The presence of nitric oxide synthase (NOS) activity is demonstrated in the tropical
marine cnidarian Aiptasia pallida and in its symbiotic dinofiagellate algae, Symbiodinium
bermudense. Enzyme activity was assayed by measuring the conversion of arginine to
citrulline. Biochemical characterization of NOS from Aiptasia was characterized with
respect to cellular localization, substrate and cofactor requirements, inhibitors,
and kinetics. In response to acute temperature shock, anemones retracted their tentacles.
Animals subjected to such stress had lower NOS activities than did controls. Treatment
with NOS inhibitors caused tentacular retraction, while treatment with the NOS substrate
L-arginine inhibited this response to stress, as did treatment with NO donors. These
results provide a preliminary biochemical characterization of, and suggest a functional
significance for, NOS activity in anthozoan-algal symbiotic assemblages.
