Question

______ is a growth inhibitor hormone in plants.
a. Auxin
b. Cytokinin
c. Abscisic acid
d. Gibberellic acid

Answer 1

Hint: This hormone was first isolated by Carne and Adicott from cotton fruits. Earlier it was known as dormin and inhibitor B, later it was identified that both of them were the same substance.

Complete answer
The plant growth regulator hormone abscisic acid inhibits the growth of plants. It acts antagonistically to the growth-promoting hormones which include auxin, gibberellins, and cytokinins. It induces dormancy and helps to overcome stressful conditions.

Additional Information:
- The roles of abscisic acid in plants are as follows:
- It causes inhibition of seed germination.
- Induces abscission in plant parts like leaves, fruits, and flowers.
- Dormancy in seeds and buds is stimulated by the action of abscisic acid
- Abscisic acid causes inhibition of RNA synthesis.
- Promotes senescence in leaves and branches.
- It induces stomatal closure.
- It causes inhibition of plant metabolism.

Roles of plant growth promoters are as follows:
- Auxins: It helps in apical dominance, cell elongation, cell division, prevents abscission, weed eradication, parthenocarpy, shortening of internodes, sweetening of fruits, and flowering.
- Gibberellins: Help in internodal growth, seed germination, breaking of seed dormancy, parthenocarpy, flowering in long-day plants, elongation in dwarf plants, bolting and hastens maturity period.
- Cytokinins: They promote cell division, nutrient mobilization, delay senescence, morphogenesis, and breaking of dormancy in seeds.

So, the correct answer is,” Abscisic acid is a growth inhibitor hormone in plants.”

Note: Along with abscisic acid other plant growth inhibitors are also present. Some examples are maleic hydrazide, morphactins, para-ascorbic acid, coumaric acid, and cinnamic acid. Abscisic acid increases the tolerance of plants to various kinds of environmental stresses like floods and drought and therefore it is also known as the stress hormone of plants.