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Epidermis
Plant Anatomy 254 lec 5
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plant Anatomy 254 lec.5
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• The epidermis is a system of cells.
• Vary in structure and function.
• Form the covering of the primary plant
body.( the layer of cells in contact with the
external environment of the plant)
• It may last through the life of a given plant
part or it may be replaced by other
protective tissue (periderm)
plant Anatomy 254 lec.5
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• It is usually one layer of cells in
thickness.
• Sometimes the protoderm (meristems that
will differentiate into epidermis) divide
parallel (periclinally X anticlinally)with
the surface and their derivatives may
divide again resulting in tissue with many
related layers (multiple epidermis) (in
leaves, velamen: multiple epidermis
covering aerial roots in epiphytic plants)
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velamen
layers of
dead, hollow
cells
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• Multiple epidermis (multiseriate epidermis)
in leaves
the outermost layer has epidermal
characteristics where as those beneath
developed into a tissue with few or no
chloroplasts.
May function in water storage
Sometimes subepidermal layers resemble the
multiple epidermis but derived from ground tissue so to
differentiae between subepidermal layers and epidermis is
by developmental studies.
plant Anatomy 254 lec.5
Rajaa Abueideh
• Function of epidermis:
• Restricts transpiration (contains cutin (fatty
material) within outer wall and on its surface
(cuticle))
• Gas exchange (presence of stomata)
• Mechanical support (compact arrangement of cells
and presence of tough cuticle layer)
• Absorption ( thin walled and presence of root hairs)
• Water storage (xerophytic plants)
• Site of light perception involved in circadian leaf
movement and photoperiodic induction
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• Shape & Composition of Epidermis:
• Unspecialized cells + specialized cells
• Most of epidermal cells are tubular.
In elongated plant parts as stems,
petioles, vein ribs of leaves, leaves of
monocots the epidermal cells are
elongated parallel with the long axis of
plant part.
In leaves, petals, ovaries and ovules the
epidermis may have wavy vertical walls
plant Anatomy 254 lec.5
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Epidermis in stems
Epidermis in leaves
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plant Anatomy 254 lec.5
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• Epidermal cells have living protoplasts.
• May store products of metabolism.
• They contain plastids with few grana so are
deficient in chlorophyll (epidermis of plants of
shady habitats contains
photosynthetically active chloroplasts)
plastids may contain starch (amyloplasts, also
chromoplasts may present) protein and crystals.
• Vacuoles may contain anthocyanin
plant Anatomy 254 lec.5
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• Specialized epidermal cells:
Guard cells
Subsidiary cells
Trichomes (epidermal appendages)
Idioblasts = cells in a tissue that differ in size,
form or contents from cells of the tissue) (cells
containing tannins, oils, crystals and other
substances: silica cells , cork cells)
Bullliform cells (in monocot leaves) elongated
bubble like cells
Sclerenchyma may present (sclereids or fibers)
Secretory cells in some plants
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plant Anatomy 254 lec.5
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• Development of epidermis :
• Epidermis differentiates from
meristematic surface layer
(protoderm or dermatogen) by
periclinal division in the developing
embryo.
plant Anatomy 254 lec.5
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Mature epidermis retains it potential for
growth for long time.
- in perennial stems form periderm in
late life or not at all, the epidermis
continues to divide (anticlinal Division:
at right angle to the surface) in response to
increase in stem width and when
periderm is formed the source of
meristematic phellogen may be the
epidermis
- the adventitious buds arise from
epidermis.
plant Anatomy 254 lec.5
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• The cell wall of epidermal cell:
- Varies in thickness in different plants and in
different parts of the same plant.
- In thin walled epidermis the outer wall is the
thickest
- thick walled epidermis is found in leaves of
conifers, the thick wall probably secondary ,
lignified
- The thick wall may be silicified as in grasses
- Primary pits and plasmodesmata present.
plant Anatomy 254 lec.5
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Thick walled epidermis
in leaves of conifers
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• The epidermal wall contains wall fatty substance
cutin
• Cutin occurs: (stained using sudan IV dye)
– within the wall between cellulose
micells.
- as separate layer the cuticle on the
outer surface of the epidermis, that varies in
thickness and its development depending on
environmental conditions
Cutininization: the process of impregnation with
cutin
Cutilicularization: the formation of cuticle
plant Anatomy 254 lec.5
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• Cuticle is found in all plant surfaces exposed to
the air, but sometimes present in the absorbing
region of the root. Even the root hairs
• Cuticle is covered with wax either:
- in smooth flat-lying form
- as rods or filaments growing from the surface
(epicuticular waxes)
• The composition of cuticle and cutinized wall is
complex (cellulose, pectic compounds, cutin,
waxes and other substance)
plant Anatomy 254 lec.5
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plant Anatomy 254 lec.5
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• A depression in the cuticle over the aticlinal
wall where the wax layers are thinner, so water
loss and materials uptake occur easily there
(common in epidermis of leaves)
• Cutin and waxes are synthesized in living
protoplasts and migrate to the surface through
the cell wall.
• Sometimes cuticular layers are formed in cortical
cells for protection (cuticular epithelium)
• In some roots the epidermis is worn away by
friction with soil particles so it is replaced by
exodermis (sclerenchyma)
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Stomata
• Stomata are openings (pores or
apertures) in the epidermis.
• For gaseous exchange (water
released, CO2 uptake)
• Occur on most plant surfaces above
ground especially on green
photosynthetic stems and leaves and
on floral parts.
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Guard cell may be covered
with wax
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• Stomata varies on different parts of the same
leaf and on different leaves on same plant. It is
affected by environmental conditions
• In leaves it may occur on both sides or only on
one side which is usually the lower one.
• Vary depending on their position relative to
epidermis could be : -even with other epidermal
cells
- raised above
- below the surface of
epidermal cells (sunken stomata as in
gymnosperms)
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Raised stomata
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• Bound by two specialized epidermal cells (guard cells)
that change in shape to open or close the stomata.(wall
away from pore is thicker than the other, [k+] increase,
starch consumed during opening of pore)
( stoma: the pore and two guard cells)
Guard cells have nuclei and chloroplasts that accumulate
starch
• Guard cells (as seen from the surface)are either:
kidney shaped (in most plants) cuticle covering these
cells extends over surface facing stomatal pore and
substomatal cavity.
or dumbbell-shaped (some monocot plants as Poaceae
and Cyperaceae)
The two guard cells are interconnected through pores in
the bulbous ends of those guard cells
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• Stomata may be surrounded by cells
that differ in shape and in contents
(sometimes) from ordinary epidermal
cells (subsidiary cells) which
participate in osmotic changes
involved in movements of guard cells.
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plant Anatomy 254 lec.5
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• Development of guard cells and
stomata :guard cells results from
unequal division of the protodermal cells
results in formation of short cells and long
cells, guard cells results from short cells
(larger nuclei, nucleoli, simple plastids, more enzymes,
more nucleohistones, proteins ,DNA and RNA)
• The stomata occur when the intercellular
space between the guard cells swells and
the connection between the cells is
weakened so separate forming the pore.
plant Anatomy 254 lec.5
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Undifferentiated
epidermal cell
Protodermal cell
Larger
daughter cell
Guard
mother cell
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plant Anatomy 254 lec.5
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• Development of subsidiary cells:
Subsidiary cells may arise from the same
precursor as the stoma or from other cells.
There are three stomatal types depending
on ontogeny (development, differentiation and growth)
During development, a protodermal cell undergoes
un equal mitotic division to produce larger
daughter cell and meristemoid (guard cell
mother cell)
plant Anatomy 254 lec.5
Rajaa Abueideh
Ontogenetic stomatal types:(types of stomata
based on development of subsidiary cells)
1- agenous: the meristemoid give rise directly to
guard cells and no subsidiary cells
2- mesogenous: the meristemoid cell gives rise to
guard cells and subsidiary cells by several
mitotic divisions
3- perigenous: the meristemoid give rise to guard
cells and subsidiary cells formed from
neighboring cells
plant Anatomy 254 lec.5
Rajaa Abueideh
• Types of stomata based on arrangement of
mature subsidiary cells: The same species may show
more than one type of stomata.
1- Anomocytic (irregular celled): stomata lack subsidiary
cells
2- Anisocytic (unequal celled): stomata with three unequal
subsidiary cells (one smaller than the other two)
3- Diacytic (cross celled): stomata with one pair or more
than one pair of subsidiary cells with their common wall at
right angles to guard cells
4- Paracytic (parallel celled): stomata have one or more
subsidiary cells at either side of the guard cells
5- Actinocytic (radiate celled): several subsidiary cells with
perpendicular longitudinal axes to outline of the guard
cells.
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Diacytic stomata
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Paracytic stomata
Actinocytic stomata
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Anomocytic stomata
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plant Anatomy 254 lec.5
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Anisocytic stomata
plant Anatomy 254 lec.5
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Trichomes
• Are variable appendages of the epidermis.
• Vary widely in form and function .
• Could be glandular and non glandular hairs, stinging
hairs,scales, papillae and root hairs
• Could be unicellular or multicellular, branched or
unbranched
• Occur on all parts of the plant surface
• May persist through the life of a plant or may fall off
early.
• Some of the hairs remain alive , others die and become
dry.
• May be used for taxonomic purposes.
plant Anatomy 254 lec.5
Rajaa Abueideh
• Their function:
- Can insulate the mesophyll from excessive
heat
- May serve to remove salts from the leaf
tissue so prevent the accumulation of toxic
salts in the plant
- defense against insects even sometimes it
may houses insects and larvae.
- Secretory trichomes participate in
chemical defense (resin, volatile oils,
proteolytic enzymes , poisonous
substance)
plant Anatomy 254 lec.5
Rajaa Abueideh
• Morphological groups of trichomes:
1) hairs - glandular (with unicellular or multicellular
stalk and a secretory head with one to several cells)
- Non-glandular : simple
-unicellular or
- multicellular – uniseriate
-multiseriate
branched
- Stellate (star shaped)
- dendroid (branched hair)
Hairs of cotton seeds are unicellular and develop
secondary walls at maturity (developed by elongation
of protodermal cell)
2)Scales (peltate hairs)
3) Water vesicles which are enlarged epidermal cells
٤) Root hairs
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Cotton hair seeds
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Glandular trichomes
Stinging hairs
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