PLANT PHYSIOLOGY , Vol 115, Issue 2 803-815, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Quantum Yields and Rate Constants of Photochemical and Nonphotochemical Excitation Quenching (Experiment and Model)
A. Laisk, V. Oja, B. Rasulov, H. Eichelmann and A. Sumberg
Tartu Ulikooli Molekulaar-ja Rakubioloogia Institut, Riia tn. 181, Tartu, EE2400, Estonia (A.L, V.O., H.E., A.S.)
Sunflower (Helianthus annuus L.), cotton (Gossypium hirsutum L.), tobacco
(Nicotiana tabacum L.), sorghum (Sorghum bicolor Moench.), amaranth
(Amaranthus cruentus L.), and cytochrome b6f complex-deficient transgenic
tobacco leaves were used to test the response of plants exposed to differnt
light intensities and CO2 concentrations before and after photoinhibition
at 4000 [mu]mol photons m-2 s-1 and to thermoinhibition up to 45[deg]C.
Quantum yields of photochemical and nonphotochemical excitation quenching
(YP and YN) and the corresponding relative rate constants for excitation
capture from the antenna-primary radical pair equilibrium system (k[prime]P
and k[prime]N) were calculated from measured fluorescence parameters. The
above treatments resulted in decreases in YP and K[prime]P and in
approximately complementary increases in YN and K[prime]N under normal and
inhibitory conditions. The results were reproduced by a mathematical model
of electron/proton transport and O2 evolution/CO2 assimilation in
photosynthesis based on budget equations for the intermediates of
photosynthesis. Quantitative differences between model predictions and
experiments are explainable, assuming that electron transport is organized
into domains that contain relatively complete electron and proton transport
chains (e.g. thylakoids). With the complementation that occurs between the
photochemical and nonphotochemical excitation quenching, the regulatory
system can constantly maintain the shortest lifetime of excitation
necessary to avoid the formation of chlorophyll triplet states and singlet
oxygen.
