Question

Chromosome doubling for producing polyploid plants is carried out by
A. PEG
B. NAA
C. EMS
D. Colchicine

Answer 1

Hint: It is a natural mitotic inhibitor that is obtained from a plant. There are mainly three kinds of polyploids, these are – autopolyploids, allopolyploids and segmental allopolyploids.

Complete Answer:
(I) The polyploids that have the same basic set of chromosomes multiplied are known as Autopolyploids.
For example, if a diploid species has two similar sets of chromosomes (AA), an autopolyploid will have three (AAA; autotriploid) or four (AAAA; autotetraploid) or more similar sets of chromosomes.
(II) The polyploids that result from doubling of chromosome number in the F1 hybrid that is derived from two markedly different species are called allopolyploids.
For example, if A represents a set of chromosomes (genome) in species X and B represents a set of chromosomes in species Y, then F1 hybrid will have one A and one B set of chromosomes represented as AB. The doubling of chromosomes in F1 hybrid (AB) will give rise to an allopolyploid genome AABB.
(III) Segmental polyploids are intermediate between autopolyploids and allopolyploids. The different genomes in allopolyploids are not totally different from each other. However, the segments of chromosomes are homologous to each other. They pair together and form multivalents during meiosis. Such polyploids are called segmental polyploids.

- Polyploids may occur naturally or may be artificially produced. Polyploidy in plants is mainly induced by treatment with aqueous solution of a drug called colchicine.
- Colchicine is an alkaloid extracted from seed and corm of a plant Colchicum autumnale. It has the property to arrest and break the spindle fibres during cell division which in turn prevents septum formation and causes doubling of chromosome number.
- For the first time successful doubling of chromosome number was established by Levan and Eigsti. Effective concentration of colchicine and direct contact of growing tissue with the drug solution are the prerequisites for the success of colchicine treatment

1. PEG (Poly Ethylene Glycol) is a synthetic compound used in somatic hybridisation method (hybridoma technology) as a fusion agent.
2. NAA (α-Naphthalene Acetic Acid) is a synthetic plant hormone. It belongs to the auxin family and induces rooting in plants.
3. EMS (Ethyl Methanesulfonate) is a chemical mutagen that causes random mutations in DNA and RNA by nucleotide substitution.

Thus, the correct answer is D, i.e., colchicine.

Note: It is surprising that colchicine does not affect the plant from which it is extracted i.e. Colchicum autumnale. This is due to the presence of an anti colchicine in the plant.