Plant Body Organization

Plant Body Organization
Epidermis
The epidermis is a specialized cell layer characterized by anticlinal cell
divisions. It forms the outer cell layer in most plant tissues. It may be
replaced by periderm (bark) in plants with secondary growth.
Epidermis
Pine leaf
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Plant Body Organization
Epidermis
The epidermis may be a homogeneous layer surrounding a tissue like the
stem or may differ depending on whether the epidermal layer is on the
biological top (adaxial) and bottom (abaxial) of some organs like leaves.
Adaxial
Abaxial
Leaf cross-section
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Plant Body Organization
Epidermis – Uniseriate Epidermis
The epidermis can be uniseriate (single layer) or multiseriate (two or more layers).
Most plants have a single uniseriate epidermal layer.
Uniseriate epidermis in a tomato leaf
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Plant Body Organization
Epidermis – Multiple Epidermis
A multiseriate or multiple epidermis has two or more cell layers derived originally
from meristematic protoderm tissue. The cells of the multiple epidermis appear
distinct from the inner organ tissue derived from the ground meristem.
The multiple epidermis
in a fig (Ficus) leaf.
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Plant Body Organization
Epidermis – Multiple Epidermis
The multiple epidermis
in a peperomia leaf is
many layers thick.
Epidermis
Mesophyll
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Plant Body Organization
Epidermis – Multiple Epidermis
In epiphytic orchids, aerial roots
contain an outer velamen layer that is
considered a multiple epidermis.
Chlorophyll
layer
The epidermal velamen cells are
modified to absorb atmospheric water.
Velamen
layer
Velamen
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Plant Body Organization
Epidermis – Hypodermis
A hypodermis is a subepidermal layer similar to a multiple epidermis
except that the cells are derived from ground tissue rather than
protoderm or epidermis. Ontogenetic studies are necessary to
differentiate between hypodermal and multiple epidermal layers.
Epidermis
Hypodermis
Mesophyll
Banana (Musa) leaves produce a hypodermal layer.
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Plant Body Organization
Epidermis
In most cases, the epidermis
contains few chloroplasts and is
generally non-pigmented.
However, the epidermis in petals,
fruits and some leaves can
contain anthocyanin pigments.
Vinca (Catharanthus) petal
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Velvet plant (Gynura) leaf
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Plant Body Organization
Epidermis
From a surface view, leaf epidermal cells show various sizes and shapes
from prismatic to undulating cells resembling jigsaw puzzle pieces.
Corn (Zea)
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Coneflower (Echinacea)
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English ivy (Hedera)
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Plant Body Organization
Epidermis – Specialized Structures
The epidermis is not a
homogeneous group of
cells.
Trichome
A epidermal surface can
also contain trichomes,
stomates and other
specialized cells.
Trichomes and stomates
are described in detail
under the cell types
section.
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Stomate
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Plant Body Organization
Epidermis – Specialized Structures
The epidermis can contain
sclereid cells or be composed
entirely of sclereids as is
seen in the seed coats of
physical dormant seeds.
Macrosclereids
Seed coat in eastern redbud (Cercis).
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Plant Body Organization
Epidermis – Specialized Structures
The epidermis in certain monocots (especially the grasses) can have
specialized cells called bulliform cells. These are large highly vacuolated
cells that are thought to be involved with leaf folding and unfolding.
Bulliform cells
Rye grass (Lolium) leaf
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Plant Body Organization
Epidermis – Specialized Structures
In some cases, crystals or salt deposits can be seen in
epidermal cells.
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Plant Body Organization
Epidermis – Multiple Epidermis – Specialized Structures
The leaves of plants within certain families (Moraceae, Acanthaceae, and
Cucurbitaceae) can produce an epidermal cell type called a lithocyst that
contains a calcium carbonate formation called a cystolith.
Lithocyst
Cystolith
Fig (Ficus) leaf
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Plant Body Organization
Epidermis – Specialized Structures
The epidermal cells that form the seed coat or outer pericarp in some seeds
or fruits can contain mucilage. When the seeds imbibe, the hydrophilic
mucilage rapidly expands and extrudes from the epidermal cells.
Mucilage
Outer
pericarp
Endocarp
Seed
coat
Chia seed (nutlet) depositing
mucilage during seed development.
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Outer pericarp extruding mucilage
after hydration.
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Plant Body Organization
Epidermis – Specialized Structures
Electron micrograph of Chia seed following hydration.
Inner
pericarp walls
Outer
pericarp wall
Mucilage
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Plant Body Organization
Epidermis - Cuticle
The epidermis is covered with an outer layer or cuticle. The cuticle contains cutin,
which is a waxy, water insoluble polymer. The cuticle functions to reduce water
loss and may act as a defensive barrier to insect and disease attack.
Water beading on the waxy leaf
surface of sacred lily (Nelumbo).
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Waxy
Alstroemeria leaf.
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Waxy stem of Kentucky
Coffeetree (Gymnocladus)
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Plant Body Organization
Epidermis - Cuticle
In addition to the cuticle layer, additional waxes can be
deposited on the cuticle’s surface called epicuticular waxes.
Epicuticular
wax
Cuticle
Epidermis
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Plant Body Organization
Epidermis - Cuticle
The epicuticular wax covering can form as a relatively smooth
surface or form in rod-like filaments of wax.
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