This PPT intends to explore the morphology, ultra-structure biochemical nature of the plant cell wall for UG students.

1. CELL BIOLOGY
Welcome to Cell Wall
by
N.sannigrahi, Associate Professor,
Nistarini College, D.B.Road, Purulia(W.B)
India

2. PLANT CELL

3. PLANT CELL WALL

4. PLANT CELL WALL-OVERVIEW
• The plant cell wall is a thick,rigid, semi-elastic, semi-transparent complex
structure that fulfills a diverse array of functions throughout the plant lifecycle. In
addition to maintaining structural integrity by resisting internal hydrostatic
pressures, the cell wall provides flexibility to support cell division, a biochemical
scaffold that enables differentiation, and a pathological and environmental barrier
that defends against stress (Scheller and Ulvskov, 2010; Hamann, 2012; Tucker
and Koltunow, 2014).
• The cell wall hosts a wide range receptors, pores and channels that regulate
molecular movement and responses to local and long-range elicitors including
hormones, sugars, proteins, and RNAs. Consistent with a role in many processes,
plant cell wall structure is incredibly varied, not only between plant species but
also between tissue types. In general, two wall types surrounding plant cells are
often referred to as the primary wall and secondary wall. A dynamic primary wall
is established in young cells during division and acts to provide flexibility and
basic structural support, protecting the cell, and mediating cell-cell interactions.
The thicker and more durable secondary wall lies between the primary wall and
plasma membrane, and is deposited at a later stage when the cell has stopped
growing and dividing. The secondary wall is seen as a crucial adaptation that
allows terrestrial plants to withstand and facilitate upright growth.

5. CELL WALL-OVERVIEW
• Typical components of the cell wall include cellulose(9-15%), non-cellulosic, and
pectic polysaccharides(2-8%), proteins(1-2%), phenolic compounds, and
water(30-60%), Microfibrils(20-40%).
• The major components (>90%) are polysaccharides, the structure, and
biosynthesis of which have been extensively reviewed in recent times (Atmodjo
et al., 2013; Pauly et al., 2013; Rennie and Scheller, 2014; Kumar et al., 2016). In
brief, cellulose is a water insoluble carbohydrate found in both primary and
secondary cell walls whose fibrous structure enables the maintenance of
structural integrity. Pectins, which are arguably the most complex and
heterogeneous of the cell wall polysaccharides, exist predominantly in the
primary cell wall and have roles in expansion, strength, porosity, adhesion, and
intercellular signaling. Other abundant non-cellulosic polysaccharides include
xyloglucan, β-1,3:1,4-glucan, xylan, mannan, and callose, which fulfill various
roles in mechanical support, reserve storage and development. In contrast to
cellulose, the pectic and non-cellulosic polysaccharides can be further
distinguished by sugar substitutions and side chains that are attached to the
polysaccharide backbone during biosynthesis (Scheller and Ulvskov, 2010).
These substituents influence solubility, viscosity, and interactions with other
polysaccharides and proteins within the cell wall.

6. CELL WALL-FUNCTIONS
• (i) Protects the protoplasm against mechanical injury,
• ii) Protects the cell from attack of pathogens,
• (iii) Provides rigidity and shape to the cell,
• (iv) Counteracts osmotic pres-sure.
• (v) Gives strength to the land plants to withstand gravitational forces,
• (vi) By its growth the wall helps in cell expansion,
• (vii) Pits present in the wall help produce a protoplasmic continuum or simplest amongst cells,
• (viii) Walls prevent bursting of plant cells by inhibiting excessive endosmosis.
• (ix) Wall has some enzymatic activity connected with metabolism,
• (x) In many cases, wall takes part in offence and defense,
• (xi) Cutin and suberin of the cell wall reduce the loss of water through transpiration,
• (xii) Walls of sieve tubes, tracheids and vessels are specialised for long distance transport,
• (xiii) Some seeds store food in the form of hemicellulose in cell wall.

7. CHEMICAL COMPOSITION
• 1. Matrix: Water— 60%. Hemicellulose— 5- 15% Pectic Substances-2-8%.
Lipids-0.5-3.0%. Proteins— 1-2%
• 2. Micro fibrils:20-40%
• Cellulose/fungus cellulose— 10-15%.
• 3. Other Ingredients:0-0.25%
• Lignin, cutin, suberin, silica (silicon dioxide), minerals (e.g., iron, calcium,
carbonate), waxes, tannins, resins, gum— variable.
• Hemicelluloses consists of xylan, arabinoxylan, glucomannan, xyloglucan,
mannose & glucuronic acid.
• Pectic substances-Hateropolymer of methyl esters of galacturonic acid.
• Ligin-aromatic polymer of long chains of phenolic alcohols,
• Cutin-complex structure of hydroxy fatty acids,
• Suderin-units of saturated and monounsaturated dicarboxylic acids, along with
Calcium carbonate & calcium silicate in some members of Cyperaceae, Poaceae
etc.

8. STRUCTURE OF CELL WALL
• Structure of Cell Wall:
• A cell wall can have upto three parts— middle lamella, primary wall and
secondary wall.
• Middle Lamella:
• It is a thin, amorphous and cementing layer between two adjacent cells. Middle
lamella is the first layer which is depos-ited at the time of cytokinesis . It is just
like brick work of the common wall be-tween two adjacent rooms.
• Middle lamella is absent on the outer side of surface cells. It is made up of
calcium and magnesium pectates. The softening of ripe fruits is caused by partial
solubilisation of pectic compounds to produce jelly-like consistency.

9. CELL WALL LAYERS-IMAGE

10. PRIMARY WALL
• Primary Wall:
• It is the first formed wall of the cell which is produced inner to the middle lamella. The primary
wall is com-monly thin (0.1-3.0 µm) and capable of exten-sion. It grows by intussusceptions or
addition of materials within the existing wall. Some cells possess only primary wall, e.g., leaf
cells, fruit cells, of cortex and pith.
• Primary wall consists of a number of micro fibrils embedded in the amorphous gel like matrix or
ground substance. In the majority of plants, the micro fibrils are formed of cellulose. They are
synthesized at plasma membrane by particle rosettes (terminal com-plexes) having cellulose
synthetize enzyme.
• The wall is made of a polymer of P, 1-4 acetyl glucosamine or fungus cellulose in many fungi.
Fungus cellulose is similar to chitin present in the exoskeleton of insects. Micro fibrils are
oriented variously according to the shape and thickening of the wall. Usually they are arranged in
a loose network due to incomplete cross-linking.
• The matrix of the wall consists of water, pectin, hemicelluloses and glycoproteins. Pectin is the
filler substance of the matrix. Proteins are structural and enzymatic. Protein expansin (Me Queen-
Mason et al, 1992) is involved in loosening and expansion of cell wall through incorporation of
more cellulose. Hemicellulose binds micro fibrils with matrix.

11. SECONDARY WALL

12. SECONDARY WALL
• Secondary Wall:
• It is produced in some mature cells when the latter have stopped growth, e.g.,
tracheids, vessel elements, fibres, collenchyma’s. Secondary wall is laid inner to the
primary wall by accretion or deposition of materials over the surface of existing
structure. It is thick (3—10 µm) and made up of at least three layers, sometimes
more (e.g., latex tube of Euphorbia milli). They are named as S1, S2, S3, Sx, etc.
• The innermost layer of the secondary wall is sometimes distinct both chemically as
well as in staining properties due to the presence of xylans. It is then called tertiary
wall, e.g., tension wood in gymnosperms. Secondary wall may be absent, irregularly
deposited or formed uniformly in the cells. This results in differentiation of cells—
parenchyma, collenchyma, sclerenchyma, tracheids and vessels.
• The composition of secondary wall is basically similar to the primary wall in having
cellulose micro-fibrils embedded in a matrix of pectin and hemicelluloses. Cellulose
mi-cro-fibrils of the secondary wall lie close, parallel and at an angle to the
longitudinal axis of the cell. Their orientation is different in the different layers of the
secondary wall. A number of different materials may be deposited in the wall. Parts

13. ULTRASTRUCTURE-FIBRILS SHOWING MICROFIBRILS, MICELLE

14. SECONDARY WALLS-MICELLES, MICROFIBRILS-----
• Like the primary wall, the secondary cell wall has the same microfibrils embeded in
gel like matrix of hemicellulose, pectin & protein.Impregnation of lignin may occur
in the wood elemenys like tracheids and vessels.
• Microfibrils are composed of micelles, the smallest strructural unit of the cell
wall.Each micelle consists of approx. 100 cellulose chains.About 20 micelles
produce a microfibril with a cross sectional area of about 62500 A.Again about 250
microfibrils form a fibril.
• The orientation of the microfibrils and the micelle in the secoindary wall differ in
species to species as well as the different organs.It is localised in certain regions to
the formation of different types of sculptures to provide strength to the cell wall to
resist different variations.
• Various sculptures-annular, spiral, scalriform, reticulate and pitted-simple or
bordered

15. DIFFERENT TYPES OF PITS

16. PIT-STRUCTURE
• In the secondary walls, some depressions are formed due to uneven deposition of the
materials-called pits.
• A pit consists of-Pit membrane, Pit chsmber & Pit aperture.
• A pit may be simple having uniform width of pit chamber & pit aperture
• A pit may be bordered having flash shapoed pit which becomes narrow towards the
pit aperture.
• Besides the above type of modifications, some other type of sculptutrres are formed-
Tradecule, Crassulae and Wart structures.
• Trabculae-Rod or bar like thickened projections of the vwall which traverse the cell
lumen extending across form one tangential wall to the other.
• Crssulae-Linear or crescent type of thickening of intercellular materials and primary
walls occur along the outer and lower margins of pit pairs encircling them.
• Wart Structures-Inner surface of the secondary wall have wart like structure

17. SURFACE VIEW OF BORDERED PITS

18. DIFFERNT TYPES OF PITS

19. PLASMODESMATA

20. CELL TO CELL CONNECTIVITY

21. PLASODESMATA-APOPLAST & SYMPLAST
• Plasmodesmata or Plasmodesma(sing.) are the protoplasmic bridges between the
adjacent plant cells.A plasmodema consists of a fine pore or channel with 20-40 nm
in diameter in the cell walls and middle lamella of two adjacent cells.It contains a
simple or branched tubule known as desmotubule that connects the endoplasmic
reticula of two cells.
• When the plasmodesmata of all cells of a plant produce a continuous protoplasmic
or living connection known as symplast.
• The non-living continum of all the cells of a plant made up of cell walls ,
intercellular spaces is called symplast.
• The main function of plasmodesmata is to transfer stimuli, nutrients and other
materials between two adjacent cells.
• Thus, the plant cell wall is the tresure of beauty to itslf as well as the lovers of beauty
of a plant biologists.

22. HOPE, YOU HAVE THE BEAUTY OF CELL WALL.THANKS A LOT