Question

Most commonly used chemicals to break dormancy requiring light in seeds (of oats, lettuce, gladiolus etc.) are
(A) Potassium nitrate
(B) Kinetine
(C) Thiourea
(D) NAA
Choose the correct answer from the options given below

• A. (A), (B), (C) and (D)
• B. (B), (C) and (D) only
• C. (B) and (D) only
• D. (A) and (C) only

Hint:

Potassium nitrate ($0.1 - 0.2\%$) and Thiourea ($0.5 - 1.0\%$) are the standard chemical solutions recommended by seed testing associations (like ISTA) to break dormancy and ensure uniform germination during laboratory seed testing.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Certain seeds are photoblastic, meaning they require exposure to light to initiate germination.
In these seeds, light is detected by the phytochrome system, which triggers gibberellin synthesis and breaks dormancy.
Specific chemical compounds can bypass this light requirement, allowing photoblastic seeds to germinate in the dark.

Step 2: Detailed Explanation:
Let us analyze the chemicals used to break light-requiring seed dormancy:
(A) Potassium nitrate ($KNO_3$):
Potassium nitrate is a widely used chemical treatment in seed testing laboratories to break physical and physiological dormancy.
It is highly effective in substituting for the light requirement in photoblastic seeds of wild oats (*Avena fatua*), grasses, and vegetables, promoting rapid germination in the dark.
Thus, (A) is correct.
(C) Thiourea ($H_2NCSNH_2$):
Thiourea is a sulfur-containing compound known for its ability to break seed dormancy.
It is highly effective in replacing the light requirement in light-sensitive seeds, such as certain cultivars of lettuce (*Lactuca sativa*) and gladiolus corms.
It functions by stimulating metabolic activity and counteracting endogenous inhibitors like abscisic acid.
Thus, (C) is correct.
While cytokines like Kinetin can stimulate germination, they are not used as the standard, primary chemicals for breaking light-requiring dormancy in these crops.
Auxins like naphthaleneacetic acid (NAA) do not break light-requiring seed dormancy and can actually inhibit germination at higher concentrations.
Therefore, Potassium nitrate and Thiourea are the primary chemicals used for this purpose.

Step 3: Final Answer:
The chemicals used to break light-requiring seed dormancy are (A) and (C) only.
This corresponds to Option (D).