Correct option is D
Explanation-
Photomorphogenesis - This is the light-mediated development in plants. In dark (skotomorphogenesis), seedlings are etiolated (long hypocotyl, closed cotyledons, no chlorophyll). In light (photomorphogenesis), seedlings develop short hypocotyls, open green cotyledons.
Phytochrome is a photoreversible pigment involved in red/far-red light perception It exists in two forms:
Form - Absorbs - Converts to - Function
Pr (inactive) - Red light (~660 nm) - Pfr - Accumulates in dark
Pfr (active) - Far-red light (~730 nm) - Pr - Triggers photomorphogenesis
Red light exposure converts Pr → Pfr → initiates photomorphogenesis
Far-red light exposure reverses Pfr → Pr → inhibits photomorphogenesis
Statement A - Far-Red light followed by Red light
Far-red converts all Pfr → Pr (inactive)
Then Red converts Pr → Pfr (active)
Final state = Pfr → Photomorphogenesis occurs
Statement B- Far-Red → Red → Dark
This results in minimal or no photomorphogenesis due to the degradation of Pfr in the dark phase following red light.
→ No Photomorphogenesis occurs
Statement C - Red light followed by Far-Red light
Red: Pr → Pfr (active)
Far-red: Pfr → Pr (inactive)
Final state = Pr → No photomorphogenesis
Statement D - Dark → Far-Red → Red
Initially in dark: mostly Pr
Far-red: nothing major happens (some Pfr → Pr if present)
Red: Pr → Pfr
Final state = Pfr → Photomorphogenesis occurs
Statement E - Far-Red → Dark → Red
Far-red: converts Pfr → Pr (inactive)
Dark: nothing changes
Red: Pr → Pfr
Final state = Pfr → Photomorphogenesis occurs
Statement F - Red → Dark → Far-Red
Red: Pr → Pfr
Dark: no change
Far-Red: Pfr → Pr
Final state = Pr → No photomorphogenesis
Correct Answer: Option d: A, D and E
