Download Ergastic cell content

Ergastic Substances &
Sclerenchyma Cells
Ergastic Substances or Cell Inclusions
Cell Inclusions are non-living substances present
in the cells.
They are also called ergastic substances or
ergastic bodies. They may be present in soluble
or insoluble state and can be organic or
inorganic in nature.These are present in
components or sub-components of cell. They
are raw materials or products of
metabolism.THEY may be exported or expelled
from the cell.
The cell inclusions belong to three categories:-
Reserve food
Excretory or secretory products
Mineral matter
 Reserve food: They are of four main types• Starch
• Glycogen
• Fat droplets
• Aleurone grains
Starch grains occur in plant cells. The grains
are found in chloroplasts and amyloplasts. As
such they are insoluble. The grains may occur
singly when they are called simple. They are
called compound starch grains when two or
more of them occur in amyloplasts.
Here SIMPLE STARCH grains of potato and wheat
repectively
COMPOUND STARCH grains in avena
and potato
Each starch grain has a central proteinaceous
area called HILUM. Starch is deposited around
it in the form of layers. Depending upon the
position of hilum,a starch grain may be
concentric or eccentric.
FAT DROPLETS: Fat droplets or globules occur
abundantly inside the seeds either in
endosperm(e.g., Castor,Coconut) or
cotyledons(e.g., Groundnut,Mustard
ALEURONE GRAINS
They represent the storage proteins which are generally
insoluble and occur inside special leucoplasts called
aleuroplasts. Depending upon their internal
structure,aleurone grains are of four types:
• Amorphouus
• Protein matrix containing a crytalloid
e.g., outer layer of endosperm in
wheat,maize,barley,grains.
• Protein matrix with globoid
• Protein matrix having both crytalloid and globoid
inclusion, e.g, endosperm cells of castor seeds.
CRYSTALLOID is crystal like protein-carbohydrate
body while glboid contains lipid and phytin
EXCRETORY OR SECRETORY
PRODUCTS:
They are of several types like:
• Essential oils
• Alkaloids
• Resins
• Gums
• Tannins
• Waxes
• Latex etc.
Tanniferous bodies are widely distributed in
different parts of the plant body and they are
particularly abundant in leaves,vascular
tissues,periderm,unripe fruits,seed coat. They
are small granular or rounded
particles,yellow,red or brown in color.These
phenolic compounds are commercially useful in
tanning industry.
Other soid and semi-solid substances,such as
oils,fats and waxes also occur frequently. Oils
and fats are common reserve materials of
seeds,while waxes occur usually as protective
covering on the epidermis.
MINERAL MATTER(CRYSTALS)
Crystals of different composition,which are byproducts
of the metabolic processes of the cells,occur in
different parts of the plant.
Calcium oxalate crystals are most common in plants.
Their shape varies considerably and may be
elongated,needlelike,rectangular,rhomboidal,sphaeroidal or prismatic.
• The elongated crystals when occurring solitary are
known as styloids and when in bundles they are
called raphides. Crystals of inorganic compounds,
such as silica and gypsum although uncommon are
also present in some plants.
• In moneyplant,
Needle-shaped
Raphides appear as
Scratches on slide.
• In Opuntia,arranged
In the form of spheres“Sphaeroraphides”
• Silicon salts are often deposited in the cell walls of grasses.
Cystoliths, which are internal outgrowth of cell wall occur in
many plants.
e.g., Ficus
Calcium carbonate
Crystals present in
Sacs
-appear like bunch of
Grapes,”CYSTOLITH”
Sclerenchyma cells
Mature sclerenchyma
cells are dead and have secondary cell walls
thickened with cellulose and
usually impregnated with lignin. In contrast to
collenchyma, which is pliable(able to
fold), sclerenchyma is elastic.Unlike the
collenchyma, mature sclerenchyma is composed
of dead cells. with extremely thick cell
walls (secondary walls) that make up to 90% of
the whole cell volume. It is the hard, thick
walls that make sclerenchyma cells important
strengthening and supporting elements in plant
parts that have ceased elongation
TYPES
• There are two types of sclerenchyma cells,
namely sclereids and fibres.
Fibres: The cells are needle-shaped with pointed tips, thick
walls and rather small lumen. Secondary cell walls,
impregnated with, are formed. Simple pits are also present.
Fibres are abundant in the vascular tissue of angiosperms,
i.e. flowering plants.
.
• Contrasting are hard fibres that are mostly
found in monocots. Typical examples are the
fibres of many grasses, agaves. Their cell walls
contain, besides cellulose, a high proportion
of lignin. Starting at the centre of the fibre
are the thickening layers of the secondary wall
deposited one after the other. Growth at both
tips of the cell leads to simultaneous
elongation.
. During development ,the layers of secondary
material seem like tubes, of which the outer
one is always longer and older than the next.
After completion of growth the missing parts
are supplemented, so that the wall is evenly
thickened up to the tips of the fibres.
ECONOMIC FIBRES
• The phloem fibres of dicotyledons represent bast
fibres and these are classofied as soft fibres because
lignified or not,they are relatively soft and flexible.
Some of the well-nown sources and usages of bst
fibres are hemp(Cannabis sativa),jute(Corchorus
capsularis),flaax(Linum usitatissimum),textiles(e.g.,
linen).
• Phloem fibres of some dicotyledons are used for
making paper.
The fibres of monocotyledons-usually called leaf fibres
because they are obtained from leaves-are classified
as hard fibres. Examples of sources and uses of leaf
fibres are Manila hemp(Musa textilis),Pineapple
fibre(Ananas comosus) and Sisal(Agave sisalana).
Leaf fibres of monocotyledons(together with the xylem)
serve as raw material for making paper.
• Sclereids: The cells are irregular in shape. The
cell walls are thick, hard and lignified which
makes the lumen very small. Simple pits
(canals) are found in the thickened cell walls
and link adjacent cells. Sclereids are commonly
found in fruit and seeds. These have a shape of
a star.
• They are small bundles of sclerenchyma tissue
in plants that form durable layers, such as the
cores of apples. They can be grouped into
bundles, can form complete tubes located at
the periphery or can occur as single cells or
small groups of cells within parenchymatissues.
But compared with most fibres, sclereids are
relatively short
On the basis of their shape and thickness of
walls sclereds have been variously classified:
Astrosclereids: They are starshaped(stellate) cells found in the leaves of
Nymphaea and stems and leaves of Thea
Brachysclereids or Stone cells: They are
short roughly isodiametric sclereids,occurring
in the cortex,pith and phloem of
stems(Cinnamomum),pulp of fruits(Pyrus)
Macrosclereids: They
are elongated columnar
Sclereids distributed in
Seeds and fruits in the
Form of a layer
(leguminous seeds)
Macrosclereids
Osteosclereids: They are bone or
barrel shaped and dilated at ends.
They occur in the leaves and seed coat of many cot
many monocotyledons.