Download Parenchyma cells

Cell types
Parenchyma
Parenchyma are diverse cells
that can have many different
shapes and be very specialized in
their function.
Based on function common
parenchyma cells can grouped as:
Ground tissue
Chlorenchyma
Storage tissue
Aerenchyma
Transfer cells
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Parenchyma – Ground tissue
The basic parenchyma
cell form is found in
the ground tissue of
the cortex and pith.
Cortex
Pith
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Parenchyma – Ground tissue
Ground tissue parenchyma
cells have a primary cell wall
and are usually isodiametric
or polyhedral in shape.
Primary
cell walls
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Parenchyma – Ground tissue
Parenchyma cells contain
a nucleus and retain the
ability for future cell
division.
When they are first
formed, they are densely
cytoplasmic and have
several small vacuoles.
As the cells enlarge, the
vacuole size increases and
intercellular spaces can
form between cell walls.
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Cytoplasm Nucleus
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Intercellular spaces
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Parenchyma – Ground tissue
In a mature ground parenchyma
cell, the cell is usually longer than
wide.
The smaller vacuoles merge into
one large central vacuole with the
cytoplasm and organelles pushed
to the periphery of the cell.
Intercellular
space
Cytoplasm
Chloroplasts
Central
vacuole
Primary cell
wall
Electron micrograph of a single parenchyma cell
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Parenchyma – Chlorenchyma
Parenchyma cells in the leaf actively involved
with photosynthesis are termed chlorenchyma.
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Parenchyma – Chlorenchyma
Chlorenchyma can be divided into
the leaf palisade layer and the
spongy mesophyll cells.
Tomato leaf
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Parenchyma – Chlorenchyma
The palisade layer is usually two to four cell layers deep and develops under the
epidermis on the top (adaxial) side of the leaf. Palisade cells are densely packed
together in regular files and are longer than wide. Chloroplasts stain intense red.
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Parenchyma – Chlorenchyma
The spongy mesophyll cells occur below the palisade layer and are loosely packed
together. This creates air chambers that allows carbon dioxide to move from
the stomata on the underside of the leaf to these chloroplast containing cells.
Adaxial
epidermis
Palisade
mesophyll
Vascular
bundle
Spongy
mesophyll
Abaxial
epidermis
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Stomates
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Parenchyma – Chlorenchyma
This electron micrograph shows mesophyll parenchyma cells
with an active nucleus and numerous chloroplasts.
Mesophyll
cell
Nucleus
Chloroplasts
Epidermis
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Parenchyma – Chlorenchyma
The needle leaves in conifers (like pine) lack a distinct palisade layer and
the cells in the spongy mesophyll have plicate shape.
Mesophyll
cells
Epidermis
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Stomate
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Parenchyma – Storage tissue
There are several distinct
storage tissues in plants.
Examples include:
Storage parenchyma
- Seed tissue
- Root tissue
Ray parenchyma
Storage parenchyma containing starch
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Parenchyma – Storage tissue (Seeds)
The endosperm is designed to store food for the developing embryo and seedling.
Endosperm
Shoot meristem
Coleoptile
Radicle
Coleorhiza
Scutellum
Pericarp
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A photomicrograph of a corn seed (actually a fruit – caryopsis)
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Parenchyma – Storage tissue (Seeds)
The endosperm is composed of storage parenchyma cells filled with lipid
bodies, protein bodies and especially amyloplasts containing starch.
Protein bodies in legume endosperm.
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Amyloplasts in grain endosperm.
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Parenchyma – Storage tissue (Seeds)
In cereal grains, the endosperm is non-living at maturity except for the outer
peripheral layer of the endosperm that is living and is called the aleurone layer.
These cells produce the enzymes used to degrade starch to sugar during
germination. The aleurone is a specialized parenchyma cell that has cell wall
ingrowths and membranes characteristic of secretory cells.
Aleurone
cells
Endosperm cells
containing starch
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Wheat
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Parenchyma – Storage tissue (Roots)
Most mature roots have the
capacity to store food reserves.
In some species, the root is further
modified as a fleshy storage organ.
Food crops like sweet potatoes, carrots and beets are modified storage roots.
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Parenchyma – Storage tissue (Roots)
The internal structure of a
storage root is similar to nonfleshy roots except that there
is more extensive parenchyma
tissue where the food reserves
are stored.
Cross-section
of a peony
tuberous root.
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Storage
parenchyma
Vascular
cylinder
Vascular
cambium
Periderm
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Parenchyma – Storage tissue (Roots)
Storage reserve accumulation in root
parenchyma cells in Ranunculus.
Cortical parenchyma
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Storage parenchyma
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Storage bodies
starch
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Parenchyma – Storage tissue (Roots)
In beets, the increase in storage root size is due to concentric rings of
vascular cambium and storage parenchyma cells.
Vascular
cambium
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Storage
parenchyma
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Parenchyma – Storage tissue (Roots)
A closer look at a vascular
bundle in beet storage roots
shows that the storage
parenchyma cells surround a
vascular bundle with only a
few secondary xylem cells
(red stain), a line of vascular
cambial cells and numerous
phloem elements.
Xylem
Phloem
The phloem is the major
transport system used to
load and unload the root
with food reserves.
Vascular cambium
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Storage parenchyma
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Parenchyma – Storage tissue (Rays)
Dilated ray
A second major type of
parenchyma used for
storage is ray parenchyma.
Ray parenchyma cells
grow horizontal to the
developing stem providing
the radial transport
system for expanding
stems.
Rays
Secondary xylem
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Parenchyma – Storage tissue
Ray cells are important
storage tissues for
carbohydrates and proteins
especially over the winter
in stems.
These stored materials are
used to support new spring
shoot and leaf growth.
Rays can form in the
secondary xylem and
phloem tissue.
Secondary xylem
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Rays
Phloem
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Parenchyma – Storage tissue
Rays may be a single cell wide (uniseriate) or several cells wide (multiseriate).
Uniseriate ray
Xylem
Fibers
Multiseriate ray
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Parenchyma – Storage tissue
Rays in conifers form files
of uniseriate cells.
Cambium
Rays
Xylem
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Parenchyma – Aerenchyma
Aerenchyma can occur in leaves, stems or roots and act as air passages.
They occur commonly in water logged roots and naturally in aquatic plants.
Large intercellular
spaces are typical of
arenchyma tissue.
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Parenchyma – Aerenchyma
Lotus (Nelumbo) produces an edible
root with large arenchyma tissue
air spaces.
They help move air down into the
submerged roots.
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Parenchyma – Aerenchyma
Aerenchyma with large
intercellular spaces is
common in the mesophyll
cells of water
(hydrophytic) plants.
It is easily seen in the
mesophyll tissue in the
leaf of a floating water
lily.
Air in aerenchyma spaces
help the leaf to float.
Leaf cross-section in Water lily (Nymphaea )
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Parenchyma – Aerenchyma
Pickerelweed (Pontederia) petiole
The intercellular spaces in
aerenchyma tissue commonly
forms from elongating cells
moving away from each other
to create larger intercellular
spaces (schizogenous
formation).
Alternatively, intercellular
spaces can form when cells
disintegrate to leave a large air
space (lysigenous formation).
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Parenchyma – Aerenchyma
These stellate parenchyma cells in the
aerenchyma in the aquatic pickerelweed
(Pontederia) is an example of
schizogenous intercellular formation.
Each cell has 6 to 8 “arms” that form as
the cells move apart and only a portion
of the middle lamella remains attached
between cells. The intercellular spaces
are triangular in shape.
Single
stellate
cell
Arms
Intercellular
spaces
Middle
lamella
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Parenchyma – Aerenchyma
Stellate parenchyma cells form as perforated septa (diaphragms) in aerenchyma
tissue. Diaphragms may help regulate air flow through stem or petiole tissue.
Diaphragm
Stellate parenchyma
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Parenchyma – Aerenchyma
The regular patterned formation of
intercellular spaces and remnant
tissue in the intercellular spaces in
parrot feather stem suggest they are
formed lysigenously through cell loss.
Intercellular
spaces
Stem cross-section in Parrot feather (Myriophyllum)
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Parenchyma – Aerenchyma
A lattice cell structure is common in the aerenchyma of several aquatic plants
including water hyacinth (Eichhornia) and pickerelweed (Pontederia). This
honeycomb effect provides stability and strength with a minimum of
structural material and the air spaces provide buoyancy to the stem or leaf.
Vascular
bundle
Lattice
cells
Cortex
Petiole cross-section in pickerelweed (Pontederia)
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Parenchyma – Transfer cells
Transfer cells are specialized
parenchyma cells with cell wall
ingrowths that increase
plasmamembrane surface area.
Companion cell
They specialize in short
distance transport of
specialized substances.
Sieve tube
member
Transfer cells are associated
with tissues like leaf veins,
glands, nectaries, and resin
ducts.
Companion cell in the phloem is a classic example
of a transfer parenchyma cell involved with
unloading sucrose from sieve elements.
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Parenchyma – Transfer cells
Transfer cells can be illustrated in the resin duct in a pine stem. The duct has a
single layer of epithelial transfer cells that surrounds an open lumen space.
Epithelial cells secrete resin into the duct canal.
Lumen
Resin duct
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Ergastic cells filled
with tannin
Epithelium
transfer cells
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