Variations in Chlorophyll and Carotenoid Pigmentation Among Prochloron (Prochlorophyta) Symbionts in Diverse Marine Ascidians

High-performance liquid chromatography (HPLC) was used to separate and quantify chlorophylls a and b as well as major carotenoid pigments present in freeze-dried preparations of diverse Prochloron- didemnid associations and in Prochloron cells separated from host colonies. Both chlorophyll a and b were consistently observed in each association. Chlorophyll a : b ratios ranged from 4.14 to 19.71. Ratio differences reflected species differences among didemnid hosts, which proved consistent over time and space. Generally good agreement was found between ratios determined in isolated cell preparations and in symbiotic colonies (in hospite). These values are 1.5 to 5-fold higher than ratios determined in a variety of eukaryotic green plants. The carotenoids in Prochloron are quantitatively and qualitatively similar to those found in various freshwater and marine cyanophytes from high-light environments. However, Prochloron differs from most cyanophytes in the absence of myxoxanthophyll and related glycosidic carotenoids. The consistent presence of chlorophyll b and individuality in carotenoid pigmentation render Prochloron biochemically distinct from cyanophytes, despite the fact that cells of both prokaryotic groups are often found in light-saturated environments