review: root anatomy three regions – meristematic – elongation – maturation

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