FIG. 5.
Recovery of fluorescence yield in the light by the addition of DCMU. Peak fluorescence of dark-adapted cells of Oscillatoria strain U-Stink treated with 18 μM hydrogen sulfide (squares) decreased relative to FP of the sulfide-free control (with FP of the control defined as having a relative intensity equal to 1). After DCMU addition and under white light, all PS II reaction centers were closed, leading to a recovery of maximal fluorescence yield under low light (diamonds). This recovery was not observed under steady-state illumination if cells were assayed in the presence of sulfide but the absence of DCMU (triangles).