Pigment composition, photosynthesis and fine structure of a non-blue-green prokaryotic algal symbiont (Prochloron sp.) in a didemnid ascidian from Hawaiian waters

Cells of a unicellular, green-coloured alga found growing endozoically in a didemnid ascidian around Hawaiian shores have been shown by electron microscopy to be clearly prokaryotic, like blue-green algae. The cell wall is like that of cyanophytes and there are no organelles. However, the thylakoids tend to occur in pairs or stacks, as in green eukaryotic algae. They contain no detectable amounts of bilin pigments (such as those characterizing blue-green algae) but have two distinct chlorophylls, chromatographically and spectroscopically identified as chlorophyll a and chlorophyll b (a combination characterizing green plants). Both intact didemnids, containing the algae cells and isolated algae cells were capable of vigorous photosynthetic oxygen production in light. These features suggest that the algal endosymbiont discussed here should be referred to the new algal division, Prochlorophyta.