Download Bi 151 – Plant Morpho

9/14/2014
Bi 151
Plant Morpho-anatomy
Lecture 6
Epidermis
• covers the primary plant body
• derived from protoderm
Epidermis and Periderm
Jan Lorie M. Robil, M.Sc.
apical meristem of Syringa vulgaris
Epidermis
Epidermis
•
•
•
•
•
• waterproof the
plant thereby
restricting
evaporation
Regular epidermal cells
cuticle
stomata (guard cells)
trichomes (and emergences)
other special epidermal cells
Epidermis
• control gaseous
exchange into
and out of plant
– via stomatal
apparatus
epidermis of Psilotum nudum
– due to cuticle on
surface which
contains cutin
and cutan
epidermis of Psilotum nudum
Epidermis
• produce root
hairs in roots
– for water
and nutrient
absorption
• pore (stoma)
• pair of guard
cells
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Epidermis
Epidermis
• other important functions
• usually one cell layer thick (uniseriate)
– mechanical support
– light perception
• affects photoperiodism and circadian
rhythms
Transverse section
of stem epidermis of
cosmos (Cosmos)
Epidermis
• but in some plants a multiple epidermis
(multiseriate) forms via periclinal division
Multiple epidermis
Piperaceae : Peperomia caperata
Moraceae : Ficus elastica
Orchidaceae : Epidendrum radicans
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Velamen of Orchidaceous roots
Multiple epidermis of Epidendrum radicans root
Hypodermis
• originated from cortical (ground) meristem
Transverse section of
leaf blade of oleander
(Nerium oleander)
Transverse sections of the leaves of three species of Pleiochiton and of Clidemia blepharodes. (9)
P. ebracteatum. (10) P. micranthum. (11) P. setulosum. (12) C. blepharodes. Scale bar 100mm.
Medinilla magnifica
M. teysmannii
Melastomataceae: Medinilla teysmanni
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Development of Epidermal Cells
• In grasses (Poaceae),
cell division is
asymmetrical producing
a short and long cell.
• The short cell is called
the meristemoid.
– It gives rise to guard cells
and other associated
cells (cork cells, silica
cells, trichomes etc).
Melastomataceae: Medinilla magnifica
• the meristemoid produces the
guard mother cell.
Development of Epidermal Cells
• a meristemoid may inhibit the formation of
other meristemoids near it
Development of Epidermal Cells
Development of Epidermal Cells
• In roots, the cell
that gives rise to
a root hair is
called the
trichoblast
• Epidermal cells (even stomates)
are totipotent
• Epidermis retains the potential for growth
for long periods of time in some plants.
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Acer pensylvanicum 20 year
old, 20 cm in diameter stems
may still retain the original
epidermis
Composition of Epidermis
• Regular epidermal cells
– aka Pavement cells
• Generally, epidermal
cells are tabular in
shape
Tradescantia upper leaf epidermis
Composition of Epidermis
Composition of Epidermis
• Stomata – specialized complex (pore +
pair of guard cells)
• Trichomes - found in most plants; variety of
functions
• Idioblastic substances
– regulates transpirational water loss
– the pore where CO2 enters the plant
• may be accompanied by distinct
neighboring or subsidiary cells
– e.g. tannins, oils, crystals
– In grasses (Poaceae), silica cells may be paired with
cork cells, the latter with suberized walls
• The epidermis in seeds and scales may be
composed of sclerenchyma fibers or sclereids
Epidermal Cell Wall
Epidermal Cell Wall
• Varies in thickness
among different
plants, different parts
of same plant, and
even different walls of
one cell.
• Conifers often
have very thick
leaf epidermal
cells; so thick
that the cell
lumen can be
lost via
lignification.
– Guard cells have
uneven cell wall
thickness
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Epidermal Cell Wall
• Grasses:
epidermal cell
walls are
impregnated
with silica
(silicified)
phytoliths
Epidermal Cell Wall
Tiny silica “daggers” line
the edge of a blade of
grass.
• Outer wall of epidermal cells has a cuticle
chiefly composed of cutin and cutan
• cutinization = impregnation with cutin
• cuticularization = formation of the cuticle
Nicotiana
Arctostaphylos
Cuticle
• found on all plant parts exposed to air
(even roots and root hairs)
• also varies in thickness
Yucca
Ficus
Structure of Plant Cuticle
Structure of Plant Cuticle
Starting at base:
• Plasma membrane
• Cell wall
• Pectinaceous layer (cont. middle lamella)
• Cuticular layer
• Cuticle proper
• Epicuticular wax
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Structure of Cuticle
Epicuticular Wax
• The cuticle can be variously sculptured
Taxus
Syringa
Pisum
Solanum
Epicuticular Wax
Epicuticular Wax
Development of epicuticular
wax filaments on the abaxial
surface of a sorghum
(Sorghum bicolor) leaf sheath.
A, wax fi laments emerging
from cork cells adjacent to
silica cells (sc). Initially the fi
laments appear as circular
secre-tions. B, with further
development, the secretions
appear as short cylinders. C,
D, with continued
development, the secretions
form clusters of epicuticular
wax fi laments.
Development
of cuticle
Stomata
Stomata
• Terminology
• The cuticle
covers the
guard cells and
even extends
into the
substomatal
chamber.
– guard cells
– subsidiary cells
– aperture (pore)
– ledge
– substomatal chamber
– epistomatal chamber
– stomatal crypt
Sorghum bicolor)
Cuticular ”horns”
ledges
stomatal
crypt
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Location of stomata on the leaf
Location of stomata on the leaf
• Hypostomatic - stomates restricted to the
abaxial side
• Amphistomatic - stomates on both the abaxial
and adaxial sides
• Epistomatic - stomates are on the adaxial side,
e.g. floating leaves such as Nymphaea.
• No stomata
– submerged leaves in aquatic plants
– scale leaves in holoparasites in Balanophoraceae
Transverse section of water lily leaf (Nymphaea) showing
stomata on the upper epidermis
Shapes of Stomata
• usually reniform (eudicots)
• bone- or dumbbell-shaped in grasses
• sunken in gymnosperms (e.g. Pinus)
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Position in Relation to Epidermis
Position in Relation to Epidermis
• Stomates the same
level as epidermis
• Stomates sunken
– guard cells sunken
into the epidermis
– common in
xerophytes and
especially conifers.
– with a substomatal
cavity (or chamber)
directly below
– form zones of large
intercellular spaces in
virtually every leaf
Canna
Ficus
Position in Relation to Epidermis
Position in Relation to Epidermis
• Stomates within
stomatal crypts
• Stomates are
buried in deep
folds in the leaf
of xerophytes
– depression in the
epidermis where
stomates are
aggregated
– these cut down on
water loss
– found in xerophytes
such as Nerium
– as seen in Yucca
and beach grass
Amophila arenaria
Nerium
Yucca
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Amophila arenaria
Position in Relation to Epidermis
• Stomates are raised
above the surface
Mechanisms of Stomatal
Functions
1. Wall thickenings. Most along pore wall
(ventral side), least on anticlinal wall (dorsal
side)
2. Microfibrils in radial arrangement (radial
micellation).
3. K+ fluxes and osmotic condition
4. Environment influences stomatal opening
and closing: heat, [CO2], abscisic acid.
When turgid they are open, when flacid they
are closed.
Formation of Guard Cells
• Protoderm cell divides but unequally
• Smaller one forms the guard cell
• Subsidiary cells (if present) may come
from the same or different mother cell as
guard cells
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Formation of Guard Cells
Types of Stomate Development
1. Mesogenous (middle origin) - guard cells
and subsidiary cells come from same
mother cell
2. Perigenous (around origin) - guard cells
and subsidiary cells come from different
mother cells.
3. Mesoperigenous - guard cells and only
one subsidiary cell from same mother
cell, other s.c. of different origin.
Mesogenous
Perigenous
Dianthus
Graptopetalum
Mesoperigenous
Pelargonium
Types of Stomatal Complexes
1. anomocytic - (irregular celled): no
differentiation of the epidermal cells
around the guard cells.
2. anisocytic (unequal celled): 3 subsidiary
cells around the guard cells, one of
different size.
3. paracytic (parallel celled): 1 or more
subsidiary cells are parallel to guard cells.
Vigna
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Types of Stomatal Complexes
Types of Stomatal Complexes
4. diacytic (cross celled): 2 subsidiary cells
with walls perpendicular to guard cells.
5. actinocytic (radiate celled): several
subsidiary cells radiate from around the
guard cells.
6. cyclocytic (cyclic celled): subsidiary cells
in 1-2 rings around guard cells.
7. tetracytic (four celled): guard cells
surrounded by 4 subsidiary cells.
8. amphianisocytic: double ring, inner ring
of 3 subsidiary cells.
9. amphiparacytic: enclosed by 2 rings of 2
subsidiary cells aligned to guard cells.
Types of Stomatal Complexes
Trichomes
• Originate from the epidermis
Trichomes
• Not to be confused with structures like:
– spines which are modified leaves or stipules
– thorns which are modified branches
– prickles which originate from the epidermis
but include tissue beneath in the cortex
– warts (a bark feature)
– and other emergences
spines of Acacia
thorns of Gleditsia
prickles of Rosa
warts of Celtis
• hairs, trichomes and emergences are
collectively termed as indumentum
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Trichomes
Functions
• various kinds of trichomes are not
homologous among plants that produce
them, they are analogous
• may function alive or dead
• may be classified as non-glandular and
glandular (to be discussed in external secretory structures)
• Living
– digestive hairs, e.g. in insectivorous plants
– often glandular and secrete compounds that
are beneficial, e.g. nectar
– mucilage, wastes, protects against water loss
and herbivory
– absorption
Functions
• Dead
– as a barrier to water loss and prevent animal
grazing
– aquatic plants for flotation, e.g. Pistia
(Araceae)
– protects against ionizing radiation
carnivorous plant Drosera showing digestive hairs
trichomes of aquatic fern, Salvinia
trichomes of floating leaves of Pistia stratiotes
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high-altitude, xerophytic plant, Espeletia killipii
hairy inflorescence of Espeletia killipii
Review types of
Non-glandular
trichomes
Other special epidermal cells
• Bulliform cells
– common to grasses (Poaceae)
– cause the leaves of many grass species to
fold inward during hot weather to reduce
transpiration
Zea mays
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