Modeling of chlorophyll a fluorescence kinetics in plant cells. Derivation of a descriptive algorithm.

In this chapter, we present the model and simulation of light-driven chlorophyll fluorescence induction in 10–20 min dark-adapted intact leaves and thylakoids. The algorithm for it has been derived from analyses of fluorescence kinetics upon excitation with single- (STF), twin- (TTF) and repetitive STF excitations. These analyses have led to definition and formulation of rate equations that describe the sequence of electron transfer steps associated with the oxidation of the oxygen evolving complex (OEC) and the reduction of the primary plastoquinone acceptor QA of photosystem II (PS II) in multi turnover excitation (MTF). The model considers heterogeneity in reaction centers (RCs) associated with the S-states of the OEC and incorporates the presence of a 20–35% fraction of QB nonreducing RCs that probably is identical with the S0 fraction. The fluorescence induction algorithm (FIA) considers a photochemical O—J—D, a photo-electrochemical J—I and an I—P component (phase), which probably is associated with a photoelectric interaction between PS I and PS II. The photochemical phase incorporates the kinetics associated with the double reduction of the acceptor pair of pheophytin (Phe) and plastoquinone QA[PheQA] in QBnonreducing RCs and the associated doubling of the variable fluorescence, in agreement with the three-state trapping model (TSTM) of PS II. Application of and results with the algorithm are illustrated for a variety of MTF-induced OJDIP curves, measured in dark-adapted leaves and thylakoids under various light and dark conditions.