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MERISTEMS<br />
mERISTEMS<br />Retain the ability to divide indefinitely<br />Very little differentiation<br />RESULT of divisions: NEW ce...
Cytological characteristics<br />Thin-walled<br />Iso-diametric<br />Richer protoplasm<br />Devoid of reserve materials an...
DIFFERENTIATION<br />Process of growth and morpho-physiological specialization of the cells<br />
STAGES Of development of Primary meristems<br />Promeristem = apical initials + derivatives<br />Initial = cells which rem...
Apical  meristema. shoot apexb. root apex<br />
A. Shoot apex<br />Shoot apex-  where new leaves and tissues of the stem arise<br />Models of tissue organization in the s...
Apical cell theory<br />*Pteridophytes- apical cell (1 initial) or apical initials– tetrahedral (pyramidal), base is direc...
Histogen theory (Hanstein, 1868)<br />Histogen theory (Hanstein, 1868)<br />	1. dermatogen – outermost<br />	2. plerome – ...
Comments <br />All cells have basically equal potential of differentiation <br />One zone of apical meristem may contribut...
Tunica- corpus theory (Schmidt, 1924)<br />Two regions: TUNICA and CORPUS<br />No constant relationship can be traced betw...
TUNIca<br />Outermost layer<br />Surrounds the inner cell mass (corpus)<br />Anticlinal division<br />Enlarges in surface ...
corpus<br />Inner cell mass<br />Divides in all directions<br />Enlarges in volume<br />TYPES<br />A. Usual – 1. CMC<br />...
Zonation in shoot apex<br />Central zone– (waiting meristem)- promeristem<br />	- corpus + portions of tunica <br />	- giv...
Origin of leaves<br />Initiated by periclinal divisions at the side of the apical meristem<br />Origin: tunica or corpus<b...
B. Root apex<br />Bi-directional production of cells<br />Subterminal in position<br />No lateral appendages (leaves, bran...
Root apex<br />Protoderm<br />Meristem of the cortex<br />Meristem of the vascular cylinder<br />Promeristem<br />columell...
Root apices<br />Single apical cell or initials (vascular cryptogams)<br /> Angiosperms : CLOSED and OPEN type (~ Histogen...
Angiosperm root apex<br />Epidermis and root cap– common origin<br />Dermatocalyptrogen; eudicots<br />
Epidermis and cortex –common initials<br />Root cap –calyptrogen; monocots<br />
Columella<br /><ul><li>the central core of the</li></ul>rootcap is distinct from <br />the peripheral part in having <br /...
b. Open type<br />- without any boundaries with reference to the derivative regions of the root<br />
Quiescent center- low mitotic activity<br />                             - reservoir of cells<br />                       ...
Intercalary meristems<br />Isolated meristematic regions that are disjunct from the subapicalmeristematic region<br />Inse...
Lateral meristem<br />Parallel to the circumference of the organ<br />Vascular cambium (VC) and cork cambium<br />Involved...
Vascular cambium<br />Fascicular + interfascicular cambium<br />Fascicular cambium – came from procambium<br />Interfascic...
Vascular cambium<br />1. Fusiform initials<br />	-- elongated and tapered <br />	-- tracheary elements, fibers, xylem and ...
Vascular cambium<br />Intense vacuolation<br />Walls -- 1’ pit fields with plasmodesmata<br />Periclinal division– radial ...
1. Storied or stratified cambium<br />    -- fusiform initials are arranged in horizontal rows so that their ends are at t...
Cork cambium<br />Phellogen<br />One type of initials<br />Rectangular in xs; regular polygons in ls<br />Vacuolated; may ...
Primary thickening in monocots <br />
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Meristems

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Meristems

  1. 1. MERISTEMS<br />
  2. 2.
  3. 3. mERISTEMS<br />Retain the ability to divide indefinitely<br />Very little differentiation<br />RESULT of divisions: NEW cells are added<br />Position<br />APICAL MERISTEMS<br />INTERCALARY MERISTEMS<br />LATERAL MERISTEMS<br />Origin<br />PRIMARY <br />SECONDARY <br />
  4. 4. Cytological characteristics<br />Thin-walled<br />Iso-diametric<br />Richer protoplasm<br />Devoid of reserve materials and crystals<br />Plastids  proplastids<br />Vacuoles small, not obvious, scattered<br />
  5. 5.
  6. 6. DIFFERENTIATION<br />Process of growth and morpho-physiological specialization of the cells<br />
  7. 7. STAGES Of development of Primary meristems<br />Promeristem = apical initials + derivatives<br />Initial = cells which remain within the meristem<br />Partly differentiatiatedmeristematic zone:<br />Protoderm<br />Procambium<br />Ground meristem<br />
  8. 8.
  9. 9.
  10. 10. Apical meristema. shoot apexb. root apex<br />
  11. 11.
  12. 12.
  13. 13. A. Shoot apex<br />Shoot apex- where new leaves and tissues of the stem arise<br />Models of tissue organization in the shoot apex<br /> A. Apical cell theory<br /> B. Histogen theory<br /> C. Tunica-corpus (most accepted in angiosperms)<br />
  14. 14. Apical cell theory<br />*Pteridophytes- apical cell (1 initial) or apical initials– tetrahedral (pyramidal), base is directed towards the surface of the apex<br /> *Gymnosperms- surface meristem; (apical initials– periclinal)<br /> central mother cells<br />
  15. 15.
  16. 16.
  17. 17. Histogen theory (Hanstein, 1868)<br />Histogen theory (Hanstein, 1868)<br /> 1. dermatogen – outermost<br /> 2. plerome – central<br /> 3. periblem – between 1 and 2<br />Each develop from independent group of initials (histogens)<br />Meristems are destined from the beginning to produce certain tissues<br />
  18. 18.
  19. 19. Comments <br />All cells have basically equal potential of differentiation <br />One zone of apical meristem may contribute cells to another one<br />
  20. 20. Tunica- corpus theory (Schmidt, 1924)<br />Two regions: TUNICA and CORPUS<br />No constant relationship can be traced between the particular initials of the promeristem and the inner tissues of the shoot<br />2 regions can be distinguished by their plane of cell division<br />
  21. 21.
  22. 22.
  23. 23. TUNIca<br />Outermost layer<br />Surrounds the inner cell mass (corpus)<br />Anticlinal division<br />Enlarges in surface area<br />Layer: 1-9<br />
  24. 24. corpus<br />Inner cell mass<br />Divides in all directions<br />Enlarges in volume<br />TYPES<br />A. Usual – 1. CMC<br /> 2. rib meristem<br /> 3. peripheral<br />B. Opuntia -- + cambium-like transition zone<br />
  25. 25. Zonation in shoot apex<br />Central zone– (waiting meristem)- promeristem<br /> - corpus + portions of tunica <br /> - gives rise to:<br />Rib zone or pith rib meristem<br /> - below central zone; center location<br /> - becomes the pith<br />Peripheral zone or peripheral meristem<br /> - encircles the other zones<br /> - most meristematic (eumeristem)<br /> - densest protoplast and smallest dimensions<br /> - gives rise to leaf primordia,procambium, cortical ground tissue<br />
  26. 26.
  27. 27.
  28. 28.
  29. 29. Origin of leaves<br />Initiated by periclinal divisions at the side of the apical meristem<br />Origin: tunica or corpus<br />Division  leaf buttress<br />Affects Periodic changes in shape of shoot apex<br />BRANCHING<br />Where do branches originate?<br />Superficial layers --- exogenous<br />Axillary buds<br />
  30. 30.
  31. 31. B. Root apex<br />Bi-directional production of cells<br />Subterminal in position<br />No lateral appendages (leaves, branches)<br />Branches occur beyond region of most active growth<br />Endogenous branching<br />Grows uniformly (no nodes and internodes)<br />
  32. 32. Root apex<br />Protoderm<br />Meristem of the cortex<br />Meristem of the vascular cylinder<br />Promeristem<br />columella<br />CLOSED TYPE- the initials are already discrete immediately adjacent to the central cells<br />Calyptrogen- intials of the root cap<br />OPEN TYPE – tissue systems become distinct only some distance away from the central cells<br />
  33. 33. Root apices<br />Single apical cell or initials (vascular cryptogams)<br /> Angiosperms : CLOSED and OPEN type (~ Histogen theory)<br />a. CLOSED – 3 tiers or layers of initials<br /> - apex of central cylinder<br /> - cortex<br /> - root cap<br />
  34. 34.
  35. 35.
  36. 36.
  37. 37. Angiosperm root apex<br />Epidermis and root cap– common origin<br />Dermatocalyptrogen; eudicots<br />
  38. 38. Epidermis and cortex –common initials<br />Root cap –calyptrogen; monocots<br />
  39. 39. Columella<br /><ul><li>the central core of the</li></ul>rootcap is distinct from <br />the peripheral part in having <br />few or no longitudinal divisions.<br />
  40. 40.
  41. 41. b. Open type<br />- without any boundaries with reference to the derivative regions of the root<br />
  42. 42. Quiescent center- low mitotic activity<br /> - reservoir of cells<br /> - may be due to hormones ( high levels of auxin) , pressure exerted by rapidly dividing neighbouring cells (antagonistic direction of cell growth)<br />
  43. 43.
  44. 44. Intercalary meristems<br />Isolated meristematic regions that are disjunct from the subapicalmeristematic region<br />Inserted between differentiated tissue regions<br />Internodes mature basipetally<br />Nodes mature first<br />Stems of monocots: internodes and leaf sheaths; in Equisetum<br />
  45. 45.
  46. 46. Lateral meristem<br />Parallel to the circumference of the organ<br />Vascular cambium (VC) and cork cambium<br />Involved in growth in thickness (VC)<br />Dicotyledons and gymnosperms<br />
  47. 47. Vascular cambium<br />Fascicular + interfascicular cambium<br />Fascicular cambium – came from procambium<br />Interfascicular cambium – interfascicular parenchyma<br />Develops between primary xylem and phloem<br />2’ XYLEM- centripetal; 2’ PHLOEM- centrifugally<br />
  48. 48.
  49. 49. Vascular cambium<br />1. Fusiform initials<br /> -- elongated and tapered <br /> -- tracheary elements, fibers, xylem and phloem parenchyma, sieve elements<br />2. Ray initials<br /> -- smaller; isodiametric<br /> -- vascular rays<br />
  50. 50. Vascular cambium<br />Intense vacuolation<br />Walls -- 1’ pit fields with plasmodesmata<br />Periclinal division– radial wall are thicker<br />Procambium – gabled ends; stain deeply; <br />Cambium – flat ends; long and short cells; intense vacuolation<br />
  51. 51.
  52. 52. 1. Storied or stratified cambium<br /> -- fusiform initials are arranged in horizontal rows so that their ends are at the same level<br />2. Non- storied<br /> -- fusiform initials partially overlap one another<br />
  53. 53. Cork cambium<br />Phellogen<br />One type of initials<br />Rectangular in xs; regular polygons in ls<br />Vacuolated; may have chloroplasts and tannins<br />No intercellular spaces<br />Part of the periderm<br />Origin: external to VC– epidermis, cortex, phloem parenchyma<br />
  54. 54.
  55. 55. Primary thickening in monocots <br />

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