Clotrimazole, a Model Compound for the Host Release Factor of the Coral Plesiastrea versipora

Abstract

Crude homogenates of animal host tissues stimulate the release of photosynthetic products from symbiotic dinoflagellates isolated from corals and several other invertebrates. It is believed that specific ‘host release factors’ stimulate the symbiotic algae to release water-soluble compounds, chiefly glycerol and amino acids, to the host. Crude host homogenates also contain compounds which sometimes inhibit photosynthesis in isolated algal cells, although this inhibition is not apparent in the intact association. Therefore, use of crude homogenates in translocation experiments may sometimes lead to inconsistent results. We have found that the commercially available synthetic fungicide, clotrimazole (mycosporin), a chemical analogue of naturally occurring mycosporine-like amino acids, can be used as a model for the host release factor of the coral Plesiastrea versipora(Lamarck). Clotrimazole stimulated isolated algal cells from P. versipora to release carbon fixation products to the external medium. Chromatography experiments showed that the released compounds were similar to those found when algae were incubated with crude homogenates of P. versipora. We propose that, in Plesiastrea versipora, clotrimazole may be used as an internal control in experiments using crude host homogenate and in screening partially purified fractions for ‘host factor’ activity. Clotrimazole is the first commercially available compound found to have effects similar to the ‘host factor’ of a coral.