Question

The chromosome number in plants can be increased by

• A. Hormone treatment
• B. Colchicine treatment
• C. Heat treatment
• D. None of the above

Answer 1

The correct option is B Colchicine treatment

Autotetraploids arise by the doubling of a 2n complement to 4n. This doubling can occur spontaneously, but it can also be induced artificially through the application of chemical agents that disrupt microtubule polymerization. This process normally takes place in the formation of spindle fibres in cells undergoing division.

A commonly used agent is colchicine, an alkaloid drug extracted from the autumn Crocus. In colchicine-treated cells, an S phase of the cell cycle occurs, but not chromosome segregation or cell division. As the treated cell enters telophase, a nuclear membrane forms around the entire doubled set of chromosomes. Thus, treating diploid (2n) cells for one cell cycle leads to tetraploids (4n), with exactly four copies of each type of chromosome. Treatment for an additional cell cycle produces octaploids (8n), and so forth. This method works in both plant and animal cells, but generally plants seem to be much more tolerant of polyploidy.