Photoinhibition in Euglena gracilis: Involvement of reactive oxygen species |
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Authors: | H Tschiersch E Ohmann |
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Institution: | (1) Martin Luther Universität Halle-Wittenberg, Institut für Pflanzen- und Zellphysiologie, Am Kirchtor 1, D-06108 Halle/S, Germany |
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Abstract: | Photoinhibition of isolated Euglena gracilis thylakoids was characterised by a drastic decline in PSII photochemistry, chlorophyll-a fluorescence and an enhanced degradation of the 32-kDa protein. The process of protein degradation, as shown by studies of 14C] atrazine binding, was clearly slower than the other events. The activity of PSI was not affected. Decrease of electron-transport activity and loss of herbicide binding were prevented in the presence of various antioxidants and enzymes which protect against free radicals; however, the protection was not total. The strongest effect was observed by addition of dimethylsulfoxide, a potent hydroxyl-radical (OH*) quencher. Furthermore, combinations of various protective substances were even more effective in reducing photoinhibition. Different reactive oxygen species, including H2O2, superoxide radicals and OH* radicals were obviously involved in photoinhibition. These results were confirmed by the addition of potential OH*-radical-generating substances. Simultaneous enhancement of OH*-radical formation and photoinhibitory damage were observed in these cases. The involvement of this highly toxic species could be shown directly by a colorimetric test, thus enabling its light-mediated formation during photoinhibition to be quantified for the first time. In all, the data indicate that a site in PSII is the origin of radical formation involved in photoinhibition and that H2O2 is an important precursor in the formation of hydroxyl-radicals.Abbreviations Chl
chlorophyll
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DCPIP
2,6-dichlorphenolindophenol
- DMSO
dimethyl sulfoxide
- FM
maximum fluorescence
- FV
variable fluorescence
- Fecy
ferricyanide
- MSA
methane sulfinic acid
- MV
1,1 dimethyl-4,4 bipyridylium dichloride
- OH*
hydroxyl radical
- PBQ
p-phenylbenzoquinone
- PDA
p-phenylenediamine
- PPFD
photosynthetic photon flux density
- SOD
superoxide dismutase
This reasearch was supported by a grant from the Volkswagen-Stiftung. |
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Keywords: | Activated oxygen species Euglena Hydroxyl radical (quantification) Photoinhibition of photosynthesis |
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