UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2001 Meeting


Section: Biophysics; Medical Physics


Title:
Chlorophyll Thermoluminescence contribution in the in vivo study of cold stress effects upon photosynthetic device in plants


Authors:
Miruna ROMAN1,2, Jean-Marc DUCRUET2


Affiliation:
1 INFLPR, Sectia Laseri, PO Box MG-36, 76900 Bucharest-Magurele

2 CEA-Saclay, Section de Bioenergetique, bat 532, 91191 Gif sur Yvette cedex, France


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Keywords:


Abstract:
The chlorophyll luminescence emission named "afterglow" (AG, a luminescence bump observable in intact photosynthetic material: leaves, algae, whole chloroplasts) originates from photosystem II. After an illumination, a fraction of the PS-II centres contains oxidized secondary acceptor QB. The AG emission corresponds to a progressive reduction of QB by electrons coming from stroma reductants (via a part of the cyclic photosynthetic pathway and/or of the chlororespiratory chain), followed by a radiative charge recombination between QB- and the oxidized S2/3 states of the oxygen-evolving complex. We investigated the mechanisms of the AG emission in pea, maize and lettuce leaves. The cyclic electron transfer around photosystem I and the AG emission are both inducible by increasing temperature above 30°C. For this reason, thermoluminescence provides a better resolution of the AG emission than luminescence decays recorded at constant temperature. Using chlorophyll fluorescence induction kinetics, we have shown that temperature increase causes a partial reduction of the plastoquinones pool. White (or actinic) light illumination or glucose infltration in leaves, two treatments which induce the cyclic pathway, also caused a downshift of the AG band. We used these results to study some mechanisms of cold-acclimation in pea or maize: (1) the AG emission decreased in the cold-sensitive pea varieties, not in the tolerant ones, after an acclimation at 5°C for several days, reflecting a decrease in the photosynthetic potential ([ATP+NADPH]), which can be ascribed to a phosphate limitation in chloroplasts (2) an actinic light induced a downshift of the AG TL band, which reversed more slowly in the dark for the cold-tolerant maize inbred lines than for the cold-sensitive ones, suggesting an induction of the cyclic electron transfer. This induction would be triggered by an accumulation of soluble carbohydrates in the hardened cold-tolerant maize lines during an actinic illumination.