LAB 4, first part

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LAB 4, first part

• ROOTS

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ROOT UNIQUE CHARCTERISTICS

• Stele vascular cylinder central vein
• Root hairs (only on very young roots)
• Endodermis with waxy Casparian strips for
  controlling sap quality
• Pericycle for making branch roots and wood

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In all herbaceous roots the endodermis d is the
innermost layer of the cortex e.
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• The spaces between the compact parenchyma cells
  in the endodermis have Casparian strips of waxy,
  impermeable secretions. The Casparian strips
  prevent any movement of molecules between the
  cortex and the vascular tissue UNLESS the
  molecules go through (not around) the cell
  membranes of the endodermal cells.

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U Wisc
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symplast, the cytoplasm which may connect to
other cells by plasmodesmata gap junctions.

• Once a material gets through a membrane, it is
  within the plants symplast
• You recall, of course, that cell membranes
  control the entry and exit of materials in cells

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APOPLAST the part of tissue which is NOT
protected by membranes

• When a material is in a cell wall or within a
  dead cell (like xylem and schlerenchyma), it can
  diffuse freely without crossing membranes through
  the apoplast, non-cytoplasmic areas throughout
  the plant.
• Like coffee soaking up through a paper napkin

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• Notice that the
  endodermis
  separates the root epidermal
  and cortex apoplast from the
  apoplast of the rest of the plant. Thus, the
  endodermis is modified to control the entry of
  materials absorbed by the root hairs before the
  vascular tissue transports them to the rest of
  the plant sometimes it can keep harmful
  substances in the soil out of the rest of the
  plant. The endodermis also prevents valuable
  materials from phloem sap from
• oozing out into the dirt.

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• The root epidermal and cortex apoplast are
  separated from the apoplast of the rest of the
  plant. The Casparian strips of the endoderm
  separate the two apoplasts.
• The only connection between the vascular tissue
  and the outer root is the SYMPLAST.
• Nothing gets into the symplast unless it goes
  through a cell membrane.

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http//www.sciencemag.org/cgi/content/full/280/53
71/1906

• Ion flow from soil to leaf. After initial
  diffusion into the root cell (apoplastic) wall
  space (A), the ion is transported across the
  outer cell membrane or plasma membrane into the
  cytoplasm of an epidermal or cortical cell (B).
  (Several layers of cortical cells are represented
  by only one.) Once in the cytoplasm the ion moves
  through intercellular connections or
  plasmodesmata (C) into a cell of the stele and
  then leaves the "symplast" across the plasma
  membrane of a stelar cell (D) and enters a
  vessel, which is, when mature, extracellular or
  apoplastic space. (Diffusion through cell wall
  space back into the medium is prevented by the
  impermeable "Casparian strip.") The ion then
  moves into the shoot (E) and eventually is
  transported across the plasma membrane of, this
  time, a leaf cell (F) into its cytoplasm.

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The pericycle b is a meristem which produces
branch roots
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U Wisc
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U Wisc
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Root or stem? Monocot or dicot?
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dicot roots have a few xylem spokes

• Like a star with3 or 4 or 5 or 6points
• and xylem fills the entire star area.
• Phloem is inpatches between

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Monocots have multiple xylem spokes

• Monocots have
• special stars
• like Moravians.
• The middle of the
• xylem star
• does not mature.

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Monocot phloem, like dicot phloem, is in patches
between xylem star points.
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Monocot or dicot?
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Next class is Wednesday

• wood background in morning
• lab roots wood
• party next Friday