What happens when we pour a few drops of distilled water in the crushed pieces of root nodules
Answers
Answer:
Rhizobium can fix nitrogen only in conditions such as those prevailing in a root nodule. These are very difficult to reproduce in the laboratory. Therefore the aim is to remove all microbes from outside nodule by chemical sterilisation. Then to grow Rhizobium by inoculating a fixed nitrogen-containing culture medium with a sample taken from inside the root nodule.
Rhizobium fixes gaseous nitrogen from the air into compounds plants can use to help them grow. An enzyme complex called nitrogenase catalyses this reaction. Nitrogenase activity is sensitive to the presence of oxygen. Root nodules may appear pink because they contain leghaemoglobin. This is the only haemoglobin found in plants. It absorbs oxygen and provides anaerobic conditions for bacteria in the root nodules.
Rhizobium is a facultative anaerobe – it can grow without oxygen. It can fix nitrogen only in anaerobic conditions. It is usually considered to be an obligate mutualist when fixing nitrogen in the root nodule. It can be grown when not in a root nodule on a that containing a source of fixed nitrogen and a source of carbon and energy. These sources are provided in the MYEA medium by yeast extract (nitrogen) and Mannitol (carbon and energy).
Rhizobium can also grow free-living in soil although not fixing nitrogen. Commercial legume seeds are often coated with these organisms. In soil the cells are rod-shaped (as when growing on MYEA medium), whereas in the nodule and when fixing nitrogen they are Y-shaped, known as ‘bacteroids’.
The nitrogen fixed by bacteria in root nodules will fertilise the soil. This happens when organic nitrogen compounds diffuse from plant material dispersed after death or eaten by animals, or after seed dispersal.