CRITERIA OF ESSENTIALITY OF ELEMENTS

2. The chemical form in which elements are applied to
plants is called as nutrient.
Nutrition may be defined as the supply and absorption
of chemical compounds needed for plant growth and
metabolism.
Mineral nutrient is generally used to refer to an
inorganic ion obtained from the soil and required for
plant growth.

3.  Non-Mineral Nutrients
 Mineral Nutrients
Seventeen chemical elements
are known to be important to
a plant growth & survival. We
can divide these elements
under main groups.

4. Non - Mineral Nutrients :
Non - Mineral Nutrients are
C, H, and O. These are
found in air and water.
Mineral Nutrients :
There are 14 mineral
nutrients. These nutrients are
divided in to 2 groups-
Macronutrients
Micronutrients

5. Macronutrients:
Macronutrients are needed in large quantities
in concentration of 1000 microgram per gram
of dry-matter or more.
Macronutrients can divide in to 2 major
groups. They are,
Primary Nutrients - N, P, K
Secondary Nutrients - Ca, Mg, S

6. Micronutrients-
◦ Micronutrients are the elements which are
essential for plant growth only in very small
quantities in concentration of equal to or less
than 100 microgram per gram of dry matter or
more.
◦ The Micronutrients are-
Mn Cl
Cu Fe
Mo Zn
B Ni

7. Macro or Major
elements
Micro or Minor
or Trace elements
Primary
elements
Secondary
elements
CHO (air)
NPK (soil) Ca, Mg, S
Basic nutrients
Cation
Fe,
Mn,
Cu,
Zn, Ni,
Anion
Mo,
B, Cl

8. CRITERIA OF ESSENTIALITY OF ELEMENTS
Term essential mineral element - Arnon and Stout
(1939).
According to them an element to be considered
essential, three criteria must be met:
1. A given plant must be unable to complete its life
cycle in the absence of mineral elements.
2. The function of the element must not be replaceable
by another mineral element
3. The elements must be directly involved in plant
metabolism.

9. Epstein (1972)
1. An element is essential, if plant can not
complete its life cycle due to its absence.
2. An element is essential, if it is a part of molecule
which itself is essential in plants like nitrogen in
protein and magnesium in chlorophyll.

10. Beneficial elements:
The elements, the essentiality of which for
growth and metabolism has not been
unequivocally established, but which are shown
to exert beneficial effects at very low
concentrations are often referred to as beneficial
elements, or potential micronutrients.

11. Nicholas (1961)- proposed term ‘Functional
nutrient’.
Functional nutrient- Any mineral element that
functions in plant metabolism whether or not its
action is specific.
Eg. Sodium, Cobalt, Vanadium and Silicon
To describe the level of nutrient element in plants
the following terms are proposed.
1. Deficient
2. Toxic

12. Based on the mobility, elements are also classified
into three types.
1. Mobile elements : N, P, K, S and Mg
2. Immobile elements : Ca, Fe and B
3. Intermediate in mobility : Zn, Mn, Cu, Mo

13.  Classification of elements according to their role and physiological functions
(Mengel and Kirkby, 1987)
 Plant nutrients have been divided into four basic groups.
1. The first group of essential elements form the organic (carbon) compounds of
the plant. Plants assimilate these nutrients via biochemical reactions
involving oxidation and reduction.
2. The second group is important in energy storage reactions or in maintaining
structural integrity. Elements in this group are often present in plant tissues
as phosphate, borate and silicate esters in which the elemental group is
bound to the hydroxyl group of an organic molecule (i. e. sugar- phosphate).
3. The third group is present in plant tissues as either free ions or ions bound to
substances such as pectic acid present in the cell wall of particular
importance or their roles as enzyme cofactors and in the regulation of
osmotic potentials.
4. The fourth group has important roles in reactions involving electron transfer.

14. Nutrient
elements
Uptake Biochemical function
1st Group
C, H, O, N,
S
In the form of CO2,
HCO3
-, H2O, O2,NO3
-,
NH4
+, SO4
-2
This group includes nutrients
that are part of organic
compounds.
2nd Group
P, B, Si
In the form of
phosphates, boric acid
or borate, silicate
from the soil solution.
Nutrients that are important in
energy storage or structural
integrity.
3rd Group
K, Na, Mg,
Ca, Mn, Cl
In the form of cations
from the soil solution
except chlorine
Nutrients that remain in ionic
form.
4th Group
Fe, Cu,
Zn, Mo
In the form of ions or
chelates from the soil
solution
Nutrients that are involved in
redox reactions.

15. Factors influencing nutrient availability
1. Natural supply of nutrients
2. Soil pH
3. Relative activity of micro organisms
4. Fertility addition in form of commercial
fertiliser, organic manure
5. Soil temperature, moisture, aeration
6. Presence of plants and cropping system

16. UPTAKE OF NUTRIENTS BY PLANTS
Mineral uptake is the process in which minerals
enter the cellular material, typically following the
same pathway as water.
Normal entrance portal for mineral uptake – roots.
During transport through plant, minerals exit xylem
and enters cell that require them.
Plants absorb mineral in ionic form: NO3
-, HPO4
-,
K+ etc

17. Certain terms are associated with the uptake of
substances.
Sorption: When a molecule, ion or atom come in
contact with some surface.
Divided into two parts
Adsorption: Binding of ions or molecules to a
surface (e.g., of a soil particle or a root).
Absorption: When a molecule, ion or atom enters
inside the cell.

19. Physiology of nutrient uptake :
Mineral nutrients are found either as soluble fractions
of soil solution or as adsorbed ions on the surface of
colloidal particles.
Various theories proposed to explain the mechanism of
mineral salt absorption can be placed in two broad
categories:
I) Passive Absorption
II) Active Absorption

20. Passive absorption
It is the absorption of minerals without direct
expenditure of metabolic energy.
In this,
1. Mineral salt absorption is not affected by
temperature and metabolic inhibitors.
2. Rapid uptake of ions occurs when plant tissues
are transferred from a medium of low conc. to
high conc.

21. a) Channel proteins: The specific proteins in the
membrane form channels (channel proteins), which
can open and close, and through which ions or H2O
molecules pass in single file at very rapid rates.
b) Transporters or Co-transporters or carriers: After
binding a molecule or ion, the transporter undergoes a
structural change specific to a specific ion or molecule.
As a result, the transport rate across a membrane is
slower than that associated with channel proteins.

22. Three types of transporters have been identified:
1. Uniporters: Transport one molecule at a time down a
concentration gradient.
2. Antiporters: Catalyze movement of one type of ion or
molecule against its concentration gradient.
Examples of antiporter transport are H+/Na+ and H+ /Ca+2
transport into the vacuole.
3. Symporters: Catalyze movement of one type of ion or
molecule against its concentration gradient coupled to
movement of a different ion or molecule in the same
direction.

24. c) Aquaporins
These are class of proteins relatively abundant in plant
membranes.
Aquaporins form water channels in the membranes and the
activity appears to be regulated in response to water
availability.

25. Major hypothesis which explain mechanism of passive
transport are:
1. Diffusion
2. Facilitated diffusion
3. Mass flow theory
4. Ion exchange hypothesis
Contact exchange theory
Carbonic acid theory

26. Passive transport mechanism:
1. Diffusion:
In this process ions or molecules move from the
place of higher concentration to lower
concentration. It needs no energy.
2. Facilitated diffusion:
For small polar species specific proteins in the
membrane facilitate the diffusion down the
electrochemical gradient. This mechanism is
referred to as facilitated diffusion.

30. Carbonic acid theory

31. Active absorption
Active transport of ions from outer space of cell to the
inner space is generally occurs against concentration
gradient and hence requires metabolic energy. This
energy is obtained from metabolism of the cell
directly or indirectly.
Active transport across a selectively permeable
membrane occurs through ATP-powered pumps that
transport ions against their concentration gradients.

32. Major hypothesis that explain mechanism of active transport
of ions:
1. Carrier concept – transport by a carrier protein.
2. Cytochrome pump – transport by electrochemical gradient
generated by electron transport.