Cells and Tissues of the Plant Body

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Cells and Tissues of the Plant Body

• Chapter 23

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Plant Growth

• Plants grow from apical meristems
• Specific points of growth on stems and roots
• Cells retain the potential to differentiate
• Allows plants to adapt to enviroment
• Make new organs
• Change organs from one to another

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Apical Meristems

• Found at the tips of all roots and stems
• Primarily involved with extension of the plant
  body
• Initials maintain and perpetuate the meristem
• Divide and one cell remains the initial and the
  other becomes a derivative ( body cell)

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Meristematic Tissues
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Primary Meristems

• Primary meristematic tissues are throughout the
  plant
• Protoderm, procambium, and ground meristem
• Partially differentiated
• Involved in primary growth
• Add to the plant throughout the plants life
• Indeterminate growth

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Shoot Meristems
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Root Meristems
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Growth, Morphogenesis and Differentiation

• Growth increase in size
• Due to mitosis and cell enlargement
• Morphogenesis change in shape or form
• Planes in which they divide and expand create the
  shape
• Differentiation change in gene expression
• Changes from identical cells to cells that
  express different proteins and do different tasks

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Internal Organization of the Plant

• Organized into tissues and tissue systems
• Based on their position throughout the plant
• Ground tissue system, vascular tissue system,
  dermal tissue system
• Precursors of these tissues in the primary
  meristems

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Internal Organization of the Plant

• Distribution of tissues based on plant taxa and
  plant part
• May be simple or complex
• All are distributed layers of ground tissue
• Covered in epidermal tissue
• Difference is in distribution of ground tissue to
  vascular tissue

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Parenchyma cells

• Occur throughout the body
• In rays or in continuous masses
• Retain meristematic ability
• Only primary cell walls
• Important in regeneration and healing
• Involved in photosynthesis storage and healing
• Living at maturity

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Transfer Cells

• Parenchyma cells with wall ingrowths
• Increase area of plasma membrane
• Movement of solutes over short distances
• Occur in association with xylem and phloem

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Collenchyma Cells

• Support Growing organs
• Living at maturity
• Beneath epidermis in stems and petioles
• Borders veins
• Unevenly thickened primary walls
• Allows growth with strength

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Sclerenchyma

• May form in masses or in small groups
• Thick, lignified cell walls
• Strength and support
• Two types
• Fibers- long and slender, occur in bundles
• Sclerids- short, single or aggregates

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Vascular Tissues - Xylem

• Xylem- water conducting tissue
• Also in support and storage
• Tracheids and vessel elements
• 2 cell walls, no protoplasts and pits in their
  walls
• Vessels have perforation plates lacking cell
  walls at the end
• Makes vessels continuous with each other
• Tracheids less specialized, water must pass
  through pit membranes
• Only have tracheids in gymnosperms

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Xylem
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Xylem

• Variety of 2 cell wall thickenings
• Rings or spirals
• Differentiation involves programmed cell death
• Vascular tissue also has parenchyma and fibers
  for support and storage

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Vascular Tissues - Phloem

• Food conducting tissue
• Also conducts AAs, lipids, hormones, proteins
  and signal molecules
• Sieve elements
• Sieve areas which connect adjacent cells
• Sieve cells and sieve-tube elements
• Sieve cells in gymnosperms
• Sieve-tube elements in angiosperms

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Sieve-Tube Members

• Most sieve areas in overlapping regions
• Alive at maturity, but very little protoplast or
  organelles
• Associated with albuminous cells
• Life support system
• Cannot survive without

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Sieve-Tube Members

• Lined end to end, no ovelapping
• Alive at maturity, but very little protoplast or
  organelles
• Companion cells derived from same mother cells
• Life support

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Dermal Tissues

• Outermost covering of the plant body
• Variable in function and structure
• Most unspecialized for mechanical protection
• Covered with cuticle
• Typically lack chloroplasts

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Guard Cells

• Contain chloroplasts
• Regulate opening and closing of stomata
• Movement of gases
• Aerial parts of the plant most abundant in leaves
• Associated with subsidiary cells

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Trichomes

• Root, shoot and leaf
• Rot hairs for absorption
• Protection from sun and insects
• For absorption from air

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Periderm

• Replaces the epidermis in stems and roots that
  have secondary growth
• Have lenticels to provide aeration
• Consists of protective cork that is not living
• Has a cork cambium

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