Minerals are essential inorganic nutrients that are required for plant growth and development. There are two types of minerals: macronutrients which are needed in large amounts and micronutrients which are needed in trace amounts. Hydroponics is a method used to study mineral requirements of plants by growing them in nutrient solutions. Essential minerals meet certain criteria and are involved in key metabolic processes in plants. Nitrogen is an important macronutrient that plants obtain through nitrogen fixation by symbiotic bacteria in root nodules of legumes or free-living soil bacteria. The nitrogen is then assimilated into amino acids and proteins in plants.

1. MINERAL NUTRITION

2. Subtopics
Minerals and its importance
Essential Minerals- Classification
Minerals- Roles and properties
Absorption and Translocation
Metabolism of Nitrogen

3. Introduction
• Living organism- Macromolecules (Carbohydrates,
proteins & fat), water and minerals for growth and
development.
• Def.- A mineral is a chemical element which naturally
occurs as inorganic nutrients in the food and soil, and
are essential for the proper functioning of the plant and
animal body.
• Other than carbon, hydrogen, oxygen & sulphur- organic
molecules

4. Methods to study Mineral requirements of Plants
• Julius von Sachs, German botanist in
1860- that plants could be grown to
maturity in a defined nutrient solution in
complete absence of soil- hydroponics.
• Method involves growing plants in purified
water & specific mineral nutrient salts-
nutrient solution is aerated for optimum
growth
• Concentration required is determined-
adding/removing mineral solution- identify
essential elements & deficiency

6. • Hydroponics- commercial production of vegetables such
as tomato, seedless cucumber and lettuce

7. Criteria for Essentiality of minerals
• Minerals present in soil enters plant- roots
• Criteria for essentiality of mineral elements:
a) The element must be absolutely 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.
b) The requirement of the element must be specific and not replaceable
by another element. In other words, deficiency of any one element
cannot be met by supplying some other element.
c) The element must be directly involved in the metabolism of the plant.

8. • Based on quantitative requirement by plants:
1) Macronutrients
2) Micronutrients
MACRONUTIENTS
• Large amounts in plant tissues (in excess of 10 mmole Kg-1 of dry
matter)
• Carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium,
calcium and magnesium- CO2, H2O & soil
MICRONUTRIENTS
• Trace elements, less than 10 mmole Kg-1 of dry matter
• iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel
• Higher plants- sodium, silicon, cobalt and selenium

9. Classification of Elements based on function
• Based on diverse function:
1. Structural Elements: Components of biomolecules
(Carbohydrates, proteins, lipids & nucleic acid). Eg. C, H, O & N
2. Energy related chemical compounds: Provide energy to plants.
Eg. Mg in chlorophyll & Phosphorus in ATP
3. Elements activate & inhibit enzymes: Activates or inhibits
enzymes during metabolism. Eg. Mg2+ - activator of ribulose
bisphosphate carboxylaseoxygenase & phosphoenol pyruvate
carboxylase-photosynthetic carbon fixation; Zn2+ - an activator of
alcohol dehydrogenase & Mo of nitrogenase- nitrogen
metabolism.
4. Elements altering water potential: Alters osmotic potential of cell.
Eg. K- opening and closing of Stomata; regulates water potential
of cells

15. Toxicity of Micronutrients
• Micronutrients- low
amounts
• Decrease- deficiency,
moderate increase- toxicity
• Any mineral ion
concentration in tissues that
reduces the dry weight of
tissues by about 10 per cent
is considered toxic.
• Critical concentration- vary &
toxicity level vary with
different plants
• Excess micronutrients-
Toxicity Eg. Manganese
toxicity

16. Manganese Toxicity
• Brown spots around chlorotic
veins
MODE OF TOXICITY:
a) Manganese competes with
iron and magnesium for
uptake
b) Magnesium for binding with
enzymes
c) Inhibit calcium translocation in
shoot apex.
RESULT:
• Excess of manganese- Induce
deficiencies of iron,
magnesium and calcium.

17. Absorption of Elements
• Studies carried on cells/tissues/organs- occurs in 2 phase:
1. First phase- Rapid uptake of ions- ‘free space/ outer space’- the
apoplast; passive; occurs through ion-channels, the trans-
membrane proteins which functions as selective pores.
2. Second phase- Ions are taken slowly- inner space- the
symplast; entry and exit of ions require metabolic energy
• Inward movement- Influx & Outer movement- Efflux
Translocation of Solutes
• Occurs through- xylem along with the ascending stream of water,
which is pulled up through the plant by transpirational pull.
• Xylem sap- mineral salts

18. Soil as reservoir of Essential elements
• Nutrients essential for growth & development- weathering &
breakdown of rocks
• Enrich soil with dissolved ions & inorganic salts
• Since nutrients derived from rock minerals so their role-
mineral nutrition
• Other function of soil- harbour nitrogen- fixing bacteria,
microbes, holds water, supplies air to the roots & act as a
matrix that stabilises the plant
• Deficiency of macro- nutrients (N, P, K, S, etc.) & micro-
nutrients (Cu, Zn, Fe, Mn, etc.)- supplied through fertilizers as
per need

19. Metabolism of Nitrogen
• Nitrogen- macronutrient; constituent of -amino acids, proteins,
hormones, chlorophylls & vitamins
• Plant gets N through soil (limited) & from air (atmospheric N2)
• Plants have to compete with microbes for limited nitrogen present
in soil
• Metabolism of Nitrogen:
1. Nitrogen Cycle
2. Biological Nitrogen fixation

20. Nitrogen Cycle
• Def.- A continuous series of natural processes by which nitrogen
passes successively from air to soil to organisms and back to air or
soil involving principally nitrogen fixation, nitrification, decay, and
denitrification
• The process of nitrogen cycle:
i. Nitrogen fixation
ii. Ammonification
iii. Nitrification
iv. Denitrification

21. Nitrogen Fixation:
• The process of conversion of nitrogen (N2) into ammonia (NH3)
• Lightning, ultraviolet radiations converts free nitrogen to nitrogen
oxides (NO, NO2, N2O); Industrial combustion, forest fires,
automobile exhausts and power-generating stations- sources of
atmospheric nitrogen oxides.
• Nitrogen oxides converts to Ammonia
N2 Nitrogen oxides NH3
Ammonification:
• The process of decomposition of organic nitrogen of plants and
animals into ammonia (NH3)
• Ammonia volatilises and re-enters the atmosphere but most of it
is converted into nitrate (NO2
-)

22. Nitrification:
• Ammonia is oxidised to nitrite (NO2
-) by the bacteria
Nitrosomonas / Nitrococcus.
• The nitrite is further oxidised to nitrate (NO3
-) with the help of the
bacterium Nitrobacter.
• These nitrifying bacteria are chemoautotrophs.
• Nitrate- absorbed by plants & transported to leaves where nitrate
reduce to form ammonia (NH3) & forms amine group of amino
acids
Denitrification:
• Nitrate present in the soil reduce to nitrogen by the process of
denitrification. Denitrification is carried by bacteria Pseudomonas
and Thiobacillus.

24. Biological Nitrogen Fixation
• Reduction of nitrogen to ammonia by living organisms is called
Biological Nitrogen Fixation (N2 NH3)
• Certain prokaryotes (bacteria) fixes nitrogen – enzyme
nitrogenase & called N2 fixers
• Nitrogen-fixing microbes can be classified as follows:
– Free living : Aerobic (Azotobacter, Beijernickia ), Anaerobic
(Rhodospirillum), Cyanobacteria (Nostoc, Anabaena),
Bacillus.
– Symbiotic – with leguminous plants (Rhizobium), with non-
leguminous plants (Frankia).

25. Symbiotic Nitrogen Fixation:
• Commonly seen in legume-bacteria relationship.
• Bacteria Rhizobium (rod- shaped) forms nodules at root in
legumes
• Nodules- small outgrowths on roots, central portion of nodule is
pink- leguminous haemoglobin or leg-haemoglobin
• Microbe, Frankia produces nitrogen-fixing nodules on the roots of
non-leguminous plants (e.g., Alnus).
• Rhizobium and Frankia are free living in soil, but as symbionts,
can fix atmospheric nitrogen.

26. Nodule Formation:
• Interaction between Rhizobium & roots of host plants
• Step involved includes:
1. Multiplication of Rhizobia & colonization of it around roots
2. Attachment of bacteria to epidermal & root hair cells
3. Root hair curls & bacteria invade root hair
4. An infection thread is produced- carries bacteria to cortex
5. Initiation of nodule formation in the cortex
6. Release of bacteria from the thread into the cells which leads
to the differentiation of specialised nitrogen fixing cells.
7. The nodule thus formed, establishes a direct vascular
connection with the host for exchange of nutrients.

27. • Root nodule- contains necessary biochemical components such
as the enzyme nitrogenase and leghaemoglobin.
• The enzyme nitrogenase is a Mo-Fe protein and catalyses the
conversion of atmospheric nitrogen to ammonia

28. • Nitogenase Enzyme:
• Highly sensitive to molecular oxygen, anaerobic condition
• Nodule- ensures enzyme is protected from oxygen due presence
of leg- haemoglobin (oxygen scavenger)
• Rhizobium- live as aerobes under free living condition
(Nitogenase- not operational) but during nitrogen fixing-
anaerobic (to protect nitrogenase)
• For enzyme to catalyse reaction- 8 ATP for each NH3 produced
• Energy required is obtained through respiration of host cells

29. Fate of Ammonia:
• Ammonia (toxic) once formed is protonated to form NH4
+ (ammonium)
ion
• Nitrate assimilate in most plants
• Ammonia (NH4
+) used to synthesise amino acids in plants:
1. Reductive amination- In these processes, ammonia reacts with α-
ketoglutaric acid and forms glutamic acid
2. Transamination
Transfer of amino group from one amino acid to the keto group of a keto
acid- Transaminase catalyses all such reactions.
Eg- Asparagine and glutamine - aspartic acid and glutamic acid
(asparagine synthetase and glutamine synthetase.)