Prochloron (Prochlorophyta): Biochemical Contributions to the Chlorophyll and RNA Composition

The prochlorophyte Prochloron, a symbiont of the colonial ascidian Didemnum molle, was collected in the Indian Ocean around Giravaru (Maldives) in depths between 1 and 40 m. The chlorophyll a to b ratio of the algal symbionts was higher in colonies living between 1–6 m, compared to that determined for Prochloron from a depth of 30 m. This property for chromatic adaptation in correlation with changes in the total content of chlorophyll is dependent upon environmental factors. The association between Didemnum and Prochloron is only a facultative symbiosis. The size of the colonies, growing near the water surface is large (up to 3 cm), and it gradually decreases to 0.2 cm in a depth of 30 m dim locations. At a depth of 40 m the tunicates do not contain the algal symbionts. Applying quantitative preparative isolation and sensitive immunological as well as biochemical detection techniques we have no evidence for the existence of poly(A) stretches in RNA species from Prochloron. Moreover, we failed to detect both sn/scRNAs and their proteins, typically associated with them in RNP complexes from eukaryotes. From the data we suggest that mRNA synthesis proceeds in Prochloron in a way similar to prokaryotes.