In greengram, nitrogen fixation starts at the age of
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- Initial Nodule Formation: 10-14 days after sowing.
- Initiation of Nitrogen Fixation: 18-21 days after sowing.
Active, healthy nodules can be identified by their pinkish-red interior, which indicates the presence of leghemoglobin.
Step 1: Understanding the Concept:
Legumes like greengram (Vigna radiata) form a symbiotic relationship with Rhizobium bacteria.
The bacteria colonize the plant's root hairs, forming specialized structures called nodules where they convert atmospheric nitrogen into a form the plant can use. Detailed Explanation:
The establishment of active nitrogen fixation is a gradual biological process:
- After seed germination, the roots release chemical signals (flavonoids) that attract Rhizobium bacteria.
- The bacteria infect the root hairs, initiating cell division that forms the root nodules.
- This infection and early nodule development phase takes about 10 to 14 days.
- By 15 to 18 days, the nodules develop functional vascular connections with the plant.
- Active nitrogen fixation (mediated by the nitrogenase enzyme) begins around 18 to 21 days after sowing.
- At this stage, the nodules develop a pinkish-red interior due to the presence of leghemoglobin, which regulates oxygen levels to protect the nitrogenase enzyme.
- Nitrogen fixation increases as the plant grows, peaking during the flowering stage (around 35 to 45 days) before declining as the plant matures. Step 2: Final Answer:
In greengram, symbiotic nitrogen fixation begins 18-21 days after sowing.
