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  Section: General Biotechnology / Plant Biotechnology
 
 
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Biological Nitrogen Fixation

 
     
 
Factors Affecting Nodule Development
There are many factors which affect formation and longevity of nodules in roots of leguminous plants. These are (i) concentration of inorganic nutrients, (ii) soil temperature (optimum temperature between 25 and 30°C favors nodulation; it is inhibited at cooler and warmer extremes), (iii) light and shading (high light increases nodule numbers, whereas shading depresses nodule weight), (iv) CO2 concentration (high CO2 concentration increases nodule numbers), (v) addition of nitrogen (on addition of nitrogen both numbers and weight of nodules are reduced), and (vi) rhizosphere microorganisms. 

Moreover, carbohydrate storage in plant is increased in abundance of light and CO2 concentration as a result of which the numbers and weight of nodules are increased. Nitrogen retards carbohydrate concentration; therefore, carbohydrate : nitrogen ratio (CNR) theory may be applicable to support nodulation.
 

Content

Non-Symbiotic N2 fixation

 

Diazotrophy

 

Ecology of diazotrophs

 

Special features of diazotrophs

 

 

Sites of N2 fixation

 

 

Nitrogenase and reductants

 

 

Presence of hydrogenase

 

 

Self regulatory systems

 

Mechanism of N2 fixation

Symbiotic N2 fixation

 

Establishment of symbiosis

 

 

Host specificity and root hair curling

 

 

Infection of root hairs

 

 

Nodule development

 

 

Nodule development and maintenance

 

Factors affecting nodule development

 

Mechanism of N2 fixation in root nodules

Genetics of diazotrophs

 

Nod genes

 

Nif genes

 

 

Nif gene cloning

 

Hup genes


 
     
 
 
     



     
 
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