Fig. 1. Heat stress induces fluorescence of the NO-sensitive probe DAF-FM in A. pallida. (A) Optical cross-section through a tentacle of symbiotic A. pallida incubated at an ambient temperature of 25°C (left) and after 24 h of heat stress at 33°C (right), with inset showing expelled host cells with algae. The DAF-FM (510-530 nm) NOdependent fluorescent signal is colored yellow; algal autofluorescence is colored red. (B) Quantification of relative fluorescence intensity of NO-sensitive DAF-FM (510-530 nm) in tentacles as a function of heat stress (N=3 anemones per treatment; bars represent means + s.d.; t-test, P=0.0015).