Biological Fixation cont.
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The growth of all organisms depend on the availability of Nitrogen (e.g. amino acids)
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Nitrogen in the form of Dinitrogen (N2) makes up 80% of the air we breathe but is
essentially inert due to the triple bond (NN)
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In order for nitrogen to be used for growth it must be "fixed" (combined) in the form
of ammonium (NH4) or nitrate (NO3) ions.
Three processes are responsible for most of the nitrogen fixation in the biosphere:
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atmospheric fixation
biological fixation
industrial fixation
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Biological nitrogen fixation requires a complex set of enzymes and a huge
expenditure of ATP.
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Although the first stable product of the process is ammonia, this is quickly
incorporated into protein and other organic nitrogen compounds.
Nodulation in Legumes
Infection Process
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Attachment
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Root hair curling
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Localized cell wall degradation
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Infection thread
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Cortical cell differentiation
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Rhizobia released into cytoplasm
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Bacterioid differentiation (symbiosome formation)
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Induction of nodulins
Nodule Metabolism
Oxygen metabolism
• Variable diffusion barrier
• Leghemoglobin
Nitrogen metabolism
• NH3 diffuses to cytosol
• Assimilation by GOGAT
• Conversion to organic-N for transport
Carbon metabolism
• Sucrose converted to dicarboxylic acids
• Functioning TCA in bacteroids
• C stored in nodules as starch