Repeaters Online Note

MINERAL NUTRITION

The process of absorption and utilisation of various mineral ions by plant for their growth and
development is called Mineral nutrition.
 Mineral nutrients (mineral elements): Nutrients obtained from soil.
 Non mineral nutrients: Carbon, Hydrogen and Oxygen (mainly obtained from air and water)
 Hydroponics (Soilless culture, Solution culture, Water culture)
• It is a technique of growing plants in nutrient solution .
• By this method essential elements and their deficiency symptoms could be identified.
• This method was first demonstrated by Julius Von Sachs in 1860 (German botanist).
• Commercially developed by William F Gericke in 1930 (University of California).
• These methods require purified water and mineral nutrient salts
 Defined (balanced) nutrient solution
Solution containing various mineral elements in the proper proportion is called Defined nutrient
solution.
Example:
1. Knop’s solution
2. Sach’s solution
3. Hoagland’s solution. It is widely used and it contains all the nutrients needed for plant growth.

• Nutrient solution must be aerated to obtain optimum growth.

 Economic importance
Commercial production of Tomato, seedless Cucumber and Lettuce
 Advantages of Hydroponics

1) High yield
2) Out of season vegetables and flowers can be obtained
3) To study about Toxicity, Deficiency symptoms etc.
 Disadvantage of Hydroponics
1) Costly
2) Need the help of an expert to prepare nutrient solution
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 Aeroponics
• In this technique roots are supplied with nutrient mist .
• Developed by Weathers and Zobel
• In aeroponics plant show a very good growth of root hair. It is used for research purposes .

ESSENTIAL MINERAL ELEMENTS

• More than 60 elements are found in plants
Example
Selenium  Astragalus,
Gold  Phacelia
Radioactive Strontium  Plants growing near Nuclear Test Site
• There are techniques that are able to detect the low concentration of mineral ions (10 -8 g/mL)

ESSENTIAL ELEMENTS
Essential elements: They are essential for normal growth, development and metabolism.
 CRITERIA FOR ESSENTIALITY
Proposed by Arnon and Stout
1) Necessary for supporting normal growth and reproduction. In the absence of the element the
plants do not complete their life cycle or set the seeds.
2) The element must be specific and not replaceable by another element . (Deficiency of any one
element cannot be met by supplying some other element.)
3) It must be directly involved in the metabolism of the plant.

 Beneficial (functional) elements

Some plants require certain elements other than essential elements. They have some special role in
plants.
• Silicon (Si)  Grass, Diatoms and Equisetum
• Sodium (Na ) C4 plants and Halophytes
• Cobalt (Co)  Wheat
• Selenium ( Se) Astragalus
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ADDITIONAL POINTS
• Aluminium (Al ) Ferns
• Gallium (Ga)  Aspergillus
• Gold (Au)  Equisetum
• Vanadium (V)  Scenedesmus ( a green algae)

 Classification of Essential elements

 I) Based on Quantitative requirement ( Hoagland)

1) Macro Nutrients ( Macro Elements or Major Elements): Require more than 10 m mole Kg-1
of dry matter.
Macronutrients are Carbon, Oxygen, Hydrogen, Nitrogen, Potassium, Calcium, Magnesium,
Phosphorous and Sulphur.
2) Micro Nutrients (Micro nutrients, Micro elements ,Trace elements): Require less than
10 m mole Kg-1 of dry matter.
Micronutrients are Iron, Chlorine, Boron, Manganese, Zinc, Copper, Nickel and Molybdenum.
 II) Based on Function
1) Component of biomolecules (structural element of cell) : C,H,O and N
2) Component of energy related chemical compound: Example: Magnesium in Chlorophyll
and Phosphorous in ATP.
3) Activate or inhibit enzymes :

• Magnesium is an activator for both ribulose biphosphate carboxylase-oxygenase

(RuBisCO) and phosphoenol pyruvate carboxylase (PEPcase).
• Zn2+ is an activator of alcohol dehydrogenase.
• Mo activates Nitrogenase during nitogen metabolism.

4) Alter osmotic potential: Potassium  opening and closing of stomata.

 Repeaters Online Note

ADDITIONAL POINTS
• Critical elements: N,P and K. They are deficient in agricultural soil due to leaching and
withdrawal by plants.
• Balancing elements : Ca, Mg and K
• Tracer elements: These are radioactive isotope of elements which are used to detect various
metabolic pathway in plants.
• Electron transport elements : Fe and Cu
• Osmotic concentration of cell sap : K and Cl
• Buffering action: Phosphate
• Framework elements : C,H and O

ROLE OF MACRO NUTRIENTS

 Nitrogen:
Required in the greatest amount.
It is absorbed mainly as NO3 – though some are also taken up as NO2 – or NH4 + .
Required : All parts of a plant, particularly the meristematic tissues and the metabolically active
cells.

Functions:
1) Major constituents of proteins, nucleic acids, vitamins, hormones and chlorophyll.
 Nitrogen is a limiting nutrient for both natural and agricultural eco-systems because plants
compete with microbes for the limited nitrogen that is available in soil.
 Insectivorous plants overcome nitrogen deficiency of its body by catching and digesting small
insects.

 Potassium:
• It is absorbed as potassium ion (K+ ).
• Most abundant intracellular cation
Required: More abundant quantities in the meristematic tissues, buds, leaves and root tips.
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Functions:
1) Maintain anion-cation balance in cells,
2) Protein synthesis
3) Opening and closing of stomata,
4) Activation of enzymes
5) Maintenance of the turgidity of cells.

 Phosphorus:
Absorbed in the form of phosphate ions (either as H2PO4- or HPO42- ).
Functions:
1) Phosphorus is a constituent of cell membranes, certain proteins, nucleic acids and nucleotides.
2) It is required for all phosphorylation reactions.
• Glomus helps in absortion of phosphorus from soil.

 Calcium:
Plant absorbs in the form of calcium ions (Ca2+ )
Required : meristematic and differentiating tissues. It accumulates in older leaves.
Functions:
1) Calcium is used in the synthesis of cell wall, particularly as calcium pectate (Ca and Mg pectates)
in the middle lamella.
2) It is also needed during the formation of mitotic spindle.
3) It is involved in the normal functioning of the cell membranes.
4) It activates certain enzymes.
5) Regulating metabolic activities.
 Magnesium:
Absorbed in the form of divalent Mg2+.
Functions:
1) Constituent of the ring structure of chlorophyll.
2) Helps to maintain the ribosome structure.
3) It activates the enzymes of respiration and photosynthesis .
4) Synthesis of DNA and RNA.
5) Middle lamella is made up of Ca and Mg pectates.
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 Sulphur:
Plants obtain sulphur in the form of sulphate (SO 42-)
Functions:
1) Sulphur is present in two amino acids – cysteine and methionine
2) Main constituent of several coenzymes, vitamins (thiamine and biotin), Coenzyme A and
ferredoxin( Fe and S containing protein).
3) The characteristic odour of Crucifers( Mustard, Cabbage etc.), Onion and Garlic is due to the
presence of Sulphur containing compounds.

ROLE OF MICRO NUTRIENTS

 Iron:
• Plants obtain iron in the form of ferric ions (Fe3+).
• It is required in larger amounts in comparison to other micronutrients.
Functions:
1) It is an important constituent of proteins involved in the transfer of electrons like ferredoxin and
cytochromes.
2) It is reversibly oxidised from Fe2+ to Fe3+ during electron transfer.
3) It activates catalase enzyme.
4) It is essential for the formation of chlorophyll.

 Manganese:
It is absorbed in the form of manganous ions (Mn 2+).
Functions:
1) Activation of enzymes in photosynthesis, respiration and nitrogen metabolism.
2) The best defined function of manganese is in the splitting of water ( Photolysis) to liberate oxygen
during photosynthesis

 Zinc:
Plants absorb zinc in the form of Zn 2+ ions.
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Functions:
1) It activates various enzymes, especially carboxylases.
2) It is also needed in the synthesis of auxin.
3) Activation of Alcohol dehydrogenase

 Copper:
It is absorbed as cupric ions (Cu2+).
Functions:
1) It is essential for the overall metabolism in plants.
2) Like iron, it is associated with certain enzymes involved in redox reactions
3) It is reversibly oxidized from Cu+ to Cu2+
4) Copper is a constituent of plastocyanin.

 Boron :
It is absorbed as BO3 3− or B4O7 2− .
Functions:
1) Pollen germination
2) Cell elongation
3) Cell differentiation.
4) Carbohydrate translocation.
5) Boron is required for uptake and utilisation of Calcium
6) Membrane functioning
7) Helps to increase fruit size

 Molybdenum:
• Plants obtain it in the form of MoO 2 2+ ( molybdate ions).
• It is required in least quantity.

Functions:
1) It is a component of several enzymes, including nitrogenase and nitrate reductase both of which
participate in nitrogen metabolism.
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 Chlorine:
It is absorbed in the form of chloride anion (Cl– ).

Functions:
1) It helps in determining the solute concentration and the anion cation balance in cells. (Along with
Na+ and K+ )
2) It is essential for the water-splitting reaction in photosynthesis(Photolysis), a reaction that leads to
oxygen evolution.

 Nickel
Plants absorb Nickel in the form of Ni2+
Functions:
1) It is the component of enzymes such as urease and hydrogenase.
 Critical concentration

• The concentration of Essential elements below which the plant growth is retarded termed as

Critical concentration.

• The concentration of the essential element above the critical concentration causes Toxicity and

below causes Deficiency symptom (Hunger sign)

 DEFICIENCY SYMPTOMS

1) Chlorosis: Loss of chlorophyll leading to yellowing in leaves.

It is caused by the deficiency of N, K, Mg, S, Fe, Mn, Zn and Mo.

2) Inhibition of cell division. Due to Lack or low level of N, K, S and Mo.

3) Delay flowering : Low concentration of N, S and Mo in plants

4) Necrosis: Death of tissue, particularly leaf tissue.

It is due to the deficiency of Ca, Mg, Cu and K.

 Repeaters Online Note

ADDITIONAL POINTS

Premature leaf fall  P

Die back disease  Cu and K

Wilting  Cl

Exanthema (Rough and split bark disease)  Cu

Death of root and shoot tip, Small size of fruit, Internal cork disease ( in Apple)  B

Bushy habit of shoot, shortening of internode  K

Little leaf disease, Khaira disease in Paddy  Zn

Grey speck disease  Mn

Whip tail disease  Deficiency of Mo in Crucifers

Leaf tip necrosis  Ni

 Toxicity

• Any mineral ion concentration that reduces the dry weight of tissue by about 10 percentage is

considered as toxic .

• Toxicity symptoms are difficult to identify and toxicity levels for any element vary for different

plants.

• Example: Manganese toxicity

• Manganese competes with iron and magnesium for uptake .

• Manganese compete with magnesium for binding with enzymes .

• Manganese also inhibits calcium translocation into shoot apex.

• Symptom of Manganese toxicity : Brown spots surrounded by chlorotic veins

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 MOBILE ELEMENTS: N,K and Mg. Deficiency symptom first appear in senescent leaves.

 IMMOBILE ELEMENT : Ca. Deficiency symptom first appear in younger part.

RELATEVLY LESS MOBILE: S

 MECHANISM OF ABSORPTION OF ELEMENTS

• Mineral absorption of elements occurs in two phases
1) Rapid and passive absorption of ions into the outer space or free space (cell wall or
intercellular spaces)- Apoplast pathway.
It does not involve crossing the cell membrane.
• 2) Active uptake of ions into the inner space (cytoplasm) -Symplast pathway.
Neighbouring cells are connected ( intercellular movement) through Plasmodesmata .Water
has to enter the cells through the cell membrane, hence the movement is relatively slower.
• The trans-membrane proteins that function as selective pores.

 FLUX
Movement of ions is called of flux . Inward movement is called influx and outward movement is
called efflux .

 SOIL AS RESERVOIR OF ESSENTIAL ELEMENTS

• Weathering of rocks enriches the soil with dissolved ions and inorganic salts.
• Mineral salts are translocated through the xylem along with ascending stream of water by
transpiration pull.

• Soil not only supplies minerals but also harbours nitrogen-fixing bacteria and other microbes.
• Soil holds water, supplies air to the roots and acts as a matrix that stabilises the plant.
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NITROGEN CYCLE

Atmospheric N2

Denitrification

Biological N2 Industrial N2 Electrical N2

fixation fixation fixation
Pseudomonas
Thiobacillus
NH3 Nitrosomonas NO2 Nitrobacter
Ammonification NO3
Nitrococcus
Nitrification - Soil
Bacillus vulgaris
Bacillus ramosus

Decaying
Biomass
Plant Biomass

Animal Biomass

• Nitrogen is a limiting nutrient for both natural and agricultural eco-systems.

• The process of conversion of nitrogen (N2 ) to ammonia is called nitrogen fixation.
• Lightning and ultraviolet radiation convert nitrogen to nitrogen oxides (NO, NO 2 , N2O).
• Ammonification: Decomposition of organic nitrogen of dead plants and animals into
ammonia is called Ammonification.
• Some of this ammonia volatilises and re-enters the atmosphere but most of it is converted
into nitrate by Nitrifying bacteria.
• Nitrification: Conversion of ammonia into nitrate . This process consists of 2 steps
1) Ammonia is first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococcus.
2NH 3 + 3O 2 → 2NO 2− + 2H + + 2H 2 O
2) The nitrite is further oxidised to nitrate with the help of the bacterium Nitrobacter.
2NO −2 + O 2 → 2NO3−

• Nitrifying bacteria are chemoautotrophs.

 Repeaters Online Note

Denitification : Nitrate present in the soil is reduced to Nitrogen. This process is carried out by
Pseudomonas and Thiobacillus.

N2 Fixers
Aerobic : Azotobacter, Beijernikia, Azospirillum

I. Free Living Anaerobic : Rhodospirillium, Clostridium

Facultative aerobe : Some Bacillus species

Facultative anaerobe : Some other species of Bacillus

Blue Green Algae : Nostoc, Anabaena, Oscillatoria, Aulosira,

Cylindrospermum, Trichodesmium

Bactera Rhizobium Leguminous Plants

Nostoc Cycas
II. Symbiotic Blue Green Algae
Anabaena Azolla

Alnus (Alder)
Filamentous Bacteria Frankia Casuarina
(Actinomycetes) Non legumes
Myrica

ADDITIONAL POINTS
III. Fungi – Yeast, Pullaria ( Pullularia)
IV. Chemosynthetic – Desulphovibrio, Nitrifying bacteria
V. Photosynthetic – Chlorobium, Chromatium, Rhodospirillum
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Symbolic N2 fixation

 Rhizobium is Free living, Aerobic, Gram negative and Rod shaped bacterium.

 Root Nodules acts as a site for symbiotic N2 fixation.

 It contains Nitrogenase enzyme and Leghaemoglobin

1. Nitrogenase enzyme

• It catalyses the conversion of atmospheric N2 into NH3

• Ammonia is the first stable product of N2 fixation
• Nitrogenase enzyme is sensitive to oxygen
• It is made up of 2 sub units
1. Fe-protein 2. Mo-Fe protein
N 2 + 8e − + 8H + + 16ATP Nitrogenase
  → 2NH 3 H 2+ 16ADP
+ +
16Pi

The energy (ATP molecule) is obtained from respiration of the

host cell.
2. Leghaemoglobin (Leguminous haemoglobin)
 It is a pink coloured pigment present in root nodule

Functions
1) Oxygen scavenger
2) Provides oxygen to the bacteria
 In leghaemoglobin Globin part is provided by the plant and Haem is provided by bacteria
 In Rhizobium there are 3 types of genes in organizing N2 fixing apparatus.
1) nif – gene – formation of Nitrogenase enzyme
2) nod-genes – Nodule formation
3) fix – gene – Nitrogen fixation
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NODULE FORMATION

• Leguminous root secrete certain chemical substance called growth factor into the soil
• Rhizobia multiply and colonise surroundings of the root.
• Bacteria produce Nod (Nodulation) factor which help in the production of Lectin by root
hair.
• Lectins help them to attach the root hair.
• When the bacteria aggregate at the tip of the root hair curling occurs.
• Cell wall disintegrate and plasma membrane invaginate and grow into tube like structure
towards cortex known as infection thread.
• Bacteria in the infection thread enlarge and are covered by an extracellular polysaccharide.
This structure is called Bacteriod.
• Inside the cortex bacteriod is again surrounded by another membrane known as
Peribacterial (Peribacteriodal) membrane which is in plant origin.
• Leg haemoglobin is synthesized and it is localized within the Peribacteriodal membrane.
• Bacteria produce Cytokinin and plant cell produces Auxin. These hormones stimulate the
cell division of inner cortical cells and pericycle cells. It leads to the formation of knob like
root nodule.
• A mature nodule establishes direct vascular connection with the root for the exchange of
nutrients.
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SYNTHESIS OF AMINO ACID

• Plants absorb nitrate from the soil and is transported to leaves. In leaves , it is reduced to
form Ammonia and the ammonia is protonated to form NH 4+ (ammonium) ion.
NO3− Nitrate
 reductase
   →−2
NO    NH H+
 3→
Nitrite reductase
+ 4+ →
NH

• Ammonium ion is toxic to plants and hence cannot accumulate in them.

• Ammonium ion is used to synthesise amino acids in plants.
1) Reductive Amination
In this process NH4+ react with alpha ketoglutraric acid and forms glutamic acid (Amino acid)
α Ketoglutaric acid + NH +4 + NAD(P)H Gluamate
    Glutamic
dehydrogenase
→ acid (Glutamate) H 2 O + NAD(P)
+

2) Transamination

H
H
R1 C COO + R2 C COO R1 C COO + R2 C COO
NH3 O
NH3
Amino - donor Amino - acceptor
• It involves the transfer of amino group from one amino acid to the keto group of a ketoacid.
• Glutamic acid is the main aminoacid in which other aminoacids are formed through
Transamination. The enzyme transaminase catalyses all such reaqctions..
Eg. Oxalo acetic acid + Glutamic acid α Ketoglutaric acid + Aspartic acid
 AMIDES
• Derivatives of aminoacids in which hydroxyl group (OH) is replaced by amino group (NH2).
They contain more Nitrogen than aminoacids and are structural part of most proteins.
• They are transported to other parts of the plant via xylem vessels.
Eg :1) Asparagine is formed from Aspartic acid.
2) Glutamine is formed from Glutamic acid
 UREIDES
It’s form of fixed nitrogen present in Soyabean. These compounds have particularly high Nitrogen
to Carbon ratio.