Variability of the portion of functional PS2 reaction centres in the light of a fluorometric study

The paper contains a preliminary analysis of the links between the portion fc of functional PS2 reaction centres in the photosynthetic apparatus of marine phytoplankton and environmental factors. The analysis is based inter alia on fluorometric measurements of fc (see Kolber & Falkowski 1993) in water sampled from different depths and trophic types of sea. From the statistical generalisations was derived an analytical form of the relationship between fc, and the optical depth and trophic type of sea (the trophicity index was taken to be the surface concentration of chlorophyll a). According to this relationship, fc rises as the trophicity of the sea does so. Moreover, there is a certain optimal optical depth for each type of water at which the number of functional PS2 reaction centres reaches a maximum. Above or below this depth the value of fc falls. At the present stage of investigations it seems reasonable to assume that this drop in the number of functional PS2 reaction centres close to the surface is due to the destructive effect of excessive irradiance. On the other hand, their reduced number at greater depths, below the fc maximum, can be attributed to the deficit of light and the consequent destruction of reaction centres.