FLUORESCENCE INDUCTION FROM PHOTOSYSTEM-II - ANALYTICAL EQUATIONS FORTHE YIELDS OF PHOTOCHEMISTRY AND FLUORESCENCE DERIVED FROM ANALYSIS OF A MODEL INCLUDING EXCITON-RADICAL PAIR EQUILIBRIUM AND RESTRICTED ENERGY-TRANSFER BETWEEN PHOTOSYNTHETIC UNITS

The theoretical relationships between the fluorescence and photochemic al yields of photosystem II (PSII) and the fraction of open reaction c entres are examined in a model based on the following assumptions: (a) a homogeneous, infinite PSII domain; (b) exciton-radical pair equilib rium; and (c) different rates of exciton transfer between 'core' and ' peripheral' antenna beds. Simple analytical relations are examined for the yields and their time-courses in induction experiments. Variation of the inter-unit transfer rate allows continuous transition from the case of 'separated units' to the pure 'lake' model. Widely used relat ions for estimating the fraction of closed reaction centres from the c omplementary area of the fluorescence, or the photochemical yield from fluorescence levels are derived. An experimental induction curve is a nalysed, considering its composition of 'alpha' and 'beta' centres. Th e sigmoidicity of the induction kinetics is characterised by a single parameter J (corresponding to Joliots' 'p'), that is shown to depend o n both the connectivity of the photosynthetic units and on reaction ce ntre parameters. On the other hand, the relation between J and the ext reme fluorescence levels (or the deviation from the linear Stern-Volme r dependence of 1/Phi(f) on the fraction of open traps) is only contro lled by antenna connectivity. Experimental data are more consistent wi th a model of 'connected units' for PSIIalpha than with the pure 'lake ' model.