Cell Wall

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  • (A) In the first step, Golgi vesicles, some of which are interconnected via fusion tubes, aggregate in the spindle midzone area. This structure is called the fusion tube network (FTN). The transition from the first to the second stage of cell plate formation can be inhibited by caffeine. (B) Formation of a tubulo-vesicular network (TVN). The contents of the vesicles, mainly pectins, represent the precursors from which the new middle lamella is assembled outside the cell. In the next stage, vesicle fusion increases, forming a tubulo-vesicular network (TVN), and the membranes become coated with either clathrin or other proteins. (C) In the third stage, the central region of the growing cell plate forms a tubular network (TN), with vesicle fusion occurring at the growing edges where the remaining microtubules are located. (D) In the final stage, the cell plate contacts and adheres to the plasma membrane of the parent cell. At the same time the tubular network expands to form a fenestrated sheet. (E) At the end of mitosis, the phragmoplast disappears, the cell enters interphase, and microtubules reappear in the cytosol near the plasma membrane, where they play a role in the deposition of cellulose microfibrils during cell wall growth (see Chapter 15). (F) Electron micrograph of a cell plate forming in a root tip of a beet, (Beta vulgaris) (10,000×) MT, microtubule; VE, vesicles; N, nucleus; NE, nuclear envelope; P, cell plate. (A–E from Staehelin and Hepler 1996; F from B. Gunning and M. Steer, Plant Cell Biology: Structure and Function, Jones and Bartlett, 1996.)Stages of cell plate development. A, the fusion of Golgi-derived secretory vesicles (sv) at the equatorial zone, among phragmoplast microtubules (mt) and a cytoplasmic fuzzy matrix (fm). B, fused Golgi-derived vesicles give rise to tubulo-vesicular network covered by a “fuzzy coat.” C, a tubular network (TN) forms as the lumen of the tubulovesicularnetwork (TVN) becomes filled with cell wall polysaccharides, especially callose. Fuzzy matrix surrounding the network and microtubules disappears, further distinguishing this stage from the tubulo-vesicular network. D,the tubule areas expand, forming an almost continuous sheet. Numerous finger-like projections extend from the margins of the cell plate and fuse with the plasma membrane (pm) of the parent cell wall (pcw) at the site previously occupied by the preprophase band. E, maturation of the cell plate into a new cell wall. (After Samuels et al., 1995.Reproduced from The Journal of Cell Biology 1995, vol. 130, 1345–1357, by copyright permission of the RockefellerUniversity Press.)
  • Primary plasmodesmata form during cytokinesis when Golgi-derived vesicles containing cell wall precursors fuse to form the cell plate (the future middle lamella). Rather than forming a continuous uninterrupted sheet, the newly deposited cell plate is penetrated by numerous pores (Figure 1.27A), where remnants of the spindle apparatus, consisting of ER and microtubules, disrupt vesicle fusion.Further deposition of wall polymers increases the thickness of the two primary cell walls on either side of the middle lamella, generating linear membrane-lined channels (Figure 1.27B). Development of primary plasmodesmata thus provides direct continuity and communication betweencells that are clonally related (i.e., derived from the samemother cell)
  • Cell Wall

    1. 1. CELL WALL<br />
    2. 2. CELL WALL<br />Gross Structure<br />Detailed Structure<br />Chemistry<br />Features<br />
    3. 3. GROSS STRUCTURE<br />
    4. 4. Middle lamella<br />Cement; amorphous subs.<br />Bet. P-walls of neighboring cells<br />Pectic substances (Ca, Mg pectate)<br />
    5. 5. Primary wall<br />First wall the develops on new cell<br />Cellulose, pecticcpds., non-cellulosic polysaccharides and hemicellulose<br />May be lignified<br />Assoc. with living protoplasts<br /> --eg. meristematic cells, parenchyma, collenchyma<br />
    6. 6. Secondary wall<br />Formed in the inner surface of P-wall<br />Same content as Pwall ( &gt; cellulose) + lignin<br />In cells that ceased to grow; devoid of protoplast at maturity<br /> * xylem ray, xylem parenchyma – still living<br />Mechanical support<br />Compound middle lamella *<br />= 3-layered or 5-layered<br />= middle lamella + 2 P-walls (+ 2 S-walls)<br />*if middle lamella is obscured<br />
    7. 7. Formation of wall<br />
    8. 8. Cell plate- precursor of cell wall; rich in pectins<br />Phragmoplast- a complex<br />of microtubules and ER that forms during late anaphase or early telophase from dissociated spindle subunits.<br />
    9. 9.
    10. 10. Fine structure of the wall<br />Cellulose fibrils<br />Matrix (non-cellulosic):<br /> - with lignin, cutin, suberin, hemicelluloses etc. <br />
    11. 11.
    12. 12.
    13. 13. Ml- middle lamella<br />Pm- plasma membrance<br />
    14. 14. Levels of organization of cell wall <br />Long chains of linked glucose residues<br />Micellae – bundles of cellulose molecules or ELEMENTARY FIBRIL = ~40 cellulose molecules<br />Microfibril<br />Bundles of microfibril<br />
    15. 15.
    16. 16. CHEMISTRY OF WALLS<br />Cellulose<br />Pectic substances<br />Gums and mucilages<br />Lignin<br />Fatty substances<br />
    17. 17. Cellulose<br />Hydrophilic crystalline compound<br />Repeating monomers of glucose<br />
    18. 18. Pectic substances<br />Amorphous colloidal substances<br />Plastic and hydrophilic<br />
    19. 19. Gums and mucilages<br />Appear as a result of physiological or pathological disturbances that induce breakdown of walls and cell contents<br />
    20. 20. Lignin<br />Phenolic compounds<br />May be found in middle lamella, primary wall, and secondary wall<br />hydrophobic filler that replaces the wall’s water<br />compressive<br />strength and bending stiffness<br />Microbial attack resistance<br />
    21. 21. Fatty substances<br />Cutin, suberin, waxes<br />Waxes- glaucous condition; assoc. with cutin and suberin<br />Suberin- cork cells of periderm; endodermis and exodermis; prevents apoplastic transport<br />Cutin- cuticle layer; epidermis of aerial parts<br />Cutinization, suberization- impregnation in cell wall<br />Cuticularization- formation of layer<br />
    22. 22. Cellulose<br />Tensile strength (bend under compressive stress)<br />Incrustation– eg. Lignification<br />Cell wall growth<br /> A. intussusception<br /> B. apposition<br /> C. mosaic growth<br /> D. multinet growth<br />
    23. 23. Intussusception<br />Material of new wall is laid down bet. Particles of the existing substance of the expanding wall<br />
    24. 24. Apposition<br />Growth is due to the centripetal addition of new layers one upon the other<br />
    25. 25. Mosaic growth<br />Fibrillar texture in certain wall areas become loosened as a result of turgor pressure and afterwards mended by deposition of new microfibrils in the gaps caused by the strain<br />
    26. 26. Multinet growth<br />separation of crossed microfibrils and alteration in their orientation<br />transverse  longitudinal<br />
    27. 27. Special structures of the cell wall<br />Primary pit fields<br />Pits<br />Crassulae<br />Trabeculae<br />Wart structures<br />Cystoliths<br />
    28. 28. Primary pit fields<br />Primordial pits/ primary pit fields<br />Certain areas of primary wall of young cells remain thin<br />May appear beaded in xs<br />
    29. 29.
    30. 30.
    31. 31. Plasmodesmata<br />Plasmodesmata- connnect protoplasts of neighboring cells<br /> - transport; relay of stimuli<br /> * symplast- 2 or more interconnected protopolast<br /> * apoplast – cell walls, intercellular spaces and lumen<br />desmotubule<br />
    32. 32.
    33. 33.
    34. 34.
    35. 35. Pits<br />Portions of the cell wall that remained thin even as secondary wall is formed<br />Primary wall only<br />Can develop over primary pit fields<br />Function?<br />
    36. 36.
    37. 37. Pits<br />TYPES:<br /> a. simple pit<br /> b. bordered pit—S-wall develops over the pit cavity to form an overarching roof<br />
    38. 38. Simple pits<br />Branched simple pits (ramiform)<br />Found in parenchyma cells with thickened walls, libriform fibers, sclereids, phloem fibers<br />
    39. 39. Bordered pits<br />Structure:<br />Pit cavity / pit chamber<br />Pit aperture<br />Pit border<br />Pit canal, inner and outer aperture (very thick S-wall)<br />water-conducting and mechanical xylem cells (vessel elements, tracheids, etc.)<br />
    40. 40.
    41. 41.
    42. 42.
    43. 43. Angiosperm<br />Gymnosperm<br />
    44. 44.
    45. 45. Pit-pair<br />Pit cavity – break in S-wall<br />Pit membrane/ closing membrane –primary wall + middle lamella<br />Pit aperture<br />
    46. 46. Types of pit-pair<br />Simple pit pair<br />Bordered pit pair<br />Half bordered pit pair<br />Blind pit<br />Unilateral compound pitting <br />
    47. 47. Torus<br />pit membrane thickening; disc shaped<br />flexible; can go median or lateral<br />Aspirate condition (lateral)– latewood and all heartwood<br />Coniferales, Gnetales<br />
    48. 48. Margo<br />– porous pit membrane around the torus<br /> --conifer tracheids<br /> -- occurs through matrix dissolution<br />
    49. 49. Shape of pit aperture<br />Round, elliptic, linear<br />In thick cell walls: <br /> *inner aperture becomes long and narrow<br /> *outer aperture remains circular round<br /> * pit canal is funnel-shaped<br /> *fiber-tracheid feature<br />
    50. 50.
    51. 51. Bordered pits arrangement<br />Scalariform<br />Opposite<br />Alternate <br />
    52. 52. crassulae<br />Linear or crescent-shaped thickenings of the primary wall and middle lamella<br />gymnosperms<br />
    53. 53. trabeculae<br />Rod shape thickenings of the wall which traverse the cell lumen radially<br />
    54. 54. References<br />Fahn, A. 1990. Plant Anatomy, 4th ed.. Pergamon Press<br />Esau, K. 1958. Plant Anatomy. John Wiley and Sons, Inc.<br />Evert, R. 2006. Esau’s Plant Anatomy. John Wiley and Sons, Inc.<br />

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