This presentation describes the nutrient uptake in plants. it explains the passive and active uptake of nutrient uptake. which are further explained as diffusion, facilitated diffusion, carrier proteins, channel proteins, ion exchange & contact exchange.

1. Nutrient
uptake
By: Dr. Sunita Sangwan
Assistant professor, Dept of Botany
Higher education Dept. Haryana

2. Introduction
Mineral uptake is the process in which minerals enter the
cellular material, typically following the same pathway as
water.
The most normal entrance portal for mineral uptake is through
plant roots.
During transport throughout a plant, minerals can exit xylem
and enter cells that require them.
Mineral ions cross plasma membranes by a chemiosmotic
mechanism.
Plants absorb minerals in ionic form: nitrate (NO3− ), phosphate
(HPO4− ) and potassium ions (K+); all have difficulty crossing a
charged plasma membrane.

3. Types of Nutrient Uptake
Passive
uptake
Active
uptake

4. Passive absorption
It is the absorption of minerals without direct expenditure of
metabolic energy.
In passive absorption Mineral salt absorption is not affected by
temperature and metabolic inhibitors.
Rapid uptake of ions occurs when plant tissues are transferred
from a medium of low concentration to high concentration.

5. Passive
absorption
1. Simple
Diffusion
2. Facilitated
Diffusion
a) Carrier Proteins
b) Channel
Proteins
3. Ion
Exchange
a) Contact
exchange theory
b) Carbonic Acid
Exchange Theory
4. Donnan
Equillibrium

6. 1. Simple Diffusion
• It is the movement of solutes along the concentration gradient.
• The chemical potential gradient ( only in uncharged molecule
transfer) of the solute being transported act as force or energy for
transport and movement continue till it reaches equilibrium.
• In case of charged molecules both concentration and electric
charge determine the movement.
• Due to bilipid nature of cell
membrane polar molecules
passes more rapidly than non-
polar and impermeable to most
of ions of large size.

7. Objection to Simple Diffusion
Theory
1. It does not explain the
accumulation of ions
against concentration
gradient.
2. Rate of transport of
minerals in plants is much
greater than the rate of
diffusion.
3. Cell membrane is
impermeable to most of ions
due to chargre& hydration
size.

8. 2. Facilitated Diffusion
• It is the process of rapid & selective diffusion of insoluble
& large solute particles across the membrane. It is
facilitated by various transporter proteins present in the
cell membrane which are of two types
a) Carrier Proteins
b) Channel proteins

9. 3. Ion Exchange
• If an ion is absorbed from the outer medium, either a similar
charged ion will come out of the cell or it will carry an
opposite charged ion with it to maintain the equilibrium.
• Two theories were proposed for ion exchange:
a) Contact Exchange Theory
b) Carbonic Acid Exchange Theory

10. a) Contact Exchange Theory
According to this theory, the ions adsorbed on the clay micelles
get adsorbed to the root in exchange for hydrogen ions,
previously, adsorbed on the root.
Ions adsorbed on solid particles oscillate within a small space.
When two particles are close enough, the oscillation space of an
ion adsorbed to one particle overlaps the oscillation space of an
ion adsorbed to another particle. Thus exchange of ions may take
place.

11. b) Carbonic Acid Exchange Theory
• The soil solution provides medium for exchange of ions
between the root and clay micelles.
• Carbon dioxide released in respiration of root forms carbonic
acid by reacting with water of the soil solution.
• Carbonic acid then dissociates in the soil solution to form H⁺
and HCO₃⁻ ions.
• H⁺ ions are adsorbed to the clay micelles in exchange for
cations, such as K⁺ , which are released into the soil solution.
From here they may diffuse to the root, where they may be
adsorbed in exchange for H⁺ ions.

12. 3. Carbonic exchange theory
Carbonic
Acid Exchange
Theory

13. 3. Donnans’ Equilibrium
Theory
• The accumulation of ions inside the cells without involving
expenditure of the metabolic energy can be explained by Donnan’s
equilibrium theory.
• According to this theory there are certain pre-existing ions inside
the cell which cannot diffuse outside through membrane. Such ions
are called as in-diffusible or fixed ions. However, the membrane is
permeable to both anions and cations of the outer solutions.
• Suppose there are certain fixed anions in the cell which is in
contact with outer solution containing anions and cations. Normally
equal number of anions and cations would have diffused into the
cell through an electrical potential to balance each other, but to
balance the fixed anions more cations will diffuse into the plant
cell.
• This equilibrium is known as Donnan’s equilibrium.

14. • So, according to Donnan Equlibrium , the movement of ions
inside and outside takes place until the ratio of cations inside
to the cations outside equals to the anions outside to the anions
inside.

15. • Suppose a cell has potassium salt of a large indifusable organic anion
(A-). It is placed in a solution of KBr. K+ is present already in the cell,
therefore the external K+ can not directly diffuse inwardly, however
Br- will enter the cell due to its diffusion gradient. Since the internal
(A-) does not diffuse out to balance the ionic equilibrium of the
external solution the externally situated K+ ions also passes inwardly
to maintain electrical or Donnan equilibrium. The result will be
increased K+ and decreased anion Br- concentration in the interior as
compared to external solution.

16. 4. Mass flow theory
According to this theory ions are absorbed by the root along
with mass flow of water under the effect of transpiration.
This theory failed to explain the salt accumulation against
osmotic gradient.
An increase in transpiration pull increases the uptake of ions
by the roots, (the uptake of ions by free diffusion).
Thus, mass flow of ions through the root tissues occurs due to
transpiration pull in the absence of metabolic energy.

18. Active Absorption:
• The active transport of ions from the outer space of the cell to the inner
space is generally occurs against the concentration gradient and hence
requires metabolic energy, this energy is obtained from metabolism of the
cell either directly or in directly.

19. Theories of
Active transport
1. Protein Carrier
theory
2 . Cytochrome
Pump
3. Lecithin Carrier
theory

20. 1. Protein Carrier theory
According to this hypothesis the carrier protein picks up an ion
from one side of the membrane and discharges it on the other side.
The picking up and discharge of the ion requires energy. Energy is
obtained by hydrolysis of ATP.
ATP changes into ADP and energy released is used to change the
conformation of the carrier which may be ATPase itself, so that the
ion is picked up on one side of the membrane and released on the
other.
After discharge of an ion, carrier protein is reprimed to pick up an
other ion. The carrier protein may carry one ion inwards and may
exchange it with another ion at the inner surface of membrane, so
that the other ion is carried by the same carrier outwards.

22. 2. Cytochrome Pump Salt
Respiration theory
• This theory was proposed by Lundegardh and Burstrom
(1933), who believed that there is a definite correlation
between respiration and anion absorption.
• According to them, the absorption of anion was accompanied
by an increase in the rate of respiration.
• The transport of anions takes place through cytochrome
system, so the cytochrome acts as carrier.
• The part of respiration which is enhanced due to anion
absorption is termed as salt respiration where as respiration in
distilled water is called ground respiration.

23. The main assumptions of this
theory are:
1. Mechanism of anion and cation absorption is different.
2. The absorption of anions is independent of cations
3. The oxygen concentration gradient exist from outer surface
to inner surface of the membrane which favors the
oxidation on outer side & reduction at inner side surface.
4. Anions are absorbed through Cytochrome chain by an active
process.
5. The cations are absorbed passively.

24. Mechanism of Cytochrome Pump
Salt Respiration theory
• Dehydrogenase reactions on inner side of membrane give rise to protons
(H+) ions and electrons (e-).
• The election travels over the cytochrome chain towards outside the
membrane so that the "Fe" of the cytochrome become reduced to Fe++ on the
outer surface and “Fe” is oxdised to (Fe+++) on the inner surface.
• On the outer surface, the reduced cytochrome is further oxidised by oxygen
releasing the electron and taking an anion (A- )
• The electron thus released unites with H+ and oxygen to form water.
• The anion (A-) travels over the cytochrome chain towards inside surface.
• At the inner surface the oxdised cytochrome become reduced by taking an
electron produced through the dehydrogenase reactions and the anion (A-)
released.
• As a result, a cation (M+) moves passively from outside to inside to balance
the Anion (A- ).

26. Demerits of Lundegardh's
theory:
• It does not explain selective absorption of ions.
• It principally concerned with active absorption of only
anions, but cations passively absorbed and transported.
• It fails to explain uptake of ions under anaerobic conditions.
• It also fails to explain the absorption of anions in the
membrane like tonoplast, plasma membrane where the
enzymes of electron transport chain are not present.

27. ATPase /protein lecithin
theory
• This theory was suggested by Bennet Clarke (1956).
According to his theory -
• Carrier molecule composed of protein with the phospholipids called
as lecithin. Phosphate group in the phosphatide is regarded as active
centers of carrier.
• The ions are liberated on the inner surface of the membrane by
decomposition of the lecithin by the enzyme lecithinase.
• The regeneration of the carrier lecithin from phosphatide acid and
choline takes place in presence of enzymes viz. choline acetylase and
choline esterase and ATP.
• ATP acts as the energy source for active transport.

29. Factors affecting ion
absorption
Oxygen
Light
H + ion
concentration
Presence of
other ions
Growth
Aging
Temperature

30. 1. Temperature
• Absorption of mineral salt is affected by change in
temperature. In general, an increase in temperature results
increase in the absorption of salts up to a certain optimum
level.
• At very high temperature the absorption is considerably
inhibited. The inhibition might be due to denaturation of
proteins which are directly or indirectly involved in mineral
salt absorption.
• The change in temperature also affects the process of diffusion.
• The rate of diffusion depends upon the kinetic energy of
diffusing molecules or ions which, in turn, dependent upon
temperature.

31. 2- Hydrogen ion concentration
(pH).
• Change in the hydrogen ion concentration (pH) of the soil
solution affects the availability of ions to the plants.
• In general, decrease in the pH of soil solution accelerates the
absorption of anions.
• For example, boron is taken up as the un-dissociated acid,
H3BO3 as the H2BO3? ions. It is absorbed at lower pH.
• In contrast to the anions, increase in pH will favour the
absorption of cations.
• However, pH values across the physiological range may
damage the plant tissue and inhibit the salt absorption.

32. 3. Light
• Light has no direct effect, but indirectly by transpiration and
photosynthesis, influences salt absorption.
4. Oxygen
• The active salt absorption is inhibited by the absence of
oxygen.
5. Growth.
• Active cell division, elongation and developmental processes
promote the absorption of mineral salts.

33. 5. Interaction with other ions
• The absorption of one ion is affected by the presence of other ions in
the medium.
• For example, Viets (1944) demonstrated that the absorption of
potassium is affected by the presence of calcium, magnesium and
other polyvalent cations in the soil solution.
• Epstein (1978) demonstrated the interaction of several ions (K, Cs,
Li, Rb and Na) as competitive for binding sites on carriers. For
example, K, Rb and Cs compete with one another for the same
binding sites. Li and Na, on the other hand, are not competitive
because they have different binding sites.
6. Aging
• As the root matures it increases the surface area which is favourable
for salt absorption, but due to heavy suberization the mineral salt
uptake is greatly reduced.

34. Video links
• https://youtu.be/7l_Lso85Geg Ion Absorption Part 1
• https://youtu.be/Z2DeDLFAU0g Ion Absorption Part 2
• https://youtu.be/JeFNerazAuk Factors affecting Ion
absorption