Theoretical Simulation of Temperature Induced Increase of Quantum Yield of Minimum Chlorophyll Fluorescence ΦF(0)

The measured minimum chlorophyll fluorescence intensityF0of barley leaves rises upon linear heating in the temperature range 32–52°C whereas the maximum fluorescenceFMgradually decreases. The rise ofF0is thought to be connected with the blocking of electron transport in the reaction centre of PSII (RCII), however a clear interpretation has not yet been settled. In this paper, we have theoretically simulated bothFMandF0temperature dependencies in the temperature range 25–60°C based on a monomolecular model. The fluorescence quantum yields ΦF(0)and ΦF(M)were expressed as functions of the rate constants of the deexcitation processes and the fraction of open RCII [P]. The temperature dependence of the rate constants was expressed by exponential functions (1/T)1/2exp(−EA/RT) or exp(−EA/RT). A fitting of theFMdependence served to obtain some yet unknown rate constants. In the temperature interval where the functional RCIIs are supposed to convert gradually into the blocked ones the value [P] was tuned to converge gradually to 0 yielding the increase of ΦF(0). The model enabled us to express the theoretical dependencies of quantum yields of internal conversion, intersystem crossing and energy transfer to PSI in reasonable accordance with the known experimental facts. The simulation supports the view that the temperature increase ofF0is predominantly caused by a blocking of RCII.