Mineral Nutrition

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PRÏÑÇÏPÅL STÅGËS ÏÑ THË ÑØDÜLË FØRMÅTÏØÑ

01

Rhizobia multiply and colonise the surroundings of

the roots and get attached to epidermal and root

hair cells.

Root hair curl and the bacteria invade the root-hair. 02

An infection thread is produced carrying the bacteria

into root cortex, where they initiate nodule formation.

03

The bacteria are released from thread into cells. It

leads to differentiation of specialised nitrogen fixing

cells.

04

The nodule establishes a direct vascular connection

with the host for exchange of nutrients.

05

Soil

particles

Root hair

Bacteria

Inner cortex and

pericycle cells

under division

Infection

thread

containing

bacteria

Mature nodule

Hook

Bacteria

(a)

(b)

(c)

(d)



Nodule contains nitrogenase enzyme & leg-haemoglobin.



Nitrogenase (Mo-Fe protein) catalyses the conversion of nitrogen to NH3,

the first stable product of N2 fixation.

N

+2 H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

N

N

Enzyme

Substrate

[nitrogen gas (N2)]

Reduction

Reduction

Reduction

Binding

of substrate

(nitrogenase)

Product

[ammonia (NH3)]

Release

of products

Free nitrogenase

can bind another

molecule of N2

+2 H

+2 H

H

H

N

H

N

N

N

N

N

N

N

N