Question

Coralloid roots contain symbiotic cyanobacteria, which fix nitrogen and in association with root tissues, produce beneficial amino acids. Which of the gymnosperms exhibit this type of roots?
A. Cycas
B. Pinus
C. Lycopodium
D. Dryopteris

Answer 1

Hint: The coralloid root is developed in the Cycas. It is produced in clusters at the base of the stem and comes out over the ground. It is dichotomously branched and a greenish-brown in a colour. It contains the algal zone in the cortex. The plant takes several years to grow, sexual reproduction takes place after 10 years of exclusive vegetative growth

Complete step by step answer: The coralloid roots are found in the Cycas which contains the symbiotic cyanobacteria. These organisms perform the fixation of nitrogen with the help of nitrogenase. The nitrogen fixation produces beneficial amino acids such as asparagine and the citrulline for the growth of the plant. The cyanobacteria present inside the coralloid roots of Cycas are chemoheterotrophic and specifically adapted to symbiosis. Not all the cyanobacteria live in symbiosis, only a few species form association with the Cycas. All Cyanobacteria in the symbiosis with the Cycas have the ability to fix the nitrogen. In addition to the normal roots, Cycas develop specialized organs called the coralloid roots. Coralloid roots are formed in clusters at the base of the stem because of its apogeotropic growth that protrudes out over the ground.
Therefore, the correct answer is option A.

Note: The coralloid roots of Cycas are the harbour blue-green algae like the Nostoc, Anabaena, etc. and are not the VAM (vesicular-arbuscular mycorrhiza) which shows a symbiotic association with the fungus. Cycas species are threatened worldwide and almost all the species are listed in IUCN Red List.