, Volume 27, Issue 1, pp 4155
First online:
A theoretical and experimental analysis of the q_{P} and q_{N} coefficients of chlorophyll fluorescence quenching and their relation to photochemical and nonphotochemical events
 Michel HavauxAffiliated withLaboratoire de Physiologie végétale
 , Reto J. StrasserAffiliated withLaboratoire de Physiologie végétale
 , Hubert GreppinAffiliated withLaboratoire de Physiologie végétale
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The initial (F_{0}), maximal (F_{M}) and steadystate (F_{S}) levels of chlorophyll fluorescence emitted by intact pea leaves exposed to various light intensities and environmental conditions, were measured with a modulated fluorescence technique and were analysed in the context of a theory for the energy fluxes within the photochemical apparatus of photosynthesis. The theoretically derived expressions of the fluorescence signals contain only three terms, X=J_{2}p_{2F}/(1−G), Y=T/(1−G) and V, where V is the relative variable fluorescence, J_{2} is the light absorption flux in PS II, p_{2F} is the probability of fluorescence from PS II, G and T are, respectively, the probabilities for energy transfer between PS II units and for energy cycling between the reaction center and the chlorophyll pool: F_{0}=X, F_{M}=X/(1−Y) and F_{S}=X(1+(YV/(1−Y))). It is demonstrated that the amplitudes of the previously defined coefficients of chlorophyll fluorescence quenching, q_{P} and q_{N}, reflect, not just photochemical (q_{P}) or nonphotochemical (q_{N}) events as implied in the definitions, but both photochemical and nonphotochemical processes of PS II deactivation. The coefficient q_{P} is a measure of the ratio between the actual macroscopic quantum yield of photochemistry in PS II (411) in a given light state and its maximal value measured when all PS II traps are open (412) in that state, with 413 and 414. When the partial connection between PS II units is taken into consideration, 1q_{P} is nonlinearily related to the fraction of closed reaction centers and is dependent on the rate constants of all (photochemical as well as nonphotochemical) excitonconsuming processes in PS II. On the other hand, 1q_{N} equals the (normalized) ratio of the rate constant of photochemistry (k_{2b}) to the combined rate constant (k_{N}) of all the nonphotochemical deactivation processes excluding the rate constant k_{22} of energy transfer between PS II units. It is demonstrated that additional (qualitative) information on the individual rate constants, k_{N}k_{22} and k_{2b}, is provided by the fluorescence ratios 1/F_{M} and (1/F_{0})−(1/F_{M}), respectively. Although, in theory, 415 is determined by the value of both k_{2b} and k_{N}k_{22}, experimental results presented in this paper show that, under various environmental conditions, 416 is modulated largely through changes in k _{N}, confirming the idea that PS II quantum efficiency is dynamically regulated in vivo by nonphotochemical energy dissipation.
Key words
energy dissipation quantum yield photochemistry PS II Title
 A theoretical and experimental analysis of the q_{P} and q_{N} coefficients of chlorophyll fluorescence quenching and their relation to photochemical and nonphotochemical events
 Journal

Photosynthesis Research
Volume 27, Issue 1 , pp 4155
 Cover Date
 199101
 DOI
 10.1007/BF00029975
 Print ISSN
 01668595
 Online ISSN
 15735079
 Publisher
 Kluwer Academic Publishers
 Additional Links
 Topics
 Keywords

 energy dissipation
 quantum yield
 photochemistry
 PS II
 Industry Sectors
 Authors

 Michel Havaux ^{(2)}
 Reto J. Strasser ^{(2)}
 Hubert Greppin ^{(2)}
 Author Affiliations

 2. Laboratoire de Physiologie végétale, 3 place de l'Université, CH1211, Genève 4, Switzerland