File:Fpls-02-00028-g007.png

English: Chl a fluorescence transient of a cell suspension of dark-adapted Synechococcus sp. PCC 7942 (Anacystis nidulans) plotted on a logarithmic time scale (from about a few μs to about 1000 s). Exciting light was 650 nm; 3000 μmol photons m-2 s-1. The figure was modified and reproduced from Tsimilli-Michael et al. (2009). Abbreviations: O, initial (minimum) step; J and I, intermediate levels; P, peak level; S, a semi-steady state level; M, a maximum level; and T, the terminal steady state level, not quite reached in this experiment (see Govindjee and Papageorgiou, 1971). This fluorescence transient (or fluorescence induction) is quite different from that observed in green algae and higher plants, where the “OPS” transient dominates. Cyanobacteria in darkness are usually in what is called “state 2” (low fluorescence state) and it takes a long time (almost 100 s) to be transferred to “state 1” (high fluorescence state). For a recent historical review on “state changes,” see Papageorgiou and Govindjee (2011).