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CHAPTER 36
LECTURE
SLIDES
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Plant Form
Chapter 36
Plant Body Organization
• A vascular plant consists of
• Root system
– Anchors the plant
– Used to absorb water and ions
• Shoot system
– Consists of supporting stems, photosynthetic
leaves, and reproductive flowers
– Iterative unit consists of internode, node, leaf,
and axillary bud
3
4
• 3 basic tissue types
– Dermal – outer protective cover
– Ground – function in storage, photosynthesis,
and secretion
– Vascular – conducts fluids and dissolved
substances
• Tissues consist of one or more cell types
• Tissue systems – each of these tissue
types extends through root and shoot
systems
5
• Distinguishing plant cell types based on
– Size of vacuoles
– Living or not at maturity
– Thickness of secretions found in their
cellulose cell walls
• Some cells have only a primary cell wall of
cellulose, synthesized at the protoplast (cell
membrane)
• Some cells have more heavily reinforced cell walls
with multiple layers of cellulose
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7
• Meristems
– Clumps of small cells with dense cytoplasm
and large nuclei
– Act as stem cells do in animals
– One cell divides producing a differentiating
cell and another that remains meristematic
– Plant biologists use term meristem cell rather
than stem cell to avoid confusion
– Extension of shoot and root produced by
apical meristems
– Lateral meristems produce an increase in
shoot and root diameter
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9
• Apical meristem
• Located at tips of stems and roots
• Give rise to primary tissues which are
collectively called the primary plant body
• Apical meristems composed of delicate
cells that need protection
– Root cap protects root apical meristem
– Leaf primordia protect shoot apical meristem
10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Young leaf
primordium
Shoot apical
meristem
Older leaf
primordium
Lateral bud
primordium
100 µm
dermal tissue
ground tissue
vascular tissue
Root apical
meristem
Root cap
400 µm
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(top left, right): © Dr. Robert Lyndon; (bottom left, right): © Biodisc/Visuals Unlimited
• Apical meristem gives rise to the three
tissue systems by first initiating primary
meristems
– 3 primary meristems
• Protoderm – forms epidermis
• Procambrium – produces primary vascular tissue
• Ground meristem – differentiates into ground
tissue
– Some plants have intercalary meristems
• Arise in stem internode
• Add to internode length
12
• Lateral meristems
– Found in plants that exhibit secondary growth
– Give rise to secondary tissues which are
collectively called the secondary plant body
– Woody plants have two types
• Cork cambium produces outer bark
• Vascular cambium produces secondary vascular
tissue
– Secondary xylem is the main component of wood
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14
Plant Tissues
• Three main types of tissue
– Dermal
• On external surfaces that serves a protective
function
– Ground
• Forms several different internal tissue types and
can participate in photosynthesis, serve a storage
function, or provide structural support
– Vascular
• Conducts water and nutrients
15
Dermal Tissue
• Forms the epidermis
• One cell layer thick in most plants
• Forms the outer protective covering of the
plant
• Covered with a fatty cutin layer
constituting the cuticle
• Contains special cells, including guard
cells, trichomes, and root hairs
16
• Guard cells
– Paired sausage-shaped cells
– Flank a stoma – epidermal opening
• Passageway for oxygen, carbon dioxide, and water
vapor
– Stomatal patterning genes reveal a
coordinated network of cell–cell
communication that informs cells of their
positions relative to other cells and
determines cell fate
17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stomata
Guard cells
Epidermal cell
a.
4 µm
c.
200 µm
Stoma
Epidermal cell
Guard cells
b.
71 µm
a: © Brian Sullivan/Visuals Unlimited; b-c: © EM Unit, Royal Holloway, University of London, Egham, Surrey
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• Trichomes
– Cellular or multicellular
hairlike outgrowths of
the epidermis
– Keep leaf surfaces cool
and reduce
evaporation by
covering stomatal
openings
– Some are glandular,
secreting substances
that deter herbivory
19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Trichome cell
1.
Trichome
a.
Trichomepromoting
proteins,
including
GL3
Trichomeinhibiting
proteins
Activation
3.5 mm
2. Trichome initiation ON
Inhibition
Trichome
develops
Trichome will
not develop
3. Trichome initiation OFF
Neighboring cell
b.
3.5 mm
c.
a-b: Courtesy of Allan Lloyd
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• Roots hairs
– Tubular extensions of
individual epidermal
cells
– Greatly increase the
root’s surface area
and efficiency of
absorption
– Should not be
confused with lateral
roots
21
Ground Tissue
• 3 cell types
• Parenchyma
– Function in storage, photosynthesis, and
secretion
• Collenchyma
– Provide support and protection
• Sclerenchyma
– Provide support and protection
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• Parenchyma cells
– Most common type of plant cell
– Living protoplasts – may live many years
– Function in storage, photosynthesis, and
secretion
– Less specialized than other plant cells
• Collenchyma cells
– Provide support for plant organs
– Allow bending without breaking
– Living protoplasts – may live many years
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• Sclerenchyma cells
– Tough thick walls
– Usually lack living protoplasts at maturity
– Secondary cell walls often contain lignin
– Two general types – both strengthen tissues
• Fibers – long, slender cells that are usually
grouped in strands
• Sclereids – variable shape, often branched, may
occur singly or in groups
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Vascular Tissue
• Xylem
– Principal water-conducting tissue
– Vessels
• Continuous tubes of dead cylindrical cells
arranged end-to-end
– Tracheids
• Dead cells that taper at the end and overlap one
another
– Vessel members tend to be shorter and wider
than tracheids
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• Xylem
– Also conducts inorganic ions such as nitrates,
and supports the plant body
– Transpiration – diffusion of water vapor from
plant
– In addition to conducting cells, xylem typically
includes fibers and parenchyma cells (ground
tissue cells)
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• Phloem
– Principal food-conducting tissue in vascular
plants
– Contains two types of elongated cells
• Sieve cells (seedless vascular plants and
gymnosperms) and sieve tube members
(angiosperms)
• Living cells that contain clusters of pores called
sieve areas or sieve plates
• Sieve-tube members are more specialized (more
efficient)
– Associated with companion cells
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30
Roots
• Simpler pattern of organization and
development than stems
• Four regions are commonly recognized:
– Root cap
– Zone of cell division
– Zone of elongation
– Zone of maturation
Boundaries
not clearly
defined
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32
• Root cap
– No equivalent in stems
– Contains two types of cells that are formed
continuously by the root apical meristem
• Columella cells – inner
• Root cap cells – outer and lateral
– Functions mainly in protection of the delicate
tissues behind it
– Also in the perception of gravity
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• Zone of cell division
– Derived from rapid divisions of the root apical
meristem
– Contains mostly cuboidal cells, with small
vacuoles and large central nuclei
• Daughter cells of apical meristem
– Apical meristem daughter cells soon
subdivide into the three primary tissues
• Protoderm, procambium, and ground meristem
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• Zone of cell division
– Patterning of these tissues begins in this zone
– WEREWOLF (WER) gene
• Suppresses root hair development
– SCARECROW (SCR) gene
• Necessary for differentiation of endodermal and
ground cells
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• Zone of elongation
– Roots lengthen because cells become several
times longer than wide
– Width also increases slightly
– No further increase occurs above this zone
– Mature parts of the root, except for increasing
in girth, remain stationary for the life of the
plant
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• Zone of maturation
– Elongated cells become differentiated into
specific cell types
– Root surface cells become epidermal cells
• Have very thin cuticle
• Include root hair and nonhair cells
– Parenchyma cells produced by cortex (ground
meristem)
• Inner boundary becomes endodermis
– Casparian strips
• Stele – tissues interior to endodermis
– Pericycle
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40
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phloem
Casparian strip
Xylem
Cortex
H2O
Pericycle
H2O
Endodermal cell
Epidermis
Cortex
Monocot
Endodermis
Location of
Casparian strip
Primary phloem
Pericycle
Primary xylem
Pith
1250 µm
385 µm
Endodermis
Location of
Casparian strip
Primary xylem
Eudicot
Endodermis
Cortex
Primary phloem
Epidermis
Pericycle
48 µm
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8 µm
(top left): © Carolina Biological Supply Company/Phototake; (top right): Photo by George S. Ellmore; (bottom left): © Lee W. Wilcox; (bottom right):
Photo by George S. Ellmore
Stages in the differentiation of
plant tissues
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Modified Roots
• Most plants produce either/or:
– Taproot system – single large root with small
branch roots
– Fibrous root system – many small roots of
similar diameter
– Some plants, however, produce modified
roots with specific functions
– Adventitious roots arise from any place other
than the plant’s root
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Modified Roots
•
•
•
•
•
•
•
•
Prop roots: Keep the plant upright
Aerial roots: Obtain water from the air
Pneumatophores: Facilitate oxygen uptake
Contractile roots: Pull plant deeper into soil
Parasitic roots: Penetrate host plants
Food storage roots: Store carbohydrates
Water storage roots: Weigh 50 kg or more
Buttress roots: Provide considerable stability
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Prop roots
Aerial roots
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Pneumatophores
Water storage roots
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Buttress roots
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Stems
• Like roots, stems contain the three types
of plant tissue
• Also undergo growth from cell division in
apical and lateral stems
• Shoot apical meristem initiates stem tissue
and intermittently produces primordia
– Develop into leaves, other shoots, and even
flowers
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49
• Leaves may be arranged in one of three
ways
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•
•
•
•
•
•
Node – point of attachment of leaf to stem
Internode – area of stem between two nodes
Blade – flattened part of leaf
Petiole – stalk of leaf
Axil – angle between petiole/blade and stem
Axillary bud – develops into branches with
leaves or may form flowers
• Terminal bud – extends the shoot system during
the growing season
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• Major distinguishing feature between
monocot and eudicot stems is the
organization of the vascular tissue system
– Monocot vascular bundles are usually
scattered throughout ground tissue system
– Eudicot vascular tissue is arranged in a ring
with internal ground tissue (pith) and external
ground tissue (cortex)
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Eudicot
Monocot
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• Vascular tissue arrangement is directly
related to the stem’s ability for secondary
growth
– In eudicots, a vascular cambium develops
between the primary xylem and phloem
• Connects the ring of primary vascular bundles
– In monocots, there is no vascular cambium –
no secondary growth
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57
• Rings in the stump of a tree reveal annual
patterns of vascular cambium growth
– Cell size depends on growth conditions
– In woody eudicots and gymnosperms, the
cork cambium arises in the outer cortex
• Produces boxlike cork cells on outside and
parenchyma-like phelloderm cells on inside
• Collectively called the periderm
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Internal Stem Structure
59
• Periderm – cork cambium, cork, and
phelloderm
– Forms outer bark
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• Lenticels – Cork cambium produces
unsuberized cells that permit gas exchange to
continue
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• Bulbs – swollen underground stems,
consisting of fleshy leaves
• Corms – superficially resemble bulbs, but
have no fleshy leaves
• Rhizomes – horizontal underground
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stems, with adventitious roots
• Runners and stolons – horizontal stems
with long internodes that grow along the
surface of the ground
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• Tubers – swollen tips of rhizomes that contain
carbohydrates
• Tendrils – twine around supports and aid in
climbing
• Cladophylls – flattened photosynthetic stems
resembling leaves
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Leaves
• Initiated as primordia by the apical
meristems
• Principal site of photosynthesis
• Expand by cell enlargement and cell
division
• Determinate in structure – growth stops at
maturity
• Different patterns adaptive in different
environments
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• 2 different morphological groups
– Microphyll
• Leaf with one vein branching from the vascular
cylinder of the stem and not extending the full
length of the leaf
• Phylum Lycophyta
– Megaphylls
• Several to many veins
• Most plants
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• Most eudicot leaves have a flattened
petiole
• Slender stalk called petiole
• Leaf flattening increases photosynthetic
surface
• Flattening of the leaf blade reflects a shift
from radial symmetry to dorsal–ventral
(top–bottom) symmetry
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68
• Leave may have stipules
– Outgrowths at base of petiole
– May be leaf-forming or modified as spines
• Veins
– Vascular bundles in leaves
– main veins are parallel in most monocot leaves
– Veins of eudicots form an often intricate network
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• Simple leaves contain undivided blades
– May have teeth, indentations, or lobes
• Compound leaves have blades that are
divided into leaflets
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• The leaf’s surface is covered by
transparent epidermal cells
– Most have no chloroplasts
• Epidermis has a waxy cuticle
– Different types of glands and trichomes may
be present
• Lower epidermis contains numerous
stomata flanked by guard cells
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72
• Most eudicot leaves have 2 types of
mesophyll
– Palisade mesophyll – usually two rows of
tightly packed chlorenchyma cells
– Spongy mesophyll – loosely arranged cells
with many air spaces in between
• Function in gas exchange and water vapor exit
• Monocot leaves – mesophyll is usually not
differentiated into palisade/spongy layers
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Modified Leaves
• Floral leaves (bracts) – surround true
flowers and behave as showy petals
• Spines – reduce water loss and may deter
predators
• Reproductive leaves – plantlets capable of
growing independently into full-sized plant
• Window leaves – succulent, cone-shaped
leaves that allow photosynthesis
underground
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• Shade leaves – larger in surface area but
with less mesophyll than sun-lit leaves
• Insectivorous leaves – trap insects
– Pitcher plants have cone-shaped leaves that
accumulate rainwater
– Sundews have glands that secrete sticky
mucilage
– Venus flytrap have hinged leaves that snap
shut
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