Question

The seeds requiring light for induction of germination process is termed as

• A. Positively photoblastic
• B. Long-day
• C. Negatively photoblastic
• D. Short day

Hint:

"Photo-" means light and "-blastic" refers to growth/germination. Positively photoblastic seeds (like lettuce) require light to convert \(\text{P}_r\) to the active \(\text{P}_{fr}\) form, which triggers the gibberellin pathway to initiate germination.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
While many seeds can germinate in complete darkness if moisture and oxygen are available, some seeds have absolute light requirements to break dormancy and initiate germination.
This light sensitivity is regulated by the phytochrome system, which acts as a developmental switch.

Step 2: Detailed Explanation:
Based on their germination response to light, seeds are classified into three photoblastic categories:
Positively Photoblastic Seeds (A): These seeds require exposure to light to trigger the germination process.
Light is perceived by the photoreceptor phytochrome; red light converts the inactive form (\(\text{P}_r\)) into the physiologically active form (\(\text{P}_{fr}\)), which stimulates gibberellin synthesis and breaks dormancy.
Examples include lettuce (Lactuca sativa), tobacco, and many small-seeded weeds.
Negatively Photoblastic Seeds (C): These seeds are inhibited by light and will only germinate in complete darkness (e.g., Allium species).
Photoblastically Neutral Seeds: These seeds germinate equally well in both light and darkness (e.g., most agricultural crops like wheat and maize).
Long-day (B) and Short-day (D): These terms refer to the photoperiodic requirements for flowering, not seed germination.

Step 3: Final Answer:
Seeds requiring light for germination are termed positively photoblastic, corresponding to option (A).