3. The process by which free nitrogen from the air is
combined with other elements to form organic
compounds that plants can use as nutrients.
Cyanobacteria and certain other
forms of bacteria,especially those
that live in the roots of legumes,
convert gaseous , nitrogen
into organic compounds.
The conversion of nitrogen
gas to nitrates by some
bacteria.
4.
5.
6.
7.
8.
9.
10.
11. 1. Rhizobia attracted to
root
2. Rhizobia attach to root
hairs
3. Root hair curling
4. Infection thread
formation
13. Biological nitrogen fixation was discovered by the German
agronomist Hermann Hellriegel and Dutch microbiologist
Martinus Beijerinck.
Biological nitrogen fixation can be represented by the
following equation, in which two moles of ammonia are
produced from one mole of nitrogen gas, at the expense
of 16 moles of ATP and a supply of electrons and protons
(hydrogen ions):
N2 + 8H+ + 8e– + 16 ATP = 2NH3 + H2 + 16ADP + 16 Pi
This reaction is performed exclusively by prokaryotes (the
bacteria and related organisms), using an enzyme complex
termed Nitrogenase. This enzyme consists of two proteins
– an iron protein and a molybdenum-iron protein.
15. Glucose-6-phosphate acts as a electron donor
Glucose-6-phosphate is converted to
phosphogluconic acid
NADPH donates electrons to ferrodoxin. Protons
released and ferrodoxin is reduced
Reduced ferrodoxin acts as electron carrier.
Donate electron to Fe-protein to reduce it.
Electrons released from ferrodoxin thus oxidized
Sucrose
(synthesize
d in leaves)
Sucrose (
in roots )
Glucose
and
fructose
Glucose-6-
phosphate
16. Reduced Fe-protein combines with ATP in the
presence of Mg +2
Second sub unit is activated and reduced
It donates electrons to N2 to NH3
Enzyme set free after complete reduction of
N2 to NH3