Autotrophic Nitrogen Fixing Symbiont in Cycas

Autotrophic nitrogen fixing symbiont refers to a microorganism that can fix atmospheric nitrogen into a usable form for plants. Such symbionts are commonly found in the root nodules of leguminous plants. However, one such symbiont is also found in Cycas plants.

Cycas plants are gymnosperms that belong to the family Cycadaceae. They are commonly called cycads and are native to tropical and subtropical regions. Cycas plants have an association with a prokaryotic nitrogen-fixing symbiont called Cyanobacteria.

Cyanobacteria are photosynthetic prokaryotes that can also fix atmospheric nitrogen. They are commonly found in aquatic environments, but some species can also grow in association with plants. In Cycas plants, the Cyanobacteria are found in specialized structures called coralloid roots.

The coralloid roots of Cycas plants are modified roots that have a symbiotic association with the cyanobacteria. These roots have a spongy texture and are pinkish in color due to the presence of pigments called phycoerythrins. The Cyanobacteria present in these roots fix atmospheric nitrogen and provide the plant with a source of nitrogen.

In addition to the Cyanobacteria, Cycas plants also have a mycorrhizal association with fungi. The mycorrhizal fungi help the plant absorb nutrients from the soil in exchange for carbohydrates produced by the plant through photosynthesis.

Therefore, the correct answer to the given question is option B, Cycas.