144. Nod gene products:
A. function as receptors of certain flavonoids
B. lack the ability to activate the expression of other Nod factors
C. cause activation of homeobox genes
D. are involved in photosynthesis

Understanding Nod Gene Products in Legume-Rhizobia Symbiosis

In the process of symbiotic nitrogen fixation between legumes and Rhizobium species, specific genes called Nod (nodulation) genes play a crucial role. These genes are vital for establishing a successful symbiotic interaction that leads to the formation of root nodules, where nitrogen fixation occurs.

What Are Nod Genes?

Nod genes are present in rhizobial bacteria and are responsible for producing proteins known as Nod gene products. These gene products are instrumental in recognizing plant signals and initiating the production of Nod factors, which are key signaling molecules that trigger root nodule formation in legumes.

Function of Nod Gene Products

A. Function as Receptors of Certain Flavonoids – Correct

This is the correct answer. Nod gene products, especially NodD, act as transcriptional activators and receptors for specific flavonoids released by the legume roots. These flavonoids are detected by NodD proteins, which in turn activate the transcription of other nod genes, leading to the synthesis of Nod factors.

• Flavonoids = signaling molecules secreted by legume roots

• NodD proteins = bacterial transcription factors that bind flavonoids

• Result = activation of nod gene expression and production of Nod factors

B. Lack the Ability to Activate the Expression of Other Nod Factors – Incorrect

On the contrary, Nod gene products such as NodD are essential for the activation of other nod genes. Without them, the biosynthesis of Nod factors does not occur.

C. Cause Activation of Homeobox Genes – Incorrect

Homeobox genes are involved in developmental processes in animals and plants, especially during embryogenesis. Nod gene products are not involved in activating homeobox genes.

D. Are Involved in Photosynthesis – Incorrect

Nod gene products are not related to photosynthesis. Their function is strictly associated with nodule formation and nitrogen fixation in the legume-rhizobia symbiosis.

Final Answer:

A. Function as receptors of certain flavonoids

Conclusion

Nod gene products, particularly NodD, are central to the communication between legumes and nitrogen-fixing rhizobia. By functioning as flavonoid receptors, they initiate a cascade that results in the production of Nod factors, ultimately leading to nodule formation and symbiotic nitrogen fixation—a process vital for sustainable agriculture and soil fertility.