Localization of granulatimide alkaloids in the tissues of the ascidian Didemnumgranulatum
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Ascidians are a notable source of nitrogen-bearing secondary metabolites with a wide range of biological activities. Although many biologically active compounds have been isolated from ascidians, it is often unclear whether the animal or associated microbial symbionts such as bacteria or fungi are the true biosynthetic source of the metabolites. We have addressed the question of the biosynthetic source of the alkaloids granulatimide and isogranulatimides by localizing these compounds within the ascidian. In this work, we demonstrate that granulatimide is stored in Didemnumgranulatum tunic bladder cells. Analysis by confocal fluorescence microscopy at the granulatimide emission range indicated the presence of fluorescent cells as highly vacuolated cells found dispersed in the ascidian tunic. Since this is the most exposed ascidian tissue, it is possible that these alkaloids may have a protective role, either as sunscreens and/or as feeding deterrents.
KeywordsAlkaloid Bladder Cell Microbial Symbiont Percoll Fraction Confocal Microscopic Examination
The authors are particularly grateful to Dr. Christine Salomon (University of Minnesota) for a careful reading of the manuscript and many suggestions to improve it. The authors thank the staff of CEBIMar—USP for the provision of laboratory facilities and technical support during field trips; the staff of the Laboratório de Fisiologia Celular do Plasmodium (IB-USP) for the assistance with confocal microscopy; and Gustavo M. Diaz (Universidade Estadual de Campinas, Brazil) for valuable discussions. Financial support was provided by FAPESP as grants to M.R.C. (99/11443-1) and R.G.S.B. (01/06202-7), and as a scholarship to S.P.L. The authors also thank the Universidade de São Paulo within the PROCONTES program to M.H.R.S. and R.G.S.B. All experiments complied with current Brazilian laws. The authors dedicate this work to the late Professor D. John Faulkner (Scripps Institution of Oceanography), in memoriam.
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