Correct option is B
‘Dark Reversion’ refers to the conversion of phytochrome in its active form (PFR) back to its inactive form (PR) in the absence of light.
Phytochromes are light-sensitive proteins that regulate various plant growth processes like seed germination, flowering, and photoperiodic responses. They exist in two forms:
- PR: The inactive form, which absorbs red light (around 660 nm).
- PFR: The active form, which absorbs far-red light (around 730 nm).
When phytochrome absorbs red light, it is converted from PR to PFR (photoactivation), and when it absorbs far-red light or remains in the dark, it reverts from PFR back to PR (dark reversion).
Option 1 (Conversion of PR to PFR): This is incorrect because it describes the activation of phytochrome, which occurs when red light is absorbed, not the dark reversion process.
Option 2 (Conversion of PFR to PR): This is the correct description of dark reversion, where in the absence of light, the active form PFR spontaneously converts back to the inactive form PR.
Option 3 and 4 (Export of PFR from cytosol to nucleus / Export of PR from cytosol to nucleus): These options describe the movement of phytochrome into the nucleus to regulate gene expression, but they are not related to the dark reversion process, which specifically refers to the conversion between PFR and PR in the absence of light.
Information Booster:
Dark Reversion: This term specifically refers to the process in which the PFR form of phytochrome reverts back to the PR form in darkness. The reversion is a spontaneous process and is important for resetting the phytochrome system for subsequent light exposures.
Phytochrome's Role in Light Sensing: Phytochromes are essential for regulating plant responses to light. The transition between PR (inactive) and PFR (active) enables plants to detect light conditions and synchronize their growth and development, such as in response to day-length (photoperiod) or light quality changes (red vs. far-red light).
Dark Reversion is Important: This process ensures that the plant is able to reset its light sensing mechanism in the absence of light, helping it properly respond to future light signals. Without dark reversion, the plant may remain in an incorrect physiological state, impacting processes like germination and flowering.
