Ultrastructure of unicellular red algae

Abstract

The phylum Rhodophyta is an enigmatic as semblage of organisms whose phylogenetic relationships with other eukaryotes are shrouded in uncertainty. The group was long held to be among the most primitive eukaryotes due to the lack of a centriole complex and the similarities between the red algal chloroplast and cyanobacteria (Garbary and Gabrielson 1990). This view was given further impetus when the analysis of red algal 5s ribosomal RNA indicated an early divergence from other eukaryotes (Lim et al. 1986; Hori and Osawa 1987). However, there is equally compelling evidence that red algae are not more primitive than other algal phyla. Acceptance of the endosymbiotic origin of chloroplasts renders the resemblance of red algae and cyanobacteria to be superficial (Gabrielson et al. 1985) while ultrastructural studies show typical eukaryotic cell organization (Pueschel 1990). In addition, recent studies of the 18s ribosomal subunit (Bhattacharya et al. 1990) indicate divergence of red algae to be at the same time as that of `plants, fungi, animals and most protists'.