49. A plant hormone that promotes the acquisition of desiccation
tolerance in developing seed is
(1) ABA        (2) Ethylene
(3) IAA         (4) GA3.

Correct answer: (1) ABA (Abscisic Acid)

Explanation:

• Abscisic acid (ABA) is the key plant hormone promoting the acquisition of desiccation tolerance in developing seeds.

• During seed maturation, ABA accumulates and triggers biochemical and physiological changes that protect the seed from drying out, enabling it to remain viable during dormancy.

• Ethylene is involved in ripening and senescence, but not directly in desiccation tolerance.

• Indole-3-acetic acid (IAA or auxin) regulates growth and development, not desiccation tolerance.

• Gibberellic acid (GA3) promotes seed germination and growth, opposing dormancy and desiccation tolerance.

Option-wise:

• (1) ABA — correct; central to desiccation tolerance in seeds.

• (2) Ethylene — ripening hormone, not desiccation tolerance.

• (3) IAA — growth regulator, unrelated to desiccation.

• (4) GA3 — growth promoter, antagonizes ABA effect.

ABA accumulates during seed maturation, inducing protective proteins and osmolytes that confer desiccation tolerance, enabling seeds to survive extended dry conditions until favorable germination cues occur.