Formation of root nodules,Leghaemoglobin and Symbiotic nitrogen fixation

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Rhizobia ha the ability to fix free atmospheric nitrogen of soil in nodules.They enter in the root through the soft root hair or epidermis by damaging them.In the first stage of infection the bacteria grow very profusely (rapidly)in the tip of the root hair and form the long filament in the root called infection thread.This thread reaches the endodermis and pericycle through cortex.Cell of the cortex area goes on dividing  and  forms new nodules.This young nodules pushes the paranchyma and epidermis towards outside and form small swelling on the surface of root.The size pf root nodule vary according to the plant and their occurrence .It is not necessary all the bacteria ,which infect the root produce nodules.
According to Wipf and Cooper(1939) the root nodules always contains twice the number of chromosome as against of normal somatic tissue.If the root lack double number of chromosome ,their will be no formation of root nodules.If plant do not have root nodule it cannot perform symbiotic nitrogen fixation .
Leghaemoglobin
The effect nodules are large and pink in colour .This is due to the presence of red colour leghaemoglobin.This pigment is similar to the Haemoglobin of blood and it is found inside membrane envelop and bacteroid.The chemical composition of leghaemoglobin is haem-protein and it consists of haem molity attached to the peptied chain and represent the globin part of molecule .
Functons of Leghaemoglobin
1.It represent the active site of nitrogen absorption and reduction .
2.It act as a specific electron carrier .
3.It regulate the oxygen supply in the nodules.
Mechanism of symbiotic nitrogen fixation 
Rizobium in root nodules combined with leghaemoglobin  which regulate oxygen provide two hydrogen ions abd a electron which is given by krebs cycle ,electron transport system and ferrodoxine.Further react with ammine to give rise Diamide .Again Diamides produce Hydrazzine.Which react and give two molecules of ammonia which react with kitoacid which provided by TCA ,ETS and fertodoxine .The ammonia converted into ammino acid which is consumed by host .

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