Question

Besides paddy fields, cyanobacteria are also found inside vegetative part of

• A. Pinus
• B. Cycas
• C. Equisetum
• D. Psilotum

Hint:

Remember specific symbiotic relationships in plants:
- Legumes: Host *Rhizobium* bacteria in root nodules for nitrogen fixation.
- *Cycas*: Has coralloid roots with cyanobacteria for nitrogen fixation.
- Lichens: Symbiosis between fungi and algae/cyanobacteria.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify a plant whose vegetative parts host cyanobacteria in a symbiotic relationship, in addition to their known presence in paddy fields (where they contribute to nitrogen fixation).

Step 3: Detailed Explanation:
* Cyanobacteria and Symbiosis: Cyanobacteria (like *Nostoc* and *Anabaena*) are known for their ability to fix atmospheric nitrogen. They form symbiotic associations with various plants, where the cyanobacteria provide fixed nitrogen to the plant, and the plant provides a protective environment and nutrients to the cyanobacteria.
* Paddy fields: Cyanobacteria contribute to nitrogen fixation in paddy fields, benefiting rice cultivation.
* Cycas: *Cycas* is a genus of cycads, which are gymnosperms. *Cycas* plants have specialized roots called coralloid roots that grow upwards and contain symbiotic cyanobacteria (e.g., *Nostoc* and *Anabaena*). These cyanobacteria fix atmospheric nitrogen, providing it to the *Cycas* plant. The coralloid roots are a vegetative part of the plant.
* Pinus: *Pinus* (pine) is another gymnosperm, but it forms symbiotic relationships with mycorrhizal fungi, not cyanobacteria, in its roots.
* Equisetum and Psilotum: These are pteridophytes (ferns and fern allies) and are not typically known for symbiotic associations with cyanobacteria in their vegetative parts.

Step 4: Final Answer:
Cyanobacteria are also found inside the vegetative part of *Cycas*.

Answer 2

Understanding why cyanobacteria team up with certain plants at all, through nitrogen fixation, makes it straightforward to pick out which plant among these options hosts them.

1. Pinus: Pine trees are gymnosperms that rely on a symbiosis with mycorrhizal fungi around their roots to improve water and mineral uptake, not on cyanobacteria, so this option does not fit.
2. Cycas: Cycas, another gymnosperm, develops special upward-growing roots called coralloid roots. Inside these roots, cyanobacteria such as Nostoc and Anabaena live symbiotically; they carry out nitrogen fixation using the enzyme nitrogenase, housed in specialised cells called heterocysts that maintain the oxygen-free environment nitrogenase needs. In return for fixed nitrogen compounds, the cyanobacteria receive shelter and nutrients from the plant. This coralloid root is a genuine vegetative structure of Cycas, matching the question's requirement.
3. Equisetum: This is a pteridophyte (a horsetail), and it is not known for hosting a cyanobacterial symbiosis in its vegetative tissue.
4. Psilotum: Also a pteridophyte, and similarly lacks any well-known cyanobacterial partnership of this kind.

The presence of coralloid roots specifically adapted to house nitrogen-fixing cyanobacteria makes Cycas the plant in question.

Therefore, the correct answer is Cycas.