Question

Coralloid roots help Cycas in?

Answer 1

Hint:
Coralloid roots are irregular, dichotomously branched, negatively geotropic, coral like roots which do not have root hairs and root caps. The coralloid roots contain symbiotic cyanobacteria like Nostoc and Anabaena, which fix nitrogen.

Complete answer:
In Cycas, roots are of two types: long-branched geotropic normal roots and short-branched apogeotropic roots, which are known as coralloid roots because of their irregular, coral like appearance. The coralloid roots contain symbiotic (mutually living) cyanobacteria also known as blue-green algae which fix atmospheric nitrogen and, in association with root tissues, produce some beneficial amino acids like citrulline and asparagine. The cyanobacteria have the unusual ability to form chains (filaments) of photosynthetic cells. All those that can become cyano points have the characteristic of forming:
Hormogonia: These are elongated, thin and mobile filaments, which are a kind of transient escape unit to reach the best condition of living. Hormogonia are induced by red light, auxin, chemical mediator of the host, changing of enlightenment, lack of nutrients.
Heterocysts: These are specialized, oval-shaped cells that seem larger than the other cells of a filament. They are able to fix nitrogen and are not movable. They are designed to protect denitrogenase (an enzyme needed to fix nitrogen) from oxygen. However, they are not totally closed, for they are able to communicate with their lateral vegetative neighbours in an incredible cooperation totally unusual for bacteria. Heterocysts are induced by the absence of nitrogen.

Note: Coralloid roots are negatively geotropic (apogeotropic) roots found in Cycads. The middle cortex of coralloid roots contains nitrogen fixing species of cyanobacteria named Nostoc and Anabaena. Thus, coralloid roots play an important role in supplying nitrogen to plants.