Cell Wall
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Transcript of Cell Wall
1/13/2010
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Gross StructureDetailed StructureChemistryFeatures
Cement; amorphous subs.Bet. P‐walls of neighboring cellsPectic substances (Ca, Mg pectate)
First wall the develops on new cellCellulose, pectic cpds., non‐cellulosic polysaccharides and hemicellulose
b l f dMay be lignifiedAssoc. with living protoplasts‐‐eg. meristematic cells, parenchyma, collenchyma
Formed in the inner surface of P‐wallSame content as Pwall ( > cellulose) + ligninIn cells that ceased to grow; devoid of protoplast at maturity* xylem ray, xylem parenchyma – still livingM h i l Mechanical support
Compound middle lamella *= 3‐layered or 5‐layered= middle lamella + 2 P‐walls (+ 2 S‐walls)
*if middle lamella is obscured
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Preprophase banda cortical belt of microtubules and actin filaments,
that predicts the plane of the future cell plate
PhPhragmosomea layer of cytoplasm which spreads across the future
divisioncontains 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 the vesicles and fuse with others tubulo‐vesicular network (interwoven)
(3) transformation of the tubulo‐vesicular network into a tubular network
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(4) Formation of fenestrated plate‐like structurethe dense membrane coat and the associated phragmoplast microtubules are disassembled;
Abundant accummulation of cell wall building materials
(5)the formation of numerous finger‐like projections at the margins of the cell plate that fuse with the plasma membrane of the mother cell wall
(6) maturation of the cell plate into a new cell wall.
Closing of fenestraeFormation of plasmodesmata
Cell plate‐ precursor of cell wall; rich in pectins
h l l f b lPhragmoplast‐ a complex of microtubules and ER that forms during late anaphase or early telophase from dissociated spindle subunits.
After completion of the cell plate, additional wall material is deposited inc. in thicknessNew wall material deposition mosaic fasion
Matri materials Delivered by Golgi vesiclesMatrix materials Cellulose microfibrils
Cellulose synthaseappear as rosettesexude the microfibrils on the outer surface of
the membrane.
Delivered by Golgi vesiclesCellulose synthase complex
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Rosettes are inserted in the plasma membrane and pushed forward by synthesisand crystallization of microfibrils
A. Growth in thickness1. Apposition2. Intussusception
fLignificationCutinization
B. Growth in surface (wall expansion)
Intussusception
Intussusception
Or extensionRequires: wall stress relaxation (loosening of wall structure) and turgor pressure
ll d b fControlled by: a] amt. of turgor pressureb] extensibility
*Extensibility ability to expand permanently when a force is applied to it (plastic)
affected by hormones : auxin
Marks cessation of growth (irreversible) during maturation
FACTORS: that contributed ll l(1) a reduction in wall‐loosening processes,
(2) An increase in cross‐linking of cell wall components,
(3) a change in wall composition (morerigid structure or less susceptible to wall loosening)
Cellulose fibrilsMatrix (non‐cellulosic):‐with lignin, cutin, suberin, hemicelluloses etc.
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Ml‐middle lamellaPm‐ plasma membrance
Long chains of linked glucose residuesMicellae – bundles of cellulose molecules or ELEMENTARY FIBRIL = ~40 cellulose
l lmoleculesMicrofibrilBundles of microfibril
CellulosePectic substancesGums and mucilagesLigninFatty substances
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Hydrophilic crystalline compoundRepeating monomers of glucose
Amorphous colloidal substancesPlastic and hydrophilic
Appear as a result of physiological or pathological disturbances that induce breakdown of walls and cell contents
Phenolic compoundsMay be found in middle lamella, primary wall, and secondary wallh d h b f ll h l h llhydrophobic fi ller that replaces the wall’s watercompressivestrength and bending stiffnessMicrobial attack resistance
Cutin, suberin, waxesWaxes‐ glaucous condition; assoc. with cutinand suberinSuberin‐ cork cells of periderm; endodermis Suberin‐ cork cells of periderm; endodermis and exodermis; prevents apoplastic transportCutin‐ cuticle layer; epidermis of aerial parts
Cutinization, suberization‐ impregnation in cell wall
Cuticularization‐ formation of layer
Tensile strength (bend under compressive stress)Incrustation– eg. Lignification
Cell wall growthA. intussusceptionB. appositionC. mosaic growthD. multinet growth
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Material of new wall is laid down bet. Particles of the existing substance of the expanding wall
Growth is due to the centripetal addition of new layers one upon the other
Fibrillar texture in certain wall areas become loosened as a result of turgor pressure and afterwards mended by deposition of new
f b l h d b hmicrofibrils in the gaps caused by the strain
separation of crossed microfibrils and alteration in their orientationtransverse longitudinal
Primary pit fieldsPitsCrassulae
b lTrabeculaeWart structuresCystoliths
Primordial pits/ primary pit fieldsCertain areas of primary wall of young cells remain thin
b d dMay appear beaded in xs
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Plasmodesmata‐ connnect protoplasts of neighboring cells‐ transport; relay of stimuli
l d* symplast‐ 2 or more interconnected 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 formedPrimary wall only
fCan develop over primary pit fields
Function?
TYPES:a. simple pitb. bordered pit—S‐wall develops over the pit
f h fcavity to form an overarching roof
Branched simple pits (ramiform)Found in parenchyma cells with thickened walls, libriform fibers, sclereids, phloem fibers
Structure:Pit cavity / pit chamberPit aperturePit borderPit 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‐wallPit membrane/ closing membrane –primary wall + middle lamellaPit aperture
Simple pit pairBordered pit pairHalf bordered pit pairl dBlind pit
Unilateral compound pitting
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pit membrane thickening; disc shapedflexible; can go median or lateralAspirate condition (lateral)– latewood and all heartwoodConiferales, Gnetales
– porous pit membrane around the torus‐‐conifer tracheids‐‐ occurs through matrix dissolution
Round, elliptic, linearIn thick cell walls: *inner aperture becomes long and narrow
l d*outer aperture remains circular round* pit canal is funnel‐shaped*fiber‐tracheid feature
ScalariformOppositeAlternate
Linear or crescent‐shaped thickenings of the primary wall and middle lamellagymnosperms
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Rod shape thickenings of the wall which traverse the cell lumen radially
Fahn, A. 1990. Plant Anatomy, 4th ed.. Pergamon PressEsau, K. 1958. Plant Anatomy. John Wiley and Sons, Inc.Evert, R. 2006. Esau’s Plant Anatomy. John Wiley and Sons, Inc.
Protopectin, pectin, pectic acidPlastic, amorphous colloid, hydrophilicHydration in young walls
Related to pecticSwelling property (hydrophilic)
Impregnation starts in the intercellular lamella
Cellulose molecules micelles (crystal) micellar system (porous)
f fMicrofibril consists of micellar systemAndMicrocapillaries 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 sizeElasticity‐property of recovery of the original size and shape after deformationTensile strength‐ relative to chemical composition and
microscopic and submicroscopic structure