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Is one enough? The maximal yield of Chla fluorescence induced by single or multiple turnovers of photosystem II as studied with picosecond time-resolved decay kinetics

Doug Bruce
Sergei Vasiliev
DB

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Doug Bruce

Résumé du colloque

The maximal yield of chlorophyll a fluorescence (Fm) is usually determined experimentally by the closure of photosystem II (PSII) reaction centres with a saturating pulse of light with a minimal time duration of 30 to 50 milliseconds. This duration of saturating light pulse allows for multiple turnovers of PSII which gives rise to a fluorescence yield significantly higher than that induced by a saturating single turnover flash (less than 50 microseconds). Our picosecond time resolved fluorescence apparatus was modified to allow collection of picosecond time resolved fluorescence decay kinetics over a short time window immediately following a saturating single turnover flash (Fsat) as well as after a multiturnover saturating pulse (Fm). Our data was modelled well with a global kinetic exciton radical pair equilibrium model for PSII which predicted the lower yield of Fsat to result from antenna quenching. This was verified experimentally by the observation that addition of the antenna quencher napthoquinone changed the decay kinetics of thylakoids under Fm conditions to be more like those under Fsat conditions. The additional degree of nonphotochemical quenching observed in our studies (from Fm to Fsat) is not considered in calculations of photochemical and nonphotochemical quenching parameters which are routinely calculated from Fm values. We discuss our data in terms of models for the excited state dynamics of PSII and the practical applications of the fluorescence parameters Fm and Fsat.

Contexte

Section :
Contrôle et physiologie de la photosynthèse
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Contrôle et physiologie de la photosynthèse
host icon Hôte : Université Laval

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Thème du colloque :

Contrôle et physiologie de la photosynthèse
Is one enough? The maximal yield of Chla fluorescence induced by single or multiple turnovers of ph…
Doug Bruce