Question

A seed may be dormant due to several factors including physiological parameters. One of the reasons for the physiological dormancy of seed is-

• A. Presence of anti-nutritional factors
• B. Absence of light
• C. Presence of excess stored food
• D. Absence of plant growth regulators (PGRs), hormones, etc.

Hint:

Remember the classic "ABA vs. GA" balance:
Abscisic Acid (ABA) induces and maintains dormancy.
Gibberellic Acid (GA) breaks dormancy and promotes germination.
Absence of promoting PGRs like GA keeps the seed dormant.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Seed dormancy is a physiological state in which viable seeds fail to germinate even under favorable environmental conditions (such as adequate moisture, temperature, and oxygen).
Physiological dormancy is primarily controlled by internal biochemical mechanisms, specifically the balance between plant growth regulators (PGRs) that promote or inhibit germination.

Step 2: Detailed Explanation:
The hormonal regulation of physiological seed dormancy is controlled by a dual-regulator system:
1. The Hormone Balance Theory: Dormancy and germination are regulated by the ratio of Abscisic Acid (ABA, a germination inhibitor) to Gibberellins (GA, a germination promoter).
2. Role of Inhibitors (ABA): During seed maturation, high levels of ABA are synthesized to induce and maintain dormancy, preventing premature germination (vivipary) on the parent plant.
3. Role of Promoters (GA): For a seed to break dormancy and germinate, promoting hormones—specifically Gibberellins—must be synthesized or activated.
Gibberellins trigger the transcription of hydrolytic enzymes (such as \( \alpha \)-amylase) that break down stored food to fuel embryonic growth.
If these promoting plant growth regulators (or their signal transduction components) are absent or inactive, the seed remains in a physiologically dormant state.
Thus, the absence of promoting PGRs/hormones (specifically Gibberellins) is a primary cause of physiological dormancy.
The other options, such as the presence of excess stored food (C) or anti-nutritional factors (A), do not regulate physiological dormancy.

Step 3: Final Answer:
The correct option is (D) Absence of plant growth regulators (PGRs), hormones, etc.