NONPHOTOCHEMICAL ENERGY-DISSIPATION IN PHOTOSYSTEM-II - THEORETICAL MODELING OF THE ENERGY-DEPENDENT QUENCHING OF CHLOROPHYLL FLUORESCENCE EMISSION FROM INTACT PLANT-LEAVES

Experimentally, there is a hyperbolic relationship between the maximal and minimal levels of in vivo chlorophyll fluorescence from photosyst em II (F(m)(t) and F0(t) respectively) during dark-induced relaxation of the ''energy-dependent quenching'' mechanism (q(E)). In this paper, a theoretical analysis of q(E) is presented which describes this beha viour. The dissipative process leading to q(E) is assumed to quench ex citation energy in the photosystem II (PSII) pigment antenna and is ch aracterized by a rate constant k(E) whose value is modulated by the pH gradient. Introducing this rate constant into the theoretical express ion of F0 presented in a previous paper (M. Havaux, R. J. Strasser and H. Greppin, Photosynth. Res., 27 (1991) 41-55), an equation relating F(m)(t) to F0(t) by a first-order hyperbola is derived, which allows t he macroscopic changes in the F(m)(t) amplitude to be predicted at var ious levels of q(E). A very good agreement was obtained between predic ted and experimental data. Simple fluorescence parameters are also der ived which provide relative estimates of the value of k(E) and allow ( assuming no energy exchanges between PSII units) the determination of the probability p(E) for energy dissipation via the q(E) mechanism. So me experimental applications for the rate constant k(E) are given.