A simple model relating photoinhibitory fluorescence quenching in chloroplasts to a population of altered Photosystem II reaction centers

Abstract

A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS IIα and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, FVFM, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and FVFM ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.

An Investigation of the Sustained Component of Nonphotochemical Quenching of Chlorophyll Fluorescence in Isolated Chloroplasts and Leaves of Spinach

“…It is associated with the presence of zeaxanthin and could therefore represent a more sustained modification of the LHCII system. Alternatively, it is possible that it could arise from a variety of effects on PSII, such as damage to the PSII reaction center or a downregulation of the PSII donor side, perhaps by release of Ca'+ (Krause et al, 1990;Giersch and Krause, 1991;Oquist et al, 1992;van Wijk and van Hasselt, 1993).…”

High susceptibility to photoinhibition of young leaves of tropical forest trees

“…A close correlation between Fv/FM ratio and optimum quantum yield of photosynthetic 02 evolution has been found in many cases (see Krause and Weis 1991). According to model calculations (Giersch and Krause 1991), not a strictly linear, but a quasi-linear relationship -suitable for practical use -between Fv/FM and activity of PSII can be expected. In addition, the fluorescence parameter 1-Fs/Fh (where Fs= stationary fluorescence and F~t = maximum fluorescence during illumination) was determined, which has been suggested to represent the actual quantum yield of PSII at the time of measurement (Genty et al 1989).…”

Photoinactivation of Photosystem II Induces Changes in the Photochemical Reaction Center II Abolishing the Regulatory Role of the Qb Site in the Dl Protein Degradation

“…Diuron partially retards the photoinactivation of PSII in C. reinhardtii cells exposed to a light intensity of 1500pmol m-* s-'. About 85% of PSII electron flow activity, measured as variable fluorescence (Giersh and Krause, 1991;Krause and Weis, 1991), is lost after 3 h in cells photoinactivated in the presence of diuron as compared with almost complete loss in the control cells (Fig. 1).…”