Question

Which of the following generally act as an antagonist to gibberellins?
A) Zeatin
B) Ethylene
C) ABA
D) IAA

Answer 1

Gibberellins are plant hormones that regulate stimulate the growth of main stems, especially when applied to the whole plant. They regulate various processes, including stem prolongation, germination, flowering, leaf and fruit aging.

Complete answer:
Humans have different types of hormones to perform several metabolic activities within the body.
Like humans, plants also have hormones which are collectively called as plant growth regulators, promoters, inhibitors, and phytohormones (plant hormones).
Gibberellin or Gibberellic Acid (GA) is produced in embryos, roots, and young leaves and it stimulates the growth. Gibberellin is responsible for seed germination. The hormone ABA (Abscisic acid) inhibits seed germination.
Gibberellin delays aging in plants. Abscisic acid promotes the aging of leaves.
Gibberellin is commercially obtained from fungi. It is used to facilitate the germination of seeds. It breaks discontinuation of seeds and as opposed to Abscisic acid, which induces inactivity of buds and seeds.
Due to their opposite effect on plant growth, ABA (abscisic acid) acts as antagonist to gibberellins.

Additional information: Option A is not correct because zeatin is a cytokinin derived from adenine. Both zeatinn and gibberellins promote growth of lateral buds.
Option B is not correct because Ethylene and gibberellins (GAs) play a role in the leaf expansion. They influence plant growth by mutual cross-talk and by interaction with other hormones.
Option D is not correct because both IAA (indole acetic acid) and gibberellins (GAs) stimulate cell and organ growth.

Thus the correct answer is option C. i.e., ABA.

Note: Gibberellic acid (GA) was discovered by Kurosawa, a Japanese Botanist in 1938. Chemically speaking, gibberellins are actually acidic. It is sprayed on the grapevines and used to enlarge them. It is used on cucumber plants to produce all-male flowers.