An autotrophic, prokaryotic, nitrogen fixing symbiont is present in

The correct option/answer is Cycas.

Let us understand the question step-by-step to see why Cycas contains an autotrophic, prokaryotic, nitrogen-fixing symbiont:

1. Understanding the Symbiont Characteristics:
- Prokaryotic: The organism lacks a membrane-bound nucleus and organelles.
- Autotrophic (specifically photoautotrophic): It can synthesize its own food using sunlight.
- Nitrogen-fixing: It has the ability to convert atmospheric nitrogen (N₂) into organic forms like ammonia (NH₃) that plants can use.
- Symbiont: It lives in a mutually beneficial relationship (symbiosis) with a host plant.

Cyanobacteria (specifically blue-green algae like Anabaena cycadae or Nostoc species) fit all these characteristics: they are prokaryotic, photosynthetic autotrophs, and carry out nitrogen fixation using specialized cells called heterocysts.

2. Analyzing the Host Plants (Options):
- Cycas: This is a gymnosperm that possesses specialized, dichotomously branched roots called coralloid roots. These roots grow near the soil surface and form a symbiotic association with nitrogen-fixing cyanobacteria (like Anabaena cycadae and Nostoc). The cyanobacteria live inside the middle cortex of these roots, providing fixed nitrogen to the plant while receiving shelter and carbohydrates in return.
- Cicer: Cicer arietinum (chickpea) is an angiosperm (legume). It forms symbiotic associations with Rhizobium bacteria in its root nodules. While Rhizobium is prokaryotic and nitrogen-fixing, it is a heterotrophic bacterium, not autotrophic.
- Pinus: Pinus is a gymnosperm that forms symbiotic associations with fungi (mycorrhizae) in its roots to assist in water and mineral absorption, but these fungi are eukaryotic, heterotrophic, and do not fix nitrogen.
- Sequoia: Sequoia is a giant gymnosperm that also associates with mycorrhizal fungi rather than nitrogen-fixing cyanobacteria.

Therefore, the plant that houses an autotrophic, prokaryotic, nitrogen-fixing symbiont is Cycas.