Plant Growth

• Apical meristems - apex, tip, forms three primary meristems:

  • Protoderm - dermal tissue - before dermal tissue (epidermis, outer layer of the plant)
  • Ground meristem - gives rise to ground tissue
  • Procambium - gives rise to the cambium, which produces vascular tissue
• Primary Growth - lengthens plant at shoots and roots
• Meristem - comprised of totipotent cells, retain the ability to proliferate indefinitely - keep dividing using mitosis, maintain the ability to differentiate into other types of cells (leaf, stem, branch, root).
• Primary growth makes up the bulk of the plant primary body.
• Axillary buds - by a large remain dormant, unless something should happen to the apical shoot meristem.
• Apical meristems prevent lateral meristems from growing + consuming energy from photosynthesis, encourages plant to grow taller.
• Primary Growth: Roots

  • 3 zones, start from bottom because that’s where growth starts
• Root Primary Growth

  • Zone 1: Zone of Cellular Division
  • Mitosis, one cell dividing into two identical cells which divide into 2 more
  • Apical meristems - as they divide, going to produce three primary meristems
• Root Primary Growth

  • Zone 2: Zone of Cellular Elongation
  • As they divide, quite small, nucleus takes up most of the newly divided cells
  • Cells grow, nucleus takes up less of the cell
  • No new cells, just growing in size
• Root Primary Growth

  • Zone 3: Zone of Cellular Maturation
  • See differentiation of cells
  • Form types of tissues
  • Where root hairs start to form
• • Root Cap
  • Hard bunch of tissues differentiated into root cap tissue
  • Protects apical meristem of the root
  • Secretes lubricant that acts as an oil to permit the roots to more easily pass through the soil
  • Have cells that sense gravity so they’ll move in the direction of gravity
  • Meristem that it protects also differentiates into root cap tissue
• Secondary Growth

  • Widens roots and shoots, makes plants thicker, larger diameter
  • Increases conductive tissue primarily (xylem + phloem)
  • Also increases ground tissue that provides support
  • Produces wood as structural support within plant species that have the cambium (eudicots that have the circular cambium that divides the xylem and phloem)
• Secondary Growth: Bark

  • Protects tree from damage and pathogens
  • Increases girth (provides support)
  • Lenticles - openings for gas exchange - provide a little window through the bark
• Secondary Growth: Cambium

  • Cambium produces cylinder that runs the length of roots, shoots, branches
  • Cells in cambium continuously divide to extend width of plant
  • Xylem located toward the inside of the stem - primary xylem and secondary xylem, then vascular cambium
  • On other side of cambium, secondary phloem, primary phloem, then bark (phloem, cork cambium (outer perimeter of stem), cork cells)
  • Primary xylem - developed from apical meristem
  • Secondary xylem - comes from lateral meristem during secondary growth
• Heartwood - inner dark-coloured xylem

  • Structural support, no water transport
  • Produce resins & gums that seal wounds & protect from pathogens (fungi, insects)
• • Sapwood - outer, lighter coloured xylem
  • Conducts water
• Tree Trunk Structure

  • More consistent rings throughout centre + from eudicot deciduous trees in vancouver (change in growth rate throughout year)
  • Dark ring and/or smaller rings, less favourable conditions
  • One year of growth is one light ring and one dark ring