POGONATUM : morphology, anatomy, reproduction etc.
Biological Nitrogen fixation In legumes pptx
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12. The heterocysts differ from the vegetative cells and
occur between them along the length of the trichome at
some regular intervals
Heterocysts
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15. large size, ii) thicker walls,
iii) homogenous transparent, pale yellowish
contents iv) a distinct pore either at both ends.
Position of heterocysts in the trichomes.
In some genera they occur in pairs
(Anbaenopsis, and rarely in chain.
When they singly are either terminal
(Anbaena) or intercalary in position
(Nostoc,).
Heterocysts
16. Factors controlling heterocyst formation
The reproduction of heterocysts increases under conditions of
low light , increase in the amount of phosphate in the medium
depends on the availability of carbon and ATP
Absence of carbon dioxide inhibited heterocyst
formation
-The concentration of nitrogen in the medium above a
certain level results in complete inhibition of heterocyst
production
17. Function of Heterocysts
Storehouses of reserve food material or enzymatic
substances
produce substances which stimulate growth and cell
division
Play role in sporulation
Sites of nitrogen fixation
Locus for filament breakage
26. It is the sequence of biochemical changes form free
atmospheric N2 to
complex organic compounds in plant and animal tissues
to simple inorganic compounds (ammonia, nitrate)
release of molecular nitrogen (N2) back to the atmosphere
Nitrogen cycle
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33. Nitrogen fixation
Nitrogen fixation is the natural process, either biological or
abiotic, by which nitrogen (N2) in the atmosphere is converted into
ammonia (NH3).
This process is essential for life because fixed nitrogen is required
to biosynthesize the basic building blocks of life, e.g., nucleotides
for DNA and RNA and amino acids for proteins. Nitrogen fixation
also refers to other biological conversions of nitrogen, such as its
conversion to nitrogen dioxide
34. Microorganisms that fix nitrogen are bacteria
called diazotrophs.
Some higher plants, and some animals (termites),
have formed associations (symbioses) with
diazotrophs.
Nitrogen fixation also occurs as a result of non-
biological processes. These include lightning,
industrially through the Haber-Bosch Process, and
combustion
Biological nitrogen fixation was discovered by the
Dutch microbiologist Martinus Beijerinck.
37. Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is
converted to ammonia by an enzyme called nitrogenase
The reaction for BNF is:
N2 + 8 H+ + 8 e− → 2 NH3 + H2
The process is coupled to the hydrolysis of 16 equivalents of ATP and is
accompanied by the co-formation of one molecule of H2. In free-living
diazotrophs, the nitrogenase-generated ammonium is assimilated into
glutamate through the glutamine synthetase/glutamate synthase
pathway.
Biological N2 Fixation
39. • Enzymes responsible for nitrogenase action
are very susceptible to destruction by oxygen.
(In fact, many bacteria cease production of the
enzyme in the presence of oxygen).
• Many nitrogen-fixing organisms exist only in
anaerobic conditions, respiring to draw down
oxygen levels, or binding the oxygen with a
protein such as Leghemoglobin.
41. Nitrogen fixation by cyanobacteria
• Cyanobacteria inhabit nearly all illuminated environments on Earth
and play key roles in the carbon and nitrogen cycle of the
biosphere.
• In general, cyanobacteria are able to utilize a variety of inorganic
and organic sources of combined nitrogen, like nitrate, nitrite,
ammonium, urea, or some amino acids.
• Several cyanobacterial strains are also capable of diazotrophic
growth.
• Genome sequencing has provided a large amount of information on
the genetic basis of nitrogen metabolism and its control in different
cyanobacteria.
• Comparative genomics, together with functional studies, has led to
a significant advance in this field over the past years.
• 2-Oxoglutarate has turned out to be the central signalling molecule
reflecting the carbon/nitrogen balance of cyanobacteria.
• .
42. • Central players of nitrogen control are the global
transcriptional factor NtcA, which controls the expression
of many genes involved in nitrogen metabolism, as well as
the PII signalling protein, which fine-tunes cellular
activities in response to changing C/N conditions. These
two proteins are sensors of the cellular 2-oxoglutarate level
and have been conserved in all cyanobacteria. In contrast,
the adaptation to nitrogen starvation involves
heterogeneous responses in different strains
• Nitrogen fixation by cyanobacteria in coral reefs can fix
twice the amount of nitrogen than on land–around 1.8 kg of
nitrogen is fixed per hectare per day
