BOTANY Higher Secondary Second Year - Textbooks Online

Abscisic acid
Abscisic acid (ABA) was originally discovered for its role in regulating
abscission and bud dormancy. Like other plant hormones, it has multiple
functions in the growth of plants.
Physiological effects of abscisic acid
Abscisic acid acts as growth inhibitor and induces bud dormancy in a
variety of plants.
ABA is a powerful growth inhibitor. It causes 50 per cent inhibition
of growth of oat seedlings.
As the name suggests abscisic acid is an hormone that stimulates
abscission.
ABA controls geotropic responses of roots. It stimulates positive
geotropism in roots.
Abscisic acid causes closure of stomata.
Growth inhibitors
Some organic substances produced in the plant inhibit the plant growth.
These substances are called growth inhibitors. They inhibit the elongation
in roots, stems and leaves. For example, ethylene is a potent inhibitor of
bud growth. ABA inhibits lateral bud growth in tomato.
Self evaluation
I . Choose and write the correct options.
1. Which one of the following plant hormones was first discovered?
a. Auxin b. Gibberellin
c. Cytokinin d. Ethylene
2. An example for synthetic auxin is
a. IAA b. PAA
c. ABA d. NAA
3. Apical dominance is due to
a. ethylene b. auxin
c. gibberellin d. cytokinin
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