1) The document describes the structure and composition of plant cell walls. It discusses the layers that make up primary and secondary cell walls, including the middle lamella, primary wall, and secondary wall. 2) The process of cell plate formation during cell division is summarized in 6 steps. Key structures involved include vesicles, fusion tubes, and the phragmoplast. 3) Various cell wall components are described such as cellulose, hemicellulose, pectin, and lignin. Factors influencing cell wall growth and differentiation are also outlined.

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Gross Structure
Detailed Structure
Chemistry
Features
Cement; amorphous subs.
Bet. P‐walls of neighboring cells
Pectic substances (Ca, Mg pectate)
First wall the develops on new cell Formed in the inner surface of P‐wall
Same content as Pwall ( > cellulose) + lignin
Cellulose, pectic cpds., non‐cellulosic In cells that ceased to grow; devoid of protoplast at
maturity
polysaccharides and hemicellulose * xylem ray, xylem parenchyma – still living
May be lignified
b l f d Mechanical support
M h i l
Assoc. with living protoplasts
‐‐eg. meristematic cells, parenchyma, Compound middle lamella *
= 3‐layered or 5‐layered
collenchyma = middle lamella + 2 P‐walls (+ 2 S‐walls)
*if middle lamella is obscured
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Preprophase band
a cortical belt of microtubules and actin filaments,
that predicts the plane of the future cell plate
Phragmosome
Ph
a layer of cytoplasm which spreads across the future
division
contains microtubules and actin filaments
(1) the arrival of Golgi‐derivedvesicles in the
division plane; fusion tube starts to form
Start of accumulation of cell wall materials in the lumen‐‐callose
(2) the formation of fusion tubes that grow out of (3) transformation of the tubulo‐vesicular network
the vesicles and fuse with others tubulo‐ into a tubular network
vesicular network (interwoven)
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(4) Formation of fenestrated plate‐like structure (5)the formation of numerous finger‐like projections
the dense membrane coat and the associated at the margins of the cell plate that fuse with the
phragmoplast microtubules are disassembled; plasma membrane of the mother cell wall
Abundant accummulation of cell wall building materials
(6) maturation of the cell plate into a new cell wall.
Cell plate‐ precursor of cell wall; rich in
pectins
Phragmoplast‐ a complex of microtubules
h l l f b l
and ER that forms during late anaphase or
early telophase from dissociated spindle
Closing of fenestrae subunits.
Formation of plasmodesmata
After completion of the cell plate, additional wall
material is deposited inc. in thickness
New wall material deposition mosaic fasion
Matrix materials
Matri materials Delivered by Golgi vesicles
Cellulose microfibrils Cellulose synthase complex
Cellulose synthase
appear as rosettes
exude the microfibrils on the outer surface of
the membrane.
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A. Growth in thickness
1. Apposition
2. Intussusception
Lignification
f Intussusception
Cutinization Intussusception
B. Growth in surface (wall expansion)
Rosettes are inserted in the plasma membrane and pushed forward by synthesis
and crystallization of microfibrils
Or extension
Requires: wall stress relaxation (loosening of
wall structure) and turgor pressure
Controlled by: a] amt. of turgor pressure
ll d b f
b] extensibility
*Extensibility ability to expand permanently
when a force is applied to it (plastic)
affected by hormones : auxin
Marks cessation of growth (irreversible) Cellulose fibrils
during maturation Matrix (non‐cellulosic):
FACTORS: that contribute ‐ with lignin, cutin, suberin, hemicelluloses
(1) a reduction in wall‐loosening processes,
d ll l etc.
(2) An increase in cross‐linking of cell wall
components,
(3) a change in wall composition (more
rigid structure or less susceptible to wall
loosening)
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Long chains of linked glucose residues
Micellae – bundles of cellulose molecules or
ELEMENTARY FIBRIL = ~40 cellulose
molecules
l l
Microfibril
Bundles of microfibril
Ml‐ middle lamella
Pm‐ plasma membrance
Cellulose
Pectic substances
Gums and mucilages
Lignin
Fatty substances
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Hydrophilic crystalline compound Amorphous colloidal substances
Repeating monomers of glucose Plastic and hydrophilic
Appear as a result of physiological or Phenolic compounds
pathological disturbances that induce May be found in middle lamella, primary wall,
breakdown of walls and cell contents and secondary wall
hydrophobic fi ller h
h d h b f ll that replaces the wall’s
l h ll
water
compressive
strength and bending stiffness
Microbial attack resistance
Cutin, suberin, waxes Tensile strength (bend under compressive
Waxes‐ glaucous condition; assoc. with cutin stress)
and suberin Incrustation– eg. Lignification
Suberin‐ cork cells of periderm; endodermis
and exodermis; prevents apoplastic transport
Cutin‐ cuticle layer; epidermis of aerial parts Cell wall growth
A. intussusception
Cutinization, suberization‐ impregnation in cell B. apposition
wall C. mosaic growth
Cuticularization‐ formation of layer D. multinet growth
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Material of new wall is laid down bet. Growth is due to the centripetal addition of
Particles of the existing substance of the new layers one upon the other
expanding wall
Fibrillar texture in certain wall areas become separation of crossed microfibrils and
loosened as a result of turgor pressure and alteration in their orientation
afterwards mended by deposition of new transverse longitudinal
microfibrils in the gaps caused by the strain
fb l h db h
Primary pit fields Primordial pits/ primary pit fields
Pits Certain areas of primary wall of young cells
Crassulae remain thin
Trabeculae
b l May appear beaded in xs
b d d
Wart structures
Cystoliths
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Plasmodesmata‐ connnect protoplasts of
neighboring cells
‐ transport; relay of stimuli
* symplast‐ 2 or more interconnected
l d
protopolast
* apoplast – cell walls, intercellular spaces
and lumen
desmotubule
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Portions of the cell wall that remained thin
even as secondary wall is formed
Primary wall only
Can develop over primary pit fields
f
Function?
TYPES: Branched simple pits (ramiform)
a. simple pit Found in parenchyma cells with thickened
b. bordered pit—S‐wall develops over the pit walls, libriform fibers, sclereids, phloem fibers
cavity to form an overarching roof
f h f
Structure:
Pit cavity / pit chamber
Pit aperture
Pit border
Pit canal, inner and outer aperture (very thick S‐
wall)
water‐conducting and mechanical xylem cells
(vessel elements, tracheids, etc.)
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Angiosperm Gymnosperm
Pit cavity – break in S‐wall Simple pit pair
Pit membrane/ closing membrane –primary Bordered pit pair
wall + middle lamella Half bordered pit pair
Pit aperture Blind pit
l d
Unilateral compound pitting
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pit membrane thickening; disc shaped – porous pit membrane around the torus
flexible; can go median or lateral ‐‐conifer tracheids
Aspirate condition (lateral)– latewood and all ‐‐ occurs through matrix dissolution
heartwood
Coniferales, Gnetales
Round, elliptic, linear
In thick cell walls:
*inner aperture becomes long and narrow
*outer aperture remains circular round
l d
* pit canal is funnel‐shaped
*fiber‐tracheid feature
Scalariform Linear or crescent‐shaped thickenings of the
Opposite primary wall and middle lamella
Alternate gymnosperms
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Rod shape thickenings of the wall which Fahn, A. 1990. Plant Anatomy, 4th ed..
traverse the cell lumen radially Pergamon Press
Esau, K. 1958. Plant Anatomy. John Wiley and
Sons, Inc.
Evert, R. 2006. Esau’s Plant Anatomy. John
Wiley and Sons, Inc.
Protopectin, pectin, pectic acid Related to pectic
Plastic, amorphous colloid, hydrophilic Swelling property (hydrophilic)
Hydration in young walls
Impregnation starts in the intercellular Cellulose molecules micelles (crystal)
lamella micellar system (porous)
Microfibril
f consists of micellar system
f
And
Microcapillaries liquids, lignin, waxes, cutin,
suberin, hemicellulose, pectic substances,
crystals, silica
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Plasticity
‐becoming permanently deformed when
subjected to changes in shape or size
Elasticity
‐property of recovery of the original size and
shape after deformation
Tensile strength
‐ relative to chemical composition and
microscopic and submicroscopic structure
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