Soybean Root Nodule Formation Steps

The formation of root nodules in soybean is a complex symbiotic process involving specific signaling between the plant and Rhizobium bacteria. This process is crucial for nitrogen fixation.

Sequence of Nodule Formation Events

The correct sequence of events in soybean root nodule formation is:

1. C. Roots emits signals to attract Rhizobium: Soybean roots release chemical signals, primarily flavonoids, which attract free-living Rhizobium bacteria in the soil.
2. A. Bacteria emits signals to stimulate root hairs to elongate: In response to root signals, Rhizobium bacteria produce their own signals (Nod factors). These Nod factors cause the soybean root hairs to curl and deform, initiating infection.
3. B. Cortex and pericycle cells begin division: Concurrently with root hair curling and infection thread formation, the plant's cortical and pericycle cells are triggered to divide, forming the nodule primordium, which is the initial structure of the nodule.
4. D. Bacteria within vesicles develop into bacteroids: Once inside the plant cells within the developing nodule, the bacteria are released from the infection thread into membrane-bound vesicles. Here, they differentiate into specialized, nitrogen-fixing forms known as bacteroids.

Therefore, the correct order representing the key stages is C, A, B, D.