Process of Nodule Formation in Legumes

Questions and Answers

Enriching the fertility of soil by contributing nitrogen through symbiotic nitrogen fixation by Rhizobium.

Through infection thread or at the point of emergence of lateral roots.

Leghaemoglobin

Nitrogenase

Auxin

Polysaccharides (correct)

Curling and branching of root hairs. Signup and view all the answers

Nodule. Signup and view all the answers

True Signup and view all the answers

Controls oxygen supply and protects enzyme nitrogenase in low oxygen conditions. Signup and view all the answers

Reduction of N2 to NH3 with the help of enzyme nitrogenase. Signup and view all the answers

Natural nitrogen fixation Signup and view all the answers

Study Notes

Legumes enrich soil fertility through symbiotic nitrogen fixation with Rhizobium, a practice recognized since ancient times.
Nodulation occurs when free-living Rhizobia infect host legumes via an infection thread or at lateral root emergence points.
Rhizobia transform into bacteroids, where nitrogen fixation takes place, within the nodules formed on the host roots.
Root cap cells secrete polysaccharides to create mucigel, which entraps high numbers of Rhizobia.
Initial plant response to Rhizobium is the curling and branching of root hairs, facilitating infection.
Rhizobium secretes localized auxin to soften cell walls at root hair surfaces, promoting bacteria entry.
The infection thread extends as the root hair grows, eventually trapping Rhizobia within deformed root hair cells.
The encapsulation of Rhizobia induces additional cell wall synthesis, leading to nodule formation that serves as a protective structure.

Nitrogen fixation is an anaerobic process where atmospheric nitrogen (N2) is converted into ammonia (NH3) through the action of nitrogenase.
Nitrogenase consists of two components: one containing iron (Fe) and molybdenum (Mo), while the second component lacks molybdenum.
Leghaemoglobin is crucial as it controls oxygen supply around the bacteroids, protecting nitrogenase from oxygen exposure, which can be detrimental to its activity.
The first nitrogen fixation intermediate is ammonia, which plants can absorb and utilize.

Nitrogen fixation transforms molecular nitrogen into nitrogenous compounds, making them accessible to plants.
Natural processes account for 10% of nitrogen fixation, while 90% occurs through biological means.
Nitrogen fixation can be divided into:
- Physical Nitrogen Fixation:
  - Includes both natural and industrial methods.
- Biological Nitrogen Fixation:
  - Primarily carried out by microbes such as Rhizobium in symbiotic relationships with legumes.