Photoadaptation in the Green Alga Spongiochloris Sp. A Three-Fluorometer Study |
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Authors: | Koblí?ek M Ciscato M Komenda J Kopencký J ?iffel P Masojídek J |
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Institution: | (1) Department of Autotrophic Microorganisms, Institute of Microbiology, Academy of Sciences, 379 81 Třeboň, Czech Republic;(2) Department of Plant Physiology, University of South Bohemia, 370 05 České Budějovice, Czech Republic;(3) L.U.C. Department SBG Laboratory of Botany, Universitaire Campus, B-3590 Diepenbeck, Belgium;(4) Department of Photosynthesis, Institute of Plant Molecular Biology, Academy of Sciences, 370 05 České Budějovice, Czech Republic |
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Abstract: | The dark-adapted cells of the green alga Spongiochloris sp. were exposed to "white light" of 1000 μmol(photon) m−2 s−1 for 2 h and then dark adapted for 1.5 h. Changes of photochemical activities during photoadaptation were followed by measurement
of chlorophyll (Chl) fluorescence kinetics, 77 K emission spectra, photosynthetic oxygen evolution, and pigment composition.
We observed a build-up of slowly-relaxing non-photochemical quenching which led to a decrease of the Fv/Fm parameter and the connectivity. In contrast to the depression of Fv/Fm (35 %) and the rise of non-photochemical quenching (∼ 1.6), we observed an increase in effective absorption cross-section
(20 %), Hill reaction (30 %), photosynthetic oxygen evolution (80 %), and electron transport rate estimated from the Chl fluorescence
analysis (80 %). We showed an inconsistency in the presently used interpretation schemes, and ascribe the discrepancy between
the increase of effective absorption cross-section and the photosynthetic activities on one side and the effective non-photochemical
quenching on the other side to the build-up of a quenching mechanism which dissipates energy in closed reaction centres. Such
a type of quenching changes the ratio between thermal dissipation and fluorescence without any effect on photochemical yield.
In this case the Fv/Fm ratio cannot be used as a measure of the maximum photochemical yield of PS2.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | chlorophyll fluorescence photochemical yield non-photochemical quenching connectivity electron transport rate |
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