All of the following statements concerning the actinomycetes filamentous soil bacterium Frankia are correct except that Frankia :
- can induce root nodules on many plant species
- can fix nitrogen in the free-living state
- like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex
- forms specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids
The Correct Option is B
Solution and Explanation
Frankia is a type of filamentous bacterium capable of fixing nitrogen. It establishes a mutualistic relationship with a wide range of plants. Its infection mechanism involves root hair deformation, allowing it to penetrate cortical cells and trigger the formation of nodules similar to those induced by Rhizobium in legumes. Frankia produces three distinct cell types: sporangiospores, hyphae, and diazo-vesicles. During symbiosis, diazo-vesicles play a crucial role in supplying ample nitrogen to the host plant. They facilitate reductive nitrogen fixation, a process that converts atmospheric N2 gas into ammonia. To protect this process from molecular oxygen, numerous layers of tightly stacked hopanoid lipids act as a barrier.
So, the correct option is (B): can fix nitrogen in the free-living state
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Concepts Used:
Metabolism of Nitrogen
Nitrogen Cycle
The central part of nitrogen metabolism is the Nitrogen Cycle. A nitrogen molecule is made of two nitrogen atoms held together by a solid triple covalent bond (N ≡ N). There are three central pools of nitrogen – atmosphere, soil, and biomass.
Atmospheric Pool
The process of converting atmospheric nitrogen (N2) to ammonia (NH3) is called nitrogen fixation. Atmospheric nitrogen is rooted in three ways – biological, electrical, and industrial.
Soil Pool
The above processes rooted atmospheric nitrogen into the soil. This nitrogen is then taken up by plants and animals, accordingly.
Biomass Pool
When plants and animals die, the organic nitrogen within them has degraded to ammonia the process is ‘Ammonification‘ and it returns nitrogen back to the soil.