Separation of light-induced linear, cyclic and stroma-sourced electron fluxes to P700+ in cucumber leaf discs after pre-illumination at a chilling temperature.
Pre-illumination of cucumber leaf discs at 4 degrees C with low-irradiance white light (i) led to a marked decrease in the extent of photo-oxidation of P700 (the special chlorophyll pair in the PSI reaction center) in actinic light at room temperature and (ii) hastened the post-illumination re-reduction of P700+. Quantifying the linear, cyclic and stroma-sourced electron fluxes to P700+ in two actinic light regimes, we found that there was no increase in cyclic or linear electron fluxes to account for these changes. Rather, we observed a decrease in the maximum extent of P700 photo-oxidation assayed by a strong flash superimposed on continuous, background light of wavelength 723 nm, which we interpret to represent a loss of stable charge separation in PSI due to enhanced charge recombination as a result of the pre-illumination treatment. The funneling of electrons towards fewer non-damaged PSI complexes could explain the hastened post-illumination re-reduction of P700+, aided by a slight increase in a stroma-sourced electron flux after prolonged pre-illumination at 4 degrees C. Quantifying the separate fluxes to P700+ helps to elucidate the effects of chilling of cucumber leaf discs in the light and the reasons for the hastened post-illumination re-reduction of P700+.
Fan
Da-Yong
DY
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, PR China.
Hope
Alexander B
AB
Jia
Husen
H
Chow
Wah Soon
WS
D002734:Chlorophyll / Q000378:metabolism; D003080:Cold Temperature; D018553:Cucumis sativus / Q000378:metabolism* / Q000528:radiation effects; D004579:Electron Transport / Q000528:radiation effects; D005453:Fluorescence; D008027:Light; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D013997:Time Factors
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll