This is an up to date study material for UG & PG students. It describes about Crop-water relationship; absorption; transpiration; stomatal physiology; theories of water uptake; diffusion; osmosis; nutrient uptake mechanism

1. Theory
Introduction to crop physiology and its importance in Agriculture; Plant cell: an Overview; Diffusion and osmosis; Absorption of
water, transpiration and Stomatal Physiology; Mineral nutrition of Plants: Functions and deficiency symptoms of nutrients, nutrient uptake
mechanisms; Photosynthesis: Light and Dark reactions, C3, C4 and CAM plants; Respiration: Glycolysis, TCA cycle and electron transport
chain; Fat Metabolism: Fatty acid synthesis and Breakdown; Plant growth regulators: Physiological roles and agricultural uses, Physiological
aspects of growth and development of major crops: Growth analysis, Role of Physiological growth parameters in crop productivity.
Practical
Study of plant cells, structure and distribution of stomata, imbibitions, osmosis, plasmolysis, measurement of root pressure, rate of
transpiration, Separation of photosynthetic pigments through paper chromatography, Rate of transpiration, photosynthesis, respiration, tissue
test for mineral nutrients, estimation of relative water content, Measurement of photosynthetic CO2 assimilation by Infra Red Gas Analyser
(IRGA).
References
1. Taiz, L. and zeiger,E. 2010. Plant Physiology 5th edition, Sinauer Associates, Sunderland, MA, USA. 2. Gardner, F.P., Pearce, R.B., and
Mitchell, R.L. 1985. Physiology of Crop Plants, Scientific Publishers, Jodhpur. 3. Noggle, G.R. and Fritz, G.J., 1983. Introductory Plant
Physiology. 2nd Edition. Prentice Hall Publishers, New Jersey, USA
Fundamentals of Crop Physiology [ASPH1201]
Pradipta Banerjee, Ph.D.
Dept. of Biochemistry & Crop Physiology
CUTM, Paralakhemundi, Odisha

2. i. Constituent of protoplasm
ii. Act as universal solvent
iii. Act as reagent
iv. Maintenance of turgidity.
Crop-Water Relation
 Water potential (ψ) of protoplasm is equal and opposite to diffusion
pressure deficit (DPD) or suction pressure (SP).
 Unit of ψ is MPa (mega Pascal)
 It is a relative value, depends on concentration, pressure, gravity at a
given temperature
 WP of pure water is 0 (highest value)
 Presence of solute particle reduces free energy of water, thus ψ
decreases (negative value), i.e., Ψ = - DPD
 Ψ = Ψs + Ψm + Ψp + Ψg
Importance of Water

3. …Crop-Water Relation

4.  Turgid cell
Ψs = -10 bars
Ψp = 10
Ψ = Ψs + Ψp = 0
 Flaccid cell
Ψ = Ψs + Ψp
Ψ = -10 + 0 = -10 bars
 Plasmolysed cell
Ψs = - 10 bars
Ψp = - 2 bars
Ψ = -12 bars
NB:
Water moves from higher water potential to lower water potential, eg., -8 bars to -10 bars
…Crop-Water Relation

5. Importance of water potential
Lower water potential in
cell/tissue
Greater ability to absorb
water
Higher water potential in
cell/tissue
Greater ability of tissue to
supply water to more
desiccated cells/tissue
Water Potential is used to measure
water deficit & water stress in
plant cells/tissues.

7.  Water molecules in a solution are not static; they are in continuous
motion, colliding with one another and exchanging kinetic energy.
The molecules intermingle as a result of their random thermal
agitation. This random motion is called diffusion. As long as other
forces are not acting on the molecules, diffusion causes the net
movement of molecules from regions of high concentration to
regions of low concentration—that is, down a concentration
gradient.
 Water can cross plant membranes by diffusion of individual water
molecules through the membrane bilayer.
 Diffusion is fastest in gases, slower in liquids, and slowest in solids.
 Diffusion is rapid over short distances but extremely slow over
long distances.
 From Fick’s first law, one can derive an expression for the time it
takes for a substance to diffuse a particular distance.
Diffusion

8. Solid into solid: In solids, diffusion occurs due to thermally-activated random motion of atoms. Example: solid
diffusion couple, such as copper into zinc. Such experiment takes place at very high temperatures, to complete
the process in a reasonable amount of time.
Solid into liquid: diffusion of KMnO4 in water
Solid into gas: smoke
Liquid into solid: diffusion of KOH solution in solidified agar
Liquid into gas: cloud
Gas into liquid: foam
Examples of Diffusion
Diffusion pressure is hypothetical term describing ability of a gas, liquid or solid to diffuse from an area of
higher concentration to an area of lower concentration.
Example: A gas filled balloon has a greater diffusion pressure than its surrounding air.

9. Simple Diffusion vs Facilitated Diffusion

10. Osmosis
 Membranes of plant cells are selectively permeable; i.e., they allow the movement of water and other small
uncharged substances across them more readily than the movement of larger solutes and charged substances
(Stein,1986).
 Like molecular diffusion and pressure-driven bulk flow, osmosis occurs spontaneously in response to a driving
force.
 In simple diffusion, substances move down a concentration gradient; in pressure-driven bulk flow, substances
move down a pressure gradient; in osmosis, both types of gradients influence transport (Finkelstein, 1987).
The direction and rate of water flow across a membrane are determined not solely by the concentration gradient of water
or by the pressure gradient, but by the sum of these two driving forces.

11.  A membrane that permits the passage of some substances while inhibiting the passage of others is said to be
selectively permeable. The movement of water molecules through such a membrane is known as osmosis.
Osmosis involves a net flow of water from a solution that has higher water potential to a solution that has
lower water potential.
 In the absence of other factors that influence water potential (such as pressure), the movement of water by
osmosis is from a region of lower solute concentration (and therefore higher water concentration) into a region
of higher solute concentration (and lower water concentration).
 The presence of solute decreases the water potential, creating a water potential gradient down which water
moves. The water potential is not affected by what is dissolved in the water, only by how much is dissolved, i.e.,
the concentration of particles of solute (molecules or ions) in the water.
 The pressure that would have to be applied to the solution to stop water movement is called the osmotic
pressure.
 The tendency of water to move across a membrane because of the effect of solutes on water potential is called
the osmotic potential (also called solute potential), which is negative.
Osmosis Is the Movement of Water across a Selectively Permeable Membrane

12. Osmotic pressure of a solution is governed by:
a) Concentration of solution
b) Ionization of solute molecules
c) Temperature
d) Hydration of solute molecules

13. Osmosis in plant cells.
The direction of the arrows indicates the direction of the
water movement; the size of the arrow indicates the relative
amount of water moving into or out of the cell. (a) In an
isotonic solution, the cell neither gains nor loses water;
water flows equally both into and out of the cell. (b) In a
hypotonic solution, the cell gains water because more water
enters the cell than leaves. (c) In a hypertonic solution, the
cell loses water because more water leaves the cell than
enters.

14.  Turgor pressure exists only when cells are relatively well hydrated.
 It is the pressure exerted by fluid in a cell that presses cell membrane against cell wall.
 Turgor is what makes living plant tissue rigid. Loss of turgor, resulting from the loss of water from plant
cells, causes flowers and leaves to wilt.
 Turgor plays a key role in the opening and closing of stomata in leaves.
 Turgor pressure in most cells approaches zero as the relative cell volume decreases by 10 to 15%.
 However, for cells with very rigid cell walls (e.g., mesophyll cells in the leaves of many palm trees), the
volume change associated with turgor loss can be much smaller, whereas in cells with extremely elastic
walls, such as the water-storing cells in the stems of many cacti, this volume change may be substantially
larger.
Turgor Pressure

15.  Water molecules exhibit a tremendous cohesiveness because of their—that is, the difference in charge
between one end of a water molecule and the other. polarity
 Because of this difference in charge, water molecules can cling (adhere) to either positively charged or
negatively charged surfaces.
 Many large biological molecules, such as cellulose, are polar and so attract water molecules.
 The adherence of water molecules (imbibate) is also responsible for the biologically important phenomenon
called imbibition.
 Imbibition (from the Latin imbibere, “to drink in”) is the movement of water molecules into substances such
as wood or gelatin, which swell as a result of the accumulation of water molecules. The pressures developed
by imbibition can be astonishingly large.
 Imbibition is essential to the germination of the seed (imbibant).
 Proteins have a very high imbibing capacity than starch (less) and cellulose (least). That is why
proteinaceous pea seeds swell more on imbibition than starchy wheat seeds.
Imbibition

16. 1. Nature of imbibant: Different types of organic substances have different imbibing capacities. Proteins have a
very high imbibing capacity, starch has less capacity and cellulose is the weakest imbiber. That is why
proteinaceous pea seeds swell more on imbibition than starchy wheat seeds
2. Temperature: The rate of imbibition increases with the increase in temperature.
3. Concentration of the solute: Increase in concentration of the solute decreases imbibition due to a decrease in
the diffusion pressure gradient between the imbibant and the liquid being imbibed.
4. Surface area of imbibant: The imbibition will be greater when the surface area of imbibant is larger.
Factors Affecting Rate of Imbibition

17. Diffusion Pressure Deficit (DPD)
 When a solvent is separated from solution, the solvent molecule being higher in concentration will diffuse towards
solution under pressure. This pressure is known as DPD.
 It can be said that this movement is due to certain deficit in diffusion pressure of solution as compared to solvent or
it is due to DPD of solution.
 The DPD of solution will always try to wipe off this deficit by pulling or sucking more solvent
 DPD is thus the pulling or sucking power, known as suction pressure.
 DPD of cell initially equal to osmotic pressure (OP)
 During osmosis, the increasing turgor pressure (TP) forces cytoplasm out against cell wall.
 Cell wall also exert an equal and opposite pressure call wall pressure (WP), due to which a decrease in DPD occurs.
 DPD = OP –TP (WP)
 DPD = IP – TP, where IP = imbibition pressure
Definition: The reduction in diffusion pressure of a substance over its pure state due to either bonding of some
of its molecules or pressure of particle of another substance is called as DPD

18.  The extensive hydrogen bonding in water gives rise to the property known as cohesion, the mutual attraction
between molecules.
 A related property, called adhesion, is the attraction of water to a solid phase such as a cell wall/glass surface.
 Cohesion, adhesion, and surface tension give rise to a phenomenon known as capillarity, the movement of
water along a capillary tube.
 In a vertically oriented glass capillary tube, the upward movement of water is due to:
(1) the attraction of water to the polar surface of the glass tube (adhesion) and
(2) The surface tension of water, which tends to minimize the area of the air–water interface.
 Together, adhesion and surface tension pull on the water molecules, causing them to move up the tube until the
upward force is balanced by the weight of the water column. The smaller the tube, the higher the capillary rise.
Adhesion, Cohesion, Capillarity

19.  Active Absorption
A) Osmotic Theory
(Atkins, 1916; Priestly,
1922)
B) Non-osmotic Theory
(Thimann, 1951;
Kramer, 1959)
 Passive Absorption
Mechanism of water absorption in plants
Active Absorption Passive Absorption
1. Occurs due to root hairs 1. Occurs due to shoot, leaves
2. Osmotic & Non-osmotic process 2. Active transpiration in aerial parts
3. Root hairs have high diffusion
pressure deficit (DPD) as compared to
soil solutions and hence water is taken
in.
3. Occurs due to tension created in
xylem sap by transpiration pull.
4. Protoplast (symplast) is involved 4. Movement of water is through free
spaces or apoplast of root and it may
include cell wall and intercellular
spaces.
5. Rate of absorption depends upon
DPD
5. Rate depends upon transpiration
6. In non-osmotic type of absorption,
respiratory energy is utilized.
6. Energy is never utilized.

20. Factors affecting water absorption rate in plants
1. External Factors
a. Available soil water: Absorption of water depends on the amount of capillary water present in the soil. Absorption
increases by increasing amount of capillary water. If, water is present in higher amount in the soil then such type of
soil is called “Water logged soil”. This soil is Physiologically dry.
b. Concentration of soil solution: Water absorption is only take place in appropriate soil solution. Soil should be
hypotonic & Plant must be hypertonic to carry out the process of endosmosis. If the concentration of soil minerals is
high, it decreases the rate of absorption & plasmolysis & wilting takes place.
c. Soil temperature: Generally, normal absorption of water take place at temperature of soil between 20 – 35°C.
Increasing or decreasing soil temperature of soil between 20 – 35°C inhibit absorption. Cold soil is as physiologically
dry.
d. Soil aeration: Absorption of water proceeds more rapidly in well aerated soil. Deficiency of oxygen in soil causes
improper respiration in roots & decreases rate of absorption. Poorly aerated soil is physiologically dry.

21. 2. Internal Factors
 Transpiration: rate of absorption is nearly directly proportional to transpiration
 Absorbing root system
 Metabolism: KCN reduce rate of absorption.
…Factors affecting water absorption rate in plants

22.  This theory depends on there being a continuous column of water from the tips of the roots through the stem and
into the mesophyll cells of the leaf. The theory is generally credited to H. H. Dixon, 1914.
 According to cohesion-tension theory, driving force for water movement in xylem is provided by evaporation of
water from the leaf and the tension or negative pressure that results.
 As water evaporates, the air–liquid interface retreats into the small spaces between cellulose microfibrils. This
creates very small curved surfaces or microscopic menisci.
 As the radii of these menisci progressively decrease, surface tension at the air–water interface generates an
increasingly negative pressure, which in turn tends to draw more liquid water toward the surface.
 Because the water column is continuous, this negative pressure, or tension, is transmitted through the column all
the way to the soil.
 As a result, water is literally pulled up through the plant from the roots to the surface of the mesophyll cells in the
leaf.
THE COHESION THEORY BEST EXPLAINS ASCENT OF XYLEM SAP

23. THE COHESION THEORY BEST EXPLAINS ASCENT OF XYLEM SAP
Tension (negative pressure) in the water column
 Evaporation into the leaf spaces causes the water–air interface
(dashed lines) to retreat into the spaces between and at the
junctions of leaf mesophyll cells.
 As the water retreats, the resulting surface tension pulls water
from the adjacent cells.
 Because the water column is continuous, this tension is
transmitted through the column, ultimately to the roots and soil
water.

24.  Transpiration is defined as the loss of water from the plant in the form of water vapor. Although a small amount
of water vapor may be lost through small openings (called lenticels) in the bark of young twigs and branches,
the largest proportion by far (more than 90%) escapes from leaves. Indeed, the process of transpiration is
strongly tied to leaf anatomy.
 The outer surfaces of a typical vascular plant leaf are covered with a multilayered waxy deposit called the
cuticle. The principal component of the cuticle is cutin, a heterogeneous polymer of long-chain—typically 16 or
18 carbons—hydroxylated fatty acids.
 The integrity of the epidermis and the overlying cuticle is occasionally interrupted by small pores called stomata
(sing. stoma).
 Transpiration may be considered a two-stage process:
(1) the evaporation of water from the moist cell walls into the substomatal air space
(2) the diffusion of water vapor from the substomatal space into the atmosphere.
TRANSPIRATION

26. Types of Transpiration

29. STOMATA

30. STOMATAL PHYSIOLOGY

31. Stomatal Opening in Succulent Plant (Scotoactive type)
 In succulent plants the stomata behave opposite what is
normal; that is, they are closed during the day and open at
night.
 As a result, the loss of water (transpiration) during the hot,
dry daytime hours is minimized.
 Carbon dioxide (CO2) uptake occurs in the dark. Thus, they
exhibit a modified form of CO2 fixation and photosynthesis
called Crassulacean Acid Metabolism.
 In crassulacean acid metabolism, CO2 is fixed into an
organic acid, malic acid, and is stored in cellular vacuoles
until the energy from sunlight is available for
photosynthesis.
Plants with fleshy, thick tissues adapted to water storage are called succulents. Some succulents (e.g., cacti)
store water only in stem and have no leaves or very small leaves, whereas others (e.g., agaves) store water mainly
in the leaves. Most succulents have deep or broad root systems and are native to either deserts or regions that
have a semiarid season.

32. Role of Stomata in Transpiration

33. Significance of Transpiration

34. Stomatal Physiology
 The integrity of the epidermis and the overlying cuticle is occasionally interrupted by small pores called stomata
(sing. stoma).
 Each pore is surrounded by a pair of specialized cells, called guard cells. These guard cells function as
hydraulically operated valves that control the size of the pore.
 The interior of the leaf is comprised of photosynthetic mesophyll cells. The somewhat loose arrangement of
mesophyll cells in most leaves creates an interconnected system of intercellular air spaces.
 This system of air spaces may be quite extensive, accounting for up to 70 percent of the total leaf volume in some
cases.
 Stomata are located such that, when open, they provide a route for the exchange of gases (principally carbon
dioxide, oxygen, and water vapor) between the internal air space and the bulk atmosphere surrounding the leaf.
Because of this relationship, this space is referred to as substomatal space.
 The cuticle is generally impermeable to water and open stomata provide the primary route for escape of water
vapor from the plant.

35. Reference: Plant Physiology, 4th Ed.; SN Pandey & BK Sinha; Vikas Publishing House Pvt. Ltd.
1. External Factors
i. Humidity: Higher relative humidity, less will be rate of transpiration & vice versa
ii. Temperature: directly proportional, every 100C rise in temperature, rate of transpiration doubled
iii. Wind speed: directly proportional
iv. Light
v. Atmospheric pressure:
vi. Water supply
vii. Spray and dust
viii. Vital activities
2. Internal Factors
i. Stomatal frequency: number of stomata per unit area
ii. Structural peculiarity of leaf
THE RATE OF TRANSPIRATION IS INFLUENCED BY ENVIRONMENTAL FACTORS

36. WHY TRANSPIRATION IS CALLED NECCESARY EVIL?
TRANSPIRATION IN RELATION TO PRODUCTIVITY
 Water Use Efficiency (WUE): Amount of dry matter produced per unit amount of water transpired
 Factors influencing water use efficiency
1. Climatic Factors
2. Agronomic practices & Crop management
3. Anti-transpirants
4. Use of mulches
5. Use of shelter belts
6. Method and quantity of water application
7. Fertilizer application
8. Weed control

37. Antitranspirants are compounds applied to the leaves of plants to reduce transpiration.
Types:
 Metabolic inhibitors reduce the stomatal opening and increase the leaf resistance to water vapour
diffusion without affecting carbon dioxide uptake. Examples include phenylmercury acetate, abscisic
acid (ABA), and aspirin.
 Film-forming antitranspirants form a colorless film on the leaf surface that allows diffusion of gases
but not of water vapour. Examples include silicon oil, waxes.
Anti-transpirants

38. Mechanism of Nutrient Uptake by Plants
1. Passive Absorption
1.1 Simple diffusion
1.2 Facilitated diffusion
1.2.1 Channel proteins
1.2.2 Carrier proteins
 Uniport
 Symport
 Antiport
2. Active Absorption
2.1 ATP-powered pump
2.2 Na+-K+ pump
2.3 Ca+2 pump

39.  Some of the transport proteins in membrane facilitate the diffusion of solutes, especially charged solutes or ions,
into the cell by effectively overcoming the solubility problem.
 The term facilitated diffusion was coined to describe this rapid, assisted diffusion of solutes across the membrane.
 In facilitated diffusion, as in simple diffusion, the direction of transport is still determined by the concentration
gradient (for uncharged solute) or electrochemical gradient (for charged solutes and ions).
 Facilitated diffusion is also bidirectional and, like simple diffusion, net movement ceases when the rate of
movement across the membrane is the same in both directions.
Facilitated Diffusion

40. Carrier proteins (also known as carriers, transporters, or simply, porters) bind the particular solute to be
transported, much along the lines of an enzyme–substrate interaction. Binding of the solute normally induces a
conformational change in the carrier protein, which delivers the solute to the other side of the membrane. Release of
the solute at the other surface of the membrane completes the transport and the protein then reverts to its original
conformation, ready to pick up another solute.
Channel proteins are commonly visualized as a charged-lined, water-filled channel that extends across the
membrane. Channels are normally identified by the ion species that is able to permeate the channel, which is in turn
dependent on the size of the hydrated ion and its charge. Diffusion through a channel is dependent on the hydrated
size of the ion because the associated water molecules must diffuse along with the ion. The number of ion channels
discovered in the membranes of plant cells is increasing. Currently there is solid evidence for K+, Cl−, and Ca2+
channels, while additional channels for other inorganic and organic ions are strongly suggested. Channel proteins
are frequently gated, which means they may be open or closed.
Two types of gates are known. An electrically gated channel opens in response to membrane potentials of a
particular magnitude. Other channels may open only in the presence of the ion that is to be transported and may be
modulated by light, hormones, or other stimuli. The precise mechanism of gated channels is not known, although it
is presumed to involve a change in the three-dimensional shape, or conformation, of the protein.
Carrier & Channel Proteins

41.  The importance of carriers lies in the selectivity they impart with respect to which solutes are permitted to
enter or exit the cell.
 Channels, on the other hand, appear to be involved wherever large quantities of solute, particularly
charged solutes or ions, must cross the membrane rapidly.
 Whereas a carrier may transport between 104 and 105 solute molecules per second, a channel may
pass on the order of 108 ions per second.
 It should also be stressed that large numbers of channels are not required to satisfy the needs of most cells.
 The rate of efflux through guard cell K+ channels during stomatal closure, for example, has been estimated at
107 K+ ions/sec — a rate that conceivably could be accommodated by a single channel.
 Many carrier and channel proteins are inducible, which means that they are synthesized by the cell only
when there is solute available to be taken up.
…Carrier & Channel Proteins

42. Passage of solutes through carrier
proteins
(a) In the simplest type, known as a
uniport, one particular solute is moved
directly across the membrane
in one direction. Carrier proteins involved
with facilitated diffusion function as
uniporters, as do all channel proteins.
(b) In the type of cotransport system
known as a symport, two different solutes
are moved across the membrane
simultaneously and in the same direction.
(c) In another type of cotransport system,
known as an antiport, two different
solutes are moved across the membrane
either simultaneously or sequentially, but
in opposite directions.
Uniport, Symport, Antiport

43.  By definition, active transport is tightly coupled to a metabolic energy source—usually, although not always,
hydrolysis of adenosine triphosphate (ATP).
 In other words, active transport requires an input of energy and does not occur spontaneously.
 Unlike simple and facilitated diffusion, active transport is also unidirectional—either into or out of the cell—and
is always mediated by carrier proteins.
 Active transport serves to accumulate solutes in the cell when solute concentration in the environment is very low.
 When used to transport solute out of the cell, active transport serves to maintain a low internal solute
concentration.
 Because active transport systems move solutes against a concentration or electrochemical gradient, they are
frequently referred to as pumps.
Active Transport

44.  Neither simple diffusion nor passive transport is capable of moving solutes against a concentration gradient or an
electrochemical gradient.
 The capacity to move solutes against a concentration or electrochemical gradient requires energy. This process is
called active transport, and it is always mediated by carrier proteins.
 The proton pump in plant and fungal cells is energized by ATP and mediated by an H+-ATPase located in the
membrane. The enzyme generates a large electrical potential and a pH gradient—that is, a gradient of protons
(hydrogen ions)—that provide the driving force for solute uptake by all the H+-coupled cotransport systems.
 By this process, even neutral solutes can be accumulated to concentrations much higher than those outside the cell,
simply by being cotransported with a charged molecule (for example, an H+). The energy-yielding first process (the
pump) is referred to as primary active transport, and the second process (the cotransporter) as secondary active
transport.
Primary & Secondary Active Transport

45. Primary and secondary active transport
of sucrose
(a) Primary active transport occurs when
the proton pump (the enzyme H+ATPase)
pumps protons (H+) against their gradient.
The result is a proton gradient across the
membrane.
(b) The proton gradient energizes
secondary active transport. As the protons
flow passively down their gradient,
sucrose molecules are cotransported
across the membrane against their
gradient. The carrier protein is known as a
sucrose-proton symporter.

46. Three types of endocytosis (a) In phagocytosis, contact between the plasma membrane and
particulate matter, such as a bacterial cell, causes the plasma membrane to extend around the particle,
engulfing it in a vesicle. (b) In pinocytosis, the plasma membrane pouches inward, forming a vesicle
around liquid from the external medium that is to be taken into the cell. (c) In receptor mediated
endocytosis, the molecules to be transported into the cell must first bind to specific receptor proteins.
The receptors are either localized in indented areas of the plasma membrane known as coated pits or
migrate to such areas after binding the molecules to be transported. When filled with receptors carrying
their particular molecules, the pit buds off as a coated vesicle.
Endocytosis

48. Criteria of Essentiality (Arnon & Stout, 1939)
I. A deficiency of a particular element makes it impossible for a plant to complete its vegetative and
reproductive cycle
II. The particular element cannot be replace by another element
III. The particular element should have some part to play in metabolism
1. Macro-nutrient (C, O, H, N, P, K, Ca, Mg, S)
 Primary Nutrients: N, P, K
 Secondary Nutrients: Ca, Mg, S
2. Micro-nutrient
Fe, Mn, Cu, Zn, Mo, B, Cl
Plant Nutrients: Macro & Micro
i. Source
ii. Function
iii. Deficiency Symptom
iv. Disease
v. Corrective measures

49. Theories of Mineral Salt Absorption
Passive Absorption
1. Diffusion Theory
2. Mass Flow Theory (Bulk Flow)
3. Ion exchange Theory
4. Donnan Equilibrium
Objection to Passive Absorption Concept
i. Rate of mineral absorption is too rapid
to be explained by passive absorption.
ii. No theory of passive absorption
adequately explains absorption &
accumulation of salts/ions against
osmotic gradient.
iii. It has been experimentally
demonstrated that there is a close
relationship between salt uptake &
metabolic activities.
Active Absorption (Street, Lundegardh, Clark, Epstein)
1. Carrier Concept Theory & its three supportive evidences:
a) Isotopic exchange
b) Saturation effect
c) Specificity
2. Protein-Lecithin as Carrier
3. Cytochrome Pump Hypothesis
4. ATP Theories

50. 1. Temperature: within a narrow range, it is directly proportional to salt absorption.
2. pH: it affects availability of ions in medium, this indirectly affects salt uptake.
3. Light: indirectly affect rate of salt absorption by affecting opening and closing of stomata and photosynthesis.
4. Oxygen tension: deficiency of oxygen decreases salt absorption as actie phase of salt absorption is inhibited by
absence of oxygen.
5. Interaction of one ion with other ion (s):
6. Growth (surface area, cell number, synthesis of new binding sites, etc.): different types of growth affect salt
absorption in different ways.
Factors Affecting Salt Absorption