1. Plant Cells.. Membrane.. Nutrients traffic.. Regulation..
Solute transport
Plant Cells.. Membrane.. Nutrients traffic.. Regulation..
Dr. Abdul Latif Khan

3. Ion transport in roots
As all plant cells are surrounded by a cell wall, Ions can be carried through the cell wall space with out entering an actual cell
The apoplast
Just as the cell walls form a continuous space, so do the cytoplasms of neighboring cells
The symplast

4. Ion transport in roots All plant cells are connected by plasmodesmata.
In tissues where large amounts of intercellular transport occurs neighboring cells have large numbers of these.
As in cells of the root tip
Ion absorption in the root is more pronounced in the root hair zone than other parts of the root.
An Ion can either enter the root apoplast or symplast but is finally forced into the symplast by the casparian strip.

5. Ion transport in roots
Once the Ion is in the symplast of the root it must exit the symplast and enter the xylem
Called Xylem Loading.
Ions are taken up into the root by an active transport process
Ions are transported into the xylem by passive diffusion

6. Membrane transport
Facilitate the passage of ions and other polar molecules
Arabidopsis thaliana contains 849 membrane proteins (4.8% of genome)
Three types of membrane transporters enhance the movement of solutes across plant cell membranes
Channels – passive transport
Carriers – passive/active transport
Pumps- active transport
Artificial vs Natural membranes. Different proteins for different molecules

7. Passive transport
Diffusion: Diffusion is the net movement of material from an area of high concentration to an area with lower concentration
Facilitated diffusion: Facilitated diffusion, also called carrier-mediated diffusion, is the movement of molecules across the cell membrane via special transport proteins that are embedded within the cellular membrane.
Osmosis: Osmosis is the diffusion of water molecules across a selectively permeable membrane. 

8. Diffusion
Facilitated Diffusion

9. Simple diffusion
Movement down the gradient in electrochemical potential
Movement between phospholipid bilayer components
Bidirectional if gradient changes
Slow process

10. Channels Transmembrane proteins that work as selective pores
Transport through these passive
The size of the pore determines its transport specifity
Movement down the gradient in electrochemical potential
Unidirectional
Very fast transport
Limited to ions and water

11. Channels
Sometimes channel transport involves transient binding of the solute to the channel protein
Channel proteins have structures called gates.
Open and close pore in response to signals
Light
Hormone binding
Only potassium can diffuse either inward or outward
All others must be expelled by active transport.
K+ form the environment, opening of stomata
Potassium channels: Inward or outward, open depending upon
Release of K+ into xylem
Closing of stomata

12. Remember the aquaporin channel protein?
There is some diffusion of water directly across the bi-lipid membrane.
Aquaporins: Integral membrane proteins that form water selective channels – allows water to diffuse faster
Facilitates water movement in plants
Alters the rate of water flow across the plant cell membrane – NOT direction

13. Carriers Do not have pores that extend completely across membrane
Substance being transported is initially bound to a specific site on the carrier protein
Carriers are specialized to carry a specific organic compound
Binding of a molecule causes the carrier protein to change shape
This exposes the molecule to the solution on the other side of the membrane
Transport complete after dissociation of molecule and carrier protein

14. (A) In the initial conformation, the binding sites on the
protein are exposed to the outside environment and can bind a proton.
(B) This binding results in a conformational change that permits a molecule of S to be
bound.
\figures\ch06\pp06091.jpg

15. binding sites and their substrates to the inside of the cell.
(C) The binding of S causes another conformational change that exposes the
binding sites and their substrates to the inside of the cell.
(D) Release of a proton
and a molecule of S to the cell’s interior restores the original conformation of the
carrier and allows a new pumping cycle to begin.
\figures\ch06\pp06092.jpg

16. Active transport
Movement of molecules (ions, glucose and amino acids) across a cell membrane in the direction against their concentration gradient, i.e. moving from an area of lower concentration to an area of higher concentration
It uses chemical energy : ATP - ADP
Two types: Primary and Secondary
Primary active transport: directly uses metabolic energy to transport molecules across a membrane
transmembrane ATPases: sodium potassium pump, calcium pump, proton pump
vacuolar ATPase
ABC (ATP binding cassette) transporter

17. Active transport
Secondary active transport: coupled transport or co-transport, energy is used to transport molecules across a membrane
Two types: Antiport and Symport
Antiport: two species of ion or other solutes are pumped in opposite directions across a membrane
e.g.  sodium-calcium antiporter: three sodium ions into the cell to transport one calcium out
Symport: downhill movement of one solute from high to low concentration

18. (A) In a symport, the energy dissipated by a proton moving back into
\figures\ch06\pp06100.jpg
(A) In a symport, the energy dissipated by a proton moving back into
the cell is coupled to the uptake of one molecule of a substrate (e.g., a sugar) into
the cell.
(B) In an antiport, the energy dissipated by a proton moving back into the cell is coupled to the active transport of a substrate (for example, a sodium ion) out
of the cell.

19. \figures\ch06\pp06110.jpg

20. \figures\ch06\pp06111.jpg

21. \figures\ch06\pp06112.jpg