Photoinactivation of the photosynthetic electron transport chain by accumulation of over-saturating light pulses given to dark adapted pea leaves |
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Authors: | Apostol Simona Briantais Jean-Marie Moise Nicolae Cerovic Zoran G Moya Ismael |
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Institution: | (1) LURE, Bat. 209D, Centre Universitaire Paris Sud, BP. 34, 91898 Orsay, France;(2) Present address: Physics Department, Faculty of Sciences, `, Valachia' University, 0200 Targoviste, Romania;(3) Present address: Lasers Department, The National Institute for Lasers, Plasma and Radiation Physics, 76900 Bucharest-Magurele, Romania |
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Abstract: | The effect of cumulative over-saturating pulses (OSP) of white light (1 s, >10 000 μmol photons m−2 s−1), applied every 20 min on pea leaves, was investigated during a complete diurnal cycle of 24 h. In dark-adapted leaves, this
treatment leads to a progressive decline of the optimum Photosystem II (PS II) quantum yield. Continuous low background light
(except far-red light) had a protective effect against this OSP-induced photoinactivation. The lack of far-red effect could
be due to its absorption mainly in PS I and not in PS II, but could be also due to the general low absorption in this wavelength
region. The photoinactivation was enhanced in leaves that had been previously infiltrated with chloramphenicol. The quantum
yield of CO2 assimilation, but not its maximal capacity, was inhibited by the OSP treatment. The most spectacular effects observed, in
addition to an irreversible quenching of Fm, was a strong inhibition of QA
− reoxidation revealed by a large increase in the Fs level and consequently by a decrease of ΔF/Fm′. Under such conditions,
we observed that the electron flow deduced from ΔF/Fm′ underestimated the real electron flow to CO2. Time-resolved Chlorophyll a fluorescence measurements showed that the reduced capacity of QA
− reoxidation in OSP treated leaves was accompanied by the appearance of a 4.7 ns component attributed to PS II charge recombination.
We suggest that a modification at the QB site may influence the redox potential of QA/QA
−, facilitating the reversion of the primary charge separation. In addition, a 1.2 ns fluorescence component accumulated, which
appeared to be responsible for the underestimation of PS II electron flow. The observed photoinactivation seemed to be different
from the photoinhibition often described in the literature, which occurs under continuous light.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | chlorophyll fluorescence diurnal cycle fluorescence lifetime phase fluorimetry photoinhibition saturating pulses |
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