Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1657, Issue 1, Pages 33-46Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2004.04.001
Keywords
chlorophyll a fluorescence induction; fluorescence lifetime; tau-Phi relationship; photochemical and thermal phase; nonphotochemical quenching; pigment-protein complex conformational change
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The relationship between the fluorescence lifetime (tau) and yield (Phi) obtained in phase and modulation fluorometry at 54 MHz during the chlorophyll fluorescence induction in dark-adapted leaves under low actinic light has been investigated. Three typical phases have been identified: (i) linear during the OI photochemical rise, (ii) convex curvature during the subsequent IP thermal rise, and (iii) linear during the PS slow decay. A similar relationship has been obtained in the fluorescence induction for the fluorescence yield measured at 685 nm plotted versus the fluorescence yield measured at 735 nm. A spectrally resolved analysis shows that the curvature of the tau-Phi relationship is not due to chlorophyll fluorescence reabsorption effects. Several other hypotheses are discussed and we conclude that the curvature of the tau-Phi relationship is due to a variable and transitory nonphotochemical quenching. We tentatively propose that this quenching results from a conformational change of a pigment-protein complex of Photosystem II core antenna during the IP phase and could explain both spectral and temporal transitory changes of the fluorescence. A variable blue shift of the 685 nm peak of the fluorescence spectrum during the IP phase has been observed, supporting this hypothesis. (C) 2004 Elsevier B.V. All rights reserved.
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