2. Primary wall
1 to 3 µm thick.
Composed mostly of
loosely interwoven fibrils of
cellulose, hemicellulose
and pectic substances.
Thin, elastic and undergoes
extension with the growth
of the cell.
Middle lamella
Development of the cell wall
starts with the formation of
middle lamella by the cell plate
after cell division.
Composed of Calcium and
Magnesium pectate.
Viscous and jelly like substance
and acts like a cementing
material between the primary
walls of adjacent cells.
PHYSICAL STRUCTURE OF CELL
WALL
Secondary wall
Laid down on the primary
wall when its growth is over.
5 to 10 µm thick.
Has three layers- outer layer
(S1), middle layer (S2) and
the inner layer (S3).
3. CELLULOSE
Long, unbranched chain of glucose
molecules linked by Beta 1,4 glycosidic
bonds
HEMICELLULOSE
Composed of glucose, xylose,
mannose and glucuronic acid
PECTIN
Contain galactose, arabinose and
galacturonic acid
LIGNIN
An insoluble aromatic polymer
resulting from the polymerization of
phenolic alcohols.
SUBERIN
Fat like material deposited in the
secondary wall of cork cell
CUTIN
Deposited on the exposed surface of
cell as a distinct layer called cuticle
C
H
P
L
S
C
4.
5. Plasma membrane
• It consists 40-50% protein and 50-60%
lipids.
• It is 7-8 nm thickness and has two
electron dense regions separated by an
electron light central region i.e., called as
trilaminar.
• The most widely accepted model of
plasma membrane is the “fluid mosaic
model” which was proposed by Singer
and Nicholson in 1972.
Two monolayers of lipid molecules
form a lipid bilayer.
The protein molecules are embedded
within the lipid bilayer.
6.
7.
8. Simple and
Bordered Pits
At certain places, secondary wall is not laid down and such
areas are simple pits – separated by a pit membrane
composed of middle lamella and primary walls.
Through these fine cytoplasmic strands called
plasmodesmata extend from the cytoplasm of one cell to
that of neighbouring cell – facilitates movement of
materials between adjacent cells.
In tracheids of Gymnosperms, the secondary wall partially
overhangs the pits – bordered pits.
9. FUNCTIONS OF
CELL WALL
1. Gives protection and mechanical support
to the plant cell.
2. Provides definite shape to plant cell.
3. It is permeable and allows materials to
pass in and out of the cell.
4. It helps in the maintenance of balance of
intracellular osmotic pressure with that
of its surroundings.
10. SWOT
ANALYSIS
Dominant mechanical
component
In primary walls 3 nm in
diameter
In secondary walls 20 nm
diameter
Includes Xyloglucan and
Xylan which are methylated
and feruloylated
Mannans are polymers of β-
1, 4 linkaged mannose
prevalent in gymnosperms
Sometimes classified as
a hemicellulose but does
not contain the equatorial
β- 1,4 linkages
Most dynamic cell wall
polymers
Acidic Polysaccharides
Homogalacturonan, the most
abundant pectin
Rhamnogalacturonan I consists
of galacturonic acid and
rhamnose residues, and anchors
arabinan, galactan, and
arabinogalactan side chains
Rhamnogalacturonan II, a highly
conserved and complex
CELLULOSE CALLOSE
HEMICELLULOSE PECTIN
Anderson and Kieber (2021)
11. Functional Interactions
Between Wall
Components
Pectins have been detected in close proximity to
cellulose by solid-state nuclear magnetic resonance
Homogalacturonan can cross-link via calcium bridges
Rhamnogalacturonan II monomers can be cross-linked
by borate diesters
Rhamnogalacturonan-I can also cross-link via ferulate
diesters
Covalently cross-linked model
Tether model
Diffuse layer model
Stratified Layer model
https://glygen.ccrc.uga.edu/ccrc/mao/intro/
https://glygen.ccrc.uga.edu/ccrc/mao/intro/ouline.htm
12. POLYMERIZATION
AND ASSEMBLY OF
CELL WALL
COMPONENTS
Matrix polysaccharides, including pectic
homogalacturonan (orange) and xyloglucan (purple) are
synthesized in the Golgi body by glycosyltransferases.
GALACTURONOSYLTRANSFERASE1 (GAUT1) and
CELLULOSE SYNTHASE-LIKE C4 (CSLC4) decorate
the polysaccharide backbones with side chains.
In the apoplast polygalacturonases (PGs, red) and
xyloglucan endotransglycosylases (XETs, dark blue) can
modify the structure of the wall to enable growth and
developmental events
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Genes identified that play a role in the trafficking of CSCs
15. Conclusion
Plant cell walls are dynamic
extracellular structures that undergo
assembly, metabolism, modification,
and controlled degradation.
Genetic identification of new players in
wall synthesis, sensing, and
modification has provided a rapidly
expanding cast of characters that carry
out various activities in the cell wall.
Mirror many of the
characteristics found in the
living protoplast.
16. THANK YOU!
These players function alone and in concert will
require new molecular-level information in living
plants.
