The use of laser saturation fluorometry for the study of mechanisms of chlorophyll a fluorescence build-up in phytoplankton under conditions of mineral nutrition shortage

The increase in the intensity of chlorophyll a fluorescence of phytoplankton under conditions of shortage of mineral nutrition was found to have two components. The first component, whose relative contribution to the overall process of fluorescence intensity change makes up 60-75%, is of a recombination origin and is due to a disruption of the electron transport between the intermediate acceptor Pheo and the primary quinone acceptor $Q_A$ in the reaction center of photosystem II (PS II). The second, nonrecombination, component is due either to weakening of the bond between the light-harvesting antenna and the PS II reaction center, or to disruption of the electron transport between the primary donor P680 and Pheo. It is shown that shortage of mineral nutrition results in the formation of certain number of nonreactive PS II reaction centers with disrupted electron transport from $Q_A$ to the secondary quinone acceptor $Q_B$.