THEORETICAL SIMULATION OF TEMPERATURE-INDUCED INCREASE OF QUANTUM YIELD OF MINIMUM CHLOROPHYLL FLUORESCENCE PHI(F(0))

The measured minimum chlorophyll fluorescence intensity F-o of barley leaves rises upon linear heating in the temperature range 32-52 degree s C whereas the maximum fluorescence F-M gradually decreases. The rise of Fo is thought to be connected with the blocking of electron transp ort in the reaction centre of PSII (RCII), however a clear interpretat ion has not yet been settled. In this paper, we have theoretically sim ulated both F-M and F-o temperature dependencies in the temperature ra nge 25-60 degrees C based on a monomolecular model. The fluorescence q uantum yields Phi(F(o)) and Phi(F(M)) were expressed as functions of t he rate constants of the deexcitation processes and the fraction of op en RCII [P]. The temperature dependence of the rate constants was expr essed by exponential functions (1/T)(1/2) exp(-E-A/RT) or exp(-E-A/RT) . A fitting of the F-M dependence served to obtain some yet unknown ra te constants. In the temperature interval where the functional RCIIs a re supposed to convert gradually into the blocked ones the value [P] w as tuned to converge gradually to 0 yielding the increase of Phi(F(o)) . The model enabled us to express the theoretical dependencies of quan tum yields of internal conversion, intersystem crossing and energy tra nsfer to PSI in reasonable accordance with the known experimental fact s. The simulation supports the view that the temperature increase of F -o is predominantly caused by a blocking of RCII. (C) 1998 Academic Pr ess.