Question

Rosette habit of cabbage can be changed by the application of
a. ABA
b. IAA
c. GA
d. Ethephon

Answer 1

Plant growth regulators are chemical substances that help to control the mechanism of growth in plants. These are small, simple organic molecules of diverse chemical composition produced naturally in higher plants that control the growth and other physiological functions. These are required by plants in very small amounts.

Complete answer:

ABA- It is a slightly acidic growth hormone that functions as a growth inhibitor by counteracting with other growth hormones. Its production is stimulated under stress conditions so it is also known as stress hormone.

IAA- Indole 3-Acetic acid is a natural auxin that performs many physiological activities in the plants like initiating and promoting cell division in tissues like cambium, apical dominance, root initiation, prevention of abscission layer, etc.

GA- The physiological effects of gibberellic acid are stem elongation, leaf expansion, reversal of dwarfism, breaking of dormancy, enzyme formation and bolting.
When plants like cabbage are treated with gibberellin, dwarf stem produces 6-8 feet tall plant. This is due to enormous elongation of internodes and such type of rapid growth in stem of rosette plants is called bolting.

Ethephon- It is the most widely used compound used as a source of ethylene. It is used to control fruit ripening in plants like tomatoes and apples.

Hence, the correct answer is option (C).

Note: Plant growth regulators are classified into two categories on the basis of functions they perform in the plant body:
Plant growth promoters- They exhibit growth promoting activities such as cell division, cell enlargement, flowering, etc.
Plant growth inhibitors- They are involved in various growth inhibiting activities like abscission and dormancy.