Question

ABA acts antagonistically to
(a) Ethylene
(b) Cytokinin
(c) Gibberellic acid
(d) IAA

Answer 1

Hint: This is an important hormone of plants that is responsible for the growth and development of plants including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence.

Complete answer:
 The abscisic acid acts antagonistically to gibberellic acid as shown in the table given below:

Abscisic acid	Gibberellic acid
Abscisic acid inhibits the growth of plants.	Gibberellic acid promotes the growth of the plant.
Dormancy of seeds and buds is induced by abscisic acid.	Dormancy of seeds and buds is removed by gibberellic acid.
It inhibits the germination of seed.	It induces the germination of seed.
Flowering in short-day plants is promoted by abscisic acid.	Flowering in long-day plants is promoted by gibberellic acid.
Cellular transcription and translation are also inhibited by abscisic acid.	Cellular transcription and translation are also promoted by gibberellic acid.
It promotes the abscission of the leaf.	It prevents the abscission of the leaf.
It promotes the closing of stomata.	It helps in the opening of stomata.
It also promotes the abscission of flowers and fruits in plants.	It promotes the development of fruits in plants.
It inhibits the synthesis of RNA and proteins.	It promotes the synthesis of RNA and proteins.
It inhibits the activity of enzyme amylase and also the conversion of starch to glucose and thereby it inhibits the germination of seed.	During the seed germination process, the gibberellic acid promotes the activity of enzyme amylase to hydrolyze the starch to glucose.
It has no role in the sexuality of flowers.	This can bring about change in the sexuality of flowers.

Note:
- The plants which require long nights or long periods of darkness for flowering are termed as short-day plants whereas those plants which require short nights or short periods of darkness for flowering are termed as long-day plants.
- Short day plants bloom only when they receive less than 12 hours of light whereas long day plants bloom only when they receive more than 12 hours of light.
- Abscisic acid has no role in the sexuality of flowers whereas gibberellic acid can bring about change in the sexuality of flowers.