Changes in Photosystem II fluorescence in Chlamydomonas reinhardtii exposed to increasing levels of irradiance in relationship to the photosynthetic response to light |
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Authors: | Stefan Falk Jerry W Leverenz Göran Samuelsson Gunnar Öquist |
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Institution: | (1) Department of Plant Physiology, University of Umeå, S-901 87 Umeå, Sweden |
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Abstract: | The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 mol m–2s–1 on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780 mol m–2s–1 where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600 mol m–2s–1 where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of QB-reducing centers and 3) a second photoinhibitory range above 1600 mol m–2s–1 where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS II centers and a large increase in spill-over in energy to PS I.Abbreviations Chl
chlorophyll
- DCMU
3,(3,4-dichlorophenyl)-1,1-dimethylurea
- FM
maximal fluorescence yield
- Fpl
intermediate fluorescence yield plateau level
- F0
non-variable fluorescence yield
- Fv
total variable fluorescence yield (FM-F0)
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initial slope to the light response curve, used as an estimate of initial quantum yield
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convexity (rate of bending) of the light response curve of photosynthesis
- LHC
light-harvesting complex
- Pmax
maximum rate of photosynthesis
- PQ
plastoquinone
- Q
photosynthetically active photon flux density (400–700 nm, mol m–2s–1)
- PS
photosystem
- QA and QB
primary and secondary quinone electron acceptor of PS II |
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Keywords: | Chlamydomonas convexity chlorophyll a fluorescence Photosystem II heterogeneity photoinhibition photosynthesis PS II repair cycle |
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