Question

Which one of the following generally acts as an antagonist to gibberellins?
A. NAA
B. ABA
C. IAA
D. Zeatin

Answer 1

Hint: Like hormones like insulin, glucagon, adrenaline, etc. in humans, plants also have hormones that are responsible for the growth and maturation of the plant. Plant hormones are also called ‘Phytohormones’.

Complete answer: Gibberellins are found in higher plants and are acidic in nature. It allows the elongation of stem and internodes. It is also responsible for the sex expression of plants e.g. it promotes maleness in cannabis. They also induce flowering and delay senescence.
Options A and C: Auxin meaning ‘to grow’ is the phytohormone responsible for the growth of the roots and promotes apical dominance. It is present in all parts of the plant and is transported. Indole-3-acetic acid (IAA) and Indole butyric acid are natural auxins present in plants. 2,4-D and NAA are artificially produced.
Option B: Abscisic acid or ABA, in short, promotes the senescence of leaf, i.e., fall of leaves happens due to abscisic acid. Gibberellin breaks the dormancy of seeds and as opposed to Abscisic acid, which induces dormancy of buds and seeds.
Option D: Cytokinins are named from the name cytokinesis and are responsible for cell division and growth of shoot and stem. It also allows the formation of the chloroplast. Natural cytokinins present in plants are Zeatin and isopentenyl adenine. It also delays the senescence of leaves and overcomes apical dominance. The artificially produced cytokinins are kinetin, diphenylurea, thidiazuron.
Hence, the correct answer is option (B), i.e., as ABA is an antagonist to gibberellins.

Note: Antagonist is a chemical compound or substrate that acts opposite to the targeted substance or shows the effects that are opposite or inhibits the effects of the targeted substance.