Relationships between the extent of CEF and the photoinhibition sensitivity in three different Symbiodinium strains. A, Effects of high temperature on PSII photoinhibition. The cells were preincubated at 25°C (left) and 33°C (right) for 1 h in the dark and were subsequently exposed to light at 500 µmol photons m−2 s−1. The maximum quantum yield of PSII, i.e. Fv/Fm, was measured at each time point after dark incubation for 10 to 15 min. The asterisks indicate statistically significant differences compared with the corresponding data from Mf1.05b (*P < 0.05 and **P < 0.01, Student’s t tests). B, Effects of elevated temperatures on the P700+ reduction rate. The cells were incubated at temperatures ranging from 25°C to 36°C for 15 min in the dark before the measurements. DCMU was subsequently added, and the rate constant of P700+ reduction was taken as demonstrated in Figure 1. The values are presented as means ± sd from three independent experiments.