Looking for classes? Ksquare Career Institute, Bengaluru →
All of the following statements concerning the actinomycetous filamentous soil bacterium Frankia are correct EXCEPT that Frankia -
A
Forms specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids
B
Can induce root nodules on many plant species
C
Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex
D
Cannot fix nitrogen in the free-living state
Detailed Solution
Frankia is a filamentous actinomycete that forms nitrogen-fixing root nodules (actinorhizae) on certain non-leguminous plants such as Alnus and Casuarina.
It forms specialised thick-walled vesicles at the tips of its hyphae; the walls contain hopanoid lipids that limit the entry of oxygen and so protect the nitrogenase. This statement is correct.
In hosts such as Alnus it enters through deformed root hairs and stimulates cell division in the cortex, much as Rhizobium does. This statement is correct.
According to the answer key of this paper, the statement that Frankia can induce root nodules on many plant species is the incorrect one, because its host range is restricted to the actinorhizal plants (a limited number of genera such as Alnus, Casuarina and Myrica), unlike the wide range implied.
Note: Frankia can in fact fix nitrogen in the free-living state as well, inside its vesicles, so the statement that it cannot fix nitrogen in the free-living state is also inaccurate; this question is disputed.
It forms specialised thick-walled vesicles at the tips of its hyphae; the walls contain hopanoid lipids that limit the entry of oxygen and so protect the nitrogenase. This statement is correct.
In hosts such as Alnus it enters through deformed root hairs and stimulates cell division in the cortex, much as Rhizobium does. This statement is correct.
According to the answer key of this paper, the statement that Frankia can induce root nodules on many plant species is the incorrect one, because its host range is restricted to the actinorhizal plants (a limited number of genera such as Alnus, Casuarina and Myrica), unlike the wide range implied.
Note: Frankia can in fact fix nitrogen in the free-living state as well, inside its vesicles, so the statement that it cannot fix nitrogen in the free-living state is also inaccurate; this question is disputed.