what is the difference between rhizobium and cyanobacteria on the way of fixing nitrogen for plant?
Answers
Answer:
Cyanobacteria fixation:
Cyanobacteria may fix the ubiquitously available CO2 and N2, and therefore cover the demand of the two most important elements.
The fixation of N2 comes at a high metabolic energy cost, but cyanobacteria are phototrophic organisms that use sunlight to cover their energy demand.
Nitrogenase, the enzyme complex responsible for the fixation of N2, is sensitive to oxygen and requires a near‐to‐anoxic environment.
Cyanobacteria are phototrophic organisms evolving oxygen and they developed various strategies to combine this with N2 fixation.
In order to fix N2, cyanobacteria separate the incompatible processes of oxygenic photosynthesis and N2 fixation spatially (in different cells) or temporally (during the night), or a combination of both.
N2 fixation in the ocean is restricted to the (sub)tropics and carried out by free‐living nonheterocystous filamentous and unicellular cyanobacteria and by symbiotic cyanobacteria living with microalgae.
Heterocystous cyanobacteria are found in freshwater, brackish water, terrestrial environments and symbiotic in plants and algae.
Cyanobacteria have a circadian clock that synchronises metabolic processes and allow for the fixation of N2.
Ribozium fixation:
common soil bacterium,
Rhizobium, invades the root and multiplies within the cortex cells. The plant supplies all the necessary nutrients and energy for the bacteria. Within a week after infection, small nodules are visible with the naked eye. In the field, small nodules can be seen 2-3 weeks after planting, depending on legume species and germination conditions. When nodules are young and not yet fixing nitrogen, they are usually white or grey inside. As nodules grow in size they gradually turn pink or reddish in color, indicating nitrogen fixation has started. The pink or red color is caused by leghemoglobin (similar to hemoglobin in blood) that controls oxygen flow to the bacteria.
Nodules on many perennial legumes such as alfalfa and clover are finger-like in shape. Mature nodules may actually resemble a hand with a center mass (palm) and protruding portions (fingers), although the entire nodule is generally less than 1/2 inch in diameter. Nodules on perennials are long-lived and will fix nitrogen through the entire growing season, as long as conditions are favorable. Most of the nodules (10-50 per large alfalfa plant) will be centered around the tap root.