Question

Symbiotic nitrogen fixation in non-leguminous plants is carried out by
A. Azotobacter
B. Bradyrhizobium
C. Clostridium
D. Frankia

Answer 1

Hint: The symbiotic association of non-leguminous plants which help them in their nitrogen requirement is with the fungi of Actinomycetes whereas the leguminous plants associate themselves with bacteria.

Complete answer:
Plants cannot take nitrogen from the atmosphere and they rely on the different forms of nitrogen so that they can absorb it and utilize it in their metabolism processes. The forms which plants can take are nitrate and nitrites.
 The leguminous plants form a symbiotic relationship with the bacteria which help the plants in getting nitrogen. They do so by transforming the atmospheric nitrogen into a form suitable for plants and then fix it in the soil from where the plants can take them with the help of root nodules. These bacteria can either be free living or they can live on the root nodules of plants.
The same mechanism Is followed by the non-leguminous plants. But instead of the bacteria the non-leguminous plant forms a relationship with the fungi. The class of fungi with which they associate is Actinomycetes.
Among all the given options, only one of them is fungi and the rest all of them are bacteria. The bacteria in the option are Clostridium, Azotobacter, and Bradyrhizobium. The only fungi of the group is Frankia. It is situated at the root nodules and in exchange with the nitrogen it gets sugar and other nutrients from the plant.
So, the correct answer is “Option D”.

Note:
The bacteria Clostridium which is given in the option is a nitrogen fixing bacteria but also it is a pathogen which is responsible for causing various harmful diseases like tetanus, diarrhea. The cause of this bacteria causing problems is because of the modification in its 16s rRNA.