review: root anatomy three regions – meristematic – elongation – maturation
TRANSCRIPT
Review: Root Anatomy• Three regions – Meristematic– Elongation – Maturation
• Root hairs and branching greatly increase the surface through which water and dissolved minerals can be absorbed.
Functions of Roots• Absorption • Anchorage • Storage • Conduction of water • Hormone synthesis
TODAY
TOMORROW
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?
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
Water Transport into the Roots
Water flows from
SOIL
EpidermisRoot CortexEndodermisXylem
via osmosis
Water Transport into the Roots
• Cells are usually interconnected via plasmodesmata.
• Their plasma forms a continuum (a
“symplast”).
Water Transport into the Roots
• The transport of substances from cell to cell via
plasmodesmata is called symplastic transport.
Water Transport into the Roots
• Apoplastic transport is when water is transported between
cells through the extra-cellular space.
Water Transport into the Roots
• The endodermis functions as a last checkpoint for the passage of dissolved minerals into the vascular tissue
Water Transport into the Roots
• Minerals already in the symplast when they reach the endodermis continue through the endodermis and pass into the xylem
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.
Water Transport into the Roots
• The only way to get through the endodermis is through the symplastic route.
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
Water Transport into the Roots
• Once through the endodermis layer, the water and minerals are now free to enter the xylem tracheids and vessels.
Uptake of water through root epidermis by osmosis
Water that crosses theroot hair plasma membraneenters the symplast system
Water that does not cross theroot hair plasma membraneenters the apoplast system
The Casparian Strip blocks passage of water unless itis moving via the symplast
Water moves into thexylem for transport
up the plant