Question

Which of the following is essential for nitrogen fixation in legumes?
A. Anthocyanin
B. Phycocyanin
C. Phycoerythrin
D. Leghaemoglobin

Answer 1

Hint: Nitrogen fixation bacteria like Rhizobium have a symbiotic association with legume plants.

Complete Answer:
- Legume plants such as alfalfa, soybeans, clover, etc, show symbiotic association with bacteria rhizobium, and this association is not obligatory.
- Symbiotic association is when two or more organisms are living together. When plants require nitrogen, it releases signals that attract rhizobium toward plants and attaches to the plant root which is the entry point for the bacteria and the site for nitrogen fixation.
- Genes of plants and rhizobium are expressed which leads to the formation of root nodules. The nodules contain oxygen-binding red pigment heme protein called leghemoglobin.
- As nitrogen-fixing enzyme nitrogenase is highly sensitive to oxygen, the leghemoglobin protects it from inactivation by the oxygen.

Therefore, the correct answer is option D. Leghaemoglobin.

Additional information: Beside free-living soil bacteria, blue-green algae (a bacterium), lichens, are some biological nitrogen fixation organisms.Bacteria and host legume interactions are highly specific.
For example, Rhizobium melilotii will only nodulate alfalfa legume plants. Structurally leg hemoglobins are similar to that of hemoglobin and myoglobins, they differ only in little sequence.

Note: Symbiotic association between legumes and rhizobia will not be always but only when plants require nitrogen.