ULTRASTRUCTURE AND SUPRAMOLECULAR ORGANIZATION OF PHOTOSYNTHETIC MEMBRANES OF SOME MARINE RED ALGAE

The ultrastructure and supramolecular organization of photosynthetic m embranes in four species of marine red algae (Porphyra yezoensis, Porp hyra leucosticta, Erythrocladia subintegra, Pterothamnion crispum) wer e studied both in replicas of rapidly frozen cells and in ultrathin se ctions. Because the thylakoids in red algal chloroplasts are not stack ed, freeze-fractured thylakoid membranes exhibit only two types of fra cture faces (EF and PF). In all four species the PF reveals numerous, tightly packed, but randomly distributed particles (density range from 3530 to 4970 particles mu m(-2) for Porphyra yezoensis). The particle size distribution is uniform in the two types of fracture faces with an average diameter of about 11.3-11.6 nm in all four algae. The phyco bilisomes of Porphyra yezoensis and Erythrocladia subintegra have the approximate shape of a compressed rotation ellipsoid with the followin g dimensions; Porphyra yezoensis, length 52.8 +/- 1.2 nm, thickness 24 .4 +/- 0.6 nm, height 34.6 +/- 1 nm; Erythrocladia subintegra, length 45.1 +/- 0.7 nm, thickness 23.1 +/- 0.5 nm, height 29.4 +/- 0.9 nm. In Porphyra yezoensis, Porphyra leucosticta and Erythrocladia subintegra both the phycobilisomes and EF particles are organized into rows with a spacing of 70-80 nm in Porphyra yezoensis, 65-75 nm in Porphyra leu costicta and 53.8-55 nm in Erythrocladia subintegra. EF particle compl exes with four subunits were found in Porphyra yezoensis. In Pterotham nion crispum the shape of the phycobilisomes is hemiellipsoidal. The p hycobilisomes seem to be organized into rows; their centre to centre p eriodicity is c. 60 nm. Porphyra yezoensis cells possess about 770 +/- 58 phycobilisomes mu m(-2) of thylakoid surface, whereas the number o f EF particles is about 1270 +/- 203 mu m(-2) Thus, the ratio of phyco bilisomes to EF particles is c. 0.6. In Erythrocladia subintegra the r atio of phycobilisomes to EF particles is about 0.7. Of special intere st is the ocurrence of a crystalline matrix in pyrenoids of Porphyra l eucosticta and the absence of phycobilisomes in the intrapyrenoid thyl akoids of Porphyra yezoensis and Erythrocladia subintegra.