of food throughout a plant is
known as translocation.
• Sugar from mesophyll cells in the leaves
and other sources must be loaded before it
can be moved.
• Often sieve tube members accumulate very
high sucrose concentrations – 2 to 3 times
higher than concentrations in the mesophyll
– so phloem requires active transport using
proton pumps
• At the sink end of a sieve tube, the phloem
unloads its sugar. Phloem unloading is a
highly variable process; its mechanism
depends upon the plant species and the type
of organ. In any case, the concentration of
sugar in the sink cells is lower than in the
phloem because the sugar is either
consumed or converted into insoluble
polymers like starch.
• Phloem moves at up to 1 m/hour – too fast
to be by diffusion. So phloem also moves
via bulk flow – pressure drives it.
Translocation
Secondary Growth
• Occurs in perennials
• A ring of vascular cambium produces secondary xylem and
phloem
• Wood is the accumulation of these secondary tissues,
especially xylem
The Plant Body: Secondary Growth: The Vascular Cambium
Woody Stem
periderm (consists of
cork, cork cambium,
and secondary cortex)
BARK
vascular cambium
secondary
phloem
HEARTWOOD
SAPWOOD
Annual Rings
• Concentric rings of secondary xylem
• Alternating bands of early and late wood
• Early wood
– Xylem cells with large diameter, thin walls
• Late wood
– Xylem cells with smaller diameter, thicker
walls
Types of Wood
• Hardwood (oak, hickory)
– Dicot wood
– Xylem composed of vessels, tracheids,
and fibers
• Softwood (pine, redwood)
– Gymnosperm wood
– Xylem composed mostly of tracheids
– Grows more quickly
Resources
•
•
•
•
•
Plants in Motion:
Movement of Water in Plants
Transport in Plants
Root Pressure
Water Transport in 3 Parts