roots

• Main functions of roots

  • Anchorage
  • Absorption
  • Conduction
• Storage is not a main function of roots
• Characteristics of roots

  • Non-green (due to absence of chlorophyll)
  • No nodes and internodes
  • No leaf and buds
  • Grows towards gravity (positively geotropic)
  • Grows towards water (positively hydrotopic)
  • Negatively phototropic (grow away from light)
• Taproot system


  Consists of 1 prominent main root with smaller lateral roots branching from it
• Taproot system


  • Strong anchorage (goes deep)
  • Main root of dicot plants
• Fibrous root system


  Several adventitious roots of approximately equal size that arise from the base of the stem
• Fibrous root system


  • Doesn't branch profusely, shallow and spread horizontally (no strong anchorage)
  • Main root of monocots
• Root cap

  Covering of cells over root tip that protects delicate meristematic tissue directly behind it
• Root cap

  • Contains statocytes involved in gravity perception
  • If cap is removed, root will grow randomly
  • Secretes mucilage to ease root movement
  • Involved with soil microbiota communication
• Root hair

  Extension of epidermal cell of root that increases absorptive capacity of root
• Root hair

  • Short-lived, unicellular extensions of epidermal cells near growing root tip
  • Increase surface area of root in contact with moist soil
• Pericycle

  Layer of cells just inside endodermis of root
• Pericycle


  • Gives rise to lateral roots
• Primary Eudicot Roots

  • Outer protective covering - epidermis
  • Ground tissues - cortex, pith (in certain roots)
  • Endodermis - innermost layer of cortex that prevents water and dissolved materials from entering xylem by passing between cells
• Cortex


  Consists of parenchyma cells
• Cortex


  • Usually stores starch
• Endodermis


  Innermost layer of cortex that prevents water and dissolved materials from entering xylem by passing between cells
• Casparian strip


  Band of waterproof material around radial and transverse cells of endodermis
• Casparian strip


  • Ensures that water and minerals enter xylem by only passing through cells
• Vascular tissues


  • Xylem
  • Phloem
• Herbaceous eudicot root


  • Has a solid mass of xylem and phloem
• Monocot roots


  • Have pith
  • Lack vascular cambium
• Pathway of water from soil through various root tissues

  1. Root hair

  2. Epidermis

  3. Cortex (symplast or apoplast)

  4. Endodermis

  5. Pericycle

  6. Xylem
• Water moves from root xylem to stem xylem then rest of plant
• Symplast


  Transport continuum consisting of cytoplasm of plant cells, connects cells by plasmodesmata
• Symplast

  • Consists of cytosol and plasmodesmata
• Apoplast


  Transport continuum consisting of interconnected porous plant cell walls where water moves freely
• Apoplast

  • Consists of everything external to plasma membrane
  • Cell walls
  • Extracellular spaces
  • Interior of vessel elements and tracheids
• Prop root


  Adventitious root that arises from stem and provides support for plant
• Contractile root


  Contracts and pulls plants to desirable depth in soil
• Contractile root

  • Found on bulbs and corms
• Pneumatophores

  Aerial root produced by swampy habitat trees
• Pneumatophores


  • May facilitate gas exchange in atmosphere and submerged roots
• Buttress roots


  Swollen bases that hold trees upright
• Buttress roots


  • Aid in distribution of shallow roots
  • Found in rainforest trees
• Photosynthetic roots


  Roots that do photosynthesis
• Photosynthetic roots

  • Orchids
• Suckers


  Aboveground stems that develop from adventitious buds on root
• Suckers

  • Asexual reproduction method of some roots
• Symbiotic roots

  Have symbiotic relationships with other plants