Lecture 9 Outline (Ch. 35)
I.
Overview of plant systems
II.
Major plant cell types
III. Three plant tissues
IV. Three plant organs
V.
Plant growth
A. Meristems
B. Primary vs secondary
C. Cell elongation &
division
VI. Summary
Plant Structure, Growth, Development
Plants are notably different from animals:
1. SA:V ratio
2. Mobility
3. Growth
4. Response to environment
5. Cell structure
Setting the scene - animal bodies
Cells  Tissues  Organs  Systems
Plant Cell Types
Plant cell structure recap
Cell wall, plasmodesmata
Primary wall (some have
secondary wall), middle lamella
Plant Cell Types
1) Parenchyma (most abundant):
Flexible, thin-walled cells; living
• plant metabolism:
Photosynthesis;
hormone secretion;
sugar storage
Parenchyma cells in
Elodea leaf,(w/chloroplasts)
• thin wall permeable to gasses
• large central vacuole
• able to divide and differentiate
Plant Cell Types
2) Collenchyma:
Thick-walled (uneven); living
• Offers support
(flexible & strong)
• Able to elongate
• Grouped in
strands, lack
secondary wall
Collenchyma cells sunflower
Plant Cell Types
3) Sclerenchyma: Thick, hard-walled; Dead
• Offer support (e.g. hemp
Sclereid cells
in pear (LM)
Cell wall
Fiber cells in ash tree
fibers; nut shells)
• Thick secondary walls
with lignin
• Rigid (cannot elongate)
• Two types –
sclereids and fibers
Plant Tissue Systems
1) Dermal Tissues
• Outer covering
• Protection
2) Vascular Tissues
• “Vessels” throughout plant
• Transport materials
3) Ground Tissues
• “Body” of plant
• Photosynthesis; storage; support
Made mostly of basic cell types:
Parenchyma
Collenchyma
Sclerenchyma
Plant “bodies”
Plants, like multicellular
animals, have organs
composed of different
tissues, which in turn
are composed of cells
• Each plant organ has
dermal, vascular, and
ground tissue systems
Three Basic Plant Organs:
Roots, Stems, and Leaves
Dermal
tissue
Ground
tissue Vascular
tissue
Think about plant “bodies” in
comparison to animal bodies:
A. For humans list example:
CELL TYPES
TISSUES
ORGANS
B. For plants list:
3 CELL TYPES
3 TISSUE SYSTEMS
3 ORGANS
Plant Tissues - Dermis
Dermal Tissue System (Covering of Plant):
1) Epidermal Tissue
(epidermis): Outer layer
Cuticle: Waxy covering reduces evaporation/ predation
Root Hairs: extended root
surface - Increase absorption
2) Peridermal Tissue (periderm):
• Only in woody plants (“bark = dead cells”)
• Protection; support
Plant Tissues - Dermis
Special Dermal Cells – Trichomes & Root hairs
• Trichomes
• Roots hairs
– Hair-like outgrowths of
– Tube extensions from
epidermis
epidermal cells
– Keep leaf surfaces cool and
– Greatly increase the root’s
reduce evaporation
surface area for absorption
Plant Tissues - Dermis
Special Dermal Cells – Guard Cells
Stomata
Guard cells
Epidermal cell
a.
4 µm
Stoma
Epidermal cell
Guard cells
b.
71 µm
c.
200 µm
Paired sausage-shaped cells
Flank a stoma – epidermal
opening
• Passageway for oxygen,
carbon dioxide, and water
vapor
Plant Tissues - Vascular
Vascular tissues made up of multiple cell types:
Arranged in multiple
bundles or central cylinder
Xylem – water and nutrients
Phloem – dissolved sugars and metabolites
Plant Tissues - Vascular
1) Xylem (dead at maturity): water and minerals roots to shoots
A)
B)
C)
Tracheids: Narrow, tube-like cells
Vessel Elements: Wide, tube-like cells
Fibers
1) Xylem:
Tracheids:
Plant Tissues - Vascular
- Most vascular plants
- Long, thin, tapered ends,
lignified secondary walls
- Water moves cell to cell
through pits
Vessel elements:
- Wider and shorter
- Perforation plates ends of
vessel elements
- water flows freely though
perforation plates
Plant Tissues - Vascular
2) Phloem (living at maturity) cells:
A) Sieve Tubes: Wide, tube-like cells
B) Companion Cells: support and regulate sieve tubes
Plant Tissues - Vascular
2) Phloem (living at maturity)
- Moves water, sugar, amino acids
& hormones
Sieve tube elements/members
• Long narrow cells stack end to end
• Pores in end walls (sieve plates)
• Lack most cellular structures including:
distinct vacuole, Some cytoskeletal
elements, Nucleus, Ribosomes
Companion Cells:
• Adjacent to every sieve tube
element
• Non-conducting.
• Regulate both cells
• Connected by numerous
plasmodesmata
Plant Tissues – Ground Tissue
• Tissues that are neither
dermal nor vascular are
ground tissue
• Ground tissue internal to
the vascular tissue is
pith; ground tissue
external to the vascular
tissue is cortex
• Ground tissue includes
cells specialized for
storage, photosynthesis,
and support
– Includes parenchyma,
collenchyma,
sclerenchyma
Plant Organs: Roots - Overview
• Roots need sugars from photosynthesis;
• Shoots rely on water and minerals absorbed
by the root system
• Root Roles:
- Anchoring the plant
- Absorbing minerals and water
- Storing organic nutrients
Plant Organs: Roots - Comparisons
Taproots:
Typical of dicots,
primary root forms
and small branch
roots grow from it
Fibrous roots:
In monocots mostly,
primary root dies,
replaced by new
roots from stem
Plant Organs: Roots – Structure and Development
• Four regions:
– Root cap
Protection, gravity detection
– Zone of cell division
Mitotic divisions
– Zone of elongation
Cells lengthen, no division
– Zone of maturation
Cells differentiate, outer layer
becomes dermis
Plant Organs: Roots – Vasculature
Epidermis
Dicot
Monocot
Cortex
Endodermis
Vascular
cylinder
100 m
(a) Root with xylem and
phloem in the center
Pericycle
Core of
parenchyma
cells
Xylem
Phloem
100 m
(b) Root with parenchyma in the
center
50 m
Endodermis
Pericycle
Xylem
Phloem
Key
to labels
Dermal
Ground
Vascular
Prop roots
Roots – Many Plants Have
Modified Roots
“Strangling”
aerial roots
Storage roots
Buttress
roots
Pneumatophores
Water storage
Plant Organs: Stems - Overview
Stem: an organ made of
– Alternating nodes,
points of leaf attachment
– Internodes, stem length
between nodes
• Axillary bud - can form
a lateral shoot/branch
• Apical (terminal) bud near the shoot tip,
lengthens a shoot
• Apical dominance
maintains dormancy in
most non-apical buds
Apical bud
Node
Internode
Apical
bud
Vegetative
shoot
Axillary
bud
Stem
Shoot
system
Vasculature - Stems
• In most monocot stems, the vascular bundles are scattered
throughout the ground tissue, rather than forming a ring
Phloem
Xylem
Sclerenchyma
(fiber cells)
Ground
tissue
Ground tissue
connecting
pith to cortex
Pith
Epidermis
Key
to labels
Cortex
Epidermis
Vascular
bundle
Dermal
Vascular
bundles
Ground
1 mm
(a) Cross section of stem with vascular bundles forming
a ring (typical of eudicots)
Dicot
Vascular
1 mm
(b) Cross section of stem with scattered vascular bundles
(typical of monocots)
Monocot
Stems – Many Plants
Have Modified Stems
Rhizomes
Bulbs
Storage leaves
Stem
Stolons
Stolon
Tubers
So far we have covered the
organs stems and roots:
Match each term number with a letter for the image:
1. Monocot stem
A.
B.
C.
D.
2. Monocot root
3. Dicot stem
4. Dicot root
Plant Organs: Leaves - Overview
The leaf is the main photosynthetic
organ of most vascular plants
Shoot
system
Leaves generally have
Leaf
Blade
Petiole
a flattened blade
and a stalk called the
petiole - joins the leaf to node
of the stem
Leaves – Structure
• Leaves are several layers thick – different cell types
Key
to labels
Sclerenchyma
fibers
Cuticle
Dermal
Ground
Vascular
Stoma
Upper
epidermis
Palisade
mesophyll
Spongy
mesophyll
Lower
epidermis
Xylem
Phloem
Vein
Guard
cells
Cuticle
Plant Organs: Leaves
• Leaf epidermis
contains stomata allow CO2 exchange
• Stomata flanked by
two guard cells, control
open vs. closed
Plant Organs: Leaves - Comparisons
Monocots and dicots differ in the arrangement of veins,
the vascular tissue of leaves
Most dicots have
branch-like veins and
palmate leaf shape
Monocots have parallel
leaf veins and longer,
slender blades
Leaves – Plants have
modified leaves for
various functions
Tendrils
Spines
Storage
leaves
Reproductive leaves
Bracts
Plant Classification – Monocots vs. Dicots
Basic categories of plants based on structure and function
Plant Growth
Plant Growth:
1) Indeterminate: Grow throughout life
2) Growth at “tips” (length) and at
“hips” (girth)
Growth patterns in plant:
1) Meristem Cells: Dividing Cells
2) Differentiated Cells: Cells specialized in structure & role
• Form stable, permanent part of plant
Plant Growth
1) Primary Growth:
• Apical Meristems:
Mitotic cells at “tips” of roots / stems
length
1) Increased length
2) Specialized structures (e.g. fruits)
2) Secondary Growth:
girth
• Lateral Meristems:
Mitotic cells “hips” of plant
Responsible for increases in stem/root diameter
Plant Growth – primary growth
Plant Growth in woody plants (secondary growth)
Two lateral meristems: vascular cambium and cork cambium
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
• thicker, stronger stems
Vascular Cambium:
between primary xylem
and phloem
Plant Growth
Stem – Secondary Growth:
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Produces inside stem:
A) Secondary xylem
- moves H2O, inward
B) Secondary phloem
- moves sugars, outward
Vascular Cambium:
Plant Growth
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Most recent cork cambium
Cork
Bark
Layers of
periderm
A hammock is hung between two trees in his
backyard by a young man who is 15 years old.
If he returns 20
years later to find
his hammock, how
will the position of
the hammock have
changed?
Plant Growth – cell growth
Plant cells have cellulose microfibrils in the cell wall
These can be
enzymatically
loosened, and
the cell
expanded by
storing water
in the central
vacuole. Later
the fibrils
reattach.
Plant Growth – asymmetric divisions
Often plant cells divide unequally in specifying cell types.
For example, to form guard cells of stomata, the first division
is toward one end of the cell. The second division is rotated
90 degrees.
Two guard cells
Unspecialized
epidermal cell