Question

The steps involved in the process of soyabean root nodule formation are:
A. Bacteria emits signals to stimulate root hairs to elongate
B. Cortex and pericycle cells begin division
C. Roots emits signals to attract Rhizobium
D. Bacteria within vesicles develop into bacteroids
Choose the correct answer from the options given below:

• A. B, C, D, A
• B. C, A, B, D
• C. A, C, B, D
• D. D, A, C, B

Hint:

Nodule order: Call (Roots attract) $\rightarrow$ Answer (Bacteria signal) $\rightarrow$ Build (Cells divide) $\rightarrow$ Fix (Become bacteroids).

Answer 1

The Correct Option is B

Concept: Nodule formation in legumes like soybean is a complex symbiotic process involving a specific "molecular dialogue" between the plant roots and Rhizobium bacteria.

Step 1: The Initial Attraction.
The process begins with the plant. The Roots emit signals (flavonoids) to attract Rhizobium (C). This establishes the first contact between the host and the symbiont.

Step 2: Bacterial Response and Host Change.
In response to the plant signals, the Bacteria emit signals (Nod factors) to stimulate root hairs to elongate (A) and curl. This captures the bacteria in a "shepherd's crook" structure.

Step 3: Invasion and Nodule Development.
As the infection thread moves inward, signals trigger the plant's internal tissues. The Cortex and pericycle cells begin division (B) to form the physical structure of the nodule.

Step 4: Final Differentiation.
Finally, after being released into the plant cells, the Bacteria within vesicles develop into bacteroids (D)—the specialized, non-dividing form of the bacteria that actually performs nitrogen fixation.