Trace the events starting from coming in contact of rhizobium to a leguminous root till to the ammonia formation. add a note on importance of leg haemoglobin
Dear Student,
Rhizobium sp. is a bacteria that forms a symbiotic association with roots of leguminous plants. Formation of root nodule is a key event for establishment of symbiosis.
The steps include:
1. Plant and bacterium recognize each other and the bacteria attaches itself to the root hair. Root hairs release chemicals to attract the bacteria.
2. In response, Rhizobium produes nodulation factors (Nod factors), type of oligosaccharides that acts as a chemical signal to elicit morphological changes in the plant host and causes curling up of the root hair cell. The factors are produced by the nod genes.
3. At the tip of the root hair , the cell wall degenerates and Rhizobium invades the cell through a specialized intracellular tube- like structure called the infection thread (IT).
4. As IT grows further and invades the cortical cells, it brings along the bacteria to these cells.
5. As the bacteria rapidly multiplies in these cells, they form specialized bacterial cells called bacteriods (rod -shaped). The growth of bacteria forms swollen tumour like structures called nodules. Inside it, a group of bacteriods is surrounded by a peribacterial membrane, outside which leg haemoglobin is present. Many bacteriods are present in a nodule and are surrounded by the plant cytoplasmic membrane. This whole structure is called symbiosome and here nitrogen fixation starts.
6. A mature root nodule is formed that has its vascular tissue continuous with those of the roots. These tissues supply nutrients to the nodule and carry the fixed nitrogenous compounds to the rest of the plant.
Refer to the image below:
Role of leghaemoglobin :
This is a reddish- pink coloured protein pigment that is present in the root nodule and is a very efficient oxygen scavenger. Its main function is to maintain a low oxygen concentration for the proper functioning of nitrogenase enzyme as it requires hypoxic conditions to be functional and to deliver oxygen to the respiring bacteriods to meet the high ATP demands of N2 fixation.
Ammonia formation:
The free nitrogen is fixed by the bacteria and converted into ammonia by nitrogenase. The free nitrogen is bound to the enzyme and is not released until it is completely reduced to ammonia. For this process, a reducing power (NADPH, FMN2, ) and source of energy (ATP) is required. Refer to the image below:
The reaction of biological N2 fixation is:
N2 + 8e- + 8H+ +16ATP-------------> 2NH3 +16 ADP +16Pi
Regards
Rhizobium sp. is a bacteria that forms a symbiotic association with roots of leguminous plants. Formation of root nodule is a key event for establishment of symbiosis.
The steps include:
1. Plant and bacterium recognize each other and the bacteria attaches itself to the root hair. Root hairs release chemicals to attract the bacteria.
2. In response, Rhizobium produes nodulation factors (Nod factors), type of oligosaccharides that acts as a chemical signal to elicit morphological changes in the plant host and causes curling up of the root hair cell. The factors are produced by the nod genes.
3. At the tip of the root hair , the cell wall degenerates and Rhizobium invades the cell through a specialized intracellular tube- like structure called the infection thread (IT).
4. As IT grows further and invades the cortical cells, it brings along the bacteria to these cells.
5. As the bacteria rapidly multiplies in these cells, they form specialized bacterial cells called bacteriods (rod -shaped). The growth of bacteria forms swollen tumour like structures called nodules. Inside it, a group of bacteriods is surrounded by a peribacterial membrane, outside which leg haemoglobin is present. Many bacteriods are present in a nodule and are surrounded by the plant cytoplasmic membrane. This whole structure is called symbiosome and here nitrogen fixation starts.
6. A mature root nodule is formed that has its vascular tissue continuous with those of the roots. These tissues supply nutrients to the nodule and carry the fixed nitrogenous compounds to the rest of the plant.
Refer to the image below:
Role of leghaemoglobin :
This is a reddish- pink coloured protein pigment that is present in the root nodule and is a very efficient oxygen scavenger. Its main function is to maintain a low oxygen concentration for the proper functioning of nitrogenase enzyme as it requires hypoxic conditions to be functional and to deliver oxygen to the respiring bacteriods to meet the high ATP demands of N2 fixation.
Ammonia formation:
The free nitrogen is fixed by the bacteria and converted into ammonia by nitrogenase. The free nitrogen is bound to the enzyme and is not released until it is completely reduced to ammonia. For this process, a reducing power (NADPH, FMN2, ) and source of energy (ATP) is required. Refer to the image below:
The reaction of biological N2 fixation is:N2 + 8e- + 8H+ +16ATP-------------> 2NH3 +16 ADP +16Pi
Regards