Evidence for ciliary pigment localization in colored ciliates and implications for their photosensory transduction chain: a confocal microscopy study.

In this study we report for the first time the localization of a photoreceptor pigment in the cilia of the colored heterotrich ciliates Blepharisma japonicum red and blue form, Fabrea salina, and Stentor coeruleus, as result of a confocal microscopy investigation. Optical sectioning confocal microscopy has been used for studying the spatial distribution of the pigment in the cell body, surprisingly showing that, besides its expected presence in the cortical region immediately below the cell membrane, it is located in the cilia too. In order to ascertain possible differences in the pigment fluorescence properties along the cell body, we have measured emission spectra from different parts of it (anterior, posterior, and cilia). Our results clearly indicate that in all cases the spectra are the same, within experimental errors. Finally, we have evaluated the pigment relative fluorescence efficiency of these ciliates. In an ordered scale from lower to greater efficiency, we have S. coeruleus, B. japonicum blue, B. japonicum red, and F. salina. The possible implications of our findings for the process of photosensory transduction are discussed.