Two forms of phycobilisomes in the Antarctic red macroalga Palmaria decipiens (Palmariales, Florideophyceae)

The phycobilisomes (PBS), the light-harvesting antennae, from the endemic A ntarctic red macroalga Palmaria decipiens were isolated on discontinuous su crose gradients in two discrete bands and not in one as expected. To exclud e methodical faults, we also isolated PBS from the temperate Palmaria palma ta and the unicellular red algae Porphyridium cruentum and Rhodella violace a. In P. palmata the PBS were separated in two discrete bands, whereas the PBS from Porphyridium and Rhodella were found in one band. The double-bande d PBS (PBSup and PBSlow) from P. decipiens were further characterized by ab sorption and fluorescence spectroscopy, native and SDS-PAGE as well as by n egative staining. The phycobiliproteins RIII-phycoerythrin, RI-phycocyanin and allophycocyanin were identified and 3 gamma -subunits were described. T he PBSup and PBSlow. showed no significant differences in their absorption spectra and phycobiliprotein ratios although the negative stained PBSlow we re smaller. Differences were found in their low molecular mass subunit comp lexes, which are assumed to be r-phycocrythrin. The polypeptide pattern of the PBSup and PBSlow showed no differences in the molecular masses of their subunits and linker polypeptides, but in their percentage distribution. Th e results suggest that the PBSlow is a closer packed and PBSup a little mor e loosely aggregated hemiellipsiodal PBS form. We discuss the ecophysiologi cal function of two PBS forms in P. decipiens and suggest advantages in the rapid acclimation to changes in environmental light conditions.