FIGURE 7.

Kinetics of hydrogen peroxide decomposition in cultures of Anabaena and Synechocystis. A, cultures were grown to mid-exponential phase, diluted to a concentration of 3.5 μg of chlorophyll ml⁻¹ and incubated under normal light conditions in the presence or absence of 0.1 mm NH₂OH, which inhibits the catalase-peroxidase activity. At time 0, hydrogen peroxide was added to a final concentration of 0.5 mm. The remaining amounts of hydrogen peroxide were monitored using the ferrous oxidation of xylenol orange assay. ▴ and △, Synechocystis in the absence (▴) or presence (△) of NH₂OH; ● and ○, Anabaena in the absence (●) or presence (○) of NH₂OH. B, effect of hydrogen peroxide on Anabaena and Synechocystis survival. Cyanobacterial cultures in mid-exponential growth phase diluted to a concentration of 2.5 μg of chlorophyll ml⁻¹ were incubated for 24 h under standard light conditions in the presence of up to 10 mm hydrogen peroxide.