Photoacclimation involves modulation of the photosynthetic oxygen-evolving reactions in Dunaliella tertiolecta and Phaeodactylum tricornutum.

Net energy accumulation by marine microalgae at very low photon fluxes involves modulation of several attributes related to both the growth and photosynthetic physiology of these organisms. Here we studied flash-induced oscillatory patterns in oxygen evolution by previously dark-adapted cells of the green alga Dunaliella tertiolecta (Butcher) and the diatom Phaeodactylum tricornutum (Bohlin). The activity of the oxygen-evolving complex was found to be species-specific and influenced by photoacclimation. Results from measurements of oxygen flash yield obtained for these organisms grown under light-saturating conditions are directly comparable to those previously reported in the literature for other microalgae and higher plants. However, similar measurements on cells grown in low-light and/or light-starved conditions indicate an increased level of backward transitions (double misses) leading to the formation of super-reduced states (i.e. S and S). Thus, in this communication, we present the first evidence that super-reduced states can be generated in vivo and speculate, on how they may be physiologically important.