This slide is made for the educational purposes..

1. Transport of solute across
the cell membrane of plants
BY:- SATYA SWARUP PATRA
CLASS :- +3 FINAL YEAR

2. CONTENTS :-
 Introduction to solute transport
 Ion channels
 Carrier
 Pump and Its type
 Secondary active transport
• Symport
• Antiport

3. Introduction to Solute Transport
 The mineral salts are absorbed by plants in their ionic from and
are transported within plants.
 Certain solutes such as sugar are transport across the membrane
in uncharged state.
 These solutes are transported due to their concentration gradient
i.e. the gradient of chemical potential on two sides of the
membrane.
 In case of charged particle the charged solutes carries an electric
charge so their transport depends up on the electric potential
 From the above we come in conclusion that the transport of
solute across the membrane depends upon their Electro-chemical
potential gradient.
 The movement of solute in the cytosol is knows as influx, while
the exit is called efflux.

4.  According to recent researches it is identified that various
trans membrane transporter are responsible for the
movement of solute across the cell membrane.
 These trans membrane transporter protein are highly
specified with complex structure.
 These proteins are grouped in three categories;
I. Ion channel
II. Carrier
III. Pumps

5. Ion channel
 Ion channel are trans membrane protein which functions as
selective pores through which ion can diffuse easily across the
membrane.
 The transport of ion through channel is always passive.
 These channels are not open all the time but are gated . The opening
and closing of the channel is depends upon the external stimuli.
 Every ion carries a charge and are mobile, their diffusion across the
membrane established due to an electric current, which is detected
by a special technique known as ‘patch-clamp electrophysiology’.
 Ion can diffuse through an open channel with rapidity as high as 108
s-1.
 The ion channels which allows inward flow of ion is known as
inward rectifying channel.

6.  The ion channels which allows outward flow of ion is known as
outward rectifying channel.
 Ca2+ channels are inward rectifying while anion channels are
always outward.
 K+ is exceptional. It can diffuse inward or outward across the
membrane through channels
 Many channel proteins are inducible i.e., they are synthesized by
the cell when a particular solute is available for absorption.

7. Carrier
 These trans-membrane transporter proteins does not form pores in
membrane, they selectively binds the solute to be transported to a
specific site on them.
 This causes conformational change in carrier protein which exposes
the solute to other side of the membrane.
 After the solute is released from the binding site, the carrier protein
reverts back to its original conformation to pick up a fresh solute
molecule.
 Carrier mediated transport of solutes enables transport of much
wider range of solutes, but is slower as compared to channel
mediated solute transport.
 The channel mediated solute transport are of two types ;
• Passive transport
• Active transport

8.  Passive transport :- Carrier mediated passive transport of solutes
occurs along the electrochemical potential gradient and does not require
expenditure of energy. It also called as facilitated diffusion.
 Active transport:- Carrier mediated active transport of solutes takes
place against the electrochemical potential gradient and requires
additional input of energy that chiefly comes from hydrolysis of ATP. In
such cases, the carrier proteins are called as ‘pumps’ and the transport of
solutes is called as primary active transport.

9. Pumps
 The membrane transporter proteins involved in primary active transport
of solute are known as pumps.
 Most of the pumps transport ions such as H+ and Ca2+ across the
membrane and are known as ion pumps.
 Ion-pumps may be of two types i.e. Electroneutral pump and Electrogenic
pump.
 Electro neutral pumps are those which are associated with transport of
ions with no net movement of charge across the membrane.
 Electro genic pumps are those which are associated with transport of
ions with net movement of charge across the membrane.
 H+-ATPase, H+-PPase and Ca2+-ATPase are most common electrogenic
pumps in plant cells and their direction is outward.

10. i. Proton-ATPase pumps (H+-ATPase)
• These pumps are also known as P-type ATPases and are found in
plasma membrane, tonoplast and possibly other cell membranes.
These are structurally distinct and operate in reverse of F-type
ATPases i.e., they hydrolyse ATP instead of synthesizing it.
• The H+– ATPase protein (also known as P-type ATPase) is a
single chain polypeptide with 10 hydrophobic trans membrane
segments or domains.

11. • These segments are joined by hydrophilic loops which projected into the
cytosol and cell wall (apoplast). The ATP binding site is believed to be an
aspartic acid residue (D) situated on loop connecting 4th and 5th
segments towards cytosilic side.
• Hydrolysis of ATP causes conformational change in the protein and one
H+ ion is transported from cytosol to outside across the plasma
membrane.
ii. Proton-Pyrophosphatases pumps(H+-PPase)
• There are mainly found in tonoplasts but may also occur in membrane of
Golgi-bodies. They pumps protons into the lumen of vacuole and Golgi-
cisternae.
• These pumps appear to work in parallel with vacuolar ATPases to create
protons gradient across the tonoplast. This enzyme protein consists of a
single polypeptide chain with molecular mass of 80 kD and utilizes
energy from hydrolysis of inorganic pyrophosphate (PPi).
• Free energy released by hydrolysis of PPi is less than that obtained from
hydrolysis of ATP. Vacuolar H+–PPase transport only one H+ per PPi
molecule hydrolysed.

12. iii. Calcium Pumping ATPases (Ca2+-ATPases)
• These are found in plasma membrane, tonoplast and possibly
other cell membranes such as those of chloroplasts and ER.
• These pumps couple hydrolysis of ATP with translocation of
Ca2+ across the membrane.
iv. ATP-Binding Casette Transporters
• Certain large metabolites such as anthocyanin’s and other
secondary plant products are removed from the cytosol and
transported across the tonoplast to the vacuole through ABC-
transporters located on tonoplast that consume ATP directly.

13. Secondary Active Transport
 A large number of nutrients are transported across the cell membranes
against the electro chemical potential gradients by secondary active
transport mechanism.
 They utilizes the energy stored in proton-electrochemical potential
gradient across the membrane.
 The H+-ATPase pumps serves as proton trans locating carrier proteins
and the hydrolysis of ATP is conserved in the form of proton gradient
across the membrane (more protons are accumulating on the out side),
which creates a proton motive force.
 The proton motive force can drive a solute molecule or ion against their
chemical or electrochemical potential gradient through the same carrier
protein
 The proton motive force is responsible for returning back H+ ion to
cytosol.
 This is called secondary active transport and it of two types ;
a. Symport
b. Antiport

14. a) Symport :-
When influx of protons is coupled with movement of other solute in the
same direction, the cotransport mechanism is celled as symport and the
carrier protein is called as symporter.
b) Antiport :-
When influx of protons is coupled with efflux of other solute, the
cotransport mechanism is called as antiport and the carrier protein
involved is called as antiporter.