Question

Write short notes on rhizobium-legume symbiosis.

Answer 1

Certain nitrogen-fixing bacteria, such as Rhizobium species, form a symbiotic association with the roots of leguminous plants. The bacteria enter the root hairs and stimulate the proliferation of inner cortical cells, leading to the formation of root nodules. These nodules are reddish due to the pigment leghemoglobin. Inside these nodules, Rhizobium bacteria fix atmospheric nitrogen into ammonium ions, which the plant can use for amino acid and protein synthesis. The plant provides carbohydrates to the bacteria as an energy source. This symbiosis enriches the soil with nitrogen, improving soil fertility and benefiting subsequent crops. Legumes inoculated with Rhizobium can fix 50 to 150 kg of nitrogen per hectare. This biological nitrogen fixation is eco-friendly and reduces the need for chemical fertilizers.