Co-localization of chloroplast DNA and ribulose-1,5-bisphosphate carboxylase/oxygenase in the so-called pyrenoid of the siphonous green alga Caulerpa lentillifera (Caulerpales, Chlorophyta)

The pyrenoid of the siphonous green alga Caulerpa lentillifera J. Agardh contains DNA. The pyrenoid was separated from the cell to examine whether it is a true pyrenoid. Chloroplast DNA (ct-DNA) was observed in the core of the isolated pyrenoid, using fluorescence microscopy after staining with the DNA-specific fluorochrome, 4'6-diamidino-2-phenyl-indole (DAPI). SDS-PAGE analysis indicated that the pyrenoid contained two major polypeptides of Molecular weight, 52kDa and 14kDa, respectively, and several minor components. Native-PAGE and SDS-PAGE: in combination with western blotting using an antibody against the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) showed the two major polypeptides to be the large and small subunits of RUBISCO, respectively. Using immunofluorescence microscopy it was found that most of the RUBISCO in the chloroplast was localized in the pyrenoid cores in both C. lentillifera and C. okamurae Weber van Bosse and in three other siphonous green algae, Avrainvillea amadelpha (Montagne) A. et E.S. Gepp, Chaetomorpha sp. and Valonia confervoides Harvey. It was dispersed throughout the stroma in the pyrenoid-lacking Caulerpa brachypus Harvey.