Question

The plant pigment, which is associated with the photoperiodism in plants is -

• A. Chlorophyll
• B. Lycophyll
• C. Xanthophyll
• D. Phytochrome

Hint:

To distinguish these pigments, remember that Chlorophyll is for Photosynthesis, whereas Phytochrome is for Photoperiodism and photomorphogenesis (light-sensing).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Photoperiodism is the physiological response of plants to the relative lengths of day and night, governing critical developmental processes such as flowering, seed germination, and bud dormancy.
This light-sensing mechanism is controlled by specialized photoreceptor proteins.

Step 2: Detailed Explanation:
Let us analyze the biochemical pigments listed in the options:
- Phytochrome: This is the key regulatory photoreceptor chromoprotein associated with photoperiodism in plants.
It exists in two interconvertible conformational states:
1. $P_r$: The inactive state that absorbs red light ($\approx 660\text{ nm}$).
2. $P_{fr}$: The active state that absorbs far-red light ($\approx 730\text{ nm}$).
The ratio of $P_{fr}$ to $P_r$ acts as a biochemical switch, sensing the length of the night period and regulating transcription factors that control flowering in short-day and long-day plants.
- Let us evaluate why other options are incorrect:
- Chlorophyll: The primary green pigment responsible for capturing light energy during photosynthesis, not involved in photoperiodic signaling.
- Lycophyll: A carotenoid pigment contributing to yellow/orange coloration in some fruits, with no light-signaling function.
- Xanthophyll: An accessory photosynthetic pigment involved in light-harvesting and photoprotection (energy dissipation), not photoperiodism.
Therefore, Phytochrome is the correct pigment associated with photoperiodic control.

Step 3: Final Answer:
The plant pigment associated with photoperiodism is Phytochrome.