Cell wall in plants- introduction, cell wall layers, functions, sugars the building blocks of cell wall, macromolecules of cell wall, cell wall architecture, biosynthesis and assembly

1. JAI NARAIN VYAS UNIVERSITY, JODHPUR
Department of botany
Paper- 101
Seminar topic : - Cell
wall
Submitted
to :
Dr . VINOD
KATARIA
Submitted by :
Anmol Mertiya
M.sc Previous
1
stsem

2. CONTENS
1. Introduction
2. Cell Wall Layers
3. Functions Of The Plant Cell Wall
4. Sugars :- Building Blocks Of The Cell
Wall
5. Macromolecules Of The Cell Wall
6. Cell wall architecture
7. Cell wall biosynthesis and assembly
8. References

3. INTRODUTCTION
:-
Discovery of cell :- Cell wall was
first observed and name by
Robert Hooke in 1665.
In 1804, Karl Rudolphi and
J.H.F.Link proved that cells had
indepent cell wall .
The outermost structure of most
plant cells is a dyanamic and
rigid layer called cell wall (

4. Cell Wall Layers :-
There are three major
regions of the wall.
1. middle lamella.
2 . Primary cell wall
3. Secondary cell wall
a | Cell wall containing cellulose microfibrils, hemicellulose, pectin, lignin and soluble proteins.
b | Cellulose synthase enzymes are in rosette complexes, which float in the plasma membrane.
c | Lignification occurs in the S1, S2 and S3 layers of the cell wall.

5. Middle Lamella :
This Outer Cell Wall Layer Contains Polysaccharides
Called Pectins.
• Pectins Aid In Cell Adhesion By Helping The Cell Walls
Of Adjacent Cells To Bind To One Another.
Primary Cell Wall :
This Layer Is Formed Between The Middle Lamella And
Plasma Membrane.
• It Is Primarily Composed Of Cellulose
• Microfibrils (15-30%) ,
• Petic Polysaccharides (30%) ,
• Cross Linking Glycans (Hemicellulose (25%) And
• Protein (20%) .
• The Primary Cell Wall Provides The Strength And
Flexibility Needed To Allow For Cell Growth.

6.  This layer is formed between the primary
cell wall and in some plant cells.
 This rigid layer strengthens and supports
the cell. In addition to cellulose and
hemicellulose, some secondary cell walls
contain lignin.
• Lignin strengthens the cell wall and aids in
water conductivity in plant vascular tissue
cells.
Secondary wall :

7. Middle lamella, Primary cell wall
and Secondary cell wall :-
• While all plant cells have a middle lamella and primary cell
wall, not all have a secondary cell wall.

8. Functions of the plant cell wall :
• maintaining/determining cell shape .
• support and mechanical strength .
• prevents the cell membrane from bursting in a hypotonic medium.
• controls the rate and direction of cell growth and regulates cell
volume
• ultimately responsible for the plant architectural design and
controlling plant morphogenesis .
• metabolic role.
• physical barrier to: (a) pathogens
• (b) water in suberized cells.
• However, remember that the wall is very porous and allows the free
passage of small molecules, including proteins up to 60,000.
• economic products - cell walls are important for products such as
paper, wood, fiber, energy, shelter, and even roughage in our diet.

9. Sugars : Building
Blocks Of The Cell Wall
:-
 Polysaccharides are long chains of sugar
molecules covalently linked at various
positions, some being decorated with side
chain of various lengths.
 Sugars represent a vast spectrum of
polyhydroxyl “aldehydes” ( aldoses ) and
“ketones” ( ketoses ) that can be grouped
according to their chemical formula,
configuration , and stereochemical
conformation.

10.  Many sugars have the empirical
formula ( CH2O )n, from which the
term carbohydrate is derived.
Haworth
project
1. Pyranose 2.
Furanose
(5 membered ring
)
( 6 membered ring
)
Chair Puckere

11. Sugars: building blocks of the cell wall
The monosaccharides in cell wall polymers are derived from glucose.

12. Macromolecules of the cell
wall
1. Cellulose
2. Callose
3. Cross-linking glycans
4. Pectin
5. Protein
6. Aromatic substance

13. o Cellulose is the principal scaffolding component
of all plant cell walls.
o Cellulose is the most adundant plant
polysaccharide for 15-30% of the dry mass of
all primary cell and a much larger percentace of
secondary wall
o Made of (1→4)β-D-glucan chains hydrogen bonded
to one another along their length
o Groups of 30 to 40 of these chains laterally
hydrogen bond to form crystalline or para-
crystalline microfibrils
1. Cellulose

15. 2. Callose
 Callose differs from cellulose in consisting of
(1→3)β-D-glucan chains, which can form
helical duplexes and triplexes
 Callose is made by a few cell types at specific
stages of wall development, such as in
growing pollen tubes and in the cell plates of
dividing cells
 Callose is also made in response to wounding
. Callose synthesis may also occue at
the wall in response to abiotic or biotic stress.

17. 3. Cross-linking glycans
 The most common hemicelluloses in cell walls are
xyloglucans (XyGs) and Glucuronoarabinoxylans ( GAXs
).
 The XyG having β(1,4)-linked glucose residues that have
α(1,6)-linked xylosyl side chains.
 The GAXs having β(1,4)-linked xylose residues. For ex
. glucuronic acid to produce glucuroxylan .
 Both XyGs & GAXs may also be modified by acetylation,
which affects their capacity to cross-link to other cell wall
components.
 XyG is main hemicellulose in dicots primary walls &
functions to cross-link cellulose microfibrils .
 Although GAXs are major hemicelluloses in secondary
cell walls, they are also prominent in primary walls of

18. Structure of cross linking glycans

19. 4. Pectins
Pectins a mixture of heterogeneous, branched, and
highly hydrated polysaccharides rich in D-
galacturonic acid—have been defined classically as
material extracted from the cell wall by Ca2+-
chelators such as ammonium oxalate, EDTA,
EGTA, or cyclohexane diamine tetraacetate.
Pectins perform many functions:
• determining wall porosity
• providing charged surfaces that modulate wall pH
and ion balance.
• regulating cell–cell adhesion at the middle lamella.
• serving as recognition molecules that alert plant cells
to the presence of symbiotic organisms, pathogens,

20. Two types of pectine
1. HGA 2. RGⅠ
( Homogolacturonan) (Rhamnogalacturonan-Ⅰ
Homopolymers of (1→4)α-D Gal A
2 parts
1.xylogalacturonamn 2. RG Ⅱ
(Rhamnogalacturonan -Ⅱ)
Rod- like
heteropolymer of
peating (1 → 2) α -1
Rha ( 1→ 4) α -
D Gal A disaccaride
unite

21. Structure of pectins

22. 5. Structural proteins
 Structural proteins of the cell wall are encoded by
large multigene families.
 Although the structural framework of the cell wall
is largely carbohydrate , structural proteins may
also form networks in the wall.
 There are four major classes are structural
proteins :
1. hydroxy proline - rich glycoproteins ( HRGPs)
2. proline – rich proteins ( PRPs )
3. glycine – rich proteins ( GRPs )
4. Arabinogalactan proteins ( AGPs )

23. Structure of structural proteins

24. 6 .Aromatic substances :
 Aromatic substances are present in the
nonlignified walls of commelinoid species.
 The primary walls of the commelinoid orders
of monocots and the Chenopodiaceae
contain significant amounts of aromatic
substances in their nonlignified cell walls-a
feature that makes them fluorescent under
ultraviolet (UV) light.
 Hydroxycinnamic acid are also reduced in the
plant to hydroxycinnamoyl alcohols, which
form the common precursors for lignin and

25. Cell wall architecture
 The primary wall consists of
three structural networks:
o Cellulose and cross-linking
glycans
o Matrix pectic polysaccharides
o Structural proteins or a
phenylpropanoid network

26. • Walls of angiosperms are
arranged in two distinct types of
architecture
1. Type I walls- most dicots and the noncommelinoid
monocots contain about equal amounts of XyGs
(xyloglucans) and cellulose
 In Type I walls the cellulose-XyG framework is
embedded in a pectin matrix that controls, among
other physiological properties, wall porosity.
HGA is thought to be secreted as highly methyl-
esterified polymers, and the enzyme pectin
methylesterase (PME), located in the cell wall,
cleaves some of the methyl groups to initiate binding
of the carboxylate ions to Ca2+.

27. 2. Type II walls- commelinoid monocots
contain cellulose microfibrils similar to those of
the Type I wall; instead of XyG, however, the
principal polymers that interlock the microfibrils
are GAXs (glucuronoarbinoxylans).
 In general, Type II walls are pectin-poor, but an
additional contribution to the charge density of
the wall is provided by the α-L-GlcA units on
GAX. These walls have very little structural
protein compared with dicots and other
monocots but they can accumulate extensive
interconnecting networks of phenylpropanoids,
particularly as the cells stop expanding.

29. Cell wall biosynthesis and assembly :
 Origin of cell wall takes place from cell
plate during cytokinesis.
 Many cell wall vesicles provided by GB
and ER combine to form a cell plate.
 After some physical and chemical
changes, the cell plate ( rich in pectin )
grows on both sides to form a middle
lamella, which glues neighbouring plant
cells.
 After which primary wall and secondary
walls are laid down on the middle lamella

30.  After a wall forms, it can grow
and mature through a process:-
1. Synthesis
2. Secretion
3. Assembly
4. Expansion ( in growing cells )
5. Cross-linking and secondary wall
fomation

32. Cell walls for food, feed, fuel, and
fibers
 Wood
 Paper
 Textiles
 Fruits and vegetables for humans and
animals
 Jams, jellies, thickening agents,
emulsifiers
 Dietary fiber
 Biomass
 Biofuel: cellulosic ethanol

33. REFERENCES
 Alberts , B., Bray, D., Lewis, J., Raff, m.,
Roberts, K. And Watson, J. D. 1999. Molecular
Biology Of Cell . Garland Publishing , Inc. , New
York.
 Buchanan, B. B. ,Gruissem, W. And Jones , R. L.
2000. Biochemistry And Molecular Biology Of
Plants. American Society Of Plant Physiologists,
Maryland, USA
 https://jcs.biologist.org