Fig. 4. Nitric oxide mediates bleaching in A. pallida. (A) Bleaching (% expulsion; bars represent means + s.d.; N=3 anemones per treatment) of anemones incubated for 24 h at 25°C with the NO donor SNP (1 mmol l^-1) with (filled bars) or without (open bars) the NO scavenger cPTIO (1 mmol l^-1). Control anemones (without SNP) released <1% of their algae. Incubation with SNP resulted in a significant increase in bleaching (t-test, P=0.021) while co-incubation with cPTIO significantly decreased this effect (t-test, P=0.0368). (B) Bleaching (% expulsion; bars represent means + s.d.; N=3 anemones per treatment) of anemones incubated for 24 h at 25°C (control) or 33°C, with or without cPTIO (20 mmol l^-1). There was a significant difference between the two heat-stress treatments (t-test, P=0.0176). (C) NO-dependent DAF-FM fluorescence in control, heatstressed or SNP-treated anemones with or without 20 mmol l^-1 cPTIO. Bars sharing the same letter are not significantly different (two-way ANOVA, P<0.001; Tukey HSD, P<0.05).