This document summarizes nitrogen metabolism in plants. It discusses the significance of nitrogen for plant growth, the need for nitrogen fixation, and various methods of nitrogen fixation including biological and industrial processes. Biological nitrogen fixation is carried out by blue-green algae, free-living bacteria like Azotobacter, and symbiotic bacteria like Rhizobium. The steps of symbiotic nitrogen fixation between Rhizobium and legumes are described, including nodule formation, nitrogen fixation in the nodule, and assimilation of fixed nitrogen into amino acids in plants.

1. N I T R O G E N M E TA B O L I S M
I N P L A N T S
BY : D AYA N J I S H E R PA A N D
N A G A R A M S O W M YA
D E P T. O F B OTA N Y A N D P L A N T
P H Y S I O LO G Y

2. SIGNIFICANCE OF NITROGEN
• Main source of Nitrogen is air which contain about 78% percent Nitrogen
by volume.
• From air it reaches into the soil.
• Participates in protein synthesis.
• In the formation of protoplasm, Nucleic acid purines and pyrimidines
bases, chlorophyll ,alkaloids and many coenzymes.
• Deficiency –Chlorosis
• Reduction in cell division, cell growth, late flowering.

3. NEED FOR NITROGEN FIXATION
• Atmospheric N2 or molecular dinitrogen (N2) is relatively inert triply
bonded di atomic form , to be used in other ways.
• Does not easily react with other chemicals to form new compound.
• Fixation process frees Nitrogen atom from triply bonded diatomic form.
• Only some of the organism like insectivorous plant, certain bacteria,
blue green algae and few fungi have the potentiality to utilise Nitrogen
directly an fix it.

4. NITROGEN FIXATION
• It is the process by which nitrogen in the earths atmosphere is
converted into ammonia NH3 or other molecules available in living
organisms.
• The chemical process by which atmospheric N2 is assimilated into
organic compounds, especially by certain microorganisms as a part of
nitrogen cycle.
• From non usable form N2 into more reactive usable forms ammonia
,nitrate and nitrite

5. METHOD OF N2 FIXATION
INDUSTRAIL
ATMOSPHERIC
NON
BIOLOGICAL
SYMBIOTIC
NON-
SYMBIOTIC
BIOLOGICAL

6. ATMOSPHERIC NITROGEN FIXATION
• By photochemical and electrochemical reaction
N2+O2 2NO(nitric oxide)
• The Nitrous oxide formed combines with oxygen to form nitrogen dioxide.
2NO+O2 2NO2
• Nitrogen dioxide readily dissolve in water to product nitric and nitrous acids;
2NO2 +H2O HNO3+HNO2
• These acid readily release the hydrogen forming nitrate and nitrite ions which can be
readily utilized by plants and microorganisms.
HNO3 H++ NO3 (nitrate ions) , HNO2 H+ + NO2(nitrite ions)

7. INDUSTRIAL NITROGEN FIXATION
• The process that convert atmospheric nitrogen to ammonia by a
reaction with H2 using metal catalyst under high temperature and
pressures.
• The Haber process, also called the Haber –Bosch process, is an artificial
nitrogen fixation process and is the main industrial procedure for the
production of Ammonia today

8. BIOLOGICAL NITROGEN FIXATION
Carried out by
Blue green algae : Nostoc , Anabaena
Free living bacteria : Azotobacter
Symbiotic bacteria: Rhizobium
The overall stoichiometric of biological nitrogen fixation is represented by
following equation
N2+8H+ +16 ATP --------2NH3 + H2 + 16ADP + 16pI

9. • Biological nitrogen fixation occur in the presence of the enzyme
nitrogenase which is found inside the Nitrogen fixing prokaryote.
• The enzyme nitrogenase is in fact an enzyme complex consist of two
metallo-proteins .i.e. Fe- protein and Fe Mo- protein and none of these
two components alone can catalyse the reduction of N2 to NH3.
• A source of reducing equivalents (ferredoxin or flavodoxin in vivo), ATP
and proton are required.
• Nitrogenase enzyme complex is sensitive to O2 biological nitrogen
fixation require anaerobic condition.

10. • Leghaemoglobin acts as an oxygen scavenger and generate anaerobic condition for
nitrogen fixation.

11. SYMBIOTIC NITROGEN FIXATION
• The symbiosis between rhizobia and leguminous
host plant
• Family- leguminosae
• Rhizobium leguminosarum

12. STEPS INVOLVED IN SYMBIOTIC NITROGEN FIXATION
NODULE FORMATION
Growth stimulating substance such as biotin, thiamine, amino acids etc. are
secreted by the root of the symbiont which enhances the growth of Rhizobia
over other microbes.
The reaction between polysaccharides (cellulose ) present on the surface of
rhizobia cell and the lectin secreted on the root hair helps in the recognition of
the correct host plant by specific Rhizobium.
CURLING OF ROOT HAIR
• Bacteria release Nod factor, which results in curling of root hairs
• Then it forms the infection thread ( by the root cell) through the hair tip.

13. NODULE FORMATION AND LEGHAEMOGLOBIN
Rhizobia enter into the cell. The bacteria stimulates the inner cortical tissue to divide
form an organized mass of infected plant tissue which is protruded out and appear as
nodule
After their release into cortical cells the Rhizobia stop dividing and enlarge.

14. NITRIFICATION
Nitrification
occur in
two steps
NH3-N
Nitrosomonas
NO2-N
NO2-N
Nitrobacter
NO3-N
Significance of
Nitrification
the most plants, Nitrate is
the preferred chemical
form of Nitrogen uptake
from soil or water

15. NITROGEN ASSIMILATION
• It is the formation of organic nitrogen
compounds like amino acids from
inorganic compounds present in
environment.
• Plant absorb N2 from soil in the form
of Nitrates and ammonium ion.
SYNTHESIS OF AMINO ACIDS
α- ketoglutarate+ NH4 
Glutamate

16. TRANSAMINATION
Refers to the transfer of an amine group from one molecule to another.
This reaction is catalysed by the family of enzymes called transaminases.
Glutamic acids --- other amino acids synthesized

17. REFERENCES