Ground Tissues
Parenchyma
Collenchyma &
Sclerenchyma
Plant Anatomy 254, lec 4
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Parenchyma
• The main representative of ground tissue
system.
• Found as
- a continuous tissue in plant organs
(cortex, pith of stems, cortex of roots,
ground tissue of petioles, mesophyll of
leaves)
- individual or group of cells in complex
tissue system ( xylem and phloem)
Plant Anatomy 254, lec 4
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• Function of parenchyma:
Parenchyma cells vary in function depending
on their location and participation in the
activities, but they are capable of changing
their activity.
Also parenchyma cells can resume
meristematic activity (wound healing,
regeneration, formation of adventitious
roots and shoots, isolated parenchyma are
capable of producing the entire plant)
Plant Anatomy 254, lec 4
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• Cell contents:
• Depending on the activities of parenchyma
cells.
- Contains numerous chloroplasts
Chlorenchyma (mesophyll of leaves, some
types of stems in cortex, may occur in pith)
- Vacuolated cells and form lacunate tissue
- Secretory parenchyma rich in protoplasm
that is rich in ribosomes, Golgi bodies and
ER depending on type of secretion.
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• May contain special ergastic substances
- Starch storing cells with amyloplasts
(seeds, underground storage organs).
- Store protein or fat (parenchyma in seeds
or embryo).
- Contain chromoplasts (in flowers and
fruits)
- May accumulate anthocynanin or tannin in
vacuoles
- May contain different types of crystals.
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• Shape and arrangement of cells:
-Typically
parenchyma cells are isodiametric not spherical,
with many faces (approximately 14 facets: polyhedron)
- May be elongated or lobed
- Cells vary in size
- Presence of intercellular spaces:
- storage parenchyma in stems and roots
has abundant intercellular spaces
- storage parenchyma in endosperm of
seeds are compact, if present with small
intercellular spaces
- parenchyma in mesophyll has extensive
intercellular spaces for gas exchange
(aerenchyma) also
Plant Anatomy
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in plants waterlogged
soils
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Folded parenchyma
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Parenchyma with intercellular space
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aerenchyma
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Plant Anatomy 254, lec 4
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• Cell wall in parenchyma cells:
• Mostly with primary thin cell wall
•
middle lamella may or may not be distinguishable.
• Plasmodesmata are common.
• Sometimes the primary wall becomes very thick as in
- some storage parenchyma as those in
endosperm of seeds. (coffee and persimmon) the
carbohydrates of these thick walls serve as reserve
material utilized by the embryo during germination
- some parenchyma (transfer cells) that function
in short-distance transport of solutes between cells
• Some parenchyma cells develop secondary walls
(lignified) making it difficult to distinguish it from
sclerenchyma (sclerified parenchyma)
Plant Anatomy 254, lec 4
- parenchyma
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and in xylem
Parenchyma with thick primary
cell wall in endosperm of
persimmon
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Parenchyma with
primary cell wall
Plant Anatomy 254, lec 4
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Sclerified
parenchyma
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Plant Anatomy 254, lec 4
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Collenchyma
• Thick primary walled cells
• For support with flexibility (strong flexible cells)
• Closely related to parenchyma; with living
protoplasts capable of resuming meristematic
activity with primary nonlignified cell wall.
• When collenchyma cells are induced to resume
meristematic activity (cork cambium) it retains
active protoplast and removes the wall
thickenings.
Plant Anatomy 254, lec 4
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Plant Anatomy 254, lec 4
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• Cell wall in collenchyma cells:
• Thick primary cell wall with uneven thickening:
- thickness in corners of the cells (angular
collenchyma)
- angular collenchyma with intercellular
space (lacunar collenchyma)- intercellular
space may or may not present.
- thickness on two opposite (inner and
outer tangential walls) (lamellar or plate
collenchyma)
Plant Anatomy 254, lec 4
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Angular collenchyma
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Plant Anatomy 254, lec 4
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Lacunar
collenchyma
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Plant Anatomy 254, lec 4
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Lamellar or plate
collenchyma
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• In addition to cellulose the cell wall
contains large amount of pectin
(hydrophilic bounded to water) and
hemicellulose but with no lignin.
• The thickening of cell wall is deposited
while the cell is growing and the process is
complicated.
• Primary pits are often present especially in
cells with uniform thickness.
Plant Anatomy 254, lec 4
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• Distribution of collenchyma in the plant:
• Occurs in the peripheral regions of stem and leaf.
Directly beneath epidermis or a few layers removed
from it.
• Frequently forms a continuous layer around
circumference of axis (stem and leaf petiole). May
occurs in strands
• In leaf blade occurs in ribs especially the larger
one. Occurs on both sides or one side of ribs
• Roots rarely have collenchyma.
• Differs from thick walled parenchyma associated
with vascular tissue which has uniformly thickened
walls (collenchymatous parenchyma)
Plant Anatomy 254, lec 4
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• The structure of collenchyma in relation to
function:
• Function of collenchyma is support of growing
leaves and stems.
• their walls becomes thick during development
• The thickening is plastic and capable of
extension so does not hinder the elongation of
stem and leaf.
• Found in developing plant parts subjected to
mechanical stress (wind)
Plant Anatomy 254, lec 4
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• In old plant parts collenchyma may
harden or may be change to
sclerenchyma by deposition of
secondary lignified wall
Plant Anatomy 254, lec 4
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Sclerenchyma
• with secondary lignified cell wall.
• Function in mechanical support.
• May be confused with sclerified
parenchyma or water conducting cells of
xylem.
Plant Anatomy 254, lec 4
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• Can be divided into two categories:
- Sclereids: isodiametric to elongated
- Fibers: long slender cells, longer than
wider
• May or may not retain their protoplast at maturity
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Sclereids
Fibers
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Sclereids
• Vary in shape.
• Their secondary lignified cell wall commonly have simple
pits
• Are of several types:
1- Brachysclereids (stone cells): isodiametric – elongated
2- Macrosclereids (rod cells): columnar
3- Osteosclereids (bone cells): columnar with enlarged
ends
4- Astrosclereids (star cells): with lobes or arms coming
from central body
5-Trichosclereids (hairlike cells): branched
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Brachysclereids (stone cells)
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Plant Anatomy 254, lec 4
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Astrosclerieds
(star cells)
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Plant Anatomy 254, lec 4
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Osteosclereids
(Bone cells)
Macrosclereids
(rod cells)
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Plant Anatomy 254, lec 4
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Trichosclereids
(hairlike cells)
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Macrosclereids
(rod cells)
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• Distribution of sclereids:
• In stems -as continuous layer on the
periphery of the vascular region
- as groups of sclereids in pith
(brachysclereids)
- astrosclereids in cortex
• In leaves – in mesophyll (diffuse),
associated with ends of small veins
(terminal)
- sometimes form part of
epidermis
(macrosclereids, trichosclereids,
astrosclereids)
Plant Anatomy 254, lec 4
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• In fruits – in flesh of fruit
(brachysclereids)
- in endocarp
(macrosclereids)
• In seeds – in seed coat epidermis or
the layer (s) beneath epidermis
(macroslereids, osteosclereids)
Plant Anatomy 254, lec 4
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Fibers
• Fibers are long cells.
• With secondary thick walls, that varies in the
degree of lignification The wall is hard and not
hydrated as the wall in collenchyma
• Function in support in plant parts that do not
elongate
• Usually occur in strands.
Plant Anatomy 254, lec 4
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• Fibers found in various parts of plants,
could be of two types depending on site
where they are found:
- extraxylary fibers: fibers located
outside xylem tissue
- phloem fibers (primary phloem
fibers , secondary phloem fibers)
- perivascular bundle fibers
(sheath, cap: on side or two sides )
- xylary fibers: fibers located in xylem
Plant Anatomy 254, lec 4
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Perivascular
bundle sheath
Perivascular
bundle cap
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Primary
Phloem
fibers
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Plant Anatomy 254, lec 4
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Secondary
phloem
fibers
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Xylary
fibers
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Plant Anatomy 254, lec 4
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• Economic Fibers:
• Mostly are phloem fibers
• Could be classified as soft fibers and
flexible because of amount of lignin (flax:
used in textiles (linen)), some phloem
fibers used for paper making.
• Leaf fibers of monocots obtained from
leaves (hard fibers : strongly lignified
walls) (Senseviria)
• Leaf fibers of monocots (with xylem) serve
as raw material for making paper (corn ,
sugar cane)
Plant Anatomy 254, lec 4
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