2. Minerals and its importance
Essential Minerals- Classification
Minerals- Roles and properties
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.
4. • Other than carbon, hydrogen, oxygen & sulphur- organic
molecules
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.
5. • Method involves growing plants in
purified water & specific mineral nutrient
saltsnutrient solution is aerated for
optimum growth
• Concentration required is
determinedadding/removing mineral
solution- identify essential elements &
deficiency
9. 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.
• Based on quantitative requirement by plants:
10. 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
11. 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.
12. 4. Elements altering water potential: Alters osmotic potential of
cell. Eg. K- opening and closing of Stomata; regulates water
potential of cells
13.
14.
15.
16.
17.
18. 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
19. • Excess micronutrientsToxicity Eg. Manganese toxicity
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
21. RESULT:
• Excess of manganese- Induce deficiencies of iron, magnesium and
calcium.
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
transmembrane 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
22. • Occurs through- xylem along with the ascending stream of water,
which is pulled up through the plant by transpirational pull.
• Xylem sap- mineral salts
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 rolemineral
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
23. • Deficiency of macro- nutrients (N, P, K, S, etc.) & micronutrients
(Cu, Zn, Fe, Mn, etc.)- supplied through fertilizers as per need
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
24. 2. Biological Nitrogen fixation
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
Nitrogen
Fixation:
• The process of conversion of nitrogen (N2) into ammonia (NH3)
25. • 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
-
)
Nitrification:
26. • 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:
27. • Nitrate present in the soil reduce to nitrogen by the process of
denitrification. Denitrification is carried by bacteria Pseudomonas
and Thiobacillus.
28.
29. 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
nonleguminous plants (Frankia).
Symbiotic Nitrogen Fixation:
• Commonly seen in legume-bacteria relationship.
30. • 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.
Nodule Formation:
31. • 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.
32. • 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
• Nitogenase Enzyme:
• Highly sensitive to molecular oxygen, anaerobic condition
33. • 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 fixinganaerobic (to protect
nitrogenase)
• For enzyme to catalyse reaction- 8 ATP for each NH3 produced
• Energy required is obtained through respiration of host cells
Fate of Ammonia:
34. • 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
αketoglutaric 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
