Roots

root types - 2 types

• taproot - enlarged radical root in most dicots
  • smaller lateral roots branch off
  • stores food, reaches for water deep underground
• fibrous roots - mass of small roots, in most monocots
  • extensive, clings to soil
  • prevents erosion

root structure - split into 4 regions

• root cap - made of inner columella cells, outer root cap cells
  • columella cells - function in perception of gravity
  • protects tissues behind it as it grows
  • golgi bodies secrete slimy substance to outside >> eases root through soil
  • constantly replaced by new cells
• zone of cell division - where cells divide ever 12-36 hours
  • daughter cells of apical meristem
  • quiescent center - group of cells at the center of apical meristem, divides slowly
  • inner cell layer >> endodermis, intercellular flow of water
• zone of elongation - cells from primary meristems elongate >> roots lengthen
  • small vacuoles merge/grow >> occupies 90% of cells’ volume
  • no more size increase beyond zone of elongation
• zone of maturation - where cells become differentiated
  • root hairs form on each epidermal cell, only stays functional for a few days
  • cortex - made of parenchyma cells, functions as food storage
  • Casparian strips - bands of suberin (fatty substance) that blocks intercellular transport
  • pericycle - cylinder of parenchyma cells interior to the endodermis, becomes lateral roots or vascular cambium
  • primary xylem differentiated as solid core in center of roots
  • primary phloem differentiated as groups of cells
  • secondary tissues added >> primary tissues are replaced

modified roots - usually either taproot (single large root) or fibrous (many smaller roots) 

• adventitious root - produced from anyplace other than the plant root
• prop roots - grows from the lower stem to brace plants against the wind
• aerial roots - extends into the air to prevent water loss
• pneumatophores - spongy outgrowths formed by plants in swamps
• contractile roots - roots spiral to pull plant deeper into the soil
• parasitic roots - found in plants w/o chloroplasts
• food storage roots - contains extra parenchyma cells
• water storage roots - found in members of pumpkin family
• buttress roots - in figs, tropical trees; provides stability at base of trunk