Review: Root Anatomy

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Review Root Anatomy

• Three regions
• Meristematic
• Elongation
• Maturation

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• Root hairs and branching greatly increase the
  surface through which water and dissolved
  minerals can be absorbed.

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Functions of Roots

• Absorption
• Anchorage
• Storage
• Conduction of water
• Hormone synthesis

TODAY
TOMORROW
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Uptake of Ions by the Roots WHAT?

• Root hairs bring nitrates, phosphates, sulphates,
  and a variety of other essential inorganic
  nutrients into the plant

Why are these nutrients needed?
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Uptake of Ions by the Roots HOW?

• Root interception
• Root grows and intercepts ions
• Simple diffusion
• Ions move down their concentration gradient
• No energy expense by plant
• Example K
• Mass flow
• Bulk flow of water into the root carries ions
  to root
• Delivers N, Ca, Mg, S
• Active transport
• Ions move against their concentration gradient
• Requires a specific protein pump in the cell
  membrane
• Energy expense by plant

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Water Transport into the Roots

• Water flows from

Epidermis
Root Cortex
Endodermis
Xylem
SOIL
via osmosis
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Water Transport into the Roots

• Cells are usually interconnected via
  plasmodesmata.
• Their plasma forms a continuum (a symplast).

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Water Transport into the Roots

• The transport of substances from cell to cell via
  plasmodesmata is called symplastic transport.

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Water Transport into the Roots

• Apoplastic transport is when water is transported
  between cells through the extra-cellular space.

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Water Transport into the Roots

• The endodermis functions as a last checkpoint for
  the passage of dissolved minerals into the
  vascular tissue

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Water Transport into the Roots

• Minerals already in the symplast when they reach
  the endodermis continue through the endodermis
  and pass into the xylem

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Water Transport into the Roots

• Minerals that reach the endodermis via the
  apoplast encounter a waxy layer on the endodermis
  that blocks their entry into the xylem called the
  Casparian strip.

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Water Transport into the Roots

• The only way to get through the endodermis is
  through the symplastic route.

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Water Transport into the Roots

• Water and minerals following the apoplastic route
  must first cross the plasma membrane of the
  endodermis cells and enter the symplast system.

This ensures that no minerals can enter the
vascular system with out first being checked by
the plasma membrane
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Water Transport into the Roots

• Once through the endodermis layer, the water and
  minerals are now free to enter the xylem
  tracheids and vessels.

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The Casparian Strip blocks passage of water
unless it is moving via the symplast
Uptake of water through root epidermis by osmosis
Water moves into the xylem for transport up the
plant
Water that does not cross the root hair plasma
membrane enters the apoplast system
Water that crosses the root hair plasma
membrane enters the symplast system