2. • Nitrogen is present in atmosphere in organic
and inorganic form.
• 90% of N2 present in atmosphere is in organic
form and plants take only nitrogen in form of
ammonia and nitrates.
• Plants itself can’t fix the atmospheric nitrogen
because N2 atom having triple bond which
require 945kJ energy to break this bond.
NITROGEN IN ATMOSPHERE
3. • Major substance in plants next to water.
• Building blocks
• Constituent elements of chlorophyll,
cytochromes, alkaloids and many vitamins.
• Play important role in metabolism , growth
reproduction.
NITROGEN IS ESSENTIAL FOR PLANT
GROWTH
5. TYPES OF NITROGEN FIXATION
NITROGEN FIXATION
NON -
BIOLOGICAL
BIOLOGICAL
NON-
SYMBIOTIC
SYMBIOTIC
6. NITROGEN FIXATION
NON-BIOLOGICAL (ATMOSPHERIC) NITROGEN
FIXATION
N2 lightining and photochemical rxn NO3-
10% of nitrogen is converted into nitrate.
BIOLOGICAL NITROGEN FIXATION
N2 nitrifying bacteria NH4+
90% of nitrogen is converted into ammonia.
7. TWO TYPES OF BIOLOGICAL FIXATION
• NON-SYMBIOTIC
• SYMBIOTIC
8. NON-SYMBIOTIC
• Fixation is carried out by free living
microorganism.
• And by some blue green algae: Oscillatoria,
Nostoc, Anabaena etc.
Aerobic bacteria
(eg: Azotobacter ,
Azospirrilum)
Anaerobic bacteria
(eg:Clostridium,
Chlorobium)
9. SYMBIOTIC
• Fixation of free nitrogen by microorganisms in
soil living symbiotically inside the plant.
Nodule formed
(root nodules eg:
bacterial-Rhizobium
forms nodules
Stem nodules eg:
Sesbania)
Nodule not formed
(eg: Azolla-Anabaena
association
Cycas –Nostoc and
Anabaena association)
10. SYMBIOTIC NITROGEN FIXATION
(in non-leguminous plant)
• Some other plant also produces root nodules
Alnus - Frankia
Parasponia – Rhizobium
• Gymnosperm root -Podocarpus
11. SYMBIOTIC NITROGEN FIXATION
(in leguminous plant)
• Association with roots of plant provides –
- food and shelter to bacteria
- bacteria supply fixed nitrogen to plant.
• And these nitrogen fixing bacteria is called
Diazotrophs.
• 2500 species of family leguminosae (pea,
beans, soybean,alfa-alfa) produce root
nodules with Rhizobium species.
12. NITRATES ARE RECYCLED VIA
MICROBES
Nitrification
Nitrification
Ammonium NH4
+
Ammonification
Nitrite NO2
-
Soil organic nitrogen
Animal
protein
Root
uptake
Nitrate
NO3
-
Plant
protein
14. Nitrification
• Inorganic NH4+ nitrosomonas genera NO2-(nitrite)
nitrobacter genera
NO3-(nitrate)
These nitrifying bacteria are called
chemoautotrophs .
It is oxidative and energic process.
15. Liebig’s law of minimum
Growth is controlled not by the total of
resources available ,but by the resources
present in minimum amount . Only by
increasing the amount of the limiting nutrient
growth of a plant can be improved
16. DENITRIFICATION
• Denitrifying bacteria uses nitrates as final e-
acceptor rather than O2 during repiration.
• Ex: Thiobacillus denitrificans , Micrococcus
denitrificans.
• NO3- NO2- NO N2O N2
• This process occur in anerobic condition.
17. Plant utilize nitrogen in form of NH4+.So NO3- and
NO2- must be changed into NH4+.
NO3- NO2- NH4+ amino acid
amino acid
NH4+ & NO3-(absorb most)
NO2-(less absorb)
r
o
o
t
Plant
18. Conversion of Nitrate into Nitrite
• Reductive process.
• Nitrate reductase enzyme is involved.
• Electron donar is NADPH or NADH and
released e- is accepted by NO2.
• Process occur in cytosol.
NADPH NAD(P)+
NO3- nitrate reductase NO2-
• Nitrate reductase is homodimer with 3
prosthetic group(FAD,heme,Mo).
19. Conversion of nitrite into ammonia
• Reductive process.
• Enzyme is nitrite reductase.
• This process occur in plastids of shoot and
proplastids of root.
• NADPH/reduced Fd are electron donor.
• Fe4-S4, sirroheme, are two prosthetic group for
this enzyme.
• NO2- nitrite reductase NH4+
20. • Now the conversion of ammonia into ammino
acid includes two pathways:
• Minor pathway
• Major pathway
21. Minor pathway
-ketogluterate + NH4+ NADH glutamate
This pathway is present in all organism including
human beings also. This is the process of reductive
amination.
NH4+,NADH
22. Major pathway
NH4+ + glutamate ATP dependent/ Mg+2,Mn glutamine
This process occur in all organism
23. • Glutamine plant bacteria glutamate
• glutamine + -ketogluterate reduction NADH
glutamate synthase
2molecule
of glutamate
This process occur in only plants and bacteria.
Most of the NH4+ is incorporated into glutamate.
24. Transamination
• Amino acid (glutamate/ glutamine)
transaminase
another amino acid
So different type of amino acid can be formed
due to this process.
25. NODULE FORMATION IN ROOTS OF
LEGUMINOUS PLANTS
• RHIZOBIUM
• Gram negative
• Non spore forming
• Micro – aerobic
• Belongs to proteobacteria
• Types of rhizobium
Bradyrhizobium-slow growing sp.
Rhizobium- fast growing sp.
26. • Roots of leguminous plants secrete flavinoid ,
isoflavinoid , homoserine compound.
• These compounds are chemotactic so attract
rhizobium bacteria & induces the expression
of nodD gene
• nodD gene nodD protein
activates
nod D factor(nod A,
nod B,nodC)
27. Cont…….
• Protein rhicadhesin is Ca+ binding protein
responsible for attachment of bacteria to
surface roots of plant.
28. CHEMICAL NATURE OF nod D FACTOR
• It is a Lipochitin oilgosaccharide.
• Basic unit is n-acetyl d-glucosamine having
B - 1,4 glycosidic bond.
nodD factor
29. ACTION OF nodD FACTOR
• Curling of root hair
• Mitogenic agent so enhance the cell division
in cortical cells which produces an outgrowth
called nodule.
30. CURLING OF ROOT HAIR
• Bacteria attaches to root
hair
• Plasma membrane
invaginates
• Invaginate memberane
elongates and forms
infection thread (produce
golgi derived membrane
vesicles)
• Membrane continues to
elongate
31. FORMATION OF ROOT NODULE
• Bacterial cell reaches upto
cortical cells
• Bacterial cell divide in extra-
ordinary manner
• Membrane bound structures are
formed called bacteriods
• Covered by peribacterium
membrane
• Bacteriod stops to divide.
