What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobiuml What is their role inN2fixation?

The conditions necessary for the fixation of atmospheric nitrogen by Rhizobium bacteria, which form symbiotic associations with leguminous plants, include:

1. Presence of Leguminous Plants: Rhizobium bacteria form symbiotic relationships with leguminous plants, such as peas, beans, and clover. These plants provide the bacteria with a suitable habitat within specialized structures called root nodules.

2. Presence of Root Nodules: Rhizobium bacteria infect the root hairs of leguminous plants and induce the formation of specialized structures called root nodules. Inside these nodules, the bacteria colonize plant cells and establish a symbiotic relationship with the host plant.

3. Adequate Oxygen Levels: The process of nitrogen fixation requires anaerobic conditions because the enzyme nitrogenase, responsible for converting atmospheric nitrogen (N2) into ammonia (NH3), is highly sensitive to oxygen. Therefore, the interior of the root nodules maintains low oxygen levels to facilitate nitrogen fixation.

4. Presence of Leghemoglobin: Leghemoglobin, a protein similar to hemoglobin found in animals, plays a crucial role in maintaining low oxygen levels within the root nodules. Leghemoglobin binds and transports oxygen, preventing its accumulation in the nodule interior and protecting nitrogenase from oxygen damage.

5. Optimal pH and Temperature: Rhizobium bacteria function optimally under specific pH and temperature conditions conducive to their growth and metabolic activity. The pH range for optimal nitrogen fixation varies depending on the specific Rhizobium strain and environmental conditions.

The role of Rhizobium bacteria in nitrogen fixation involves several steps:

1. Infection and Nodule Formation: Rhizobium bacteria colonize the root hairs of leguminous plants and trigger the formation of root nodules through a series of molecular signals and chemical responses. The plant cells undergo structural and physiological changes to accommodate the bacteria and form symbiotic associations.

2. Nitrogen Fixation: Within the root nodules, Rhizobium bacteria possess the enzyme nitrogenase, which catalyzes the conversion of atmospheric nitrogen (N2) gas into ammonia (NH3), a form of nitrogen that plants can readily assimilate. This process, known as nitrogen fixation, provides the host plant with a direct source of nitrogen for essential metabolic processes, including protein synthesis and growth.

3. Ammonium Assimilation: Once produced, ammonia (NH3) is assimilated by the plant and incorporated into organic compounds, such as amino acids, nucleotides, and chlorophyll. These nitrogen-containing compounds are essential for various cellular functions and contribute to the overall growth and development of the plant.

In summary, Rhizobium bacteria play a vital role in nitrogen fixation by establishing symbiotic relationships with leguminous plants and converting atmospheric nitrogen into a form that can be utilized by the host plant for growth and development. The conditions necessary for nitrogen fixation include the presence of leguminous plants, root nodules, low oxygen levels, optimal pH and temperature, and the presence of leghemoglobin to protect nitrogenase from oxygen damage.