Effect of Na2HPO4 on slow fluorescence induction and photosynthesis in broad bean leaves

Regular changes in slow fluorescence induction (SFI) were found in broad bean (Vicia faba L.) leaves treated with Na2HPO4 solutions of various concentrations. The plot of F-M/F-T vs concentration (F-M and F-T are maximum and steady-state fluorescence, respectively) had its maximum in the range of 10(-6)-10(-3) M, depending on the treatment period; F-T grew with the Na2HPO4 concentration, while the half-time of fluorescence quenching (tau(1/2)) decreased. We observed a positive correlation between the rate of photosynthesis per mg chlorophyll and the SFI parameter, the F-M/F-T ratio (r = 0.87, P > 0.999). We concluded that the level of inorganic phosphate in the cell could limit photophosphorylation and photosynthesis.