Temperature-dependent changes in Photosystem II heterogeneity support a cycle of Photosystem II during photoinhibition |
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Authors: | Esa Tyystjärvi Eva-Mari Aro |
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Institution: | (1) Department of Biology, University of Turku, SF-20500 Turku, Finland |
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Abstract: | High light treatments were given to attached leaves of pumpkin (Cucurbita pepo L.) at room temperature and at 1°C where the diffusion- and enzyme-dependent repair processes of Photosystem II are at a minimum. After treatments, electron transfer activities and fluorescence induction were measured from thylakoids isolated from the treated leaves. When the photoinhibition treatment was given at 1°C, the Photosystem II electron transfer assays that were designed to require electron transfer to the plastoquinone pool showed greater inhibition than electron transfer from H2O to paraphenyl-benzoquinone, which measures all PS II centers. When the light treatment was given at room temperature, electron transfer from H2O to paraphenyl-benzoquinone was inhibited more than whole-chain electron transfer. Variable fluorescence measured in the presence of ferricyanide decreased only during room-temperature treatments. These results suggest that reaction centers of one pool of Photosystem II, non-QB-PS II, replace photoinhibited reaction centers at room temperature, while no replacement occurs at 1°C. A simulation of photoinhibition at 1°C supports this conclusion.Abbreviations BSA
bovine serum albumin
- Chl
chlorophyll
- DCMU
3-(3,4,-dichlorophenyl)-1,1,-dimethylurea
- DCPIP
dichlorophenol-indophenol (2,6-dichloro-4((4-hydroxyphenyl)imino)-2,5-cyclohexadien-1-one)
- DPC
diphenyl carbazide (2,2 -diphenylcarbonic dihydrazide)
- FeCN
ferricyanide (hexacyanoferrate(III))
- app
apparent quantum yield of photosynthetic oxygen evolution
- MV
methyl viologen (1,1 -dimethyl-4,4 -bipyridinium dichloride)
- PPBQ
phenyl-p-benzoquinone
- PPFD
photosynthetic photon flux density
- PQ
pool plastoquinone
- QB
secondary quinone acceptor of PS II
- RT
room temperature
- WC
whole chain electron transfer |
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Keywords: | mechanism of photoinhibition chill-induced photoinhibition Cucurbita pepo quinone acceptors non-QB-PS II PS II heterogeneity |
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