Chapter 23 Cells and Tissues of the Plant Body

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Chapter 23Cells and Tissues of the Plant
Body
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Outline

• Growth after germination
• Meristems
• Growth, morphogenesis, differentiation
• Internal organization of plants
• Ground tissues
• Vascular tissues
• Dermal tissues

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Growth after Germination

• Embryogenesis produces shoot/root apical
  meristems
• vertical growth
• Meristems undifferentiated, perpetually young
  tissue from which new cells arise
• Apical meristems located at tips of all roots and
  shoots
• consists of group of cells (initials
  derivatives)
• initials divide to produce other sister
  meristem cells (initial) body cells
  (derivatives)
• derivatives divide then undergo differentiation

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Primary Meristems

• Primary meristems protoderm, procambium, ground
  meristem
• arise during embryogenesis
• partially differentiated meristematic cells that
  give rise to specific tissues
• 1º growth results from extension of plant body
  and formation of primary tissues
• primary plant body results
• 2º growth results in thickening
• Indeterminate growth in plants via meristems

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Development

• Development sum of events that progressively
  form organisms body
• determined by genetic x environment interaction
• light quality and quantity, daylength, gravity,
  moisture, nutrients
• 3 processes of development growth,
  morphogenesis, differentiation

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Growth, Morphogenesis, Differentiation

• Growth irreversible ? in size
• due to cell enlargement and division
• shape/form determined by planes of cell division
  and expansion
• Morphogenesis acquisition
  of particular
  shape or form
• Differentiation process of
  genetically identical cells
  become
  different from one
  another and meristematic cells
• depends on gene
  
  expression/position
  of
  tissue

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Internal Organization

• Tissue systems groups of tissues made of
  associating cells distinct from other cells
• 3 tissue systems dermal, ground (fundamental),
  vascular
• arise from protoderm, ground meristem, procambium
  respectively
• simple tissues one cell type
• complex tissues 2 cell types

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Internal Organization

• Dermal tissue system epidermis, periderm
• Ground tissue system parenchyma, collenchyma,
  sclerenchyma
• Vascular tissue system xylem (X), phloem (P)
• Pattern of tissue distribution
• vascular imbedded in ground, which covered by
  dermal

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Ground Tissue

• Dianas Talk

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Vascular Tissues

• Xylem water conducting tissue
• Phloem food conducting tissue
• Connected throughout plant body

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Vascular Tissues Xylem

• 3 func.
• water/mineral transport (tracheary elements)
• support (fibers)
• food storage (parenchyma, fibers)
• Derived from procambium VC
  
• 1 and 2 growth respectively
• Conducting cells in X
  tracheary elements (tracheids
  and
  vessel elements)
• Characteristics
• elongated
• lack protoplasts (dead) at maturity
• 2 walls w/ pits

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Vascular Tissues Xylem

• Tracheids
• only type tracheary element in gymnosperms
• angiosperms have both tracheids and vessel
  elements
• lack perforations
• pit membranes w/ thin 1 wall
• 2 pit membranes pit-pair
• advantage
• less risk of collapse due to air bubbles
• disadvantage
• ? efficient b/c narrower

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Vascular Tissues Xylem

• Vessel elements have perforations
• perforation area lacking 1 and 2 wall
• perforation plate area containing perforations
• typically end of cell
• vessel long stack of vessel elements
• advantage
• more efficient b/c wider
• disadvantage
• ? risk of collapse due
  embolism

Simple
Scalariform
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Vascular Tissues Xylem

• 2 wall thickenings in tracheary elements
• ringlike (annular) or spiral (helical) in 1
  xylem
• allow minimal extension
• more solid in 2 xylem
• ? rigidity
• ? extensibility

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Vascular Tissues Xylem

• Differentiation of vessels
• apoptosis programmed cell death
• protoplast dies
• walls remain except at ends

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Vascular Tissues Phloem

• 3 func.
• food transport (sieve elements)
• support (sclerenchyma)
• food storage (parenchyma)
• Conducting cells in P sieve elements (sieve
  cells and sieve-tube elements)
• sieve area cluster of pores
• allows connection btwn protoplasts of cells
• Characteristics
• living at maturity but lacking nucleus
• tonoplast, ribosomes, Golgi and cytoskeleton (to
  clear path for transport)
• pores lined w/ callose (polysaccharide)

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Vascular Tissues Phloem

• Sieve cells
• uniform small pores
• ? specialization
• only type sieve element in gymnosperms

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Vascular Tissues Phloem

• Sieve-tube element (STE)
• large pores born on sieve plates
• typically on ends
• stacking of members sieve tubes
• only type sieve element in angiosperms

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Vascular Tissues Phloem

• STE associated w/ companion cells
• parenchymal
• have nucleus
• connected to STM by
  plasmodesmata
• func.
• delivery of molecules/ATP/
  proteins to sieve-tubes
• dies when STE dies
• Sieve cells in gymnosperms
  associated w/ albuminous cells
• similar to companion cells

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Dermal Tissues

• Epidermis outermost cell layer of 1 plant body
• func.
• protection
• lack chloroplasts
• covered by cuticle of cutin/wax
• ? water loss
• may contain guard cells/trichomes/
  other
  specialized cells

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Dermal Tissues

• Guard cells
• func.
• regulate opening/closing of stomata (pores on
  leaf surface)
• gas exchange
• lots of chloroplasts
• assoc. w/ subsidiary cells

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Dermal Tissues

• Trichomes
• funcs.
• water/mineral absorption
• root hairs and trichomes on epiphytic lvs
• reflection of radiation
• ? leaf temps./transpiration
• pubescence
• secretion of salts and toxins
• mechanical and chemical defense
• trapping prey

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Dermal Tissues

• Periderm
• replaces epidermis in plants w/ 2 growth
• consists of
• nonliving, heavily suberized cork (phellum)
• outside CC
• living cork cambium
  (phellogen)
• living parachyma
  (phelloderm)
• inside CC
• lenticels
• func. gas exchange

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