The rate constant of photoinhibition, measured in lincomycin-treated leaves, is directly proportional to light intensity

Pumpkin leaves grown under high light (500-700 micromole of photons m-2.s-1) were illuminated under photon flux densities ranging from 6.5 to 1500 micromole.m-2.s-1 in the presence of lincomycin, an inhibitor of chloroplast protein synthesis. The illumination at all light intensities caused photoinh...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1996-03, Vol.93 (5), p.2213-2218
Main Authors: Tyystjarvi, E. (University of Turku, Turku, Finland.), Aro, E.M
Format: Article
Language:English
Subjects:
ANTIBIOTICOS
ANTIBIOTIQUE
Botany
Chlorophylls
CUCURBITA PEPO
Fluorescence
Flux density
FOTOINHIBICION
FOTOSINTESIS
FOTOSISTEMAS
Kinetics
Leaves
Light
LUMIERE
LUZ
METABOLISME DES PROTEINES
METABOLISMO PROTEICO
OXIRREDUCION
OXYDOREDUCTION
PHOTOINHIBITION
Photons
PHOTOSYNTHESE
Photosynthesis
PHOTOSYSTEME
Plants
PROTEOLISIS
PROTEOLYSE
Quantum mechanics
Thylakoids
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Summary:Pumpkin leaves grown under high light (500-700 micromole of photons m-2.s-1) were illuminated under photon flux densities ranging from 6.5 to 1500 micromole.m-2.s-1 in the presence of lincomycin, an inhibitor of chloroplast protein synthesis. The illumination at all light intensities caused photoinhibition, measured as a decrease in the ratio of variable to maximum fluorescence. Loss of photosystem II (PSII) electron transfer activity correlated with the decrease in the fluorescence ratio. The rate constant of photoinhibition, determined from first-order fits, was directly proportional to photon flux density at all light intensities studied. The fluorescence ratio did not decrease if the leaves were illuminated in low light in the absence of lincomycin or incubated in darkness in the presence of lincomycin. The constancy of the quantum yield of photoinhibition under different photon flux densities strongly suggests that photoinhibition in vivo occurs by one dominant mechanism under all light intensities. This mechanism probably is not the acceptor side mechanism characterized in the anaerobic case in vitro. Furthermore, there was an excellent correlation between the loss of PSII activity and the loss of the D1 protein from thylakoid membranes under low light. At low light, photoinhibition occurs so slowly that inactive PSII centers with the D1 protein waiting to be degraded do not accumulate. The kinetic agreement between D1 protein degradation and the inactivation of PSII indicates that the turnover of the D1 protein depends on photoinhibition under both low and high light
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.93.5.2213