Inverse dark reversion of phytochrome: An explanation
1Department of Plant Biology, The University, NE1 7RU, Newcastle upon Tyne, UK.
Planta
|January 21, 2014
Summary
Phytochrome (P) in dehydrated pea tissue exhibits unique photoreversible reactions. These reactions, involving intermediates like P650 and P698, explain apparent "inverse dark reversion" in seeds, challenging previous interpretations.
Area of Science:
- Plant photobiology
- Biochemistry of photoreceptors
- Molecular mechanisms of light signaling
Background:
- Phytochrome (P) is a key photoreceptor regulating plant development.
- The photoconversion between red-absorbing (Pr) and far-red absorbing (Pfr) forms is crucial.
- Dehydration and partial rehydration can alter phytochrome's photochemical properties.
Purpose of the Study:
- To investigate the behavior of phytochrome in dehydrated and partially rehydrated pea epicotyl tissue.
- To elucidate the mechanisms behind "apparent inverse dark reversion" observed in seeds.
- To re-evaluate the established understanding of phytochrome photoreversibility under stress conditions.
Main Methods:
- Freeze-drying of pea epicotyl tissue containing phytochrome in the Pr form.
- Exposure to red and far-red light to induce photoconversion.
- Spectrophotometric analysis to measure phytochrome intermediates (P698, P650) and their dark reversion.
- Partial rehydration using a glycerol-water mixture.
Main Results:
- In freeze-dried tissue, red light forms P698, which reverts to Pr in darkness, not Pfr.
- Partially rehydrated tissue shows slow Pfr formation from intermediates in the dark after red light exposure.
- These dark reactions mimic "apparent inverse dark reversion" seen in seeds.
Conclusions:
- The phenomenon of "inverse dark reversion" is attributed to slow dark production of Pfr from intermediates under dehydration stress, not a Pr to Pfr transformation.
- A separate phytochrome form is not responsible for inverse dark reversion.
- Dehydration significantly impacts phytochrome's photochemical behavior and dark reversion pathways.
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