Emission of fluorescence from chlorophyll a in vivo due to nanosecond pulsed laser excitation

A model was proposed and tested experimentally to describe the emission of fluorescence by chlorophyll a in vivo as a result of pulsed laser excitation. This model takes into account the migration of excitons between various photosynthetic units, singlet-singlet annihilation of excitons, pigment bleaching, and also the influence of various states of the photosystem II reaction centers. A method was developed to measure the average number of excitons reaching a photosystem II reaction center during a pulse. This involved two-pulse laser excitation. It was found that the rates of exciton capture by the reaction centers were the same for the PIQ and P ⁺IQ ^– states of the photosystem II reaction centers, whereas the rate of exciton capture in the P ⁺I ^–Q ^– state was half that for the PIQ ^– state.