CYTOCHEMICAL STUDIES ON PROCHLOROPHYTES: LOCALIZATION OF DNA AND RIBULOSE 1,5‐BISPHOSPHATE CARBOXYLASE‐OXYGENASE1

Publisher Website
Google Scholar
Abstract
We studied the distribution of the DNA‐containing region and the ribulose 1,5‐bisphosphate carboxylase‐oxygenase (RuBisCo) content of polyhedral bodies in three different prochlorophyte cell types in a search for broad evolutionary affinities of these chlorophyll b‐containing prokaryotes. DNA was localized by DAPI staining and electron microscopy utilizing monoclonal anti‐DNA antibody 2C‐10 plus a secondary antibody labeled with colloidal gold. Antibodies against the large RuBisCo subunit from a higher plant raised in rabbits were used to localize RuBisCo in polyhedral bodies. We studied Prochloron Lewin cells from two different didemnid ascidian hosts (Lissoclinum patella and Didemnum molle) collected in Palau, West Caroline Islands, and cells of Prochlorothrix hollandica Burger‐Wiersma, Stal, and Mur grown in laboratory culture. Cells of the blue‐green alga Anabaena 7120 were studied for comparison. The DNA distribution was markedly different in the two Prochloron cell types. The thylakoids in cells from L. patella were concentrically arranged around a large central vacuole; the DNA‐containing stromal areas appeared in thin sections as a concentric arcs between the thylakoid stacks. The central vacuole was lacking in cells from D. molle, and the thylakoid stacks and strands of DNA‐containing stroma showed a more haphazard arrangement. In the filamentous Prochlorothrix the DNA‐containing stroma was largely limited to a central nucleoid structure running the length of the cell. Although the DNA arrangements in Prochloron might be considered “chloroplast‐like” since DNA‐containing stroma is distributed, as in chloroplasts, in scattered sites among photosynthetic membranes, this is not so in Prochlorothrix, where there is an axial nucleoid, as in many filamentous cyanobacteria. Our anti‐RuBisCo antibodies were selectively bound to the polyhedral bodies of all three cell types, indicating that Prochloron and Prochlorothrix, like many other autotrophic prokaryotes, possess typical carboxysomes.