THEORY OF FLUORESCENCE INDUCTION IN PHOTOSYSTEM-II - DERIVATION OF ANALYTICAL EXPRESSIONS IN A MODEL INCLUDING EXCITON-RADICAL-PAIR EQUILIBRIUM AND RESTRICTED ENERGY-TRANSFER BETWEEN PHOTOSYNTHETIC UNITS
J. Lavergne et Hw. Trissl, THEORY OF FLUORESCENCE INDUCTION IN PHOTOSYSTEM-II - DERIVATION OF ANALYTICAL EXPRESSIONS IN A MODEL INCLUDING EXCITON-RADICAL-PAIR EQUILIBRIUM AND RESTRICTED ENERGY-TRANSFER BETWEEN PHOTOSYNTHETIC UNITS, Biophysical journal, 68(6), 1995, pp. 2474-2492
The theoretical relationships between the fluorescence and photochemic
al yields of PS II and the fraction of open reaction centers are exami
ned in a general model endowed with the following features: i) a homog
eneous, infinite PS II domain; ii) exciton-radical-pair equilibrium; a
nd iii) different rates of exciton transfer between core and periphera
l antenna beds. Simple analytical relations are derived for the yields
and their time courses in induction experiments. The introduction of
the exciton-radical-pair equilibrium, for both the open and closed sta
tes of the trap, is shown to be equivalent to an irreversible trapping
scheme with modified parameters. Variation of the interunit transfer
rate allows continuous modulation from the case of separated units to
the pure lake model. Broadly used relations for estimating the relativ
e amount of reaction centers from the complementary area of the fluore
scence kinetics or the photochemical yield from fluorescence levels ar
e examined in this framework. Their dependence on parameters controlli
ng exciton decay is discussed, allowing assessment of their range of a
pplicability, An experimental induction curve is analyzed, with a disc
ussion of its decomposition into alpha and beta contributions. The sig
moidicity of the induction kinetics is characterized by a single param
eter J related to Joliot's rho, which is shown to depend on both the c
onnectivity of the photosynthetic units and reaction center parameters
. On the other hand, the relation between J and the extreme fluorescen
ce levels (or the deviation from the linear Stern-Volmer dependence of
1/Phi(f) on the fraction of open traps) is controlled only by antenna
connectivity. Experimental data are consistent with a model of connec
ted units for PS IIalpha, intermediate between the pure lake model of
unrestricted exciton transfer and the isolated units model.